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QL
66fi
L25U4
1987X
Rept.
iiversity of California Publications
ZOOLOGY
Volume 118
Phylogenetic Systematics of
Iguanine Lizards
A Comparative Osteological Study
by Kevin de Queiroz
PHYLOGENETIC SYSTEMATICS OF IGUANINE LIZARDS
A COMPARATIVE OSTEOLOGICAL STUDY
KEPT.
Phylogenetic Systematics of
Iguanine Lizards/
A Comparative Osteological Study
by Kevin de Queiroz
A Contribution from the Museum of Vertebrate Zoology
of the University of California at Berkeley
yti»%K«^*^
UNIVERSITY OF CALIFORNIA PRESS
Berkeley • Los Angeles • London
UNIVERSITY OF CALIFORNIA PUBLICATIONS IN ZOOLOGY
Editorial Board: Peter B. Moyle, James L. Patton,
Donald C. Potts, David S. Woodruff
Volume 118
Issue Date: December 1987
UNIVERSITY OF CALIFORNIA PRESS
BERKELEY AND LOS ANGELES, CALIFORNIA
UNIVERSITY OF CALIFORNIA PRESS, LTD.
LONDON, ENGLAND
ISBN 0-520-09730-0
LIBRARY OF CONGRESS CATALOG CARD NUMBER: 87-24594
© 1987 BY THE REGENTS OF THE UNIVERSITY OF CALIFORNIA
PRINTED IN THE UNITED STATES OF AMERICA
Library of Congress Cataloging-in-Publication Data
De Queiroz, Kevin.
Phylogenetic systematics of iguanine lizards: a comparative
osteological study / by Kevin de Queiroz.
p. cm. — (University of California publications in zoology:
v. 118)
Bibliography: p.
ISBN 0-520-09730-0 (alk. paper)
1. Iguanidae — Classification. 2. Iguanidae — Evolution.
3. Iguanidae — ^Anatomy. 4. Anatomy, Comparative. 5. Reptiles —
Qassification. 6. Reptiles — Evolution. 7. Reptiles — Anatomy.
I. Title. II. Series.
QL666.L25D4 1987
597.95— dc 19 87-24594
CIP
Contents
Li^f of Illustrations, vii
List of Tables, x
Acknowledgments, xi
Abstract, xii
INTRODUCTION 1
Historical Review, 1
Goals of This Study, 10
MATERIALS AND METHODS 1 3
Specimens, 13
Phylogenetic Analysis, 13
Basic Taxa, 14
The Problem of Variation, 14
Construction of Branching Diagrams, 16
IGUANINE MONOPHYLY 18
COMPARATIVE SKELETAL MORPHOLOGY 2 1
Skull Roof, 21
Palate, 39
Braincase, 44
Mandible, 49
Miscellaneous Head Skeleton, 59
Axial Skeleton, 69
Pectoral Girdle and Sternal Elements, 81
Pelvic Gridle, 86
Limbs, 89
Osteoderms, 89
NONSKELETAL MORPHOLOGY 92
Arterial Circulation, 92
Colic Anatomy, 93
External Morphology, 94
vi Contents
SYSTEMATIC CHARACTERS 100
Skeletal Characters, 100
Nonskeletal Characters, 104
CHARACTER POLARITIES AND THE PHYLOGENETIC INFORMATION
CONTENT OF CHARACTERS 1 06
ANALYSIS OF PHYLOGENETIC RELATIONSHIPS 1 17
PreHminary Analysis, 1 17
Lower Level Analysis, 122
PHYLOGENETIC CONCLUSIONS 130
Preferred Hypothesis of Relationships, 130
Character Evolution within Iguaninae, 130
COMPARISONS WITH PREVIOUS HYPOTHESES 132
DIAGNOSES OF MONOPHYLETIC GROUPS OF IGUANINES 135
Iguaninae Bell 1825, 135
Dipsosaurus Hallowell 1854, 141
Brachylophus Wagler 1830, 143
Iguanini Bell 1825, 145
Ctenosaura Wxtgmonn 1828, 146
Sauromalus T)\xvi\€n\ 1856, 157
Amblyrhynchina, new taxon, 160
Amblyrhynchus Bell 1825, 163
Conolophus Fitzinger 1843, 165
IguaninaBell 1825, 167
Iguana Laurenti 1768, 168
Odwra Harlan 1824,170
Appendix I: Specimens Examined, 175
Appendix II: Polarity Determination Under Uncertain Outgroup
Relationships, 179
Appendix III: Polarity Determination for Lower Level Analysis, 185
Appendix IV: Polarity Reevaluation for Lower Level Analysis, 187
Literature Cited, 191
List of Illustrations
FIGURES
1 . "The phylogeny and relationships of North American iguanid genera," after Mittleman
(1942), 6
2. "Grouping and possible phylogeny of the genera of iguanids occurring in the United
States," after H. M. Smith (1946), 7
3. "Phylogenetic relationships of the Madagascar Iguanidae and the genera of iguanine
Hzards," after Avery and Tanner (1971), 9
4. Etheridge's phylogeny of the Iguanidae, 1 1
5. Skull of Brae hy lop hus vitiensis, 22
6. Skull and mandible of Brae hy lop hus vitiensis, 23
7. Posteroventral views of iguanine premaxillae, 24
8. Dorsal views of the preorbital portions of iguanine skulls, 25
9. Dorsal views of the skulls of Cyclura cornuta and Sauromaliis obesus, 11
10. Posterodorsal views of the anterior orbital regions oi Brachylophus fasciatm and
Conolophus pallidus, 28
11. Dorsal view of the skull of Amblyrhynchus cristatus, 29
12. Ventral views of iguanine frontals, 31
13. Dorsal views of the parietals in an ontogenetic series of Iguana iguana, 34
14. Lateral view of the skull of Ctenosaura similis, 36
15. Lateral views of the posterolateral comers of iguanine skulls, 38
16. Posterodorsal views of disarticulated right palatines of Iguana delicatissima and
Conolophus subcristatus, 40
17. Posterodorsal views of the right orbits of five iguanines and Morunasaurus annularis,
41
18. Ventral view of the skull of Iguana delicatissima, 43
19. Anterolateral views of the left orbitosphenoids in an ontogenetic series of Iguana
iguana, 45
20. Ventral views of the posterior portion of the palate and anterior portion of the braincase
of Sauromalus varius and Amblyrhynchus cristatus, 46
21. Ventral views of iguanine neurocrania, 47
22. Lateral views of the right mandibles of Iguana delicatissima and Amblyrhynchus
cristatus, 50
23. Lingual views of the left mandibles of three iguanines, 51
24. Lateral views of the right mandibles of Conolophus pallidus and Cyclura cornuta, 52
vu
viii List of Illustrations
25. Lateral views of the right mandibles of Iguana delicatissima, Sauromalus obesus, and
Amblyrhynchus cristatus, 53
26. Lateral views of the right mandibles of Dipsosaurus dorsalis, Brachylophus vitiensis,
and Iguana iguana, 55
27. Medial views of the left mandibles of Iguana delicatissima and Conolophus
subcristatus, 56
28. Dorsal views of the posterior ends of the right mandibles in ontogenetic series of
Ctenosaura hemilopha and Amblyrhynchus cristatus, 57
29. Dorsal views of the posterior ends of the right mandibles in an ontogenetic series of
Dipsosaurus dorsalis, 58
30. Lingual views of left maxillary teeth of four iguanines and Basiliscus plumifrons, 62
31. Hypothetical character phylogeny for the iguanine pterygoid tooth patch, 65
32. Corneal view of the left scleral ring of Ctenosaura similis, 67
33. Ventral views of the iguanine hyoid apparati, 68
34. Twentieth presacral vertebra of Brachylophus vitiensis, 70
35. Lateral views of the twentieth presacral vertebrae of Sauromalus obesus and
Ctenosaura pectinata, 11
36. Dorsolateral views of the twentieth presacral vertebrae of Dipsosaurus dorsalis and
Sauromalus obesus, 73
37. Dorsal views of caudal vertebrae of Dipsosaurus dorsalis from different regions of the
tail, 76
38. Lateral views of the ninth caudal vertebrae of Dipsosaurus dorsalis and Iguana iguana,
79
39. Presacral and sacral vertebrae and ribs of Dipsosaurus dorsalis in ventral view, 80
40. Pectoral girdles of three iguanines, 82
41. Dorsal views of the pelvic girdles of Sauromalus obesus and Ctenosaura pectinata, 86
42. Bones of the anterior limb of Brachylophus fasciatus, 87
43. Right hind limb skeleton of Brachylophus fasciatus, 88
44. Right tarsal region of Brachylophus fasciatus, 90
45. Anterodorsal views of pedal digit II of three iguanines, 97
46. Minimum-step cladograms for eight basic taxa of iguanines resulting from a
preliminary analysis of 29 characters, 119
47. Alternative interpretations of character transformation for homoplastic characters on a
minimum-step cladogram, 121
48. Alternative interpretations of character transformation for homoplastic characters on a
minimum-step cladogram, 122
49. Minimum-step cladograms resulting from an analysis of 26 characters in a subset of
iguanines, 127
50. Consensus cladogram for the three cladograms illustrated in Figure 49, 128
51. Phylogenetic relationships within Iguaninae, according to the present study, 131
52. Geographic distribution of Di/?^o^aMrM5, 141
53. Geographic distribution of firacA}'/<9/p/zM5', 144
List of Illustrations ix
54. Geographic distribution of CreAio5flMra, 147
55. Cladogram illustrating phylogenetic relationships within Ctenosaura, 154
56. Geographic distribution of Sawroma/t^, 158
57. Geographic distribution of Amblyrhynchina {Amblyrhynchus and Conolophus), 161
58. Geographic distribution of /^Mana, 169
59. Geographic distribution of C}'c/Mra, 171
60. All nine possible fully resolved cladogram topologies for four unspecified outgroups
and an ingroup, 179
61. Dendrograms corresponding with the nine cladograms in Figure 60 after each is
rerooted at the outgroup node, 180
62. Examples of polarity inferences for different arrangements of outgroup character state
distributions, 182
63. All possible cladogram topologies for two unspecified outgroups and an ingroup
before and after rerooting at the outgroup node, 185
64. All possible cladogram topol9gies for two unspecified near outgroups, one more
remote outgroup, and an ingroup before and after rerooting at the outgroup node, 186
PLATE
1. Lateral and dorsal views of the skull oi Amblyrhynchus cristatus, 91
List of Tables
1 . The iguanine genera, 2
2. Position of the parietal foramen, 32
3. Numbers of premaxillary teeth, 60
4. Numbers of presacral vertebrae, 7 1
5. Distributions of character states of 95 characters among four outgroups to iguanines
and the polarities that can be inferred from them, 108
6. Distributions of character states of 95 characters among eight iguanine taxa, 112
7. Distributions of character states of 29 characters used in the preliminary analysis, 118
8. Polarity inferences for lower-level analysis, using Brachylophus and Dipsosaurus as
outgroups, 124
9. Distributions of character states of 26 characters among six taxa within Iguanini, 125
10. Distributions of character states of 19 characters among basic taxa within Ctenosaura
(in the broad sense) and three close and two more distant outgroups, 153
11. Summary of polarity inferences for seven cases of character-state distribution among
four outgroups of uncertain relationships to the ingroup, 181
12. Summary of polarity inferences for four cases of character-state distribution among
two outgroups of uncertain relationships to the ingroup, 1 85
13. Summary of polarity inferences for six cases of character-state distribution among two
near outgroups whose precise relationships to the ingroup are unresolved, and one
more remote outgroup exhibiting a fixed character state, 1 87
Acknowledgments
Many people have helped me toward the completion of this study in ways big and small.
Over the years I have undoubtedly forgotten the contributions of some of them, and I
apologize for this. Of those I have not forgotten, I want to thank the following people for
lending me specimens under their care: Pere Alberch, Walter Auffenberg, James Berrian,
Robert Bezy, Steven Busack, Joseph Collins, Ronald Crombie, Mark Dodero, Robert
Drewes, William Duellman, Anne Fetzer, George Foley, Harry Greene, L. Lee Grismer,
W. Ronald Heyer, J. Howard Hutchinson, Charles Meyers, Peter Meylan, Mark Norell,
Gregory Pregill, Jose Rosado, Albert Schwartz, Jens Vindum, Van Wallach, John Wright,
George Zug, Richard Zweifel, and especially Jay Savage and Richard Etheridge whose
collections provided the majority of the specimens examined in this study.
I am also grateful to various teachers, friends, and colleagues who helped my ideas on
systematics and iguanine biology unfold through countless discussions: Troy Baird, Aaron
Bauer, Theodore Cohn, Michael Donoghue, Richard Estes, Richard Etheridge, Jacques
Gauthier, Eric Gold, David Good, George Gorman, Scott Lacour, Eric Lichtwardt, James
Melli, Sheldon Newberger, Mark Norell, Michael Novacek, David Wake, and Andre
Wyss. Linda Condon-Howe, Charles Crumly, Sanae and John Moorehead, Douglas
Preston, Doris Taylor, and the late Kenneth Miyata generously provided lodging while I
was visiting museums. Richard Estes, Richard Etheridge, Darrel Frost, Gregory Pregill,
David Wake, and Edward Warren, provided valuable comments on earlier versions of the
manuscript. David Cannatella and Rose Anne White gready assisted in the preparation of
camera-ready-copy.
Finally, I want to give special thanks to Karen Sitton for providing emotional support
in her unique and charming way and to Richard Etheridge and Richard Estes for their
influence on both my academic and personal development.
This study partially fulfilled the requirements of a Master's degree in Zoology at San
Diego State University, but was completed at the University of California, Berkeley. The
research and preparation of the manuscript were supported in part by a grants from the
Society of Sigma Xi, the San Diego State University Department of Zoology, the Theodore
Roosevelt Memorial Fund of the American Museum of Natural History, and the Graduate
Student Research Allocation Fund of the Department of Zoology, University of California
at Berkeley.
XI
Abstract
Iguaninae is a monophyletic taxon of tetrapodous squamates (lizards) that can be
distinguished from other iguanians by at least five synapomorphies. Skeletal variation
within Iguaninae is described and forms the basis of systematic characters used to
determine phylogenetic relationships among eight basic taxa, the currendy recognized
iguanine genera. Evolutionary character polarities are determined by comparison with four
closely related taxa, basiliscines, crotaphytines, morunasaurs, and oplurines.
The distributions of derived characters among iguanine taxa suggest that: (1) Either
Brachylophus or Dipsosaurus is the sister group of the remaining iguanines (Iguanini). (2)
Dipsosaurus is a monophyletic taxon diagnosed by at least six synapomorphies. (3)
Brachylophus is a monophyletic taxon diagnosed by at least eight synapomorphies. (4)
Iguanini, containing Amblyrhynchus, Conolophus, Ctenosaura, Cyclura, Iguana, and
Sauromalus, is a new monophyletic taxon diagnosed by at least three synapomorphies. (5)
vWithin Iguanini, the relationships among four t2Lxa.-Ctenosaura, Sauromalus,
Amblyrhynchina, and Iguanina-are unresolved. (6) Ctenosaura is a monophyletic taxon
'diagnosed by at least three synapomorphies. (7) Enyaliosaurus is monophyletic, but it is a
subgroup of Ctenosaura rather than a separate taxon. If Enyaliosaurus is separated from
Ctenosaura, then Ctenosaura is not monophyletic. (8) Sauromalus is a monophyletic taxon
diagnosed by at least 24 synapomorphies, many of which are convergent in
Amblyrhynchus. (9) Amblyrhynchina is a new monophyletic taxon containing the
Galapagos iguanas Amblyrhynchus and Conolophus, and is diagnosed by at least 1 1
synapomorphies. (10) Amblyrhynchus is a monophyletic taxon diagnosed by at least 28
synapomorphies and is perhaps the most divergent iguanine from the most recent common
ancestor of all of them. Many of the unique features of Amblyrhynchus appear to be
related to its unique natural history. (11) Conolophus is a monophyletic taxon diagnosed
by at least eight synapomorphies and cannot, therefore, be considered ancestral to
Amblyrhynchus. (12) Iguanina is a new monophyletic taxon composed oi Iguana and
Cyclura and is diagnosed by at least three synapomorphies. (13) Iguana is a monophyletic
taxon diagnosed by at least seven synapomorphies. (14) Monophyly of Cyclura is a
problem in need of further study. Although three ostensible synapomorphies support
monophyly of Cyclura, other derived characters suggest that some Cyclura shared a more
recent common ancestor with Iguana than with other Cyclura.
Summaries of Iguaninae and its monophyletic subgroups down to the level of the eight
basic taxa are provided; each summary includes the type of the taxon, etymology of the
taxon name, a phylogenetic definition, geographic distribution, a list of diagnostic
synapomorphies, the fossil record, and various comments.
xu
INTRODUCTION
Containing approximately 55 genera and more than 600 species, Iguanidae is one of the
largest families of lizards. Its members occur primarily in the New World, from southern
Canada to austral South America including the Galapagos Archipelago and much of the
West Indies. Iguanids also occur on the island of Madagascar and in the Comores
Archipelago in the western Indian Ocean, and on the Fiji and Tonga island groups in the
southwestem Pacific.
For over 100 years, systematists have attempted to discover the pattern of
interrelationships among the genera in the family Iguanidae, but, because of the
bewildering morphological diversity within this family, the task is far from complete.
Nevertheless, many systematists have recognized suprageneric groups of iguanids (e.g.,
Wagler, 1830; Dumeril and Bibron, 1837; Fitzinger, 1843; Gray, 1845; Cope, 1886, 1900;
Boulenger, 1890; H. M. Smith, 1946; Savage, 1958; Etheridge, 1959, 1964a). One of the
earliest of these suprageneric groups to be recognized consists of the genera currently
known informally as iguanines. This assemblage is also one of the most readily diagnosed
on the basis of uniquely derived features. As currently conceived, there are eight genera
and 31 species of iguanines (Etheridge, 1982). The iguanine genera are listed in Table 1,
which also gives the number of included species, their habits, and the geographic
distribution for each genus.
HISTORICAL REVIEW
The concept of an iguanine group is remarkably old, predating the publication of Darwin's
Origin of Species (1859). This accomplishment is even more surprising when one realizes
that all iguanines are native to regions far from western Europe, where systematists were
developing the concept of an iguanine group. These systematists undoubtedly had few
specimens at hand, and must have relied heavily on each others' character descriptions.
Although I have been unable to see all of the potentially relevant literature, I attempt to trace
and summarize the history of iguanine higher systematics.
The Eighteenth Century. Although the eighteenth century was an important one for
biological systematics as a whole, it was not so important for iguanine systematics. A
convenient date to begin a historical discussion of iguanine systematics is 1758, when
Linnaeus published the tenth edition of his Systema Naturae, the starting point of
zoological nomenclature. Linnaeus himself was neither interested in nor fond of the
"lower" tetrapods. He placed all tetrapodous squamates in two genera, one of which
1
University of California Publications in Zoology
TABLE 1. The Iguanine Genera
Genus
(common name)
Number of
Species
Habits
Geograpiiic
Distribution
Amblyrhynchus Bell 1825
(Marine Iguanas)
BrachylophusWagler 1830
(Banded Iguanas)
Conolophus Fi\zingcT 1843
(Galapagos Land Iguanas)
Clenosaura Wiegmann 1828
(Spiny-tailed Iguanas)
1
Terrestrial, saxicolous,
semimarine
Rocky coasts of various
islands of the Galapagos
Archipelago, Ecuador.
2
Arboreal
Various South Pacific islands
of the Fiji and Tonga groups.
2
Terrestrial
Islands of the Galapagos
Archipelago, Ecuador.
9
Terrestrial, arboreal
Lowlands of Mexico and Central
America, including various
offshore islands, as far south
as Panama.
Cyclura Harlan 1824
(West Indian Ground Iguanas)
Terrestrial
Dipsosaurus Hallowell 1854
(Desert Iguanas)
Iguana Laurenti 1768
(Green Iguanas)
SauromalusYyumtnl 1856
(Chuckwallas)
Terrestrial
Arboreal
Terrestrial, saxicolous
The Bahama Islands; Cayman
Islands; Navassa, Mona, and
Anegada islands; and Cuba,
Hispaniola, and Jamaica, and
their nearby islets.
Deserts of the southwestern
United States, northwestern
mainland Mexico, Baja
California, and various islands
in the Gulf of California.
Lowlands of Mexico, Central
America, and South America to
southern Brazil and Paraguay;
in the Caribbean northward
through the Lesser Antilles to
the Virgin Islands.
Deserts of the southwestern
United States, northwestern
mainland Mexico, Baja
California, and various islands
in the Gulf of California.
Sources: Etheridge (1982) and Gibbons (1981).
Phylogenetic Systematics oflguanine Lizards
contained Lacerta iguana (=Iguana iguana), the single known iguanine, and animals now
placed in at least 12 different families, including crocodilians and amphibians. He
considered them to be "foul and loathsome animals" (Linnaeus, 1758, translated in Goin et
al., 1978). At the close of the eighteenth century only three of the currently recognized
iguanine species (now placed in two genera) had been described, giving the systematists of
that century, such as Laurenti (1768) and Lacepede (1788), Uttle of a group to recognize.
The Nineteenth Century. Major advances in iguanine systematics came during the
nineteenth century. Many important natural histories and systems or classifications of
squamates appeared during these years, and by 1856 all of the currently recognized
iguanine genera had been described.
The concept of a natural iguanine taxon emerged during the first half of the nineteenth
century. Most of the authors of classifications published during this period recognized a
close relationship among at least some of the iguanine genera. Those that did not recognize
a complete and exclusive group for the iguanines known at the time failed to do so for one
or both of two reasons. Brongniart (1805), Latreille (1825), Fitzinger (1826, 1843),
Wagler (1830), and Dumeril and Bibron (1837) grouped all the known iguanines together,
but included some noniguanines with them. Although all the iguanines were sometimes
placed together as part of a continuous list, it is not evident that they were considered to
form their own subgroup within some larger group. Other authors such as Daudin (1805),
Merrem (1820), Cuvier (1829, 1831), and Wagler (1830) failed to place all iguanines in a
single group. Daudin, Cuvier, and Wagler included Brachylophus with the agamids, while
Merrem did the same for Ctenosaura.
At least three authors can truly be said to have recognized an iguanine group before
1850. I have two criteria for determining the true recognition of an iguanine group. First,
all of the iguanine taxa known to the author (or at least all those listed in the classification)
were included in the group; and second, no other taxa were included. Cuvier's (1817)
"Les Iguanes proprement dits" consisted of what are now Iguana iguana, I. delicatissima,
Cyclura cornuta, and Brachylophus fasciatus, although he later removed Brachylophus and
placed it among the agamids (Cuvier, 1829, 1831). Wiegmann (1834) placed only the
genera Cyclura, Ctenosaura, Iguana, Brachylophus, and Amblyrhynchus in his family
Dendrobatae, Tribus II, b, ***, B. Like many of his contemporaries, Wiegmann
constructed his classification as a hierarchy of sets and subsets that would also function as
a key.
The most fully developed early concept of an iguanine group appears to have been that
of Gray (1831a, 1845). In 1831, Gray placed all known iguanines (equivalent to what are
now 10 species in five genera) by themselves in a single genus, Iguana. Fourteen years
later, he recognized nine different iguanine genera. Because these nine genera (again
equivalent to five modem genera) formed one entire set in his hierarchical classification, it
is evident that Gray still recognized the unity of the iguanine group.
Progress in iguanine systematics, though less rapid than in the previous fifty years,
continued through the second half of the nineteenth century. The last two iguanine genera
that are still recognized, Dipsosaurus and Sauromalus, were described, but at first they
University of California Publications in Zoology
were not explicitly included with the rest of the iguanines in an exclusive group. The
concept of an iguanine group, exclusive of Dipsosaurus and Sauromalus, was refined with
more detailed anatomical descriptions. Beginning with Boulenger's (1885) monumental
Catalogue of the Lizards in the British Museum, I undertake here a more detailed
chronological treatment of the history of iguanine higher systematics.
Boulenger (1885) listed all of the genera that are now called iguanines in a nearly
continuous sequence in his catalogue, reflecting their position in his key as those iguanids
having femoral pores and the fourth toe longer than the third but lacking spines on the head
and an enlarged occipital scale. Nevertheless, the distantly related Hoplocercus (Etheridge
in Paull et al., 1976) breaks the continuity of the iguanines in the list, and, in terms of
Boulenger's characters, some iguanines are closer to certain non-iguanine iguanids than to
other iguanines. Boulenger did not explicitly delimit subgroups within Iguanidae or any
other family, and we can only guess about his precise ideas concerning such relationships.
Cope (1886) appears to have been the first to use the name Iguaninae as a formal taxon
for iguanine lizards. He further provided characters, both external and skeletal, by which
members of this group could be distinguished from other iguanids. Cope's Iguaninae
included Cyclura, Ctenosaura, Cachryx, Brachylophus, Iguana, Conolophus, and
Amblyrhynchus, but failed to include Dipsosaurus and Sauromalus. The genera
Aloponotus and Metopoceros were synonymized with Cyclura.
In response to Cope, Boulenger (1890) provided what he considered to be osteological
evidence for the separation of Metopoceros and Cyclura, and briefly described the skulls of
"the iguanoid lizards allied to Iguana." Except for the recognition of Metopoceros and the
omission of Cachryx, the genera included in this discussion were the same as Cope's
(1886) Iguaninae. Dipsosaurus and Sauromalus were again left out of the group.
Cope later (1900) greatly expanded his Iguaninae, and named two additional iguanid
subfamilies, Anolinae and Basiliscinae. This new Iguaninae was a catch-all group for
those iguanids that lacked midventrally continuous postxiphistemal inscriptional ribs, had
simple clavicles, and lacked a left hepatopulmonary mesentery— in other words, those
iguanids that lacked the distinctive features of anolines and basiliscines. Although this new
Iguaninae was almost certainly an unnatural group, Cope recognized a slightly expanded
version of his earlier (1886) Iguaninae as a discrete subset of his new and more inclusive
group of the same name. This unnamed subset was characterized by the presence of
femoral pores and of vertebrae with zygosphenal articulations. It contained Dipsosaurus
and Sauromalus along with the genera included in his earlier Iguaninae; and it is therefore
identical in generic content to the iguanine group as currently conceived.
The Twentieth Century. During the first three-fourths of the twentieth century, the
concept of an iguanine group underwent considerable change. The efforts of nineteenth-
century authors such as Cope and Boulenger seem to have been largely ignored, and at
least two authors envisioned the ancestry of most other North American iguanids within
iguanines. This idea seems to have resulted from the misconception that iguanines were
"primitive" iguanids and were, therefore, potential ancestors of other iguanid taxa; the
integrity of the group was deemphasized or completely overlooked. Nevertheless, by the
Phylogenetic Systematics oflguanine Lizards
mid-1960's the iguanines had been resurrected as a natural group, the same group that
Cope (1900) had recognized at the turn of the century.
In his landmark paper on squamate systematics. Classification of the Lizards, Camp
(1923) dealt primarily with the interrelationships of the lizard families. Nevertheless, his
treatise contains scattered but intriguing comments on relationships at lower taxonomic
levels. About the throat musculature of iguanines, he said:
In the "Cyclura group" comprising the genera Iguana, Amblyrhynchus,
Ctenosaura, Brachylophus, Sauromalus, and Cyclura, the superficial bundle [of the
M. mylohyoideus anterior] is very specialized and consists of definitely directed
fibers not connected with the skin. Detailed resemblances are present in this group
which I have outlined in manuscript and which will not be repeated here. Suffice it
to say that the group appears to be a natural one, on the basis of the musculature
with close resemblances prevalent between Sauromalus and Cyclura, and
Ctenosaura and Brachylophus. (Camp, 1923:371)
Unfortunately, the whereabouts of the manuscript mentioned in this passage are unknown
tome.
Mittleman (1942) reviewed the genus Urosaurus and commented briefly on the
relationships among the genera of North American iguanids, except Anolis. He implied
that the North American iguanids formed a monophyletic group descended from
Ctenosaura (Fig. 1) and that the similarities among Ctenosaura, Dipsosaurus, and
Sauromalus were retained primitive features:
Dipsosaurus is probably the most primitive of the North American Iguanidae
(excepting Ctenosaura, which is properly a Central and South American form), and
possesses several points in common with Ctenosaura, most easily observed of
which is the dorsal crest; the genera further show their relationship in the similarity
of the cephalic scutellation which is essentially simple, and shows no particular
degree of differentiation. Sauromalus is considered a specialized offshoot of the
Crotaphytus, or more properly, prQ-Crotaphytus stock, by reason of its solid
sternum, as well as the five-lobed teeth; the simple type of cephalic scalation
indicates its affinity with the more primitive Dipsosaurus-Ctenosaura stock.
(Mittleman, 1942:112-113)
H. M. Smith (1946:92) seemed to adopt a modified version of Mittleman's views on
the phylogeny of North American iguanids (Fig. 2). His herbivore section {Ctenosaura,
Dipsosaurus, and Sauromalus) was considered to be ancestral to the other North American
Iguanidae, save Anolis, with Sauromalus hypothesized to share a more recent common
ancestry with these other iguanids than with either Ctenosaura or Dipsosaurus. Smith's
subsequent comments (1946:101), however, indicate that he recognized affinities of
Ctenosaura, Dipsosaurus, and Sauromalus to iguanids occurring outside of the United
University of California Publications in Zoology
Streptosaurus
Petrosaurus -^
Crotaphytus
Callisaurus
Uma
Holbrookia
Uta ,,
y Urosaurus
\ /"
Sceloporus
\
Sator
Phrynosoma
Dipsosaurus
Ctenosaura
Primitive Iguanid Type
FIG. 1. "The phylogeny and relationships of North American iguanid genera," after Mittleman
(1942:113).
States. In addition to the three genera found in or near the United States, Smith's herbivore
section contained other "large, primitive iguanids," namely Amblyrhynchus, Conolophus,
Cyclura, and Iguana. Smith's Handbook dealt with the lizards of the United States and
Canada; those iguanines whose ranges did not enter this area were apparently omitted from
his phylogram for convenience. In any case. Smith could not have considered his
herbivore section to be monophyletic in the more restricted modem sense, since the group
was considered to be ancestral to other North American iguanids.
Savage (1958) explicitly challenged Mittleman's (1942) implication that the North
American iguanids formed a natural group:
Insofar as can be determined at this time, the so-called Nearctic iguanids form two
diverse groups that can only be distantly related. These two sections are
Phylogenetic Systematics oflguanine Lizards
FIG. 2. "Grouping and possible phylogeny of the genera of iguanids occurring in the United States,"
after H. M. Smith (1946:92). Roman numerals apparently refer to the following: (I) leaf-toed section, (II)
herbivore section, (III) sand-lizard section, (IV) rock-lizard section, (V) pored utiform section, (V) horned-
lizard section, and (VII) poreless utiform section.
distinguished by marked differences in vertebral and nasal structures and include
several genera not usually recognized as being allied to Nearctic forms. (Savage,
1958:48)
Savage's "iguanine line" contained Amblyrhynchus, Brachylophus, Conolophus,
Crotaphytus, Ctenosaura, Cyclura, Dipsosaurus, Enyaliosaurus {=Ctenosaiira, part),
Iguana, and Sauromalus. This group was distinguished from the "sceloporine line" by two
primary characters: the presence of accessory vertebral articulations, the zygosphenes and
zygantra, and the possession of a relatively simple, S-shaped nasal passage with a concha
present (Dipsosaurus-lypt of Stebbins, 1948). Other osteological and integumentary
features characteristic of the majority of the genera in each line were also given.
8 University of California Publications in Zoology
The currently recognized iguanine group is based on the work of Etheridge. In his
paper on the systematic relationships of sceloporine lizards, Etheridge (1964a) showed that
the two primary characters used by Savage (1958) to diagnose the iguanines were actually
more widespread within the Iguanidae, and were thus insufficient to diagnose the group.
He listed four fundamental differences between Crotaphytus and Savage's other iguanines,
and asserted that if Crotaphytus was considered to be an iguanine, no character or
combination of characters could be used to diagnose that group. Once he removed
Crotaphytus from the group, the iguanines were readily diagnosed by their unique caudal
vertebrae. Except for his recognition of Enyaliosaurus as a genus separate from
Ctenosaura, Etheridge's (1964a) concept of the iguanines is identical to that held today
(Etheridge, 1982).
Despite the long history of iguanines as a recognized group and the great interest in
many aspects of iguanine biology (e.g., Burghardt and Rand, 1982; Troyer, 1983), the
interrelationships among the iguanine genera and the relationships of iguanines to other
iguanians remain largely unknown. Commonly held beliefs are that Ctenosaura and
Cyclura are closely related (Barbour and Noble, 1916; Bailey, 1928; Schwartz and Carey,
1977), and that the same is true of the Galapagos iguanas Amblyrhynchus and Conolophus
(Heller, 1903; Eibl-Eibesfeldt, 1961; Thornton, 1971; Higgins, 1978). As mentioned
above, Mittleman (1942) and H. M. Smith (1946) have offered dendrograms depicting
their views on the relationships of the North American iguanines.
Recent studies have examined diverse data for clues about the interrelationships among
the iguanine genera, but have met with limited success. Zug (1971) studied the arterial
system of iguanids. He published shortest-connection networks for more than 40 iguanid
genera, some based on his arterial characters and others based on characters obtained from
the literature, most of which were osteological. Other shortest-connection networks
constructed from data on arterial variation within various suprageneric assemblages of
iguanids, including iguanines, were also presented. Nevertheless, Zug doubted the
usefulness of his arterial characters in iguanid systematics, stating: "The arterial characters
employed herein appear to be of minimal value in iguanid classification. At the intrafamilial
level, they are disruptive and form groups of questionable zoogeographic unity" (Zug,
1971:21).
There has been but a single study in which the relationships among all known iguanine
genera were sought, that of Avery and Tanner (1971). These authors provided
descriptions of the iguanine skeleton, head and neck musculature, tongue, and hemipenes,
and gave a number of osteological measurements. They based their hypothesis of
relationships on mean length-width ratios of bones, assuming that "a difference of forty or
less points between means of the same bone indicates a close relationship" (Avery and
Tanner, 1971:67). Large numbers of such similarities were taken to indicate close
phylogenetic relationship among taxa and were used in some unspecified way to construct a
phylogenetic diagram (Fig. 3). Avery and Tanner examined small series (never more than
five individuals of a single species), giving no consideration to allometric changes in the
ratios that they used. I suspect that many of these ratios are correlated with a single
Phylogenetic Systematics oflguanine Lizards
Sauromalus
Ctenosaura
Cyclura
Iguana
Conolophus
Amblyrhynchus
Pre-Ctenosaura-lguana Stock
Opiurus
Dipsosaurus
Brachylophus
Chalarodon
Iguanid Ancestor
FIG. 3. "Phylogenetic relationships of the Madagascar Iguanidae and the genera of iguanine lizards,"
after Avery and Tanner (1971:71).
variable, size, and should not therefore be used as independent evidence for relationship.
Furthermore, these authors made no attempt to assess the evolutionary polarity of their
characters by comparison with other iguanids.
Karyological data on iguanines have been practically useless for systematic purposes.
At the crude level of karyotypic analysis commonly applied to lizards, in which only
numbers and sizes of chromosomes and their centromeric positions are determined,
iguanines are conservative. All species of Conolophus, Cyclura, Ctenosaura,
Dipsosaurus, and Sauromalus that have been studied possess a karyotype known to be
10 University of California Publications in Zoology
widespread within Iguanidae and found in several other lizard families as well (Paull et al,
1976). Only Iguana iguana has been reported to differ from this seemingly primitive
condition in that this species supposedly lacks one pair of microchromosomes (Cohen et
al., 1967), but even this finding was contradicted in another study (Gorman et al., 1967;
Gorman, 1973).
Iguanine relationships have only been studied superficially with relatively new and
increasingly popular biochemical techniques. Gorman et al. (1971) presented evidence for
close relationship among iguanines based on immunological studies of lactic
dehydrogenases and serum albumins in turtles and various diapsids. Higgins and Rand
(1974, 1975) showed that the serum proteins and hemoglobins of Amblyrhynchus and
Conolophus were more similar to each other than to those of Iguana. Unfortunately, other
iguanines were not examined. Wyles and Sarich (1983) performed immunological
comparisons of the serum albumins of 10 species of iguanines including representatives of
all eight genera. However, antisera were prepared to the albumins of only four of the
species, and comparisons with all others are given only for the antisera to the albumins of
Amblyrhynchus and Conolophus. Because of the incompleteness of the data, only very
general phylogenetic inferences can be drawn from them.
The unique colon of iguanines was studied by Iverson (1980, 1982), who reported that
the iguanine colon differed from that of all other iguanids and most other lizards in the
possession of transverse valves or folds. However, Iverson (1980) felt that the variation in
these structures within iguanines was of httle value for inferring phylogenetic relationships.
Peterson (1984) has recently surveyed the scale surface microstructure of iguanids.
Although some intergeneric variation in the morphology of the scale surface is known to
occur in iguanines, representatives of only three iguanine genera {Iguana, Dipsosaurus, and
Sauromalus) have been studied at this time.
One final hypothesis about iguanine relationships deserves mention. At the prompting
of a colleague (Ernest Williams) some twenty-five years ago, Richard Etheridge drew up a
phylogenetic diagram depicting his views on the interrelationships among the iguanid
genera. The character basis for this diagram was not specified, and Etheridge (pers.
comm., 1981) informs me that the relationships shown among the iguanine genera were
strongly influenced by his knowledge about the geographic distributions of these animals.
Although he never intended the diagram to be published, it has been published in modified
form (Paull et al., 1976; Peterson, 1984), and has also appeared in several graduate theses.
I reproduce the original diagram here (Fig. 4), noting that its creator does not grant the
hypothesis the conviction seemingly implied by a branching diagram.
GOALS OF THIS STUDY
A detailed study aimed at revealing the pattern of phylogenetic relationships among the
various iguanine lizards is sorely needed. It would provide invaluable information for the
many people studying other aspects of iguanine biology, particularly in an evolutionary
context. I have attempted such a study here with the following as my goals: (1) to provide
Phylogenetic Systematics oflguanine Lizards
11
Uracentron Ophrv^oessoides
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Op\uro5
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42 University of California Publications in Zoology
edge of the palatine is generally present (condition 2). Sauromalus obesus is similar to
Amblyrhynchus and Ctenosaura in this regard, but specimens of S. ater, S. hispidus, and
S. varius exhibit condition 4, in which the maxilla contributes to the ventral rim of the
foramen, rather than condition 2 (samples of other species of Sauromalus are too small
upon which to base generaUzations).
Brachylophus and Dipsosaurus are unique among iguanines in the positions of their
infraorbital foramina, though at different ends of the morphological spectrum. In
Brachylophus, the infraorbital foramen is entirely within the palatine. A suture extending
from the foramen to the lateral edge of the maxillary process of the palatine (condition 2)
was observed in all four B. vitiensis examined but was absent (condition 1) in over half of
the specimens of B.fasciatus. Dipsosaurus is the only iguanine that commonly exhibits
condition 5, in which the infraorbital foramen emerges between palatine and maxilla. In
some specimens, a small posteriorly or laterally directed process is present at the medial
edge of the foramen; in others it is absent. When present, the process is smaller than that
seen in other iguanines (some Sauromalus) in which this process fails to contact the jugal
laterally.
Because of the high intrageneric variation in the position of the infraorbital foramen, I
recognized three characters each with one apomorphic state rather than one character with
four or five: one for the size of the portion of the palatine immediately posterior (or
posteromedial) to the infraorbital foramen, a second for the presence or absence of contact
between this part of the palatine and the jugal, and a third for whether or not the infraorbital
foramen lies entirely within the palatine.
The infraorbital foramina of the four outgroups examined in this study generally differ
from any of those seen in iguanines. Basiliscines and morunasaurs exhibit a condition
similar to that described above as condition 4, but the process of the palatine at the medial
edge of the infraorbital foramen is directed posteriorly rather than laterally (Fig. 17F).
Chalarodon and some Oplurus possess condition 5, while other Oplurus possess the
condition described for basiliscines and morunasaurs. Individual crotaphytines may also
exhibit the basiliscine-morunasaur condition, but in other individuals the infraorbital
foramen is located between palatine and jugal as in some iguanines. In the latter case,
however, the contact of the posteriorly directed process of the palatine with the jugal results
from extensive medial development of the jugal, rather than from lateral extension of the
process of the palatine as in iguanines.
The differences between iguanines and the four outgroups indicate either that some
morphological change occurred between the most recent common ancestor of iguanines and
their closest relatives among these four outgroups or that no living iguanine species is
characterized by the condition that was present in the most recent common ancestor of the
group (though some individual specimens may be). Nevertheless, differences between
iguanines and the outgroups are minor enough that the polarities of all three characters can
be assessed. Because no iguanines possess the same morphology of the infraorbital
foramen seen in the outgroups, no iguanine is scored plesiomorphic for all three characters.
Phylogenetic Systematics oflguanine Lizards
43
FIG. 18. Ventral view of the skull oi Iguana delicatissima (MCZ 16157), showing the medial curvature
of the pterygoids and concomitant abrupt narrowing of the pyriform recess. Scale equals 1 cm.
Abbreviations: pa, palatine; pt, pterygoid; vo, vomer.
Pterygoids (Figs. 5B,C, 6A, 18). These paired bones are the posteriormost palatal
elements. Each pterygoid bears three processes: an anteriorly directed palatine process, an
anterolaterally directed transverse process, and a longitudinally compressed and posteriorly
directed quadrate process. The ventral surface of the palatine process often bears small
teeth. Anterior to the pterygoid notches, where the basipterygoid processes of the
basisphenoid articulate with the pterygoids, the medial edges of the pterygoids of most
iguanines curve towards the midline, resulting in a sudden narrowing of the pyriform
recess (interpterygoid vacuity) (Fig. 18). In contrast, the medial edge of the pterygoids in
Brachylophus is relatively straight, and the pyriform recess narrows more gradually from
posterior to anterior (Fig. 5B).
Outgroup comparison suggests that the condition seen in Brachylophus is
plesiomorphic. Among the four outgroups, only crotaphytines exhibit the strongly curved
44 University of California Publications in Zoology
medial borders of the pterygoids, though a moderate curvature occurs in some oplurines.
Thus, depending upon the relationships among ingroup and outgroups, either the polarity
of this character will be equivocal, or the interpretation that the relatively straight medial
border of the pterygoids is plesiomorphic will be favored.
Ectoptery golds (Figs. 5A,B, 6A). Each ectopterygoid lies at the posterior margin of
the suborbital fenestra forming a brace between the jugal and maxilla anterolaterally and the
pterygoid posteromedially. Near the posteromedial comer of the suborbital fenestra, the
ectopterygoid may contact the palatine, usually on the dorsal surface of the palatal bones.
Contact between ectopterygoid and palatine in this region is the common condition only in
Conolophus among iguanines, and occurs in about half of the Iguana delicatissima
examined. This contact occurs rarely in some other iguanine species. Ectopterygoid-
palatine contact in this region was not observed in any of the four outgroups and is
therefore considered apomorphic.
The ectopterygoid may also contact the palatine near the anterolateral comer of the
suborbital fenestra. This condition is clearly derived for iguanines on the basis of outgroup
comparison, but does not appear to be characteristic of any iguanine species. Only
Amblyrhynchus exhibits the anterolateral ectopterygoid-palatine contact commonly, but
even here it occurs in less than half of the specimens examined. Because the apomorphic
state of this character is not characteristic of any iguanine species and because diagnostic
apomorphies of Amblyrhynchus are plentiful, I have chosen to ignore this character in the
phylogenetic analysis.
BRAINCASE
The iguanine braincase (Figs. 5A,B, 6A), or neurocranium, is composed of four pairs of
endochondral bones-orbitosphenoids, prootics, opisthotics, and exoccipitals-and three
unpaired ones-basisphenoid, basioccipital, and supraoccipital. The parasphenoid, a dermal
bone, is also described here because of its intimate association with the basisphenoid.
Parasphenoid and basisphenoid as well as exoccipitals and opisthotics are fused to each
other even in juveniles, and all other elements except orbitosphenoids fuse with
neighboring braincase elements late in ontogeny. In some very large specimens, even the
orbitosphenoids are fused with one another. Although the stapes and epipterygoids are
splanchnocranial elements, they are included in this section because of their close
associations with the braincase.
Orbitosphenoids (Fig. 19). The orbitosphenoids are paired, crescent-shaped bones
lying within the membranes that separate the brain cavity from the orbits. Each
orbitosphenoid is continuous with five orbital cartilages: the septal cartilage and planum
supraseptale anterodorsally, the pila accessoria and pila antotica posterodorsally, and the
hypochiasmatic cartilage ventrally (Oelrich, 1956). Although consistent differences in the
shapes of the orbitosphenoids exist between iguanine taxa, these differences seem to be
related to differences in body size. In large iguanines, the orbitosphenoids undergo
considerable ontogenetic changes in shape resulting from progressive outward ossification
Phylogenetic Systematics of I guanine Lizards
45
FIG. 19. Anterolateral views of the left orbitosphenoids of three Iguana iguana-(A) RE 454, (B) JMS
245, (C) JMS 713-showing ontogenetic change in the shape of these bones resulting from progressive
ossification outward along the orbital cartilages. Scale equals 1 mm. Abbreviations: he, hypochiasmatic
cartilage; pac, pila accessoria; pan, pila antotica; pis, planum supraseptale.
along the orbital cartilages (Fig. 19). Thus, the posterodorsal edge of each orbitosphenoid
first develops a posterior process where it joins the pila accessoria and pila antotica, and
this process later bifurcates following the two diverging orbital cartilages. The ventral and
anterodorsal ends of the bone elongate by a similar process and, in the case of the latter, the
two orbitosphenoids may eventually meet and fuse at the midline. Small iguanines
generally fail to develop the bifurcating posterodorsal processes of the orbitosphenoids
seen in adults of larger species, and I have never observed medial fusion of the two bones
at their anterodorsal ends in small iguanines.
Epipterygoids (Fig. 6A). The epipterygoids are thin, rod-shaped bones extending from
the palate to the skull roof. Ventrally, the epipterygoids sit in depressions in the dorsal
surfaces of the palatines, but dorsally their articulations with the parietal are either weak or
lacking. I found no differences in epipterygoid morphology among iguanine genera that
might serve as systematic characters.
Prootics (Fig. 6A). The paired prootics form the lateral walls of the neurocranium.
They are sutured to the supraoccipital dorsomedially, to the exoccipitals posteriorly, to the
basioccipital posteroventrally, and to the basisphenoid ventromedially. Although the
46
University of California Publications in Zoology
B
FIG. 20. Ventral views of the posterior portion of the palate and anterior portion of the braincase of (A)
Sauromalus varius (RE 308) and (B) Amblyrhynchus cristatus (RE 1508), showing differences in the length
of the parasphenoid rostrum. Scale equals 1 cm. Abbreviations: bptp, basipterygoid process; bs,
parabasisphenoid; pr, pyriform recess; ps, parasphenoid rostrum; pt, pterygoid.
morphology of the prootics is complex, I have found no characters in these bones that
might serve to elucidate relationships among the basic taxa used in this study.
Parabasisphenoid (Figs. 5B, 6A, 20, 21). Because the parasphenoid and basisphenoid
of iguanines are always fused postembryonically, I describe them as a single element. The
parasphenoid rostrum extends anteriorly like a thin, flat blade from the main body of the
parabasisphenoid on the midline. Compared to those of all other iguanines as well as those
of basiliscines, crotaphytines, morunasaurs, and oplurines, the parasphenoid rostrum of
Amblyrhynchus is relatively short (Fig. 20). Even the parasphenoid rostra of other short-
skulled taxa, such as the basiliscine Corytophanes, are much longer.
The main body of the parabasisphenoid is an unpaired median bone that forms the
anterior floor of the brain cavity. It is sutured with the prootics laterally and with the
basioccipital posteriorly. Anterolaterally, two large basipterygoid processes meet the
anteromedial surfaces of the quadrate processes of the pterygoids at the pterygoid notches,
forming a movable joint between palate and braincase.
Boulenger (1890) first noted variation in the form of the parabasisphenoid (Fig. 21)
among different iguanines. In most iguanines, the ventrolateral edges of the
parabasisphenoid, the cristae ventrolaterals, are strongly constricted behind the
Phylogenetic Systematics oflguanine Lizards
47
oc
FIG. 21. Ventral views of the neurocrania of (A) Sauromalus varius (RE 451), (B) Ctenosaura
hemilopha (RE 325), (C) Iguana iguana (RE 1006), and (D) Cyclura nubila (RE 337), showing differences
in the width of the parabasisphenoid and the size of its posterolateral processes. Scale equals 1 cm.
Abbreviations: bo, basioccipital; bs, parabasisphenoid; eo, exoccipital-opisthotic; oc, occipital condyle;
pro, prootic; ps, parasphenoid rostrum; sot, spheno-occipital tubercle.
basipterygoid prcx;esses, giving the ventral outline of the braincase roughly the shape of an
hourglass (Fig. 21A,B). In contrast, the cristae ventrolaterales of Iguana are widely
separated, extending in almost straight lines from the basipterygoid processes posteriorly to
the spheno-occipital tubercles and giving the ventral outline of the braincase the shape of a
box (Fig. 21 C). Cyclura is variable in this character, though all species have relatively
broad parabasisphenoids (Fig. 2 ID) compared to those of most other iguanines. C.
carinata has the narrowest basisphenoid, while that of C. pinguis is at least as wide as that
of some Iguana delicatissima; other species are intermediate. In at least some of those
48 University of California Publications in Zoology
Cyclura with wide parabasisphenoids, this bone becomes relatively wider during
postembryonic ontogeny. All basiliscines, crotaphytines, morunasaurs, and oplurines have
the parabasisphenoid strongly constricted behind the basipterygoid processes, indicating
that this condition is plesiomorphic for iguanines.
A second part of the iguanine parabasisphenoid exhibits two distinct morphologies that
are constant within genera. The parabasisphenoids of all iguanines except Ctenosaura bear
large posterolateral processes that extend along the anterolateral edges of the lateral
processes of the basioccipital, reaching or closely approaching the spheno-occipital
tubercles (Fig. 21A,C,D). In Cyclura (Fig. 21D) and especially in Iguana (Fig. 21C),
widening of the parabasisphenoid obliterates the distinctness of its posterolateral processes;
their existence is inferred from the lateral extent of the parabasisphenoid along the lateral
processes of the basioccipital. Unlike other iguanines, the posterolateral processes of the
parabasisphenoid are very short or absent in Ctenosaura (Fig. 2 IB), a condition that may
be related to the elongation of the skull in this taxon. Only Crotaphytus (but not Gambelia)
among the outgroups examined exhibits a condition similar to that of Ctenosaura; therefore,
I considered the possession of long posterolateral processes of the parabasisphenoid to be
plesiomorphic.
Basioccipital (Figs. 5B, 21). The basioccipital forms the posterior floor of the brain
cavity and makes up the large medial portion of the occipital condyle. It bears prominent
ventrolaterally directed lateral processes that are capped by the spheno-occipital tubercles.
These tubercles fuse to the lateral processes late in ontogeny. The basioccipital is sutured
to the exoccipitals dorsolaterally, to the prootics anterolaterally, and to the parabasisphenoid
anteriorly. Although iguanine basioccipital morphology is variable, I found no obvious
characters that bear on intergeneric relationships.
Exoccipitals and Opisthotics (Figs. 5C, 21). The exoccipitals are indistinguishably
fused to the opisthotics in postembryonic developmental stages of all iguanines. These
compound bones form the posterior sides of the brain cavity and the lateral edges of the
foramen magnum. They meet the supraoccipital dorsomedially, the prootics anteriorly, and
the basioccipital ventromedially. The paroccipital processes of the opisthotics extend
laterally to contact the supratemporals, bracing the posterolateral comers of the skull. The
relative length of the paraoccipital processes varies among iguanine genera, but differences
are complicated by positive allometry of this feature both within and among taxa (though
the correlation is less precise in the latter case). Apparently the braincase widens more
slowly than the skull as a whole. As the paraoccipital processes elongate, they also become
more posteriorly oriented.
Each exoccipital-opisthotic bears two prominent crests laterally: the crista
interfenestralis, which lies between the fenestra ovalis and the fenestra rotunda; and the
crista tuberalis, which bounds the antrum of the fenestra rotunda posteriorly. Variation
exists in the degree to which the crista tuberalis slants inward dorsally and to which it
obscures the crista interfenestralis in posterior view, but this variation is too great within
iguanine genera to be useful for inferring relationships among them. Dipsosaurus is unique
among iguanines in possessing a sharp, laterally directed point on each crista
Phylogenetic Systematics oflguanine Lizards 49
interfenestralis. Although this process is absent or very small in basiliscines,
crotaphytines, morunasaurs, and oplurines, it is present in some sceloporines. I consider
Dipsosaurus and these sceloporines to have developed a pointed process on the crista
interfenestralis convergently.
Stapes. The stapes, or columella, is a sound-transmitting bone that extends from the
fenestra ovalis (foramen ovale of Oelrich, 1956) in the braincase to a point just behind the
posterior crest of the quadrate. In Ufe it is attached to the external tympanic membrane via a
cartilaginous extracolumella, which is often damaged during skeletal preparation. The
stapes of Amblyrhynchus is robust compared to those of all other iguanines and most other
iguanids, although some sceloporines also have a thick stapes (Axtell, 1958; Earle, 1962).
MANDIBLE
There are seven bones present in the mandibles of all iguanines (Fig. 6B,C); from anterior
to posterior these are: dentary, splenial, coronoid, angular, surangular, prearticular, and
articular. The articular is a splanchnocranial endochondral bone; the remaining bones are
dermal. In some noniguanine iguanids, either splenial or both splenial and angular may be
absent (Etheridge and de Queiroz, 1988).
Dentary (Figs. 6B,C, 22). The dentary is the anteriormost bone in the mandible and
extends posteriorly to about the level of the apex of the coronoid. It is the only tooth-
bearing bone in the lower jaw. Anterior to the splenial, Meckel's cartilage, which extends
from the articular bone to the anterior end of the mandible, is completely enclosed in a bony
tube formed by the dentary. In some other iguanids (e.g., morunasaurs) the groove for
Meckel's cartilage is completely open lingually, while in others (e.g., crotaphytines) the
dorsal and ventral edges of the groove meet to close the tube but remain separated by a
suture. In one late embryo of Amblyrhynchus (SDNHM 45156), Meckel's groove is
closed but retains a suture; however, in all postembryonic iguanines the upper and lower
dentary portions of Meckel's groove are closed and fused.
A series of mental foramina are positioned along the labial face of the anterior half of
the dentary. In all iguanines except Amblyrhynchus and in all outgroups examined, these
foramina lie in a line about halfway between the dorsal and ventral edges of the dentary,
and the dorsal edge of the dentary where it meets the coronoid is approximately level with
the dorsal border of the surangular just posterior to the coronoid (Fig. 22A). The dorsal
border of the dentary in Amblyrhynchus is high, well above the level of the dorsal border
of the surangular, and the row of mental foramina lies more than halfway down the labial
surface of the dentary (Fig. 22B).
Splenial (Fig. 6B,C, 23). The exposed portion of the splenial is roughly diamond-
shaped and lies on the lingual face of the mandible wedged into the posterior end of the
dentary. Posterodorsally, the splenial contacts the coronoid and the surangular;
posteroventrally it is bounded by the angular. The relative size of the splenial is variable in
iguanines, with that of Sauromalus being smaller than those of the other genera. Although
there is considerable variation in the size of the splenial among the four outgroups used in
50
University of California Publications in Zoology
FIG. 22. Lateral views of the right mandibles of (A) Iguana delicalissima {MCL 60823) and (B)
Amblyrhynchus cristatus (RE 1396), showing differences in the relative heights of the dentary (den) and
surangular (sur) and in the position of the row of mental foramina (mf). Scale equals 1 cm.
this study, all have a relatively larger splenial than Sauromalus. Therefore, I consider a
small splenial to be apomorphic for iguanines.
The anterior inferior alveolar foramen pierces the mandible on its lingual surface at a
point between one-third and one-half the way back from the anterior end of the jaw (Fig.
23). In most iguanines, this foramen lies within the suture between the splenial and the
dentary at the anterior end of the splenial or along its anterodorsal edge. The coronoid may
extend anteriorly between splenial and dentary so that it forms the posterior margin of the
anterior inferior alveolar foramen (Fig. 23A) in some Brachylophus, Dipsosaurus, and
Sauromalus. Varying amounts of this anterior extension of the coronoid may be covered
by the splenial lingually, excluding the coronoid from the border of the foramen (Fig.
23B). This condition occurs in Conolophus, Ctenosaura, Iguana, most Cyclura, and in
some Brachylophus, Dipsosaurus, and Sauromalus. In Brachylophus, the splenial is
truncated, and the anterior inferior alveolar foramen sometimes lies entirely within the
dentary. In Amblyrhynchus, the coronoid extends far anteriorly, and the foramen lies
between it, rather than the dentary, and the splenial (Fig. 23C).
Phylogenetic Systematics oflguanine Lizards
51
an
amf
den
amf
amf
aiaf
FIG. 23. Lingual views of the left mandibles of (A) Sauromalus varius (RE 512), (B) Iguana
delicatissima (MCZ 60823), and (C) Amblyrhynchus crisiatus (RE 1091), showing differences in the bones
that surround the anterior inferior alveolar foramen. Scale equals 0.5 cm. Abbreviations: aiaf, anterior
inferior alveolar foramen; amf, anterior mylohyoid foramen; an, angular; cor, coronoid; den, deniary; pre,
prearticular; sp, splenial.
52
University of California Publications in Zoology
B
FIG. 24. Lateral views of the right mandibles of (A) Conolophus pallidas (RE 1382) and (B) Cyclura
cornuta (RE 383), showing differences in the size of the labial process of the coronoid (shaded). Scale
equals 1 cm.
Basiliscines, crotaphytines, morunasaurs, and oplurines have their anterior inferior
alveolar foramina either between splenial and dentary or entirely within the splenial. Both
conditions are found in all four outgroups. The splenial is relatively larger in most of these
outgroups than in any iguanine, which may account for the fact that the foramen of
iguanines does not lie entirely within this bone. Because location of the anterior inferior
alveolar foramen between splenial and dentary is the only condition that occurs in both
ingroup and outgroups, I considered this to be the plesiomorphic condition. The other two
positions of the foramen, entirely within the dentary and between coronoid and splenial,
were considered to be separate modifications of the plesiomorphic condition.
Coronoid (Figs. 6B,C, 23, 24). This bone forms a large dorsal process (coronoid
eminence) immediately posterior to the tooth row, which serves as the insertion for jaw
adductor muscles. It also bears one lateral and two medial ventrally directed processes that
straddle the body of the lower jaw. Ahhough absent in many iguanids, the large process of
the coronoid that extends over the labial surface of the mandible is present in all iguanines
(Fig. 24). This labial extension of the coronoid is most strongly developed in adult
Conolophus, in which its ventral border reaches halfway or farther down the mandible and
covers the posterolateral end of the dentary (Fig. 24A). In most other iguanines, the labial
process of the coronoid is relatively small (Fig. 24B), but in Amblyrhynchus and
Brachylophus the size of the process is intermediate between that of Conolophus and those
of other iguanines. In both Amblyrhynchus and Conolophus the labial process of the
coronoid is relatively small at hatching and increases in size during postembryonic
ontogeny. The labial process of the coronoid is very small in basiliscines, crotaphytines,
and oplurines. Morunasaurs and other iguanids that possess a large labial process of the
Phylogenetic Systematics oflguanine Lizards
53
i£Ocm) (Tttirffma
> "
FIG. 25. Laterial views of the right mandibles of (A) Iguana delicatissima (MCZ 60823), (B)
Sauromalus obesus (RE 467), and (C) Amblyrhynchus cristatus (RE 1396), showing differences in the
lateral exposure of the angular (shaded). Scale equals 1 cm.
54 University of California Publications in Zoology
coronoid have a relatively slight ventral extension of this process compared to
Amblyrhynchus, Brachylophus, and especially Conolophus.
Angular (Fig. 6B,C, 25). The angular is located on the ventral surface of the mandible,
forming sutures with the splenial anterodorsally and the prearticular posterodorsally on the
lingual surface of the mandible and with the dentary anteriorly and the surangular
posteriorly on the labial side. In Brachylophus, Ctenosaura, Cyclura, Dipsosaurus, and
Iguana, the angular extends far up the labial surface of the mandible so that it is easily seen
in lateral view (Fig. 25 A). The angulars of Amblyrhynchus, Conolophus, and Sauromalus
are restricted labially so that they are barely visible from the lateral side (Fig. 25B,C).
Compared to those of other iguanines, the angular of Sauromalus is relatively narrow.
Because the angulars of basiliscines, crotaphytines, morunasaurs, and most oplurines are
wide posteriorly and extend far up the labial surface of the mandible, I considered these to
be plesiomorphic conditions. In Oplurus, the width and labial exposure of the angular are
variable owing to varying degrees of reduction in this bone.
Surangular (Fig. 6B,C, 26, 27). This bone forms the dorsal portion of the mandible
posterior to the coronoid and anterior to the articular facet. It fuses with the prearticular late
in ontogeny. Dorsal to its suture with the angular on the labial surface of the jaw, the
anterior extent of the iguanine surangular is variable (Fig. 26). In Amblyrhynchus,
Brachylophus, and Dipsosaurus the exposed part of the surangular barely extends to the
level of the apex of the coronoid, being covered by the dentary anterior to this level (Fig.
26A,B). In Conolophus, it extends slightly farther, to the level of the anterior slope of the
coronoid eminence. The surangulars of Iguana and Cyclura extend far forward, well
beyond the anterior slope of the coronoid eminence and often anterior to several of the
posteriormost dentary teeth (Fig. 26C). Sauromalus and Ctenosaura are intermediate and
variable within species; the surangular in each of these genera usually extends beyond the
anterior slope of the coronoid eminence, but falls short of the tooth row. Some members
of both genera exhibit a condition similar to that of Conolophus, and some Ctenosaura have
a surangular that extends beyond the posteriormost dentary tooth.
Although the outgroups used in this study are also variable in the anterior extent of the
surangular, in none does it extend as far forward as in Iguana and Cyclura. Therefore, in
the absence of other information, it seems that a great anterior extent of the surangular is a
synapomorphy of these two taxa. If the basic taxa used in this study are monophyletic,
then a similar condition seen in some Ctenosaura must either be convergent, or the
character may have arisen initially as a polymorphism, or some Ctenosaura have reverted to
the ancestral morphology.
On the lingual side of the mandible, ventral to the apex of the coronoid in the arch
between the ventral feet of this bone, a small portion of the surangular is variably visible in
iguanines (Fig. 27). In most iguanines, this part of the surangular is relatively large and
has the shape of a dome above the prearticular (Fig. 27 A). In Amblyrhynchus,
Conolophus, and Cyclura cychlura, the prearticular extends further dorsally, either
completely excluding the surangular from the lingual surface of the mandible (Fig. 27B) or
leaving only a thin sliver of it exposed. Although few small specimens were examined.
Phylo genetic Systematics of I guanine Lizards
55
B
FIG. 26. Lateral views of the right mandibles of (A) Dipsosaurus dorsalis (RE 359), (B) Brachylophus
vitiensis (MCZ 160254), and (C) Iguana iguana (RE 453), showing differences in the anterior extent of the
surangular (shaded). Scale equals 0.5 cm.
there appears to be a transformation of this part of the surangular from exposed to
unexposed during the postembryonic ontogenies of Amblyrhynchus and Conolophus.
Some intraspecific variation exists in this feature; but other than the taxa in which the
unexposed portion of the surangular is the common condition, only in Brachylophus
56
University of California Publications in Zoology
FIG. 27. Medial views of the left mandibles of (A) Iguana delicatissima (MCZ 16157) and (B)
Conolophus subcristatus (MVZ 77314), showing differences in the exposure of the surangular (shaded)
below the coronoid (cor). Scale equals 1 cm.
fasciatus, Cyclura nubila, and Sauromalus varius does this condition appear to be more
than a rare variant.
Except for Corytophanes and Oplurus quadrimaculatus, all outgroups examined have a
relatively large, dome-shaped portion of the surangular visible lingually between the ventral
feet of the coronoid. In Corytophanes, however, lingual restriction of the surangular
results from ventral extension of the coronoid rather than dorsal extension of the
prearticular, the condition in iguanines. For this reason, as well as the hypothesis that
Basiliscus rather than Corytophanes is the sister group of the other two basiliscine genera
(Etheridge and de Queiroz, 1988), I considered the superficially similar conditions seen in
Corytophanes and in some iguanines to be nonhomologous. Thus, the large lingual
exposure of the surangular between coronoid and prearticular is interpreted as
plesiomorphic.
Prearticular (Figs. 6B,C, 28, 29). This bone forms the ventromedial portion of the
posterior end of the mandible. The prearticular bears two processes for the insertion of jaw
adductor and abductor muscles, the posteriorly directed retroarticular process and the
medially directed angular process. The retroarticular process is large in all iguanines, but
the relative size of the angular process is variable. In all iguanines except Amblyrhynchus,
the angular process is small at hatching and increases in relative size as the animal grows
(Fig. 28A-C). The angular process of Amblyrhynchus is very small in juveniles and
increases in relative size only slightly during postembryonic ontogeny (Fig. 28D-F); even
in large adults it has only about the same relative size as those of young of other iguanine
genera.
Except for Corytophanes and Laemanctus, all outgroup taxa examined (including those
that are small as adults) have relatively large angular processes. Thus, if basiliscines are
the sister group of iguanines, then the polarity of this character is equivocal; if not, then the
development of a large angular process during ontogeny must be considered to be
plesiomorphic. Because Amblyrhynchus exhibits the nontransforming ontogeny, strict
LU
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Phylogenetic Systematics oflguanine Lizards 69
of Amblyrhynchus, Conolophus, and Sauromalus are relatively short, often less than two-
thirds the length of the first ceratobranchials (Fig. 33B). Iguana iguana and both species of
Brachylophus have long second ceratobranchials, invariably much longer than the first
ceratobranchials (Fig. 33C). The long second ceratobranchials support the gular fans seen
in these species.
Another variable character in the hyoid skeletons of iguanines is the proximity of the
two second ceratobranchials to one another. In all iguanines except Amblyrhynchus and
Sauromalus, these elements contact each other along the midline for most or all of their
lengths (Fig. 33A,C); sometimes they are separated by a small gap where they meet the
body of the hyoid. In Amblyrhynchus and Sauromalus the second ceratobranchials are
largely or entirely separated from one another (Fig. 33B).
Most of the outgroup taxa examined in this study have second ceratobranchials of
intermediate size, these elements being slightly shorter than the first ceratobranchials.
Some Basiliscus have slightly longer second ceratobranchials, but they are not nearly as
long as those of Brachylophus and Iguana iguana. Crotaphytus and Gambelia have short
second ceratobranchials, about half the length of their first ceratobranchials. Thus, very
long second ceratobranchials are almost certainly apomorphic for iguanines, and, unless
crotaphytines are the sister group of iguanines, short ones are probably also apomorphic.
Separation of the second ceratobranchials along the midline is unequivocally apomorphic,
based on the outgroups used in this study.
AXIAL SKELETON
Presacral Vertebrae (Figs. 34, 35, 36, 37). The presacral vertebrae (Fig. 34) of all
iguanines are procoelous and possess supplementary articular surfaces, zygosphenes and
zygantra, medial to the zygapophyses. Iguanine cervical vertebrae, defined as those
vertebrae anterior to the first one bearing a rib that attaches to the sternum (Hoffstetter and
Gasc, 1969) and including the atlas and axis, invariably number eight. From four to seven
ventrally keeled intercentra are present on the atias, the axis, and between the centra of the
anterior cervical vertebrae, decreasing in size posteriorly. The intercentrum of the axis
fuses with its centrum late in postembryonic ontogeny. There is regional differentiation in
the shape of the presacral vertebrae: the anterior and posterior presacrals are relatively short
compared to those in the middle of the column.
The number of presacral vertebrae in iguanines ranges from 23 to 27 (Table 4). Most
species exhibit a strong statistical mode of 24 presacral vertebrae, with occasional variants
having 23 or 25. I judge this to be the plesiomorphic condition because it is seen in all
species of basiliscines, crotaphytines, morunasaurs, and oplurines that I have examined.
Within the genus Ctenosaura, three species, C. clarki, C. defensor, and C.
quinquecarinata, have a modal number of 25 presacral vertebrae. Because the apomorphic
condition occurs in only some Ctenosaura, this character reveals nothing about
relationships among my basic taxa. I used differences in modal numbers of presacral
vertebrae as a character only in an analysis of relationships within Ctenosaura.
70
University of California Publications in Zoology
con
FIG. 34. Twentieth presacral vertebra of Brachylophus vitiensis (MCZ 160255) in (A) lateral (anterior
to left), (B) dorsal, and (C) ventral views. Scale equals 2 mm. Abbreviations: con, condyle; cot, cotyle;
ns, neural spine; po, postzygapophysis; pr, prezygapophysis; s, synapophysis for articulation of rib; zy,
zygosphene.
Phylogenetic Systematics oflguanine Lizards
71
TABLE 4. Numbers of Presacral Vertebrae
Number of Presacral Vertebrae
Taxon
N
23
24
25 26
27
Amblyrhynchus cristatus
11
100%
Brachylophus fasciatus
13
77
23%
vitiensis
4
100
Conolophus pallidus
subcristatus
9
11
9%
100
91
Ctenosawa acanthura
5
80
20
baked
12
100
clarld
10
90 10%
defensor
5
40 20% 20
20%
hemilopha
palearis
pectinata
22
8
13
100
100
100
quinquecarinata
similis
12
6
8
83
92
17
Cyclura carinata
collei
4
0
25
75
comuta
13
100
cychlura
3
100
nubila
8
100
pinguis
ricordii
1
4
100
100
rileyi
1
100
Dipsosaurus dorsalis
35
3
94
3
Iguana delicatissima
3
100
iguana
20
95
5
Sauromalus ater
5
80
20
australis
2
50
50%
hispidus
obesus
15
23
93
4% 83
7
13
slevini
3
100
varius
10
100
Note: The figures given are percentages of the total number of specimens. Modes are in
italics. Numbers between columns represent specimens with sacral asymmetries.
72
University of California Publications in Zoology
FIG. 35. Lateral views of the twentieth presacral vertebrae of (A) Sauromalus obesus (RE 1578) and (B)
Ctenosaura pectinata (RE 641), showing differences in the height of the neural spine. Scale equals 0.5 cm.
Abbreviations: con, condyle; ns, neural spine; pz, postzygapophysis; s, synapophysis.
Sauromalus differs from other iguanines in the morphology of its presacral vertebrae.
In this genus, the neural spines of the presacral vertebrae are short (Fig. 35A); from the
base of the postzygapophysial articular surfaces to the top of the neural spine they measure
less than 50% of the total height of the vertebrae. In most other iguanines the neural spines
make up more than 50% of the total vertebral height (Figs. 34A, 35B), though there is
considerable variation in this category. This variation includes both interspecific
differences in adult morphology and ontogenetic increase in neural spine height within
species. Ctenosaura bridges the morphological gap between the two categories, with some
members (e.g., C. clarki) approaching the condition seen in Sauromalus. Outgroup
comparison yields equivocal results concerning the polarity of the different conditions of
Phylogenetic Systematics oflguanine Lizards
73
FIG. 36. Dorsolateral views of the tweniieth presacral vertebrae of (A) Dipsosaurus dorsalis (KdQ 22)
and (B) Sauromalus obesus (RE 1578), showing absence and presence, respectively, of bony separation
(arrows) between the prezygapophyses and the zygosphenes. Scale equals 1 mm.
74 University of California Publications in Zoology
neural spine height. Crotaphytines, Hoplocercus, Chalarodon, and some Opiums have
short neural spines; those of Laemanctus, Morunasaurus, and other Oplurus are roughly
intermediate; and those of Basiliscus, Corytophanes, and Enyalioides are tall, reaching
extreme heights in adult male Basiliscus. Because of this ambiguous evidence, I did not
use neural spine height as a character at the first level of phylogenetic analysis within
iguanines, though it was used later at a lower hierarchical level.
The zygosphenes oi Dipsosaurus differ from those of other iguanines (Fig. 36). In this
taxon, the articular surfaces of the zygosphenes are connected laterally to those of the
prezygapophyses by a continuous arc of bone (Fig. 36A). All other iguanines have a deep
anterior notch separating the articular surfaces of the zygosphenes from those of the
prezygapophyses (Fig. 36B).
In their weakest form, zygosphenes are mere out-tumings of the medial surfaces of the
prezygapophysial facets that face dorsolaterally (Hoffstetter and Gasc, 1969). When more
strongly developed, the articular surfaces of the zygosphenes are oriented laterally or
ventrolaterally, eventually coming to face directly opposite those of the prezygapophyses.
The final stage in the expression of the zygosphenal half of the accessory vertebral
articulation appears to be the separation of the zygosphenes from the prezygapophyses by a
notch. Thus, Dipsosaurus is the only iguanine that does not exhibit full development of the
zygospheneal articulations. Although the degree to which the zygosphene-zygantrum
articulation is developed may be positively correlated with size in iguanids (Etheridge,
1964a), this fact alone cannot account for its relatively weak development in Dipsosaurus,
the smallest iguanine. Outside of Iguaninae, Corytophanes, which is about the same size
(snout-vent length) as Dipsosaurus, possesses the deep notch separating zygosphenes from
prezygapophyses, while Petrosaurus that are larger than Dipsosaurus do not.
Outgroup comparison provides equivocal evidence concerning the plesiomorphic
zygosphenal morphology for iguanines. Among the outgroups examined in this study, the
vertebrae of basiliscines and some Enyalioides resemble those of most iguanines in having
strongly developed zygosphenes and zygantra with deep anterior notches between the
articular surfaces of the zygosphenes and those of the prezygapophyses. Crotaphytines
and most morunasaurs have weakly developed accessory vertebral articulations: the
articular surfaces of the zygosphenes are continuous with the medial portions of those of
the prezygapophyses, and, unlike those of all iguanines, they face dorsolaterally rather than
ventrolaterally. The zygosphene-zygantrum articulations are very weakly developed in
Oplurus and Chalarodon. Therefore, some nonhomology between morphologically similar
vertebrae is required under the assumption of iguanine monophyly. Either the notch in the
basiliscine accessory articulation (and that of some Enyalioides) is convergent with the one
in iguanines, or its absence in Dipsosaurus is convergent (and possibly also a reversal)
with a similar condition seen in other outgroups.
Sacrum (Fig. 39). Like all tetrapodous squamates, iguanines characteristically have
two sacral vertebrae, although some specimens have asymmetrical sacra of the form
reported by Hoffstetter and Gasc (1969) involving three vertebrae (Table 4). I recognize
Phylo genetic Systematics of I guanine Lizards 75
two characters in the sacra of iguanines, both involving the pleurapophyses of the posterior
sacral vertebra.
The posterior edges of the pleurapophyses of the posterior sacral vertebrae of iguanines
may or may not bear posterolaterally directed processes (Hofstetter and Gasc, 1969: Fig.
50). These processes are usually present, though not invariably so, in Amblyrhynchus,
Brachylophus, Conolophus, Dipsosaurus, and Sauromalus, and are present in the single
specimen of Cyclura pinguis examined; they are absent in Ctenosaura, Iguana, and other
Cyclura. When present, each process lies posteroventral to a foramen in the posterior
surface of the second pleurapophysis. Occasionally, a process may develop dorsolateral to
the foramen; this process and the one described previously do not seem to be homologous
on positional grounds.
Given the outgroups used in this study and their uncertain relationships, outgroup
analysis is useless for assessing the plesiomorphic condition of this character. The
processes are absent in basiliscines and Hoplocercus, present in the Enyalioides, variably
present in Oplurus, Chalarodon, Gambelia, and Morunasaurus, and present in
Crotaphytus. Therefore, I did not employ this character in phylogenetic analysis at the
level of all iguanines.
The canal leading to the foramen that emerges alongside the posterior edge of each
posterior sacral pleurapophysis has its medial opening on the ventral surface of the same
pleurapophysis. This ventral foramen is almost always present in all iguanines except
Conolophus. In Conolophus, the ventral foramen may also be present, but more often it is
absent, and an open groove is left in place of the enclosed canal. The condition seen in
Conolophus is almost certainly apomorphic, since all four outgroups generally possess the
foramen and enclosed canal.
Caudal Vertebrae (Figs. 37, 38). Iguanine caudal vertebrae are highly variable, but
possess many common structural features. The neural spines of the anterior caudal
vertebrae are taller than their presacral counterparts, but they gradually decrease in size
posteriad and increase their posterior orientation until they vanish toward the end of the tail.
Complete haemal arches, positioned intercentrally, begin between the centra of the second
and third or the third and fourth caudal vertebrae. They are oriented posteroventrally and,
like the neural spines, decrease in size and increase in posterior orientation, moving
posteriorly, until they vanish near the end of the tail. The bases of the haemal arches may
form continuous basal bars or they may be separate. Small, paired elements, presumably
serially homologous with the bases of the haemal arches, or otherwise incomplete haemal
arches, often precede the first complete arch.
Four vertebral series (Fig. 37) can be recognized in the caudal sequence of iguanines
(Etheridge, 1967). The anterior seven to fifteen caudal vertebrae bear a single pair of
laterally or posterolaterally oriented transverse processes (fused caudal ribs) and lack
autotomy septa (fracture planes) (Fig. 37A). In the following series, each vertebra bears
two pairs of transverse processes that are either parallel or diverge from one another (Fig.
37B). The vertebrae in this second series and the remaining two series may or may not
have autotomy septa. Species that lack autotomy septa generally have a shorter double-
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University of California Publications in Zoology
B
D
FIG. 37. Dorsal views of caudal vertebrae of Dipsosaurus dorsalis (KdQ 22): (A) number 4, (B) number
9, (C) number 15, and (D) number 28. Scale equals 1 mm. Abbreviations: fp, fracture plane; ns, neural
spine; prz, prezygapophysis; tp, transverse process.
process series and more frequently possess bilaterally asymmetrical transverse processes.
The transverse processes decrease in size posteriorly and, although the members of the
posterior pair are as large or larger than those of the anterior pair, it is usually the former
that disappear first (although the alternative is not uncommon), resulting in a third series
with a single pair of transverse processes (Fig. 37C). These processes, presumably
serially homologous with the anterior transverse processes of the second series, based on
their anterior position on the vertebrae, continue to decrease in size until they vanish,
leaving a fourth series whose vertebrae lack transverse processes (Fig. 37D). A variable
number of vertebrae at the end of this last series are nonautotomic.
Phylogenetic Systematics oflguanine Lizards 77
The number of caudal vertebrae in iguanines varies from as few as 25 in Ctenosaura
defensor to over 70 in Iguana iguana. Because this number varies considerably within
species, much of the variation is difficult to partition into character states nonarbitrarily.
Nevertheless, an apparent gap exists between Sauromalus and some Ctenosaura, which
have fewer than 40 caudal vertebrae, and all other iguanines, which have more than this
number.
Outgroup comparison does not clearly indicate the plesiomorphic number of caudal
vertebrae in iguanines. Most outgroup species have numbers of caudal vertebrae near or
bridging the gap seen in iguanines. Hoplocercus is unique among outgroup taxa in having
a very short (fewer than 20 vertebrae), spiny tail, even more extreme than those of certain
Ctenosaura, and lacking any complete haemal arches. Because of this ambiguity, I used
the number of caudal vertebrae as a systematic character only at a level less inclusive than
all iguanines.
Unlike other iguanines, Amblyrhynchus, Brachylophus, Conolophus, and Iguana
delicatissima lack autotomy septa along their entire caudal sequences throughout
postembryonic ontogeny, and thus presumably are unable to autotomize their tails. This
does not mean, however, that these lizards cannot regenerate their tails, for caudal
regeneration occurs in both Brachylophus fasciatus (Etheridge, 1967) and B. vitiensis. In
these cases, regeneration was associated with a broken vertebra rather than intervertebral
separation, supporting Etheridge's (1967) suggestion that regeneration is a function of
trauma to the vertebra rather than autotomy itself (but see Bellairs and Bryant, 1985). It is
noteworthy that all iguanines that lack caudal fracture planes are insular forms. Caudal
autotomy is generally thought to be an adaptation for escaping predators (Congdon et al.,
1974; Turner et al., 1982), and the intensity of predation is often less severe on islands
(Carlquist, 1974).
I am unable to resolve the polarity of this character with the four outgroups used in this
study. The basiliscines Laemanctus and Corytophanes, the crotaphytine Crotaphytus, and
the morunasaur Hoplocercus lack autotomy septa, but in other members of all of these
groups and in all oplurines examined, the septa are present. Thus, monophyly of each of
the outgroups and of iguanines requires multiple homoplastic events no matter which
condition, presence or absence of autotomy septa, is considered to be plesiomorphic for
iguanines. Because of the ambiguity involved in this character, I withheld an initial
decision on its polarity and used it only at a hierarchical level below that of all iguanines.
The beginning of the second series of caudal vertebrae varies both within and among
iguanine species. High overlap among species in the range of this character within species
renders much of this variation useless as systematic characters, but one character can be
recognized for the purpose of comparisons among the basic taxa used in this study. In
Brachylophus and Dipsosaurus, the series of caudal vertebrae with two pairs of transverse
processes per vertebra begins at the eighth to the tenth caudal vertebra; in all other
iguanines, this series begins at the tenth or a more posterior vertebra. Because of
intraspecific variation in the beginning of this second series of caudal vertebrae, a given
78 University of California Publications in Zoology
specimen may not be assignable to one or the other group, but a species (sample) can be so
assigned.
Unfortunately, the pathway of character-state transformation cannot be analyzed by
outgroup comparison without making additional assumptions about the character. None of
the four outgroups used in this study, nor any other iguanian, possesses caudal vertebrae
with two pairs of transverse processes (Etheridge, 1967). Nevertheless, a close
correspondence between the beginning of the series of caudal vertebrae with two pairs of
transverse processes and the beginning of the series of autotomic vertebrae in iguanines
suggests that the latter might be used as the character instead. Unfortunately, not all
iguanines (nor all outgroup taxa) possess autotomic caudal vertebrae. Therefore, in order
to use this character I first must assume that the beginning of the series of caudal vertebrae
with two pairs of transverse processes in taxa that lack autotomy septa corresponds with
the beginning of the autotomic series in those taxa that possess autotomy septa. Second, I
must assume that the beginning of the autotomic series in taxa that lack vertebrae with two
pairs of transverse processes corresponds with the beginning of the series of vertebrae with
two pairs of transverse processes.
Under these assumptions, outgroup comparison can be used with those outgroups
possessing autotomic vertebrae, but it provides ambiguous evidence concerning the
plesiomorphic condition of this character. The autotomic series of Basiliscus begins in a
range that has the tenth caudal vertebra in its midst. That of Gambelia begins posterior to
the tenth vertebra, while those of Enyalioides, Morunasaurus, and oplurines begin anterior
to the tenth vertebra. The polarity decision for this character will thus vary depending upon
the relationships among iguanines and the four outgroups. Because these relationships are
unknown, I withheld a decision on the polarity of this character in phylogenentic analysis at
the level of all iguanines.
Lazell (1973:1-2) citing Etheridge (in litt.) distinguished Iguana from Cyclura by the
presence of "a low fmlike process above the neural arch of no more than six anterior caudal
vertebrae" in the former, compared to the "high, fmlike processes above the neural arches
of all the caudal vertebrae" in the latter. The processes in question are presumably
ossifications of the dorsal skeletogenous septum. When the remaining iguanine genera are
considered, there appears to be a continuum in the height of these processes rather than two
discrete morphologies, low and high. Even within an organism, the morphology of these
processes differs among the caudal segments. In most iguanines, the processes on the
anterior caudal vertebrae are merely thin, midsagittal extensions of the anterior edges of the
neural spines. Moving posteriorly along the column, apices form on the processes, and the
processes themselves are displaced anteriorly, sometimes becoming entirely separated from
their respective neural spines. The height of the processes increases, then gradually
decreases, moving anterior to posterior. Although the midsagittal processes generally
disappear short of the end of the tail, they are present (Fig. 3 8 A) well beyond the anterior
third of the caudal sequence (determined by vertebra number, not by distance from the
beginning of the tail) in all genera except Brachylophus and Iguana. The situation in
Brachylophus and Iguana differs from the one described above in that the processes are
Phylogenetic Systematics oflguanine Lizards 79
con + .. / . f/^ipv^.^^ con-
FIG. 38. Lateral views of the ninth caudal vertebrae of (A) Dipsosaurus dorsalis (KdQ 22) and (B)
Iguana iguana (MVZ 78384), showing differences in the size of the dorsal midsagittal processes. Scale
equals 2 mm; anterior is to iJie right. Abbreviations: con, articular condyle; ns, neural spine; p, dorsal
midsagittal process.
relatively small and do not continue as far posteriorly in the caudal sequence (Fig. 38B).
Although they may be present beyond the sixth caudal vertebra, I have never observed
them beyond the tenth. The caudal sequences oi Brachylophus and Iguana consist of more
than 55 vertebrae; thus, the processes are not present beyond the anterior fifth of the
sequence.
Although the evidence is somewhat equivocal, outgroup comparison favors the
interpretation that the condition of the midsagittal processes of the caudal vertebrae seen in
Brachylophus and Iguana is apomorphic. The alternative condition occurs in
crotaphytines, morunasaurs, and oplurines, but basiliscines are similar to Brachylophus
and Iguana. In basiliscines, the small, fmlike processes are rarely found posterior to the
fifth caudal vertebra. Basiliscines, Brachylophus, and Iguana are all arboreal, suggesting a
possible functional relationship between the morphology of the caudal vertebrae and use of
the tail in arboreality.
Ribs (Fig. 39). Variation in the numbers and the morphology of various kinds of ribs
has served as the basis for characters in previous systematic studies of iguanids (Etheridge,
1959, 1964a, 1965b, 1966); but iguanines are conservative in most of these features. Like
those of all iguanids, iguanine ribs are holocephalous and most have two parts: a bony
dorsal portion and a cartilaginous ventral portion, the inscriptional rib (Etheridge, 1965b).
The length of the inscriptional ribs is highly variable from one region of the vertebral
column to another, and at the posterior end of the presacral series these elements are often
lacking.
Cervical ribs, those ribs anterior to the first ribs that are attached to the sternum,
typically number four pairs in iguanines, beginning on the fifth presacral vertebra (very
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University of California Publications in Zoology
atlas
intercentra
sternum
sternal ribs
postxiphisternal ribs
cervical ribs
xiphisternal ribs
sacrum
FIG. 39. Presacral and sacral vertebrae and ribs oi Dipsosaurus dor salts in ventral view. The drawing is
a composite.
rarely on the fourth) and ending on the eighth. The bony portions of the first two cervical
rib pairs are short, while the second two are much longer, about the same length as the
anterior thoracic ribs. The next four (rarely three) rib pairs, on presacral vertebrae nine
through twelve, are sternal ribs, attached ventromedially to the lateral borders of the
sternum through their cartilaginous ventral portions. Two (rarely three; sometimes one in
Sauromalus) pairs of xiphisternal ribs follow the sternal ribs. These ribs articulate dorsally
Phylogenetic Systematics of I guanine Lizards 8 1
with vertebrae 13 and 14, and their cartilaginous ventral portions unite with one another
before attaching to the posterior end of the sternum. The remaining ribs are simply termed
postxiphisternal. The bony anterior postxiphistemal ribs are often as long as their
xiphisternal counterparts, but there is a progressive reduction in their length posteriorly.
The posteriormost ribs are shorter than the sacral pleurapophyses. Lumbar vertebrae,
posterior presacral vertebrae lacking ribs, are not found in iguanines. Very rarely, the ribs
of the posteriormost presacral segment are fused to the vertebra.
Etheridge (1965b) described variation in the abdominal skeleton (postxiphistemal
inscriptional ribs) of iguanids. All iguanines were reported to exhibit a pattern in which all
postxiphistemal inscriptional ribs are attached to their corresponding dorsal bony ribs. In
some iguanines, all of these inscriptional ribs end free, while in others the members of one
or more of the anterior pairs may join midventrally to form continuous chevrons. Based on
Etheridge's (1965b) findings and my own observations, the iguanine genera exhibit the
following morphologies in the abdominal skeleton: (1) continuous chevrons absent
(Dipsosaurus, Sauromalus); (2) continuous chevrons present or absent (Amblyrhynchus,
Conolophus, Ctenosaura, Cyclura, Iguana); and (3) continuous chevrons present
(Brachylophus). The number of continuous chevrons and other enlarged postxiphistemal
inscriptional ribs may exhibit taxon-specific pattems, but because the fragile abdominal
skeleton is often destroyed in skeletal preparations, I have not been able to examine enough
specimens to assess these pattems adequately.
In the outgroups that I have examined, postxiphistemal inscriptional ribs that form
continuous midventral chevrons are found only in momnasaurs; however, because they
share the common feature of having at least some inscriptional ribs that bear no traces of
attachment to the bony ribs, Etheridge (pers. comm.) believes that the oplurine pattem is a
transformation of that seen in momnasaurs. Basiliscines and crotaphytines are similar to
Dipsosaurus and Sauromalus in their lack of continuous chevrons. Thus, evidence bearing
on the polarity of this character is equivocal, and I did not use it in my initial analysis of
relationships among iguanine genera.
PECTORAL GIRDLE AND STERNAL ELEMENTS
The iguanine pectoral girdle and stemal elements (Fig. 40) are closely associated and form
a complex functional unit composed of six pairs of elements plus two median, unpaired
ones. Some of these elements are composed entirely of calcified cartilage, while others are
bony. All iguanines possess all 14 elements: suprascapulae, scapulae, coracoids,
epicoracoids, clavicles, interclavicle, sternum, ana xiphistema.
Suprascapulae (Fig. 40). These are paired fan-shaped elements composed of calcified
cartilage that extend continuously from the dorsal edges of the scapulae. The suprascapulae
lie just extemal to the posterior cervical and the anterior thoracic bony ribs. They are not
attached directly to the axial skeleton, but ride over the bony portions of the ribs. As in
most squamates, the only direct skeletal attachments between pectoral girdle and axial
skeleton are through the stemum and cartilaginous portions of the anterior thoracic ribs. In
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University of California Publications in Zoology
FIG. 40. Pectoral girdles of (A) Brachylophus fasciatus (RE 1866), (B) Ctenosaura hemilopha (RE
1341), and (C) Sauromalus obesus (RE 411). A is a lateral view; anterior is to the right. B and C are
ventral views. Calcified cartilage is stippled. Scale equals 1 cm. Abbreviations: acf, anterior coracoid
fenestra; cf, coracoid foramen; cl, clavicle; cor, coracoid; epc, epicoracoid; gf, glenoid fossa; icl,
interclavicle; pcf, posterior coracoid fenestra; sc, scapula; scf, scapulocoracoid fenestra; sf, scapular fenestra;
sr, sternal ribs; ssc, suprascapula; st, sternum; stf, sternal fontanelle; xi, xiphistemum.
Phylogenetic Systematics oflguanine Lizards 83
most iguanines, the surfaces of the scapulae and suprascapulae form a continuous, laterally
convex arc, but in Sauromalus the junction of these surfaces is angular and the
suprascapulae are oriented more horizontally than in other iguanines. The condition of the
suprascapulae in Sauromalus is presumably related to the depressed body form of these
animals, and on the basis of outgroup comparison is almost certainly apomorphic.
Scapulae, Coracoids, and Epicoracoids (Fig. 40). The scapula and coracoid of each
side are closely associated and function as a single unit. Although separated by a suture
throughout most of the period of growth, the two bones fuse to form a single
scapulacoracoid element near the attainment of maximum size. Prominent features of the
scapulocoracoids are the glenoid fossae for the articulation of the humeri, which lie at the
junctions between scapulae and coracoids along their posterior edges, coracoid foramina
anteroventral to the glenoid fossae, and three or four (rarely two) scapulocoracoid
fenestrations on each side of the girdle, the functional significance of which is discussed by
Peterson (1973).
The scapulocoracoid fenestrations pierce the pectoral girdle along the anterior margins
of the scapulae and coracoids, between these bones and the cartilagenous epicoracoids
(Fig. 40). Following the terminology of Lecuru (1968a), from dorsal to ventral the four
pairs of fenestrations are: (1) scapular fenestrae, which lie anterodorsally within the
scapulae; (2) scapulocoracoid fenestrae, situated at the junctions between scapulae and
coracoids; (3) anterior (primary) coracoid fenestrae, located within the coracoids; and (4)
posterior (secondary) coracoid fenestrae, also located within the coracoids but
posteroventral to the anterior coracoid fenestrae. All iguanines invariably possess the
scapulocoracoid and the anterior coracoid fenestrae; the scapular fenestrae and the posterior
coracoid fenestrae may be present or absent.
Scapular fenestrae are invariably present in all iguanines except Amblyrhynchus and
Sauromalus, in which they are small or occasionally absent. Outgroup analysis yields
equivocal results concerning the polarity of these character states. Scapular fenestrae are
present in crotaphytines, the single Enyalioides oshaughnessyi examined, Chalarodon, and
Oplurus cuvieri; they are absent in basiliscines, other morunasaurs, and Oplurus
quadrimaculatus (in which the large "scapulocoracoid" fenestrae may be homologous with
the scapular plus the scapulocoracoid fenestrae of other oplurines). Because of this
ambigiuty, I used the presence or absence of scapular fenestrae as a systematic character
only at a level less inclusive than all iguanines.
The presence of posterior coracoid fenestrae is more variable intragenerically than the
presence of scapular fenestrae. Posterior coracoid fenestrae are invariably absent in
Brachylophus (Fig. 40A); usually absent in Dipsosaurus; usually present in
Amblyrhynchus, Ctenosaura (Fig. 40B), Cyclura, and Sauromalus (Fig. 40C); and
invariably present in Conolophus and Iguana. The amount of variability differs among the
genera in the third group. Posterior coracoid fenestrae are frequently absent in
Amblyrhynchus and Sauromalus, in which all species are variable in the presence of these
fenestrae except S. australis and S. slevini, both of which are represented by small samples
(n=2). The absence of a posterior coracoid fenestra is rare in Ctenosaura; it has been
84 University of California Publications in Zoology
detected in only some members of three species, C. clarki, C. hemilopha, and C. similis.
In Cyclura, the absence of a posterior coracoid fenestra was observed only in two out of
eight C. nubila, one of which lacked the fenestra unilaterally.
According to Peterson (1973), the presence of a posterior coracoid fenestra is
associated with large size and/or the presence of a proximal belly of the M. biceps.
Because a posterior coracoid fenestra is present in the species of Ctenosaura that reach
smaller maximum sizes than Brae hy lop hus, in which the fenestra is absent, presence of the
fenestra cannot be strictly size-dependent. The association of the fenestra with a proximal
belly of the M. biceps was not examined in the present study.
Although the evidence is somewhat ambiguous, outgroup comparison favors the
interpretation that the absence of posterior coracoid fenestrae is plesiomorphic for
iguanines. Basiliscines and oplurines invariably lack these fenestrae. Morunasaurs
generally lack posterior coracoid fenestrae, but in rare cases very small ones are present.
Crotaphytines generally possess posterior coracoid fenestrae, although they are
occasionally absent in Gambelia. If the general rather than the invariable presence or
absence of posterior coracoid fenestrae is considered to be the systematic character, then
outgroup comparison will either yield equivocal results or indicate that the absence of
posterior coracoid fenestrae is plesiomorphic, depending on the relationships among
iguanines and the four outgroups.
Clavicles (Fig. 40). Iguanine clavicles are boomerang-shaped, paired bones lying
along the anterior margin of the pectoral girdle. They articulate ventromedially with the
anterior median end of the interclavicle and dorsolaterally with the anteroventral edges of
the suprascapular Compared with those of certain other iguanids, the clavicles of
iguanines are relatively simple, generally lacking sharp, ventrally directed processes (hooks
of Etheridge, 1964a) and ventromedial fenestrae, although small fenestrae are sometimes
present in Conolophus.
Sauromalus differs from other iguanines in having slender clavicles, which are more or
less elliptical in cross section. The clavicles of other iguanines have thin lateral shelves,
making them wider when viewed anteriorly, although some Ctenosaura approach the
condition seen in Sauromalus. Because the clavicles of all outgroup taxa examined except
Oplurus quadrimaculatus are wide with thin lateral shelves, this condition must be
considered plesiomorphic for iguanines.
Interclavicle (Fig. 40). This median, unpaired bone is the ventralmost in the pectoral
girdle. In iguanines it bears the shape of a "T" or an arrow, formed by a lateral process at
the anterior end on each side and a median posterior process. The anterior process seen in
certain other squamates (Lecuru, 1968b) is virtually absent.
The extent of the posterior median process of the interclavicle varies among iguanines
and is here assessed by the location of the posterior tip of the bone relative to the lateral
comers of the sternum and the sternal attachments of the cartilaginous sternal ribs.
Amblyrhynchus and Sauromalus (Fig. 40C) have short interclavicles that do not extend
posteriorly beyond the lateral corners of the sternum, where the first pair of sternal ribs
attaches. In all other iguanines except Conolophus pallidus and Cyclura nubila the
Phylogenetic Systematics oflguanine Lizards 85
posterior process of the interclavicle extends beyond this level (Fig. 40B) and, depending
on the taxon, it may extend beyond the points of attachment of the second or even the third
sternal-rib pairs. Conolophus pallidus and Cyclura nubila have interclavicles of
intermediate length. In these taxa the interclavicle extends to about the level of the lateral
comers of the sternum or slightly beyond. The width of the posterior process appears to be
related to its posterior extent: short interclavicles are usually wider than long ones. The
correlation is not strict, however, for some Sauromalus have narrow posterior processes.
Among the outgroups examined, only some Crotaphytm have an interclavicle that does
not extend posteriorly beyond the lateral comers of the sternum. I therefore considered the
short interclavicle to be apomorphic for iguanines.
Another variable feature of iguanine interclavicles is the angle between each lateral
process and the posterior process. All species exhibit at least 10° of variation in this feature
with significant intertaxic overlap. For this reason I recognize only two categories as
character states. Amblyrhynchus and Sauromalus (Fig. 40C) have roughly T-shaped
interclavicles, with the angle between the lateral and posterior processes ranging from 75°
to 90°. Other iguanines have arrow-shaped interclavicles (Fig. 40B); the angle formed by
the lateral and posterior processes is usually less than 75°. Although the angle in question
overlaps the first category in some members of both species of Brachylophus and
Conolophus, as well as in some Cyclura nubila, the lower limits of the range of angles in
these species is well below that in Amblyrhynchus and Sauromalus. Outgroup comparison
indicates that the arrow-shaped interclavicle is plesiomorphic. Among basiliscines,
crotaphytines, morunasaurs, and oplurines, I have found T-shaped interclavicles only in
the basiliscines Laemanctus serratus and Corytophanes hernandesii.
Sternum and Xiphisterna (Figs. 37, 40). The sternum of iguanines is shaped like a
diamond or a pentagon and is composed of calcified cartilage. In embryos and some
hatchlings, the sternal plate is paired, but the two halves fuse in late embryonic or early
postembryonic ontogeny to form a single median element. Anterolaterally, the sternum
meets the epicoracoids in a tongue-in-groove articulation, the coracostemal joint, which
permits posterolateral- anteromedial movements of the scapulocoracoid units relative to the
sternum (Jenkins and Goslow, 1983). The posterolateral borders of the sternal plate are
the attachment sites for the cartilaginous ventral portions of four thoracic rib pairs (sternal
ribs) and two others that attach via the xiphistema. A sternal fontanelle may be present
(Fig. 40B) or absent (Fig. 40C).
In most iguanines, the sternal fontanelle is long and narrow and is covered partially or
completely by the posterior process of the interclavicle. In Amblyrhynchus and
Sauromalus the sternal fontanelle is often small, and in the latter it may be subdivided into
two or three small, round holes. In some specimens of both taxa the fontanelle is absent.
Absence or small size of the sternal fontanelle is unequivocally apomorphic on the basis of
the outgroups used in this study.
Sternal shape is variable in iguanines and is partly related to another feature, the
proximity of the two sternal-xiphistemal attachments to one another and the midline. In
most iguanines the xiphistema attach to the sternum very close to the midline and to one
86
University of California Publications in Zoology
B
-^ /®p
aip
FIG. 41. Pelvic girdles of (A) Sauromalus obesus (RE 467) and (B) Ctenosaura pectinata (RE 419) in
dorsal view. Scale equals 1 cm. Abbreviations: aip, anterior iliac process; ep, epipubis; hi, hypoischiac
cartilage; il, ilium; is, ischium; it, ischial tuberosity; pi, proischiac cartilage; pu, pubis.
another, yielding a diamond-shaped sternum (Fig. 40B). In Sauromalus the xiphistema are
widely separated from one another, and the sternum is pentagonal (Fig. 40C).
Amblyrhynchus is somewhat intermediate, having a small but distinct gap between its
xiphistema; however, the shape of its sternum is much closer to that of most other
iguanines than to that of Sauromalus.
Most members of all outgroup taxa examined have diamond-shaped sterna with the
xiphistema in close proximity to each other. The exceptions are Oplurus quadrimaculatus
and Crotaphytus, which approach the condition seen in Sauromalus to a greater or lesser
degree, respectively. Although the pentagonal stemum with widely separated xiphistema is
probably apomorphic, the ambiguity is sufficient to force me to use this character only at a
less inclusive level than that of all iguanines.
PELVIC GIRDLE
The iguanine pelvic girdle (Fig. 41) consists of three pairs of bones: dorsal ilia, which
articulate with the sacral pleurapophyses; posteroventral ischia; and anteroventral pubes.
Cartilaginous epipubes, and proischiac and hypoischiac cartilages, are situated on the
midline between the pubes and the anterior and posterior parts of the ischia, respectively.
An obvious difference in the shape of the pelvic girdle separates Sauromalus (Fig. 41 A)
from all other iguanines (Fig. 4 IB). Relative to those of other iguanines, the pelvis of
Sauromalus is short and broad, clearly an apomorphic condition on the basis of the
outgroups examined.
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University of California Publications in Zoology
ac
FIG. 43. Right hind limb skeleton of Brachylophusfasciatus: (A) femur; (B) tibia, fibula, and proximal
tarsals; and (C) distal tarsals, metatarsals, and phalanges. Scale equals 1 cm. Abbreviations: ac,
astragalocalcaneum; f, fibula; t, tibia; I-V, digits 1-5.
Phylogenetic Systematics oflguanine Lizards 89
Another unique feature occurs in some Sauromalus, notably S. varius. In these
animals the ischium is excavated mesial to the posteriorly directed ischiac tubercle,
enhancing the distinctness of this structure. Because this character varies within a single
genus, it is uninformative about relationships among the basic taxa used in this study.
I disagree with Lazell's (1973:1-2) statement that "In Dipsosaurus and Sauromalus the
ilial shaft tapers abruptly posteriorly and the anterior iliac process is rather weakly
developed." The ilial shaft of Sauromalus is narrower at its posterior terminus than those
of other iguanines, but it does not taper abruptly. In Dipsosaurus the ilial shaft may taper
abruptly, but it is broad near its posterior end like that of other iguanines except
Sauromalus. While the anterior iliac process of Sauromalus does appear to be relatively
small, that of Dipsosaurus is not.
LIMBS
Iguanine hmbs exhibit considerable variation, but I have chosen not to use this variation as
the basis for systematic characters. All iguanines possess the same bony elements in their
limbs, but the proportions of the various limb bones vary considerably among iguanine
taxa. Nevertheless, these proportions seem to be very plastic features, so plastic that I was
unable to establish polarities with any confidence. Therefore, I give only a general
description of this variation and devote most of the section to the description of characters
that do not vary among iguanines but that may be useful at higher levels of comparison.
Compared to those of other iguanines, the limb bones of Brachylophus are relatively
long, while those of Amblyrhynchus and Sauromalus are relatively short. These
proportional differences are most evident in the long bones, metapodials, and phalanges.
Proportional differences in the carpal and tarsal elements (mesopodials) are less obvious.
All iguanines possess the following bones in the forelimb (Fig. 42): humerus, radius,
ulna, radiale, ulnare, pisiform, lateral centrale, five distal carpals, five metacarpals, and 17
phalanges. According to Carroll (1977), the first distal carpal of modem lizards is
homologous with the medial centrale of other diapsids. As in other iguanids (Renous-
Lecuru, 1973), the intermedium is absent. The phalangeal formula of the manus is
2:3:4:5:3. An entepicondylar foramen is present in the humerus.
The hind limbs of iguanines (Figs. 43, 44) consist of femur, tibia, fibula,
astragalocalcaneum, two distal tarsals proximal to metatarsals three and four, five
metatarsals, and 18 phalanges. The phalangeal formula of the pes is 2:3:4:5:4 which, like
that of the manus, is presumably plesiomorphic for squamates.
OSTEODERMS
Two large Amblyrhynchus (JMS 126, 127) have dermal ossifications that apparently
formed within the large, conical scales overlying the nasal, prefrontal, and frontal bones
(PI. 1), confirming Camp's (1923:307) observation that osteoderms are present in this
taxon. Osteoderms, which differ from the rugosities that develop on various bones of the
90
University of California Publications in Zoology
tlV
FIG. 44. Right tarsal region of Brachylophus fasciatus. Scale equals 0.5 cm. Abbreviations: a,
astragalus; c, calcaneum; f, fibula; ml-V, metatarsals 1-5; t, tibia; till and tlV, distal tarsals 3 and 4.
dermal skull roof in certain iguanids, are unknown in iguanids other than Amblyrhynchus
(Etheridge and de Queiroz, 1988), and their presence is thus considered derived within
iguanines. Although Conolophus has enlarged, conical head scales overlying the nasal,
prefrontal, and frontal bones similar to, yet smaller than, those seen in Amblyrhynchus, I
have never observed osteoderms in Conolophus. The osteoderms of Amblyrhynchus are
easily removed along with the skin, judging from their absence in most skeletal
preparations of Amblyrhynchus, and it is therefore possible that Conolophus also
possesses osteoderms. I will assume that osteoderms are absent in Conolophus until their
presence is demonstrated.
Phylogenetic Systematics oflguanine Lizards
91
J
Plate 1. Dorsal (above) and lateral (below) views of the skull oi Amblyrhynchus crisiatus (JMS 127),
showing osteoderms.
NONSKELETAL MORPHOLOGY
Iguanines exhibit considerable morphological variation in functional systems other than the
skeleton, and I have therefore used certain nonskeletal characters for which relatively
complete data on variation, both among all iguanine genera and for the four outgroups,
were easily obtained. Characters in this section were taken from diagnoses in revisions,
reviews, and faunal accounts as well as from the few comparative studies of nonskeletal
anatomy of iguanines. I also include some obvious characters that I noticed in the course
of this study.
ARTERIAL CIRCULATION
Zug (1971) was pessimistic about the systematic utiUty of the variation that he found in the
patterns of the major arteries of iguanids. Nevertheless, I found at least three characters in
his descriptions, as well as one additional character, that suggest monophyletic groups
within Iguaninae. Other arterial characters may also be useful for phylogenetic studies
within this taxon, but have not yet been studied in sufficient detail. Still other characters
are either invariant among iguanines (e.g., branching pattern of the carotid arches,
separation of the origins of dorsal aorta and subclavians) or variable within iguanine genera
(e.g., separate origin of mesenteries versus origin from a common trunk), and thus cannot
be used for examining relationships among these genera. These characters may be useful at
different hierarchical levels.
It should be noted that Zug (1971) surveyed nearly all genera of Iguanidae, which
limited him to relatively small samples for each genus (a maximum of four specimens for
any iguanine genus). Zug did not examine Conolophus; my data are based on dissection of
a single C. subcristatus (CAS 12058).
Zug reported that the subclavians of Brachylophus and Dipsosaurus are covered
laterally by a thin, flat ligament, while those of other iguanines pass laterally beneath
(=dorsal to?) a muscle bundle. My own observations on Dipsosaurus reveal muscle fibers
in the thin sheets of tissue that cover the subclavians just lateral to their origins from the
right systemic arch. Furthermore, whether muscular or ligamentous, the structures that
cover the subclavians are the posterior portions of the paired M. rectus capitis anterior or
their tendons, which originate on the ventral surfaces of the cervical vertebrae and insert on
the exoccipitals and basioccipital lateral to the occipital condyle. Thus, even if the reported
difference exists, it is a difference in the muscles rather than in the subclavian arteries.
92
Phylogenetic Systematics oflguanine Lizards 93
The subclavians of Conolophus exhibit neither of the patterns described by Zug for
other iguanines. In this taxon, the subclavians lie posterior and ventral to the origins of the
M. rectus capitis anterior and are thus not covered by this muscle. For these reasons I use
only the difference between the subclavians of Conolophus and those of all other iguanines
as a systematic character.
According to Zug (1971), in Dipsosaurus and Brachylophus the dorsal aorta originates
dorsal to the heart (by union of the left and right systemic arches), while in other iguanines
it originates posterior to the heart. My observations on Dipsosaurus (n=l) and Sauromalus
(n=l) reveal a profound difference supporting this distinction. In Dipsosaurus the systemic
arches unite to form the dorsal aorta about as far posterior as the middle of the heart and the
anterior end of the ninth vertebra. In Sauromalus the systemic arches remain paired much
further posteriorly; they unite well behind the heart, near the middle of the 13th vertebra.
Conolophus, however, is intermediate. The dorsal aorta in this taxon originates at about
the level of the posterior end of the heart and the anterior end of the 1 0th vertebra. Because
Zug did not discuss variation within his two categories, I arbitrarily placed Conolophus
with those iguanines in which the dorsal aorta originates posterior to the heart.
Finally, I note minor exceptions to some of Zug's observations. In the single
Dipsosaurus that I examined, the heart reaches the transverse axillary plane rather than
being entirely anterior to this plane. In the single Sauromalus that I examined, the coeliac
originates between, but separate from, the two mesenteric arteries.
COLIC ANATOMY
Iverson (1980) studied colic anatomy in iguanines. Variation within this group exists in the
presence of colic valves, irregular colic folds, circular valves, semilunar valves, and in the
number of colic valves. Although Iverson considered iguanine colic anatomy to be of
limited phylogenetic value, at least two characters seem to be potentially useful for inferring
phylogenetic relationships among iguanines. Nevertheless, because all of the colic
modifications that characterize subsets of iguanines appear to be transformations of
characters unique to iguanines, their polarity cannot be established by outgroup comparison
until certain phylogenetic relationships within iguanines are determined. For example, one
cannot use noniguanine outgroups to infer that colic folds are plesiomorphic relative to colic
valves, or vice versa, because neither condition occurs in these outgroups.
The fact that noniguanines possess neither of the conditions found in iguanines is only
a problem if these conditions are homologous members of a transformation series.
Otherwise, each condition could be said to be lacking in the outgroups and therefore to be a
separate apomorphic state. If they are homologous, however, one is forced to detennine
the apomorphy of the alternative conditions relative to each other. I assume homology
between the colic valves and colic folds, because they share the common property of being
infoldings of the same tissue components of the colic wall (Iverson, 1980). I also assume
homology between circular and semilunar valves. The only difference between these two
morphologies is whether or not the infolded tissue extends around the entire perimeter of
94 University of California Publications in Zoology
the colon (Iverson, 1980). Because of the difficulties involved in outgroup comparison
with the colic characters, I used them only at hierarchical levels less inclusive than
Iguaninae as a whole.
Although much variation exists in the modal number of colic valves among iguanine
taxa, this number is positively correlated with (maximum?) body size and does not change
significantly during the postembryonic ontogeny of a given species (Iverson, 1980). Lack
of a thorough study of the relationship between valve number and body size makes
comparison of taxa that differ in body size problematic, and I have chosen not to use the
numbers of different types of colic valves as systematic characters.
EXTERNAL MORPHOLOGY
Unlike the arterial and colic characters, which were obtained from comparative studies, the
following characters were taken primarily from generic diagnoses or are based on personal
observations. No adequate comparative descriptions of these characters exist in the
literature, and I therefore describe them in more detail than the arterial and colic characters.
The scutellation of the iguanine head is complex and is potentially the source of many
systematic characters. I note here only some obvious intertaxic differences and characters
that have been used by previous authors.
Scales of the Snout and Dorsal Head. In most iguanines the snout terminates anteriorly
in a median, azygous rostral scale. Sauromalus differs from all other iguanines in that it
usually lacks an unpaired, median rostral (H. M. Smith, 1946: Fig. 38); the anteriormost
snout scales above the lip are paired and separated by a median suture that meets the lip
margin. According to Gates (1968), this character occurs in about 78% of S. obesus. All
basiliscines, crotaphytines, morunasaurs, and oplurines possess a median, azygous rostral
scale, indicating that the condition seen in Sauromalus is apomorphic within iguanines.
The other scales in the snout region also exhibit differences among iguanines. In most
taxa they are relatively small, about the same size as the remaining dorsal cephalic scales.
In Iguana and some Cyclura, however, these scales form large plates. Interspecific
variation in this character is great within Cyclura (figures in Schwartz and Carey, 1977),
ranging from the small scales much like those of other iguanines in C carinata, C. pinguis,
and C. ricordii to the large plates of C. cychlura and C. nubila. Cyclura collei and C. rileyi
are intermediate, and the horns of C. cornuta are difficult to compare with the conditions
seen in other taxa. Because outgroup comparison suggests that enlarged rostral scales are
apomorphic (only Lxiemanctus among the outgroups examined has enlarged snout scales),
either (1) the occurrence of this feature in Iguana and some Cyclura is convergent; (2) it
indicates that Iguana is the sister group of some part of a paraphyletic Cyclura; or (3)
enlarged snout scales is a synapomorphy oil guana plus Cyclura, and some Cyclura have
evolved small snout scales secondarily. Only a consideration of other characters can
resolve this question.
Amblyrhynchus and Conolophus are similar to one another and differ from all other
iguanines in the scalation of the dorsal surface of the head. In these two genera the dorsal
Phylogenetic Systematics oflguanine Lizards 95
head scales are pointed and conical, giving the head a rugose texture. This condition is
more strongly developed in Amblyrhynchus than in Conolophiis. All other iguanines have
flat or only slighdy domed dorsal head scales. In Sauromalus hispidus these scales are
more strongly pointed than in the other taxa, but the condition is not nearly as extreme as in
the Galapagos iguanas.
Like most iguanines, crotaphytines, oplurines, and most basiliscines have relatively flat
head scales. Laemanctus serratus is the only basiliscine with conical head scales, but these
scales are confined to the casque on the back of the head and do not extend onto the frontal
and nasal regions as in the Galapagos iguanas. The dorsal head scales of morunasaurs are
variable. In Hoplocercus and Morunasaurus these scales are convex but not pointed; in
Enyalioides they are pointed and conical, but are relatively much smaller than those of the
Galapagos iguanas. Thus, the condition of the dorsal head scales in Amblyrhynchus and
Conolophus is not seen in any of the outgroups and must be considered apomorphic.
Superciliaries. Etheridge and de Queiroz (1988) noted variation in the superciliary
scales of iguanines. In Dipsosaurus these scales are elongate anteroposteriorly and overlap
one another extensively, especially in the anterior portion of the row. Amblyrhynchus and
Sauromalus possess the opposite extreme in which the superciliaries are roughly
quadrangular and nonoverlapping. The remaining iguanines are intermediate, with only
moderate overlap of the superciliaries. Outgroup comparison indicates that the condition of
the superciliaries has been relatively plastic at this level of comparison, making
determination of its polarity ambiguous. Quadrangular, nonoverlapping superciliaries
occur in morunasaurs and the basiliscine Corytophanes. Elongate, strongly overlapping
superciHaries occur in oplurines, and an intermediate condition occurs in crotaphytines and
the basiliscines Basiliscus and Laemanctus.
Suboculars. The morphology of the subocular scales is also variable in iguanines
(Etheridge and de Queiroz, 1988). Dipsosaurus and Ctenosaura have one long and several
shorter suboculars. In all other iguanines except Amblyrhynchus, which is intermediate,
all of the suboculars are approximately equal in size. The condition of the suboculars in the
four outgroups is too variable to allow inference about the polarity of this character.
Basiliscines, morunasaurs, and some Crotaphytus have suboculars that are subequal in
size. Other Crotaphytus have one moderately elongate subocular. Gambelia and oplurines
have one very long subocular and several much shorter ones.
Anterior Auricular Scales (Van Denburgh, 1922). Sauromalus differs from all other
iguanines in the scales that border the tympanum anteriorly, the anterior auricular scales.
From two to five of these scales are enlarged relative to the neighboring scales and project
posterolaterally over the tympanum, offering protection to this delicate membrane. In all
other iguanines except Dipsosaurus, the anterior auricular scales are small and the
tympanum is completely exposed. Dipsosaurus possesses a row of slightly enku-ged
anterior auricular scales. Outgroup comparison indicates that the enlarged anterior
auriculars of Sauromalus are apomorphic. Basiliscines, Crotaphytus, Hoplocercus,
Morunasaurus, and some Enyalioides lack enlarged anterior auricular scales, while in
Gambelia and oplurines they are only slightly enlarged, roughly comparable to those of
96 University of California Publications in Zoology
Dipsosaurus. Some Enyalioides possess one or two seemingly nonhomologous large,
pointed scales dorsal to the tympanum. Some sceloporines have anterior auriculars fully as
large in proportion to their body size as those of Sauromalus; I consider this to be
convergent.
Gular Region. All iguanines possess a transverse gular fold, although it is relatively
weakly developed in Amblyrhynchus compared to other iguanines. A midsagittal gular
expansion, or dewlap, is variably developed, but in no iguanine is it as highly extensible as
in Anolis. A large dewlap is present in male Brachylophus fasciatus (Boulenger, 1885;
Gibbons, 1981) and in both sexes of B. vitiensis (Gibbons, 1981), Ctenosaura palearis
(Bailey, 1928), and Iguana. It is absent in Amblyrhynchus, Conolophus, most
Ctenosaura, Dipsosaurus, and Sauromalus, but is weakly developed in Cyclura
(Boulenger, 1885) and Ctenosaura bakeri (Bailey, 1928). The presence of a dewlap is not
a simple dichotomy, as evidenced by the intermediate condition in Cyclura and Ctenosaura
bakeri; nevertheless, a morphological gap exists between those taxa possessing a large
dewlap and those in which it is weakly developed or absent.
A prominent gular fold occurs in all outgroup taxa used in this study and is, therefore,
inferred to be plesiomorphic for iguanines. Although the absence of a dewlap is the most
common condition among the outgroups, sufficient variation exists that this condition
cannot be inferred to be plesiomorphic for iguanines as long as higher-level relationships
remain unresolved. The dewlap is absent in Basiliscus, Laemanctus, crotaphytines,
Hoplocercus, Morunasaurus, and oplurines, but it is present in Corytophanes and male
Enyalioides (Boulenger, 1885).
Although a dewlap is developed to varying degrees in different iguanines, only the two
species of Iguana possess a gular crest, a midsagittal row of enlarged scales extending
below the throat along the edge of the dewlap. Because a gular crest is lacking in all
outgroup taxa examined except Corytophanes, its presence in Iguana is inferred to be
apomorphic.
Middorsal Scale Row. A row of scales aligned along the dorsal midline is present in all
iguanines except Sauromalus. When present, the scales of the middorsal row are
differentiated from the neighboring scales, although the degree of differentiation is highly
variable. This variation ranges from the small, rounded knobs that form the row in
Dipsosaurus to the tall curved spikes of large Amblyrhynchus and Iguana. In some
Cyclura (Schwartz and Carey, 1977) and Ctenosaura (Bailey, 1928), the crest formed by
the series of modified middorsal scales is interrupted in the shoulder or the sacral region.
The presence of a middorsal scale row in the outgroups is highly variable, making it
impossible to determine polarity at this level of analysis. A middorsal scale row is present
in most basiliscines, Enyalioides, Morunasaurus annularis, and Chalarodon; it is absent in
crotaphytines, Laemanctus serratus, Morunasaurus groi, Hoplocercus, and Oplurus.
Subdigital Scales of the Pes (Fig. 45). The conspicuous combs on the toes of Cyclura
have long been used to diagnose this genus and especially to separate it from Ctenosaura
(Barbour and Noble, 1916; Bailey, 1928; Schwartz and Carey, 1977). Similar toe
denticulations, however, are known to occur in other iguanines (Gibbons, 1981). These
Phylogenetic Systematics oflguanine Lizards
97
aks
FIG. 45. Pedal digit II of (A) Sauromalus obesus (MVZ 35978), (B) Brachylophus fasciatus (CAS
54664), and (C) Cyclura carinata (CAS 54647) in anterodorsal view, showing differences in the morphology
of the subdigital scales. Scale equals 1 cm. Fused subdigital scales are shaded. Abbreviations: aks,
anterior keels of subdigital scales.
98 University of California Publications in Zoology
denticulations are formed by enlarged keels on the anterior edges of the subdigital scales.
Varying degrees of enlargement of these keels are seen in iguanines. In Sauromalus the
anterior keels of the subdigital scales are nearly the same size as the posterior ones (the
subdigital scales are usually bi- or tricarinate), and the subdigital scales are roughly
bilaterally symmetrical with respect to the long axis of the toe (Fig. 45 A). In Dipsosaurus
and Iguana the anterior keels of the subdigital scales are slightly larger than their posterior
counterparts, and the subdigital scales are asymmetrical. Further enlargement of the
anterior keels and a concomitant increase in the asymmetry of the pedal subdigital scales is
seen in Amblyrhynchus, Conolophus, Brachylophus (Fig. 45B), and Cyclura (Fig. 45C)
(increasing in size roughly in that order). Much of this variation can be seen within
Ctenosaura.
All subdigital scales do not exhibit equal enlargement of the keels, which are usually
largest under the first phalanx of digit II and the first and second phalanges of digit HI.
Cyclura and Ctenosaura defensor differ from other iguanines in that the scales bearing these
largest keels are fused at their bases, giving the scales the appearance of a comb when
viewed anteriorly (Fig. 45C). In Cyclura these combs are formed under the first phalanx
of digit II and the first and second phalanges of digit III (illustrated in Barbour and Noble,
1916: Plates 13-15); in Ctenosaura defensor they occur only under the first phalanx of digit
III.
Enlargement of the anterior keels of the subdigital scales is present in all outgroups
examined in this study except basiliscines, though the degree of enlargement is variable.
Basiliscines cannot be compared with iguanines because they have but a single median keel
on the subdigital scales. In oplurines and crotaphytines the keels are moderately enlarged
as in Dipsosaurus, but in morunasaurs (especially Morunasaurus) they are very large.
Thus it is not possible to determine the precise plesiomorphic size of the keels of iguanines.
Nevertheless, two conditions seen in iguanines can be considered to be apomorphic.
Because the subdigital scales of all outgroups (except basiliscines) bear large anterior keels,
the small anterior keels and concomitant symmetry of the subdigital scales in Sauromalus
are apomorphic. Fusion of the bases of the subdigital scales with enlarged anterior keels is
not seen in any outgroup and must also be considered apomorphic.
Hands and Feet. The hands and feet of Amblyrhynchus are partially webbed
(Boulenger, 1885), which is presumably related to the semi-aquatic habits of these lizards
and is unique among iguanids.
Caudal Squamation. One of the supposedly diagnostic features of Ctenosaura is a tail
armed with strong, spinous scales (Bailey, 1928); however, similar caudal squamation also
occurs in most Cyclura (Barbour and Noble, 1916; Schwartz and Carey, 1977). Within
these two taxa the caudal squamation is highly variable among species. In some Cyclura
(e.g., C. cornuta), the caudal scales in adjacent verticils are of similar size and are not
spinous, a condition like that seen in most other iguanines. In the remaining Cyclura and in
Ctenosaura the tail bears whorls of enlarged, spinous scales at regular intervals along its
length. These whorls are separated by verticils of smaller scales that are smooth or much
less spinous (except the middorsal scale row). The number of verticils between the whorls
Phylo genetic Systematics of I guanine Lizards 99
of enlarged, spinous scales is variable along the tail, generally decreasing posteriorly. The
maximum number of rows between whorls of enlarged scales ranges from none in some
Ctenosaura defensor (Bailey, 1928; Duellman, 1965) to about six in Cycliira nubila
(Schwartz and Carey, 1977). Within Ctenosaura, there appears to be a negative correlation
between the size of the scales in the enlarged whorls and both the number of scale rows
between them and the relative length of the tail.
The evolution (or loss) of spinose tails appears to have occurred repeatedly within
iguanids. Like most iguanines, basiliscines, crotaphytines, Chalarodon, and some
Enyalioides have more or less uniform caudal squamation without spinous scales. Other
Enyalioides, Morunasaurus, Hoplocercus, and Oplurus have whorls of enlarged spinous
scales separated by smaller scales. The short, spinose tail of Hoplocercus is as extreme as
anything seen in Ctenosaura. Although it seems likely that tails with whorls of enlarged,
spinous scales are apomorphic within iguanines, this polarity is equivocal unless
assumptions are made about either the relationships among outgroups and ingroup or those
within morunasaurs and oplurines.
Cross-sectional Body Shape. Sauromalus differs from all other iguanines in its cross
sectional body shape. All other iguanines are either laterally compressed or cylindrical in
cross section, while Sauromalus is strongly depressed. The shape of the body of
Sauromalus and several other of its distinctive skeletal features (e.g., low neural spines,
horizontal orientation of the suprascapular short and broad pelvic girdle) are probably
redundant characters. They are treated separately here because (1) the correlation among
them is only hypothesized, and (2) some of them are known to change without
accompanying changes in the others (e.g., not all depressed lizards have suprascapulae that
form sharp angles with the scapulae).
Cross-sectional body shape in members of the four outgroups examined in this study
varies in such a way that it is impossible to determine the plesiomorphic shape for
iguanines. Basiliscines are laterally compressed. Some morunasaurs are compressed
{Enyalioides) while others are depressed {Hoplocercus), and both crotaphytines and
oplurines are depressed, though generally not as strongly as Sauromalus.
SYSTEMATIC CHARACTERS
Based on the descriptions of the iguanine skeleton and other anatomical features given
above, I recognize the following systematic characters for use in phylogenetic analysis.
SKELETAL CHARACTERS
L Ventral surface of premaxilla (Fig. 7): (A) bears large posterolateral processes; (B)
posterolateral processes absent.
2. Posteroventral crests of premaxilla (Fig. 7): (A) small, do not continue up the sides
of incisive process and are not pierced by foramina for maxillary arteries; (B) large,
continue up sides of incisive process and are pierced or notched by foramina for maxillary
arteries.
3. Anterior surface of rostral body of premaxilla: (A) broadly convex; (B) nearly flat.
4. Nasal process of premaxilla I (Figs. 6, 14, 45): (A) slopes backwards; (B) nearly
vertical.
5. Nasal process of premaxilla II (Fig. 8): (A) wholly or partly exposed dorsally
between nasals; (B) covered dorsally between nasals.
6. Size of nasals and nasal capsule (Figs. 5, 9, 11): (A) nasal capsule of moderate
size, nasals relatively small; (B) nasal capsule enlarged, nasals relatively large.
7. Bones in anterior orbital region (Fig. 10): (A) lacrimal contacts palatine behind
lacrimal foramen; (B) prefrontal contacts jugal behind lacrimal foramen.
8. Frontal (Figs. 5, 9, 11): (A) longer than wide, or length approximately equal to
width; (B) wider than long.
9. Large paired openings at or near frontonasal suture: (A) absent; (B) present.
10. Cristae cranii on ventral surface of frontal (Fig. 12): (A) extend in a smooth
continuous curve from frontal onto prefrontals; (B) frontal portions project anteriorly,
forming a step between frontal and prefrontal portions.
11. Paired cristae on ventral surface of frontal medial to cristae cranii (Fig. 12): (A)
absent or weakly developed; (B) strongly developed, united as a single median crest
anteriorly and together with the cristae cranii forming pockets in the anteroventral surface of
the frontal.
12. Dorsal borders of orbits (Figs. 5, 9, 11): (A) more or less smoothly curved; (B)
wedge-shaped.
13. Position of parietal foramen (Figs. 5, 9, 11; Table 2): (A) on the frontoparietal
suture; (B) variable (either A or C); or (C) within the frontal bone.
100
Phylogenetic Systematics of I guanine Lizards 101
14. Supratemporals: (A) extend anteriorly more than halfway across the posterior
temporal fossae; (B) extend anteriorly no more than halfway across the posterior temporal
fossae.
15. Maxilla I: (A) relatively flat or concave laterally; (B) flares outward ventral to the
row of supralabial foramina.
16. Maxilla II (Figs. 5, 14): (A) premaxillary process of maxilla lies roughly in the
same plane as the remainder of the maxilla; (B) premaxillary process of maxilla curves
dorsally.
17. Lacrimal: (A) large; (B) intermediate; (C) small.
18. Ventral process of squamosal (Fig. 15): (A) large; (B) small or absent.
19. Squamosal (Fig. 15): (A) separated from or barely contacting dorsal end of
tympanic crest of quadrate; (B) abuts against dorsal end of tympanic crest of quadrate.
20. Septomaxilla: (A) flat, or with a weak ridge on anterolateral surface; (B) with a
pronounced longitudinal crest.
21. Anterior dorsal surface of palatines (Fig. 16): (A) with a low medial ridge; (B)
with a high medial crest.
22. Infraorbital foramen I (Fig. 17), process of palatine projecting posterolaterally or
laterally behind the infraorbital foramen: (A) large; (B) small or absent.
23. Infraorbital foramen II (Fig. 17), process of palatine projecting posterolaterally or
laterally behind the infraorbital foramen: (A) fails to contact jugal; (B) contacts jugal.
24. Infraorbital foramen III (Fig. 17): (A) located on the lateral or posterolateral edge
of the palatine; (B) located entirely within the palatine (may or may not be connected by a
suture to the lateral edge of the palatine).
25. Pterygoids (Figs. 5, 18): (A) medial borders relatively straight anterior to the
pterygoid notch, pyriform recess narrows gradually; (B) medial borders curve sharply
toward the midline anterior to the pterygoid notch, pyriform recess narrows abruptly.
26. Ectoptery golds: (A) fail to contact palatines near posteromedial corners of
suborbital fenestrae; (B) usually contact palatines near posteromedial corners of suborbital
fenestrae.
27. Parasphenoid rostrum (Fig. 20): (A) long; (B) short.
28. Cristae ventrolaterals of parabasisphenoid (Fig. 21): (A) strongly constricted
behind basipterygoid processes; (B) intermediate; (C) widely separated.
29. Posterolateral processes of parabasisphenoid (Fig. 21): (A) present and large; (B)
small or absent.
30. Laterally du-ected points on cristae interfenestrahs: (A) absent; (B) present.
31. Stapes: (A) thin; (B) thick.
32. Relative heights of dorsal borders of dentary and surangular on either side of
coronoid eminence (Fig. 22): (A) approximately equal; (B) dorsal border of dentary well
above that of surangular.
33. Splenial: (A) large; (B) small.
102 University of California Publications in Zoology
34-35. Anterior inferior alveolar foramen (Fig. 23): (A) always between splenial and
dentary, the coronoid may or may not contribute to its posterior margin; (B) entirely within
the dentary in some specimens (others A); (C) between splenial and coronoid.
36. Labial process of coronoid (Fig. 24): (A) small; (B) intermediate; (C) large.
37. Angular I (Fig. 25): (A) extends far up the labial surface of the mandible and is
largely visible in lateral view; (B) does not extend far up the labial surface of the mandible
and is barely visible in lateral view.
38. Angular II: (A) wide posteriorly; (B) narrow posteriorly.
39. Surangular (Fig. 26): (A) exposed laterally only about as far forward as the apex
of the coronoid or the anterior slope of this bone, and never anterior to the last dentary
tooth; (B) exposed laterally well anterior to the apex of the coronoid and often anterior to
the last dentary tooth.
40. Lingual exposure of surangular between ventral processes of coronoid (Fig. 27):
(A) a dome-shaped portion exposed; (B) largely or completely covered by prearticular.
41. Angular process of prearticular (Fig. 28): (A) increases substantially in relative
size during postembryonic ontogeny, becoming a prominent structure in adults; (B)
increases only slightly in relative size during postembryonic ontogeny, remaining relatively
small even in adults.
42. Retroarticular process (Figs. 28, 29): (A) tympanic and medial crests converge
posteriorly to give the process a triangular outline in both juveniles and adults; (B)
tympanic and medial crests converge posteriorly in juveniles, but the posterior ends
separate during ontogeny so that the process assumes a quadrangular outline in adults.
43-44. Modal number of premaxillary teeth (Table 3): (A) fewer than seven; (B)
seven; (C) more than seven.
45. Crowns of premaxillary teeth: (A) lateral cusps small or absent; (B) lateral cusps
large.
46. Crowns of posterior marginal teeth I (Fig. 30): (A) tricuspid; (B) four-cusped; (C)
polycuspate (5 to 10 cusps); (D) serrate.
47. Crowns of tricuspid posterior marginal teeth II (Fig. 30): (A) individual lateral
cusps much smaller than apical cusp; (B) individual lateral cusps relatively large, subequal
to apical cusp in size.
48. Pterygoid teeth I (Fig. 31): (A) entire row lies along the ventromedial edge of the
pterygoid adjacent to the pyriform recess; B) posterior portion of row displaced laterally.
49. Pterygoid teeth II (Fig. 31): (A) entire row single throughout ontogeny; (B)
posterior portion of row doubles ontogenetically; (C) entire row doubles ontogenetically.
50. Pterygoid teeth III (Fig. 31): (A) anterior portion of tooth patch present; (B)
absent (posterior end of suborbital fenestra used as reference point).
51. Pterygoid teeth IV (Fig. 31): (A) usually present; (B) usually absent.
52-53. Hyoid I (Fig. 33): (A) second ceratobranchials short, often less than two-
thirds the length of the first ceratobranchials; (B) intermediate, from two-thirds the length
of the first ceratobranchials to slightly longer than the first ceratobranchials; (C) long, much
longer than the first ceratobranchials.
Phylogenetic Systematics of I guanine Lizards 103
54. Hyoid n (Fig. 33): (A) second ceratobranchials in medial contact with one another
for most or all of their lengths; (B) separated from one another medially for most or all of
their lengths.
55. Neural spines of presacral vertebrae (Figs. 34, 35): (A) tall, making up more than
50% of the total vertebral height; (B) short, making up less than 50% of the total vertebral
height.
56. Zygosphenes (Fig. 36): (A) connected to prezygapophyses by a continuous arc of
bone; (B) separated from zygapophyses by a deep notch.
57. Sacrum I: (A) posterolateral processes of second pleurapophyses (usually)
present; (B) (usually) absent.
58. Sacrum II: (A) foramina in the ventral surfaces of the second pleurapophyses
(usually) present; (B) (usually) absent.
59. Number of caudal vertebrae: (A) more than 40; (B) fewer than 40.
60. Autotomy septa in caudal vertebrae: (A) present (Fig. 37); (B) absent.
61. Beginning of the autotomic series of caudal vertebrae or beginning of the series of
caudal vertebrae with two pairs of transverse processes (Fig. 37): (A) at or before the 10th
caudal vertebra; (B) at or behind the 10th caudal vertebra.
62. Thin, midsagittal processes on the dorsal surface of the caudal centra anterior to the
neural spines (Fig. 38): (A) relatively large and present well beyond the anterior third of
the caudal sequence; (B) relatively small and confined to the anterior fifth of the caudal
sequence.
63. Postxiphistemal inscriptional ribs: (A) do not form continuous chevrons (Fig. 39);
(B) variably form continuous chevrons; (C) invariably form continuous chevrons.
64. Suprascapulae: (A) situated primarily in a vertical plane and forming a continuous
arc with the scapulocoracoids; (B) situated primarily in a horizontal plane and forming an
angle with the scapulocoracoids.
65. Scapular fenestrae (Fig. 40): (A) large, invariably present; (B) small or absent.
66. Posterior coracoid fenestrae (Fig. 40): (A) usually absent; (B) usually present.
67. Clavicles: (A) wide, with a prominent lateral shelf; (B) narrow, the lateral shelf
small or absent.
68. Posterior process of the interclavicle (Fig. 40): (A) extends posteriorly beyond the
lateral corners of the sternum; (B) does not extend beyond the lateral corners of the
stemum.
69. Lateral processes of the interclavicle (Fig. 40): (A) usually forming angles of less
than 75° with the posterior process and giving the interclavicle the shape of an arrow; (B)
forming an angle of between 75° and 90° with the posterior process and giving the
interclavicle the shape of a T.
70. Sternal fontanelle (Fig. 40): (A) present and of moderate size; (B) small or absent.
71. Stemum-xiphistemum (Fig. 40): (A) sternum diamond-shaped (quadrilateral), the
xiphisterna in close proximity; (B) intermediate; (C) sternum pentagonal, the xiphisterna
widely separated.
72. Pelvic girdle (Fig. 41): (A) long and narrow; (B) short and broad.
104 University of California Publications in Zoology
12). Anterior iliac process: (A) large; (B) small.
74. Osteoderms (PI. 1): (A) absent; (B) present.
NONSKELETAL CHARACTERS
75. Heart (Zug, 1971): (A) does not extend posterior to the transverse axillary plane;
(B) extends posterior to the transverse axillary plane.
76. Subclavian arteries (Zug, 1971; present study): (A) covered ventrally by the
posterior end of the M. rectus capitis anterior; (B) not covered by the M. rectus capitis
anterior.
11. Dorsal aorta (Zug, 1971): (A) right and left systemic arches unite to form the
dorsal aorta above the heart; (B) origin of dorsal aorta posterior to heart.
78. Coeliac artery (Zug, 1971): (A) arises from the dorsal aorta anterior to and
separate from the two mesenteric arteries; (B) arises posterior to the mesenteries, between
the mesenteries, or continuous with one or the other of the mesenteries.
79. Colic wall (Iverson, 1980): (A) forms one or more transverse valves; (B) forms
numerous irregular transverse folds.
80. Colic valves (Iverson, 1980): (A) all valves semilunar; (B) one or more valves
circular (semilunar valves may be present or absent).
81. Rostral scale: (A) median and azygous; (B) subdivided by a median suture.
82. Scutellation of snout region: (A) consists of many small scales subequal in size to
those of superorbital and temporal regions; (B) consists of relatively few large scales.
83. Dorsal head scales: (A) flat or slightly convex; (B) pointed and conical.
84. Superciliary scales (Etheridge and de Queiroz, 1988): (A) quadrangular and non-
overlapping; (B) intermediate; (C) elongate and strongly overlapping.
85. Subocular scales (Etheridge and de Queiroz, 1988): (A) all subequal in size; (B)
one or two suboculars moderately elongate; (C) one subocular very long, the rest shorter.
86. Anterior auricular scales: (A) all relatively small or one row slighriy enlarged; (B)
one row of scales anterior to tympanum pointed and gready enlarged, extending posteriorly
over tympanum.
87. Gular fold: (A) conspicuous; (B) weakly developed.
88. Dewlap: (A) small or absent; (B) present and large.
89. Gular crest: (A) absent; (B) present.
90. Middorsal scale row: (A) present; (B) absent.
91. Pedal subdigital scales I (Fig. 45): (A) anterior keels larger than posterior ones,
scales asymmetrical; (B) anterior and posterior keels approximately equal in size, scales
roughly symmetrical with respect to the long axis of the toe.
92. Pedal subdigital scales II (Fig. 45): (A) individual scales entirely separate; (B)
scales with greatly enlarged anterior keels fused anteriorly at bases.
93. Toes: (A) unwebbed; (B) partially webbed.
Phylogenetic Systematics of I guanine Lizards 105
94. Caudal squamation: (A) caudal scales in adjacent verticils approximately equal in
size, smooth or keeled but not spinous; (B) tail bears whorls of enlarged, strongly spinous
scales.
95. Cross-sectional body shape: (A) laterally compressed or cylindrical; (B) strongly
depressed.
CHARACTER POLARITIES AND THE
PHYLOGENETIC INFORMATION CONTENT
OF CHARACTERS
Character- State distributions for the 95 characters among the four outgroups and the
polarities inferred from these distributions are summarized in Table 5. Distributions of the
characters among the basic taxa (genera) of iguanines are given in Table 6. Not
surprisingly, the number of characters that exhibit variation within a basic taxon is
correlated with the number of recognized species in the taxon.
Each character can be placed in one of four categories depending on its phylogenetic
information content:
I. Unambiguous synapomorphies of basic taxa (characters 1, 2, 3, 4, 6, 9, 11, 12, 14,
15, 16, 17-2, 20, 22, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36-2, 38, 41, 42, 46-3, 47,
49-2, 58, 64, 67, 72, 74, 75, 76, 81, 86, 87, 89, 91, 93). The derived condition of
each of these characters is found in only one of the basic taxa and is characteristic of the
taxon in which it is found. These characters support the monophyly of particular
iguanine genera but provide no information about relationships among them.
II. Ambiguous synapomorphies of basic taxa (characters 10, 13-2, 24, 28-2, 53, 78,
82, 92). The derived condition of each of these characters is characteristic of one of the
basic taxa but is also variably present in one or more other basic taxa. These characters
are either (1) synapomorphies of one basic taxon that have arisen convergently in part
of another one; (2) synapomorphies of one entire basic taxon plus part of another one
that are indicative of the paraphyletic status of the latter; or (3) synapomorphies of a
clade consisting of two or more basic taxa that have subsequently reversed within some
of them. These characters may or may not provide information about relationships
among basic taxa.
III. Derived characters shared by two or more basic taxa (characters 5, 7, 8, 13, 17,
18, 19, 21, 23, 25, 28, 36, 37, 39, 40, 45, 46, 46-2, 48, 50, 51, 52, 54, 62, 66, 68,
69, 70, 77, 83). The derived condition of each of these characters is characteristic of
more than one of the basic taxa and may or may not occur variably in one or more of
the others. These characters are the primary data relevant to an analysis of relationships
106
Phylogenetic Systematics oflguanine Lizards 107
among the basic taxa. Because of character incongruence, the interpretation of these
characters as synapomorphies is not always straightforward, and a reasonable
interpretation of any one character must take the others into consideration. Some of the
similarities are undoubtedly homoplastic and must ultimately be interpreted as more
than one synapomorphy.
IV. Characters of undeterminable polarity (characters 43, 44, 55, 56, 57, 59, 60, 61,
63, 65, 71, 73, 79, 80, 84, 85, 88, 90, 94, 95). These characters are too variable
either within or among the outgroups, or both, for any reasonable inference to be made
about their polarity. Therefore, these characters cannot be used as evidence for
phylogenetic relationships within Iguaninae until either the relationships of the
outgroups to iguanines are determined (Maddison et al., 1984) or some phylogenetic
structure within iguanines is established so that some iguanines can serve as outgroups
to others in an analysis of a less inclusive group (Watrous and Wheeler, 1981).
108
University of California Publications in Zoology
TABLE 5. Distributions of Character States of 95 Characters Among Four Outgroups to
Iguanines and the Polarities That Can Be Inferred From Them
Character
Ba
Oi
Cr
itgroup
Mo
Op
Polarity
Inference
1
A
A
A
A
A=0, B=l
2
A
A
A
A
A=0, B=l
3
A
A
A
A
A=0, B=l
4
A
A
A
A
A=0, B=l
5
A
Al
A
A
A=0, B=l
6
A
A
A
A
A=0, B=l
7
A
B
A
A
A=0, B=l
8
A
A
A
A
A=0, B=l
9
A
A
A
A
A=0, B=l
10
A
A
A
A
A=0, B=l
11
A
A
A
A
A=0, B=l
12
A
A
A
A
A=0, B=l
13
A,C
A
A,N
A
A=0, B=l, C=2
14
A
A
A
A
A=0, B=l
15
A
A
A
A
A=0, B=l
16
A
A
A
A
A=0, B=l
17
A
A
C2
A
A=0, B=l, C=2
18
A,B
A
A
A
A=0, B=l
19
A
A
A
A
A=0, B=l
20
A
A
A
A
A=0, B=l
21
A
A
A
A
A=0, B=l
22
A
A
A
A,B
A=0, B=l
23
A
A,B3
A
A
A=0, B=l
24
A
A
A
A
A=0, B=l
25
A
B
A
A
A=0, B=l
Phylogenetic Systematics of /guanine Lizards
109
TABLE 5 (continued)
Character
Ba
Outgroup
Cr Mo
Op
Polarity
Inference
26
A
A
A
A
A=0, B=l
27
A
A
A
A
A=0, B=l
28
A
A
A
A
A=0, B=l, C=2
29
A
A,B
A
A
A=0, B=l
30
A
A
A
A
A=0, B=l
31
A
A
A
A
A=0, B=l
32
A
A
A
A
A=0, B=l
33
A
A
A
A
A=0, B=l
34
A,X
A,X
A,X
A,X
A=0, B=l, C=0
35
A,X
A,X
A,X
A,X
A=0, B=0, C=l
36
A
A
A
A
A=0, B=l, C=2
37
A
A
A
A,B
A=0, B=l
38
A
A
A
A,B
A=0, B=l
39
A
A
A
A
A=0, B=l
40
A,X
A
A
A,B
A=0, B=l
41
A,B
A
A
A
A=0, B=l
42
A
A
A,B
A
A=0, B=l
43
B,C
A,B
A,B'^,C
A
9
•
44
B,C
A,B
A,B4,C
A
?
45
A
A
A
A
A=0, B=l
46
A
A
A,C
A
A=0, B=1,C=2, D=3
47
A
A
A
A
A=0, B=l
48
A
A
A
A
A=0, B=l
49
A
A
A
A
A=0, B=l, C=2
50
A
A
A
A
A=0, B=l
51
A
A
A
A
A=0, B=l
52
B
A
B
B
A=l, B=0, C=0
no
University of California Publications in Zoology
TABLE 5 (continued)
Character
Ba
Outgroup
Cr Mo
Op
Polarity
Inference
53
B
A
B
B
A=0, B=0, C=l
54
A
A
A
A
A=0, B=l
55
A
B
A,B
A,B
?
56
B
A
A,B
A
9
•
57
B
A,B
A,B
A,B
7
58
A
A
A
A
A=0, B=l
59
A
A
A,B
A,B
7
60
A,B
A,B
A,B
A
7
•
61
A,B,N
B,N
A,N
A
7
62
B
A
A
A
A=0, B=l
63
A
A
C
C5
7
64
A
A
A
A
A=0, B=l
65
B
A
A,B
A,B^
7
66
A
B
A
A
A=0, B=l
67
A
A
A
A,B
A=0, B=l
68
A
A3
A
A
A=0, B=l
69
A,B
A
A
A
A=0, B=l
70
A
A
A
A
A=0, B=l
71
A
A,B
A
A,C
7
72
A
A
A
A
A=0, B=l
73
A,B
A
B
A
7
74
A
A
A
A
A=0, B=l
75
A
A
A7
A8
A=0, B=l
76
A
A
-
-
A=0, B=l
77
A
A
A7
A,B
A=0, B=l
78
A,X
A
B7
A
A=0, B=l
Phylogenetic Systematics oflguanine Lizards 111
TABLE 5 (continued)
Character
Ba
Oi
itgroup
Mo
Op
Polarity
Inference
79
X
X
X
X
?
80
X
X
X
X
7
•
81
A
A
A
A
A=0, B=l
82
A,B
A
A
A
A=0, B=l
83
A,X
A
A,B
A
A=0, B=l
84
A,B
B
A
C
7
•
85
A
A,B,C
A
C
7
86
A
A
A
A
A=0, B=l
87
A
A
A
A
A=0, B=l
88
A,B
A
A,B
A
7
89
A,B
A
A
A
A=0, B=l
90
A
B
A,B
A,B
7
91
A,X
A
A
A
A=0, B=l
92
A
A
A
A
A=0, B=l
93
A
A
A
A
A=0, B=l
94
A
A
A,B
A,B
?
95
A
B
A,B
B
7
Note: Abbreviations: Ba, basiliscines; Cr, crotaphytines; Mo, morunasaurs; Op,
oplurines. Character- state codes correspond with those given in the list of systematic
characters, with the following additions: N, not applicable; X, character state not found in
iguanines; -, no data. Polarity codes are as follows: 0, plesiomorphic; 1, apomorphic; 2,
derived from 1; 3, derived from 2.
^Some intermediate between A and B.
^Lacrimal absent in some.
^Probably not homologous with condition A in iguanines (see text).
^Sample too small to determine mode.
^Descriptively condition A but thought to be derived from C for other reasons (see text).
^Descriptively condition B but may be derived from A (see text).
iHoplocercus not examined.
^Intermediate.
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^^
c
■\
c>
FIG. 46. Minimum-step cladograms for eight basic taxa of iguanines, resulting from a preliminary
analysis of 29 characters (Table 7). Two different cladograms (A and B) account for the taxic distribution of
derived characters with 46 character transformations. Synapomorphies of the numbered nodes and basic taxa
are given in the text.
120 University of California Publications in Zoology
The consistency indices (Kluge and Farris, 1969) for eacli of the characters on each of the
two minimum-step cladograms are given in Table 7. The C-index is a measure of the
deviation of a character from a perfect fit (C-index of 1.00) to a given cladogram.
Synapomorphies for the various nodes of the cladograms are given below by the number of
the character and the letter of the character state as designated in the list of systematic
characters. Convergent characters are underlined; characters involving reversal are marked
with an asterisk. Because only characters whose derived states are shared by two or more
of the basic taxa were used in this analysis, any character interpreted as a synapomorphy of
a basic taxon necessarily exhibits homoplasy.
Figure 46A: Node 1: 18-B*, 25-B*; Node 2: 23-B*; Node 3: 48-B, 66-B, 77-B;
Node 4: 46-B*. 46-C or-D*; Node 5: 37-B, 52-53-A; Node 6: 5-B, 7-B, 8-B, 17-B or-C,
21-B, 36-B or-C. 40-B, 45-B, 46-B or-A*, 50-B. 83-B; Node 7: 19-B, 28-B or-C, 39-B;
Amblyrhynchus: 18-A*. 46-A*, 54-B. 68-B. 69-B. 70-B: Brachylophus: 25-A*, 36-B.
62-B: Conolophus: 51-B: Ctenosaura: none; Cyclura: none; Dipsosaurus: 13-C. 46-B.
50-B. 51-B (last two characters are redundant); Iguana: 18-A*. 62-B; Sauromalus: 13-B.
23-A*, 54-B. 68-B. 69-B. 70-B.
The synapomorphies of the second cladogram (Fig. 46B) are identical to those of the
first (Fig. 46A), with the following exceptions: Node 1: 18-B*, 23-B*; Node 2: 25-B,
46-B,-C, or-D*; Node 4: 46-C or-D*; Brachylophus: 36-B. 62-B; Ctenosaura: 46-A*.
Six of the homoplastic characters on the first minimum-step cladogram (Fig. 46A) can
be interpreted in more than one way, each involving the same number of phylogenetic
transformations. These alternative interpretations are diagrammed in Figure 47. Character
25-B can be interpreted as convergent synapomorphies of Dipsosaurus on the one hand and
of all other iguanines except Brachylophus (node 3) on the other hand (Fig. 47A).
Alternatively, it can be interpreted as a synapomorphy of all iguanines that has reversed in
Brachylophus (Fig. 47B). Characters 54-B, 68-B, 69-B, and 70-B can be interpreted as
convergent synapomorphies of Amblyrhynchus on the one hand and of Sauromalus on the
other (Fig. 47C). Alternatively, these characters can be interpreted as synapomorphies of
the Galapagos iguanas plus Sauromalus (node 5) that have reversed in Conolophus (Fig.
47D). Two alternative interpretations of character 46 are diagrammed in Figure 47E and F.
Both interpretations require five phylogenetic transformations.
Alternative interpretations of homoplastic characters on the second minimum-step
cladogram (Fig. 46B) are identical to those on the first (Fig. 46A), with the following
exceptions: Character 25-B has only one possible minimum-step interpretation; it is a
synapomorphy of all iguanines except Brachylophus (node 2). Character 23-B can either
be interpreted as convergent synapomorphies of Brachylophus on the one hand and the taxa
united above node 3 (Fig. 48A) on the other hand, or it can be interpreted as a
synapomorphy of all iguanines that has subsequently reversed in Dipsosaurus (Fig. 48B).
The same alternative interpretations of character 46 are available for the second minimum-
step cladogram as for the first, but two additional alternatives exist (Fig. 48C,D).
Of the six subterminal nodes on each of the two minimum-step cladograms resulting
from the preliminary analysis, three (nodes 3, 6, and 7) are well supported. That is, these
Phylogenetic Systematics oflguanine Lizards
121
Di Br Ct Am Co Sa Ig Cy Di Br Ct Am Co Sa Ig Cy
Am
Co
Sa Am
Co
Sa
Am Co
FIG. 47. Alternative interpretations of character transformation for homoplastic characters on a
minimum-step cladogram (Fig. 47A). A and B are alternative interpretations for character 25; C and D for
characters 54, 68, 69, and 70; E and F for character 46. Solid squares represent transformations to the
derived condition; open squares represent reversals; half-solid squares represent intermediate slates.
nodes are diagnosed by more than two derived characters that are unique and unreversed
and strongly outweigh conflicting characters. Node 1 is also well supported, but it is
supported by the results of an analysis at a more inclusive hierarchical level. Node 2 is the
most weakly supported, for it supports the monophyly of different groups of basic taxa on
the two minimum-step cladograms.
122
University of California Publications in Zoology
Am Co
Am Co
FIG. 48. Alternative interpretations of character transformation for homoplastic characters on a
minimum-step cladogram (Fig. 47B). A and B are alternative interpretations for character 23; C and D for
character 46. Solid squares represent transformations to the derived condition; open squares represent
reversals; half-solid squares represent intermediate states.
LOWER-LEVEL ANALYSIS
In an attempt to gain better resolution of iguanine phylogenetic relationships, I performed
an analysis at a lower hierarchical level (node 3), using Brachylophus and Dipsosaurus as
outgroups in order to determine the polarities of characters that were undeterminable at the
level of all iguanines. I chose node 3 for this analysis because it is the most inclusive
group within iguanines whose monophyly is well supported.
The precise relationships oi Brachylophus and Dipsosaurus to the rest of the iguanines
are problematical. One of the minimum-step cladograms resulting from the preliminary
analysis has Dipsosaurus as the sister group of all other iguanines (Fig. 46A), while the
other has Brachylophus in this position instead (Fig. 46B). The second hypothesis might
at first appear to be better supported, because Dipsosaurus shares two derived characters
with the other iguanines (characters 25-B and 46-B,-C, or-D), while Brachylophus shares
only one derived character (23-B) with them. However, character 46 has four equally
simple alternative interpretations, and in only two of these (Fig. 48C,D) does it support a
sister-group relationship between Dipsosaurus and all iguanines other than Brachylophus.
Phylogenetic Systematics of I guanine Lizards 1 23
Under the other two alternative interpretations, the presence of the first derived state in
Dipsosaurus is considered to be convergent, as in Figure 47E and F. For this reason, I
have chosen to leave the relationships among Brachylophiis, Dipsosaurus, and the new
ingroup (node 3) unresolved in the assessment of polarities for the lower-level analysis,
I used the same basic methodology for determining polarities in the lower-level analysis
(Appendix III) that I used in the preliminary analysis, where the relationships of the
outgroups to the ingroup are uncertain (Appendix II). For reasons presented in Appendix
III, I considered polarity to be determinable only when both Brachylophus and
Dipsosaurus exhibit the same character state.
Using Brachylophus and Dipsosaurus as additional outgroups for analysis at a lower
hierarchical level, I was able to determine polarities for 13 of the 20 characters whose
polarities could not initially be determined (Table 8). The number of premaxillary teeth
turns out to be two characters (hence the numbering in the character list as characters 43-
44) representing transformations in opposite directions from the ancestral condition, a
mode of seven premaxillary teeth. Although character 84 (superciliary scales) differs in
Brachylophus and Dipsosaurus, it seems reasonable to conclude that state A is derived,
since it is found in neither Brachylophus nor Dipsosaurus and represents one end of a
continuum that has the conditions seen in these two taxa at the other end. Both
Brachylophus and Dipsosaurus exhibit the same state for character 61, but this character is
irrelevant to an analysis of relationships at the level in question because it does not vary
within the new ingroup. Characters 56 and 80 also do not vary within the ingroup, but
their polarities are undeterminable because Brachylophus and Dipsosaurus exhibit different
conditions.
The use oi Brachylophus and Dipsosaurus as additional outgroups for an analysis of
relationships at a lower hierarchical level necessitates a reevaluation of the polarities of
those characters whose polarities had already been determined using more remote
outgroups. The reasoning behind polarity reevaluation is similar to that behind polarity
assessment and is presented in Appendix IV. Under this reasoning, the only characters
whose polarity assessments needed to be changed after reevaluation were character 18
(polarity reversed) and character 46 (changed to undeterminable). Character 46 is a four-
state character, and what becomes undeterminable is whether state A or state B is ancestral.
Therefore, I have lumped states A and B as state 0 and consider states C and D to be
successively more derived conditions (i.e., C = 1, D = 2).
Eight of the characters used in the preliminary analysis of relationships among all
iguanines cannot be used in the analysis of relationships of all iguanines other than
Brachylophus and Dipsosaurus, either because they must be interpreted as synapomorphies
of a basic taxon that are convergent with a condition found in Brachylophus or Dipsosaurus
(characters 13, 51, and 62) or because they do not vary within the new ingroup (characters
25, 48, 66, and 77). These characters were removed from consideration, and the
remaining characters were combined with those whose polarities were newly determined,
using Brachylophus and Dipsosaurus as outgroups, and whose derived states characterized
124
University of California Publications in Zoology
TABLE 8. Polarity Inferences for Lower-level Analysis Using Brachylophus and
Dipsosaurus as Outgroups
Character
Brachylophus
Outgroup
Dipsosaurus
Polarity
Inference
43
B
B
A=l, B=0, C=0
44
B
B
A=0, B=0, C=l
55
A
A
A=0, B=l
56
B
A
?1
57
A
A
A=0, B=l
59
A
A
A=0, B=l
60
B
A
?
61
A
A
91
•
63
C
A
7
65
A
A
A=0, B=l
71
A
A
A=0, B=l, C=2
73
A
A
A=0, B=l
79
A
A
A=0, B=l
80
A
B
?1
84
B
C
A=1;B,C=0
85
A
C
7
88
B
A
?
90
A
A
A=0, B=l
94
A
A
A=0, B=l
95
A
A
A=0, B=l
Note: Character-state codes correspond with those in the list of systematic characters.
Polarity codes are as follows: 0, plesiomorphic; 1, apomorphic; 2, derived from 1.
^Character does not vary in the ingroup.
more than one of the basic taxa. The data set for this lower-level analysis consists of 26
characters, and is presented with the characters recoded to eliminate variation within the
basic taxa (Table 9).
Phylogenetic Systematics oflguanine Lizards
125
TABLE 9. Distributions of Character States of 26 Characters Among Six Taxa Within a
Subset of Iguaninae
Taxon
Character
5 7 8 17 18 19 21 23 28 36 37 39 40
Amblyrhynchus
1
1
1
1
1
0
1
0
1
1
0
1
Conolophus
1
1
1
1
0
0
1
0
1
1
0
1
Ctenosaura
0
0
0
0
0
0
0
0
0
0
0
0
Cyclura
0
0
0
0
0
1
0
1
0
0
1
0
Iguana
0
0
0
0
1
1
0
1
0
0
1
0
Sauromalus
0
0
0
0
0
0
0
0
0
0
1
0
0
CI
1.00
1.00
1.00
1.00 0.50
1.00
1.00 0.50
1.00
1.00
1.00
1.00 1
00
Taxon
Character
45 46 50 52 54 57 65 68 69 70 71 83 84
Amblyrhynchus
1
0
1
1
1
0
1
1
1
1
1
1
1
Conolophus
1
0
1
1
0
0
0
0
0
0
0
1
0
Ctenosaura
0
0
0
0
0
1
0
0
0
0
0
0
0
Cyclura
0
1
0
0
0
0
0
0
0
0
0
0
0
Iguana
0
1
0
0
0
1
0
0
0
0
0
0
0
Sauromalus
0
1
0
1
1
0
1
1
1
1
1
0
1
CI
1.00 0.50
1.00
1.00 0.50 0.50 0.50 0.50 0.50 0.50 0.50
1.00 0
50
Note: Characters have been recoded to eliminate variation within basic taxa as well as
derived states that characterize single basic taxa (not including Brachylophus and
Dipsosaurus). Consistency indices (CI) for the characters are also given; these are identical
for the three minimum-step cladograms based on the characters in this table (Fig. 49A,B,C)
and their consensus cladogram (Fig. 50).
126 University of California Publications in Zoology
Three fully resolved cladograms of equal and minimum length can be constructed from
the 26 characters used in the lower-level analysis (Fig. 49). These cladograms differ only
in the position of Ctenosaura, which in turn depends on the interpretation of character 57,
the presence or absence of posterolaterally directed processes on the pleurapophyses of the
second sacral vertebra. The derived absence of these processes occurs in Ctenosaura,
Iguana, and some Cyclura, but was scored absent for the latter taxon in order to simplify
analysis. This is one of only two derived characters out of the set of 26 that occurs
invariably in Ctenosaura and is relevant to the placement of this taxon within the restricted
ingroup. The only other derived character that occurs invariably in Ctenosaura (character
23-B) also occurs in all ingroup taxa except some Sauromalus. Therefore, provided that
Sauromalus is monophyletic, this character is most reasonably interpreted as a
synapomorphy of the entire ingroup that has reversed in some Sauromalus. If the sister-
group relationship between Iguana and Cyclura, based on other characters, is accepted,
then character 57-B might be interpreted as convergent in Iguana on the one hand and in
Ctenosaura on the other. If so, Ctenosaura can have any of the relationships illustrated in
Figure 49; given this information alone, there is no reason to prefer any one of these
alternative placements over the others. Alternatively, character 57-B might be interpreted as
a synapomorphy of a clade consisting of Ctenosaura, Iguana, and Cyclura that has
subsequendy reversed within Cyclura. Because Cyclura is actually variable for this
character, the hypothesis of acquisition and reversal requires fewer phylogenetic
transformadons than does that of convergence (two instances versus three). Although one
of the three cladograms (Fig. 49A) would be favored under such an interpretation, the
difference is so small that little importance can be attached to it in terms of resolving the
placement of Ctenosaura. Therefore, I consider the relationships of Ctenosaura within the
restricted ingroup to be uncertain.
Because the three minimum-step cladograms resulting from the lower-level analysis
differ only in the placement of Ctenosaura, I present diagnostic synapomorphies for a
single consensus cladogram (Adams, 1972) that leaves the relationships of Ctenosaura
unresolved (Fig. 50). This consensus cladogram is identical to the other three in terms of
evolutionary steps, requiring 37 phylogenetic character transformations out of the absolute
minimum of 26 (C-index = 0.70), which would only obtain if all characters had compatible
distribudons among basic taxa. The consistency indices (Kluge and Farris, 1969) for the
characters on the consensus cladogram (Fig. 50) are identical to those on the three
minimum-step cladograms (Fig. 49A,B,C) from which it was derived. These are given in
Table 9. Synapomorphies for the nodes of the consensus cladogram (Fig. 50) are given
below, with convergent characters underlined and characters involving reversal marked
with an asterisk.
Node 1: 23-B*; Node 2: 37-B, 52-A; Node 3: 5-B, 7-B, 8-B, 17-B or-C, 21-B, 36-B
or-C, 40-B, 45-B, 50-B, 83-B; Node 4: 19-B, 28-B or-C, 39-B, 46-C or-D;
Amblyrhynchus: 18-A. 54-B. 65-B. 68-B. 69-B. 70-B. 71-B. 84-A: Conolophus: none;
Ctenosaura: 57-B; Cyclura: none; Iguana: 18-A, 57-B; Sauromalus: 23-A*, 46-C. 54-B,
65-B. 68-B. 69-B. 70-B. 71-C. 84-A.
Phylogenetic Systematics of I guanine Lizards
m
FIG. 49. Minimum-step cladograms resulting from an analysis of 26 characters (Table 9) in a subset of
iguanines. Three different cladograms (A, B, and C) account for the taxic distribution of derived characters
with 37 character transformations.
128
University of California Publications in Zoology
.i-"
^
<>
s^
^^
.V
.^^'
o^^
.<>
^^^
'^
O^
A'
,<>
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A'
.">
S^^
c
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FIG. 50. Consensus cladogram for the three cladograms illustrated in Figure 49. The consensus
cladogram is also a minimum-step cladogram in that it requires the same number of character
transformations as do the three fully resolved cladograms upon which it is based. Synapomorphies for the
numbered nodes and the basic taxa are given in the text.
Eight of the eleven homoplastic characters can be interpreted in two different ways,
each involving the same number of phylogenetic transformations on the minimum- step
cladograms. The alternative interpretations of character 57 have already been discussed.
Its derived state is either convergent in Ctenosaura and Iguana, or it is a synapomorphy of a
monophyletic group composed of Ctenosaura, Iguana, and Cyclura that has subsequently
reversed in Cyclura. Characters 54, 65, 68, 69, 70, 71, and 84 are either convergent in
Amblyrhynchus and Sauromalus or they are synapomorphies of a monophyletic group
composed of Amblyrhynchus, Conolophus, and Sauromalus that have subsequently
reversed in Conolophus.
Although all three of the subterminal nodes on the consensus cladogram (not including
node 1, which is a conclusion of a higher-level analysis) are supported by at least two
derived characters, every one is contradicted by some other characters. Node 2, suggesting
a sister-group relationship between Sauromalus and the Galapagos iguanas, is supported
by two characters: reduced labial exposure of the angular bone (37-B) and short second
ceratobranchials (52-53-A). Nevertheless, the possession of polycuspate or serrate
marginal tooth crowns (character 46-B or-C) suggests that Sauromalus is more closely
Phylogenetic Systematics oflguanine Lizards 129
related to Iguana and Cyclura, while the lack of lateral contact between palatine and jugal
posterior to the infraorbital foramen (character 23-A) suggests that Sauromalus may be the
sister group of all other iguanines in the lower-level analysis. However, this character is
actually variable within Sauromalus and may have reversed within this taxon.
Node 4, suggesting a sister-group relationship between Iguana and Cyclura, is
supported by four characters: squamosal abuts against dorsal end of quadrate (19-B);
cristae ventrolateralis of parabasisphenoid relatively widely separated (28-B or-C);
surangular extends far forward on lateral surface of mandible (39-B); and polycuspate or
serrate marginal tooth crowns (46-C or-D). One of these characters (46) actually suggests
monophyly of a more inclusive group consisting of Sauromalus, Iguana, and Cyclura.
Another character, absence of posterolateral processes on pleurapophyses of second sacral
vertebra (character 57-B), suggests a sister-group relationship between Iguana and
Ctenosaura, although most Cyclura also lack the processes. Yet another character, large
ventral process of the squamosal (18- A), suggests a sister-group relationship between
Amblyrhynchus and Iguana (the homology of this character is dubious but cannot be ruled
out on morphological grounds alone).
Node 3, suggesting a sister-group relationship between Amblyrhynchus and
Conolophus, is the best-supported node. It is diagnosed by 10 derived characters: nasal
process of premaxilla covered dorsally between nasals (5-B); prefrontal contacts jugal
behind lacrimal foramen (7-B); frontal wider than long (8-B); reduction of lacrimal (17-B
or-C); medial crest on anterior dorsal surface of palatine (21-B); enlarged labial foot of
coronoid (36-B or-C); surangular covered lingually below coronoid (40-B); premaxillary
teeth with large lateral cusps (45-B); anterior portion of pterygoid tooth patch absent (50-
B); and pointed, conical dorsal head scales (83-B). Nevertheless, seven derived characters
suggest a sister-group relationship between Amblyrhynchus and Sauromalus: medial
separation of second ceratobranchials (54-B); reduction or loss of scapular fenestrae (65-
B); short posterior process of interclavicle (68-B); T-shaped interclavicle (69-B); reduction
or loss of sternal fontanelle (70-B); medial separation of xiphisterna (71-B or-C); and
quadrangular, nonoverlapping superciliary scales (84- A). Conolophus lacks all of these
derived characters. Therefore, if a sister-group relationship between Amblyrhynchus and
Conolophus is accepted, then the derived characters shared by Amblyrhynchus and
Sauromalus must either be convergent or reversed in Conolophus.
PHYLOGENETIC CONCLUSIONS
PREFERRED HYPOTHESIS OF RELATIONSHIPS
Figure 51 summarizes my conclusions about phylogenetic relationships among the genera
of iguanine lizards, based on the two analyses discussed above as well as a consideration
of variation within basic taxa. Synapomorphies of the various taxa are given in the
Diagnoses section, below. Although this is not the most fully resolved cladogram that can
be obtained from the characters used in this study, it indicates the best-supported
monophyletic groups. The differences between this cladogram and the most fully resolved
cladogram that can be obtained from these data are as follows: (1) Either Brachylophus or
Dipsosaurus can be considered the sister group of all other iguanines on a fully resolved
cladogram. Since both hypotheses are equally reasonable in terms of the characters
discussed here, I leave the relationships among Brachylophus, Dipsosaurus, and the
monophyletic group composed of all other iguanines unresolved. (2) Although it is
possible to place Ctenosaura as the sister group of the clade composed of Iguana and
Cyclura, this conclusion is based on one of two possible interpretations of a single
character, and this character must later be lost within the clade that it is supposed to
diagnose. I prefer to leave the relationships of Ctenosaura to Sauromalus, Iguana and
Cyclura, and Amblyrhynchus and Conolophus unresolved. (3) Finally, a fully resolved
cladogram places Sauromalus as the sister group of the Galapagos iguanas, while I leave
the relationships of Sauromalus to Ctenosaura, the Galapagos iguanas, and Iguana and
Cyclura unresolved. The reasons for these differences are discussed more fully in the
sections on phylogenetic analysis, above, and the diagnoses of the monophyletic groups of
iguanines, below.
CHARACTER EVOLUTION WITHIN IGUANINAE
Although the primary goal of this study was to determine the relationships among the
genera of iguanine lizards, I was only partially successful in this endeavor. Other than
Iguaninae as a whole, I recognize only three monophyletic groups composed of more than
one of the basic taxa, whereas a fully resolved dichotomously branching phylogeny would
have six such groups. Failure to resolve relationships cannot be attributed to a lack of
morphological variation within Iguaninae, for derived characters-which are sometimes
numerous- support the monophyly of each of the basic taxa. Therefore, it seems that most
of the character evolution within iguanines occurred after the lineages leading to the extant
130
Phylogenetic Systematics oflguanine Lizards
131
Iguaninae
FIG. 51. Phylogenetic relationships within Iguaninae according to the present study.
genera had already diverged from one another. Accepting this proposition might lead one
to conclude that these lineages separated during a relatively brief time interval and that they
have been evolving separately for a long time. Implicit in this conclusion, however, is the
assumption that rates of character evolution are similar in separately evolving lineages.
This assumption is contradicted by the distribution of derived characters among the basic
taxa and the relationships that can be resolved by them. For example, Amblyrhynchus
possesses more obvious derived characters not found in Conolophiis than does either
Brachylophus or Dipsosaurus, even though Conolophus apparendy shared a more recent
common ancestor with Amblyrhynchus than it did with either Brachylophus or
Dipsosaurus. Given that the characters used in this study are representative of overall
phenotypic evolution, one must conclude that the lineage leading to Amblyrhynchus has
evolved more rapidly than those leading to Brachylophus and Dipsosaurus.
COMPARISONS WITH PREVIOUS HYPOTHESES
Although a close relationship among some or all of the taxa currently placed in Iguaninae
was recognized by several nineteenth-century authors, no explicit hypotheses about
phylogenetic relationships among the various iguanine genera appeared until the twentieth
century. The phylogenetic relationships proposed here are both similar in some respects
and different in others when compared with previous hypotheses about iguanine
relationships. In this section, I evaluate these previous hypotheses in light of the results of
the present study.
Barbour and Noble (1916) and Bailey (1928) both hypothesized a close relationship
between Cyclura and Ctenosaura, and Schwartz and Carey (1977) further proposed that
Cyclura originated from Ctenosaura. Neither of these hypotheses is supported by the
results of the present study. First, Ctenosaura possesses at least three characters that are
derived relative to the condition seen in Cyclura (premaxillary process of maxilla curves
dorsally; short posterolateral processes of parabasisphenoid; elongate subocular scale), and
thus cannot be considered ancestral to the latter. Second, Cyclura shares more derived
characters with Iguana than it does with Ctenosaura, implying that Cyclura shared a more
recent common ancestor with Iguana than with Ctenosaura. The relationships among these
three taxa are discussed further in the comments on Cyclura in the Diagnoses section,
below.
Mittleman (1942) proposed a phylogenetic scheme for the North American iguanids,
including Ctenosaura, Dipsosaurus, and Sauro ma I us (Fig. 1). This phylogeny was
modified slighdy by H. M. Smith (1946), who removed Ctenosaura from a position of
direct ancestry to all other North American iguanids and placed Dipsosaurus and
Sauromalus close to a group composed of what are now considered the sceloporines and
crotaphytines rather than to just part of this radiation (compare Figs. 1 and 2). Although
Smith did not include iguanines other than those occurring within or very near to the United
States in his branching diagram, it is clear from his comments on the "herbivore section"
(group II in Fig. 2) that he also considered Iguana, Amblyrhynchus, Conolophus, and
Cyclura to be part of this group.
Common to the Mittleman (1942) and Smith (1946) phylogenies is the notion that
iguanines are ancestral to the other North American iguanids-that is, that some iguanines
shared a more recent common ancestor with these other iguanids than they did with other
iguanines. This idea seems to be related to another notion held by both Mittleman and
Smith, namely that iguanines are "primitive" iguanids. According to Mittleman
(1942:1 12), "Dipsosaurus is probably the most primitive of the North American Iguanidae
132
Phylogenetic Systematics of I guanine Lizards 133
(excepting Ctenosaura, which is properly a Central and South American form)." H. M.
Smith (1946:101) says of his herbivore section (iguanines), "this includes the large,
primitive iguanids."
The notions that iguanines are "primitive" iguanids and that they are ancestral to
sceloporines and crotaphytines are false. While it is true that iguanines lack certain derived
features seen in these other groups, this is simply a manifestation of the mosaic nature of
evolution, for the converse is also true. Sceloporines and crotaphytines lack derived
characters seen in iguanines. Iguanines are derived relative to sceloporines and
crotaphytines in numerous characters, among them the possession of caudal vertebrae with
two pairs of transverse processes, the posterior location of the supratemporal bone,
herbivory and associated morphological adaptations (flared tooth crowns, colic valves),
and large body size. Because some of the derived characters of iguanines occur nowhere
else within Iguanidae, iguanines cannot be considered ancestral to any other iguanids.
In the early 1960's, Etheridge constructed a phylogeny for iguanines as part of his
scheme of relationships for the entire Iguanidae (Fig. 4). This scheme was never intended
to be published (Etheridge, pers. comm.), and it is difficult to evaluate because the reasons
for the various groupings were not specified. Other than differences in resolution, the
results of the present study differ from Etheridge's scheme in two primary ways: While I
consider Dipsosaurus and Brachylophus to be outside of a monophyletic group formed by
the remaining iguanines, Etheridge considered Brachylophus to be the sister group of the
Galapagos iguanas, and he considered Dipsosaurus to be the sister group of Sauromalus.
Although the relationships proposed by Etheridge can be supported by particular shared,
derived characters (e.g., lack of autotomy septa in caudal vertebrae oi Brachylophus and
the Galapagos iguanas; anterior position of parietal foramen in Sauromalus and
Dipsosaurus), the weight of the evidence suggests different relationships and necessitates
that the distribution of these derived characters is partly the result of convergence. The full
evidence leading to this conclusion is given in the diagnoses of the various monophyletic
groups recognized in the present study and will not be repeated here.
The only published study dealing with relationships among all the iguanine genera is
that of Avery and Tanner (1971). As I noted in the Introduction, these authors used an
artificial system for assessing similarity, used many characters that are probably correlated,
made no attempt to determine character polarity, and did not specify how their similarity
data were used to construct their phylogenetic tree. Furthermore, Avery and Tanner's
conclusions are obscured by self-contradictory, vague, and ambiguous statements. For
example, they state (p. 69) that "the osteological characters . . . indicate that Oplurus and
Chalarodon are more closely related to each other than to the iguanines, and Oplurus is the
Madagascarian genus most closely related to the Western Hemisphere iguanines." In one
place (p. 68), Avery and Tanner claim that Ctenosaura is certainly ancestral to the Western
Hemisphere iguanines, but their phylogenetic tree (Fig. 3) suggests that Dipsosaurus, a
Western Hemisphere iguanine, is not derived from Ctenosaura, and later (p. 73) they seem
to consider Ctenosaura ancestral to only Cyclura and Sauromalus. One of Avery and
Tanner's 1 1 numbered conclusions is that Iguana and Ctenosaura evolved from a common
134 University of California Publications in Zoology
ancestral stock. This statement is uninformative, for they consider all iguanines to have
evolved from a common ancestor; it is also misleading when compared with their
phylogenetic tree (Fig. 3). For these reasons, I find it impossible to compare my
conclusions with those of Avery and Tanner.
Wyles and Sarich (1983) published the results of immunological comparisons for 10
species of iguanines representing all eight genera. Given the limitations of these data, their
results are in general agreement with the relationships proposed here. Wyles and Sarich's
comparisons are incomplete in that antisera were prepared to only four of the iguanine
species, and immunological distances to all other iguanines in the study are given for the
antisera to only two of the four, Amblyrhynchus and Conolophus. Assuming that
immunological distance is roughly proportional to time of divergence, Wyles and Sarich's
data suggest (1) that Amblyrhynchus and Conolophus are sister taxa; (2) that the Galapagos
iguanas are roughly equally closely related to Ctenosaura, Cyclura, Iguana, and
Sauromalus; and (3) that they are more distantly related to Dipsosaurus and Brachylophus.
All of these conclusions are in agreement with those of the present study.
DIAGNOSES OF MONOPHYLETIC GROUPS
OF IGUANINES
In this section I provide discussions of the monophyletic groups of iguanines at and above
the level of the basic taxa used in this study (traditional genera). For each taxon I include:
(1) the type on which the taxon is based, (2) the etymology of the name, (3) a phylogenetic
definition (de Queiroz, 1987; Gauthier et al, 1988), (4) the current distribution, (5) a
diagnosis consisting of hypothesized synapomorphies, (6) fossil records, and (7) various
comments. Synonyms are not provided; those of the basic taxa can be found in Etheridge
(1982).
Iguaninae Bell 1825
Type genus: Iguana Laurenti 1768.
Etymology: Modification of Iguana, the name of its type genus.
Definition: The most recent common ancestor of Brachylophus, Dipsosaunis, and
Iguanini, and aU of its descendants.
Distribution: Southwestern United States southward through Mexico, Central America,
and northern South America to southern Brazil and Paraguay; the West Indies; the
Galapagos Islands; lies Wallis; and the Fiji and Tonga island groups.
Diagnosis: Iguanines are moderate to large iguanians that can be distinguished from
other iguanians by the following synapomorphies:
1. Vertebrae in part of caudal sequence bear two pairs of transverse processes
(Etheridge, 1967).
2. Transverse colic folds or valves present (Iverson, 1980, 1982).
3. Crowns of posterior marginal teeth laterally compressed, anteroposteriorly flared,
often with four or more cusps (Etheridge, 1964a).
4. Supratemporal lies primarily on posteromedial surface of supratemporal process of
parietal.
5. Herbivorous (H. M. Smith, 1946; Iverson, 1982).
Fossil record: The diagnosis and description of iguanines presented here enable me to
reject the possible iguanine relationships of certain fossil taxa. In their description of
135
136 University of California Publications in Zoology
Paradipsosaurus mexicanus. Fries et al. (1955:15) stated that this animal "would appear to
approach more closely to the northern crested lizard Dipsosaurus than to any of the other
iguanids that presently live in Mexico and the southwestern United States." However, the
similarities they cite (broad, flat parietal table elevated well above level of supratemporal
arch; unrestricted supratemporal fossa; deep, broad snout without pronounced
nasolachrymal ridges; forward opening nares), provide no evidence for a close relationship
to Dipsosaurus, since they are all plesiomorphic for Iguania. Of the five diagnostic
iguanine synapomorphies identified in this study, only the morphology of the tooth crowns
can be assessed in Paradipsosaurus. Unlike the teeth of iguanines, those of
Paradipsosaurus are said to be a little dilated and noncuspidate (Fries et al., 1955).
Furthermore, while all postembryonic iguanines and various other iguanids have a
relatively small splenial and have the dentary portion of Meckel's groove closed and fused,
both derived features within Iguania, the splenial of Paradipsosaurus is relatively large and
Meckel's groove is open (Estes, 1983). Therefore, although Paradipsosaurus and
Dipsosaurus share the derived condition of having the parietal foramen located within the
frontal bone, this similarity is convergent, since Paradipsosaurus is not an iguanine. Estes
(1983) reached similar conclusions concerning the relationships of this fossil.
Gilmore (1928) described Parasauromalus olseni based on a fragment of a right dentary
from the Eocene of Wyoming. Although he did not specifically propose that it was related
to the iguanine Sauromalus, Gilmore considered the teeth of the fossil to resemble those of
Sauromalus ater most closely, made his comparisons with this species only, and named the
fossil as if to suggest a close relationship with Sauromalus (para means near). If new
material has been correctly referred to Parasauromalus (Estes, 1983), then this taxon is not
an iguanine and therefore cannot be closely related to Sauromalus. Contrary to Gilmore's
(1928) statements, the tooth crowns oi Parasauromalus are not particularly similar to those
oi Sauromalus. They are only slightly flared and tricuspid (Estes, 1983), while those of
Sauromalus are strongly flared and polycuspate. The supratemporal of Parasauromalus lies
on the lateral surface of the supratemporal process of the parietal (figured by Estes, 1983),
whereas the supratemporal of iguanines lies in a derived position on the medial surface.
The splenial of Parasauromalus is relatively large and the Meckelian groove closed but
unfused (Estes, 1983), primitive iguanian characters not retained by any iguanine.
The oldest fossils referred to Iguaninae for which this reference cannot be rejected are
Lower Miocene in age: Tetralophosaurus (Olson, 1937), a fragment of a lower jaw from
Nebraska referred to Dipsosaurus by Estes (1983); a fragment of a lower jaw and a sacral
vertebra from Florida (Estes, 1963); and another fragment of a lower jaw from Texas,
referred to either Ctenosaura or Sauromalus by Stevens (1977). Because of their
fragmentary nature, these specimens are not definitely referable to Iguaninae on the basis of
synapomorphies. The oldest fossil that is clearly iguanine is a nearly complete skull from
the Pliocene of southern California (Norell, 1983). These and other fossil records are
given under the least inclusive taxon to which they belong or are most closely related.
Phylogenetic Systematics of I guanine Lizards 1 37
Comments: Three of the five iguanine synapomorphies are presumably part of a single
"adaptive syndrome." Both the iguanine dentition (Hotton, 1955) and colic valves
(Iverson, 1980, 1982) are thought to be adaptations for a third iguanine character,
herbivory. However, because this correlation of form and function does not extend to all
herbivorous lizards, dentition, diet, and colic anatomy are here treated as separate
characters.
Although Iguaninae was first used by Cope (1886), Bell (1825) is credited with
authorship under the principle of coordination (Article 36, third edition of the International
Code of Zoological Nomenclature). The content of Iguaninae as defined here differs from
that of Cope's (1886) Iguaninae in that the former includes Dipsosaurus and Sauromalus
while the latter does not. Iguaninae as defined here is identical in content to an unnamed
subset of Cope's (1900) more inclusive Iguaninae and to Etheridge's (1964a, 1982)
informal "iguanines."
In addition to the diagnostic iguanine characters given above, acceptance of the
phylogenetic relationships proposed in this paper requires that the reduction or loss of the
ventral process of the squamosal (character 18- A) be interpreted as an iguanine
synapomorphy that has subsequently reversed in Amblyrhynchus and Iguana.
In order to facilitate diagnosis of the monophyletic subgroups of iguanines, I have
reconstructed a hypothetical ancestral iguanine. This hypothetical ancestor has the derived
characters of iguanines as a whole but lacks the derived characters of its monophyletic
subgroups. The reason for constructing a hypothetical ancestor is that my diagnoses for
the monophyletic subgroups of iguanines consist exclusively of synapomorphies, while it
may also be useful to know what primitive features are retained by members of particular
monophyletic subgroups. Members of any monophyletic subgroup of iguanines possess
the condition found in the hypothetical ancestor unless an alternative state of the same
character is listed as a diagnostic synapomorphy either of the taxon in question or of a
larger monophyletic taxon of iguanines within which the taxon in question is included. It
should be kept in mind that the presence of a primitive character properly indicates only that
the specimen possessing it does not belong to the taxon diagnosed by the derived
alternative condition. It does not preclude the possibility that the specimen in question,
perhaps some newly discovered fossil, is not most closely related to the taxon diagnosed
by the derived condition.
The hypothetical ancestral iguanine is thought to have possessed the following
morphological features (numbers and letters correspond with those in the list of systematic
characters):
1-A. Ventral surface of premaxilla bears large posterolateral processes.
2-A. Posteroventral crests of premaxilla small, not continuing up sides of incisive
process and not pierced by foramina for maxillary arteries.
3-A. Anterior surface of premaxilla broadly convex.
4-A. Nasal process of premaxilla slopes posteriorly.
5-A. Nasal process of premaxilla exposed broadly between nasals.
6-A. Nasal capsule of moderate size, nasals relatively small.
138 University of California Publications in Zoology
1-A.. Lacrimal contacts palatine, and prefrontal fails to contact jugal behind lacrimal
foramen.
8-A. Frontal longer than wide.
9-A. Paired openings near frontonasal suture small or absent.
10-A. Cristae cranii of frontal form a smooth, continuous curve from frontal to
prefrontal.
1 1-A. Frontal cristae medial to cristae cranii absent or weakly developed.
12-A. Dorsal borders of orbits form a more or less smooth curve.
13- A. Parietal foramen lies on frontoparietal suture.
14- A. Supratemporal extends anteriorly more than halfway across posterior temporal
fossa.
15-A. Lateral surfaces of maxillae relatively flat or concave below supralabial
foramina.
16-A. Premaxillary process of maxilla not curving dorsally; maxillary and premaxillary
teeth lie in the same plane.
17-A. Lacrimal relatively large.
18-B. Ventral process of squamosal reduced or absent.
19-A. Squamosal does not abut against tympanic crest of quadrate.
20-A. Septomaxilla without pronounced longitudinal crest on anterolateral surface.
2 1-A. Palatine without high crest on dorsomedial surface.
22-A. Large posterolateral process of palatine behind infraorbital foramen present.
23-A. Posterolateral process of palatine behind infraorbital foramen fails to contact
jugal. Contact of this process with the jugal may be a synapomorphy of all iguanines that
has been lost secondarily in Dipsosaurus.
24-A. Infraorbital foramen located on lateral or posterolateral edge of palatine.
25-A. Medial borders of pterygoids relatively straight anterior to pterygoid notch,
pyriform recess narrows gradually anteriorly. Sharply curved medial pterygoid borders
and a pyriform recess that narrows abruptly may be a synapomorphy of all iguanines that
has been secondarily lost in Brachylophus.
26-A. Ectopterygoid fails to contact palatine at posteromedial comer of suborbital
fossa.
27-A. Long parasphenoid rostrum.
28-A. Cristae ventrolaterals of parabasisphenoid strongly constricted behind
basipterygoid processes.
29-A. Posterolateral processes of parabasisphenoid large, extending far up anterior
edges of lateral processes of basioccipital.
30-A. Laterally directed pointed process of cristae interfenestralis absent.
3 1-A. Stapes relatively thin.
32-A. Dorsal edges of dentary and surangular on either side of coronoid eminence
approximately equal in height.
33-A. Splenial relatively large.
Phylogenetic Systematics of I guanine Lizards 139
34-35-A. Anterior inferior alveolar foramen lies between splenial and dentary;
coronoid may or may not contribute to its posterior margin.
36- A. Labial process of coronoid present but relatively small.
37-A. Angular extends far up lateral surface of mandible and is easily visible in lateral
view.
38-A. Angular wide posteriorly.
39-A. Surangular does not extend anteriorly to last dentary tooth on labial surface of
mandible.
40- A. Dome-shaped portion of surangular visible below coronoid on lingual surface of
mandible.
41 -A. Angular process of prearticular increases substantially in relative size during
postembryonic ontogeny, becoming a prominent structure in adults.
42- A. Outline of retroarticular process triangular rather than quadrangular in all
postembryonic developmental stages.
43-44-B. Mode of seven premaxillary teeth.
45-A. Lateral cusps of premaxillary teeth small or absent.
46-A. Posterior marginal teeth tricuspid. The presence of a fourth cusp may be a
synapomorphy of all iguanines, with secondary loss in Amblyrhynchus and in some
Brachylophus and Ctenosaura. Alternatively, the ancestral iguanine may have been
polymorphic for the presence of a fourth cusp (again with secondary loss in
Amblyrhynchus and some Ctenosaura).
41- A. Individual lateral cusps of tricuspid marginal teeth much smaller than apical
cusp.
48- A. Entire pterygoid tooth row lies close to ventromedial edge of pterygoid.
49-A. Pterygoid tooth patch consists of a single row of teeth throughout
postembryonic ontogeny.
50-A. Pterygoid tooth patch extends anteriorly beyond level of posterior edge of
suborbital fenestra.
51 -A. Pterygoid teeth present.
52-53-B. Second ceratobranchials from two-thirds length to slightly longer than first
ceratobranchials.
54-A. Second ceratobranchials in medial contact for most or all their lengths.
55-A. Neural spines of presacral vertebrae tall, more than 50% of total vertebral
height.
56-A. Zygosphenes connected to prezygapophyses by continuous arc of bone.
57-A. Posterolateral processes present on pleurapophyses of second sacral vertebra.
58- A. Foramina present in ventral surface of pleurapophyses of second sacral vertebra.
59-A. More than 40 caudal vertebrae.
60- A. Caudal autotomy septa present. The polarity of this character is questionable.
61 -A. Autotomic caudal series (or series of caudal vertebrae with paired transverse
processes) begins at or before 10th caudal vertebra. The polarity of this character is
questionable.
140 University of California Publications in Zoology
62-A. Dorsal midsagittal fins of caudal vertebrae anterior to neural spines relatively
large and present well beyond anterior third of caudal sequence.
63- A or -B. Postxiphisternal inscriptional ribs do not form continuous chevrons, or
anteriormost pairs do only variably.
64-A. Suprascapulae oriented primarily vertically and form a continuous arc with the
scapulocoracoids.
65- A. Scapular fenestrae present and large.
66-A. Posterior coracoid fenestrae absent.
67- A. Clavicles wide, with prominent lateral shelves.
68-A. Posterior process of interclavicle extends well beyond lateral corners of
sternum.
69-A. Interclavicle arrow-shaped, lateral processes forming angles of less than 75°
with posterior process.
70- A. Sternal fontanelle present and of moderate size.
71-A. Sternum diamond-shaped, xiphisternal rods attach close to midline.
72-A. Pelvic girdle relatively long and narrow.
73-A. Large anterior iliac process.
74-A. Cephalic osteoderms absent.
75-A. Heart lies entirely anterior to transverse axillary plane.
76- A. Subclavian arteries covered ventrally by posterior end of M. rectus capitis
anterior.
77- A. Right and left systemic arches unite to form dorsal aorta above heart.
78-A. Coeliac artery arises from dorsal aorta anterior to and separate from mesenteric
arteries.
79-A. Colic wall with one or more transverse valves.
80-A. All colic valves semilunar. The polarity of this character is questionable.
81- A. Median azygous rostral scale present.
82-A. Snout scales small and numerous, approximately same size as those of
supraorbital and temporal regions.
83-A. Dorsal head scales flat or only slighdy convex.
84-B. Superciliary scales moderately elongate and partially overlapping. It is also
possible that the ancestral iguanine had elongate and strongly overlapping superciliaries.
85-A or -B. Subocular scales subequal in size, or one or two moderately elongate.
86-A. Anterior auricular scales small or only slighdy enlarged.
87- A. Gular fold well developed.
88- A. Dewlap small or absent. The polarity of this character is questionable.
89-A. Gular crest of enlarged scales absent.
90-A. Middorsal scale row present.
91-A. Pedal subdigital scales asymmetrical, anterior keels larger than posterior ones.
92- A. Pedal subdigital scales lack greatiy enlarged anterior keels fused at their bases to
form combs.
93-A. Toes unwebbed.
Phylogenetic Systematics of [guanine Lizards
141
FIG. 52. Geographic distribution oi Dipsosaurus (modified from Stebbins, 1966).
94-A. Caudal scales in adjacent verticils approximately equal in size, smooth or keeled
but not spinous.
95- A. Body laterally compressed or roughly cylindrical.
Dipsosaurus Hallowell 1 854
Type species (by monotypy): Crotaphytus dorsalis Baird and Girard 1852.
Etymology: (Greek) Dipsa, thirst(y), + sauros, lizard. Dipsosaurus was first known
from the "Colorado Desert" of western North America, as Hallowell (1854:92) described it
"a country without water."
Definition: The most recent common ancestor of the populations of Recent
Dipsosaurus dorsalis and all of its descendants.
Distribution: Deserts of the southwestern United States in southeastern California,
southern Nevada, southwestern Utah, and western Arizona, southward into Mexico
through western Sonora and northwestern Sinaloa and into Baja California to its southern
end, including various islands in the Gulf of California (Fig. 52).
1 42 University of California Publications in Zoology
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies (here and afterwards the parenthetical numbers and letters
correspond with those in the list of systematic characters):
1. Large, paired openings at or near frontonasal suture present (9-B).
2. Parietal foramen located entirely within frontal bone (13-C). This character occurs
also in Cyclura carinata and variably in some Ctenosaura, Sauromalus, and other Cyclura.
3. Lateral process of palatine behind infraorbital foramen small or absent (22-B).
4. Medial borders of pterygoids curve sharply toward midline anterior to pterygoid
notch; pyriform recess narrows abruptly (25-B). This character occurs in all other
iguanines except Brachylophus and may thus be a synapomorphy of Iguaninae that has
reversed in Brachylophus.
5. Lateral pointed processes on cristae interfenestralis present (30-B).
6. Posterior ends of lateral and medial crests of retroarticular process diverge
ontogenetically, so that outline of retroarticular process is quadrangular in large specimens
(42-B).
7. Crowns of posterior marginal teeth with four cusps (46-B). An increase in tooth
cuspation characterizes all other iguanines except Amblyrhynchus and some Brachylophus
and Ctenosaura; therefore this character may be a synapomorphy of a more inclusive group
that has reversed in certain taxa.
8. Pterygoid teeth usually absent (50-B, 51-B), This character also occurs in
Conolophus. When present, the pterygoid teeth of Dipsosaurus lie along the medial edge
of the pterygoid, while those of Conolophus lie more laterally, supporting the conclusion
that the absence of pterygoid teeth in these two taxa is convergent.
9. Colon with one or more circular valves (80-B). This condition occurs also in all
other iguanines except Brachylophus and may be a synapomorphy of a more inclusive
group.
10. Superciliary scales greatly elongate and strongly overlapping (84-C). The derived
status of this character is questionable.
11. One subocular scale much longer than others (85-C). The derived status of this
character is questionable.
Fossil record: Olson (1937) described Tetralophosaurus minutus based on a fragment
of a lower jaw from Lower Miocene deposits in Nebraska. The specimen was referred to
Dipsosaurus by Estes (1983), who stated that it was indistinguishable from D. dorsalis, but
this conclusion is based on overall similarity. Almost complete skulls and dentaries from
the PUocene of southern California have been referred to Dipsosaurus by Norell (1983).
Comments: Failure of the lateral palatine process to contact the jugal behind the
infraorbital foramen (character 23) suggests that Dipsosaurus is the sister group of all other
iguanines. However, the gently curving medial pterygoid borders and wide pyriform
recess of Brachylophus (character 25) suggest that this taxon, rather than Dipsosaurus, is
Phylogenetic Systematics of I guanine Lizards 143
the sister group of all other iguanines. The weaker tendency of Brachylophus to develop
fourth cusps on the posterior marginal teeth might be taken as further evidence in favor of
the latter hypothesis, but the character is variable in Brachylophus and has reversed several
other times within iguanines. At least three other characters might be used to support one
or the other of these alternative hypotheses, but these characters must be used with caution
because their polarities are unclear. These are: (1) the lack of a notch separating
zygosphenes from prezygapophyses in Dipsosaurus (character 56); (2) the absence of
circular colic valves in Brachylophus (character 80); and (3) the low number of colic valves
in Dipsosaurus (Iverson, 1982). Camp (1923) noted another character in which all
iguanines except Dipsosaurus share what appears to be a derived condition (Conolophus
was not examined): a high degree of separation of the M. mylohyoideus anterior
superficialis. Because of this contradictory information, I have chosen to leave the
relationships among Dipsosaurus, Brachylophus, and the monophyletic group consisting
of the remaining iguanines (Iguanini) unresolved. I am not aware of any characters
suggesting that Dipsosaurus and Brachylophus are sister taxa.
Brachylophus Wagler 1830
Type species (by monotypy): I guana fas data Brongniart 1800.
Etymology: (Greek) Brachys, short, + lophos, a crest. The name presumably refers to
the relatively short scales of the dorsal crest in B.fasciatus, the type species.
Definition: The most recent common ancestor of B.fasciatus and B. vitiensis and all of
its descendants.
Distribution: Numerous islands in the Fiji Islands group, Tongatapu in the Tonga
Islands group, and lies Wallis northeast of Fiji, all in the southwestern Pacific Ocean (Fig.
53).
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1. Lateral process of palatine behind infraorbital foramen contacts jugal (23-B). This
character occurs in all iguanines except Dipsosaurus and some specimens of Sauromalus,
and may be a synapomorphy of a more inclusive group.
2. Infraorbital foramen located entirely within palatine bone, may or may not be
connected to lateral edge of palatine by suture (24-B). This character also occurs in some
Amblyrhynchus, some Ctenosaura, and some Sauromalus, in which it is interpreted as
convergent.
3. Anterior inferior alveolar foramen located entirely within dentary (34-35-B). This
character occurs only in Brachylophus within Iguaninae, but does not occur in all
specimens.
144
University of California Publications in Zoology
FIG. 53. Geographic distribution oi Brachylophus (from Gibbons, 1981; Etheridge, 1982).
4. Labial process of coronoid moderately large (36-B). The enlarged labial coronoid
process of Amblyrhynchus and Conolophus is interpreted as convergent.
5. Second ceratobranchials much longer than first ceratobranchials (52-53-C). The
long second ceratobranchials oil guana iguana are interpreted as convergent.
6. Zygosphenes separated from prezygapophyses by a deep notch (56-B). This
character occurs in all iguanines except Dipsosaurus, and may be a synapomorphy of a
more inclusive group.
7. Caudal autotomy septa absent (60-B). Although the outgroup evidence is
equivocal, I have assumed that the presence of caudal autotomy, and the intravertebral septa
that facilitate it, are primitive for iguanines. The absence of caudal autotomy septa in
Amblyrhynchus and Conolophus on the one hand and in Iguana delicatissima on the other
are interpreted as convergent.
8. Midsagittal processes on dorsal surfaces of caudal centra anterior to neural spine
relatively small and confined to anterior fifth of caudal sequence (62-B). This character
also occurs in Iguana, in which it is interpreted as convergent.
9. Anterior postxiphistemal inscriptional ribs enlarged and members of at least one pair
united midventrally to form continuous chevrons (63-C). Midventrally continuous
chevrons formed by the first pair of postxiphistemal inscriptional ribs occur in various
other iguanines but not invariably within species, as in Brachylophus. Unlike other
Phylogenetic Systematics of I guanine Lizards 1 45
iguanines, Brachylophus also exhibits enlargement of the second and third postxiphisternal
inscriptional ribs, which may also unite to form continuous chevrons.
10. Large dewlap present (88-E). The two species oi Brachylophus differ in that a
large dewlap is present in both sexes of B. vitiensis but only in male B.fasciatus
(Gibbons, 1981). The polarity of this character is uncertain. If presence of a large dewlap
is derived, then the phylogenetic relationships proposed here require that it has evolved
convergently in Iguana and in some species of Ctenosaura.
In addition, the following derived character occurs in some Brachylophus:
Posterior marginal teeth with a fourth cusp (46-B). This character occurs in all other
iguanines except Amblyrhynchus and some Ctenosaura; it may thus be a synapomorphy of
a more inclusive group, perhaps of all iguanines.
Fossil record: Bones thought to be remains of Brachylophus are known from
archaeological sites on Tongatapu and Lifuka in the Tonga Islands group (approximately
2000 years before present). If correcdy referred, these bones indicate that Brachylophus
once reached much larger sizes than they do today (Etheridge, pers. comm.; Pregill, pers.
comm.).
Comments: Gibbons (1981) discusses the authorship oi Brachylophus, crediting the
name to Wagler (1830), since Cuvier (1829) had used the informal apellation les
Brachylophes. The relationships oi Brachylophus to Dipsosaurus and other iguanines are
discussed in the comments on Dipsosaurus, above.
IguaniniBell 1825
Type genus: Iguana Laurenti 1768.
Etymology: Modification of Iguana, the name of its type genus.
Definition: The most recent common ancestor of Ctenosaura, Sauromalus,
Amblyrhynchina, and Iguanina, and all of its descendants.
Distribution: Southwestern United States southward through Mexico, Central America,
and northern South America to southern Brazil and Paraguay, the West Indies, and the
Galapagos Islands.
Diagnosis: Members of this taxon can be distinguished from other iguanines
{Brachylophus and Dipsosaurus) by the following synapomorphies:
1. Lateral process of palatine contacts jugal behind infraorbital foramen (23-B). This
character does not occur in some Sauromalus, where it is interpreted as a reversal. It does
occur in Brachylophus and may thus be a synapomorphy of a more inclusive group.
146 University of California Publications in Zoology
2. Medial borders of pterygoids curve sharply toward midline anterior to pterygoid
notch; pyriform recess narrows abrupdy (25-B). This character occurs also in Dipsosaurus
and may be a synapomorphy of a more inclusive group.
3. Crowns of posterior marginal teeth with four or more cusps (46-B,-C, or-D). This
character occurs also in Dipsosaurus and some Brachylophus, and may be a synapomorphy
of all iguanines. It has reversed in Amblyrhynchus and some Ctenosaura.
4. Posterior portion of pterygoid tooth patch displaced laterally away from medial
border of pterygoid (48-B). Pterygoid teeth are absent in most Conolophus, but when
present they lie away from the medial pterygoid border. This character develops during
postembryonic ontogeny and is not always evident in small specimens.
5. Zygosphenes separated from prezygapophyses by a deep notch (56-B). This
character occurs also in Brachylophus and may be a synapomorphy of a more inclusive
group.
6. Sequence of autotomic caudal vertebrae or that of vertebrae with two pairs of
transverse processes begins at or behind 10th caudal vertebra (61-B). The polarity of this
character is questionable.
7. Posterior coracoid fenestra usually present (65-B). This character exhibits some
variation within basic taxa.
8. Right and left systemic arches unite to form dorsal aorta posterior to heart (77-B).
9. One or more circular colic valves present (80-B). This character occurs also in
Dipsosaurus and may be a synapomorphy of a more inclusive group.
Fossil record: The earliest fossils that are clearly referable to Iguanini are from the
Pliocene of southern California. Among extant Iguanini these fossils appear to be most
closely related to Iguana (Norell, 1983). Stevens (1977) considered a dentary fragment
from the early Miocene of Texas to be either Ctenosaura or Sauromalus. If correctly
referred, this would be the oldest record of Iguanini. These and other fossil records are
given under the least inclusive taxa to which they belong or are most closely related.
Comments: Although this is the first use of Iguanini, Bell (1825) is credited with
authorship under the principle of coordination (Article 36, third edition of the International
Code of Zoological Nomenclature). Iguanini contains all the really large iguanines, and
large body size may be an additional synapomorphy of this taxon. Some Ctenosaura are
relatively small, but this probably represents a secondary reduction in size (see comments
on Ctenosaura, below). Relationships among four recognizable monophyletic subgroups
of Iguanini are uncertain and are discussed in greater detail in the comments on Ctenosaura,
Sauromalus, Amblyrhynchina, Iguanina, and Cyclura.
Ctenosaura Wiegmann 1 828
Type species (subsequent designation by Fitzinger 1843): Ctenosaura cycluroides
Wiegmann 1828 = Lacerta acanthura G. Shaw 1802.
Phylogenetic Systematics of I guanine Lizards
147
FIG. 54. Geographic distribution of Ctenosnura (from Peters and Donoso-Barros, 1970; H. M. Smith,
1972; Etheridge, 1982).
Etymology: (Greek) Ktenos, comb, + sauros, lizard, referring to the dorsal crest of
enlarged scales.
Definition: The most recent common ancestor of the extant species of Ctenosaura
(acanthura, baked, clarki, defensor, hemilopha, palearis, pectinata, quinquecarinata, and
similis) and all of its descendants.
Distribution: Lowlands of Mexico and Central America from southeastern Baja
California and the middle of Sonora in western Mexico and near the Tropic of Cancer in
eastern Mexico southward through most of Central America to central Panama, as well as
Isla de Providencia, Isla de San Andres, the Tres Marias Islands, and various offshore
islands in the eastern Pacific, the western Caribbean, and the Sea of Cortez (Fig. 54).
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1 . Premaxillary process of maxilla curves dorsally; premaxillary teeth set higher than
maxillary teeth (16-B). This character is not present in small specimens.
148 University of California Publications in Zoology
2. Posterolateral processes of parabasisphenoid absent or relatively small (29-B).
3. Posterolateral processes on pleurapophyses of second sacral vertebra absent (57-B).
This character also occurs in Iguana and most Cyclura, and may be a synapomorphy of a
more inclusive group.
4. One subocular scale very long (85-C). The polarity of this character is
questionable. An elongate subocular occurs also in Dipsosaurus, in which it is interpreted
as convergent.
5. Tail bears whorls of enlarged, spinous scales (94-B). This character occurs also in
most Cyclura, in which it is interpreted as convergent.
Other derived characters occur only in some Ctenosaura and may provide useful
information concerning relationships within this taxon:
1. Prefrontal contacts jugal behind lacrimal foramen (7-B). This character also occurs
in Amblyrhynchus, Conolophus, and some Cyclura; within Ctenosaura, prefrontal-jugal
contact is characteristic only of C clarki and may be a synapomorphy of that taxon.
2. Crista cranii forms step rather than smooth curve between frontal and prefrontal (10-
B). This character also occurs in Conolophus; within Ctenosaura it occurs only in C.
defensor and may be a synapomorphy of that taxon.
3. Parietal foramen located entirely within frontal (13-B). This character occurs also in
Dipsosaurus and in some Cyclura and Sauromalus; within Ctenosaura it varies as much
within species as among them, and it is therefore uninformative about relationships among
these species.
4. Infraorbital foramen located entirely within palatine (24-B). This character also
occurs in Brachylophus and in some Amblyrhynchus and Sauromalus; within Ctenosaura it
varies as much within species as among them, and it is therefore uninformative about
relationships among these species.
5. Surangular extends anteriorly well beyond coronoid apex and sometimes beyond
posteriormost dentary tooth (39-B). This character occurs also in Iguana and Cyclura; its
pattern of variation within Ctenosaura needs further study.
6. Crowns of posterior marginal teeth polycuspate (46-C). This character occurs also
in Iguana, Cyclura, and Sauromalus; within Ctenosaura it occurs only in C. defensor and
may be a synapomorphy of that taxon.
7. Crowns of posterior marginal teeth tricuspid (46- A). Within Ctenosaura this
character, a presumed reversal, occurs in C. bakeri and C. quinquecarinata.
8. Posterior portion of pterygoid tooth patch doubles ontogenetically (49-B). This
character, or a further modification of it, occurs also in Iguana and some Cyclura. Since
members of the small species of both Ctenosaura and Cyclura do not exhibit ontogenetic
doubling of the tooth row, and since small maximum size in these taxa is thought to be
derived (see comments on Iguanini, above), it is likely that this character is a
synapomorphy at a higher level and that failure to double the pterygoid tooth row is derived
within Ctenosaura.
9. Fewer than 40 caudal vertebrae (59-B). This character also occurs in Sauromalus;
within Ctenosaura it occurs in C. clarki and C defensor.
Phylogenetic Systematics of I guanine Lizards 1 49
10. Large dewlap (88-B). The polarity of this character is questionable. Large
dewlaps occur also in Brachylophus and Iguana; within Ctenosaura they occur only in C.
palearis.
Fossil record: The oldest fossils referred to Ctenosaura are from the Holocene of
Mexico (Langebartel, 1953; Ray, 1965; Estes, 1983). Stevens (1977) suggested that a
fragment of a left dentary from the early Miocene of Texas was probably close to
Ctenosaura.
Comments: Bailey (1928:7) claimed that "it is impossible to distinguish between the
genus Ctenosaura and its near allies by means of skeletal characters." This is false.
Osteological synapomorphies are identifiable not only in Ctenosaura but also in all of the
other iguanine taxa that have traditionally been assigned the rank of genus. Even within
Ctenosaura, monophyletic groups can be recognized on the basis of skeletal characters.
At least three characters suggest a close relationship among Ctenosaura, Iguana, and
Cyclura: extension of the surangular well anterior to the coronoid apex (39-B); tendency of
the pterygoid tooth row to double ontogenetic ally (49-B,-C); and absence of posterolateral
processes on the pleurapophyses of the second sacral vertebrae (57-B). Nevertheless, I
have left the relationships of Ctenosaura to other Iguanini unresolved because all three of
these characters are ambiguous. The first is variably present in Ctenosaura, the third is
variable in Cyclura, and the second is variable in both Ctenosaura and Cyclura. Thus,
provided that the monophyly of each of these taxa is accepted, every one of these characters
must involve homoplasy. If the homoplasy is interpreted as acquisition of the derived state
of these characters in the most recent common ancestor of Ctenosaura, Cyclura, and
Iguana, with subsequent reversal in certain taxa, then the close relationship among these
three taxa might still be advocated. At present, however, the homoplasy can just as
reasonably be interpreted as convergence, in which case the close relationship is not
supported. I prefer to leave the relationships of Ctenosaura within Iguanini unresolved
until additional evidence suggests that one of the alternative interpretations of homoplasy in
the characters that vary within basic taxa is more plausible. The relationship between
Ctenosaura and Cyclura is discussed further in the comments on Cyclura, below.
The species bakeri, clarki, defensor, palearis, and quinquecarinata, here included in
Ctenosaura, are sometimes placed in a separate genus, Enyaliosaurus. Etheridge (1982)
reviewed the history of the problem as follows:
The most recent taxonomic revision and key for the genus Ctenosaura is that of
Bailey (1928), but several important papers on individual species or groups of
species have appeared subsequentiy. Bailey recognized 13 species, including those
forms with a relatively small body size and a short, strongly spinose tail referred by
some authors to Enyaliosaurus. Following Gray's (1845) description of
Enyaliosaurus the name was seldom used until its revival by Smith and Taylor
(1950: 75). In this work the species clarki, defensor, erythromelas, palearis and
150 University of California Publications in Zoology
quinquecarinata were allocated to Enyaliosaurus, but no justification was provided
for the revival of the genus. Duellman (1965: 599), followed Smith and Taylor in
recognizing the validity of Enyaliosaurus, placed erythromelas in the synonymy of
defensor, provided a key to the species, and suggested that: "Enyaliosaurus
doubtless is a derivative of Ctenosaura, all species of which are larger and have
relatively longer tails and less well-developed spines than Enyaliosaurus." Meyer
and Wilson (1973) referred Ctenosaura bakeri to Enyaliosaurus, but Wilson and
Hahn (1973: 114-5) returned bakeri to Ctenosaura, commenting that: "John R.
Meyer is currently studying the problems of the relationship of the species now
grouped in Enyaliosaurus to those now grouped in Ctenosaura. He (pers. comm.)
advised us that he considers the two genera inseparable, and that bakeri appears to
be closely related to both palearis (now in Enyaliosaurus) and similis (now in
Ctenosaura)." In addition, Ernest Williams of Harvard University has informed me
(pers. comm.) that based on an unpublished study of the group by him and Clayton
Ray, he does not believe the recognition of Enyaliosaurus is warranted. At the
present time the problem of the relationships of Ctenosaura and Enyaliosaurus are
under study by Diderot Gicca of the Florida State Museum. (Etheridge, 1982:9-10)
More recently, Gicca (1983) recognized the genus Enyaliosaurus.
Evidence for the monophyly of Ctenosaura in the broad sense of Bailey (1928) has
been presented above. An evaluation of the monophyletic status of Ctenosaura in the
narrow sense, and of Enyaliosaurus, required a phylogenetic analysis using the species of
both as basic taxa. In this analysis, I have used primarily characters recognized by
previous workers, in particular, Bailey (1928), Smith and Taylor (1950), and Ray and
Williams (unpubl.). When possible, all characters were checked on specimens. My
analysis is based on the following 19 characters representing a minimum of 23
phylogenetic transformations. The polarities of these characters were determined using
Amblyrhynchina, Iguanina, Sauromalus, Dipsosaurus, and Brachylophus as outgroups.
The character-state codes are as follows: 0, ancestral; 1, derived; 2, further derived; etc.
Letter codes are used for characters whose polarities were considered undeterminable.
1. Maximum snout-vent length: (0) greater than 190 mm; (1) less than 190 mm.
Maximum snout-vent lengths for the various taxa are as follows: acanthura = 215 mm
(MCZ 16074, Bailey, 1928; 315 mm according to Ray and Williams, unpubl., but they
include pectinata in acanthura); bakeri = 210 mm (USNM 25324, Bailey, 1928); clarki =
154 mm (UMMZ 112711, Duellman and Duellman, 1959); defensor = 155 mm (HM 3420,
Bailey, 1928); hemilopha = approximately 400 mm (H. M. Smith, 1972; the largest
specimen that Bailey [1928] presents data for is AMNH 2073 with a snout- vent length of
260 mm); palearis = 254 mm (CAS 69308, A. Bauer, pers. comm.); pectinata = 305 mm
(MCZ 2726, Bailey, 1928); quinquecarinata = 169 mm (Hidalgo, 1980; Gicca, 1983); and
similis = 489 mm (Fitch and Hackforth-Jones, 1983). A cutoff of 190 mm was chosen,
partly because of an apparent gap and partly because all other species of Iguanini reach
greater maximum snout- vent lengths than this.
Phylogenetic Systematics of I guanine Lizards 151
2. Modal number of presacral vertebrae (Table 4): (0) 24; (1) 25.
3. Modal number of premaxillary teeth (Table 3): (0) seven; (1) five. Although
Ctenosaura defensor is the only species with a mode of five premaxillary teeth (range 5-6),
the occurrence of five. premaxillary teeth in some specimens of C. clarki and C.
quinquecarinata, but in no other Ctenosaura, suggests that these three species form a
monophyletic group.
4. Anterior orbital region (Fig. 10): (A) lacrimal contacts palatine behind lacrimal
foramen; (B) prefrontal contacts jugal behind lacrimal foramen.
5. Cristae cranii (Fig. 12): (0) form smooth curve from frontal to prefrontal; (1)
frontal portions protrude anteriorly forming a step from frontal to prefrontal.
6. Parietal roof: (0) remains deeply notched posteriorly throughout ontogeny, so that
the braincase is broadly exposed in dorsal view; (1) extends posteriorly as a flat shelf
during postembryonic ontogeny, so that the braincase comes to be largely covered in dorsal
view. This character is partially correlated with character 1, body size.
7. Ontogenetic convergence of lateral edges of parietal roof: (A) eventually meet
posteriorly and form a midsagittal crest, giving the parietal roof a Y-shaped outline; (B) fail
to meet, or meet but fail to form a midsagittal crest, giving the parietal roof a trapezoidal or
triangular outline. This character is partially correlated with character 1, body size.
8-9. Crowns of posterior marginal teeth: (AO) with a maximum of four cusps; (BO)
with a maximum of five or more cusps; (Al) with a maximum of three cusps.
10. Pendulous dewlap: (0) absent; (1) present but small; (2) present and large.
11. Parietal eye: (0) conspicuous externally; (1) external signs inconspicuous or
absent. This character may also be manifested in a reduction in the parietal foramen in C.
defensor, but my osteological sample of this taxon is small (N=l).
12. Dorsal crest scales I: (0) conform in color and pattern to adjacent body scales;
adjacent crest scales similar in size; (1) unicolored and differing from body color; large,
flap-like crest scales separated by one or more smaller scales.
13. Dorsal crest scales II: (0) high-keeled, large, and conspicuous, at least in neck
region; (1) low-keeled to flat, inconspicuous throughout length of crest.
14. Middorsal scale row: (0) continuous from neck onto tail, or narrowly interrupted
in sacral region; (1) broadly discontinuous in lumbosacral region.
15. Scales of anterodorsal surface of leg: (0) not enlarged or spinous; (1) enlarged and
spinous on shank but not on thigh; (2) enlarged and spinous on both shank and thigh. An
additional state could be recognized, since C. clarki and C. quinquecarinata have large
anterodorsal thigh scales compared to those of most other Ctenosaura, but these scales are
not as large as in C. defensor, and they are not spinous.
16. Subdigital scales at the base of pedal digit 111: (0) with relatively small anterior
keels or with moderately large anterior keels that are separate from those of adjacent scales;
(1) with relatively large anterior keels fused at their bases to form a comb.
17. Tail: (0) strongly spinose proximally, but not distally, and always longer than
body (snout- vent length/total length = 0.27-0.45), more than 30 caudal vertebrae; (1) tail
152 University of California Publications in Zoology
strongly spinose throughout its length and almost the same length as the body (snout- vent
length/total length = 0.48-0.56), fewer than 30 caudal vertebrae.
18. Anterior (referring to first 10) whorls of strongly spinous caudal scales: (0)
always separated by at least two rows of intercalary scales; (1) at least some separated by
only one intercalary scale row, others by two or more; (2) none (or only the first) separated
by two intercalary scale rows, but all separated by at least one; (3) intercalary scales of
proximal whorls greatly reduced or absent.
19. Snout region: (0) not inflated, sloping gradually downward; (1) inflated
anteriorly, sloping abruptly downward.
Height of the vertebral neural spines may also be a useful character, but I have chosen
not to use it because I have no postcranial skeletons of C. defensor and C. palearis.
The distributions of these character states among basic taxa within Ctenosaura (sensu
lato) and three near (Amblyrhynchina, Iguanina, Sauromalus) and two more distant
(Dipsosaurus, Brachylophus) outgroups are given in Table 10. Ctenosaura bakeri from
Isla de Utila and those from Isla de Roatan are scored separately because they differ in at
least three of the characters used in this analysis. Only those from Utila, the type locality,
are included in the analysis of relationships.
The phylogenetic relationships suggested by the characters in Table 10 (except character
19, the derived state of which occurs only in the Roatan population of C. bakeri) are
diagrammed in Figure 55. Synapomorphies for the subterminal nodes and the basic taxa
are given below. Characters whose polarities were initially undeterminable were placed on
the cladogram after it was constructed using only those characters whose polarities were
determinable using other iguanines as outgroups. Ignoring the Roatan ctenosaurs and
intraspecific variation, these relationships require a total of 25 character transformations,
three more than the minimum number required by the characters themselves (C-index =
0.88). C-indices for the individual characters are given in Table 10.
Node 1: Ctenosaura Wi^gmdiXm 1828
See above. The characters of the hypothetical ancestral Ctenosaura can be
reconstructed by taking the first state of each of the 19 characters in the character list.
1).
Node 2 (unnamed)
1. Parietal roof extends posteriorly over braincase during postembryonic ontogeny (6-
Ctenosaura acanthura
No synapomorphies identified.
Ctenosaura pectinata
No synapomorphies identified.
Phylogenetic Systematics of I guanine Lizards 153
TABLE 10. Distributions of Character States of 19 Characters Among Basic Taxa Within
Ctenosaura (in the broad sense) and Three Close and Two More Distant Outgroups
Taxon
Character
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
acanthwa OOOAO lAAOOOOOOOOOOO
bakeriqj\i\2L) OOOI--OBAI 10100100 0,1 0
te)ten (Roatan) OOOAOOBA 1 00000 1 00 0,1 1
clarki llOBOOBAOOOOl 0,1 10120
(kfensor 111A10BB001010,121130
hemilopha OOOAOOAAOOOOOIOOOIO
palearis 000A00BA020100 10020
pectimta OOOAO lAAOOOOOOOOOOO
quinquecarinata 1 1 OA,BOOBA 1 00000 1 0020
similis OOOAOOAAOOOOOOOOOOO
CI 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.6 1.0
Amblyrhynchina 0 0 0 B 0,1 0 A,B A 0,1 0 0 02 0 0 0 0 0^ N^ 0
Iguanina 0 0 Of^ A,B 0 0 A,B B 0 1,2 0 0 0 0 0 0,1 0^ 0,n3o,1
Sauromalus 0 0 1^ A 0 0 B B 0 0 0 N^ N^ 1^ o'' 0 O^'^ N^ 0
Dipsosaurus 1 OOAOOBAOOOO 1 OOOO^N^O
Brachylophus 0 0 0 A 0 0 A,B A 0,1 0,1 0 0 0 0 0 0 0^ N^ 0
Note: Character-state codes correspond with those used in the character list. A dash indicates the lack of
data. Consistency indices (CI) for each character on the minimum-step cladogram for these characters (Fig.
55) are also given. The consistency indices were calculated ignoring intraspecific variation.
^50% have seven and 50% have six (N = 2).
^Large, conical crest scales are separated by smaller ones in Conolophus.
^Not spinose in Amblyrhynchus, Conolophus, Iguana, Sauromalus, Dipsosaurus, and Brachylophus.
^Greater than seven in Cyclura.
^Some species have modes of four or six.
^Middorsal scale row entirely absent.
^In S. hispidus the entire leg has enlarged, spinous scales.
^Tail about same length as body but not spinose.
154
University of California Publications in Zoology
■5^
<>
C
ty
O
FIG. 55. Cladogram illustrating phylogenetic relationships within Ctenosaura. Synapomorphies for
the numbered nodes and basic taxa are given in the text.
Node 3 (unnamed)
1. Some anterior whoris of strongly spinous caudal scales separated by one or fewer
rows of smaller scales (18-1,-2, or-3). This character does not occur in all C. bakeri, a
case most simply interpreted as a character reversal.
Ctenosaura hemilopha
1. Middorsal scale row broadly discontinuous in lumbosacral region (14-1). This
character also occurs in some C. clarki and C. defensor, in which it is interpreted as
convergent.
Phylogenetic Systematics of I guanine Lizards 1 55
Node 4: Enyaliosaurus Gvd.y \M5
1. Lateral edges of parietal roof fail to meet, or meet and fail to form a midsagittal crest;
outline of parietal roof trapezoidal or triangular (7-B).
2. Scales on anterodorsal surface of shank enlarged and spinous (15-1 or-2).
Node 5 (unnamed)
1. Pendulous dewlap present (10-1 or-2),
2. Dorsal crest scales unicolored and differing in color from adjacent body scales;
large, flap-like crest scales separated by one or more smaller scales (12-1).
Ctenosaura baked
1. Crowns of posterior marginal teeth with a maximum of three cusps (9-1). This
character occurs also in C. quinquecarinata, where it is interpreted as convergent.
In some: anterior whorls of strongly spinous caudal scales always separated by at least
two rows of smaller scales (18-0). This is interpreted as a case of character reversal.
Ctenosaura palearis
1. Large pendulous dewlap present (10-2).
2. All anterior whorls of strongly spinous caudal scales (except sometimes the first)
separated by one or no intercalary scale rows (18-2 or-3). This character occurs also in C.
defensor, C. clarki, and C. quinquecarinata, in which it is interpreted as convergent;
altematively, it may be a synapomorphy of a more inclusive group (Enyaliosaurus).
Node 6 (unnamed)
1. Maximum snout- vent length less than 190 mm (1-1).
2. Mode of 25 presacral vertebrae (2-1).
3. All anterior whorls (except sometimes the first) of strongly spinous caudal scales
separated by one or no intercalary scale rows (18-2 or 3). This character occurs also in C.
palearis, where it is interpreted as convergent; altematively, it may be a synapomorphy of a
more inclusive group.
The occurrence of five premaxillary teeth in at least some specimens, as well as
enlargement of the scales on the anterodorsal surface of the thigh, may also be
synapomorphies of this group.
Ctenosaura quinquecarinata
1. Crowns of posterior marginal teeth with a maximum of three cusps (9-1). This
character occurs also in C bakeri, in which it is interpreted as convergent.
In some: prefrontal contacts jugal behind lacrimal foramen (4-B). This character
occurs also in C. clarki, in which it is interpreted as convergent.
156 University of California Publications in Zoology
Node 7 (unnamed)
1. Dorsal crest scales low-keeled to flat; inconspicuous throughout length of crest (13-
1).
2. Tail strongly spinose throughout its length, and about same length as body (snout-
vent/tail length = 0.48-0.56); fewer than 30 caudal vertebrae (17-1).
In some: middorsal scale row broadly discontinuous in lumbosacral region (14-1),
This character occurs also in C. hemilopha.
Ctenosaura clarki
1. Prefrontal contacts jugal behind lacrimal foramen (4-B). This character occurs also
in some C. quinquecarinata, in which it is interpreted as convergent.
Ctenosaura defensor
1. Mode of five premaxillary teeth (3-1).
2. Frontal portion of crista cranii projects anteriorly to form a step from frontal to
prefrontal bones (5-1).
3. Crowns of posterior marginal teeth with a maximum of five or more cusps (8-B).
4. External signs of parietal eye inconspicuous or absent (11-1).
5. Scales on anterodorsal surface of thigh enlarged and spinous (15-2).
6. Anterior keels of subdigital scales at base of pedal digit III enlarged and fused at
their bases to form a comb (16-1).
7. Proximal rows of smaller scales between whorls of enlarged, spinous caudal scales
small or absent (18-3).
The results of the present analysis indicate that Enyaliosaurus (including bakeri,
palearis, quinquecarinata, clarki, and defensor) is a monophyletic group, but that
Ctenosaura in the narrow sense (acanthura, pectinata, similis, and hemilopha) is not.
Ctenosaura hemilopha appears to have shared a more recent common ancestor with
Enyaliosaurus than with the other Ctenosaura (in the narrow sense). However, the
character that suggests an exclusive common ancestry for hemilopha and Enyaliosaurus, a
reduction in the number of intercalary scale rows between the whorls of enlarged, spinous
caudal scales, is problematical, in that it does not occur in all bakeri. Nevertheless, if
bakeri and palearis are sister taxa, it is simpler to interpret the incongruence as a reversal in
some bakeri rather than four separate acquisitions of the derived condition (1-in hemilopha,
2-in some bakeri, 3-in palearis, 4-in the common ancestor of quinquecarinata, clarki, and
defensor). In any case, the monophyly of Ctenosaura in the narrow sense is doubtful even
if this character is rejected, for there are no derived characters found in acanthura, pectinata,
similis, and hemilopha that are not also found in the other taxa. Rather than the two being
separate taxa, Enyaliosaurus appears to be a subgroup of a more inclusive Ctenosaura.
There currentiy exist several problems concerning species-level taxa within Ctenosaura.
Smith and Taylor (1950) considered the specimens from the west coast of Mexico assigned
to C. acanthura by Bailey (1928) to be C. pectinata. Based on a conflict between the
Phylogenetic Systematics of I guanine Lizards 157
supposed geographic ranges of the species and the actual geographic distribution of
specimens possessing the diagnostic characters of each species, Ray and Williams
(unpubl.) considered pectinata to be a synonym of acanthura. The primary character used
by Bailey (1928) to distinguish between these two taxa was whether the middorsal scale
row was continuous (pectinata) or interrupted {acanthura) in the sacral region, but Hardy
and McDiarmid (1969) claim that this character is variable within pectinata from western
Mexico. Nevertheless, synonymizing pectinata with acanthura on the basis of such data
rests on an assumption that the two taxa are not broadly sympatric.
Stejneger (1901) described Ctenosaura bakeri from Utilla (Utila) Island, Honduras, and
Bailey (1928) surmised that it may also occur on Bonacca (Guanaja) and Ruatan (Roatan)
islands. Specimens collected subsequently on Roatan have been considered to be C. bakeri
(Wilson and Hahn, 1973; Meyer and Wilson, 1973), but they differ from the Utila
specimens in several ways (Table 10), including characters suggesting that they may not
even be one another's closest relatives. The populations from the two islands are probably
best considered separate species.
Sauromalus Dumeril 1856
Type species (by monotypy): Sauromalus ater Dumeril 1856.
Etymology: (Greek) Sauros, lizard, + omalos, flat.
Definition: The most recent common ancestor of the Recent species of Sauromalus
(ater, australis, hispidus, obesus, slevini, and varius) and all of its descendants.
Distribution: Deserts of the southwestern United States in southeastern California,
southern Utah and Nevada, and western and central Arizona, southward into Mexico in
western Sonora and eastern Baja California as well as various islands in the Gulf of
California (Fig. 56).
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1. Parietal foramen located variably within frontal (13-B). This character occurs also
in some populations of Ctenosaura and Cyclura; the parietal foramen is invariably located
within the frontal in Dipsosaurus and Cyclura carinata.
2. Splenial relatively small (33-B).
3. Angular does not extend far up labial surface of dentary and is not visible, or is only
barely visible in lateral view (37-B). This character also occurs in Amblyrhynchus and
Conolophus; thus, it is either convergent or a synapomorphy of a more inclusive taxon.
4. Angular reduced and narrow posteriorly (38-B).
5. Modal number of premaxillary teeth fewer than seven (absolute range 3-7; range of
modes for species 4-6) (43-44- A). This character also occurs in Ctenosaura defensor.
158
University of California Publications in Zoology
FIG. 56. Geographic distribution of Sauromalus (from C. E. Shaw, 1945; Gates, 1968; Etheridge,
1982).
6. Crowns of posterior marginal teeth with five or more cusps (46-C). This character
occurs in Cyclura and Iguana and may thus be a synapomorphy of a more inclusive group.
It also occurs in Ctenosaura defensor, in which it is interpreted as convergent.
7. Second ceratobranchials of hyoid apparatus short, often less than two-thirds the
length of the first ceratobranchials (52-53-A). This character also occurs in
Amblyrhynchus and Conolophus, in which it is either convergent or a synapomorphy of a
more inclusive taxon.
8. Second ceratobranchials not in contact medially for most or all of their lengths (54-
B). This character also occurs in Amblyrhynchus, in which it is interpreted as convergent.
9. Neural spines of presacral vertebrae short, less than 50% of total vertebral height
(55-B).
10. Fewer than 40 caudal vertebrae (59-B). This character occurs also in Ctenosaura
clarki and C. defensor, in which it is interpreted as convergent.
11. Postxiphistemal inscriptional ribs never form continuous midventral chevrons (63-
A). The polarity of this character is questionable. It also occurs in Dipsosaurus, in which,
if derived, it is interpreted as convergent.
12. Suprascapular cartilages situated primarily in a horizontal plane, and each forms an
angle rather than a smooth curve with the scapula (64-B).
Phylogenetic Systematics of I guanine Lizards 1 59
13. Scapular fenestrae small or absent (65-B). This character occurs also in
Amblyrhynchus, in which it is interpreted as convergent.
14. Clavicles narrow, the lateral shelf small or absent (67-B).
15. Posterior process of interclavicle does not extend beyond lateral comers of sternum
(68-B). This character also occurs in Amblyrhynchus, in which it is interpreted as
convergent.
16. Lateral processes of interclavicle form angles of between 75° and 90° with posterior
process, interclavicle roughly T-shaped (69-B). This character also occurs in
Amblyrhynchus, in which it is interpreted as convergent.
17. Sternal fontanelle small or absent (70-B). This character occurs also in
Amblyrhynchus, in which it is interpreted as convergent.
18. Sternum pentagonal; xiphistema widely separated (71-B). This condition is
approached in Amblyrhynchus.
19. Pelvic girdle short and broad (72-B).
20. Anterior iUac process small (73-B).
21. Heart extends posterior to transverse axillary plane (75-B).
22. Rostral scale divided by a median suture (81-B).
23. Superciliary scales quadrangular and non-overlapping (84- A). This character also
occurs in Amblyrhynchus, in which it is interpreted as convergent.
24. Enlarged anterior auricular scales (85-B).
25. Middorsal scale row absent (89-B).
26. Anterior and posterior keels of subdigital scales approximately equal in size;
subdigital scales roughly symmetrical with respect to long axis of toe (91-B).
27. Body strongly depressed (95-B).
Another possible synapomorphy of Sauromalus is the failure of the lateral edges of the
parietal table to meet ontogenetically. This character occurs also in Dipsosaurus and in
some Brachylophus, Ctenosaura, and Cyclura.
In addition, the following derived characters occur in some Sauromalus:
1. Lateral process of palatine behind infraorbital foramen fails to contact jugal (23-A).
This reversal occurs variably within ater, hispidus, and varius.
2. Infraorbital foramen located entirely within the palatine (24-B). This character
occurs also in Brachylophus and in some Amblyrhynchus and Ctenosaura. Within
Sauromalus it is known only in obesus, and its occurrence is variable in this taxon.
3. Coeliac artery originates between mesenteric arteries (78-B). This character occurs
also in Iguana. Its pattern of variation is poorly known, owing to small samples.
Fossil record: Estes (1983) summarized information on fossil Sauromalus, and
additional material has been described subsequendy by Norell (1986). The oldest fossils
referred to this taxon are from the Pleistocene of California, Nevada, and Arizona. Stevens
(1977) referred a fragment of a left dentary from the lower Miocene of Texas to either
Ctenosaura or Sauromalus, but thought that it was probably closer to Ctenosaura.
160 University of California Publications in Zoology
Comments: Sauromalus has a large number of derived characters supporting its
monophyly, many of which are unambiguous (i.e., they do not occur in any other
iguanine). Ahhough several of these characters, such as the height of the neural spines, the
orientation of the suprascapulae, and the shape of the pelvic girdle, may be part of a single
adaptive complex manifested externally in a depressed body form, I have treated them as
separate synapomorphies. Because various combinations of the alternative states of these
morphologies occur in certain noniguanine taxa, there is no reason to believe that they must
always occur together.
Sauromalus shares a large number of derived characters with Amblyrhynchus,
particularly in the shoulder girdle but not confined to this structure. Because
Amblyrhynchus shares even more derived characters with Conolophus, and because
Conolophus does not possess most of the derived characters shared by Amblyrhynchus
and Sauromalus, I interpret the derived characters shared by Amblyrhynchus and
Sauromalus as convergences. Perhaps this convergence results from similar functional
demands placed on the shoulder girdle by the saxicolous habits of the animals in both taxa.
The situation is complicated by the fact that all three taxa share two other derived characters:
limited lateral exposure of the surangular (37-B), and relatively short second
ceratobranchials (52-53-B). If one were to accept a sister-group relationship between the
Galapagos iguanas and Sauromalus based on these characters, then the many characters
shared by Amblyrhynchus and Sauromalus, but not Conolophus, could be interpreted as
additional synapomorphies of this hypothesized clade that have reversed in Conolophus.
However, because Sauromalus also shares a derived tooth morphology with Cyclura and
Iguana that does not occur in the Galapagos iguanas, I see no compelling reason to accept a
sister-group relationship between Sauromalus and the Galapagos iguanas. Furthermore,
even if such a relationship were accepted, interpreting the derived characters shared by
Amblyrhynchus and Sauromalus as convergent requires no more evolutionary changes than
hypothesizing a single origin for the derived state of each character, with reversal in
Conolophus.
The most recent revision of Sauromalus is that of C. E. Shaw (1945), although works
of taxonomic significance have appeared subsequendy (Cliff, 1958; Tanner and Avery,
1964; Soule and Sloan, 1966; Robinson, 1972, 1974). The boundaries, monophyly, and
relationships of the species within Sauromalus need further study.
Amblyrhynchina, new taxon
Type genus: Amblyrhynchus B&\\ 1825.
Etymology: Modification of Amblyrhynchus, the name of its type genus.
Definition: The most recent common ancestor of the extant Galapagos iguanas,
Amblyrhynchus and Conolophus, and all of its descendants.
Phylogenetic Systematics oflguanine Lizards
161
!=;::;«;
'««■ •■■•■■■* ■
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1 1 1 nT III'
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COLOMBIA
Equator
ECUADOR r
PERU
FIG. 57. Geographic distribution of Amblyrhynchina (Amblyrhynchus and Conolophus).
Distribution: Islands of the Galapagos Archipelago, Ecuador (Fig. 57).
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1. Nasal process of premaxilla covered dorsally between nasals (5-B).
2. Prefrontal contacts jugal, and lacrimal fails to contact palatine behind lacrimal
foramen (7-B). This character occurs also in some Ctenosaura (clarki) and Cyclura
(carinata, cornuta, and ricordii), in which it is interpreted as at least two separate instances
of convergence with the condition seen in Amblyrhynchina.
3. Frontal wider than long (8-B). This character occurs also in Cyclura cornuta and
Iguana delicatissima, which I interpret as two separate instances of convergence.
4. Lacrimal relatively small (17-B,-C).
5. Dorsal surface of vomerine process of palatine bears a high medial crest (21-B).
6. Labial process of coronoid relatively large (36-B,-C). This character occurs also in
Brachylophus, in which it is interpreted as convergent.
7. Angular does not extend up lateral surface of mandible and is barely visible in lateral
view (37-B). This character also occurs in Sauromalus and is either convergent or a
synapomorphy of a more inclusive taxon.
162 University of California Publications in Zoology
8. Surangular not exposed, or only barely exposed on lingual surface of mandible
between ventral processes of coronoid (40-B). This character occurs also in Cyclura
cychlura, in which it is interpreted as convergent; it also occurs as a rare variant in several
other iguanines.
9. Premaxillary teeth have large lateral cusps (45-B).
10. Anterior portion of pterygoid tooth patch absent (50-B). The entire pterygoid tooth
patch is absent in most Conolophus and Dipsosaurus; however, when present, the
pterygoid teeth of Dipsosaurus lie along the medial border of the pterygoid, those of
Conolophus are located more laterally.
11. Second ceratobranchials relatively short, often less than two-thirds the length of
the first ceratobranchials (52-53-A). This character also occurs in Sauromalus and is either
convergent or a synapomorphy of a more inclusive taxon.
12. Caudal autotomy septa absent (60-B). This character also occurs in Brachylophus
and in Iguana delicatissima, in which it is interpreted as two separate instances of
convergence.
13. Dorsal head scales pointed and conical (83-B).
Fossil record: Steadman (1981) referred to Conolophus fossils of undetermined age
from a lava tube on Isla Santa Cruz, Galapagos.
Comments: A close phylogenetic relationship between Amblyrhynchus and
Conolophus is widely accepted (Heller, 1903; Eibl-Eibesfeldt, 1961; Avery and Tanner,
1971; Thornton, 1971; Etheridge in PauU et al., 1976) but supporting evidence other than
geographic distribution has been scarce. Often the proposed close relationship between
these taxa was merely asserted or based on unspecified similarities. Avery and Tanner
(1971) did not distinguish between ancestral versus derived characters and used a highly
artificial system for assessing similarity (see Introduction). The immunological studies of
Higgins and Rand (1974, 1975; Higgins, 1977) compared the Galapagos iguanas only
with Iguana iguana among iguanines. Wyles and Sarich (1983) performed more extensive
immunological comparisons, including outgroups, but they prepared antisera to only four
of the ten iguanine taxa used in their study. The morphological data presented in this study
support the view that Amblyrhynchus and Conolophus are one another's closest living
relatives.
The relationships of Amblyrhynchina to other Iguanini are uncertain. Although
members of Amblyrhynchina share two derived characters with Sauromalus-rQducQd lateral
exposure of the angular (37-B) and short second ceratobranchials (52- A)-i do not consider
this convincing evidence for a close relationship between these taxa. At least one other
character, highly cuspate marginal teeth (46-B,C), suggests a close relationship among
Sauromalus, Iguana, and Cyclura. Convergences between Amblyrhynchus and
Sauromalus are discussed in the comments on Sauromalus, above.
Phylogenetic Systematics of I guanine Lizards 1 63
Amblyrhynchus Bell 1 825
Type species (by monotypy): Amblyrhynchus cristatus Bell 1825.
Etymology: (Greek) Amblys, blunt, + rhynchos, snout.
Definition: The most recent common ancestor of the populations of Recent
Amblyrhynchus cristatus and all of its descendants.
Distribution: Rocky coasts of islands in the Galapagos Archipelago, Ecuador (Fig.
57).
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1. Posterolateral processes on ventral surface of premaxilla absent (1-B).
2. Anterior surface of premaxillary rostral body nearly flat (3-B).
3. Nasal process of premaxilla nearly vertical (4-B).
4. Nasal capsule greatly inflated; nasal bones relatively large (6-B).
5. Frontal develops deep, paired pockets on ventral surface (1 1-B).
6. Dorsal orbital borders wedge-shaped (12-B).
7. Maxilla flares outward below row of supralabial foramina (15-B).
8. Lacrimal very small (17-C).
9. Large ventral process of squamosal (18- A). Because a reduced ventral process is
interpreted as a synapomorphy of Iguaninae, this is a character reversal. A similar
character in Iguana is interpreted as convergent.
10. Anterodorsal surface of septomaxilla bears pronounced longitudinal crest (20-B).
11. Parasphenoid rostrum very short (27-B).
12. Stapes relatively thick (31-B).
13. Dorsal edge of dentary much higher than dorsal edge of surangular on either side
of coronoid (32-B).
14. Anterior inferior alveolar foramen located between coronoid and splenial; dentary
does not contribute to its border (34-35-C).
15. Angular process of prearticular remains relatively small throughout ontogeny (41-
B).
16. Crowns of posterior marginal teeth tricuspid (46-A). This is a reversal, since the
presence of four or more cusps on the posterior marginal teeth is interpreted as a
synapomorphy of Iguanini or possibly a more inclusive group. The presence of tricuspid
posterior marginal teeth in adult Ctenosaura bakeri and C quinquecarinata is interpreted as
convergent.
17. Secondary cusps of tricuspid marginal teeth relatively large, only slightly smaller
than apical cusp (47-B).
1 64 University of California Publications in Zoology
18. Second ceratobranchials of hyoid apparatus separated from one another medially
for most or all of their lengths (54-B). This character occurs also in Sauromalus, in which
it is interpreted as convergent.
19. Scapular fenestrae small or absent (65-B). This character occurs also in
Sauromalus, in which it is interpreted as convergent.
20. Posterior process of interclavicle does not extend beyond lateral comers of sternum
(68-B). This character occurs also in Sauromalus, in which it is interpreted as convergent.
21. Lateral processes of interclavicle form angles of between 75° and 90° with the
posterior process; interclavicle roughly T-shaped (69-B). This character also occurs in
Sauromalus, in which it is interpreted as convergent.
22. Sternal fontanelle small or absent (70-B). This character also occurs in
Sauromalus, in which it is interpreted as convergent.
23. Xiphistema separated from one another medially (71-B). The xiphisterna of
Sauromalus are also separated medially but to a much greater extent. I consider this
similarity to be convergent.
24. Separable skull osteoderms develop over frontal, prefrontal, and nasal bones (74-
B).
25. Colic wall without valves but with numerous irregular transverse folds (79-B).
26. Superciliary scales quadrangular and nonoverlapping (84- A). This character also
occurs in Sauromalus, in which it is interpreted as convergent.
27. Gular fold weakly developed (87-B).
28. Digits of manus and pes partially webbed (93-B).
Other possible synapomorphies of Amblyrhynchus are a laterally compressed tail
(Tracy and Christian, 1985) and a high rate of tooth replacement associated with wide
alveolar margins of the maxilla, premaxilla, and dentary.
In addition, the following derived character occurs in some Amblyrhynchus:
Infraorbital foramen located entirely within palatine bone (24-B). This character occurs
also in Brachylophus and in some Ctenosaura and Sauromalus.
Fossil record: None.
Comments: Monophyly of Amblyrhynchus is the best- supported phylogenetic
hypothesis within Iguaninae. Sauromalus has almost as many characters that are
interpreted as synapomorphies, but it has more that require convergence elsewhere within
iguanines and, in this sense, are ambiguous. In terms of a simple tally of derived
characters used in this study, Amblyrhynchus is the most highly modified iguanine relative
to the most recent common ancestor of them all. Amblyrhynchus not only possess
numerous synapomorphies supporting its own monophyly, but also possesses those of
Amblyrhynchina and Iguanini. This high degree of morphological modification is not
surprising, given the unique natural history of these animals; Amblyrhynchus are the only
extant lizards that gain a major part of their sustenance from the sea (Darwin, 1835; Heller,
1903; Carpenter, 1966; Dawson et al., 1977; Dee Boersma, 1983). Many of the unique
Phylogenetic Systematics of I guanine Lizards 165
morphological features of Amblyrhynchus discussed in this paper are probably related to
this unique mode of existence. For example, the modifications of the teeth and colon may
be related to the unique diet of these lizards, which consists largely of marine algae
(Darwin, 1835; Carpenter, 1966; Dee Boersma, 1983). Derived characters obviously
associated with aquatic locomotion include the webbed digits and the strongly compressed
tail. The thickened stapes may be related to differences between the sound-transmitting
properties of water and air. The inflated nasal capsule and the deep pockets that develop on
the ventral surface of the frontal house enlarged nasal salt glands, which allow marine
iguanas to excrete excess salt accumulated from ingesting food with a salt concentration
similar to that of seawater (Schmidt-Nielsen and Fange, 1958). Convergences between
Amblyrhynchus and Sauromalus are discussed in the comments on the latter taxon, above.
Conolophus Fitzinger 1843
Type species (by original designation): Amblyrhynchus demarlii Dumeril and Bibron
1837 = Amblyrhynchus subcristatus Gray 1831b.
Etymology: (Greek) Konos, cone, + lophos, crest, presumably referring to the conical
scales of the dorsal crest.
Definition: The most recent common ancestor of Conolophus pallidus and C.
subcristatus and all of its descendants.
Distribution: Islands of the Galapagos Archipelago, Ecuador (Fig. 57).
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1. Lateral crests of premaxillary incisive process large and pierced or notched by
foramina for maxillary arteries (2-B).
2. Crista cranii of frontal projects anteriorly forming a step rather than a smooth curve
where it meets medial edge of prefrontal at dorsal margin of orbitonasal fenestra (10-B).
3. Supratemporals relatively small, extend one-half or less the distance across posterior
temporal fossae (14-B).
4. Ectopterygoid contacts palatine near posteromedial comer of suborbital fenestra (26-
B). This character occurs also in about half of the Iguana delicatissima examined, in which
it is interpreted as convergent.
5. Labial process of coronoid very large, extends more than two-thirds the way down
lateral surface of mandible in large specimens (36-C).
6. Pterygoid teeth usually absent (51-B). This character also occurs in Dipsosaurus;
however, when present, the pterygoid teeth of Dipsosaurus lie along the medial border of
the pterygoid while those of Conolophus are situated more laterally.
1 66 University of California Publications in Zoology
7. Foramina in ventral surface of second sacral pleurapophyses usually absent; their
place taken by open grooves (58-B). This character exists as a polymorphism in both
species of Conolophus; that is, it does not characterize all specimens.
8. Subclavian arteries not covered ventrally by M. rectus capitis anterior (76-B). This
character needs to be checked in additional specimens.
Fossil record: Steadman (1981) reported Conolophus fossils of undetermined age from
a lava tube on Isla Santa Cruz, Galapagos.
Etheridge (1964b) reported a fragmentary braincase and a body vertebra from Late
Pleistocene cave deposits on the West Indian island of Barbuda and estimated that both
were from animals about 400 mm snout-vent length. He stated that the body vertebra, with
its robust neural spine and well developed zygosphenes and zygantra, is similar to those of
large iguanines. Etheridge compared the braincase with those of various large iguanines
noting, as pointed out by Boulenger (1890), that the parabasi sphenoid "is much wider than
long and sHghtly to moderately constricted behind the [basi]pterygoid processes in Iguana
and Cyclura, about as wide as long and strongly constricted in Amblyrhynchus and
Conolophus, and much longer than wide and strongly constricted in Ctenosaura"
(Etheridge, 1964b:68). He also gave the following length-to-width ratios for the
parabasisphenoid (length measured from posterior border to apex of indentation between
basipterygoid processes, width measured at narrowest point posterior to basipterygoid
processes): Iguana .40-. 65, Cyclura .64-.72, Amblyrhynchus .79-.91, Conolophus .86-
1.10, Ctenosaura 1.45-1.96. Because the ratio of the fossil is 1.00, Etheridge concluded
that it most closely resembles Conolophus.
Based on its large size and the presence of zygosphenes and zygantra, the vertebra is
reasonably interpreted as belonging to an iguanine. Based on size, both vertebra and
braincase might tentatively be referred to Iguanini, The similar proportions of the
parabasisphenoid in the fossil and Conolophus, however, provide no evidence that the two
are closely related. The wide parabasisphenoids of Iguana and Cyclura, and the long one
of Ctenosaura, are derived conditions, while Amblyrhynchus, Conolophus, and the fossil
retain primitive proportions of this element. Furthermore, the proportions of the
parabasisphenoid in the fossil fall within the range of variation not only of Conolophus but
also of Cyclura. Etheridge's (1964b) range of .64-. 72 for the length/width of the
parabasisphenoid in Cyclura is based on C. cornuta, C.figginsi (=cychlura), C. ricordii,
and C. macleayi (=nubila), but the range is actually much greater when other Cyclura are
included. Pregill (1981) reported a ratio of .50 for a Puerto Rican fossil that he referred to
C. pinguis, and I have obtained a range of .52 (C. pinguis) to 1.10 (C. carinata). Although
neither Conolophus nor Cyclura occurs on Barbuda today, Cyclura occurs in the West
Indies, while Conolophus is restricted to the Galapagos Islands. Nevertheless, current
knowledge does not permit me to refer the Barbuda fossil to either of these taxa.
Comments: Although not as obviously modified from the ancestral Amblyrhynchina as
its sister taxon, Amblyrhynchus, Conolophus has eight derived characters not seen in
Phylogenetic Systematics of I guanine Lizards 167
Amblyrhynchus . These characters indicate that Conolophus is monophyletic and thus,
contrary to one commonly entertained hypothesis about the relationships of the Galapagos
iguanas (Thornton, 1971; Higgins, 1978), cannot be considered ancestral to
Amblyrhynchus.
IguaninaBell 1825
Type genus: Iguana Laurenti 1768.
Etymology: Modification of Iguana, the name of its type genus.
Definition: The most recent common ancestor of Cyclura and Iguana and all of its
descendants.
Distribution: Lowlands of the American mainland from Sinaloa and Veracruz, Mexico,
southward through Central America and northern South America to southern Brazil and
Paraguay as well as various Caribbean islands, including both the Greater and Lesser
Antilles.
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1 . Squamosal abuts against dorsal end of tympanic crest of quadrate ( 19-B).
2. Cristae ventrolaterales of parabasisphenoid only narrowly constricted behind
basipterygoid processes (28-B,-C). This character does not occur in Cyclura carinata.
3. Surangular exposed laterally well anterior to apex of coronoid and often anterior to
last dentary tooth (39-B). This character also occurs in some Ctenosaura and may be a
synapomorphy of a more inclusive group.
4. Crowns of posterior marginal teeth with five or more cusps (46-C,-D). This
character occurs also in Sauromalus and may be a synapomorphy of a more inclusive
group.
Another possible synapomorphy of Iguanina is the development of a dewlap. Although
the dewlap of Cyclura is relatively small compared with that of Iguana, it is larger than that
of other iguanines QxcQpt Brachylophus and some Ctenosaura.
Fossil record: The oldest known fossil referable to Iguanina is an almost complete
skull from the Pliocene of southern California (Norell, 1983). This and other fossil
Iguanina are discussed further in the sections on the fossil records of Iguana and Cyclura,
below.
Comments: The name Iguanina is first used in this work; Bell (1825) is credited with
authorship under the principle of coordination (Article 36, third edition of the International
Code of Zoological Nomenclature).
168 University of California Publications in Zoology
Although there are fewer characters supporting a sister-group relationship between
Cyclura and Iguana than there are for some of the other relationships proposed in this
paper, the monophyly of Iguanina is reasonably well supported. This sister group of
Iguanina is not obvious from the results of the present study, but the best candidates are
Ctenosaura and Sauromalus (or perhaps a group composed of both these taxa). Only
Sauromalus shares a derived character with Iguanina that is not variable within either of
these taxa, increased cuspation of the posterior marginal teeth (46-B,-C). The distribution
of other derived characters among taxa within Iguanini requires either that one or more of
the basic taxa are not monophyletic or that some kind of homoplasy is involved.
Iguana Laurenti 1768
Type species (by tautonomy): Lacerta iguana Linnaeus 1758.
Etymology: (Spanish) Iguana, a modification of the name given to these animals by
West Indian natives.
Definition: The most recent common ancestor oil guana delicatissima and /. iguana and
all of its descendants.
Distribution: Lowlands of the American mainland from Sinaloa and Veracruz, Mexico,
southward through Central America and northern South America to southern Brazil and
Paraguay; in the Caribbean northward through the Lesser Antilles to the Virgin Islands
(Fig. 58).
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1. Large ventral process of squamosal (18- A) abuts against dorsal edge of tympanic
crest of quadrate. Because the reduction of the ventral process of the squamosal is an
iguanine synapomorphy, its reelaboration in Iguana is a character reversal.
2. Cristae ventrolaterales of parabasisphenoid barely constricted behind basipterygoid
processes (28-C). This character also occurs in some Cyclura and, although I have
interpreted this as convergence, a wide parabasisphenoid may be a synapomorphy of a
more inclusive group.
3. Crowns of posterior marginal teeth serrate, with numerous small accessory cusps
(46-D).
4. Entire pterygoid tooth patch doubles ontogenetically (49-C).
5. Posterolateral processes of pleurapophyses of second sacral vertebra absent (57-B).
This character occurs also in Ctenosaura and in most Cyclura, and may be a synapomorphy
of a more inclusive group.
Phylogenetic Systematics of I guanine Lizards
169
^ -^\
ii'^'Mji
1
^-i \\
: ::::; !^
t ;:i :'■ !
S-
1
:: :!::::
: i !;:::l
: l!;:::::
::::::iy
i
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:::::::::: ::: ; ::;;
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V
IH
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: :::: :
i 7 ,^ ^
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ri /
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FIG. 58. Geographic distribution oi Iguana (from Elheridge, 1982).
6. Thin midsagittal processes on anterodorsal surfaces of caudal centra relatively small
and confined to anterior fifth of caudal sequence (62-B). This character occurs also in
Brachylophus, in which it is interpreted as convergent.
7. Coeliac artery arises posterior to mesenteric arteries, between mesenteric arteries, or
continuous with mesenteric arteries rather than anterior to them (78-B). This character also
occurs in some Sauromalus, in which it is interpreted as convergent. It needs to be
checked in larger samples.
8. Snout covered by large, platelike scales (82-B). This character also occurs in some
Cyclura and may be a synapomorphy of a more inclusive group.
9. Large dewlap present (88-B). This character also occurs in Brachylophus and in
Ctenosaura bakeri and C palearis, in which it is interpreted as two separate instances of
convergence.
10. Gular crest of enlarged scales present (88-B).
In addition, the following derived characters occur in only some Iguana:
1. Frontal wider than long (8-B). This character occurs also in Amblyrhynchina and in
Cyclura cornuta, in which it is interpreted as two separate instances of convergence.
Within Iguana it occurs only in /. delicatissima and appears to be a synapomorphy of that
taxon.
170 University of California Publications in Zoology
2. Second ceratobranchials of hyoid apparatus much longer than first ceratobranchials
(52-53-C). This character also occurs in Brachylophus, in which it is interpreted as
convergent. Within Iguana it occurs only in /. iguana and appears to be a synapomorphy
of that taxon.
3. Caudal autotomy septa absent (60-B). This character occurs also in
Amblyrhynchina and in Brachylophus, in which it is interpreted as two separate instances
of convergence. Within Iguana it occurs only in /. delicatissima and appears to be a
synapomorphy of that taxon.
Fossil record: Fossils referred to Iguana have been reported from Antigua (Wing et al.,
1968), Barbados (Swinton, 1937; Ray, 1964), Martinique (Hoffstetter, 1946), and
Montserrat (Steadman et al., 1984) in the West Indies; Ecuador (Hoffstetter, 1970); and
southern California (Norell, 1983). The oldest of these are the Pliocene specimens from
southern California. However, since Norell (1983) considers these to be outside of the
clade consisting of /. iguana and /. delicatissima, they are not Iguana according to my
definition of this taxon, although they are its closest relatives. All other fossils referred to
Iguana are either Upper Pleistocene or Holocene in age.
Comments: I consider the monophyly of Iguana to be reasonably well supported.
Nevertheless, three of the derived characters employed in this study occur in some Iguana
as well as in Qither Brachylophus (character 52-53-C), Amblyrhynchina (8-B), or both of
these taxa (60-B). The reason that I have interpreted these characters as convergent is
acceptance of the monophyly not only of Iguana but also of Iguanina and Iguanini, based
on other characters.
Within Iguana, the two currently recognized species both appear to be monophyletic;
therefore, neither can be considered to be ancestral to the other. Monophyly of I. iguana is
supported by the extreme width of the parabasisphenoid, the enlarged subtympanic scale
(Dunn, 1934; Lazell, 1973), and the elongated second ceratobranchials. Monophyly of I.
delicatissima is supported by the short frontal bone, absence of autotomy septa in the
caudal vertebrae, enlarged bony extemal nares, and possibly the failure of the septomaxillae
to reach the roof of the nasal capsule. The possibility that Iguana is a subgroup of of
Cyclura is discussed in the comments on the latter taxon, below.
Cyc/wra Harlan 1824
Type species (subsequent designation by Fitzinger 1843): Cyclura carinata Harlan
1824.
Etymology: (Greek) Kylclos, circle, -i- oura, tail, referring to the verticils of enlarged,
spinous scales on the tails of most species.
Phylogenetic Systematics of I guanine Lizards
171
FIG. 59. Geographic distribution of Cyclura (from Schwartz and Carey, 1977).
Definition: The most recent common ancestor of Recent Cyclura (carinata, collei,
comma, cychlura, nubila, pinguis, ricordii, and rileyi) and all of its descendants.
Distribution: The Bahama Islands; Cayman Islands; Mona and Anegada islands; and
Cuba, Hispaniola, and Jamaica, and their nearby islets (Fig. 59). Cyclura is nearly extinct
on Jamaica (Woodley, 1980) and has become extinct on Navassa Island in historical times
(Thomas, 1966).
Diagnosis: Members of this taxon can be distinguished from other iguanines by the
following synapomorphies:
1. Modal number of premaxillary teeth greater than seven (43-44-C). This character
applies only to populations; its presence or absence cannot always be inferred from the
condition in a single organism.
2. Presence of toe combs formed by enlargement of anterior keels of subdigital scales
and fusion of their bases (92-B). Ctenosaura defensor also possesses enlarged and fused
subdigital keels, which are interpreted as convergent; however, in this taxon, they occur
only under the first phalanx of digit III. In Cyclura the enlarged and fused subdigital keels
occur under the first phalanx of digit II and the first and second phalanges of digit III.
In addition, the following derived characters occur only in some Cyclura:
172 University of California Publications in Zoology
1 . Prefrontal contacts jugal and lacrimal fails to contact palatine behind lacrimal
foramen (7-B). This character occurs also in Amblyrhynchina and in some Ctenosaura;
within Cyclura, it occurs only in C. carinata, C. cornuta, and C. ricordii.
2. Frontal wider than long (8-B). This character occurs also in Amblyrhynchina and
Iguana delicatissima, in which it is interpreted as convergent. Within Cyclura it occurs
only in C. cornuta and appears to be a synapomorphy of this taxon.
3. Parietal foramen located variably or invariably within frontal bone (13-B,-C). This
character occurs also in Sauromalus, Dipsosaurus, and some Ctenosaura. Within Cyclura,
invariable location of the parietal foramen within the frontal is characteristic only of C.
carinata.
4. Cristae ventrolaterals of parabasisphenoid barely constricted behind basipterygoid
processes (28-C). This character occurs also in Iguana. Within Cyclura, it varies
considerably among taxa; in some (e.g., C. pinguis) the ventral surface of the
parabasisphenoid is as wide or wider than that of/, delicatissima, while in others (e.g., C.
carinata) it is relatively narrow, though still wider than in most iguanines other than Iguana
and other Cyclura (see section on fossil record of Conolophus, above).
5. Surangular not exposed or only barely exposed below coronoid on lingual surface
of jaw (40-B). This character occurs also in Amblyrhynchina, in which it is interpreted as
convergent. Within Cyclura, it characterizes only C. cychlura, although it occurs at a
moderate frequency in C. nubila.
6. Posterior portion of pterygoid tooth patch doubles ontogenetically (49-B). Within
Cyclura, this character occurs in C. cornuta, C. nubila, C. pinguis, and C. ricordii. This
character, or a further modification of it, occurs only in Iguana and some Ctenosaura and
Cyclura. Because its expression seems to depend on size, posterior doubling of the
pterygoid tooth patch may be a synapomorphy of a more inclusive group, in which case
failure to double would be a synapomorphy within Cyclura.
7. Posterolateral processes of pleurapophyses of second sacral vertebra absent (57-B).
This character occurs also in Ctenosaura and Iguana and may be a synapomorphy of a more
inclusive group. Within Cyclura, I have found the processes only in C. pinguis.
8. Snout covered by large, platelike scales (82-B). This character occurs also in
Iguana. Within Cyclura, it occurs in all taxa except C. carinata and C. ricordii.
Considerable variation in the size of these scales exists even among those Cyclura
possessing enlarged snout scales (figures in Schwartz and Carey, 1977).
9. Tail bears verticils of enlarged, spinous scales (94-B). This character occurs also in
Ctenosaura. The degree of caudal spinosity exhibits considerable variation within Cyclura
(figures in Barbour and Noble, 1916).
Fossil record: Fossil Cyclura have been reported from the Upper Pleistocene and
Holocene of Puerto Rico (Barbour, 1919; Pregill, 1981), St. Thomas in the Virgin Islands
(Miller, 1918), and New Providence Island in the Bahamas (Etheridge, 1965c; Pregill,
1982). The specimens from Puerto Rico have been referred to the extant species C.
pinguis (Pregill, 1981). A braincase and a body vertebra from the Late Pleistocene of
Phylogenetic Systematics of I guanine Lizards 173
Barbuda may also be remains of Cyclura (Pregill, 1981; see section on the fossil record of
Conolophus, above).
Comments: Cyclura is often assumed to be closely related to Ctenosaura (Barbour and
Noble, 1916; Bailey, 1928; Schwartz and Carey, 1977), which it resembles in general
body form, terrestrial habits, and the verticils of enlarged, spinous caudal scales. These
similarities were noticed at least as early as Harlan (1824), who erected Cyclura for species
that are now placed in both Cyclura (carinata) and Ctenosaura (teres = acanthura). Despite
the resemblance between Ctenosaura and Cyclura, Cyclura probably shared a more recent
common ancestor with Iguana than it did with Ctenosaura. The similarities between
Cyclura and Ctenosaura in general body form and terrestriality probably represent primitive
features retained from the common ancestor of all three taxa; and since not all Cyclura
possess the verticils of enlarged, spinous caudal scales, some form of homoplasy in tail
morphology is required no matter which relationships are accepted. Furthermore, Cyclura
and Iguana share at least three derived characters not seen in Ctenosaura: abutment of the
squamosal against the dorsal end of the tympanic crest of the quadrate (19-B); a wide
parabasisphenoid (28-B,-C); and highly cuspate posterior marginal teeth (46-C,-D).
Although the last character occurs also in Ctenosaura defensor, my analysis of relationships
within Ctenosaura indicates that this is convergent.
In addition to the characters suggesting a close phylogenetic relationship between
Iguana and Cyclura, there are other characters suggesting that Iguana is actually a subgroup
of Cyclura, as defined here. In other words, there are characters suggesting that the most
recent common ancestor of all Cyclura was also an ancestor of Iguana. Iguana shares
derived features of the cephalic scutellation, such as the enlarged snout scales and the row
of enlarged sublabials, as well as a derived widening of the parabasisphenoid with some,
but not all, species of Cyclura. There is a particularly close resemblance between Cyclura
cychlura and Iguana delicatissima in these features. Nevertheless, the toe combs, the
verticils of enlarged, spinous caudal scales, and the high number of premaxillary teeth are
derived features seen in Cyclura but not in Iguana. The morphology of the posterior
marginal teeth also varies within Cyclura, with some approaching the highly cuspate
morphology seen in Iguana much more closely than others. However, the high degree of
variation in this character, at least some of which is ontogenetic, along with small samples
and ambiguities caused by wear, prevent me from making any definite statement about the
relationships suggested by this character.
In any case, the precise relationships between Iguana and Cyclura are unclear, because
the distributions of derived characters among taxa contradict one another. I provisionally
accept the monophyly of Cyclura, but consider the issue to be in need of further study. If
the most recent common ancestor of all Cyclura was also an ancestor of Iguana, then,
according to the phylogenetic definitions of taxa adopted here. Iguana is a subgroup of
Cyclura rather than a separate taxon, and Iguanina is a synonym of Cyclura.
Appendix I
Specimens Examined
All specimens listed below are partial or complete skeletons unless otherwise indicated as
alcoholic specimen (A) or radiograph (R). Institutional abbreviations are as follows:
AMNH, American Museum of Natural History
ASFS, Collection of Albert Schwartz (Miami-Dade Community College North, Miami,
Fla.)
CAS, California Academy of Sciences
JMS, Collection of Jay M. Savage (University of Miami, Coral Gables, Fla.)
KdQ, Collection of the author (University of California, Berkeley)
KU, University of Kansas Museum of Natural History
LACM, Los Angeles County Museum of Natural History
LSUMZ, Louisiana State University, Museum of Zoology
MCZ, Museum of Comparative Zoology, Harvard University
MVZ, Museum of Vertebrate Zoology, University of California, Berkeley
RE, Collection of Richard Etheridge (San Diego State University, San Diego, Calif.)
SDNHM, San Diego Natural History Museum
UCMP, Museum of Paleontology, University of California, Berkeley
UF, Florida State Museum, University of Florida
USNM, United States National Museum of Natural History.
IGUANINES
Amblyrhynchus cristatus: JMS 126-7, 181, 222; LACM 127324; RE 338, 386, 1041,
1091, 1095, 1196, 1387, 1396, 1508, 2239; SDNHM 45156-7, 47000, 55600.
Brachylophus fasciatus: AMNH 17701; CAS 54664 (A); RE 1019, 1770, 1866, 1888,
2089, plus two radiographs of specimens whose institutions of deposition are unknown;
MCZ 5222, 5800, 15008-9; SDNHM 55289, 55601, 55603, 60429, 62341.
B. vitiensis: MCZ 158238, 160253-5.
Conolophus pallidas: JMS 61, 213-8; MCZ 79772; RE 439-40, 1382, 1446-7.
C. siibcristatus: AMNH 50798, 71304, 110167-8, 114493; CAS 12058 (A); MCZ 2027;
MVZ 77314; RE 327; SDNHM 33682, 47007, 47140; USNM 89992, 165756.
C. sp.: AMNH 14494.
175
176 Appendix I
Ctenosaura acanthura: AMNH 46483; MCZ 2176, 5013-21, 11350; SDNHM 47004,
59542-3; USNM 220217-8.
C. baked: ; LSUMZ 22275, 22293, 22367-71, 22399 (all A,R); UF 28530-33 (A,R;
28530 also skeletonized); USNM 25324 (skull drawing from Ray and Williams, unpubl.).
C. clarki: JMS 1544; MCZ 22454; MVZ 76690 (A,R), 76694 (A,R), 79256, 79293,
164865-66; RE 57, 184; USNM 21450.
C. defensor: KU 70261-2, 75528 (all A,R); MCZ 7095 (skull. A, and R); UF 41534
(A,R).
C. hemilopha: JMS 287-9, 291, X366 (R), X631-2 (R), X634-5 (R); RE 325, 491, 497-
8, 502, 1087, 1341, 1386, 1887, 1964; SDNHM 48480, 48976, 55290, 57114.
C. palearis: CAS 69297, 69299, 69307, 69310 (all A,R); MCZ 22390, 22399; MVZ
162073-5, 162305 (all A,R).
C. pectinata: JMS 238, 242, 250, 269, 692, 696, 704, 1252; RE 56, 419-21, 490, 641;
SDNHM 55291.
C. quinquecarinata: AMNH 77640; CAS 73554-62 (A,R); MCZ 24903; MVZ 79294,
128903 (A,R).
C. similis: AMNH 38949; JMS 178; MCZ 5011, 5457, 5799, 9566, 10312, 21742,
22662, 25993, 26968, 27207, 36830, 139421; RE 469, 2003, 2233, 2238.
Cyclura carinata: CAS 54647 (A); JMS 98; MCZ 59255, 139424; RE 1969; USNM
88819.
C. collei: CAS 74731 (A); MCZ 9397 (R).
C. cornuta: AMNH 57878, 114487-8; JMS 221; MCZ 9974 (R); RE 383, 1226, 1837,
1841-2, 1858, 1962, 1981-2, 1991.
C. cychlura: AMNH 74440, 76875, 76877-8; KdQ 47-8; MCZ 6915; RE 2073; USNM
64650.
C. nubila: JMS 180, 182, 273; MCZ 6915; RE 228, 337, 610; SDNHM 42957, 42960.
C.pinguis: ASFS V21995.
C. ricordii: JMS 272, 367; RE 435.
C. rileyi: MCZ 38165-69 (A); RE uncatalogued (A); UF 40744 (A), 57741.
Dipsosaurus dorsalis: JMS X320, X324, X331, X334, X336, X338, X607, X612, X618
(all R); RE 33, 355-9, 484, 661, 667, 1497, 1572-7, 1848, 1868, 1980; SDNHM 47006,
57107-9, 59538-9, 60424.
Iguana delicatissima: KdQ 21; MCZ 6097, 10975, 16157, 60823, 75388, 83228.
/. iguana: JMS 244-5, 268, 713, 1028, 1545, 1553; RE 89, 158, 424, 452-4, 468, 489,
1006, 1850, 1886, 2232; SDNHM 47001, 47008, 47010, 59466, 59540-1.
Sauromalus ater: JMS 39; KdQ 68-9; MCZ 31521; RE 1504; SDNHM 6865.
S. australis: KdQ 71, 72.
Appendix I 177
S. hispidus: JMS 172-4, 219, 239, 401, 404, 436, 915, 983; LACM 127279; RE 317,
514-5, 736, 803-5, 1042, 1384, 1927, 1974; SDNHM 6873, 47028-30, 57103-4, 59471.
S. obesus: RE 244, 354, 380, 408-11, 426, 461-7, 1578-9, 1852, 1864; SDNHM 48483,
59534.
S. slevini: MCZ 85553; RE 1340, 1367.
S. varius: JMS 175-6, 246-8; RE 308, 323, 451, 512-3, 539, 1043, 1404, 1928, 2084;
SDNHM 47024-6, 59542.
BASILISCINES
Basiliscus basiliscus: JMS 347, 362, 1449, 1567, 1577, 1583-4; RE 555.
B. plumifrons: RE 427, 2014; SDNHM 57098-100, 59467, 60430-1.
B. vittatus: RE 49, 637, 1601, 1729, 1757, 1759, 2015; SDNHM 60432.
Corytophanes cristatus: JMS 1701; KdQ 55; SDNHM 62345.
C. hernandesii: RE 1176, 1800.
Laemanctus longipes: MVZ 137673; UCMP 129880.
L. serratus: AMNH 44982; RE 619.
CROTAPHYTINES
Crotaphytus collaris: RE 85, 370-1, 404-7, 683, 1213-4, 1570, 1797, 1823, 1836, 1857;
SDNHM 60433-5.
C. insularis: SDNHM 47002.
Gambelia wislizenii: RE 425, 550, 810, 1029, 1172, 1571.
MORUNASAURS
Enyalioides heterolepis: AMNH 18232, 18278-9 (all R); MCZ 8063, 24959, 39977 (all
R).
E. laticeps: AMNH 37561 (R); MCZ 37282, 37284, 37286, 50238 (all R); RE 76, plus
three radiographs of specimens whose institutions of deposition are unknown; SDNHM
47003.
E. microlepis: AMNH 37562, 60608-9 (all R).
E. oshaughnessyi: AMNH 28869-70, 28874-6, 28894 (all R); MCZ 29297 (R); RE 1957.
E. palpebralis: AMNH 56401, 57159-61 (all R); MCZ 84035 (R).
E. praestabilis: ANMH 37554-5 (R); USNM 7796-8 (R), 222583.
Hoplocercus spinosus: AMNH 90658, 93807; CAS 93081-94, 93804-5, 101443-5 (all
R); RE 1263, 1502.
178 Appendix I
Morunasaurus annularis: AMNH 57178, 57180-2, 57199 (all R); MCZ 146375; RE 1956;
USNM 616-7, 3782 (all R).
M. groi: CAS 98001 (R).
OPLURINES
Chalarodon madagascariensis: RE 455, 457, 547.
Opiums cuvieri: JMS 330; MVZ 117597 (A,R), 128904 (A,R); RE 558, 620, 1835.
O. quadrimaculatus: AMNH 71452; RE 658.
In addition, I have examined various alcoholic specimens in the collections of Richard
Etheridge, at San Diego State University; and the Museum of Vertebrate Zoology,
University of California, Berkeley.
Appendix II
Polarity Determination Under Uncertain
Outgroup Relationships
I used a modified version of the outgroup method described by Maddison et al. (1984) and
M. J. Donoghue (pers. comm., 1982) to assess character polarities. This method assesses
the condition of the outgroup node (branch point linking the ingroup with its sister group
on a phylogenetic tree or a cladogram) in order to minimize character- state changes at all
hierarchical levels. Briefly, the cladogram for the ingroup and various outgroups is
rerooted at the outgroup node, and the conditions of the various subterminal nodes on the
rerooted cladogram are assessed using an optimization procedure similar to that of Farris
(1970). First, the terminal nodes (ends of branches) are labeled according to the condition
found in the outgroup occupying that position. Second, the subterminal nodes are assigned
character states according to the following rules: (1) If both nodes above the node in
question have the same state, assign that state to the node in question. (2) If the two nodes
above the node in question have different states, the assignment of the node in question is
equivocal (?). (3) If one node above the node in question is equivocal and the other is not,
assign the node in question the state of the unequivocal node. The state assigned to the
outgroup node (basal node of the rerooted cladogram) is taken as plesiomorphic.
Because the relationships among iguanines and the outgroups used in this study are
poorly understood, I was forced to consider all possible cladograms for four unspecified
outgroups and an ingroup, of which there are nine (Fig. 60). After these cladograms are
rerooted at the outgroup node (Fig. 61), it can be seen that not all of them need to be
considered further, since many will yield identical assessments of the condition at the
outgroup node. Complete equivalence is seen between some of the rerooted cladograms:
A = E = G, and C = F. By swiveling branches about nodes, which does not alter the
relationships implied by the diagrams, rerooted cladograms A, B, and D are found to be
equivalent. Finally, given only the distribution of character states in the ingroup and these
four outgroups, the state assigned to the outgroup node in rerooted cladograms H and I
must be identical to that of the basal node in the clade formed by the four outgroups.
Therefore, for the purposes of this analysis, rerooted cladograms H and I can be
considered to be equivalent to A and C, respectively. Only two topologies need to be
considered further, A and C (Fig. 61).
For any given character, the conditions of the outgroups can be placed on the terminal
branches of the two rerooted cladograms (Fig. 61 A, C) in all possible combinations, and
the condition of the outgroup node (i.e., the character's polarity) can be assessed. For
cases in which all four outgroups suggest a single interpretation, that interpretation is
accepted. For cases in which more than one of the states found in the ingroup also occur in
one or more outgroups, the polarity of the character is ambiguous. In such cases, I have
179
180
Appendix II
FIG. 60. All nine possible fully resolved cladogram topologies for four unspecified outgroups and an
in group (inverted triangle).
made a compromise between maximizing the total number of characters on the one hand
and using only those characters whose polarities are completely unambiguous on the other.
Table 1 1 shows polarity inferences for all possible arrangements of four outgroups on
the two rerooted cladograms (Fig. 61A,C) for seven cases of character-state distribution.
This exhausts the possible character- state distributions for two state characters, since it is
the occurrence of a given state rather than its alphabetic designation that is important (e.g.,
A/A/A/B = B/B/B/A). The following is a case-by-case discussion of possible polarity
inferences under different relationships of the four outgroups to the ingroup.
Case I (A/A/Ai/A,B): For the case in which three outgroups have one condition and the
other has both altemative conditions, all arrangements except one require that the common
state be considered plesiomorphic. The lone exception is when the variable outgroup
attaches direcdy to the basal node of the rerooted cladogram (Fig. 62A). If resolution of
relationships within this outgroup requires that state B be considered plesiomorphic for this
group, the polarity will be equivocal.
Appendix II
181
FIG. 61. Dendrograms corresponding with the nine cladograms in Figure 60 after each is rerooted at the
outgroup node.
Case II (A/A/A/B): If the outgroup possessing state B attaches directly to the basal
node of the cladogram (Fig. 62B), the polarity is equivocal. For all other arrangements,
state A must be considered plesiomorphic.
Case III (A/A/A,B/A,B): Support for the interpretation that state B is plesiomorphic is
only possible, first, if the outgroups are arranged as in Figure 62C; and second, if
resolution of the relationships within the variable outgroups requires that either state B is
plesiomorphic for the outgroup attaching directly to the basal node, while the other remains
equivocal, or state B is plesiomorphic for both. Many arrangements of the outgroups will
necessitate that state A be considered plesiomorphic, and resolution of relationships within
the variable outgroups will make many arrangements equivocal. Potential determination of
the plesiomorphic condition for the two variable outgroups upon resolution of relationships
within these outgroups makes this case very ambiguous. In fact, there is only one
arrangement in which it is impossible for the polarity inference to be equivocal (Fig. 62D).
Case rV (A/A/A,B/B): Four arrangements of four outgroups with these conditions
yield equivocal evidence for polarity (Fig. 62E-H). In two of these arrangements (Fig.
182
Appendix II
TABLE 11. Summary of Polarity Inferences For Seven Cases of Character-state
Distribution Among Four Outgroups of Uncertain Relationships to the Ingroup
Case
I
n
III
IV
VI
vn
Outgroup
Condition
A/A/A/A,B
A/A/A/B
A/A/A,B/A,B
A/A/A,B/B
A/A/B/B
A/A,B/A,B/A,B
A/A,B/A,B/B
Possible Polarity Inferences
A is plesiomorphic
Polarity is equivocal*
A is plesiomorphic
Polarity is equivocal
A is plesiomorphic
Polarity is equivocal*
B is plesiomorphic*
A is plesiomorphic
Polarity is equivocal
B is plesiomorphic*
A is plesiomorphic
Polarity is equivocal
B is plesiomorphic
A is plesiomorphic
Polarity is equivocal*
B is plesiomorphic*
A is plesiomorphic*
Polarity is equivocal
B is plesiomorphic*
Note: An asterisk (*) indicates that the conclusion in question can only be reached upon
resolution of relationships within one or more variable outgroups. See text for details.
62E,F), resolution of relationships within the variable outgroup may necessitate that state B
be considered plesiomorphic. In all other arrangements state A must be considered
plesiomorphic, although resolution of the relationships within the variable outgroup can
make the situation equivocal.
Case V {hlkfQr^): In this case, only one arrangement requires that state A be
considered plesiomorphic (Fig. 621). One other arrangement requires that state B be
considered plesiomorphic (Fig. 62J). For all other arrangements the polarity must be
considered equivocal.
Case VI {Klh,Blk,'Qlk,B): Because every outgroup but one is variable, the condition
Appendix 11
183
A A A A,B
A A A B
A A A,B A.B
Aor?
A,?, or B
A,B A,B A A
A A A,B B
A A B A,B
?orB
A,?,orB
A A,B A B
A A A,B B
B B A A
Aor?
A A B B
FIG. 62. Examples of polarity inferences for different arrangements of outgroup character-state
distributions. See text for discussion.
184 Appendix II
of the invariable outgroup (A) must always be considered plesiomorphic. However,
resolution of relationships within one or more of the variable outgroups may necessitate
that either the alternative condition be considered plesiomorphic or that the polarity be
considered equivocal.
Case VII (A/A,B/A,B/B): In this case, polarities are always equivocal and can only be
determined by the resolution of relationships within one or more of the variable outgroups.
Of course, polarities are always equivocal in the case in which all outgroups exhibit both
states (A,B/A,B/A,B/A,B).
To summarize, In cases I and II (Table 11), either the more common state must be
considered plesiomorphic or the situation is equivocal; the interpretation that the less
common state is plesiomorphic will never be favored. In the remaining five cases there will
be at least some situations in which the less common state either may or must be considered
to be plesiomorphic. Therefore, I have considered the more common state to be
plesiomorphic for characters with case I and II distributions, but have withheld polarity
decisions on characters with case III, IV, V, VI, and VII distributions, using them only at
lower hierarchical levels when certain ingroup taxa can serve as functional outgroups
(Watrous and Wheeler, 1981).
Of course, not all characters fit into the cases mentioned above. For example, there are
some characters with more than two states in the ingroup, and some in which one or more
states found in an outgroup are not comparable to any of those seen in the ingroup. In this
study, such cases are relatively rare and are discussed individually.
Appendix III
Polarity Determination for Lower Level Analysis
The polarities of 19 characters could not be determined using basiliscines, crotaphytines,
morunasaurs, and oplurines as outgroups. Therefore, I attempted to determine the
polarities of these characters for a less inclusive ingroup (node 3, Fig. '46), using
Brachylophus and Dipsosaurus as outgroups. The problem of determining polarities for
these characters is similar to that described in Appendix II, except that there are two
outgroups instead of four. With only two outgroups whose relationships to the ingroup are
uncertain, there are only two possible cladogram topologies (Fig. 63A,B). When rerooted
at the outgroup node (Fig. 63C,D), the two resulting topologies are equivalent for the
purposes of this analysis. The assessment of the condition at the outgroup node in Figure
63D must be the same as that for the node linking the two outgroups, since there are no
intervening nodes. Thus, both rerooted cladograms effectively have the two outgroups
attached direcdy to the basal (outgroup) node.
Table 12 summarizes polarity inferences for all possible arrangements of two outgroups
on the rerooted cladogram (Fig. 63C) for four cases of character-state distributions among
the outgroups. This exhausts the possible cases for a two-state character. Case I is
unambiguous: the state found in both outgroups is plesiomorphic. In case II, state A is
considered plesiomorphic, although resolution of relationships within the variable outgroup
can render the polarity equivocal. In case III, the polarity is equivocal, but resolution of
relationships within one or both variable outgroups may require that either state A or state B
be considered plesiomorphic. Case IV is completely ambiguous: no polarity inference can
be made. Because Cases I and 11 are the only cases in which only one of the two states can
be considered plesiomorphic under all possible arrangements of the outgroups on the
rerooted cladogram (Fig. 63C), I consider polarity to be determinable only for these two
cases. However, none of the characters whose polarities were undeterminable at the level
of all iguanines exhibits a Case II distribution. Thus, polarities are only determinable for
characters with Case I distributions.
185
186
Appendix III
FIG. 63. All possible cladogram topologies for two unspecified outgroups and an ingroup (inverted
triangle), before (A and B) and after (C and D) rerooting at the outgroup node.
TABLE 12. Summary of Polarity Inferences For Four Cases of Character-state
Distribution Among Two Outgroups of Uncertain Relationships to the Ingroup
Case
I
II
III
IV
Outgroup
Condition
A/A
A/A,B
A,B/A,B
A/B
Possible Polarity Inferences
A is plesiomorphic
A is plesiomorphic
Polarity is equivocal*
A is plesiomorphic*
Polarity is equivocal
B is plesiomorphic*
Polarity is equivocal
Note: An asterisk (*) indicates that the conclusion in question can only be reached upon
resolution of relationships within one or both variable outgroups.
Appendix IV
Polarity Reevaluation for Lower Level Analysis
Using Brachylophus and Dipsosaurus as outgroups to a subset of iguanines permits
determination of polarities for certain characters whose polarities were undeterminable at
the level of all iguanines. However, it also requires that the polarities of other characters be
reassessed, since character polarities for the less inclusive group may not be identical to
those for the more inclusive group. The procedure used for reassessment is similar to that
used for assessing the polarities of characters whose polarities were not initially
determinable (Appendix III), but differs in that a more distant outgroup must be considered
(Fig. 64A,B). This more distant outgroup is actually the outgroup node from the analysis
of polarities for Iguaninae as a whole. It must be considered because, unlike the case for
characters whose polarities were undeterminable at the level of all iguanines, it has been
assigned a character state. This additional branch also has the effect of rendering the two
rerooted cladograms (Fig. 64C,D) nonequivalent.
FIG. 64. All possible cladogram topologies for two unspecified near outgroups, one more remote
outgroup, and an ingroup (inverted triangle), before (A and B) and after (C and D) rerooting at the outgroup
node.
187
188
Appendix IV
TABLE 13. Summary of Polarity Inferences For Six Cases of Character-state Distribution
Among Two Near Outgroups Whose Precise Relationships to the Ingroup Are Unresolved,
and One More Remote Outgroup Exhibiting a Fixed Character State
Case
I
II
III
IV
VI
Outgroup
Condition
0/0
0/0,1
0,1
0,1/0,1
0,1/1
1/1
Possible Polarity Inferences
0 is plesiomorphic
0 is plesiomorphic
Polarity is equivocal*
0 is plesiomorphic
Polarity is equivocal
0 is plesiomorphic
Polarity is equivocal*
1 is plesiomorphic*
0 is plesiomorphic*
Polarity is equivocal
1 is plesiomorphic*
Polarity is equivocal
1 is plesiomorphic
Note: An asterisk (*) indicates that the conclusion can only be reached upon resolution of
relationships within one or both variable outgroups. Outgroup condition refers to the near
outgroups only; the remote outgroup is always assigned state zero.
Table 13 lists the possible polarity inferences for all possible arrangements of the two
near outgroups on the rerooted cladograms (Fig. 64C,D) for six cases of character- state
distributions among the two outgroups. This exhausts the possible character- state
distributions for a two-state character. The remote outgroup is always assigned state 0,
because this was inferred to be its condition based on polarity analysis at the level of all
iguanines. Unlike the case for characters whose polarities were initially undeterminable
(Appendix HI), the numerical designations for the two outgroups are significant (e.g., 0/0
is not equivalent to 1/1), since they may or may not be identical with that of the more
distant outgroup, which is always assigned state 0. Thus, there are six cases of character-
state distributions rather than only four.
For characters with Case I, II, and III distributions, I have left the polarities
unchanged, because evidence from the new outgroups suggests that either the character
polarity for the less inclusive ingroup is identical with that for Iguaninae as a whole or that
the polarity is equivocal, but in no arrangement will the reverse polarity be favored. For
Appendix rv 189
characters with Case IV and V distributions, I have changed the polarity assessment to
undeterminable, since the new outgroup evidence is compatible with either polarity
inference. For characters with Case VI distributions, I have reversed the polarity, because
the new outgroups suggest that either the old polarity is incorrect for the less inclusive
ingroup or the situation is equivocal.
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