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FIELDIANA
WDlOOrifBWBy
Geology
NEW SERIES, NO. 43
The Intramandibular Joint in Squamates, and
the Phylogenetic Relationships of the Fossil
Snake Pachyrhachis problematicus Haas
Olivier Rieppel
Hussam Zaher
March 31, 2000
Publication 1507
PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY
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Croat, T B. 1978. Flora of Barro Colorado Island. Stanford University Press, Stanford, Calif, 943 pp.
Grubb, P. J., J. R. Lloyd, and T. D. Pennington. 1963. A comparison of montane and lowland rain forest in
Ecuador. I. The forest structure, physiognomy, and floristics. Journal of Ecology, 51: 567-601.
Langdon, E. J. M. 1979. Yage among the Siona: Cultural patterns in visions, pp. 63-80. I_n Browman, D L.,
and R. A. Schwarz, eds., Spirits, Shamans, and Stars. Mouton Publishers, The Hague, Netherlands.
Murra, J. 1946. The historic tribes of Ecuador, pp. 785-821. In Steward, J. H., ed., Handbook of South
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OEOUOGf UBRAIW
FIELDIANA
Geology
NEW SERIES, NO. 43
The Intramandibular Joint in Squamates,
and the Phylogenetic Relationships of the
Fossil Snake Pachyrhachis problematicus Haas
Olivier Rieppel
Department of Geology
Field Museum of Natural History
1400 South Lake Shore Drive
Chicago, Illinois 60605-2496
U.S.A.
Hussam Zaher
Departamento de Zoologia
Instituto de Biociencias
Universidade de Sao Paulo
Caixa Postal 11461
05422-970 Sao Paulo, SP
Brasil
Accepted July 28, 1999
Published March 31, 2000
Publication 1507
PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY
© 2000 Field Museum of Natural History
ISSN 0096-2651
PRINTED IN THE UNITED STATES OF AMERICA
Table of Contents
Abstract 1
Introduction 1
Materials and Methods 2
The Intramandibular Joint in Squamates 3
The Intramandibular Joint in Varanus
and Lanthanotus 3
The Intramandibular Joint in Mosasaurs .... 7
The Compound Bone of the Ophidian
Mandible 8
The Intramandibular Joint in Scolecophi-
dians 9
The Intramandibular Joint in Anilioids 10
The Intramandibular Joint in Basal Ma-
crostomatans 18
The Skull and Lower Jaw of Pachy
rhachis 24
Character Evidence for the Monophyly
of the Pythonomorpha 29
Cladistic Analysis 49
The Phylogenetic Relationships of Pachy
RHACHIS, DlNILYSlA, AND DlBAMUS 61
Discussion: Snake Origins, and Homolo-
gy Versus Convergence 62
Notes Added in Proof 65
Acknowledgments 66
Literature Cited 66
3. Lower jaw of Lanthanotus borneensis 6
4. Lower jaw of Platecarpus 7
5. Lower jaw of Anilius scytale 11
6. Transverse section through the lower
jaw of Anilius scytale 12
7. Lower jaw of Cylindrophis ruffus 12
8. Lower jaw of Cylindrophis maculatus 14
9. Lower jaw of Melanophidium puncta-
tus, Platyplecturus madurensis, and
Pseudotyphlops philippinus 16
1 0. Lower jaw of Plecturus perroteti 17
11. Lower jaw of Python reticulatus 19
1 2. Lower jaw of Lichanura trivirgata ro-
seofusca 21
13. Lower jaw of Calabaria reinhardti and
Charina bottae 22
14. Lower jaw of Boa constrictor impera-
tor 23
15. Skull of Pachyrhachis problematicus .... 26
1 6. Lower jaw of Pachyrhachis problema-
ticus 28
17. Snake interrelationships 61
List of Tables
Data matrix for the analysis of squamate
interrelationships 50
List of Illustrations
1 . Lower jaw of Varanus 4
2. Coronoid and splenial of Varanus 5
The Intramandibular Joint in Squamates, and the
Phylogenetic Relationships of the Fossil Snake
Pachyrhachis problematicus Haas
Olivier Rieppel
Hussam Zaher
Abstract
A review of the morphology of the lower jaw in varanoid squamates, including mosasaurs,
and basal snakes (scolecophidians, anilioids, basal macrostomatans) reveals a greater degree of
variability in the differentiation of the intramandibular joint than had previously been recorded.
In particular, the mandibular joint of mosasauroid squamates and snakes differs fundamentally.
In mosasaurs, the dentary is primarily suspended from the prearticular and the posteriorly
concave splenial receives the anteriorly convex angular. In snakes, the dentary is primarily
suspended from the surangular portion of the compound bone, and the angular is the receiving
part in the mobile contact with the splenial. Characters of the intramandibular joint, along with
those resulting from a review of the cranial anatomy of the fossil snake Pachyrhachis from
the basal Upper Cretaceous of Ein Jabrud, are used in a review of squamate interrelationships.
The results corroborate macrostomatan affinities of Pachyrhachis and do not support the hy-
pothesis that snakes originated from mosasauroids, a clade of marine varanoid squamates from
the Cretaceous.
Introduction
Mosasauroids are a clade of fossil marine squa-
mates related to extant monitor lizards. Their ear-
liest fossil occurrence is in shallow marine de-
posits of early Cenomanian age (lower Upper
Cretaceous) of southern Europe. These stem-
group taxa, variously referred to as Aigialosauri-
dae and/or Dolichosauridae, remain relatively
poorly known compared to later members of the
clade, the Mosasauridae. The crown-group mo-
sasaurs adopted fully pelagic habits and include
species that were among the largest predators of
the late Cretaceous seas. Mosasaurs became ex-
tinct at the close of the Cretaceous.
The intramandibular joint has played a promi-
nent role in discussions of mosasauroid relation-
ships with snakes ever since Cope (1869) com-
mented on the ophidian affinities of his order Py-
thonomorpha. In the Pythonomorpha, Cope
(1869) included two families of mosasaurs, the
Clidastidae and the Mosasauridae. The ophidian
affinities of the Pythonomorpha were established
by Cope ( 1 869) on the basis of similarities of den-
tition, the suspension of the lower jaw, and intra-
mandibular kinetics.
More recently, cladistic support has been build-
ing in support of a monophyletic clade Pythono-
morpha that would include platynotan (varanoid)
squamates and mosasauroids as well as snakes
(Lee, 1997). Configuration of such a clade has
been corroborated by the redescription of a fossil
snake with hind limbs from the basal Upper Cre-
taceous of the Middle East (Caldwell & Lee,
1997; Lee & Caldwell, 1998). Originally de-
scribed by Haas (1979, 1980), the status of this
fossil snake taxon, Pachyrhachis problematicus,
remains problematic. Although already consid-
ered by some to be the ideal fossil link between
snakes and mosasauroids (Carroll, 1988), it was
also noted that those characters that are snakelike
in Pachyrhachis resemble relatively advanced
(macrostomatan) snakes instead of more basal
members of the group (Haas, 1979, 1980; Riep-
FTELDIANA: GEOLOGY, N.S., NO. 43, MARCH 31, 2000, PP. 1-69
pel, 1994). This controversy is still alive, as a re-
analysis of the cladistic relationships of Pachy-
rhachis showed it to be the sister taxon of ma-
crostomatan snakes rather than a primitive snake
providing a link between this group and mosa-
saurs (Zaher, 1998).
Considering Pachyrhachis as the most primi-
tive snake and "an excellent example of a tran-
sitional taxon" (Scanlon et al., 1999) between
mosasauroids and snakes (Lee, 1998) has impor-
tant consequences, as this pattern of relationships
suggests that snakes had a marine rather than ter-
restrial (fossorial) origin. Shared derived charac-
ters that have been used in support of a mono-
phyletic Pythonomorpha recall Cope's (1869)
analysis and were derived from braincase mor-
phology and its relation to jaw suspension, lower
jaw anatomy, and characters of the dentition (Lee,
1997; Lee & Caldwell, 1998). We have previously
critically assessed the characters derived in these
latter studies from squamate tooth implantation
and replacement (Zaher & Rieppel, 1999) and
from braincase morphology and its relation to jaw
suspension (Rieppel & Zaher, in press). The intra-
mandibular joint has traditionally been an impor-
tant character in discussions of snake relationships
(Camp, 1923). In their classic monograph, Mc-
Dowell and Bogert (1954) compiled a large num-
ber of characters in support of an anguimorph, or
varanoid, relationship of snakes, among which the
intramandibular joint figured prominently. Many
of the characters enumerated by McDowell and
Bogert (1954) came under severe criticism (Un-
derwood, 1957), but anguimorph, or varanoid, re-
lationships of snakes continued to be discussed
(McDowell 1972; Schwenk, 1988; see also Riep-
pel, 1988, for a review). Interestingly, the first
large-scale cladistic analysis of squamate interre-
lationships (Estes et al., 1988) did not provide
strong support for anguimorph, or varanoid, re-
lationships of snakes, which in this study were
classified as Scleroglossa (all non-iguanian squa-
mates) incertae sedis. However, parsimony anal-
ysis of this data set put snakes close to fossorial
or burrowing squamates such as dibamids and
amphisbaenians (see also Rage, 1982). Whereas
this latter hypothesis has recently gained further
support from morphological evidence (Haller-
mann, 1998), molecular data support anguimorph
relationships for snakes (Forstner et al., 1995;
Reeder, 1995). An as yet unpublished total evi-
dence approach, combining molecular (DNA) and
morphological data, unambiguously supported a
((Snake + dibamid) amphisbaenian) clade (Reed-
er, 1995).
As is true for every phylogenetic analysis, hy-
potheses of relative relationships are only as good
as the character evidence they are based on (Riep-
pel & Zaher, in press). We propose to review, in
this study, the lower jaw anatomy of varanoid
squamates and snakes in detail, bearing in mind
that superficial and potentially misleading resem-
blances can result from two factors. One is that
increased mobility in the lower jaw, as much as
increased cranial kinesis in general, results from
a reduction in bone overlap, which in turn is likely
to result from paedomorphosis (assuming the aki-
netic condition to be plesiomorphic; Irish, 1989).
The other factor results from structural constraints
in the development of an intramandibular joint.
As Gauthier (1982, p. 46; see also Underwood,
1957, p. 25) pointed out, "some similarity is to
be expected, especially since there is but one
place in a squamate mandible where a mobile
joint could form — between the dentary-splenial
and the postdentary bones." This point is partic-
ularly well borne out by comparison with the con-
vergently differentiated intramandibular joint in
Hesperornis, a fossil bird (Gregory, 1951; Gin-
gerich, 1973). The splenial, for example, will al-
ways show a reduced posterior extent in those
taxa that develop an intramandibular joint (Estes
et al., 1988). Reference to the intramandibular
joint in the analysis of snake relationships will
therefore have to transcend superficial similarities
or mere reduction characters in order to reveal
details of morphology. The characters of Lee
(1997) will, in the following, be referenced as
L97; the character evidence of Lee and Caldwell
(1998) will be referenced as LC98.
Materials and Methods
The specimens examined for this study are list-
ed below. Institutional abbreviations are bmnh,
British Museum (Natural History); fmnh, Field
Museum of Natural History; HUJ-Pal., Paleonto-
logicai Collections, Hebrew University, Jerusa-
lem. Drawings were made with a Wild binocular
M-8 equipped with a camera lucida.
Anilius scytale, fmnh 11175, 35688, uncata-
logued
Boa constrictor imperator, fmnh 22353, 22363
Calabaria reinhardti, fmnh 31372
FIELDIANA: GEOLOGY
Charina bottae, fmnh 31300
Cylindrophis ruffus, fmnh 13100, 131780
Cylindrophis maculatus, bmnh 1930.5.8.48, un-
catalogued
Lanthanotus borneensis, fmnh 747 1 1
Leptotyphlops emini, fmnh 56374
Lichanura trivirgata roseofusca, fmnh 8043
Melanophidium punctatus, bmnh 1930.5.8.119
Pachyrhachis problematicus, HUJ-Pal. 3659
Platecarpus sp., fmnh UC 600
Platyplecturus madurensis, bmnh 1930.5.8.111
Plecturus perroteti, bmnh 1930.5.8.105
Pseudotyphlops philippinus, bmnh 1978.1092
Python reticulatus, fmnh 31281, 31329
Typhlops sp., fmnh 98952
Varanus komodoensis, fmnh 22199
Varanus sp., fmnh 195576
Xenopeltis unicolor, fmnh 11524
The Intramandibular Joint in
Squamates
The Intramandibular Joint in Varanus and
Lanthanotus
Among extant varanoids {Heloderma, Lantha-
notus, and Varanus), the intramandibular joint
shows various degrees of differentiation, least de-
veloped in Heloderma, most developed in Lan-
thanotus.
In Varanus (Fig. 1), the posterior ends of the
dentary and of the splenial lie entirely in front of
the apex of the coronoid process (L97: char. 72).
In lateral view, the posterior end of the dentary
shows a more or less distinctly developed bicon-
cave posterior margin. A smaller, dorsally located
concavity or indentation receives the anterior tip
of the coronoid. The broad and, in some species,
shallow concavity below the coronoid-dentary
contact broadly overlaps the anterior end of the
surangular. The ventral margin of the dentary is
drawn out into a short posterior process that over-
laps with the anterior end of the angular. The prin-
cipal element on which the dentary is supported
is the surangular.
In lateral view, the splenial and angula/ form a
broadly overlapping, obliquely oriented contact in
Varanus. More precisely, the tapering posterior
end of the splenial superficially overlaps the broad
anterior end of the angular and curves around its
ventral margin (L97: char. 74; LC98: char. B12).
Sutural relations between the dentary and
splenial and the postdentary bones are more com-
plex in medial view of the tooth-bearing shelf of
the mandible of Varanus. The anterior tooth-bear-
ing part of the dentary forms a gentle slope (a
discrete subdental shelf is absent; L97: char. 67),
which in front of the splenial projects ventrally,
thus overhanging Meckel's canal in medial view.
The anterior part of Meckel's groove opens ven-
trally relative to the sagittal plane of the mandib-
ular ramus, as it is defined by the lateral wall of
the dentary and the medial tooth-bearing shelf
(L97: char. 69; LC98: char. B13). The anterior end
of Meckel's groove opens medioventrally in the
live animal because the lower jaw is rotated
around its long axis in such a way as to bring the
tooth row into an upright position and to expose
Meckel's cartilage medioventrally for the inser-
tion of anterior intramandibular muscles. More
posteriorly, the tooth-bearing shelf merges into
the septum that separates Meckel's canal from the
more dorsolateral ly positioned canal for the al-
veolar ramus of the mandibular division of the
trigeminal nerve. The ventral part of the posterior
margin of this intramandibular septum is deeply
concave. Its concavity defines the dorsal and an-
terior margin of the anterior inferior alveolar fo-
ramen, the posterior and ventral margin of which
is defined by the splenial as it contacts the medial
surface of the dentary. Above the posterior con-
cavity of the septum, the dentary is broadly over-
lapped by the splenial in medial view. Dorsal to
the dentary-splenial overlap, the dentary forms a
very short coronoid process defining a postero-
ventral recess (notched in lateral view but not in
medial view) into which fits the anterior dorsal tip
of the coronoid.
The splenial (Fig. 2C) itself is roughly of an
arrowhead shape in medial view. A slender and
pointed posteroventral projection overlaps the an-
terior end of the angular (L97: char. 73; LC98:
char. B12). A broad posterior dorsal projection
provides the medial closure of Meckel's canal at
the level of the anterior end of the surangular.
Posterodorsally, the splenial contacts the anterior
process of the coronoid (L97: char. 77; LC98:
char. B14), anterodorsally it contacts the posterior
end of the dentary, and posteriorly it defines the
anterior margin of the subcoronoid fossa (L97:
char. 79; LC98: char. Bl 1), below which it over-
laps the anterior end of the prearticular. Anteri-
orly, the splenial is drawn out into a tapering pro-
cess that reaches to about the midpoint of the den-
tary. Along the posterior two thirds of the length
of the splenial, a horizontal shelf projects from
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
VII hy
VII hy
Fig. 1. The lower jaw of Varanus (based on Varanus komodoensis, fmnh 22199). A, lateral view; B, medial
view; C, disarticulated medial view. Not to scale. Abbreviations for all figures: ale, alveolar nerve canal; amf, anterior
mylohyoid foramen; an, angular; ar, articular; c, coronoid; cp, compound bone; d, dentary; mf, mental foramen; pi,
palatine; pmf, posterior mylohyoid foramen; pra, prearticular; sa, surangular; saf, anterior surangular foramen; sp,
splenial; mc (or Mc), Meckel's cartilage; mg (or Mg), Meckel's groove; VII hy, chorda tympani foramen.
FIELDIANA: GEOLOGY
B
Fig. 2. The coronoid and splenial of Varanus sp.
(fmnh 195576). A, coronoid, lateral view; B, coronoid,
medial view; C, splenial, lateral view. Scale bar = 10
mm.
the lateral surface of the splenial at a level just
below the anterior mylohyoid foramen. This hor-
izontal shelf underlies Meckel's cartilage and cre-
ates a groove between itself and the laterally
curved ventral margin of the splenial, which re-
ceives the medially curved ventral margin of the
dentary. The anterior mylohyoid foramen opens
medially, but a small slitlike opening between the
medial vertical wall of the splenial and its later-
ally projecting shelf at the level of the anterior
mylohyoid foramen allows a branch of the ante-
rior mylohyoid nerve to pass into the groove that
receives the ventral margin of the dentary. The
splenial tapers off at the ventral margin of the
dentary (L97: char. 70).
The coronoid (Figs. 2A, 2B) shows a V-shaped
outline in medial view, the apex pointing upward
and forming the coronoid process. Its ventral mar-
gin is concave and defines the subcoronoid fossa
located between the coronoid and the prearticular.
In transverse section, the coronoid forms an in-
verted V, the apex pointing upward, and the base
straddling the dorsal rim of the surangular. The
main body of the coronoid carries a distinct an-
teroventral process, the anterior tip of which fits
into a recess at the posterior end of the dentary.
Below and shortly behind the coronoid-dentary
contact, the coronoid forms a medial sheet of
bone that extends in an anteroventral direction
deep (i.e., lateral) to the broad posterodorsal ex-
tension of the splenial but medial to the suran-
gular and to Meckel's cartilage. The coronoid en-
ters the posterior margin of the anterior inferior
alveolar foramen lateral to the splenial, where it
becomes drawn out into two slender and delicate
processes that follow the dorsal and ventral mar-
gins, respectively, of this foramen. The dorsal
process of the coronoid is more extensively de-
veloped than the ventral one, as it follows the dor-
sal margin of the anterior inferior alveolar fora-
men medial to the dentary and ventral to the
tooth-bearing shelf to the level of the midpoint of
the dentary; the ventral projection of the coronoid
reaches up to the midpoint of the lower margin of
the anterior inferior alveolar foramen.
At the posteroventral base of the coronoid pro-
cess, the medial shank of the coronoid is drawn
out into a posteroventral process, medially over-
lapping the ascending process of the prearticular,
which, together with the coronoid, forms the an-
terior and medial margin of the adductor fossa
(L97: char. 78; LC98: char. BIO). Because the me-
dial margin of the adductor fossa is lower than
the lateral margin in Varanus, the fossa is exposed
in both dorsal and medial views of the lower jaw
(L97: char. 80; LC98: char. B15).
The prearticular forms the floor of the adductor
fossa behind the angular and its medial wall deep
to the coronoid. At the anterior margin of the ad-
ductor fossa, the prearticular forms a dorsal pro-
cess extending upward between the (lateral) sur-
angular and the (medial) coronoid, thereby defin-
ing the posterior margin of the subcoronoid fossa.
The prearticular continues anteriorly below the
subcoronoid fossa. Its anterior end slips beneath
the posterodorsal extension of the splenial in me-
dial view (i.e., passes lateral to the splenial). Be-
low (i.e., lateral to) the splenial, the anterior end
of the prearticular tapers to a thin and pointed
process, located ventral to the anterior ventral pro-
cess of the coronoid, which runs along the ventral
margin of the anterior inferior alveolar foramen.
In summary, the dentary and splenial, on the
RTEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
B
VII hy
SP amf
amf
Fig. 3. The lower jaw of Lanthanotus borneensis (fmnh 1371 1). A, lateral view; B, medial view; C, angular and
splenial, ventral view. A, B: scale bar = 5 mm; C: scale bar = 2 mm. Abbreviations as in Figure 1.
one hand, and the postdentary bones on the other
show a complex and extensive pattern of overlap
with one another in Varanus, even though this
overlap is not revealed by the superficial suture
pattern. Lateral to Meckel's cartilage, the domi-
nant overlap is between the dentary (superficial)
and the surangular. Medial to Meckel's cartilage,
the dominant overlap is between the splenial (su-
perficial) and the coronoid plus prearticular.
The lower jaw of Lanthanotus (Fig. 3) differs
from that of Varanus by an extended contact of
the coronoid with the dentary, in both lateral and
medial views of the lower jaw. Unlike in Varanus,
the anterior end of the coronoid is essentially bi-
furcated, as it embraces the posterior end of the
dentary both laterally and medially. The lateral
anterior prong of the coronoid is shorter than the
medial anterior prong, which extends anteroven-
trally to establish a broad contact with the anterior
end of the prearticular and the posterodorsal cor-
ner of the splenial (L97: char. 77; LC98: char.
B14). Behind that anterior bifurcation, the coro-
noid straddles the longitudinal dorsal shoulder of
the surangular, as it does in Varanus. A postero-
ventral process of the coronoid descends on the
medial side of the lower jaw, medially overlap-
ping an ascending process of the prearticular,
which itself forms the anterior and medial margin
of the adductor fossa (rather than the coronoid
itself; L97: char. 78; LC98: char. BIO) and, at the
same time, the posterior margin of the subcoro-
noid fossa.
The surangular establishes a broad overlap with
the dentary lateral to Meckel's cartilage; the pos-
teroventral corner of the dentary also overlaps the
anterior end of the angular laterally. The splenial
gains no exposure in lateral view, and in medial
view it shows a reduction of the posteroventral
FIELDIANA: GEOLOGY
Fig. 4. The lower jaw of Platecarpus sp. (fmnh UC 600) in lateral view.
process, which in Varanus is distinct and overlaps
with the angular. Reduction of this process results
in a superficially vertical suture at the contact be-
tween angular and splenial in medial view of the
lower jaw. The posterodorsal extension of the
splenial is again less developed than in Varanus,
which reduces but does not obliterate the overlap
with the anteroventral process of the coronoid.
Whereas the vertical suture on the medial side
of the lower jaw suggests a relatively simple and
mobile contact between splenial and angular, the
ventral aspect of the lower jaw (Fig. 3C) reveals
that the angular-splenial contact is more complex
(L97: char. 73; LC98: char. B12). The ventral mar-
gin of the splenial is concave, receiving the convex
ventral margin of the angular. More importantly,
the angular forms a distinct anteroventral process,
which extends lateral to the posterior end of the
splenial, intercalated between the latter and the
dentary (L97: char. 74; LC98: char. B12). As in
mosasaurs (see below), the splenial is the receiving
part, the angular the received part in the intraman-
dibular articulation of Lanthanotus. Unlike in Var-
anus, the anterior tip of the relatively short splenial
lies dorsomedial to the ventral margin of the den-
tary (L97: char. 70), and in front of it Meckel's
canal opens ventrally relative to the sagittal plane
of the lower jaw between a lateral flange of the
dentary and the prominent tooth-bearing shelf
(L97: char. 69; LC98: char. B13). The splenial of
Lanthanotus was not disarticulated. It was there-
fore not possible to assess the presence of a hori-
zontal shelf projecting from the lateral surface of
the splenial, which together with the ventral margin
of the splenial would form a groove to receive the
ventral margin of the dentary, as is seen in Var-
anus. If present, however, such a medial crest must
be confined to the posteriormost part of the splen-
ial, as its anterior tapering end lies above the ven-
tral margin of the dentary.
The Intramandibular Joint in Mosasaurs
The lower jaw of mosasaurs was described by
Camp (1942) and, in more detail, by Russell
(1967). Relevant information is also provided by
Bell (1997). The main difference in the lower jaw
of Varanus and mosasaurs is that the latter have
mobilized the intramandibular joint to a greater
degree, largely through a reduction of bone over-
lap (probably due to paedomorphosis, which is
common in secondary marine reptiles; Rieppel,
1993a). In lateral view, the posterior end of the
dentary of mosasaurs {Platecarpus, fmnh UC
600) appears truncated relative to that of Varanus,
with a more or less straight posterior margin that
slopes posteroventrally (Fig. 4). The posteroven-
tral corner of the dentary forms an extensive lat-
eral overlap with the splenial. There is, however,
no evidence for any significant anterior extension
of the surangular deep to the dentary. Instead, the
surangular appears to be truncated at its anterior
end and consequently fails to overlap with the
dentary. In Platecarpus (fmnh UC 600), the den-
tary does not overlap with the surangular at all.
The contact of the splenial with the angular
again is not an overlapping one (Fig. 4). Instead,
the two elements abut against each other in a ball-
and-socket joint (Bell, 1997; Russell, 1967),
which in lateral and medial views translates into
a more or less vertically oriented contact between
the two elements (L97: char. 74; LC98: char.
B12). The posterior surface of the splenial is
broadened and round or elliptical in outline. It is
concave and forms the socket into which the
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
rounded and convex anterior surface of the an-
gular fits. In the intramandibular joint of mosa-
saurs, therefore, the splenial is the receiving part,
the angular is the received part.
In medial view, the lower jaw of mosasaurs
again differs significantly from Varanus. As de-
scribed previously (Zaher & Rieppel, 1999), the
teeth are set in a groove that runs along the dorsal
margin of the splenial. As a consequence, a den-
tary shelf overhanging Meckel's canal is not dif-
ferentiated in mosasaurs (L97: char. 67). Meckel's
canal is open along the anterior third of the length
of the mandibular ramus, but unlike in Varanus,
it opens on the medial surface of the lower jaw
because the dentary forms a ventromedial flange
in its anterior half, which wraps around the ventral
surface of Meckel's cartilage and rises up again
on the medial side of the lower jaws (L97: char.
69; LC98: char. B13). More posteriorly, the splen-
ial closes Meckel's canal in medial view. In front
of its articulation with the angular, the splenial
develops into a high flange of bone, almost com-
pletely covering the medial exposure of the den-
tary. The anterior inferior alveolar foramen is not
conspicuous in mosasaurs. A broken lower jaw of
an unidentified mosasaur (Mosasauridae indet.
fmnh PR 674) shows that, unlike in Varanus, the
splenial forms no longitudinal crest projecting
from its lateral surface, which together with the
ventral margin of the splenial would form a
groove to receive the ventral edge of the dentary.
The broken cross-section of the splenial reveals it
to be a simple vertical lamina of bone. Its poste-
rior part lies medial and ventral to the vertical
lamina formed by the posterior end of the dentary.
The ventral margin of the splenial becomes in-
creasingly thickened posteriorly, as the bone
forms the socket to receive the anterior head of
the angular. Anteriorly, the splenial tapers to a
blunt tip that terminates at a level above the ven-
tromedial dentary flange that wraps around the
ventral surface of Meckel's cartilage, i.e., not
along the ventral margin of the dentary, as in Va-
ranus (L97: char. 70), but on the medial surface
of Meckel's cartilage.
The coronoid is reduced in mosasaurs as com-
pared to Varanus. A posteromedial process may
still be present, but if so, it always remains small
(Bell, 1997; L97: char. 78; LC98: char. BIO). In
front of the apex of the coronoid process, the el-
ement extends as a relatively broad anterior pro-
cess that, as in Varanus, "is a saddle-shaped bone
straddling the longitudinal 'shoulder' ... of the
surangular which is enclosed in a deep sulcus"
(Russell, 1967, p. 53). It approaches, but does not
contact, the dentary, and it remains widely sepa-
rated from the splenial (L97: char. 75; LC98: char.
B14).
The height of the prearticular is greatly in-
creased in mosasaurs, and together with the cor-
onoid the prearticular completely conceals the
surangular in medial view of the lower jaw in
front of the adductor fossa (L97: char. 79). As
noted by Gauthier (1982), the prearticular is the
principal element from which the dentary is sus-
pended in mosasaurs, as it extends anteriorly as a
high blade that enters between the equally high
posterior part of the splenial (medially) and the
dentary (laterally).
As in Varanus, the adductor fossa of mosasaurs
is characterized by a medial margin (formed by
the prearticular) that is lower than the lateral mar-
gin (formed by the surangular). As a consequence,
the adductor fossa opens dorsally as well as me-
dially (L97: char. 80; LC98: char. B15).
By comparison to Varanus, mosasaurs have
lost the dentary-coronoid contact, lost the broad
overlap of surangular and dentary lateral to Meck-
el's cartilage, and transformed the overlapping
splenial-angular contact into a ball-and-socket
joint. Medial to Meckel's cartilage, mosasaurs
have lost the splenial-coronoid overlap due to a
reduction of the coronoid, but the relative height
of the splenial and prearticular is increased. In
summary, mosasaurs have increased one area of
support, the prearticular-splenial-dentary overlap,
at the expense of two other areas of support that
are well developed in Varanus, the splenial-cor-
onoid overlap and the dentary-surangular overlap.
The increased mobilization of the intramandi-
bular joint in mosasaurs is correlated with a loos-
ening of the mandibular symphysis. There is no
sutural contact between the anterior tips of the den-
taries. Instead, their anterior tips are smooth and
rounded, and the dentaries must have been in syn-
desmotic or ligamentous connection with each oth-
er (Cope, 1869; L97: char. 68; LC98: char. B8).
The Compound Bone of the Ophidian
Mandible
In snakes, the surangular, prearticular, and ar-
ticular fuse to form a single "compound" or
"mixed" bone during embryonic development
(Bellairs & Kamal, 1981; DeBeer, 1937), incor-
porating both dermal and chondral elements.
Among other squamates, a similar compound
FIELDIANA: GEOLOGY
bone is only found in dibamids (Greer, 1985;
Rieppel, 1984a) and in amphisbaenians (Montero
et al., 1999; Zangerl, 1944). Many details of the
embryonic development of the lower jaw of
snakes remain to be determined, but it is clear that
the elements contributing to the compound bone
fuse during embryonic development (Bellairs &
Kamal, 1981; Parker, 1879). Few authors had crit-
ical embryonic stages available to them, which
would show the dermal elements of the compound
bone present but not yet fused (Brock, 1929; Hal-
uska & Alberch, 1989; Kamal et al., 1970; Peyer,
1912); or consideration of the development of the
dermal bones of the lower jaw was not included
in the study (Genest-Villard, 1966). Several stud-
ies of cranial development in snakes do not ad-
dress the ossification sequence and pattern of der-
mal bones (see reviews in Bellairs & Kamal,
1981; Rieppel, 1993b).
However, Backstrom (1931) described in detail
the development of the dermal bones in the lower
jaw of Natrix natrix and noted that the first ele-
ments to appear are the dentary and splenial, fol-
lowed by the surangular. All five dermal elements
are present in the 6.8-mm stage (Backstrom, 1931,
Fig. 17) but are still separate from one another.
The prearticular is confined to the medial aspect
of the lower jaw (of Meckel's cartilage). It entire-
ly conceals the surangular in medial view, and
wraps around the ventral surface of Meckel's car-
tilage below the mandibular articulation. The sur-
angular develops on the lateral and dorsal aspect
of Meckel's cartilage, and it is the surangular that
forms the large anterior projection that enters be-
tween the two posterior prongs of the deeply bi-
furcated dentary. This interpretation is supported
by the position of the homologue of the anterior
surangular foramen (at least in alethinophidians),
and it is also in accordance with the observation
of Estes et al. (1970) that it is the surangular por-
tion of the compound bone that provides the main
support for the dentary in the fossil snake Dini-
lysia.
In the adult jaw, the compound bone wraps
around Meckel's cartilage. It may be raised into a
coronoid process toward its anterior end, and it
carries the adductor fossa in its posterior part. The
relation of Meckel's cartilage to the adductor fos-
sa differs in important ways in snakes as com-
pared to nonophidian squamates. In squamates
other than snakes, Meckel's cartilage is exposed
at the bottom of the adductor fossa for approxi-
mately half of its length, and fibers of the poste-
rior adductor insert into it. The compound bone
of scolecophidians appears to be a simple tubelike
structure, at least in its posterior part. In alethin-
ophidians (at least in anilioids and basal macros-
tomatans), Meckel's cartilage enters its own canal
at the bottom of the compound bone, beginning
at the level of the anterior margin of the adductor
fossa, and hence is not exposed in the latter. The
coronoid is of a much simpler structure in snakes
than in nonophidian squamates. It never forms a
saddle-shaped structure straddling the dorsal lon-
gitudinal shoulder of the surangular. Instead, the
coronoid of snakes is a simple sheet of bone that
is always applied to the medial side of the dorsal
(surangular) portion of the compound bone. It
may or may not project beyond the dorsal margin
of the compound bone at the apex of the coronoid
process. The formation of a compound bone is an
autapomorphy of snakes (or a potential synapo-
morphy shared by snakes, dibamids, and amphis-
baenians), and because of its formation, a subco-
ronoid fossa exposing the surangular between the
coronoid and the angular on the medial surface of
the lower jaw is a character that cannot be applied
or compared to snakes (L97: char. 79; LC98: char.
Bll).
The Intramandibular Joint in Scolecophidians
Scolecophidians are divergently derived and
highly autapomorphic in the structure of their
lower jaw, owing to their microphagous habits. In
Anomalepis (Haas, 1968), the surangular, articu-
lar, and prearticular have fused into a compound
bone, as in all other snakes. The coronoid is
roughly trapezoidal and forms a prominent coro-
noid process. It is applied against the medial sur-
face of the anterior part of the compound bone
and medially overlaps the contact between the
posterior end of the dentary and the anterior end
of the splenial (List, 1966; angular of Haas,
1968). The anterior end of the compound bone
overlaps and thereby supports the dorsal margin
of the posterior half of the splenial, which with
its anterior half (i.e., in front of the compound
bone) underlies and supports the posterior end of
the dentary. The posterior part of the dentary
meets the dorsal margin of the anterior half of the
angular in an oblique plane (L97: char. 73; LC98:
char. B12). Meckel's cartilage is wedged between
the coronoid medially and the splenial and den-
tary laterally. In front of the coronoid, Meckel's
cartilage comes to lie in a shallow groove that
follows the ventromedial margin of the dentary.
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
The splenial is a simple, flat strip of bone that
tapers off along the ventral margin of the dentary
(relative to the sagittal plane of the lower jaw).
Main support for the dentary is provided by the
splenial and by the coronoid in front of the com-
pound bone.
Liotyphlops closely resembles Anomalepis in
the essential features of the lower jaw, although
the shapes of individual elements are different in
detail (Haas, 1964). The simple and flat splenial
(angular of Haas, 1964) is again underlying the
anterior end of the compound bone and the pos-
terior end of the dentary. At the anterior end of
the splenial, the Meckelian groove shifts to a po-
sition on the medial side of the dentary (Haas,
1964, Fig. 20). The splenial tapers off along the
ventral margin of the dentary (relative to the sag-
ittal plane of the lower jaw).
The lower jaw of Typhlops typically comprises
five elements (Haas, 1930). The largest one is the
compound bone, the anterior end of which is
again applied against the lateral surface of the
large, roughly triangular coronoid. The tapering
anterior end of the compound bone reaches the
posterior tip of the dentary and may be accom-
panied up to this level by the anteroventral pro-
cess of the coronoid. As in anomalepids, a rela-
tively large splenial underlies the contact of the
compound bone with the dentary, but in typhlo-
pids it extends anteriorly up to the symphyseal tip
of the mandible. At the level of the anterior end
of the compound bone, the posterior part of the
splenial is located ventral to Meckel's cartilage;
in front of the compound bone, the splenial forms
a deep trough closed dorsally by the dentary,
within which lies Meckel's cartilage. Meckel's ca-
nal (groove) is therefore not exposed on the me-
dial side of the lower jaw (L97: char. 69: LC98:
char. B13). Other than in anomalepids, most ty-
phlopids show a second element at the ventral
margin of the lower jaw, sometimes vestigial, and
located behind the splenial, which supports the
dentary. The posterior element is identified as an-
gular (List, 1966), but, as in anomalepids, the
main support for the dentary is provided by the
splenial in typhlopids. In mosasaurs, it is the
prearticular that provides principal support for the
dentary; in alethinophidians (and leptotyphlo-
pids), it is the surangular as part of the compound
bone (Estes et al., 1970, p. 46; see below). In
nonophidian squamates, it is the splenial that un-
derlies the dentary, and if so interpreted, anoma-
lepids and typhlopids share a plesiomorphic char-
acter in that respect. However, the posterior ex-
tension of the splenial to a level well behind the
level of the posterior tip of the dentary may be a
synapomorphy shared by typhlopids and anoma-
lepids, whereas the position of the splenial entire-
ly lateral to Meckel's cartilage may be a synapo-
morphy of anomalepids.
Brock ( 1 932) described five bones in the lower
jaw of Leptotyphlops, i.e., the dentary, splenial,
coronoid, angular, and the compound bone. The
splenial is located entirely on the medial side of
the dentary, partially closing the posterior part of
the Meckelian groove, which is located entirely
on the medial aspect of the dentary. The dentary
is a relatively large, tooth-bearing element, with
a sloping posterior margin that establishes an ex-
tended and mobile (Haas, 1930) contact with the
compound bone. The latter is shorter and more
massively built than in other scolecophidians. An
angular underlies the anterior end of the com-
pound bone, which may meet the splenial in a
simple abutting contact if the latter projects be-
yond the posteroventral corner of the dentary
(List, 1966). The coronoid is applied to the medial
surface of the compound bone and remains widely
separated from the splenial. Unlike in anomale-
pids and typhlopids, it is the compound bone that
provides the major support for the dentary in lep-
totyphlopids. This is also the case in alethinophi-
dians, although in this group, the contact of the
compound bone with the dentary is established in
a different manner.
The Intramandibular Joint in Anilioids
Anilius shows a weak expression of the poste-
rior bifurcation of the dentary, which is charac-
teristic of alethinophidian snakes (Fig. 5).
Posterodorsally, the dentary is drawn out into a
short posterodorsal process, which together with
the coronoid and the compound bone forms the
prominent coronoid process. Medially, the poste-
rior end of the dentary forms a broad concavity
that accommodates the anterior end of the com-
pound bone. The mandibular division of the tri-
geminal nerve, along with Meckel's cartilage, is
enclosed in a canal within the compound bone.
Further anteriorly, the compound bone opens me-
dially, releasing Meckel's cartilage along with the
mandibular nerve into Meckel's groove on the
medial side of the dentary. The alveolar ramus of
the mandibular division of the trigeminal nerve
enters a separate, dorsolaterally positioned canal
that leads up to the single mental foramen, which
10
FIELDIANA: GEOLOGY
Fig. 5. The lower jaw of Anilius scytale (fmnh 35688). A, lateral view; B, medial view. Scale bar = 2 mm.
Abbreviations as in Figure 1.
opens at the anterior end of the dentary on its
lateral surface (L97: char. 76; LC98: char. C14).
Meckel's canal opens ventromedially in its pos-
terior part as the ventral rim of the dentary ex-
pands medially below Meckel's cartilage at the
level below the anterior end of the compound
bone. More anteriorly, however, Meckel's canal
opens ventrally (relative to the sagittal plane of
the lower jaw), as it does in Varanus and other
nonophidian squamates except mosasaurs (L97:
char. 69; LC98: char. B13). The dorsomedial
ledge of the dentary that overhangs the Meckelian
groove is closely comparable to the tooth-bearing
shelf of Varanus (L97: char. 67).
The compound bone of Anilius includes, as it
does in other snakes, the articular, surangular, and
prearticular. It encloses an elongate, deep and
wide adductor fossa with a well-defined medial
margin. As a consequence, the adductor fossa
opens dorsally (L97: char. 80; LC98: char. B15).
Deep to the dentary, the part of the compound
bone located lateral to Meckel's cartilage extends
further anteriorly than the medial cover of Meck-
el's cartilage, which results in a medial opening
of Meckel's canal at the anterior end of the com-
pound bone. The part of the compound bone lo-
cated lateral to Meckel's cartilage corresponds to
the surangular, and its greater anterior extension
corroborates the observation of Estes et al. (1970)
in Dinilysia and the embryological observations
of Backstrdm (1931) that, in alethinophidians, it
is the surangular that provides the principal sup-
port for the dentary.
At the anterior end of the compound bone, be-
tween the ventral margin of the latter and the pos-
terior maxillary ledge that wraps around the ven-
tral surface of Meckel's cartilage, lies a small
splint of bone. It projects anteriorly to a level
slightly in front of the medial component of the
compound bone, and it is located ventromedial to
the compound bone and, in front of the latter, ven-
tromedial to Meckel's cartilage. By comparison to
other basal alethinophidians, this element is per-
haps best interpreted as a vestigial angular, al-
though it could also represent a vestigial splenial.
Its presence was confirmed in both the lower jaw
ramus of Anilius fmnh 35688 (Fig. 5) and in a
serially sectioned skull (Fig. 6, uncatalogued
specimen).
The coronoid is a small element located at the
tip of the coronoid process on the medial surface
of the compound bone and behind the postero-
dorsally ascending process of the dentary. The
bone is truncated posteriorly but carries a short
RTEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
11
ac?, sp?
Fig. 6. Transverse section through the lower jaw of
Anilius scytale (uncatalogued). Abbreviations as in Fig-
ure 1.
anteroventral projection, which results in a weakly
concave ventral margin. Given the fusion of the
surangular and prearticular (and articular) to form
the compound bone, a subcoronoid fossa exposing
the surangular in medial view is absent in snakes
(L97: char. 79; LC98: char. Bll).
The intramandibular joint takes on a more com-
plex structure in Cylindrophis ruffus (Fig. 7, fmnh
13100, 131780). The function of the intramandi-
bular joint in Cylindrophis ruffus has been ana-
lyzed in detail by Cundall (1995). The dentary is
deeply bifurcated posteriorly, supported by a large
anterior projection of the compound bone. As de-
scribed by Zaher and Rieppel (1999), the teeth are
ankylosed to the interdental ridges on the pleura
of the dentary. At the anterior end of the dentary,
this pleura is again developed into a tooth-bearing
shelf (again without marginal thickening) that
overhangs the anterior end of Meckel's groove
(L97: char. 76). The latter opens ventrally relative
to the sagittal plane of the mandibular ramus
(L97: char. 69; LC98: char. B13). More posteri-
orly, the tooth-bearing shelf is developed into the
intramandibular septum with a concave medial
surface, separating the medial Meckelian groove
from the laterally positioned canal for the alveolar
ramus of the mandibular division of the trigeminal
VII hy
Fig. 7. The lower jaw of Cylindrophis ruffus (fmnh 131780). A, lateral view; B, medial view. Scale bar = 2 mm.
Abbreviations as in Figure 1.
12
FIELDIANA: GEOLOGY
nerve. Anteriorly, the nerve emerges from the sin-
gle, laterally placed mental foramen at the tip of
the dentary (L97: char. 76; LC98: char. CI 4). The
intramandibular septum reaches backward into the
anterior half of the gap between the dorsal and
ventral prongs of the posterior end of the dentary.
The large, laterally placed anterior prong of the
compound bone (surangular portion, see above)
thus fits snugly into a recess bounded dorsally by
the dorsal prong of the caudally bifurcated den-
tary, ventrally by the posteroventral process of the
dentary, and medially by the intramandibular sep-
tum.
Below this contact between the compound bone
and the dentary, the vertically oriented suture be-
tween angular and splenial is narrowly exposed in
lateral view (L97: char. 74). The medial view of
the lower jaw exposes the splenial and angular in
their full size, pierced by the anterior and poste-
rior mylohyoid foramen, respectively. From the
lateral surface of the splenial, at a level narrowly
below the anterior mylohyoid foramen, projects a
lateral crest. This crest underlies Meckel's carti-
lage, and, with the ventral edge of the splenial, it
forms a distinct groove that receives the ventral
edge of the dentary, which itself curves inward.
At the level of the anterior mylohyoid foramen,
the lateral shelf of the splenial is pierced by a
small foramen, which allows a ventral branch of
the anterior mylohyoid nerve to slip out of Meck-
el's canal, entering between the splenial and the
dentary. Medially, the splenial forms a dorsal ver-
tical blade that entirely closes the posterior part
of Meckel's groove in medial view. More anteri-
orly, the vertical blade of the splenial gradually
tapers to a pointed tip that lies in line with the
ventral edge of the dentary (L97: char. 70).
The coronoid is a roughly triangular bone that
is received in a shallow facet on the medial side
of the compound bone (surangular portion). To-
gether with the compound bone, it forms a prom-
inent coronoid process. The ventral margin of the
coronoid is slightly concave. Anteroventrally, the
coronoid is extended into a prominent anterior
process that remains restricted to the medial sur-
face of the compound bone and hence does not
participate in the formation of the large surangular
prong that enters between the two posterior pro-
cesses of the dentary. The anteroventral process
of the coronoid establishes an extended contact
with the anterior part of the dorsal margin of the
angular, but it remains separated from the splenial
in our specimens of Cylindrophis ruffus (L97:
char. 75; LC98: char. B14). The coronoid contacts
the splenial in specimens figured by McDowell
(1975, Fig. 6) and Cundall (1995, Fig. 6). (It
should be noted that macerating skulls with com-
mercial bleach easily dissolves thin marginal ar-
eas of bones.)
In superficial medial view, the anterior end of
the angular matches the posterior end of the splen-
ial in height. The two elements meet in a straight,
slightly posteroventrally trending suture (L97:
char. 73; LC98: char. B12). Disarticulation of the
splenial shows that the posterior surface of the
posteroventral corner of the splenial is thickened,
flat, and sloping posteroventrally, whereas the an-
terior surface of the angular is similarly thickened,
flat, and trending anterodorsally. The two ele-
ments meet face to face in a simple abutting con-
tact. Deep to this contact, the dorsomedial edge
of the angular forms a small, anteriorly projecting
prong that, on its medioventral surface, is lined
by a congruent projection of the compound bone.
This latter prong originates from the compound
bone medioventral to Meckel's cartilage. As de-
scribed above, the anterior end of the angular is
somewhat thickened, and, in addition to the com-
posite medial prong described above, its lateral
margin slightly projects anteriorly. As a conse-
quence thereof, the anterior surface of the angular
forms a vertically oriented shallow trough that is
bounded dorsomedially by the composite prong
described above and laterally by the projecting
lateral margin of the angular. The posterior end of
the splenial fits snugly into that trough on the an-
terior surface of the angular, while the horizontal
crest that projects from the lateral surface of the
splenial locks against the ventral surface of the
composite dorsomedial prong. Other than in mo-
sasaurs, therefore, the angular is the receiving part
in the intramandibular articulation, the splenial is
the received part. Posteriorly the angular tapers to
a blunt tip, which is located at the ventral margin
of the compound bone.
Behind the coronoid process, the compound
bone forms the adductor fossa, which is not as
deep and wide as it is in Anilius. However, its
medial margin is only slightly lower than the lat-
eral margin, such that the adductor fossa opens
dorsally relative to the sagittal plane of the man-
dibular ramus (L97: char. 80; LC98: char. B15).
Cylindrophis maculatus (Fig. 8, bmnh
1930.5.8.48; serially sectioned skull, uncata-
logued) is closely comparable to Cylindrophis ruf-
fus in most of the essential characteristics of the
lower jaw. The coronoid process is somewhat
lower, but the anteroventral process of the coro-
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
13
VII hy
SP amf Pmf
B
cp ' ^^^*
Mc
Fig. 8. The lower jaw of Cylindrophis maculatus (bmnh 1930.5.8.48; serially sectioned skull, uncatalogued). A,
medial view, scale bar = 2 mm; B, serial sections from the coronoid process to the anterior tip of the splenial.
Abbreviations as in Figure 1.
14
FIELDIANA: GEOLOGY
noid is larger and approaches the splenial very
closely or establishes a contact with it. Also, the
superficial splenial-angular suture as exposed in
medial view is distinctly concave anteriorly in its
ventral part, a trait that is only weakly developed
in Cylindrophis ruffus. The anterior prong pro-
jecting from the medial anterior margin of the an-
gular, and complemented medioventrally by an
anterior prong of the compound bone, is also pre-
sent in Cylindrophis maculatus, although perhaps
a little less prominently developed than in Cylin-
drophis ruffus. This prong is located at the dorsal
margin of the concavity formed by the anterior
end of the angular, such that the splenial-angular
contact is closely comparable to that described for
Cylindrophis ruffus.
The lower jaw of uropeltids (Figs. 9, 10) resem-
bles that of Cylindrophis quite closely except for
characters that result from reduction, probably as
a consequence of paedomorphosis related to small
overall size. The dentary of Melanophidium punc-
tatum (Figs. 9A, 9B: bmnh 1930.5.8.119) retains
the deep posterior bifurcation characteristic of al-
ethinophidians, but the posteroventral process of
the dentary is much reduced in Platyplecturus
madurensis (Figs. 9C, 9D: bmnh 1930.5.8.111),
vestigial in Plecturus perroteti (Fig. 10: bmnh
1930.5.8.105), and fully reduced in all other spe-
cies examined (Pseudotyphlops philippinus, bmnh
1978.1092 [Figs. 9E, 9F]; Rhinophis drummond-
hayi, bmnh 1930.5.8.67-68; Teretrurus rhodogas-
ter, bmnh 1930.5.8.98, and Uropeltis woodman-
soni, bmnh 1930.5.8.73-74). The hypothesis that
the posteroventral process of the dentary is re-
duced rather than absent within uropeltids re-
quires corroboration by reconstruction of cladistic
relationships within the clade, which is not avail-
able at this time. However, Melanophidium punc-
tatum is also plesiomorphic with respect to some
other characters of its cranial anatomy, such as the
presence of teeth on the palatine, the location of
the optic foramen, and the retention of sutures in
the occipital condyle delineating the basioccipital
from the exoccipitals (Rieppel, 1977).
The coronoid, an element of variable size and
shape, is always applied to the medial surface of
the compound bone and, together with the latter,
forms a weakly expressed coronoid process. The
coronoid retains relatively distinct anteroventral
and posteroventral processes and a concave ventral
margin in Plecturus perroteti (bmnh 1930.5.8.105)
and, to a lesser degree, in Platyplecturus maduren-
sis (bmnh 1930.5.8.111). The coronoid usually
contacts the posterodorsal process of the dentary
and at least marginally projects beyond the dorsal
margin of the compound bone, except in Pseudo-
typhlops philippinus (bmnh 1978.1092), where the
coronoid is vestigial, restricted to the medial sur-
face of the compound bone, and has lost the con-
tact with the dentary. The coronoid never contacts
the splenial in uropeltids.
In taxa with a reduced posteroventral process
of the dentary, the posterior end of this bone
wraps around the anterior end of the compound
bone in a manner very similar to that observed in
Anilius. Meckel's groove is open medially in front
of the anterior end of the compound bone except
in those taxa where the dorsal margin of the
splenial establishes a contact, in its posterior part,
with the ventral margin of the tooth-bearing shelf
of the dentary. Meckel's groove opens on the me-
dial surface of the mandible above the splenial,
but it opens ventrally (relative to the sagittal plane
of the lower jaw ramus) in front of the splenial,
with the exception of Plecturus perroteti (bmnh
1930.5.8.105), where the ventral opening of
Meckel's groove is restricted to its anterior end.
All uropeltids have a well-developed splenial
and angular, each pierced by the anterior and pos-
terior mylohyoid foramen respectively (Figs. 9,
10). The elements meet in a slightly curved, an-
teriorly concave, but essentially vertically orient-
ed suture apparent on the medial surface of the
lower jaw. This suggests a similar articulation of
angular and splenial, as is also observed in Cylin-
drophis maculatus. The disarticulated lower jaw
of Pseudotyphlops philippinus (bmnh 1978.1092),
as well as a serially sectioned head of Plecturus
perroteti (uncatalogued), reveals that the posterior
surface of the posteroventral end of the splenial
is somewhat thickened, as is the anterior surface
of the anteroventral end of the angular. The two
elements meet in a simple abutting contact, the
splenial with a weakly convex surface, the angular
with a weakly concave surface. The composite
medial prong formed by the angular and the com-
pound bone and locking the splenial in place in
Cylindrophis is absent in uropeltids, which there-
fore are characterized by a somewhat simplified
articulation between angular and splenial.
The serially sectioned head of Plecturus per-
roteti (Fig. 10C) shows the posterior mylohyoid
nerve leaving Meckel's canal through a small slit-
like aperture in the anterior ventral margin of the
compound bone to reach the posterior mylohyoid
foramen in the angular. In transverse sections, this
creates the impression that the compound bone is
drawn out into two short anteroventral processes.
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
15
VII hy
VII hy
Fig. 9. The lower jaw of Melanophidium punctatus (bmnh 1930.5.8.119: A, lateral view; B, medial view; scale
bar = 1 mm), Platyplecturus madurensis (bmnh 1930.5.8.111: C, lateral view; D, medial view; scale bar = 1 mm),
and Pseudotyphlops philippinus (bmnh 1978.1092: E, lateral view; F, medial view; scale bar = 2 mm). Abbreviations
as in Figure 1.
16
FIELDIANA: GEOLOGY
4 V*
-pmf
Mc
sp
sp
sp SP
Mc
Fig. 10. The lower jaw of Plecturm perroteti (bmnh 1930.5.8.105; serially sectioned skull, uncatalogued). A,
lateral view; B, medial view; C, serial sections from the coronoid process to the anterior tip of the splcnial. Scale
bar = 1 mm. Abbreviations as in Figure 1.
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
17
These do not, however, bridge the angular-splen-
ial contact. As in Cylindrophis, the splenial de-
velops a horizontal crest that projects from its lat-
eral surface at a level closely below the anterior
mylohyoid foramen and that underlies Meckel's
cartilage. This crest, together with the ventral
edge of the splenial, again forms a groove that
receives the ventral edge of the dentary. A small
foramen located next to the anterior mylohyoid
foramen allows a ventral branch of the anterior
mylohyoid nerve to pass through the horizontal
crest of the splenial and to continue anteriorly be-
tween the latter and the dentary. The anterior tip
of the splenial again lies at the ventral margin of
the dentary. The disarticulated mandible of Pseu-
dotyphlops philippinus (bmnh 1978.1092) reveals
the same splenial morphology.
The adductor fossa on the compound bone is
elongate and deep in Melanophidium punctatum
(bmnh 1930.5.8.119); this character again seems
to represent the plesiomorphic condition, as it is
closely comparable to Cylindrophis. In other uro-
peltids, the adductor fossa tends to be reduced to
a shallow and relatively short groove located on
the anterior half of the bone, behind the coronoid
process, and showing a foramen at its anterior and
posterior end for the passage of the mandibular
division of the trigeminal nerve. The adductor
fossa opens dorsally and medially in Melanophi-
dium punctatum (bmnh 1930.5.8.119), where it is
well developed, but it opens dorsomedially or me-
dially in those taxa where it is reduced to a shal-
low groove.
The Intramandibular Joint in Basal
Macrostomatans
The lower jaw of Xenopeltis is highly special-
ized to allow for extreme mobility (Frazzetta,
1999; McDowell, 1975; Rieppel, 1977). The den-
tary is short relative to the much elongated com-
pound bone. It is deeply bifurcated posteriorly and
carries a much elongated posterior dentigerous
process. A sliverlike coronoid is attached to the
dorsal surface of the compound bone in front of
the adductor fossa, but it does not participate in
the formation of a coronoid process (Hoge, 1964).
The anterior end of the compound bone enters be-
tween the two posterior prongs of the dentary. A
small angular and an elongate and pointed splen-
ial are applied to the medial surface of the anterior
end of the compound bone. There is no mobile
contact between angular and splenial. Indeed,
Xenopeltis differs from other snakes in that the
intramandibular joint lies between the dentary and
the compound bone, angular and splenial being
parts of the functional unit represented by the
compound bone (Frazzetta, 1999).
No lower jaw of Loxocemus hicolor was avail-
able for disarticulation, which renders it impos-
sible to comment on the internal structure of the
articulation of the splenial with the angular. In its
superficial structure, however, the mandible of
Loxocemus resembles that of other basal alethin-
ophidians and/or macrostomatans (McDowell,
1975; Rieppel, 1977). The dentary is deeply bi-
furcated posteriorly and carries the elongate pos-
terior dentigerous process characteristic of ma-
crostomatan snakes. The coronoid is a relatively
small sliver of bone that is applied to the medial
side of the compound bone, lining the anterior
margin of the coronoid process and contacting the
dentary anteriorly. The splenial and angular meet
in an abutting contact; the superficial suture on
the medial surface of the lower jaw is anteriorly
concave. An anterior mylohyoid foramen is ab-
sent in the splenial. The anterior mylohyoid nerve
passes through a notch in its dorsal margin, as is
also the case in Python (see below). The coronoid
narrowly approaches, but does not contact, the
splenial. Meckel's groove opens medially along
the splenial but ventrally (relative to the sagittal
plane of the mandibular ramus) in front of the
splenial. The adductor fossa is elongate and well
developed, with a medial margin that is lower
than the lateral margin such that the fossa opens
medially and dorsally.
The intramandibular joint of Python reticulatus
(Fig. 11, fmnh 31329) corresponds in its essential
traits to that of Cylindrophis, although it is some-
what more elaborate. In lateral view, the dentary
appears deeply bifurcated, with an elongate pos-
terior dentigerous process overlapping the anterior
lateral prong of the compound bone. The presence
of such an elongate posterior dentigerous process
is a synapomorphy of macrostomatan snakes
(Zaher, 1998). Disarticulation of the mandible
(Fig. 11) reveals an intramandibular septum with
a concave medial surface, separating the medially
open Meckelian groove from the laterally posi-
tioned canal for the alveolar nerve. This canal
opens anteriorly through the single mental fora-
men on the lateral surface of the anterior tip of
the dentary (L97: char. 76; LC98: char. C14). The
intramandibular septum reaches relatively further
back into the posterior bifurcation of the dentary
than in Cylindrophis and, together with the pos-
terior dentigerous process and the posteroventral
18
FIELDIANA: GEOLOGY
B eP
D
Fig. 1 1. The lower jaw of Python reticulatus (fmnh 31329). A, lateral view of postdcntary bones; B, medial view
of postdentary bones; C, splenial, medial view; D, dentary, lateral view; E, splcnial, lateral view. A-D, scale bar =
2 mm; E, scale bar = 5 mm. Abbreviations as in Figure 1.
process of the dentary, forms a deep recess that
receives the prominent anterior and lateral prong
of the compound bone (surangular portion).
The medial view of the dentary exposes the
Meckelian groove, which opens medially in its
posterior part as the dentary turns inward below
Meckel's cartilage but ventrally (relative to the
sagittal plane of the mandibular ramus) in front
of the splenial (L-97: char. 69; LC98: char. B13).
The tall but relatively narrow posterior portion of
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
19
the splenial covers only the posteriormost part of
the Meckelian groove in medial view. A short and
tapering process of the splenial follows the dorsal
margin of Meckel's groove, whereas a much lon-
ger anteroventral process of the splenial follows
the ventral margin of Meckel's groove, tapering
off along the ventral margin of the dentary at a
more anterior level than is characteristic of ani-
lioids (L97: char. 70). The horizontal lateral shelf
that projects from the lateral surface of the splen-
ial is set very low, close to the ventral margin of
the element (Fig. HE). It underlies Meckel's car-
tilage and, together with the ventral margin of the
splenial, forms a groove that receives the medially
curved ventral margin of the dentary. Posteriorly,
the horizontal shelf gradually tapers off in front
of the thickened posteroventral head of the splen-
ial. Again, the lateral horizontal crest of the splen-
ial is pierced by a foramen for the passage of a
ventral branch of the anterior mylohyoid nerve,
which comes to lie between splenial and dentary.
An anterior mylohyoid foramen was not observed
in Python reticulatus (fmnh 31329); the nerve
passed through a notch on the posterior dorsal
margin of the splenial, as is also the case in Py-
thon sebae and Epicrates cenchris (Frazzetta,
1959).
The relatively large and L-shaped coronoid is
applied to the medial surface of the compound
bone, together with which it forms the prominent
coronoid process. All traces of a posteroventral
process of the coronoid have disappeared, and its
ventral margin therefore is straight (L97: char. 79;
LC98: char. BIO). The anteroventral process,
however, is well developed and broadly contacts
the dorsal margin of the angular. Anteriorly, this
process of the coronoid is developed into an an-
terodorsally pointing spur that overlaps the pos-
terodorsal corner of the splenial (L97: char. 75;
LC98: char. B14).
Superficially, the angular meets the splenial in
a vertical suture (L97: char. 74), which on the
medial margin of the mandible appears slightly
convex anteriorly (L97: char. 73; LC98: char.
B12). Disarticulation of the dentary and splenial
reveals two anterior prongs or processes of the
compound bone that, together with the anteriorly
projecting lateral margin of the angular, hold the
splenial in place. The larger of these processes is
located dorsomedially to Meckel's cartilage, pro-
jecting from the prearticular portion ventral and
deep to the anterodorsally projecting tip of the
coronoid. The smaller ventral process originates
from that portion of the compound bone that is
located ventromedial to Meckel's cartilage, and it
corresponds to the single anterior process of the
compound bone seen in Cylindrophis. In Python,
the ventromedial anterior process of the com-
pound bone is not complemented by an antero-
medial prong of the angular, as it is in Cylindro-
phis. The two medial processes of the compound
bone together with the laterally projecting edge of
the angular define a deep, essentially vertically
oriented trough into which slides the posterior
margin of the vertical lamina of the splenial. The
ventral portion of the anterior part of the angular
is broadened and forms a distinct socket on its
anterior surface. Into this socket fits the equally
thickened posteroventral head of the splenial. The
intramandibular joint as a whole has reached a
greater level of complexity in Python as compared
to Cylindrophis or uropeltids.
The adductor fossa forms a deep and wide
trough on the compound bone, with well-defined
lateral and medial margins. Of these, the medial
margin is lower than the lateral margin, such that
the adductor fossa opens dorsally and medially
(L97: char. 80; LC98: char. B15).
The lower jaw of basal erycines rather closely
matches the pattern established for Python. Li-
chanura trivirgata roseofusca (Fig. 12, fmnh
8043) and Charina bottae (Figs. 13C, 13D: fmnh
31300), but not Calabaria reinhardti (Figs. 13 A,
13B: fmnh 31372), show the development of a
distinct posterior process from the posterodorsal
corner of the intramandibular septum that sepa-
rates Meckel's groove from the canal for the su-
perior alveolar nerve. This process is only vesti-
gial in Python and Calabaria (Figs. 13 A, 13B),
but in Lichanura (Fig. 12) and Charina (Figs.
13C, 13D), it is distinct and comes to lie in a well-
delineated groove or facet on the medial aspect of
the anterior prong of the compound bone (suran-
gular portion) that supports the dentary, thus add-
ing to the firmness of the dentary suspension.
Only the lower jaw of Lichanura was disarticu-
Fig. 12. The lower jaw of Lichanura trivirgata roseofusca (fmnh 8043). A, lateral view; B, medial view; C,
postdentary bones, medial view; D, splenial, medial view; E, dentary, medial view; F, splenial, lateral view. Scale
bar = 2 mm. Abbreviations as in Figure 1.
20
FIELDIANA: GEOLOGY
B
VII hy
amf
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
21
B
D
Fig. 13. The lower jaw of Calabaria reinhardti (fmnh 31372: A, lateral view; B, medial view) and of Charina
bottae (fmnh 31300: C, lateral view; D, medial view). Scale bar = 2 mm. Abbreviations as in Figure 1.
lated (Fig. 12), and it revealed some differences
in the angular-splenial contact as compared to Py-
thon. As in the latter genus, an anterior medial
prong originates from the compound bone in a
position located dorsomedial to Meckel's cartilage
and medial to the surangular portion, distinctly
projecting beyond the anterior margin of the an-
gular. And again as in Python, a second anterior
medial prong originates from the compound bone
ventromedial to Meckel's cartilage, but whereas
this process remains very small in Python, it is
elaborated into a tall vertical flange in Lichanura
and establishes contact with the more dorsally lo-
cated anterior medial projection of the compound
bone (Fig. 12C). This arrangement results in a
combined anterior projection of the compound
bone medial to the angular, whereas the latter
shows an anteriorly projecting lateral margin.
Thus, the compound bone and the angular togeth-
er define a deep vertical trough, into which slides
the posterior margin of the posterior vertical lam-
ina of the splenial. The tall ventral part of the
22
FIELDIANA: GEOLOGY
medial anterior projection of the compound bone
carries a distinct notch at the depth of the trough
that is formed by itself and the anteriorly project-
ing lateral margin of the angular. Into that notch
fits the knoblike posterior head of the horizontal
crest that projects from the lateral surface of the
splenial (Fig. 12F).
The intramandibular joint of Boa constrictor
(Fig. 14, fmnh 22363) resembles that of Licha-
nura more closely than that of Python, although
important differences are also noted. As in other
macrostomatans, the dentary is again deeply bi-
furcated posteriorly. The two posterior prongs of
the dentary, together with the intramandibular
septum, form a recess that receives the strongly
developed anterior prong (surangular portion) of
the compound bone. As in Lichanura and Cha-
rina, the intramandibular septum forms a distinct
posteromedial projection. In Lichanura and Cha-
rina, this projection comes to lie in a facet on the
VII hy
B
pmf an
Fig. 14. The lower jaw of Boa constrictor imperator (fmnh 22363). A. postdcntary bones, medial view; B,
dentary, medial view; C, postdentary bones, medial view; D, splenial, lateral view. A, B, scale bar = 10 mm; C, D,
scale bar = 5 mm. Abbreviations as in Figure 1 .
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
23
medial aspect of the compound bone and itself
remains superficially exposed in medial view. In
Boa, this process forms a distinct facet on its me-
dial surface, which receives distinct anterior pro-
cesses of the coronoid and splenial.
Unlike in Python, the angular is applied to the
ventromedial surface of the compound bone, with
no exposure in lateral view of the lower jaw. Its
anterior end its thickened, and its anterior lateral
margin is projecting anteriorly. Superficially, the
angular meets the splenial in a sigmoidal suture.
Unlike in Python, the splenial carries a distinct
and pointed posterodorsal process that fits snugly
into a triangular recess formed by the anterior dor-
sal margin of the angular and the anterior end of
the compound bone (Figs. 14C, 14D).
Medial to the angular, the compound bone
forms a pointed, cup-shaped anterior projection
that, together with the anteriorly projecting lateral
margin of the angular, forms a deep trough that
receives the posterior end of the splenial. This ar-
rangement very closely resembles Lichanura ex-
cept for the fact that the two components (dorsal
and ventral) that form the anterior projection of
the compound bone deep to the angular in the
latter genus cannot be distinguished in Boa be-
cause they are completely fused. At the bottom of
the trough between the angular and the anterior
medial projection of the compound bone, the lat-
ter carries a very distinct notch. Unlike in Python,
but as in Lichanura, the splenial is pierced by the
anterior mylohyoid foramen in Boa. As in Li-
chanura, a very distinct lateral horizontal crest
develops from the lateral surface of the splenial
at the level just below the anterior mylohyoid fo-
ramen. Together with the ventral margin of the
splenial, this horizontal crest forms a groove that
receives the medially curved ventral margin of the
dentary. A ventral division of the anterior mylo-
hyoid nerve pierces the lateral horizontal shelf of
the splenial immediately lateral to the anterior
mylohyoid foramen. Unlike in Python, the pos-
terior end of the horizontal shelf of the splenial is
developed into a distinct articular knob, more dis-
tinctly so than in Lichanura, which fits into the
notch in the anterior medial projection of the com-
pound bone deep to the angular. Of all the snakes
described in this study, Boa shows the most com-
plex differentiation of the intramandibular joint.
The differences observed in the differentiation of
the intramandibular joint indicate that a broader
survey of its structure could reveal a number of
characters that might be useful in the analysis of
the interrelationships of basal snakes.
The Skull and Lower Jaw of
Pachyrhachis
In order to assess the phylogenetic relationships
of Pachyrhachis, it is necessary to revisit the mor-
phological description and cranial reconstruction
given by Caldwell and Lee (1997) and Lee and
Caldwell (1998). After the initial description of
the dorsal aspect of the skull (Haas, 1979), the
specimen was embedded in epoxy and the ventral
side of the skull was prepared and described
(Haas, 1980). The epoxy resin covering the dorsal
surface of the skull renders it difficult to assess
some morphological details. Parts of the skull are
poorly preserved, such as the nasal complex com-
prising the nasals, vomers, and septomaxillae, as
well as parts of the palate. In general, however,
the skull is fairly well known as far as it is pre-
served, and it will suffice in the present context
to review selected parts of its anatomy.
The interpretation of the circumorbital bones in
basal snakes has long been controversial (Haas,
1964, 1968), and Pachyrhachis is no exception
(L97: char. 23; LC98: chars. C7, D3). Haas (1979)
described three bones surrounding the orbit of Pa-
chyrhachis, a dorsally located postfrontal, a pos-
teriorly located postorbital, and an ectopterygoid
that appears to floor the orbit. Lee and Caldwell
(1998) considered Haas's (1979) postorbital to
represent a postorbital fused with a postfrontal,
the latter represented by an elongate anterior pro-
cess lining the dorsal margin of the orbit and not
indicated by Haas (1979). The postfrontal as iden-
tified by Haas (1979) was interpreted as a jugal
by Lee and Caldwell (1998).
Re-examination of the holotype of Pachyrhach-
is (Fig. 15) showed the postorbital to be a distinct
element applied to the lateral wing of the parietal
at the posterodorsal corner of the orbit, with a
ventral process forming an extensive postorbital
bar. The dorsal head of the postorbital is roughly
of a triradiate structure. There is a thickened an-
terodorsal head, which is sutured to the lateral end
of the posterior surface of the transverse ridge that
is developed on the anterior end of the parietal.
From the posterior margin of this dorsal articular
head projects a small yet distinct lappet, which is
applied against the laterodorsal surface of the lat-
eral parietal wing. Although the dorsal head of the
postorbital is smaller than it is in Python, its re-
lation to the parietal closely resembles the post-
orbital-parietal contact in the latter taxon.
At the dorsal margin of the right orbit, an elon-
gate element is exposed that was interpreted as
24
FIELDIANA: GEOLOGY
the postfrontal by Lee and Caldwell (1998), who
thought it was originally fused to the postorbital
and would have lined the dorsal margin of the
orbit. Closer inspection reveals, however, that this
bony element represents a sheet of bone that ex-
poses its lateral edge dorsally and dips medially
as it disappears below the parietal. The bone in
question passes below the lateral wing of the pa-
rietal and below the proximal head of the post-
orbital. As such, it cannot represent a postfrontal,
which would originally have been fused to the
postorbital, but rather corresponds to a broken
part of the laterally descending flange of the pa-
rietal. We therefore conclude that Pachyrhachis
lacked a postfrontal.
As preserved, the ventral tip of the postorbital
is pushed against the posterior end of an elongated
element that lies in the floor of the orbit on top
of the posterior end of the maxilla, pointing an-
teromedially (the postfrontal of Haas, 1979). This
element was interpreted as a jugal by Lee and
Caldwell (1998), which would appear reasonable,
given its topological relation relative to the max-
illa and postorbital and its location mostly in front
of the latter element (L97: char. 29; LC98: char.
Dl). However, the element in question shows a
distinct broadening of its anterior end, whereas a
jugal would be expected to have a tapering ante-
rior process lining the ventral margin of the orbit.
For this reason, the element in question could just
as well be interpreted as the anterior end of an
ectopterygoid that has been broken across the
posterior end of the maxilla upon dorsoventral
compression of the skull during fossilization. We
favor this latter interpretation because it is also
supported by parsimony analysis.
The parietal of Pachyrhachis is pythonomorph
in that there is a distinct transverse ridge on its
anterior end from which originates a sagittal crest
that extends posteriorly (L97: char. 19; LC98:
char. C21). The sagittal crest ends in a knoblike
projection (the supraoccipital of Haas, 1979),
which indicates that the parietal overhung a ver-
tically oriented supraoccipital, just as in Python.
The dorsolateral surface of the parietal supports
the elongate supratemporals (L97: chars. 25-27;
LC98: chars. C5, El), which have free-ending
posterior processes from which the quadrates are
suspended (Haas, 1979; Lee & Caldwell, 1998).
The quadrate of Pachyrhachis is autapomorphous
as it develops a broad anterior lateral extension.
The mandibular condyle of the right quadrate is
preserved in articulation with the right mandible,
and the cephalic condyle of the same quadrate is
in articulation with the posterior tip of the supra-
temporal. From the posterior margin of the right
quadrate there projects a distinct medial flange,
positioned at a right angle to the broad anterior
lateral extension of the quadrate. This posterior
medial flange is most prominently developed
shortly above the mandibular condyle, but it re-
cedes along the upper half of the posterior margin
of the quadrate, tapering off toward the cephalic
condyle. The medial surface of the broad anterior
lateral extension of the quadrate shows a weakly
developed ridge that trends from the anterodorsal
corner in a posteroventral direction toward the
medially projecting shelf. Below this ridge there
is a shallow groove against which the quadrate
ramus of the pterygoid is articulated as it extends
toward the mandibular condyle of the quadrate.
Above this ridge on the medial surface of the
quadrate, between it and the medial flange pro-
jecting from the posterior margin of the latter, is
located a shallow yet distinct notch that must have
received the cartilaginous distal end of the stapes.
The medial flange projecting from the posterior
margin of the quadrate may therefore, in part at
least, correspond to the stylohyoideal process on
the quadrate of snakes. The morphology of Pa-
chyrhachis is again fairly closely comparable to
that of Python, except that the stylohyoideal pro-
cess is better defined as it projects from the pos-
terior medial margin of the quadrate in Python.
Also, the contact between stapes and quadrate
seems to be in a more ventral position in Pachy-
rhachis as compared to Python. However, the sta-
pes-quadrate articulation of Pachyrhachis is dis-
tinctly different from the morphology observed in
mosasaurs or in basal alethinophidian snakes such
as anilioids (L97: 45).
The shaft of the right stapes of Pachyrhachis is
well preserved as it projects laterally from below
the pterygoid between the quadrate posteriorly
and the coronoid anteriorly. This element was
identified as a supratemporal by Haas (1980) but
as a questionable squamosal by Lee and Caldwell
(1998). This slender blade of bone cannot repre-
sent the supratemporal, as the latter is seen in ar-
ticulation with the cephalic condyle of the quad-
rate. Its identification as a possible squamosal fol-
lowed from the fact that Lee and Caldwell (1998)
interpreted another rod-shaped element as the sta-
pes. According to their interpretation, the stapes
would project posteriorly, emerging from between
the posterior tips of the quadrate ramus of the
pterygoid and the supratemporal, respectively. For
most of its exposed part, this latter element ap-
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
25
I
I
26
FIELDIANA: GEOLOGY
pears rod-shaped indeed, but it quickly broadens
anteriorly, as is also particularly well shown (on
both sides of the skull) on radiographs. In fact,
the stapes as identified by Lee and Caldwell
(1998) represents a posterior opisthotic process
that forms a rudimentary paroccipital process, as
is developed in some basal macrostomatans such
as Python. A comparable paroccipital process is
absent in scolecophidians and anilioids. Also, the
distal end of the stapes of Pachyrhachis forms an
elongate, slender, and flattened blade of bone, as
is again seen in some basal macrostomatans such
as Python but which is different from the short
and robust stapedial shaft characteristic of anilioid
snakes.
Little detail can be identified in the dermal pal-
ate and basicranium of Pachyrhachis beyond the
general contours of the pterygoids and the elon-
gate dentigerous processes of the palatines. How-
ever, both lower jaws are comparatively well pre-
served (Fig. 16) and have been described as being
closely similar to the mandibles of mosasauroids
(Lee & Caldwell, 1998). The Meckelian canal
would be located on the medial surface of the
dentary (L97: char. 69; LC98: char. B13), the an-
terior tip of the splenial would again be located
on the medial aspect of the dentary (L97: char.
70), and the splenial would meet the angular in a
vertical suture indicative of intramandibular mo-
bility (L97: chars. 73, 74; LC98: char. B12). The
coronoid carries a short posteroventral process
(L97: char. 78; LC98: char. BIO) and a long an-
teroventral process, which is reconstructed by Lee
and Caldwell (1998) to contact the splenial (L97:
char. 75; LC98: char. B14).
In fact, the illustration given by Lee and Cald-
well (1998, Fig. 4) shows an elongated angular in
an overlapping contact with a broad splenial in
the right mandible. In the left mandible, the splen-
ial is shown in a position medial to the dentary,
but its posterior margin forms a vertical suture
with the compound bone rather than with the an-
gular, from which it remains separated.
In the ventral view of the specimen, the com-
pound bone of the left mandible is preserved in
medial view. The adductor fossa on its posterior
end faces medially and shows a sharp medial mar-
gin almost as high as the lateral margin. In front
of the adductor fossa, the dorsomedial margin of
the compound bone is lined by an elongate ante-
rior process of the coronoid, which posteriorly is
developed into the large coronoid process auta-
pomorphic for Pachyrhachis. As in other snakes,
the coronoid is applied to the medial side of the
compound bone rather than straddling the dorsal
margin of the surangular, as is characteristic of
nonophidian squamates. The dentary of the left
mandible is crushed but exposed in ventral view.
Meckel's canal is well exposed toward the ante-
rior end of the dentary, and it is bordered on both
sides by sharp edges. This indicates that Meckel's
canal originally opened ventrally relative to the
sagittal plane of the lower jaw, as is characteristic
of other snakes as well. However, the lateral and
medial components of the dentary surrounding
Meckel's canal have been crushed, as the ventro-
lateral marginal zone of the dentary can be seen
to be broken off from the rest of the bone and
flipped medially. This morphology is not compa-
rable to the mosasaur jaw, where Meckel's canal
forms a sulcus with smooth, rounded margins on
the medial surface of the dentary.
Lee and Caldwell (1998) identified a remnant
of the angular along the ventral margin of the left
mandible, although it is represented by nothing
more than a broken splint of bone and remains
separated from the supposed splenial by what ap-
pears to be the compound bone. By comparison
to the right mandible, the angular thus identified
appears to be too narrow, and the bone in question
appears to be a crushed remnant of the postero-
ventral process of the dentary instead. By con-
trast, there is what appears to be a V-shaped su-
ture line, the apex pointing backward, on the me-
dial surface of the mandible somewhat in front of
the posterior end of the coronoid, which may de-
lineate the posterior end of the angular. If cor-
rectly identified, the angular represents a relative-
ly broad, elongate, platelike element comparable
to, yet somewhat wider than, the corresponding
element of the right mandible. If correctly iden-
tified, the angular of Pachyrhachis would have to
Fig. 15. A, radiograph of the skull of the fossil snake Pachyrhachis problematicus Haas from the lower Middle
Cretaceous of Ein Jabrud; B, the right orbit of Pachyrhachis and its surrounding bones in dorsal view; C. the left
suspensorium of Pachyrhachis in ventral view. A, scale bar = 20 mm; B, C, scale bar = 5 mm. Abbreviations: c,
coronoid; ec, ectopterygoid; f, frontal; f.stp, facet for stapes; md, mandible: op. opisthotic; p. parietal; po, postorbital;
pt, pterygoid; q, quadrate st, supratemporal; stp, stapes.
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
27
an?
Fig. 16. The mandibles of Pachyrhachis problematicus Haas as exposed on the ventral side of the specimen. A,
left lower jaw; B, right lower jaw. Scale bar = 5 mm. Abbreviations as in Figure 1.
be reconstructed in broad sutural contact with the
coronoid.
Following the angular anteriorly, the relation-
ships of the elements of the lower jaw become
more obscured by extensive breakage. There is an
anteriorly tapering structure pressed between the
lateral and medial margins of Meckel's canal that,
in its totality, could represent the angular in artic-
ulation with the splenial. However, the vertical
posterior end of the splenial, shown in articulation
with the compound bone by Lee and Caldwell
(1998, Fig. 4), appears to represent a break. Fur-
thermore, the anterior tip of the supposed splenial
is separated from the dentary along the dorsal
margin of Meckel's canal by what appears to be
a very delicate fracture rather than a suture. But
even if this were a suture, the splenial would be
associated with the wrong (dorsal) margin of
Meckel's canal by comparison with other squa-
mates. The exact nature of the angular-splenial
contact cannot be unequivocally established on
the left mandible. Also, a posterior mylohyoid fo-
ramen cannot be identified on the left angular in
a comparable position to the one on the right el-
ement, although it might be represented by a fo-
ramen located more anteriorly in a depression.
The morphology and relations of the angular and
splenial are better preserved and more fully ex-
posed on the right mandible.
The preservation of the right mandible is more
complicated, but the compound bone is preserved
in more or less straight ventral view (the adductor
fossa facing upward), and it is exposed to a level
far anterior along the lower jaw. The dentary has
been twisted during dorsoventral compression of
the skull due to the overlying maxilla. The lateral
surface of the dentary is therefore more or less
exposed in the ventral view of the specimen.
There is no indication of a shallow Meckelian
groove on the anterior end of the dentary, as is
illustrated by Lee and Caldwell (1998, Fig. 4b).
Two elongated elements are located along the me-
dial margin of the compound bone and have been
interpreted as angular and splenial by Haas (1980)
and Lee and Caldwell (1998). The posterior one
of these two elements is a fairly broad and elon-
gate, platelike angular with a slightly concave
ventral margin and a broken posterior end. The
posterior mylohyoid foramen is located somewhat
in front of its midpoint. The anterior end forms a
distinct and pointed anteroventral projection that
overlaps the posterior margin of the adjacent el-
28
FIELDIANA: GEOLOGY
ement, the splenial. Above this anteroventral pro-
jection, the sloping anterior margin of the angular
is distinctly notched and thus forms the posterior
margin of the anterior mylohyoid foramen, which
is completed anteriorly by the splenial.
The splenial is an unusually broad element that
has been preserved with a broken anterior tip. It
seems to taper in its anteriormost part only and
must have reached far anteriorly along the ventral
margin of the lower jaw. It remains unclear
whether a splint of bone lying alongside the den-
tary represents the thin anterior extremity of the
splenial. But even if this possibility is discounted,
the splenial of Pachyrhachis reaches further an-
teriorly than is typical of basal alethinophidians
and hence is a character that the latter genus
shares with macrostomatans. Pachyrhachis is au-
tapomorphous, however, with respect to the broad,
platelike appearance of the angular and splenial.
The two elements also do not meet in a vertical
suture but in an overlapping contact, which fur-
thermore appears to enclose the anterior mylo-
hyoid foramen.
Another matter of debate is the number of men-
tal foramina present in the dentary of Pachy-
rhachis (L97: char. 76; LC98: char. C14). Non-
ophidian squamates typically have a series of
mental foramina lining the dentary below the
tooth row. By contrast, snakes have a single men-
tal foramen located toward the anterior tip of the
dentary. Pachyrhachis was described as retaining
two mental foramina, another supposedly primi-
tive character of the genus (Lee & Caldwell,
1998).
There is no indication of any foramen on the
damaged lateral surface of the right dentary (ex-
posed in the ventral view of the skull). By con-
trast, two foramina appear to be located toward
the anterior end of the left dentary, exposed in the
dorsal aspect of the specimen, which is now em-
bedded in epoxy. Of these, the smaller posterior
one is an undisputed mental foramen; it is also
clearly identifiable in the photograph published by
Haas (1979, Fig. 6B). By contrast, the position of
the larger anterior foramen corresponds to a notch
in the eroded ventrolateral margin of the dentary
in the photograph, which shows the specimen be-
fore it was embedded in epoxy (Haas, 1979, Fig.
6B). Indeed, the erosion of the margin of the den-
tary is obscured by the epoxy, on the "ventral"
(lower) surface of which a thin film of matrix was
left in place, lining the dentary and suggesting a
complete lateral (ventral) margin of the supposed
foramen. The bone surface is easily distinguished
from the film of matrix, however, not only by its
shiny appearance but also by a reddish hue that
is absent in the matrix. The impression of a fo-
ramen is further reinforced by a bubble, which
appears to have formed in the notch of the eroded
margin of the dentary as it was embedded in ep-
oxy. In conclusion, Pachyrhachis is characterized
by the presence of a single mental foramen, as is
characteristic of all snakes.
Character Evidence for the
M onophyly of the Pythonomorpha
The monophyly of the Pythonomorpha, with
Pachyrhachis as intermediate between mosasau-
roids and snakes, has recently been supported by
a global analysis of squamate interrelationships
(Lee, 1998). In this section, we review the char-
acter evidence used by Lee (1998; see this paper
for the primary sources of characters, if applica-
ble, and a discussion of characters other than the
comments below) for the analysis of squamate in-
terrelationships. For readers who do not have Lee
(1998) at their disposal, we give an abbreviated
definition of each character as conceived by Lee
(1998). Subtleties of character definitions may be
lost in our rendering, and the reader is encouraged
to refer to Lee (1998) to avoid possible misun-
derstandings. Our review of this data set (Table 1 ,
pp. 50 ff.) is not intended to provide a better un-
derstanding of global squamate relationships but
rather to test the monophyly of the Pythonomor-
pha on the same grounds on which it was pro-
posed. If Pachyrhachis is indeed the link between
mosasauroids and snakes, the consequence could
be that snakes have had a marine origin and that
the fossorial ecomorph evolved independently
among nonophidian squamates and within snakes
(Lee, 1998; Scanlon et al., 1999). Our review
therefore focuses on those characters that are rel-
evant to the placement of Pachyrhachis and to the
potential phylogenetic relationships of snakes
with varanoid lizards (including mosasauroids),
on the one hand, or with amphisbaenians and di-
bamids on the other.
Character 1: Premaxillary palatal foramina pres-
ent (0), absent (1). As defined by Lee (1998),
the premaxillary foramina in nonophidian squa-
mates are synonymized with the premaxillary
channels of snakes (see Kluge, 1989, for ter-
minology).
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
29
Character 2: Premaxillary lateral foramina present
(0), absent (1). There are no such lateral premax-
illary foramina in snakes, which therefore cannot
be compared and are coded as unknown (?).
Character 3: Premaxilla-maxilla contact sutural
(0), nonsutural (1).
Character 4: Alveolar ridge of maxilla straight
(0), upturned at anterior end (1).
Character 5: Dorsal process of maxilla at or in
front of (0) or behind ( 1 ) midpoint of maxilla.
The character is redundant, as it combines the
information of a retracted naris (character 16)
and the degree of posterior extension of the
maxilla below the orbit (character 7). Pachy-
rhachis is miscoded: if Lee and Caldwell's
(1998) description is correct, the maxillary-pre-
frontal contact is autapomorphic for this taxon.
However, personal inspection of the holotype
suggests (especially on the left side of skull)
that the "dorsal process of the maxilla" is, in
fact, the anterior portion of the prefrontal of
similar proportions as seen in anilioids. We
therefore code Pachyrhachis 0.
Character 6: Dorsal process of maxilla extends
dorsomedially (0), dorsolateral^ (1).
Character 7: Posterior process of maxilla long
(0), short (1).
Character 8: Lacrimal present (0), absent (1).
Character 9: Lacrimal separate (0), fused with
prefrontal (1).
Character 10: Lacrimal foramen single (0), dou-
ble (1).
Character 11: Lacrimal foramen at least partly
bordered by facial elements (0), entirely within
prefrontal (1). The primitive position of the lac-
rimal foramen in squamates is between the lac-
rimal and the prefrontal. Since snakes lack a
lacrimal, the lacrimal foramen lies between the
maxilla and the prefrontal for those terminals
we included. We have been unable to verify
Lee's (1998) assessment of the position of the
lacrimal foramen in mosasaurs (Camp, 1942;
Russell, 1967), but if he is correct, the position
of the lacrimal within the prefrontal would be
autapomorphic for mosasaurs. As such, the
character is uninformative and hence is deleted.
Character 12: Jugal present (0), absent (1). Per-
sonal investigation of the holotype of Pachy-
rhachis indicates that the jugal sensu Lee and
Caldwell (1998) most probably represents the
anterior end of the ectopterygoid, which broad-
ly overlaps the posterior end of the maxilla. The
ectopterygoid of Pachyrhachis appears to be
broken across the posterior end of the maxilla
on both sides of the skull, a consequence of the
dorso ventral compression of the skull. Dinilysia
has also been described with a jugal (Estes et
al., 1970), an assessment that has been ques-
tioned by Lee (1998). We have coded Dinilysia
with or without jugal in separate analyses to test
the effect of either assumption. Character 12
codes Dinilysia with a jugal (0), whereas char-
acter 142 codes Dinilysia without a jugal (1).
Using either one of these characters requires de-
letion of the alternative.
Character 13: Jugal does not (0), does (1) extend
anteriorly beyond midpoint of orbit. This char-
acter again could not be coded accurately for
Dinilysia because of the poor preservation of
the bone identified as a jugal (Estes et al.,
1970).
Character 14: Nasals paired (0), fused (1). Va-
ranus should be coded polymorphic for this
character until the derived nature of paired na-
sals is confirmed by cladistic analysis of var-
anid interrelationships. Scolecophidians are
polymorphic in this character. The nasal(s) of
Pachyrhachis is/are not known.
Character 15: Nasal-prefrontal contact present
(0), absent (1).
Character 16: External naris not retracted (0),
slightly retracted (1; frontal excluded), strongly
retracted (2; frontal enters external naris). Lan-
thanotus has to be coded 1 (Rieppel, 1983) or
polymorphic. The nature of the external naris is
not known in Pachyrhachis (?), although it is
most conceivable that it was retracted. Lee
(1998) coded snakes 1 for this (ordered) mul-
tistate character, but exclusion of the frontal
from the posteriorly retracted external naris is
most probably a reversal due to the burrowing
habits of scolecophidians and anilioids.
Character 17: Prefrontal smooth (0), rugose (1)
at orbital margin.
30
FIELDIANA: GEOLOGY
Character 18: Frontal(s) single (0), paired ( 1 ).
Character 19: Frontal with straight or weakly
concave (0), strongly concave (1) lateral mar-
gin. Lee (1998) coded Varanus 1 for a deeply
concave orbital margin of the frontal, yet coded
mosasaurs 0 for a slightly concave orbital mar-
gin. In fact, the concavity of the orbital margin
of the frontal is closely comparable in both
groups (1) (Russell, 1967, Fig. 83). A straight
frontal margin is derived within mosasaurs
(Bell, 1997).
Character 20: Frontal flange underlying nasal ab-
sent (0), present (1).
Character 21: Frontoparietal suture complex, in-
terdigitating (0), simple, straight transverse line
(1). We propose a redefinition of this character
as follows: Superficial delineation of frontopa-
rietal suture complex and distinctly interdigitat-
ing (0), essentially a straight transverse line ( 1 ),
frontal invading parietal (2), frontals postero-
lateral^ embraced by parietal (3). Nonophidian
squamates have a frontoparietal suture that su-
perficially forms a more or less straight line (1).
In mosasaurs, the frontal tends to develop pos-
terior processes of variable shape overlapping
the parietal (2) (Bell, 1997). In basal snakes
(Anilioidea), the parietal tends to form antero-
lateral processes embracing the frontals in a
curved suture (3). Scolecophidians (Haas, 1964,
1968; List, 1966) are polymorphic in this char-
acter (1 and 3). Anelytropsis shows character
state 1 (Greer, 1985), but Dibamus (Rieppel,
1984b; not Anelytropsis: Greer, 1985) shows
character state 3. Most amphisbaenians show
state 0. Pachyrhachis has state 1.
Character 22: Frontal enters (0), is excluded ( 1 )
from dorsal margin of orbit. Pachyrhachis has
to be coded as unknown (?) for this character
due to the uncertain nature of the splint of bone
exposed at the dorsal margin of the right orbit
(see discussion of character 24, below). Dini-
lysia is coded 0. This character is not applicable
to scolecophidians (?).
Character 23: Postfrontal large (0), small ( 1 ), ab-
sent (2). This character is partially redundant
with some of the following. We retain it as cod-
ed by Lee (1998) except in Pachyrhachis and
snakes, which we interpret as lacking a discrete
postfrontal (2). Pachyrhachis is coded as un-
known (see discussion of character 24, below).
Character 24: Postfrontal separate (0), fused to
postorbital in adult ( 1 ). This character is prob-
lematic, as it makes assumptions about ontog-
eny in fossils. By comparison to Varanus, we
agree that the postfrontal and postorbital fuse to
form a postorbitofrontal in mosasaurs (Bell,
1997). However, Lee (1998) codes Pachyrhach-
is for a fused postorbitofrontal. This coding is
based on the assumption (Lee & Caldwell,
1998) that a splint of bone exposed at the dorsal
margin of the right orbit of the holotype of Pa-
chyrhachis is the anterior process of the post-
frontal, which establishes a contact with the
prefrontal at the dorsal margin of the orbit (not
present in Varanus or mosasaurs). Alternative
interpretations would be to identify this splint
of bone as postfrontal, separate from the post-
orbital, or to identify this splint of bone as a
supraorbital (present in Python [Frazzetta,
1959], with which Pachyrhachis shares the
crested anterior end of the parietal), lying in
front of the postorbital. Re-examination of the
holotype of Pachyrhachis suggests, however,
that neither of these interpretations is correct,
as the fragment of bone exposed at the dorsal
margin of the orbit seems to be a splint of the
laterally descending flange of the parietal (see
above). Given the uncertainty of interpretation,
we conservatively code Pachyrhachis as un-
known (?) for this character (as well as for char-
acters 22 and 23). Other snakes lack the post-
frontal and hence are not comparable (?). Bau-
meister (1908) found a sutural separation of the
anterolateral process of the parietal that lines
the dorsal margin of the orbit in a uropeltid
(Rhinophis) and considered this process to rep-
resent the postfrontal. Although accepted by
Rieppel (1977), we here discard this interpre-
tation until the observation of Baumeister
(1908) is independently corroborated.
Character 25: Postfrontal not forked (0), forked
(1) medially. The postfrontal (postorbitofrontal)
is forked dorsally, i.e., clasps the frontoparietal
suture in all nonophidian squamates that retain
the mesokinetic axis (Rieppel, 1984b), includ-
ing mosasaurs. Snakes lack a postfrontal, but in
Python, the dorsal end of the postorbital is
forked, without, however, clasping the fronto-
parietal suture. This morphology is approached
by Pachyrhachis.
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
31
Character 26: Palpebral ossification absent (0),
present (1).
Character 27: Postorbital present (0), absent (1).
This character is difficult to interpret without
adding the specification of whether the post-
frontal is present or absent as a discrete ossifi-
cation (redundant with character 24). However,
as coded by Lee (1998), the character has no
bearing on snake relationships and therefore is
retained unchanged.
Character 28: Ventral process of postorbital long
(0), short (1).
Character 29: Posterior margin of orbit complete
(0), with small gap (1), with large gap (2). Be-
cause we interpret the jugal of Pachyrhachis as
an ectopterygoid, it becomes impossible to de-
cide whether Pachyrhachis has a complete or
an incomplete postorbital arch. Yet the taxon
shows a long ventral process of the postorbital,
for which reason we code the taxon as 1.
Character 30: Parietal(s) paired (0), fused (1).
Character 31: Parietal tabs (triangular flanges ex-
tending anteriorly into fossae on ventral surface
of frontals) present (0), absent (1). We have
some difficulty understanding this character. In
Varanus, the parietal bears lateral tabs project-
ing anteriorly that overlap a facet on the frontal
as part of the mesokinetic joint (Rieppel,
1979a). A similar relation of these bones, but
not as strongly expressed as in Varanus, is seen
in other nonophidian squamates. This character
is absent, however, in Platecarpus (amnh
04909) and in other mosasaurs (Bell, 1977).
Comparable anterolateral tabs of the parietal ar-
ticulating in a facet on the frontal are also ab-
sent in snakes (including Pachyrhachis), am-
phisbaenians, or dibamids, which also have lost
mesokinesis! However, given our difficulty in
understanding Lee's (1998) character definition,
we retain the coding he chose for this character.
Character 32: Parietal half as long as skull or
shorter (0), longer (1) than half of skull length.
Character 33: Pineal foramen present (0), absent
(1).
Character 34: Pineal foramen within parietal (0),
on frontoparietal suture (1), within frontal (2).
Character 35: Origin of jaw adductor muscles re-
stricted to ventral surface (0), invades dorsal
surface (1) of parietal. This character overlaps
with character 57. For reasons discussed below
(character 57), we retain this character in our
analysis but delete character 57.
Character 36: Supraoccipital exposed in dorsal
view (0), concealed in dorsal view (1) by pa-
rietal.
Character 37: Posterolateral process of parietal
distinct (0), short or absent (1).
Character 38: Upper temporal arch complete (0),
incomplete (1).
Character 39: Jugal does not (0), does (1) contact
squamosal.
Character 40: Squamosal present (0), absent (1).
Pachyrhachis is coded for presence of a squa-
mosal, but personal inspection of the holotype
confirmed that the squamosal identified by Lee
and Caldwell (1998) is, in fact, the stapes and
that the stapes identified by Lee and Caldwell
(1998) is, in fact, a posterior opisthotic (par-
occipital) process, which is also present in a
variety of basal macrostomatans (Zaher, 1998;
see also Frazzetta, 1959). The squamosal is ab-
sent in Pachyrhachis (1).
Character 41: Dorsal process of squamosal pre-
sent (0), absent (1). This character is not appli-
cable to Pachyrhachis given the reassessment
of the previous character.
Character 42: Upper temporal fenestra not re-
stricted (0), restricted (1) by postorbital.
Character 43: Upper temporal fenestra not re-
stricted (0), restricted (1) by postf rental.
Characters 42^3: These characters were coded
0 for Pachyrhachis and snakes by Lee (1998),
when in fact they are not applicable to these
taxa (?).
Character 44: Supratemporal absent (0), present
(1).
Character 45: Supratemporal on dorsolateral (0),
ventrolateral (1) surface of parietal.
32
FIELDIANA: GEOLOGY
Character 46: Supratemporal confined to skull
roof (0), forms part of paroccipital process and/
or braincase ( 1 ). In nonophidian squamates, the
supratemporal may or may not contact the distal
end of the paroccipital process. The posterior
tip of the supratemporal establishes a broad
contact with the distal tip of the opisthotic in
Varanus and a somewhat more extended but
otherwise identical contact in mosasaurs (Riep-
pel & Zaher, in press). In snakes, the paroccip-
ital process is much reduced. If present, it cor-
responds to a small posterior projection of the
opisthotic as seen in some basal macrostoma-
tans, and it is not in contact with the supratem-
poral (although the slight mobility of the supra-
temporal may change these relations in dried
skulls). Such a paroccipital process is present
in Pachyrhachis, but its relations to the supra-
temporal are obscured through dorsoventral
crushing of the skull. The posterior tip of the
opisthotic (stapes of Lee & Caldwell, 1998) is
separate from the supratemporal, however,
which indicates lack of a contact. In no case is
the supratemporal (a dermal element) part of
the braincase (endocranium), although the su-
pratemporal may be superimposed on braincase
elements. We conclude that Pachyrhachis and
snakes have to be coded 0 for this character.
Character 47: Supratemporal less than half (0), at
least half (1) of maximum skull width. This
character is misleadingly coded for mosasaurs
by Lee (1998). In a skull roof of Platecarpus
(amnh 01820), the supratemporal is less than
half the maximum width of the skull. This is
also the case for other mosasaurs (Camp, 1942;
Russell, 1967). In basal snakes, the supratem-
poral is absent or small (scolecophidians and
anilioids); it is also small or absent in dibamids
and amphisbaenians. In macrostomatans, the
supratemporal is elongated and carries a free-
ending posterior process, as it also does in Pa-
chyrhachis (Zaher, 1998). We therefore propose
to modify this character in order to account for
the presence of a free-ending posterior process
of the supratemporal in Pachyrhachis and ma-
crostomatans: supratemporal without (0) or
with ( 1 ) free-ending posterior process.
Character 48: Supratemporal does not (0), does
(1) contact prootic. In Varanus, the posterior tip
of the supratemporal lies against the lateral sur-
face of the opisthotic at the distal tip of the
paroccipital process and is in a loose syndes-
motic connection with the prootic. In mosa-
saurs, the posterior tip of the supratemporal is
somewhat expanded and forms a deeply inter-
digitating suture with the prootic (Rieppel &
Zaher, in press). In snakes, the supratemporal
shows very different relations. Due to the rel-
ative size increase of the braincase (Rieppel,
1984b), the latter comes to lie in the same plane
as the dermatocranium (rather than being sus-
pended within it. as in mosasaurs and other
nonophidian squamates). The supratemporal
thus comes to lie on top of the otic capsule,
lateral to the reduced posterolateral (supratem-
poral) processes of the parietal, which in turn
also lie on top of the otic capsule. The prootic-
supratemporal contact in snakes (including Pa-
chyrhachis) is therefore the result of a funda-
mentally different remodeling of the snake skull
(Rieppel, 1984b; Rieppel & Zaher, in press) and
is not comparable to the morphology seen in
mosasaurs and Varanus. We therefore delete
this character from the analysis (the coding re-
tained in the data matrix is that of Lee, 1998).
Character 49: Quadrate monimostylic (0), strep-
tostylic and suspended from supratemporal,
squamosal, and opisthotic ( 1 ), suspended main-
ly from supratemporal (2), suspended mainly
from opisthotic (3), suspended mainly from
squamosal (4). As worded by Lee (1998), the
definition of this character is somewhat confus-
ing. It remains unclear whether character state
1 requires equal participation of the supratem-
poral, squamosal, and opisthotic in the quadrate
suspension and whether character state 2 does
or does not allow some participation of the
squamosal and opisthotic in the quadrate sus-
pension. As shown by Russell (1967, Fig. 20;
see also Rieppel & Zaher, in press), the relation
of the paroccipital process (opisthotic) to the
supratemporal, squamosal, and quadrate is
closely similar in mosasaurs and Varanus,
where the quadrate articulates with the ventro-
lateral surface of the distal tip of the paroccip-
ital process by means of an intercalary carti-
lage. We therefore code mosasaurs as having a
squamosal-supratemporal-opisthotic articula-
tion of the quadrate (see also Camp. 1942. p.
35).
Character 50: Quadrate shaft slanting strongly
anteroventrally. almost horizontal (0). slanting
slightly anteroventrally or vertical ( 1 ). slanting
slightly or greatly posteroventrally (2). We re-
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
33
define this character as quadrate slanting
strongly anteroventrally, almost horizontal (0),
slanting slightly anteroventrally (1), positioned
vertically (2), or slanting posteroventrally (3).
These character states reflect an ontogenetic
transformation (Bellairs & Kamal, 1981), and
their assessment therefore requires that adult
material be examined. A posteroventrally slant-
ing quadrate has been designated a macrosto-
matan character (Rieppel, 1988), and although
the reconstructions of Pachyrhachis provided
by Lee and Caldwell (1998) show a vertically
positioned quadrate, it may have had a postero-
ventrally slanting quadrate in life. As preserved,
the quadrates extend posterolaterally from their
articulation with the supratemporal, yet the tip
of the right lower jaw still reaches the anterior
tip of the right maxilla, which indicates that the
quadrate and mandible have been shifted slight-
ly forward. We accordingly code Pachyrhachis
for a posteroventrally sloping quadrate (3).
Character 51: Tympanic crest on quadrate well
developed (0), weakly developed (1), absent
(2). We code Varanus 1 for a reduced tympanic
crest, not 0 for a prominently developed tym-
panic crest, as coded by Lee (1998).
Character 52: Quadrate with (0), without (1) an-
teromedial lappet.
Character 53: Orbitonasal fenestra wide (0), nar-
row (1).
Character 54: Ventromedial processes of frontal
end free ventrally (0), abutting or sutured to
each other below olfactory tracts (1), contact
parabasisphenoid (2). As worded by Lee
(1998), this character would refer to medially
descending flanges of the frontal. These are an
autapomorphy of alethinophidians (our charac-
ter 231), however, which is why we believe that
Lee (1998) is, in fact, referring to laterally de-
scending frontal flanges. In amphisbaenians, the
lateral ventral flanges of the frontals meet each
other and contact the orbitosphenoid ventrally.
The coding retained in the data matrix is that
of Lee (1998).
Character 55: Orbitosphenoid absent (0), present
(1). This character is an autapomorphy of Am-
phisbaenia and, as coded by Lee (1998), groups
Sineoamphisbaena with amphisbaenians. Its
presence in Sineoamphisbaena must be critical-
ly assessed (see character 59).
Character 56: Parietal downgrowths absent or
weak (0), prominent (1). The well-preserved
parietal of Platecarpus (amnh 01563) is closely
comparable to that of Varanus. Mosasaurs are
here coded 0.
Character 57: Parietal downgrowths pointed ven-
trally (0), sheetlike (1). Following the character
definition of Lee (1998), mosasaurs as well as
all varanoids should be coded 1. However, as
we understand it, we believe this character is
misleading. The parietal may have laterally de-
scending flanges or not: If such flanges are ab-
sent, the jaw adductors originate from the ven-
tral surface of the parietal only. If such flanges
are present, the jaw adductors "migrate" onto
the "dorsal surface" of the parietal (Estes et al.,
1988), i.e., they invade the lateral surface of
these flanges. This is the same character as
character 35. Another character is the presence
or absence of a distinct ventral projection from
the parietal as seen in some "lizards" such as
skinks (Greer, 1970). Redefined along these
lines, the character loses its importance for the
analysis of snake-mosasaur relationships and is
hence deleted from the analysis (the coding re-
tained in the data matrix is that of Lee, 1998).
Character 58: Parietal-prootic contact absent or
restricted (0), extensive (1). We believe this
character to be poorly defined. Nonophidian
squamates in general, mosasaurs included, have
an alar process of the prootic made of Zuwachs-
knochen sensu Starck (1979; the term Zuwachs-
knochen refers to a membrane bone extension
added to an element, the rest of which is pre-
formed in cartilage) that contacts the parietal.
Dibamids (Rieppel, 1984a; Greer, 1985), am-
phisbaenians (Montero et al., 1999, contra
Rieppel, 1984a), and snakes lack the alar pro-
cess of the prootic, which is also absent in
Sphenodon. They also have an extensive pari-
etal-prootic contact. We therefore redefine this
character as alar process on prootic absent (0),
or present (1).
Character 59: Parietal downgrowths end free ven-
trally (0), contact parabasisphenoid (1), contact
orbitosphenoid (2). Pachyrhachis should tech-
nically be coded as unknown (?), although we
agree to code it 1. As such, character state 1 is
34
FIELDIANA: GEOLOGY
a synapomorphy of snakes. The coding used
here for Sineoamphisbaena is the same as in
Lee (1998), although the presence of an orbi-
tosphenoid and its relations to the parietal need
to be critically reassessed in this taxon (M.
Kearney, personal communication).
Character 60: Optic foramen not enclosed by
bone (0), enclosed partially or entirely by fron-
tal (1), enclosed by orbitosphenoid (2). We be-
lieve that this character has to be broken down
in order to account for the different positions of
the optic foramen in scolecophidians, henophi-
dians, and caenophidians sensu Underwood
(1967). The character thus becomes: optic fo-
ramen not enclosed by bone (0), enclosed by
frontal (1), enclosed by orbitosphenoid (2), en-
closed by frontal and parietal (3), enclosed by
frontal, parietal, and parasphenoid (4). Acro-
chordids are autapomorphic for the position of
the optic foramen in the parietal, a character
that is not relevant to the present analysis and
hence is here ignored. Pachyrhachis has to be
coded as unknown (?). The coding used here
for Sineoamphisbaena is the same as in Lee
(1998), although the presence of an orbitosphe-
noid and its relations to the optic foramen need
to be critically reassessed in this taxon (M.
Kearney, personal communication).
Character 61: Anterior brain cavity not floored
by bone (0), floored by orbitosphenoid (1),
floored by wide cultriform process of para-
sphenoid (2). We believe this character to be
poorly defined. First, the term "anterior brain
cavity" is a poor choice of words: since the
olfactory tracts and bulbs are part of the brain,
the brain cavity extends anteriorly to a level in
front of the frontal. As coded by Lee (1998),
this character is a synapomorphy shared by mo-
sasaurs and snakes. However, the basicranium
of mosasaurs generally resembles that of Va-
ranus, with two exceptions: the sella turcica is
less recessed below the dorsum sellae, and the
dorsum sellae is less developed (Rieppel &
Zaher, in press). But mosasaurs, like any other
nonophidian squamates, have a sella turcica in
front of which the basicranium is abruptly con-
stricted to a short rostrum basisphenoidale,
which in turn terminates in a point (or narrow
cultriform process), indicating a tropibasic
skull. In snakes, the sella turcica lies at the back
end of the parabasisphenoid, and the latter ex-
tends in front of the sella turcica as a broad
element underlying the brain, with the Vidian
canal exposed on the dorsal surface and with
the lateral edges sutured to the parietal down-
growths (Rieppel, 1979b). In front of the pari-
etal, i.e., below the frontals, the parabasisphen-
oid may form a relatively broad (e.g., Cylindro-
phis) or narrow (e.g., Anilius) cultriform pro-
cess. This type of parabasisphenoid (our
definition for character state 2) is in fact a syn-
apomorphy of snakes and reflects the funda-
mental change of skull proportions in snakes
versus lizards (much elongated postorbital re-
gion, small orbits, short preorbital region). Fos-
sorial lizards such as Anniella (Rieppel, 1978),
amphisbaenians, and dibamids (Rieppel, 1984a)
approach the morphology of the ophidian par-
abasisphenoid because of similar changes in
skull proportions.
Character 62: Cultriform process of parasphenoid
in lateral view curved upward (0), straight ( 1 ).
Any aspect of this character that goes beyond
the discussion of character 61 is a preservation-
al artifact. The character is therefore deleted
from our analysis (the coding retained in the
data matrix is that of Lee, 1998).
Character 63: Trigeminal foramen (foramina)
open anteriorly (0), bordered anteriorly by pa-
rietal ( 1 ), bordered anteriorly by orbitosphenoid
and parabasisphenoid (2).
Character 64: Alar process of prootic weak (0),
extensive (1). This character is redundant with
character 58 and therefore is deleted from our
analysis (the coding retained in the data matrix
is that of Lee, 1998).
Character 65: Alar process of prootic directed
dorsally (0), anterodorsally (1). This character
is inapplicable to Pachyrhachis (unknown [?],
contra Lee, 1998), snakes, amphisbaenians. and
dibamids.
Character 66: Crista prootica well developed (0),
reduced (1). We believe that by comparison to
snakes, dibamids, and amphisbaenians, the var-
anoid genera Lanthanotus and Heloderma, as
well as xenosaurs, should be coded 0. However,
we agree to code these taxa for a weakly de-
veloped crista prootica (1), but code snakes,
amphisbaenians, and dibamids 2 for the absence
of a crista prootica.
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
35
Character 67: Lateral head vein not enclosed (0),
enclosed (1) in bony canal formed by antero-
ventral continuation of crista prootica.
Character 68: Facialis foramen single (0), double
(1). The single or double facialis foramen is
variable within Varanus (even at the species
level), as well as in mosasaurs (Rieppel & Za-
her, in press). It is also variable in snakes,
where some (scolecophidians, uropeltines)
show an intracranial course of the palatine
branch of the facial nerve. We therefore delete
this character from the analysis (the coding re-
tained in the data matrix is that of Lee, 1998).
Character 69: Hypoglossal foramen well separat-
ed (0), close or confluent (1) with vagus fora-
men.
Character 70: Occipital recess open (0), closed
(1) laterally. As defined and coded by Lee
(1998), this character requires that the presence
or absence of the crista circumfenestralis of
snakes is dealt with as a separate character. Oth-
erwise, snakes would have to be coded 1 also
(see character 73).
Character 71: Otic capsule not expanded (0), ex-
panded (1) laterally. Lee (1998) codes Sineoam-
phisbaena, Amphisbaenia, and dibamids as
having a laterally expanded otic region (1). This
reflects the relative size increase of the laby-
rinth organ in miniaturized squamate skulls
(Rieppel, 1984b), which is also observed in oth-
er fossorial squamates, including snakes. The
latter therefore have to be coded 1 also.
Character 72: Stapes light, footplate small (0),
robust, footplate large (1). As dibamids and
Amphisbaenia are coded 1 for a stapes with a
robust shaft and a large footplate, basal snakes
such as anilioids and some basal macrostoma-
tans (Xenopeltis) also have to be coded 1 . Scin-
cidae is polymorphic for this character (Riep-
pel, 1981).
Character 73: Stapedial footplate not surrounded
(0), tightly surrounded by bony ridges project-
ing from lateral surface of braincase (1). As de-
fined and coded by Lee (1998), this character
becomes a synapomorphy of mosasaurs and
snakes. Note that, in contrast to Lee (1997,
character 44) and Lee and Caldwell (1998, p.
1548), Lee (1998, p. 393) notes morphological
differences of this character between mosasau-
roids and snakes but continues to assume pri-
mary homology of these structures in his cod-
ing. However, the braincase of mosasaurs re-
sembles that of Varanus rather closely and is
not comparable to the otic region of snakes
characterized by a crista circumfenestralis (Es-
tes et al., 1970; Rieppel & Zaher, in press). We
therefore propose to redefine this character as
follows: a crista circumfenestralis, enclosing a
juxtastapedial recess, is absent (0) or present
(1). Pachyrhachis has to be coded as unknown
(?). The character is a synapomorphy of snakes.
Character 74: Basipterygoid processes long (0),
short (1). As defined by Lee (1998), this char-
acter is not applicable (not comparable) to
snakes because basipterygoid processes of
snakes (basal macrostomatans) are not homol-
ogous to those of lizards (Kluge, 1991; Rieppel
& Zaher, in press). Lee and Caldwell (1998, p.
1534) described short basipterygoid processes
in Pachyrhachis, and Lee (1998) coded Pa-
chyrhachis for short basipterygoid processes
(1), despite his claim that the nature of these
processes cannot be confirmed for this taxon
(Lee, 1998, p. 442) or the claim that distinct
basipterygoid processes are absent in this taxon
(Scanlon et al., 1999). Pachyrhachis should be
coded as unknown (?).
Character 75: Articular facet on basipterygoid
process subcircular (0), anteroposteriorly elon-
gated (1). The same comments apply to this
character as to the preceding one.
Character 76: Basal tubera located posteriorly
(0), anteriorly (1). In varanoids and mosasaurs,
the basal tubera (sphenoccipital tubercles sensu
Oelrich, 1956) are located anteriorly on the ba-
sioccipital at the ventral end of the crista tub-
eralis. In snakes, they are incorporated into the
posteroventral part of the crista circumfenes-
tralis, as the latter incorporates the crista tub-
eralis (Estes et al., 1970; Rieppel & Zaher, in
press). As defined by Lee (1998), this character
is not applicable (not comparable) to snakes.
Pachyrhachis should be coded as unknown (?).
Character 77: Posterior opening of Vidian canal
within basisphenoid (0), at basisphenoid-pro-
otic suture (1), between prootic and epiphyseal
ossification in the region of the basal tubera (2).
36
FIELDIANA: GEOLOGY
Character 78: Posterior opening of Vidian canal
situated well in front of (0), near ( 1 ) the pos-
terior end of basisphenoid. This is a somewhat
vague character, but as the braincase anatomy
of mosasaurs is rather closely comparable to
that of Varanus, they, too, should be coded 0.
Snakes should be coded 1 for character 78, yet
some snakes should be coded 1 for character 77
(Rieppel, 1979b).
Character 79: Crista tuberalis weakly developed
(0), flaring (1). As defined by Lee (1998), this
character is difficult to separate from his char-
acter 73. As coded, the character is a synapo-
morphy of Lanthanotus and Varanus, and as
such is irrelevant for the analysis of snake re-
lationships. We retain it as coded by Lee
(1998).
Character 80: Supraoccipital separated from (0),
in narrow contact with (1), in broad contact
with (2) parietal. This character is poorly de-
fined, and we propose to replace it by the fol-
lowing: posttemporal fossae present (0), re-
duced (1), absent (2).
Character 81: Supraoccipital situated ventrad or
posteroventrad (0), at same level (1) as parietal.
Scincidae and Pygopodidae are polymorphic for
this character.
Character 82: Exoccipital separate (0), fused to
opisthotic (1) in adult. Although we retain this
character as defined and coded by Lee (1998),
we believe its phylogenetic information content
to be very limited. The skull of an adult Var-
anus komodoensis (fmnh 22199; condylobasal
length: 215 mm) retains a separate exoccipital.
Character 83: Occipital condyle single (0), dou-
ble ( 1 ). Although we retain this character as de-
fined and coded by Lee (1998), we believe its
phylogenetic information content to be limited.
The double occipital condyle, formed by a pos-
terior projection of the exoccipitals beyond the
basioccipital, is strongly expressed within Gek-
kota only (Rieppel, 1984c).
Character 84: Posttemporal fenestrae present (0),
absent (1). This character is redundant with
character 80 and is therefore deleted from the
analysis (the coding retained in the data matrix
is that of Lee, 1998).
Character 85: Septomaxilla extensively sutured
(0), not sutured (1) to maxilla. Iguanids are
polymorphic for this character (Oelrich, 1956;
Etheridge, personal communication), yet in
most lizards, the main body of the septomaxilla
floors the anterior part of the external naris and
is sutured to the maxilla, premaxilla, and vomer.
In mosasaurs, the thin and bladelike septomax-
illa is not in contact with the maxilla but lies
dorsal to it and is sutured to the equally thin
vomer (Camp, 1942). There does not appear to
be any potential for independent mobility of the
septomaxilla. Mosasaurs therefore differ from
varanoids and other nonophidian squamates in
this character. However, in shape and location,
the septomaxilla in all nonophidian squamates
(including mosasaurs) is radically different
from (i.e., nonhomologous to) that of snakes,
where the septomaxilla lies lateral to the vomer
and, together with the latter, forms a chamber
for Jacobson's organ, a synapomorphy of
snakes. Pachyrhachis has to be coded as un-
known (?) because the vomers are not known.
Other snakes are also coded ? because the char-
acter as defined by Lee (1998) is not compa-
rable (not applicable).
Character 86: Septomaxillae separated by carti-
laginous gap (0), meeting on midline (1). We
delete this character from the analysis (the cod-
ing retained in the data matrix is that of Lee,
1998) because each septomaxilla is associated
with its nasal capsule, and the two septomax-
illae are always separated by the cartilage of the
internasal septum and trabecula communis. Ob-
servations to the contrary are artifacts of a dried
skull (e.g., Bellairs & Kamal, 1981, Figs. 25,
28, 32, 65).
Character 87: Medial flange on septomaxilla
short (0), long ( 1 ). Among snakes, anomalepids
have no medial flange of the septomaxilla that
turns upward (Haas, 1964, 1968).
Character 88: Septomaxillary roof for Jacobson's
organ flat (0), domed (1).
Character 89: Opening of Jacobson's organ con-
fluent with choana (0), separated from choana
by vomer and maxilla ( 1 ), separated by vomer
and septomaxilla (2).
Character 90: Vomer(s) paired (0), fused (1).
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
37
Character 91: Vomer without (0), with (1) exten-
sive contact with maxilla behind Jacobson's or-
gan.
Character 92: Vomer less than half as long (0),
at least half as long ( 1 ) as maxilla.
Character 93: Vomer platelike (0), rodlike (1). As
defined by Lee (1998), this character is prob-
lematic because of the apomorphic vomer con-
figuration in snakes. Although we retain the
character, we code basal snakes for a broad vo-
mer (0). Pachyrhachis has to be coded as un-
known (?).
Character 94: Vomer anterior or anteromedial to
palatine (0), entirely medial to palatine (1).
Character 95: Secondary palate absent (0), pre-
sent (1).
Character 96: Palatine-vomer contact short (0),
extensive (1).
Character 97: Palatine-vomer contact immobile
(0), mobile (1).
Character 98: Palatine as long as (0), half as long
as (1) vomer. Lee (1998) codes Pachyrhachis
as unknown (?) for characters 92 and 93 (vo-
mer), appropriately indicating that the vomer of
Pachyrhachis is not known, but for characters
91, 94, 96, 97, and 98, he codes Pachyrhachis
0 when in fact he should code it as unknown
again (?).
Character 99: Interpterygoid vacuity extending
(0), not extending (1) between palatines.
Character 100: Palatine without (0), with (1) dis-
tinct medial process.
Character 101: Choanal groove on palatine short
or absent (0), long (1).
Character 102: Ectopterygoid-palatine contact
absent (0), present (1). Lee (1998) coded mo-
sasaurs as lacking a contact of ectopterygoid
and palatine (maxilla enters suborbital fenestra),
but Russell (1967) described the ectopterygoid
of Tylosaurus and Plotosaurus as meeting the
posterior rim of the palatine (see also McDow-
ell & Bogert, 1954, Fig. 10). The precise dis-
position of these elements is not known in basal
mosasauroids (aigialosaurs), for which reason
we code mosasauroids as unknown (?).
Character 103: Suborbital fenestra large (0),
small (1), absent (2).
Character 104: Pyriform recess open and wide
(0), open and narrow (1), closed by broad para-
sphenoid (2).
Character 105: Pterygoid-vomer contact present
(0), absent (1).
Character 106: Pterygoid with (0), without (1)
triangular depression on ventral surface, ex-
tending from suborbital fenestra toward pala-
tobasal articulation.
Character 107: Anterior (palatine) process of
pterygoid gradually merges with (0), is distinct-
ly set off from (1) transverse (ectopterygoid)
process.
Character 108: Anterolateral process of pterygoid
extending along lateral margin of palatine ab-
sent (0), present (1).
Character 109: Epipterygoid present (0), absent
(1).
Character 110: Mandibular symphysis rigid (0),
mobile (1). As coded by Lee (1998), mosasaurs
and snakes share a mobile mandibular symphy-
sis, with the anterior ends of the dentaries being
smoothly rounded. Although this character is
shared with other tetrapods that show an intra-
mandibular joint (e.g., Tyrannosaurus rex: C.
Brochu, personal communication), we accept
this character in the present analysis for the lack
of better knowledge of mosasaur symphyseal
structure. A dentary of Platecarpus (fmnh UC
600) shows the anterior end of Meckel's groove
to taper out on the medial surface of the straight
dentary. It remains unknown what role Meck-
el's cartilage played in the formation of a mo-
bile mandibular symphysis. In snakes, the an-
terior tip of the dentary is usually curved in-
ward, and Meckel's cartilage protrudes from
Meckel's canal and extends beyond the anterior
tip of the dentary as it relates to ligaments, mus-
cle fibers, and accessory cartilages (cartilago
symphyseum, derived in snakes) in the forma-
tion of a mobile mandibular symphysis (Young,
1998). It is noteworthy that Meckel's cartilages
38
FIELDIANA: GEOLOGY
of the two mandibular ramus fuse with each
other to form a true mandibular symphysis in
scolecophidians (Young, 1998).
Character 111: Three or more (0), two or less (1)
mental foramina on dentary. Personal inspec-
tion of the holotype of Pachyrhachis reveals
rather extensive breakage at the anterior end of
the left mandible (lateral view). In spite of re-
taining the character definition of Lee (1998),
we point out that we can identify a single men-
tal foramen only, which is a synapomorphy that
Pachyrhachis shares with other snakes.
Character 112: Dentary in lateral view with
straight (0), concave (1) dorsal (alveolar) mar-
gin. As defined and coded by Lee (1998), the
straight dorsal margin of the dentary is a syn-
apomorphy shared by Pachyrhachis and mosa-
saurs, but personal inspection of the holotype
of Pachyrhachis did not allow us to determine
the correct character state for this taxon, which
is therefore coded as unknown (?). In addition,
the dentary is slightly concave dorsally in the
lower jaw of Platecarpus (fmnh UC 600), and
it is distinctly concave in Prognathodon
(Lingham-Soliar & Nolf, 1989), such that mo-
sasaurs have to be coded polymorphic for this
character.
Character 113: Dentary with large (0), small (1),
without (2) posterodorsal process extending
onto lateral surface of coronoid process. As Un-
derwood (1957) and Gauthier (1982) have em-
phasized (see discussion above), there is only
one logical place to put a joint in the lower jaw,
i.e., between dentary and postdentary bones (in
the following, all characters correlated with the
differentiation of an intramandibular joint will
be called dp-characters [for dentary-postden-
tary relation]).
Character 114: Meckel's canal an open groove
(0), closed with dentary lips in sutural contact
(1), closed with dentary lips fully fused (2).
Character 115: Anterior end of Meckel's canal at
anteroventral margin (0), on medial surface (1)
of dentary. The opening of Meckel's canal on
the medial surface of the lower jaw, instead of
along its ventromedial margin, is a mosasaur
(mosasauroid?) autapomorphy. As discussed
above, the anterior end of Meckel's canal opens
ventral relative to the sagittal plane of the man-
dibular ramus in all snakes (as in all nonophi-
dian squamates). Intramandibular muscles in-
sert into Meckel's cartilage, which, in order to
be an effective site of muscle attachment, is ex-
posed ventromedially along the ventral edge of
the lower jaw. Inspection of the holotype of Pa-
chyrhachis did not reveal a position of Meckel's
canal on the medial side of the dentary com-
parable to the mosasaur condition.
Character 116: Intramandibular septum of den-
tary does not approach (0), approaches or
reaches (1) posteriormost tooth position. In
Varanus, the posterior margin of the intraman-
dibular septum lies right below the posterior-
most tooth; the same is true for mosasaurs
(Lingham-Soliar & Nolf, 1989). As defined by
Lee (1998), the character is not applicable (not
comparable) to scolecophidians (Haas, 1964,
1968). A serially sectioned head of Anilius scy-
tale shows the intramandibular septum to ter-
minate just in front of the anterior end of the
compound bone, i.e., it terminates well in front
of the posterior tooth. The same is true for Cy-
lindrophis. In uropeltids (serially sectioned
head of Plecturus perroteti), the intramandibu-
lar septum extends to a level posterior to the
posteriormost teeth, which, by comparison to
other basal alethinophidians, reflects the short-
ened tooth row of uropeltids. Macrostomatans
become difficult to compare because of the
elongated posterior dentigerous process (see
character 133, below).
Character 117: Subdental shelf large (0), weak
(1), absent (2). As described elsewhere (Zaher
& Rieppel, 1999), the subdental shelf is a char-
acter that applies only to nonophidian squa-
mates with labial pleurodonty. It is absent in
Varanus, mosasaurs, Pachyrhachis, and snakes.
Character 118: Posterior margin of lateral surface
of dentary without notch (0), with shallow
notch (1), with deep notch (2). This is a dp-
character, which loses weight in pulling snakes
to mosasaurs plus varanoids if treated unor-
dered, as it should be. The deeply bifurcated
posterior end of the dentary of Pachyrhachis
and snakes (2) is not part of a morphocline, but
results from a restructuring of the intramandi-
bular joint, with the compound bone (surangu-
lar portion) becoming the supporting element
for the dentary. To account for polymorphism
in snakes, the character should be further sub-
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
39
divided to include the elongated posterior den-
tigerous process of the dentary, which was de-
fined as a separate character above. In spite of
these difficulties, we retain the character as de-
fined and coded by Lee (1998).
Character 119: Overlap of dentary with postden-
tary bones extensive (0), reduced (1). This is
another dp-character that is difficult to under-
stand because the dentary-postdentary articu-
lation is fundamentally different in varanoids,
mosasaurs, and snakes. We propose the follow-
ing redefinition of character states: dentary
principally supported by coronoid, surangular,
and prearticular (0, nonophidian squamates, in-
cluding varanoids), by prearticular (1, mosa-
saurs), by surangular (2, snakes).
Character 120: Splenial large (0), small (1), ab-
sent (2). Lee (1998) coded snakes for a reduced
splenial, but we code scolecophidians and ma-
crostomatan snakes for a large splenial (0).
Character 121: Splenial overlaps postdentary
bones and does (0), does not ( 1 ) expand beyond
apex of coronoid process, or splenial does not
substantially overlap postdentary bones (2).
This is another dp-character. We find the splen-
ial to substantially overlap the postdentary
bones in Varanus in medial view of the man-
dible. This overlap is reduced in Lanthanotus.
In ventral view of the mandible, however, the
articular carries a long anterior process that
broadly overlaps with the splenial. As described
above, the posterior margin of the splenial of
Lanthanotus is concave in ventral view, receiv-
ing the convex angular. In mosasaurs, there is
no overlap between the splenial and the post-
dentary bones, but the anterior surface of the
splenial is concave, receiving the convex pos-
terior head of the articular. In snakes, the splen-
ial-postdentary relations are as described
above, with extensive overlap of the splenial
with the postdentary (compound) bone in sco-
lecophidians. In summary, we propose the fol-
lowing redefinition of character states: splenial
overlaps with angular (0, all nonophidian squa-
mates except mosasaurs, scolecophidians);
splenial meets angular in an abutting contact,
the splenial being the receiving, the angular be-
ing the received element (1, autapomorphic for
mosasaurs); splenial meets angular in an abut-
ting contact, the angular being the receiving, the
splenial being the received element (2, alethin-
ophidians). Pachyrhachis is coded unknown (?)
for this character because the detailed nature of
the angular-splenial articulation remains un-
clear (see discussion above).
Character 122: Anterior tip of splenial on ventral
margin (0), on medial surface (1) of dentary.
As shown above, the position of the anterior tip
of the splenial on the medial surface of the den-
tary is an autapomorphy (uninformative char-
acter) of mosasauroids and is therefore deleted
from our analysis (the coding retained in the
data matrix is that of Lee, 1998).
Character 123: Extensive (0), reduced (1) contact
between splenial and dentary. As defined by
Lee (1998), this character is difficult to under-
stand. Mosasaurs have a very extensive splen-
ial-dentary contact. In other taxa, this contact
varies according to the degree to which Meck-
el's canal is closed medially by the splenial.
However, in all squamates examined for this pa-
per except mosasaurs, the splenial carries a lat-
eral shelf, which underlies Meckel's canal and
which, together with the ventral margin of the
splenial, locks against the ventromedial margin
of the dentary in a solid contact. In view of the
autapomorphic relation of the splenial to the
dentary in mosasaurs, the character becomes
uninformative and is deleted from our analysis
(the coding retained in the data matrix is that
of Lee, 1998).
Character 124: Splenial-angular contact, in me-
dial view, overlapping and irregular (0), straight
(vertical) and abutting (1). As defined by Lee
(1998), we find this character to overlap with
character 121. The restriction of the view to the
medial side of the mandible is artificial and
does not account for the complexity and the dif-
ferences of the splenial-angular relations in the
different taxa. As the splenial is the receiving
part of the intramandibular articulation in mo-
sasaurs and is the received part in snakes, this
character is not simply a synapomorphy linking
snakes to mosasaurs as coded by Lee (1998).
Given the redefinition of character 121 above,
we delete character 124 from our analysis (the
coding retained in the data matrix is that of Lee,
1998).
Character 125: Anteromedial process of coronoid
long (0), short (1). As defined by Lee (1998),
we believe this character to be misleading. As
40
FIELDIANA: GEOLOGY
described above, the coronoid is V-shaped in
cross-section (apex pointing dorsally) and strad-
dles the surangular in nonophidian squamates,
including mosasaurs. Its anterior contact is re-
duced in mosasaurs as compared to Varanus, as
is correctly coded by Lee. In snakes, the coro-
noid is a simple bony plate that lies against the
inside of the compound bone and hence has no
chance to overlap with the medial surface of the
dentary. In scolecophidians, the dentary lies lat-
eral to the coronoid (Haas, 1964, 1968), while
in basal alethinophidians, the posteroventral
process of the dentary (if present — vestigial or
absent in uropeltids) may extend backward to a
level behind the anterior tip of the coronoid (if
present) and at a morphological level lateral to
the coronoid. As defined, this character is not
applicable (not comparable) to snakes.
Character 126: Anterolateral process of coronoid
absent (0), present (1). As defined by Lee
(1998), this character is not applicable (not
comparable) to snakes for the same reasons as
those discussed in relation to the previous char-
acter.
Character 127: Coronoid contacts (0), does not
contact (1) splenial. The coronoid contacts the
splenial in scolecophidians and in several basal
macrostomatans. The splenial-coronoid contact
appears to be variable in Cylindrophis ruffus.
The specimen discussed above shows the ab-
sence of such a contact, which however is
shown to be present in another specimen by
McDowell (1975, Fig. 6). The drawing of the
lower jaw of Cylindrophis maculatus discussed
above shows the coronoid to approach the
splenial very closely; serial sections show the
gap between the two bones to be only 0.1 mm,
which is only marginally wider than any other
skull suture (syndesmosis).
Character 128: Ventral margin of coronoid
straight or convex (0), concave (1).
Character 129: Subcoronoid fossa (exposing sur-
angular on medial side of mandible) absent (0),
present (1).
Characters 128 and 129: As defined by Lee
(1998), dibamids should be coded 1 or poly-
morphic and amphisbaenians polymorphic for
character 128 (straight or concave ventral mar-
gin of the coronoid). If this is done, the codings
for characters 128 and 129 become practically
redundant. However, a subcoronoid fossa, ex-
posing the surangular on the medial surface of
the lower jaw, is a character that is, in fact, not
applicable (not comparable) to those taxa that
form a compound bone composed of surangu-
lar, prearticular, and articular. We opt for the
retention of character 128 with corrected coding
as indicated above and replacement of character
129 with a new character.
(Our) Character 129: Compound bone formed of
surangular, prearticular, and articular absent (0)
or present (1, dibamids, amphisbaenians,
Pachyrhachis, snakes); some amphisbaenians
may show incomplete fusion of the postdentary
bones (Zangerl, 1944; Montero et al., 1999). Si-
neoamphisbaena shares the presence of a com-
pound bone (Wu et al., 1996).
Character 130: Surangular extends medially to
the surface of the dentary terminating in a point
(0), terminating with a blunt end ( 1 ), surangular
terminates with blunt end but does not extend
far medial to the dentary (2), surangular extends
far into lateral surface of the dentary and ter-
minates in a point (3). This is another dp-char-
acter, which was miscoded for mosasaurs by
Lee (1998). In Varanus, the surangular does ex-
tend medial to the dentary and terminates blunt-
ly; probably the same is true for Lanthanotus
(the lower jaw was not disarticulated). In mo-
sasaurs, the surangular has no overlap at all
with the dentary; instead, the overlap is with
the prearticular. Dibamids and amphisbaenians
should be coded as unknown. As was done by
Lee (1998), Pachyrhachis is coded like all other
snakes except for scolecophidians.
Character 131: Surangular without (0), with (1)
dorsal flange overlapping posterior part of cor-
onoid process.
Character 132: Angular present (0), absent (1).
Character 133: Angular with wide (0), with nar-
row or without exposure ( 1 ) on medial side of
mandible.
Character 134: Fingerlike angular process present
(0), absent ( 1 ).
Character 135: Prearticular does not (0), does (1)
extend anteriorly past posterior dentary tooth
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
41
position(s). This is another dp-character which,
as coded by Lee (1998), is a synapomorphy
shared by mosasaurs, Pachyrhachis, and
snakes. However, in mosasaurs, the prearticular
extends anteriorly far beyond the posterior teeth
(1). Pachyrhachis has to be coded as unknown
(?). Scolecophidians code as 0, and alethino-
phidians as not comparable (?).
Character 136: Prearticular crest absent (0), mod-
erately well developed (1), prominent (2).
Character 137: Adductor fossa faces dorsomedi-
ally (0), dorsally (1). As coded by Lee (1998),
this character is difficult to assess. Following
the descriptions above, we propose the follow-
ing redefinition of character states: medial mar-
gin of the adductor fossa on lower jaw is low
and rounded (0), developed into a distinct ver-
tical flange (1). The coding for mosasaurs is 1,
for Pachyrhachis is 1, and for scolecophidians
is 0; anilioids are polymorphic (0 and 1), and
basal macrostomatans are 1.
Character 138: Adductor fossa narrow trans-
versely (0), inflated transversely (1). This is a
synapomorphy of the Lacertoidea that reflects
the entry of the posterior adductor into Meck-
el's canal.
Character 139: Articular fused with prearticular
and surangular (0), fused with prearticular (1),
separate (2). As defined by Lee (1998), this
character is wrongly polarized (see our discus-
sion of character 129).
Character 140: Retroarticular process in line with
rest of mandible (0), offset medially (1).
Character 141: Retroarticular process extends
straight posteriorly (0), extends posteromedially
(1). As defined by Lee (1998), the character
states of this character are often difficult to es-
tablish and appear to be redundant with char-
acter 140. The retroarticular process of mosa-
saurs is clearly deflected medially. Varanus has
a rather straight posterior retroarticular process
by comparison, but the retroarticular process of
Lanthanotus is more distinctly medially deflect-
ed. Lee (1998) coded Serpentes as 1 but sco-
lecophidians as 0. By comparison to other squa-
mates, Pachyrhachis shares with alethinophi-
dians a reduced, knobby retroarficular process,
which should be added as a different character
state (2).
Character 142: Dorsal surface of retroarticular
process with pit or sulcus (0), smoothly con-
cave (1). Lee's (1998) coding for Serpentes is
problematic. Scolecophidians have a retroarti-
cular process that is circular in cross-section
(Haas, 1964, 1968), whereas alethinophidians,
including Pachyrhachis, are not comparable,
owing to their short, knobby retroarticular pro-
cess. Furthermore, the knobby process has a
convex, not a concave, dorsal surface. To avoid
redundancy with character 141, we propose to
treat character 142 as not applicable (not com-
parable) to Pachyrhachis and snakes.
Character 143: Dorsomedial margin of retroarti-
cular process smooth (0), with distinct tubercle
or flange (1).
Character 144: Retroarticular process tapering,
narrow distally (0), not tapering, broad distally
(1).
Character 145: Retroarticular process not twisted
posteriorly (0), twisted posteriorly (1). As de-
fined by Lee (1998), this character is not appli-
cable (not comparable) to Pachyrhachis and
snakes.
Character 146: Marginal tooth implantation ac-
rodont (0), pleurodont (1), thecodont, shallow
alveoli (2), thecodont, deep alveoli (3). The pre-
maxillary, maxillary, and dentary teeth of mo-
sasaurs are not thecodont but modified (fully)
pleurodont, as are those of varanoids. Scoleco-
phidians likewise are pleurodont. Alethinophi-
dia are derived by the attachment of the tooth
base to circular interdental ridges, a character
they share with Pachyrhachis (Zaher, 1998).
According to our analysis of squamate tooth
implantation, we propose the following redefi-
nition of character states: tooth implantation ac-
rodont (0), labially pleurodont (1), modified
(fully) pleurodont (2, varanoids, mosasaurs, and
scolecophidians), or teeth ankylosed to the rim
of a shallow socket that is homologous to the
interdental ridge of nonophidian squamates (3,
Pachyrhachis, alethinophidians).
Character 147: Marginal teeth without (0), with
(1) sharp carinae. Varanus has laterally com-
pressed teeth with anterior and posterior cutting
42
FIELDIANA: GEOLOGY
edges. The same is true for mosasaurs, although
their teeth are less laterally compressed. We
find carinae to be either very weakly developed
or absent in extant snakes. If anything is pre-
sent, it is a weakly developed anterior cutting
edge. Pachyrhachis has carinae on the lateral
surface of the tooth crown, an autapomorphy of
this taxon. As defined by Lee (1998), we find
this character misleading and delete it from our
analysis (the coding retained in the data matrix
is that of Lee, 1998).
Character 148: Plicidentine absent (0), present
(1). Lee codes Pachyrhachis 1 for the presence
of plicidentine and refers to Lee and Caldwell
(1998) for justification. However, Lee and Cald-
well (1998, p. 1537) state that "marginal teeth
are hollow cones," which was confirmed by
personal observation of the holotype of Pa-
chyrhachis (particularly clear in the broken an-
teriormost tooth of the left palatine). The pres-
ence of weak striations on the enamel surface
does not, in itself, indicate the presence of pli-
cidentine, which is the character addressed by
Lee (1998). The latter taxon, as all other snakes,
therefore has to be coded for the absence of
plicidentine, the presence of which is a vara-
noid synapomorphy.
Character 149: Tooth crowns closely spaced (0),
separated by wide gaps (1). As defined by Lee
(1998), this character carries little phylogenetic
information. The modified (fully) pleurodont
teeth of varanoids have a flaring tooth base, and
although the teeth meet each other at their base
(i.e., narrow spacing of the tooth positions), the
flaring of that base still results in a wider spac-
ing of the tooth crowns than is characteristic for
nonophidian squamates, which show labial
pleurodonty (Zaher & Rieppel, 1999). In addi-
tion, the rhythm of tooth replacement in Var-
anus is timed such that the functional teeth tend
to alternate with replacement teeth, which cre-
ates gaps between the functional teeth, although
tooth positions are closely spaced (Edmund,
1960). Mosasaurs again show a basal contact
between the teeth, i.e., closely spaced tooth po-
sitions, but because of a flaring tooth base, the
tooth crowns appear more widely spaced. Flar-
ing tooth bases and a basal contact between
teeth are a derived character shared by mosa-
saurs and varanoids but are absent in other
squamates. In spite of these problems, we retain
this character in our analysis, although it ap-
pears at least partially redundant with the type
of tooth implantation (character 146).
Character 150: Replacement tooth positioned lin-
gual (0) to functional tooth, posterolingual (1)
to functional tooth, or absent (2).
Character 151: Resorption pits at base of teeth
(0), on bony tooth pedicel (1), absent (2). The
development of resorption pits starts at the base
of the teeth, i.e., in the bone of attachment, in
all squamates (snakes included). However, var-
anoids lack the development of large resorption
pits within which the replacement teeth develop
and which extend into the tooth crown. Mosa-
saur teeth are autapomorphic in that they de-
velop large resorption pits that hold the devel-
oping replacement teeth but remain restricted to
the tall tooth base formed from the bone of at-
tachment. Scolecophidians develop large re-
sorption pits, but other snakes have small re-
sorption pits, restricted to the basal bone of at-
tachment. In light of these variations, we offer
the following redefinition of character states: re-
sorption pits large, extending into tooth crown
(0); resorption pits small, restricted to bone of
attachment at the base of the tooth (1, vara-
noids, alethinophidians); resorption pits large,
restricted to tall tooth pedicel composed of the
bone of attachment (2, autapomorphic for mo-
sasaurs).
Character 152: Replacement teeth erupt upright
(0), erupt horizontally (1). The horizontal po-
sition of replacement teeth is a synapomorphy
of snakes (unknown in Pachyrhachis) that is
absent in mosasaurs (Zaher & Rieppel, 1999).
Character 153: Five or more (0), four or fewer
(1) premaxillary teeth.
Character 154: Median premaxillary tooth absent
(0), present (1).
Character 155: Median premaxillary tooth not
enlarged (0), enlarged (1).
Character 156: Premaxillary teeth similar in size
to (0), distinctly smaller than ( 1 ) anterior max-
illary teeth.
Character 157: Thirteen or more (0), twelve to
nine (1), eight or fewer (2) maxillary tooth po-
sitions.
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
43
Character 158: Thirteen or more (0), twelve to
nine ( 1 ), eight or fewer (2) dentary tooth posi-
tions.
Character 159: Palatine teeth present (0), absent
(1).
Character 160: Palatine teeth small (0), similar in
size to marginal teeth (1).
Character 161: Pterygoid teeth present (0), absent
(1).
Character 162: Pterygoid teeth small (0), similar
in size to marginal teeth (1). As defined by Lee
(1998), this character is ambiguous because
marginal teeth decrease in size from front to
back. Pterygoid teeth, where present, are al-
ways smaller than anterior maxillary or dentary
teeth in all squamates. For this reason, we de-
lete this character from our analysis (the coding
retained in the data matrix is that of Lee, 1998).
Character 163: Egg tooth single (0), paired (1).
Character 164: Centra not constricted (0), slightly
constricted (1), strongly constricted (2) in front
of condyle.
Character 165: Vertebral condyles facing poste-
riorly (0), slightly dorsally (1), dorsally (2).
Character 166: Shape of vertebral condyles in
middorsal region oval (0), round (1). Lee
(1998) coded snakes for a circular vertebral
condyle (1), but scolecophidians, various ani-
lioids, and macrostomatans all have a vertebral
condyle with an oval outline and are coded ac-
cordingly (0).
Character 167: Centra notochordal (0), not no-
tochordal (1).
Character 168: Neural spines tall processes (0),
low ridges (1).
Character 169: Zygosphenes and zygantra pre-
sent (0), absent (1).
Character 170: Articular surface of zygosphene
faces dorsally (0), lateroventrally (1).
Characters 169 and 170: As defined by Lee
(1998), these characters are redundant and have
to be combined into one: zygosphene-zygan-
trum absent (0); present with zygosphene artic-
ular surface facing laterodorsally ( 1 , Lacertidae,
Cordylidae, Gerrhosauridae: Hoffstetter &
Gasc, 1969, Fig. 42); present with zygosphene
articular surface facing ventrolaterally (2, mo-
sasaurs, snakes, Teiidae, Gymnophthalmidae).
We code character 169 accordingly but delete
character 170 from the analysis (the coding re-
tained in the data matrix is that of Lee, 1998).
Character 171: Dorsal intercentra present (0), ab-
sent (1).
Character 172: Presacral vertebrae 22 or fewer
(0), 23 to 25 (1), 26 (2), 27 to 50 (3), 50 to 1 19
(4), 120 or more (5).
Character 173: Cervical vertebrae seven or fewer
(0), eight (1), nine or more (2).
Character 174: Hypapophyses present on fourth
to sixth presacral (0), on seventh presacral and
beyond (1). As defined by Lee (1998), this
character is based on arbitrary morphological
distinctions. The number of cervical hypapo-
physes is increased in varanoids because of an
elongation of the neck (character 173). Note
that Varanus has nine cervicals with hypapo-
physes, whereas mosasaurs have eight or seven
cervicals (Russell, 1967). According to Russell,
only the anterior six or seven cervicals carry
hypapophyses in mosasaurs (in Mosasauridae
indet., fmnh PR 2103, the last hypapophysis is
on the sixth cervical). Snakes are not compa-
rable because they have no easily defined cer-
vical region of the vertebral column and the hy-
papophyses extend backward far into the trunk,
suggesting the presence of dorsal intercentra
(absent in nonophidian squamates other than
geckos). In the posterior trunk region, the hy-
papophyses are reduced to a hemal keel, but
they may be reduced more anteriorly also in
burrowing species (Hoffstetter & Gasc, 1969).
A redefinition of character states could account
for the number of cervical vertebrae (not appli-
cable, i.e., not comparable to snakes) or the
presence versus absence of trunk intercentra. In
view of the difficulties of establishing clear-cut
character state relations beyond autapomor-
phies, we delete this character in our analysis
(the coding retained in the data matrix is that
of Lee, 1998).
44
FIELDIANA: GEOLOGY
Character 175: Dorsoposterior flange on atlas
neural arch present (0), absent (1).
Character 176: Cervical intercentral not sutured
nor fused (0), sutured (1), fused (2) to preced-
ing centrum.
Character 177: Cervical intercentra neither su-
tured nor fused (0), sutured (1), fused (2) to
following centrum.
Character 178: Caudal transverse processes sin-
gle (0), double ( 1 ) in some caudals.
Character 179: Caudal transverse processes: two
prongs converge (0), diverge (1) distally.
Character 180: Caudal transverse processes pro-
ject laterally or posterolaterally (0), anterolat-
eral^ (1).
Character 181: Caudal autotomy septa present
(0), absent (1).
Character 182: Caudal autotomy septa anterior to
or within (0), posterior to (1) transverse pro-
cesses. The distinction of two character states
appears arbitrary because, in some nonophidian
squamates, the autotomy septum is anterior, in
others it is within, and in still others it is pos-
terior to the transverse processes (the coding
retained in the data matrix is that of Lee, 1998).
Character 183: Pedestals on caudal vertebrae for
chevrons weakly developed (0), prominent (1).
Character 184: Chevrons articulate with (0),
fused to (1) caudal centra.
Characters 183 and 184: For reasons discussed
below (character 185), we consider chevrons to
be absent in snakes rather than co-ossified with
the centrum, as was assumed by Lee (1998).
Character 185: Caudal chevron positioned at (0),
in front of (1) posteroventral margin of cen-
trum. As defined by Lee (1998), this character
is not applicable (not comparable) to snakes,
which have no chevrons but have hemapophys-
es instead (Hoffstetter & Gasc, 1969), and these
are located at the posterior end of centrum. As
coded by Lee (1998), mosasaurs share with var-
anoids the anterior shift of the chevrons.
Character 186: First rib on third (0), fourth (1)
cervical vertebra. This character is not appli-
cable to snakes.
Character 187: Proximal end of rib without (0),
with (1) anteroventral pseudotuberculum.
Character 188: Proximal end of rib without (0),
with (1) posteroventral pseudotuberculum.
Character 189: Lymphapophyses ("forked cloa-
cal ribs" of Lee, 1998) absent (0), present (1).
Lee and Caldwell (1998) described a distally
expanded sacral rib for Pachyrhachis and hy-
pothesized that the appearance of its distal bi-
furcation might be due to breakage. Lee (1998)
codes the distally forked sacral rib of Pachy-
rhachis as comparable to the distally forked clo-
acal ribs of other snakes, amphisbaenians, and
dibamids. Indeed, Pachyrhachis shows at least
one well-developed lymphapophysis (the sacral
rib of Lee & Caldwell, 1998), but the presence
of additional, more posteriorly located lympha-
pophyses cannot be assessed owing to poor and/
or incomplete preservation. In those basal snakes
that retain limb rudiments, these do not establish
contact with the lymphapophyses, and the same
might have been true of Pachyrhachis.
Character 190: Scapulocoracoid large (0), re-
duced (1), absent (2).
Character 191: Emarginations on anterodorsal
edge of scapula absent (0), present ( 1 ).
Character 192: Anterior coracoid emargination
absent (0), present (1).
Character 193: Posterior coracoid emargination
absent (0), present (1).
Character 194: Clavicle present (0), absent (1).
Character 195: Clavicle follows anterior margin
(0), curves anteriorly away from (1) scapulo-
coracoid.
Character 196: Clavicles rodlike (0), expanded
proximally with proximal notch or fenestra (1).
Character 197: Interclavicle present (0), absent
(1).
Character 198: Interclavicle cross-shaped (0),
simple rod ( 1 ).
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
45
Character 199: Anterior process of interclavicle
short or absent (0), long (1).
Characters 197 and 198: The interclavicle of
nonophidian squamates shows greater complex-
ity than is expressed by these two characters
(Camp, 1923). The absence of an anterior pro-
cess (character 199) may result in a T-shaped
or arrow-shaped interclavicle (the coding re-
tained in the data matrix is that of Lee, 1998).
Character 200: Ossified (should read calcified)
sternum present (0), absent (1).
Character 201: Sternal fontanelle absent (0), pre-
sent (1).
Character 202: Five (0), four (1), three (2), two
or fewer (3) pairs of ribs attach to the sternum.
Character 203: Postxiphisternal inscriptional ribs
not united (0), one or more pairs united along
ventral midline (1).
Character 204: Forelimbs large (0), small or ab-
sent (1).
Character 205: Ectepicondylar foramen on hu-
merus present (0), absent (1).
Character 206: Pelvis large (0), reduced (1), ab-
sent (2).
Character 207: Pelvic elements co-ossified into
single bone (0), strongly sutured to one another
(1), weakly united in nonsutural contacts (2).
As defined by Lee (1998), this character is dif-
ficult to assess throughout squamates. The skel-
eton of mosasaurs, like that of other marine rep-
tiles, is subject to skeletal paedomorphosis
(Sheldon, 1997; see also Rieppel, 1993a),
which accounts for the reduced ossification of
the pelvic elements (joined together by cartilage
in life). However, the pelvic elements are firmly
sutured to one another in basal mosasauroids
(aigialosaurs: Carroll & deBraga, 1992), which
were coded accordingly (1). The pelvis of Pa-
chyrhachis is much reduced by comparison to
that of mosasaurs, which could be a conse-
quence of its marine habits or of its being a
snake, or both. The pelvic rudiments of other
snakes are not easily comparable.
Character 208: Sacral blade of ilium with (0),
without (1) anterior process.
Character 209: Pubis short, symphyseal process
directed ventrally (0), intermediate in length,
symphyseal process directed anteroventrally
(1), elongated, symphyseal process directed an-
teriorly (2). As defined by Lee (1998), this
character is difficult to understand. The pubis
points anteroventrally in all nonophidian squa-
mates (except mosasaurs), with a medial incli-
nation to form the pubic symphysis. In mosa-
saurs, the pubis lies horizontally and points me-
dially to form the symphysis (Russell, 1967).
The pubis in Pachyrhachis is dislocated and its
natural orientation unknown. It also remains un-
known whether Pachyrhachis had a pubic sym-
physis. To these problems of comparison, we
add the observation that coding of the hind limb
in Pachyrhachis can severely skew the analysis,
depending into how many characters the hind
limb is atomized. We delete character 209 from
our analysis (the coding retained in the data ma-
trix is that of Lee, 1998).
Character 210: Pubic tubercle on posterodorsal
end of pubis (0), on shaft of pubis (1).
Character 211: Hind limbs well developed (0),
rudimentary or absent (1). We adopt Lee's
(1998) coding (1) for Pachyrhachis but note
that the incompleteness of its limb (all elements
distal to astragalus and calcaneum missing) ap-
pears to be an artifact of preservation.
Character 212: Femur gracile (0), stout (1). Lee
(1998) coded a stout femur as a derived char-
acter state shared by Pachyrhachis and mosa-
saurs. Although we retain his coding, we note
that the femur of mosasaurs is modified to form
the proximal element in a paddle; that of Pa-
chyrhachis is crushed (see also character 213,
below).
Character 213: Femur curved (0), not curved (1)
in dorsoventral plane. Lee (1998) coded Pa-
chyrhachis and mosasaurs for a straight femur.
In fact, the two taxa are not comparable in fe-
mur morphology. The femur of mosasaurs is
much reduced in length but broadened as a con-
sequence of the limb having been transformed
into a paddle. By comparison, the femur of Pa-
chyrhachis is elongate and relatively slender
(some of the robustness of the femur of Pa-
chyrhachis is due to crushing). The diaphysis
of mosasaurs retains a distinct biconcave shape,
which is not expressed in Pachyrhachis (anoth-
46
FIELDIANA: GEOLOGY
er consequence of crushing?). Given the com-
pression of the femur, the character state for
character 213 also cannot be identified for Pa-
chyrhachis. In view of these differences, and
because this character is partially redundant
with character 212, we delete character 213
from our analysis (the coding retained in the
data matrix is that of Lee, 1998).
Character 214: Distal end of tibia gently convex
(0), with notch fitting into a ridge on astragalo-
calcaneum (1). As defined by Lee (1998), this
character is difficult to understand. In fact, this
character reflects little more than the absence of
separate epiphyseal ossification centers in mo-
sasaurs, which is again due to skeletal paedo-
morphosis, whereas Pachyrhachis may lack
separate epiphyseal ossification centers because
of its marine habits or because it is a snake, or
both (all snakes lack separate epiphyseal ossi-
fication centers: Haines, 1969). As such, this
character is redundant with character 228 and
hence is deleted from our analysis (the coding
retained in the data matrix is that of Lee, 1998).
Character 215: Astragalus and calcaneum fused
(0), separate ( 1 ) in adult. This character is cod-
ed by Lee (1998) as another putative synapo-
morphy of mosasaurs and Pachyrhachis, but the
lack of fusion of astragalus and calcaneum in
mosasaurs is again due to skeletal paedomor-
phosis (marine). The character is furthermore
subject to ontogenetic variation among other
nonophidian squamates yet is not applicable
(not comparable) to other snakes. To these
problems of comparison, we add the observa-
tion that coding of the hind limb in Pachy-
rhachis can severely skew the analysis, depend-
ing on whether features of the hind limb are
lumped into few or split into many characters.
In spite of these problems, we retain this char-
acter, as it adds to the strength of the test of the
phylogenetic position of Pachyrhachis as sister
taxon of Macrostomata (see further comments
below).
Character 216: Dorsal body osteoderms absent
(0), present (1).
Character 217: Ventral body osteoderms absent
(0), present (1).
Character 218: Separable cranial osteoderms ab-
sent (0), present on periphery of skull table ( 1 ),
present across entire skull table (2).
Character 219: Separable cranial osteoderms few
and large (0), many and small (1).
Character 220: Separable cranial osteoderms
tightly connected to skull roof (0), loosely con-
nected to skull roof ( 1 ).
Character 221: Rugosities on skull roof formed
by overlying cephalic scales absent (0), with
vermiculate sculpture (1), without vermiculate
sculpture (2).
Character 222: Scleral ossicles present (0), absent
(1).
Character 223: Fifteen or more (0), 14 (1), 13 or
fewer (2) scleral ossicles.
Character 224: Scleral ossicle shape complex and
irregular (0), square ( 1 ).
Character 225: Second epibranchials present (0),
absent (1) in hyoid skeleton.
Character 226: Second ceratobranchials present
(0), absent (1) in hyoid skeleton.
Character 227: Epiphyses on skull and axial skel-
eton present (0), absent (1).
Character 228: Epiphyses on appendicular skel-
eton present (0), absent (1).
Character 227 and 228: As defined and coded by
Lee (1998), these two characters are redundant
and should be coded as a single character. The
only difference recorded by Lee (1998) is the
polymorphic coding of mosasaurs for the pres-
ence of separate epiphyseal ossification centers
in the appendicular skeleton of mosasaurs. Bell
(1997) describes the variable development of
epiphyses on postcranial elements of mosa-
saurs, but from his description it is not entirely
clear what exactly his understanding is of the
term epiphysis or, more exactly, of a separate
epiphyseal ossification center. We were unable
to confirm the presence of separate epiphyseal
ossification centers on postcranial elements of
mosasaurs in the Field Museum collections.
Separate epiphyseal ossification centers are pre-
sent, however, in stem-group mosasauroids
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
47
(Carroll & deBraga, 1992). In summary, char-
acters 227 and 228 are therefore redefined as a
single character (227): separate epiphyseal os-
sification centers present (0, nonophidian lepi-
dosaurs), absent (1, snakes). Because of the am-
biguities of description and the presence of
epiphyses in stem-group mosasauroids, mosa-
saurs are coded polymorphic for this character
in our analysis. Character 228 is deleted from
our analysis (the coding retained in the data ma-
trix is that of Lee, 1998).
Character 229: Epiphyses fuse to diaphyses of
long bones at the same time or after (0), before
(1) fusion of braincase elements.
Character 230: Postcloacal bones absent (0), pre-
sent (1).
To those characters of Lee, we add the follow-
ing three characters, which emerged from the
character discussion above:
Character 231: Medial ventral flanges of frontal,
separating olfactory tracts from one another, ab-
sent (0), present (1), This character is a syna-
pomorphy of Alethinophidia, absent in Dinily-
sia (Estes et al., 1970), and unknown in Pa-
chyrhachis.
Character 232 (new): Cartilaginous processus as-
cendens of supraoccipital present (0, mosasaurs,
Varanus, indeed all nonophidian squamates ex-
cept Gekkota and Dibamus), absent (1, Gek-
kota, Dibamus, snakes). Amphisbaenia (and 57-
neoamphisbaena), as well as Pachyrhachis and
Dinilysia, have to be coded as unknown (?).
Character 233: Elongated posterior dentigerous
process of dentary absent (0), present (1). This
character is a potential synapomorphy shared
by Pachyrhachis and macrostomatans (Zaher,
1998).
The list of characters used by Lee (1998) does not
include some features that were subject to controversy
in the analysis of the relationships of Pachyrhachis with-
in squamates by Caldwell and Lee (1997), Lee and Cald-
well (1998), and Zaher (1998). We propose to critically
review these characters in comparison to those of Lee
(1998).
Below follows a list of the characters used by Cald-
well and Lee (1997; abbreviated as CI to C8) in support
of a sister-group relationship of scolecophidians and al-
ethinophidians at the exclusion of Pachyrhachis. The
number in parentheses preceded by a D refers to the
corresponding character in Lee and Caldwell (1998).
CI (Dl): Jugal present (0), absent (1). A jugal is here
considered to be absent in Pachyrhachis. This feature is
coded under character 12 (see above).
C2 (D3): Posterior orbital margin complete (0), in-
complete (discontinuous) ( 1 ). We interpret the purported
jugal in Pachyrhachis to be part of the ectopterygoid (its
anterior ramus). Pachyrhachis had an incomplete pos-
terior orbital margin similar to boids (i.e., with a long
postorbital, almost touching the dorsal surface of the ec-
topterygoid). This character is coded under character 29
(see above).
C3 (D4): Exoccipitals not in contact (0), in contact
(1) dorsal to the foramen magnum. As pointed out by
Zaher (1998) and acknowledged by Lee (1998, p. 442),
this character cannot be scored in Pachyrhachis owing
to the poorly preserved condition of the skull in this
area. This character is thus not included in the present
analysis.
C4 (D5): Angular-coronoid contact absent (0), pre-
sent (1). The contact is absent in Leptotyphlops (Mc-
Dowell & Bogert, 1954, Fig. 13; personal observation),
uropeltids (Figs. 9, 10), Xenopeltis (Hoge, 1964, Figs.
1, 2), Corallus (Kluge, 1991, Fig. 14), and Candoia
(McDowell, 1979, Fig. 4), and it is variable in Typhlops
(see Haas, 1930, Figs. 34, 41), Cylindrophis (Figs. 7, 8),
Loxocemus (McDowell, 1975, Fig. 6; Kluge, 1991, p.
37), Eunectes (personal observation), and Boa (Kluge,
1991, p. 37; Fig. 14). Contrary to Lee's (1998, p. 442)
claim that Kluge (1991) indicated "that the contact is
present in anilioids," this author (Kluge, 1991, p. 37)
pointed out that only some erycines (Eryx) and anilioids
(Cylindrophis) "have a coronoid-angular contact." Per-
sonal observations corroborated Kluge's observations on
erycines and demonstrated that Cylindrophis is variable
in respect to this character. All snake terminal taxa (ex-
cept Dinilysia, as pointed out by Lee, 1998) used in this
study, including basal anilioids and basal macrostoma-
tans, are variable with respect to this character, preclud-
ing its use in a phylogenetic analysis.
C5 (D6): Mental foramina on dentary, two or more
(0), one (1). As already pointed out above (see character
111), Pachyrhachis retains only one foramen, as in other
snakes. This character is coded under character 29 (see
above).
Character 234 (C6 [D8]): When present, the pel-
vis is external to the rib cage, sacral contacts
usually present (0), lies within rib cage, sacral
contact absent (1). This feature has been added
to the data matrix as character 234. Dibamids
show state 1.
Character 235 (C7 [D10]): Femur well developed
(0), small (1), vestigial or lost (2). This feature
has been added to the data matrix as character
235.
48
FIELDIANA: GEOLOGY
Character 236 (C8 [Dll]): Tibia, fibula, astraga-
lus, and calcaneum present (0), absent (1). This
character has been added to the data matrix as
character 236. Dibamids are coded 0, although
tibia and fibula only are present in the hind limb
of Dibamus (Greer, 1985).
Characters 235 and 236: We note that the coding
of the limb in Pachyrhachis may be problem-
atic because of the potential of oversplitting the
character of the presence of a limb. It is obvious
that the more limb characters that are included
in the analysis, the more Pachyrhachis will be
pulled toward the root of the ophidian clade, as
its most basal member (Lee & Caldwell, 1998).
However, in this analysis, we opt for the reten-
tion of these limb characters, as they add to the
severity of the test of the hypothesis that Pa-
chyrhachis is the sister taxon of Macrostomata
(Zaher, 1998).
Lee and Caldwell (1998, p. 1550) proposed
three additional characters:
D2: Squamosal present (0), absent (1). We interpret
the squamosal of Pachyrhachis as identified by Lee and
Caldwell (1998) as the shaft of the stapes. Pachyrhachis
lacks a squamosal. This feature is coded in the present
study as character 40 (see above).
D7: Neural spines well developed (0), reduced (1).
Pachyrhachis and macrostomatans share character state
1. whereas the other snakes (including Dinilysia) show
character state 0. This feature has been coded as char-
acter 168 (see above).
Lee and Caldwell (1998, p. 1550) also listed
four characters (El to E4) found in Pachyrhachis
and alethinophidian snakes. Among these, three
(El, E2, E3) were discussed by Zaher (1998).
Only character E4 is added here as follows:
Below follows a list of the characters used by
Zaher (1998) and retained in the present study:
18: Quadrate anteriorly directed (0), vertically or pos-
teriorly directed ( 1 ). This character was discussed above
as character 50.
Character 238 (19): Tooth-bearing anterior pro-
cess of the palatine absent (0), present ( 1 ). This
character is added to the data matrix as char-
acter 238.
20: Free-ending process of the supratemporal absent
(0), present (1). This feature has been coded as character
47 (see above).
21: Dorsal surface of the prootic not concealed (0),
concealed by the supratemporal ( 1 ). This character is
here deleted from the analysis, as it is correlated with
the elongation of the supratemporal (Lee, 1998).
22: Basipterygoid process well developed, with artic-
ulating surface facing more laterally than vcntrally (0).
reduced, with articulating surface facing vcntrally ( 1 ).
This feature has been discussed under character 74 (sec
above).
Character 233 (23): Posterior dentigerous process
of the dentary absent (0), short (1), enlarged
(2). This feature has been modified to a binary
character (dentigerous process absent [0] or
present [1]) and has been added to the data ma-
trix as character 233.
Character 239 (24): Suprastapedial process of the
quadrate present (0), absent (1). Contrary to
Lee (1998, p. 443), a suprastapedial process is
present and well developed in typhlopids, less
developed in anomalepids, and ill-defined or
absent in leptotyphlopids. Scolecophidians are
thus considered to retain a suprastapedial pro-
cess. This feature has been added to the data
matrix as character 239.
Character 240: Jugal present (0), absent ( 1 ). For
further details see the discussion of character
12.
Character 237 (E4): Palatine short and broad (0),
narrow and long ( 1 ). As pointed out by Lee and
Caldwell (1998), the palatine of Pachyrhachis
and alethinophidian snakes is a long, narrow el-
ement. It is short and broad in Dinilysia and
short (vestigial?) in scolecophidians. This char-
acter is added to the present data matrix as char-
acter 237.
Cladistic Analysis
The cladistic analysis presented below is not
intended to assess global squamate interrelation-
ships, but should rather be viewed as a test of the
conclusions reached by Lee (1998). As indicated
in the character discussion above, we believe that
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
49
Table 1. The data matrix used to analyze the interrelationships of the fossil snake Pachyrhachis. Character
definitions and discussion are given in the text.
Pachyrhachis 1
1
2
3
4
5
6
7
8
9
1 0
1 1
1 2
1 3
1 4
1 5
iqn./de
1
Kuehneosauridae
?
9
0
0
0
0
0
0
0
9
?
0
0
0
0
2
Marmoretta
0
0
0
0
0
0
0
0
0
9
?
0
0
?
0
3
Rhynchocephalia
?
1
0
0
0
0
0
0/1
0
0
0
0
0
0
0
4
Ancestor
0
0/1
0
0
0
0
0
0
0
0
0
0
0
0
0
5
Iguanidae
0
0
0
0/1
0
0
0
0
0
0
0
0
1
0
0
6
Agamidae
0
0/1
0
0
0
0
0
0/1
0
0
0
0
0/1
0
0
7
Chamaeleonidae
?
f
0
0
0
0
0
0/1
0
0
0
0
1
0/1
0
8
Xantusiidae
1
0
0
0
0
0
?
?
0
0
0
0
0
1
9
Gekkonidae
1
0
0
0
0
0
1
9
0
0
0
0/1
0
0/1
1 0
Pygopodidae
0/1
0
0
0
0
0
1
?
0
0
0
0
0
0/1
1 1
Sineoamphisbaena
?
0
0
0
1
0
0
1
0
?
0
1
0
0
1 2
Dibamidae
0
0
0
0
0
0
1
9
0
0
1
?
0
1
1 3
Amphisbaenia
1
0
0
0
0/1
0/1
1
9
0
0
1
9
0
1
1 4
Lacertidae
1
0
1
0
0
0
0
0
0
0
0
0/1
0
1
1 5
Teiidae
1
0
1
0
0
0
0
0
0
0
0
1
0
0/1
1 6
Gymnophthalmidae
0
0
1
0
0
0
0/1
0/1
0
0
0
1
0
0/1
1 7
Cordylidae
0/1
0
0
0
0
0
0
0
0
0
0
0/1
0
0
1 8
Scincidae
0/1
1
0
0
0
0
0
0/1
0
0
0
0
0/1
0
0/1
1 9
Anguidae
0/1
1
0
0
0
0
0
0
0
0
0
0
1
0
0/1
2 0
Xenosauridae
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
2 1
Heloderma
0
1
0
0
0
0
0
0
0
0
0
0
1
0
0
22
Lanthanotus
0
0
0
0
1
0
1
0
0
1
0
0
1
1
0
2 3
Varanus
0
0
0
0
1
0
1
0
0
1
0
0
1
0/1 •
9
2 4
Mosasauroidea
0
0
0
0
1
0
1
0
0
0
1
0
1
0
?
25
Pachyrhachis
9
9
0
0*
0
0
9
9
0
1 *
?•
?
9
2 6
Scolecophidia
0
?
0
0
0
0
9
9
0
1
9
0/1
0
27
Dinilysia
0
9
?
0
0
0
9
9
0
0*
9
0
0
2 8
Anilioidea
0
?
0
0
0
0
9
9
0
1
9
0
0
29
Macrostomata
0
9
0
0
0
0
9
9
0
1
9
0
0
Pachyrhachis 2
1 6
1 7
1 8
1 9
2 0
2 1
2 2
2 3
2 4
2 5
2 6
2 7
2 8
2 9
3 O
ord.
ord.
ord
1
Kuehneosauridae
0
0/1
1
0
0
0
0
0
0
0
0
0
0
0
0
2
Marmoretta
0
0
0
0
9
0
0
0
0
0
9
0
0
0
1
3
Rhynchocephalia
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0/1
4
Ancestor
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0/1
5
Iguanidae
0
1
0
1
1
1
0
1 12
0
0
0
0
0
0
1
6
Agamidae
0
1
0
1
1
1
0
2
?
0
0
0
0
0
1
7
Chamaeleonidae
1
1
0
0
1
0
0/1
2
9
0
0
0
0
0
1
8
Xantusiidae
0
0
0/1
1
0
1
0
0
9
1
0
1
?
0
0/1
9
Gekkonidae
0
0
0
1
0
1
0
0
9
1
0
1
9
2
0/1
1 0
Pygopodidae
0
0
0
0/1
0
1
0/1
0
?
1
0
1
9
2
0
1 1
Sineoamphisbaena
0
1
0
0
1
1
0
1
0
0
0
0
0
0
1 2
Dibamidae
0
0
0
0
1/3*
0
1/2
9
0&1
0
1
9
2
1
1 3
Amphisbaenia
0
0
0/1
0
0*
0
2
?
0
0
1
9
2
1
1 4
Lacertidae
0
0
1
0
0
0
0
?
1
1
1
9
0
1
1 5
Teiidae
0
0
1
0
0/1
0
0
0/1
1
0
0
1
0
1
1 6
Gymnophthalmidae
0
0
1
0
0
0
0
0
1
0
0
1
0
1
1 7
Cordylidae
0
0
0/1
1
0
0/1
0
0
0
1
0/1
0
1
0
1
1 8
Scincidae
0
0
1
0
1
0
0
0/1
1
0/1
0/1
1
0
1
1 9
Anguidae
0
0
0/1
1
0
1
0/1
0
0/1
1
1
0
1
0
1
20
Xenosauridae
0
0
0/1
1
0
1
0
0
1
1
1
0
1
0
1
2 1
Heloderma
0
0
0
0
1
1
0
?
0
0
1
9
0
1
2 2
Lanthanotus
1 *
0
0
0
1
1
0
9
1
0
1
9
0
1
2 3
Varanus
2
0
1
0
1
0
0
1
1
1
0
1
1
1
24
Mosasauroidea
2
0
1 '
0
2*
0
0
1
1
0/1
0
1
0
1
2 S
Pachyrhachis
7*
0
0
9
1
?'
?•
?*
?'
0
0
0
1
1
2 6
Scolecophidia
1
0
0
0
1 &3
9
2
9
9
0
1
9
?
0/1
27
Dinilysia
?
0
0
0
0
0
1
0
9
0
0
1
2
1
2 8
Anilioidea
1
0
0
0
3
1
2
9
?
0
0&1
1
2
1
2 9
Macrostomata
1
0
0
0
1
0
2
9
?
0
0
0&1
1 &2
1
50
FIELDIANA: GEOLOGY
Table 1. Continued.
Pachyrhachla 3
3 1
32
33
34
35
36
37
38
3 9
40
4 1
42
4 3
44
4 5
ord.
ord.
1
Kuehneosauridao
1
0
0
1
1
0
0
0
0/1
0
0
0
0
0
7
2
Marmoretta
0
0
1
?
2
?
?
0
0
?
?
0
0
7
?
3
Rhynchocephalia
0
0
0
0
1
0/1
0
0
1
0
0
0
0
0
0
4
Ancestor
0
0
0/1
0/1
1/2
0
0
0
0/1
0
0
0
0
0
0
5
IguankJae
0/1
0
0
1
0/1
0
0
0
1
0
0
0
0
1
6
Agamidae
0/1
0
0
1
0/1
0
0
0
1
0
0
0
0
1
7
Chamaeleonidae
0/1
0
0/1
2
1 /2
1
0
0
1
0
0
0
0
1
8
Xantusiidae
0
0
0/1
0
0
1
1
0
0
0
1
0
1
9
GekkonkJae
1
0
1
?
0
0
0 / 1
1
?
0
0
0
0/1
1 0
Pygopodidae
1
0
1
?
0
0
0
1
?
0
0
0
0
7
1 1
Sineoamphisbaena
1
0
1
7
0
0
0
0
1
0
1
0
0
7
1 2
Dibamidae
1
1
1
7
2
0
0/1
1
?
?
0
0
7
7
1 3
Amphisbaenia
1
1
1
0
2
0/1
1
1
?
1
0
0
0
7
1 4
Lacertidae
0
0
0
0
0
1
0
0
0
0
0
1
1 5
Teiidae
0
0
0
0
1/2
0
0
0
0/1
0
0
0
1 6
Gymnophthalmidae
0
0
1
7
0/1
0
0
0
0
0
0/1
0
1 7
Cordylidae
0/1
0
0/1
0
0
0/1
0
0
0
0
1
0
1 8
Seine idae
0/1
0
0
0
0
0
0
0
0
0
0
1
1 9
Anguidae
0
0
0
0/1
0
0
0
0
0/1
0/1
0
0/1
2 0
Xenosauridae
0
0
0
0/1
0/1
0
0
0/1
0
0/1
0
0
2 1
Heloderma
0
1
?
0
0
0
1
?
0
0
0
2 2
Lanthanotus
0
1
7
1
0
0
1
?
0
0
0
23
Varanus
0
0
0
1
0
0
0
0
0
0
0
24
Mosasauroidea
0
0
0
1
7
0
0
0
0
0/1
0
0
25
Pachyrhachis
0
1
7
2
0
1
?
1 •
?•
?•
?•
0
2 6
Scolecophidia
0
1
7
2
0
1
?
7
?
?
0
27
Dinilysia
0
1
7
2
0
1
?
?
?
?
0
28
Anilioidea
1
1
7
2
0
1
?
?
?
?
0
29
Macrostomata
0
1
?
2
0
1
?
?
?
7
0
Pachyrhachla 4
4 6
47
48
49
50
5 1
52
5 3
54
5 5
5 6
57
58
59
60
•
delete
ord.
ord.
delete
1
Kuehneosauridao
?
?
4
0
0
0
0
?
0
7
7
0
7
2
Marmoretta
?
?
0
0
0
0
?
0
7
7
0
7
3
Rhynchocephalia
0
0
0
0
0
0
0
0
7
0
0
0
4
Ancestor
0
0
0/4
0
0
0
0
0
0
7
0
0
0
5
kguanidae
0
0
0
0/1
0
0
0
0
7
0
0
6
Agamidae
0
0
0
1
0
0
0
0
7
0
0
7
Chamaeleonidae
0
0
2
1
0
0
0
0
7
0
0
8
Xantusiidae
0
0
0
1
0/1
0
1
0
0
0
9
Gekkonidae
0
0
0
1
1
0
0
7
0
0
1 0
Pygopodidae
?
7
0
1
1
0
0
7
0
0
1 1
Sineoamphisbaena
7*
?
?
2
1
1
1
1
0
0
0/2
1/2
1 2
Dibamidae
o •
7
?
2
0/1
1
0
1
1
0
0
7
1 3
Amphisbaenia
7*
7
7
1 •
2
1
1
1
1
1
0
2
2
1 4
Lacertidae
0
0
0
0
0
0
0
7
0
0
1 5
Teiidae
0*
0
0
0
0
0
0
1
0
0
0
1 6
Gymnophthalmidae
0
0
0
0
0/1
0
1
0
0
0
1 7
Cordylidae
0
0
0
0
0
1
0
0
0
1 8
Scincidae
0
0
0
0
0
0/1
0
0
0
1 9
Anguidae
0
0
0/1
0
0
0/1
1
0
0
2 0
Xenosauridae
0
0
0
0
0
0
7
0
0
2 1
Heloderma
0*
0
0
0
1
0
0
?
0
0
22
Lanthanotus
0'
0
1
0
0
0
7
0
0
2 3
Varanus
0*
0
1
1
0
0
7
0
0
24
Mosasauroidea
0*
1 '
2
0
0
0
0'
1 *
0
0
2 5
Pachyrhachis
0*
1
2
3*
2
7
?
0
7
7*
2 6
Scolecophidia
0
0
3
0
2
2
0
0
1
2 7
Dinilysia
0
0
2
2
2
7
2
0
0
7
2 8
Anilioidea
0
0
2
2
2
2
0
0
1/3
29
Macrostomata
0
1
2
3
2
2
0
0
3/4
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
51
Table 1. Continued.
Pachyrhachis 5
6 1
6 2
63
6 4
6 5
6 6
67
6 8
6 9
70
7 1
7 2
7 3
7 4
7 5
delete
| delete
delete
1
Kuehneosauridae
0
?
0
?
?
?
?
?
?
?
0
?
?
0
0
2
Marmoretta
?
?
?
7
?
?
0
?
?
7
7
?
7
0
0
3
Rhynchocephalia
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
Ancestor
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5
Iguanidae
0
0
0
0/1
0/1
0
0
0
0
0
0
0
0
0
0/1
6
Agamidae
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
7
Chamaeleonidae
0
7
0
0
0
0
0
0
0
1
0
0
0
0
0
8
Xantusiidae
0
?
0
1
1
0
1
0
0
0
0
0
0
0
0
9
Gekkonidae
0
0
0
1
1
0
0/1
0
0
0
0
0
0
0
0
1 0
Pygopodidae
0
0
0
1
1
0
1
0
0
0
0
0
0
0
0
1 1
Sineoamphisbaena
1
?
7
?
?
0
0
0
7
1
1
1
0
0
0
1 2
Dibamidae
0
?
0
0
?•
2*
0
0
1
1
1
1
0
0
0
1 3
Amphisbaenia
1
1
2
1
?•
2*
0
0
1
1
1
1
0
0/1
0
1 4
Lacertidae
0
0
0
1
1
0
0
0
0
0
0
0
0
0
1
1 5
Teiidae
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
1 6
Gymnophthalmidae
0
?
0
1
1
0
0/1
0
0
0
0
0
0
0
0
1 7
Cordylidae
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
1 8
Scincidae
0
0
0
1
1
0
0
0
0
0
0
0/1 *
0
0
0/1
1 9
Anguidae
0
0/1
0
1
1
0/1
0
0
1
0
0
0/1
0
0
0
2 0
Xenosauridaa
0
0
0
1
1
1
0
0
1
0
0
0
0
0
0
2 1
Heloderma
0
?
0
1
1
1 •
0
0
1
0
0
0
0
0
1
2 2
Lanthanotus
0
7
0
1
1
1
0
1
1
0
0
0
0
0
1
2 3
Varanus
0
0
0
1
1
0
0
1
1
0
0
0
0
0
1
24
Mosasauroidea
0*
1
0
1
1
0
0
1
1
0
0
0
0*
1
1
25
Pachyrhachis
2
1
1
?*
?
?
?
?
?
?•
?•
?
?•
?
2 6
Scolecophidia
2
1
?
?
2
0
1
1
0
1
1
1
?
7
27
Dinilysia
2
1
?
?
2
0
?
?
0
1
1
1
?
?
28
Anilioidea
2
1
?
7
2
0
1
1
0
1
1
1
?
?
29
Macrostomata
2
1
?
?
2
0
1
1
0
1
0&1
1
?
?
Pachyrhachis 6
7 6
77
7 8
79
80
8 1
8 2
83
8 4
8 5
8 6
87
8 8
89
9 0
ord.
ord.
delete
delete
1
Kuehneosauridae
0
?
?
?
?
0
0
0
0
?
?
?
?
?
?
2
Marmoretta
0
0
0
?
?
?
0
?
?
?
?
?
?
?
?
3
Rhynchocephalia
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
Ancestor
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5
Iguanidae
0
0
0
0
0*
0
0
0
0/1 •
0
0
0
0
0
6
Agamidae
0
0
0
0
0
0
0
0
0
0
0
0
0
0
7
Chamaeleonidae
0
0
0
0
0*
0
0
0
?
?
?
?
0
1
8
Xantusiidae
0
0/1
0
0
0*
0
0
0
0
0/1
1
9
Gekkonidae
0
0
0
0/1 *
0
0
0
0
0
0/1
1 0
Pygopodidae
0
0
0
1/2*
0/1 •
0
0
0
0
1
1 1
Sineoamphisbaena
?
0
0
1 *
0
0
0
0
0 _J
1
0
1 2
Dibamidae
2
1
0
2*
1
0
1
0
0
2
0
1 3
Amphisbaenia
2
0
0
2*
0/1
0
1
0
0
1
0
1 4
Lacertidae
0
1
0
0
0/1 *
0
0
0
0
0
0
0
1 5
Teiidae
0
0
0
0
0*
0
0
0
0
0
0
0
1 6
Gymnophthalmidae
0
0
0
0
0*
0
0
0
0
0
0/1
0
1 7
Cordylidae
0
0/1
0
0
0*
0
0
0
0
0
0
0
1 8
Scincidae
0
0/1
0
0
0/1/2
' 0/1 *
0
0
0
0
0/1
0/1
1 9
Anguidae
0
1
0/1
0
0/1 *
0
0
0
0
0
0
2 0
Xenosauridae
0
0/1
0
0
0*
0
0
0
0
0
0
2 1
Heloderma
0
1
1
0
0
0
0
0
0
0
0
22
Lanthanotus
1
1
0
1
0*
0
0
0
0
0
0
23
Varanus
1
0
0
1
0*
0
0
0
0
0
0
24
Mosasauroidea
1
0
0*
0
0*
0
0
0
1
1
0
0
25
Pachyrhachis
?
?
?
?
2
?
7
?
7
?
?
2
?
2 6
Scolecophidia
?
1
0
0
2
0
7
0&1
2
0
27
Dinilysia
?
?
0
0
2
0
?
?
?
7
?
0
2 8
Anilioidea
?
1
0
0
2
0
7
1
2
0
2 9
Macrostomata
?
0
0
0
2
0
?
1
2
0
52
FIELDIANA: GEOLOGY
Table 1. Continued.
Pachyrhachls 7
9 1
92
93
94
95
9 6
97
98
99
1 00
101
102
1 03
1 04
105
ord.
ord.
1
Kuehneosauridae
0
0
0
0
0
?
?
0
?
0
?
0
0
1
0
2
Marmoretta
0
0
?
0
0
0
?
0
1
7
0
0
0
1
?
3
Rhynchocephalia
0
0
0
0
0
0
0
0
0
0
0
0
0
0/1
0
4
Ancestor
0
0
0
0
0
0
0
0
0/1
0
0
0
0
1
0
5
Iguanidae
0
0
0
0
0
0
0
0
0
0
0
0
0
0/1
6
Agamidae
0
0
0
0
0
0
0
0
1
0
0
0
0
0/1
7
Chamaeteonidas
0
0
1
0
0
0
0
0
1
0, 1
0/1
0
0
0
8
Xantusiidae
0
0
0
0
0
0
0
0
0
0/1
0
0
9
Gekkonidae
0
0
0
0
0
0
0
0
0
0/1
0
0
1 0
Pygopodidao
0
0
0
0
0
0
1
0
0
0/1
0
0
1 1
Sineoamphisbaena
1
0
0
0
1
0
0
0
0
1
2
0
1 2
DbamkJae
1
0
0
1
1
0
0
0
0
1
1
1
1 3
Amphisbaenia
1
0
0
0
1
0
0
0
0
1
2
2
0/1
1 4
Lacertidae
0
0
0
0
0
0
0
0
0
0
0
0/1
1 5
Teiidae
0
0
0
0
0
0
0
0
0
1
0
1
1 6
Gymnophthalmidae
0
0
0
0
0
0
0
0
0
0
0
1
1 7
Cordylidae
0
0
0
0
0
0
0
0
0
0
0
0
1 8
Seine idae
0
0
0
1
0
0
0
0
0
0
0
0
1 9
Anguidae
0
0
0
0
0
0
0
0
0
0/1
0
0
20
Xenosauridae
0
0/1
0
0
0
0
0
0
0
0
0
0
0
2 1
Heloderma
0
1
0
0
0
0
1
0
0
1
0
0
22
Lanthanotus
0
0
0
0
0
0
1
0
0
1
0
0
23
Varanus
0
1
0
0
0
0
1
0
0
0
1
0
0
24
Mosasauroidea
0
1
0
0
0
0
1
0
0
?•
0
1
25
Pachyrhachis
?•
7
?•
0
?•
?•
?•
0
0
0
0
26
Scolecophidia
0
0
1
0
0
1
0&1
0
?
0
0
27
Oinilysia
0
?
1
0
1
1
0
0
0
0
0
28
Anilioidea
0
0
1
0
0
1
0
0
0
0
0
29
Macrostomata
0
1
1
0
0
1
0
0
0
0
0
Pachy
rhachla 8
1 06
107
1 08
1 09
1 10
1 1 1
1 1 2
1 1 3
1 1 4
1 1 5
1 1 6
1 17
1 18
1 1 9
1 20
ord.
ord.
ord.
ord.
ord.
1
Kuehneosauridae
?
0
0
?
1
0
0
0
0
?
?
?
0/1
0
0
2
Marmoretta
0
7
7
0
0
0
0
2
0
0
?
0
?
0
?
3
Rhynchocephalia
0
0
0
0
0
0
0/1
0
0
0
0
1
0/1
0
2
4
Ancestor
0
0
0
0
0
0
0
0/2
0
0
0
0/1
0/1
0
0/2
5
Iguanidae
0
0
0
0/1
0
0
1
2
0/1/2
0/1
0
1/2
1
0
0/1/2
6
Agamidae
1
0
0
0
0
0
0/1
2
0
0
0
?
1
0
1/2
7
Chamaeleonidae
1
0
0
1
0
0
0
2
0
0
0
?
1
0
2
8
Xantusiidae
0
0
0
0
0
0
0
1
2
?
0
0
1
0
1
9
Gekkonidae
0/1
0
0
0
0
0
0/1
2
2
?
0
0
1
0
1
1 0
Pygopodidae
0
0
0
0
0
0
0/1
2
2
?
0
0
0/1
0
1
1 1
Sineoamphisbaena
?
?
1
7
0
7
0
2
?
?
?
7
0
0
?
1 2
DbamkJae
?
0
1
0/1
0
0
0
0
2
?
0
0
0
0
2
1 3
Amphisbaenia
0/'
?
1
0/1
0
0
on
0
0/1/2
1
0
1/2
1
0
1/2
1 4
Lacertidae
0
0
0
0
0
0
1
2
0
0/1
0
0
1
0
0
1 5
Teiidae
0/1
0
0
0
0
0
1
2
0/1
0
0
0
1
0
0
1 6
Gymnophthalmidae
1
0
0
0
0
0
0/1
2
0/2
0
0
0/1
0/1
0
0/1
1 7
Cordylidae
0/1
0
0
0
0
0
1
1
0
0
0
0
1
0
0
1 8
Scincidae
0/1
0
0
0
0
0
1
1
0/1/2
0
0
0
1
0
0/1
1 9
Anguidae
0
0
0
0
0
0
1
1/2
0
0
1
1
0
0/1
2 0
Xenosauridae
0
0
0
0
0
0
1
1
0
0
1
1
0
0
2 1
Heloderma
0
0
0
0
0
0
1
2
0
0
2
1
0*
1
2 2
Lanthanotus
0
0
0
0
0
0
1
2
0
0
2
1
0*
1
23
Varanus
1
0
0
0
0
0
1
2
0
0
2
1
0*
0
24
Mosasauroidea
0
1
0
0
0
0/1 •
2
0
1
2*
0
1
0
25
Pachyrhachis
?
?
0
7
?•
2
0
0
?
2
2
2
0
26
Scolecophidia
1
?
?
0
1
2
0
0
7
2
0
2
0
27
Dinilysia
1
0
0
0
1
2
0
0
?
2
2
2
1
28
Anilioidea
0/1
1
0
0
1
2
0
0
0
2
2
2
1
29
Macrostomata
0/1
1
0
0
1
2
0
0
?
2
2
2
0
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
53
Table 1. Continued.
Pachyrhachis 9
1 21
1 22
1 23
1 24
1 25
1 26
1 27
1 28
1 29
1 30
1 31
1 32
1 33
1 34
1 35
ord.
delete
delete
dolete
1
Kuehneosauridae
?
?
?
?
?
?
?
?
?
0
?
0
?
0
?
2
Marmoretta
?
9
?
?
0
0
?
9
?
?
0
?
?
?
9
3
Rhynchocephalia
9
9
?
?
0
0
9
0
0
0
0
0
0
0
0
4
Ancestor
?
?
?
?
0
0
?
0
0
0
0
0
0
0
0
S
Iguanidae
0*
0/1
0
0
0
r 0/1
0
0*
0
0
0
0/1
0/1
6
Agamidae
0*
1
0
0
0
0
0
0
0
0
0
0
1
7
Chamaeleonidae
0*
?
?
?
0
0
9
0
0
0
0
0
0
0/1
8
Xantusiidae
0*
0
0
0
0
0
0
0*
0
0/1
1
?
0
9
Gekkonidae
0
1
0
0
0
1
0
0*
0
0
0/1
1
0
1 0
Pygopodidao
0
1
0
0
0
1
0
0*
0
0
1
?
0
1 1
Sineoamphisbaena
9
?
9
?
?
1
9
0
9
0
0
?
0
?
1 2
Dibamidae
0*
9
?
?
1
0
9
0/1
1 •
?'
0
1
9
0
1 3
Amphisbaenia
0*
1
0
0
0/1
0
0
0/1
1 *
?*
0/1
0/1
0
0
9
1 4
Lacertidae
0
0/1
0
0
0
1
0
0*
0
0
0
0
1 5
Teiidae
0
1
0
0
0
1
0
0*
0
0
0
0
1 6
Gymnophthalmidae
0*
1
0
0
0
1
0
0*
0
0
0
0
1 7
Cordylidae
0
0
0
0
0
1
0
o •
0
1
0
0
1 8
Scincidae
0
0/1
0
0
0
1
0
0*
0
1
0
0
1 9
Anguidae
0
0
0
0
0
1
0
0*
0
0/1
0
0
20
Xenosauridae
0
0
0
0
0
1
0
0*
0
0
0
0
2 1
Heloderma
0*
0
0
0
1
0
0*
1
0
0
0
0
22
Lanthanotus
o-
0
0
1
0
0
0*
2
0
0
0
0
0
2 3
Varanus
0*
0
0
0
0
0
o-
2
0
0
0
0
0
24
Mosasauroidea
1 *
1
1
0
1
0
0
2
0
0
0
0
1
25
Pachyrhachis
?*
1
?•
?•
?•
0
1 •
3
0
0
0
0
?•
2 6
Scolecophidia
0
0
?
9
0
0
1
?
1
0
0
0
0
27
Dinilysia
2
1
9
?
0
0
1
3
0
0
0
0
?
28
Anilioidea
2
1
9
?
0/1
0
1
3
0
0/1
0
0
?
29
Macrostomata
2
1
9
?
0/1
0
1
3
0
0
0
0
9
Pachyrhachis 10
1 36
137
1 38
1 39
1 40
1 41
142
1 43
1 44
1 45
1 46
1 47
1 48
1 49
1 50
ord.
ord.
ord.
delete
1
Kuehneosauridae
0
?
0
0
0
0
0
0
1
0
0
0
0
0
2
Marmoretta
?
0
9
1 12
9
?
9
9
9
9
0
0
0
0
3
Rhynchocephalia
0
0
0
2
0
0
0
0
0
0
0/1
0
0
0
0/2
4
Ancestor
0
0
0
1/2
0
0
0
0
0/1
0
0
0
0
0
5
Iguanidae
0
0
0
0
0
0
0/1
0
0
0
0
0
0
0
6
Agamidae
0
0
0
0
0
0
0
0
0
0/1
0
0
0
2
7
Chamaeleonidae
0
0
0
0
0
0
0/1
0
0
0/1
0
0
0
2
8
Xantusiidae
1
0
0
2
0
0
0
0
0
0
0
0
0
0
9
Gekkonidae
0
0
0
0
1
1
1
0
1
1
0
0
0
0
1 0
Pygopodidae
0
0
0
0
1
1
1
0
1
0
0
0
0
0
1 1
Sineoamphisbaena
9
9
0
0/1
0
9
9
9
9
9
0
0
0
2
1 2
Dibamidae
0
0
0
0*
0
0
1
0
1
1
0
0
0
1
1 3
Amphisbaenia
0
0
0
0/1 /2
0
1
1
0
1
1
0/1
0
0
0
1
1 4
Lacertidae
1
0
1
0
0
0
0
0
0
0
0
0
0
0
1 5
Teiidae
2
0
1
0
0
0
0
0
0
0
0
0
0
0/1
1 6
Gymnophthalmidae
2
0
1
0
0
0
0
0
0
0/1
0
0
0
0/1
1 7
Cordylidae
0
0
0
0
0
1
0/1
1
1
1
0
0
0
0
1 8
Scincidae
0
0
0/1
0
0
1
1
1
1
1
0
0
0
0/1
1 9
Anguidae
0
0
0
0
0
1
1
0
1
1
0
0/1
0
1
20
Xenosauridae
0
0
0
0
0
0
1
0
0
1
0
0
0
1
2 1
Heloderma
0
0
0
0
0
1
1
0
0
1
2 *
1
1
1
2 2
Lanthanotus
0
0
0
0
0
1
1
0
0
1
2*
1
1
1
2 3
Varanus
0
0
0
0
0
1
1
0
0
1
2*
1
1
1
2 4
Mosasauroidea
0
1
0
1
0
1
1
0
1
1
2*
0*
1
1
2 5
Pachyrhachis
0
1
0
?•
9
2 '
?
9
9
9
3 •
0
o-
?
2 6
Scolecophidia
0
0
0
9
0
0
9
0
0
9
2
0
0
1
27
Dinilysia
0
1
0
9
9
?
?
9
9
9
3
0
0
9
2 8
Anilioidea
0
0/1
0
9
0
2
?
0
0
9
3
0
0
1
29
Macrostomata
0
1
0
9
0
2
?
0
0
?
3
0
0
1
54
FIELDIANA: GEOLOGY
Table 1. Continued.
Pachyrhachis 1 1
151
1 52
1 S3
1 54
155
156
157
158
1 59
160
161
162
163
1 64
1 65
ord.
ord.
delete
ord.
ord.
1
Kuehneosauridae
0
7
0
0
?
0
0
0
0
0
0
0
?
?
?
2
Marmoretta
0
7
0
0
?
0
0
0
0
0
0
?
?
?
?
3
Rhynchocephalia
0
0
0
0
?
0
0
0
0
0
0
0
?
?
?
4
Ancestor
0
0
0
0
?
0
0
0
0
0
0
0
?
?
?
5
Iguanidae
0
0
0
0
0
0
0
0/1
0
0/1
0
0
0
6
Agamidae
7
?
0
0
0/1
0
0
?
1
?
0
0/1
7
Chamaeteonidae
7
?
1
0
1
0
0
7
1
?
0
0
8
Xantusiidae
0
0
0
0
0
0
0
?
1
?
0
0
9
Gekkonidae
0
0
0
0
0
0
0
?
1
?
1
0
1 0
Pygopodidae
0
0
0
0
0
0
0
?
1
?
1
0
1 1
Sineoamphisbaena
7
?
0
1
0
1
1
?
1
?
?
0
1 2
Dbamidae
0
0
0
1
0
1/2
1
?
1
?
0
0
1 3
Amphisbaenia
0
0
0 1
1
0/1
2
2
?
1
?
0
0
1 4
Lacertidae
0
0
0
0
0/1
0
0
?
0/1
0
0
0
1 5
Teiidae
0
0
0
0
0/1
0/1
0
?
0/1
0
0
0/1
1 6
Gymnophthalmidae
0
0
0
0
0
0
0
?
1
0
0
0
1 7
Cordylidae
0
0
0
0
0
0
0
?
0/1
0
0
0
1 8
Scincidae
0
0
0
0
0
0
0
?
0/1
0
0
0
1 9
Anguidae
0
0
0
0
0
0
0
0
0/1
0
0
0
2 0
Xenosauridae
0
0
0
0
0
0
0
?
0/1
0
0
0
21
Heloderma
1 •
0
0
0
1
1
1
0/1
0
0
0
0
0
2 2
Lanthanotus
1 •
0
0
0
1
1
1
0
0
0
?
1
2
23
Varanus
1 •
0
0
0
1
1
1
7
1
?
0
2
2
24
Mosasauroidea
2*
0*
1
0
?
1
0
0
7
0
1
7
0
0/1
2 5
Pachyrhachis
?'
7
1
7
?
7
0
0
0
1
0
1
?
0
0
26
Scolecophidia
0
1
1
0
7
7
2
2
1
7
1
?
?
0
0
27
Dinilysia
7
7
7
7
?
7
0
1
0
?
0
1
?
1
?
28
Anilioidea
1
1
1
0
7
1
1
0/1
0
1
0
1
0
0
0/1
29
Macrostomata
1
1
1
0
7
1
0
0
0
1
0
1
0
0/1
1
Pachyrhachis 12
1 66
1 67
1 68
1 69
170
171
172
173
174
175
1 76
177
178
179
180
delete
ord.
ord.
delete
ord.
ord.
1
Kuehneosauridae
?
?
0
o •
?
7
1
1
0
0
0
0
0
?
0
2
Marmoretta
7
?
0
7
?
7
?
?
?
?
7
?
?
?
?
3
Rhynchocephalia
?
0
0
1 •
0
0
1
1
0
0
0
0
0
?
0
4
Ancestor
?
0
0
0/1
0
0
1
1
0
0
0
0
0
?
0
5
Iguanidae
0
0
0/1
1
0/1
1
0
0
0/1
0
0/1
1
0
6
Agamidae
0
0
0*
7
0/1
1
0
0
0
1/2
0
?
0
7
Chamaeteonidae
0
0
0*
7
0
0
0
0
0
0
0
?
0
8
Xantusiidae
0
0
0*
?
0/1
2/3
1
0
0
0
0/1
0/1
1
0
9
Gekkonidae
1
0
0
0*
?
1/2/3
1
0
0
0
0
0
?
0
1 0
Pygopodidae
1
0
0
0*
7
4
0
0
0
0
0
0
?
0
1 1
Sineoamphisbaena
0
0
0*
?
f
1
1
1
0
0
7
?
?
1 2
Dbamidae
0
1
0*
?
4/5
0
1
1
2
0
0
?
1
1 3
Amphisbaenia
0
1
0*
7
4/5
0
0/1
1
2
0
0
?
1
1 4
Lacertidae
0
0
1 •
0
1/2/3
1
0
0
0/1
0/1
0/1
1
0
1 5
Teiidae
0
0
2*
1
1/2/3
1
0
0
0
1
1
1
0
1 6
Gymnophthalmidae
0
0
0
1
1/2/3
1
0
0
0
1/2
1
1
0
1 7
Cordylidae
0
0/1
1 •
?
2/3
0/1
0
0
0
0
0
?
0
1 8
Scincidae
0
0
0"
?
3
1
0
0
1/2
0
0/1
0
0
1 9
Anguidae
0
0
0*
?
3/4
0/1
0/1
0
2
0
0/1
0
0
20
Xenosauridae
0
0
0"
?
2/3
1
0
0
2
0
0
0
2 1
Heloderma
0
0
0'
7
3
1
0
0
1/2
0
0
0
22
Lanthanotus
0
0
0*
?
3
2
1
0
1/2
0
0
0
23
Varanus
0
0
0*
7
3
2
1
0
2
0
0
0
24
Mosasauroidea
1
0
2*
1
3
7
1
1
0
0
0
0
25
Pachyrhachis
?
7
0
2'
?
5
?
1
0
2
0
0
0
26
Scolecophidia
0
0
1
2
7
5
?
?
1
2
0
0
0
27
Dinilysia
?
7
1
2
?
5
?
?
1
2
0
?
?
28
Anilioidea
0/1
0
1
2
?
5
?
?
1
2
0
0
0
29
Macrostomata
0/1
0
1
2
?
1
5
?
?
1
2
0
0
0
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
55
Table 1. Continued.
Pachyrhachls 13
181
1 82
1 83
1 84
1 85
1 86
187
1 88
1 89
190
1 91
1 92
1 93
1 94
1 95
ord.
1
Kuehneosauridae
1
7
7
9
?
?
0
0
0
0
0
0
0
7
7
2
Marmoretta
7
7
7
7
7
7
7
7
7
?
7
7
7
7
7
3
Rhynchocephalia
0
0
0
0
0
0
0
0
0
0
0/1
0
0
0
0
4
Ancestor
0/1
0
0
0
0
0
0
0
0
0
0/1
0
0
0
0
5
Iguanidae
0/1
0/1
0/1
0
0
1
0
0
0
0
0/1
0/1
0
0
6
Agamidae
1
?
0
0
0
1
0
0
0
0
0
0/1
0
0
7
Chamaeleonidae
1
7
0
0
0
1
0
0
0
0
1
0
1
7
8
Xantusiidae
0
0
0
0
0
1
0
0
0
0
0
0
0
1
9
Gekkonidae
0
1
0
0
0
1
0
0
0
0
1
0/1
0
1
1 0
Pygopodidae
0
1
0
0
0
0
1
0
0
1
0
0
0
1
1 1
Sineoamphisbaena
7
7
7
7
7
1
0
0
7
0
7
7
7
7
1 2
Dibamidae
0
0
0
0
0
0
1
1
1
1
7
7
1
7
1 3
Amphisbaenia
0/1
0
7
1
0
0
1
1
1
0/1/2
0
0
0/1
1
1 4
Lacertidae
0
0
0
0
0
1
0
0
0
0
0
0
0
1
1 S
Teiidae
0
0
0
0
0
1
0
0
0
0
0/1
1
0
1
1 6
Gymnophthalmidae
0
0
0
0
0
1
0
0
0
0
0
1
0
1
1 7
Cordylidae
0
0
0
0
0
1
0
0
0
0
0
0
0
0/1
1 8
Scincidae
0/1
0
0
0
0
1
0
0
0
0
0/1
0
0
1
1 9
Anguidae
0/1
0
0
0
0
0/1
0
0
0
0/1
0/1
0
0
1
20
Xenosauridae
0/1
0
0
0
0
1
0
0
0
0
0
0
0
1
2 1
Heloderma
1
7
0
0
1
1
0
0
0
0
0
0
0
1
2 2
Lanthanotus
1
7
1
0
1
1
0
0
0
0
0
0
0
1
2 3
Varanus
1
7
1
0
1
1
0
0
0
0
0
1
0
0/1
2 4
Mosasauroidea
1
?
1
0
1
0
0
0
0
0
0
0/1
0
0
7
2 5
Pachyrhachis
1
7
7
7
7
7
0
0
1
2
7
7
7
2 6
Scolecophidia
1
7
7
7
7
7
0
0
1
2
7
7
7
27
Dinilysia
7
7
7
7
7
7
0
0
7
7
7
7
7
7
2 8
Anilioidea
1
7
7
7
7
7
0
0
1
2
7
7
7
29
Macrostomata
1
7
7
7
7
7
0
0
1
2
7
7
7
Pachyrhachis 14
196
197
1 98
1 99
200
201
202
203
204
205
206
207
208
209
21 0
ord
ord.
ord.
delete
1
Kuehneosauridae
7
7
7
7
7
7
7
7
0
0
0
1
0
0
0
2
Marmoretta
?
?
7
7
7
7
?
7
0
7
7
7
7
7
?
3
Rhynchocephalia
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
4
Ancestor
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
5
Iguanidae
0/1
0
0
0
0
0/1
1/2
0/1
0
0
0
1
0
0
0
6
Agamidae
0
0
0
0/1
0
1
0/1
0
0
0
0
1
0
0
0
7
Chamaeleonidae
7
1
7
7
0
0/1
3
1
0
1
0
1
1
0
0
8
Xantusiidae
1
0
0
1
0
0/1
1
0
0
0
0
0
1
2
9
Gekkonidae
1
0
0/1
1
0
0/1
1/2
0
0
0
0
1
1
1
1 0
Pygopodidae
0
1
7
7
0
0
3
0
1
7
1
0
1
7
1 1
Sineoamphisbaena
7
0
7
7
7
7
7
7
0
0
7
7
7
7
1 2
Dibamidae
7
1
7
7
0
0
3
1
1
7
1
0/1
0
7
1 3
Amphisbaenia
7
1
7
7
0/1
0
3
0
0/1
1
1
0
1
7
1 4
Lacertidae
0
0
1
0
1
1
0/1
0
0
0
1
0
2
1 5
Teiidae
0
0
1
0
1
1
0
0
1
0
0
0
1
1 6
Gymnophthalmidae
0
0
1
0
1
1
0
0
1
0
0
1
2
1 7
Cordylidae
0/1
0
0
1
0
0
1 12
0/1
0
0
0
0
0
2
1 8
Scincidae
0/1
0
1
0
0/1
1
0/1
0
0
0
0/1
1
2
1 9
Anguidae
0/1
0
1
0
0
1/2
0
0/1
0
0/1
0
0/1
2
20
Xenosauridae
0
0
0
0/1
0
0
1
0
0
0
0
0
0/1
1
2 1
Heloderma
0
0
1
7
0
0
1
0
0
0
0
1
1
1
2 2
Lanthanotus
0
0
0
1
0
0
3
0
0
0
0
1
1
1
23
Varanus
0
0
0
0/1
0
0/1
2
0
0
0
0
1
0
0
24
Mosasauroidea
0
0
1
7
0
0
0
0
0
0
1 *
1
0/1
25
Pachyrhachis
7
1
7
7
1
7
7
0
1
7
1
2
1
1
2 6
Scolecophidia
7
1
7
7
1
7
7
0
1
7
1
2
1
7
7
2 7
Dinilysia
7
7
7
7
7
7
7
0
7
7
7
7
7
?
7
2 8
Anilioidea
7
1
7
7
1
7
7
0
1
7
1
2
1
7
7
2 9
Macrostomata
7
1
?
7
1
7
7
0
1
7
1/2
2
1
7
7
56
FIELDIANA: GEOLOGY
Table 1. Continued.
Pachyrhachls 15
21 1
21 2
213
214
21 5
21 6
21 7
21 8
219
220
221
222
223
224
225
delete
delete
ord.
ord.
ord.
1
Kuehneosauridae
0
0
0
0
7
0
0
0
?
7
0
?
?
7
'
2
Marmoretta
?
?
?
7
?
?
?
?
?
?
0
?
?
?
?
3
Rhynchocephalia
0
0
0
0
0
0
0
0
?
?
0
0
0
0
0
4
Ancestor
0
0
0
0
0
0
0
0
?
?
0
0
0
?
0
5
Iguanidae
0
0
0
0
0
0
0
0
?
?
0/1
0
1/2
0
0/1
6
Agamidae
0
0
0
0
0
0
0
0
?
?
0/1
0
2
0
0/1
7
Chamaeleonidae
0
0
1
0
0
0
0
0
?
?
0/1
0
2
0
1
8
Xantusndae
0
0
0
1
0
0
0
0
?
?
0/2
0
1
0
0
9
Gekkonidae
0
0
0
1
0
0/1
0
0
?
?
0
0
0
1
0
1 0
Pygopodidae
1
?
?
?
?
0
0
0
?
?
0
0
0
1
0
1 1
Sineoamphisbaena
?
?
?
?
?
0
0
0
?
?
2
?
?
?
?
1 2
Dibamidae
1
?
7
?
?
0
0
0
?
?
0
1
?
?
1
1 3
Amphisbaenia
1
7
7
7
?
0
0
0
?
?
0/2
0/1
2
?
1
1 4
Lacertidae
0
0
0
1
0
0
0
1
0
0
2
0
1/2
0
0
1 5
Teiidae
0
0
0
1
0
0
0
0
?
?
0/2
0
1
0
0
1 6
Gymnophthalmidae
0
0
0
1
0
0
0
0
?
?
0/2
0
1/2
0
1
1 7
Cordylidae
0
0
0
1
0
1
2
0
0
2
0
2
0
0
1 8
Scincidae
0
0
0
1
0
1
2
0
0
0/2
0
1/2
0
0/1
1 9
Anguidae
0/1
0
0
1
0
1
2
0
0
0/1
0
1/2
0
0/1
20
Xenosauridae
0
0
0
1
0
0
2
1
0
2
0
1
0
1
2 1
Heloderma
0
0
0
1
0
0
2
1
0
1
0
2
0
0
2 2
Lanthanotus
0
0
0
1
0
0
2
1
1
0
0
2
0
1
23
Varanus
0
0
0
1
0
0/1
0
0/2
1
1
0/1
0
0
0
1
24
Mosasauroidea
0
1
1
0
1
0
0
0
?
?
0
0
1
0
?
25
Pachyrhachis
1
1
1
0
1
0
0
0
?
?
0
?
?
?
26
Scolecophidia
1
7
7
7
7
0
0
0
?
?
0
?
?
1
27
Dinilysia
7
7
?
?
?
0
0
0
7
7
0
7
?
?
28
Anilioidea
1
7
7
7
7
0
0
0
?
7
0
?
?
1
29
Macrostomata
1
7
7
7
7
0
0
0
?
?
0
?
?
1
Pachyrhachls 16
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
delete
ord.
ord.*
1
Kuehneosauridae
7
1
1
?
7
?
7
0
0
0
0
0
0
0
0
2
Marmoretta
7
7
7
7
7
7
?
0
0
0
0
0
0
0
0
3
Rhynchocephalia
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
Ancestor
0
0/1
0/1
0
0
0
0
0
0
0
0
0
0
0
0
5
Iguanidae
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
6
Agamidae
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
7
Chamaeleonidae
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
8
Xantusiidae
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
9
Gekkonidae
0
0
0
1
1
0
1
0
0
0
0
0
0
0
0
1 0
Pygopodidae
0
0
0
?
1
0
1
0
0
1
0
0
0
0
0
1 1
Sineoamphisbaena
?
0
0
0
7
0
?
0
0
?
?
0
0
0
0
1 2
Dibamidae
1
0
0
7
0
0
1
0
1
1
0
0
0
0
1
1 3
Amphisbaenia
0/1
0
0
1
0
0
?
0
0
2
1
0
0
0
1
1 4
Lacertidae
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1 5
Tendae
0/1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1 6
Gymnophthalmidae
0/1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1 7
Cordylidae
0/1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1 8
Scincidae
0/1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1 9
Anguidae
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
2 0
Xenosauridae
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
2 1
Heloderma
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
2 2
Lanthanotus
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
23
Varanus
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
24
Mosasauroidea
?
0/1 •
0/1
?
0
0
0
0
0
0
0
0
0
0
0
25
Pachyrhachis
7
1
1
?
0
?
?
1
0
1
0
1
1
1
26
Scolecophidia
1
1
7
7
0
0
?
0
1
2
1
0
0
0
27
Dinilysia
?
1
?
?
?
0
?
0
?
?
?
0
0
0
28
Anilioidea
1
1
?
7
0
1
1
0
1
2
1
1
0/1
0
1
29
Macrostomata
1
1
7
7
0
1
1
1
1
2
1
1
1
1
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
57
many of the characters are problematic, yet some
were alternatively retained or deleted in the cla-
distic analysis as coded by Lee (1998) in order to
remain as close to the original character evidence
as possible. A large number of character states are
given as the relative size of continuous variables
(e.g., 7, 19, 23, 28, 53, 66, etc.) without reference
to some standard. Although this may cause prob-
lems for other workers attempting to critically
evaluate character-state assignments, we retained
these character codings unaltered. The same is
true for distinctions of character states that appear
to be purely arbitrary, such as "three or more"
versus "two or less" in character 111 (see also
characters 153, 157, 158, 172, 173, 174, 223).
Furthermore, the terminal taxa are coded at the
family level, which most probably will result in a
substantial degree of polymorphism as greater
scrutiny is applied to character coding. As pointed
out by Etheridge (personal communication), Ig-
uanidae are coded with a single character state for
characters 8, 15, 34, 36, 39, 45, 50, 96, 103, 132,
139, 144, 168, 179, and 180, all of which exhibit
two or more states in that taxon. It remains to be
seen to what degree polymorphism applies to oth-
er terminal taxa. Anniella, for example, would
greatly affect the coding for Anguidae if it were
to be included in that family, and might affect the
result of the analysis if it were included as ter-
minal taxon. If a terminal taxon is polymorphic
for a given character, then the plesiomorphic char-
acter state, if known, should be used for that tax-
on. Yet the plesiomorphic character state can only
be determined by phylogenetic analysis in intra-
familial relationships, and these are often not
available. Pleurodont iguanians are a case in point
(Frost & Etheridge, 1989), with potentially seri-
ous consequences for coding of the Iguanidae. A
global assessment of squamate relationships will
necessitate breaking up terminal taxa into groups
below the family level or rejecting previous ana-
lyses of intrafamilial relationships in order to de-
termine the plesiomorphic character state at the
family level.
Finally, we also note that work in progress is
likely to change several character codings for am-
phisbaenians as well as for Sineoamphisbaena
(M. Kearney, personal communication) without
threatening to change the major conclusions
reached in this paper, however. At this point, our
interest is not in the recovery of squamate history
(which is beyond the scope of this paper). Instead,
our goals are twofold. The first is to test the re-
lationships of Pachyrhachis on the basis of the
evidence proposed by Lee (1998), for which rea-
son we propose to split up Serpentes as a terminal
taxon. The second goal is to test Lee's (1998) con-
clusion that the burrowing ecomorph evolved con-
vergently in snakes and in dibamids plus amphis-
baenians, which is why we critically reexamined
the characters relevant to the groups involved, i.e.,
snakes, varanoids, and the amphisbaenian-dibam-
id clade.
The cladistic analysis of the modified data set
was performed using the software package PAUP,
version 3.1.1, developed by David L. Swofford
(Swofford, 1990; Swofford & Begle, 1993). The
search settings invariably employed the heuristic
search strategy with random stepwise addition (10
replications), and branch swapping (on minimal
trees only) was effected by tree bisection and re-
connection. A number of alternative analyses
were performed that varied with respect to three
parameters: rooting the analysis on the three out-
group taxa (Kuehneosauridae, Marmoretta, Rhyn-
chocephalia) or rooting it on the ancestor recon-
structed by Lee (1998); ordering the multistate
characters as indicated by Lee (1998; i.e., the
characters 16, 23, 29, 34, 35, 50, 51, 77, 80, 103,
104, 113, 114, 117, 118, 120, 121, 136, 139, 146,
157, 158, 164, 165, 172, 173, 176, 177, 190, 202,
206, 207, 218, 221, 223) as well as ordering one
of the newly added multistate characters (235) or
leaving all multistate characters unordered; and
retaining all characters or deleting the ones so
designated (i.e., characters 11, 48, 57, 62, 64, 68,
84, 86, 122-124, 147, 162, 170, 174, 209, 213,
214, 228). Characters rendered uninformative by
the choice of different outgroups were always ig-
nored if not deleted. Bootstrap ( 1 ,000 replications,
using identical heuristic search settings) and de-
cay analyses were run for those analyses that most
closely approach the search procedure employed
by Lee (1998), i.e., with multistate characters or-
dered, and rooting on the ancestor (our runs 2 and
4 below). All analyses were run in two alterna-
tives. Assuming presence of a jugal in Dinilysia
required retention of character 1 2 but deletion of
character 240. Conversely, assuming a jugal to be
absent in Dinilysia required character 12 to be de-
leted and character 240 to be retained. In those
analyses that retained character 240, this character
was treated as ordered and unordered, respective-
ly. The values of tree statistics in the discussion
below that are not placed in brackets are those
obtained by retention of character 1 2, deletion of
character 240 (Jugal present in Dinilysia); con-
versely, the values placed in brackets are those
58
FIELDIANA: GEOLOGY
obtained by retention of character 240, deletion of
character 12 (jugal absent in Dinilysia). Tree to-
pologies were identical under both assumptions,
but the assumption that a jugal is absent in Dini-
lysia proved slightly more parsimonious.
A first series of tests retained ordered multistate
characters as indicated above. Retaining all the
characters designated for deletion, deleting the an-
cestor, and rooting the tree on Kuehneosauridae,
Marmoretta, and Rhynchocephalia (run 1 ) yielded
two equally parsimonious trees with a tree length
(TL) of 645 [644] steps, a consistency index (CI)
of 0.462 [0.463], and a retention index (RI) of
0.690 [0.691]. Lack of resolution was restricted to
the outside of that part of the cladogram that em-
braces the anguimorphs, the amphisbaenian-di-
bamid clade, and snakes. The relative relation-
ships of the latter taxa were fully resolved and
read as follows: (Anguidae (Xenosauridae (Helo-
derma ((Lanthanotus, Varanus) (Mosasauroidea
(Sineoamphisbaena ((Amphisbaenia, Dibamus)
(Scolecophidia {Dinilysia (Anilioidea (Pachy-
rhachis, Macrostomata))))))))))). Anguimorpha is
paraphyletic in this search, mosasauroids being
the sister group to a clade including amphisba-
enians, Dibamidae, and snakes. Amphisbaenians
plus Dibamidae form the sister group of snakes,
whereas within snakes, Dinilysia is the sister tax-
on of Alethinophidia and Pachyrhachis is the sis-
ter taxon of Macrostomata.
Retaining the ordered multistate characters, re-
taining all characters designated for deletion but
deleting the outgroup taxa Kuehneosauridae, Mar-
moretta, and Rhynchocephalia and rooting the
analysis on the ancestor reconstructed by Lee
(1998) yielded (run 2) two equally parsimonious
trees, again with TL = 622 [621], CI = 0.477
[0.478], and RI = 0.690 [0.692]. The tree topol-
ogy is the same.
Retaining the ordered multistate characters but
deleting all characters so designated and deleting
the ancestor but rooting the analysis on the three
outgroup taxa Kuehneosauridae, Marmoretta, and
Rhynchocephalia (run 3) yielded four equally par-
simonious trees, with TL = 606 [605], CI = 0.460
[0.461], and RI = 0.683 [0.684]. Resolution of
the tree is greatly reduced, but varanoids, on the
one hand, and amphisbaenians-dibamids-snakes
on the other form monophyletic clades, respec-
tively. The relationships among varanoids are
(Heloderma (Mosasauroidea (Lanthanotus, Var-
anus))); those of snakes are (Sineoamphisbaena
((Amphisbaenia, Dibamidae) (Scolecophidia
(Dinilysia (Anilioidea (Pachyrhachis, Macrosto-
mata)))))). Mosasauroids turn out to be the sister
group of the Lanthanotus-Varanus clade, whereas
amphisbaenians plus dibamids again form the sis-
ter group of snakes, Dinilysia again is the sister
taxon of Alethinophidia, and Pachyrhachis again
is the sister taxon of Macrostomata.
Retaining the ordered multistate characters but
deleting all characters so designated and deleting
the three outgroup taxa Kuehneosauridae. Mar-
moretta, and Rhynchocephalia but rooting the
analysis on the ancestor (run 4) yielded again four
equally parsimonious trees, with TL = 584 [583],
CI = 0.476 [0.477], and RI = 0.683 [0.685). The
topology of the strict consensus tree is identical
to that of the previous run.
A second, parallel set of tests was run but with
all multistate characters unordered. Retaining all
characters designated for deletion, deleting the an-
cestor, and rooting the analysis on the three out-
group taxa Kuehneosauridae, Marmoretta, and
Rhynchocephalia (run 5) yielded a total of four
equally parsimonious trees, with TL = 607 [606],
CI = 0.486 [0.487], and RI = 0.690 [0.691]. The
strict consensus tree differs somewhat for the re-
lationships outside the group that comprises an-
guimorphs, amphisbaenians, Dibamidae, and
snakes, yet the relationships among the latter taxa
resemble the first run and are (Anguidae (Xeno-
sauridae (Heloderma ((Lanthanotus, Varanus)
(Mosasauroidea (Sineoamphisbaena ((Amphisba-
enia, Dibamidae) (Scolecophidia (Dinilysia (Ani-
lioidea (Pachyrhachis, Macrostomata))))))))))).
Unordering the multistate characters therefore did
not alter relationships among these latter taxa but
resulted in a decrease in the tree length and a
slight increase in the consistency index and reten-
tion index.
The same search but rooted on the ancestor (the
three outgroup taxa Kuehneosauridae, Marmoret-
ta, and Rhynchocephalia deleted), all multistate
characters unordered, and all characters retained
(run 6) resulted in two equally parsimonious trees,
with TL = 587 [586], CI = 0.501 [0.502], and RI
= 0.690 [0.691]. The relationships of the taxa un-
der consideration remain the same, however, as
those recovered in the previous search.
Finally, with deletion of all characters so des-
ignated, with all multistate characters unordered,
and rooting the analysis on the three outgroup
taxa Kuehneosauridae, Marmoretta, and Rhyn-
chocephalia (deleting the ancestor; run 7). the
analysis yielded a total of four equally parsimo-
nious trees, with TL = 567 [566], CI = 0.487
[0.488], and RI = 0.684 [0.685]. The relationships
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
59
for the taxa under consideration have slightly
changed to a monophyletic Varanoidea that in-
cludes the mosasauroids, i.e., (Anguidae (Xeno-
sauridae {(Heloderma (Mosasauroidea (Lanthan-
otus, Varanus))) (Sineoamphisbaena ((Amphis-
baenia, Dibamidae) (Scolecophidia (Dinilysia
(Anilioidea (Pachyrhachis, Macrostomata))))))))).
Deleting all characters so designated, retaining all
multistate characters as unordered, deleting the
three outgroup taxa Kuehneosauridae, Marmoret-
ta, and Rhynchocephalia, and rooting the analysis
on the ancestor (run 8) yielded two equally par-
simonious trees again, with TL = 548 [547], CI
= 0.502 [0.503], and RI = 0.683 [0.684]. The
relationships for the relevant taxa remained the
same as in the previous search.
In a final note, we would like to point out that
the stability of the (Sineoamphisbaena ((Amphis-
baenia, Dibamidae) (Scolecophidia (Dinilysia
(Anilioidea (Pachyrhachis, Macrostomata))))))
clade is not simply due to the addition of the char-
acters 231 through 239 (240)! Running analyses
parallel to the ones above with all the characters
from 231 through 239 (240) excluded (multistate
characters ordered and unordered; characters 1
through 230 all retained, or those so designated
deleted; and rooting on the three outgroup taxa
Kuehneosauridae, Marmoretta, and Rhynchoce-
phalia or on the ancestor) all reproduced that
clade, with one difference: Dinilysia invariably
falls into an unresolved trichotomy with anilioids
and the Pac/ryr/zac/n's-Macrostomata clade. The
strict consensus tree thus reads (Sineoamphisba-
ena ((Amphisbaenia, Dibamidae) (Scolecophidia
(Dinilysia, Anilioidea (Pachyrhachis, Macrosto-
mata))))). And in all these trees, the taxa Helo-
derma, Lanthanotus, Varanus, and mosasauroids
are related to that clade, either as a monophyletic
unit or as a paraphyletic assemblage with mosa-
sauroids closest to that clade. In essence, there-
fore, the addition of new characters (23 1 through
240) did not influence the basic results other than
tree statistics and some increase in resolution
among snakes.
Discussion of diagnostic characters is primarily
based on DELTRAN character optimization, as it
minimizes secondary loss of characters diagnostic
at a higher level of inclusiveness. The synapo-
morphy listings for the (Sineoamphisbaena ((Am-
phisbaenia, Dibamidae) (Scolecophidia (Dinilysia
(Anilioidea (Pachyrhachis, Macrostomata))))))
are remarkably consistent throughout the eight an-
alyses performed and discussed above (runs 1
through 8), with one exception. Runs 3 and 4 re-
tained the ordered multistate characters but delet-
ed the characters so designated. This resulted in a
loss of resolution, the (Sineoamphisbaena ((Am-
phisbaenia, Dibamidae) (Scolecophidia (Dinilysia
(Anilioidea (Pachyrhachis, Macrostomata))))))
clade falling into a polytomy with other squa-
mates. That result lengthened the list of characters
diagnostic for the root of this clade by three char-
acters. The other nodes remained closely similar
again to all other analyses performed. In the fol-
lowing, we list all the synapomorphies for the
successive nodes in that clade, along with the
character state (in parentheses). These lists cor-
respond to run 1; differences in other runs are
listed consecutively. Unequivocal synapomor-
phies (as determined in the first of the eight ana-
lyses) optimizing the same way in the ACCTRAN
and DELTRAN mode (i.e., with ci = 1) are char-
acterized by an asterisk (*). Bootstrap support and
decay indices relate to the node characterized by
the outermost brackets of the groupings.
(Sineoamphisbaena ((Amphisbaenia, Dibami-
dae) (Scolecophidia (Dinilysia (Anilioidea (Pa-
chyrhachis, Macrostomata)))))): 19 (0), 25 (0), 33
(1), 51 (2), 54 (1), 56 (1), 58 (0), 60* (1), 71*
(1), 72* (1), 75 (0), 80 (1), 98 (0), 149 (0), 155*
(1). Run 2 is identical; runs 3 and 4 add 76 (1),
157 (1), 158 (1), 174 (1), 175 (1), and 218 (0) to
that list but delete 75, 98, and 149; runs 5 and 6
add 161 and delete 80; runs 7 and 8 add 76 (1),
118 (0), 175 (1), 216 (0), and 218 (0) and delete
75, 80, 98, and 149. Run 2: bootstrap support,
69%; decay index = 5. Run 4: bootstrap support,
80%; decay index = 5.
((Amphisbaenia, Dibamidae) (Scolecophidia
(Dinilysia (Anilioidea (Pachyrhachis, Macrosto-
mata))))): 8 (1), 12 (1), 23 (2), 29 (2), 35 (2), 37
(1), 38 (1), 40* (1), 46* (0), 49 (3), 66 (2), 80
(2), 81* (1), 84* (1), 116 (0), 129* (1), 168 (1),
172 (4), 189* (1), 190 (1), 194 (1), 197 (1), 204
(1), 206 (1), 211 (1), 222* (1), 232 (1), 235 (1).
Run 2 is identical; runs 3 and 4 add 69 (1), 77
(1), 89 (2), 133 (0), 150 (1), 176 (2), 221 (0), 225
(1), and 226 (1) to that list and delete 116; runs
5 through 8 add 157 (2) and delete 190. Run 2:
bootstrap support, 77%; decay index = 3. Run 4:
bootstrap support, 85%; decay index = 7.
(Scolecophidia (Dinilysia (Anilioidea (Pachy-
rhachis, Macrostomata)))): 3* (1), 16 (1), 45 (0),
54 (2), 59* (1), 61 (2), 63* (1), 68 (1), 73* (1),
89 (2), 94* (1), 97* (1), 100* (1), 106 (1), 110
(1), 111* (1), 119* (1), 152* (1), 153(1), 154(0),
167 (0), 169 (2), 172 (5), 190 (2), 200* (1), 207
(2), 227 (1), 234 (1), 235 (2); 236 (1). Run 2 is
60
FIELDIANA: GEOLOGY
identical; runs 3 and 4 add 117 (2), 128 (0), 146
(2), and 181 (1) to that list but delete 89; runs 5
and 6 delete 172 and 235; run 7 adds 128 (0) and
deletes 172 and 235; run 8 adds 128 (0) and 181
(1) and deletes 172 and 235. Run 2: bootstrap
support, 100%; decay index = 17. Run 4: boot-
strap support, 100%; decay index = 21.
(Dinilysia (Anilioidea (Pachyrhachis, Macro-
stomata))): 49 (2), 50 (3), 102 (0), 118 (2), 121
(2), 124 (1), 130* (3), 137 (1), 146 (3), 159 (0),
161 (0). Run 2 is identical; runs 3 and 4 delete
character 102 from that list; runs 5 through 8 add
character 157 (0). Run 2: bootstrap support, 94%;
decay index = 10. Run 4: bootstrap support, 98%;
decay index = 8.
(Anilioidea (Pachyrhachis, Macrostomata)): 87
(1), 107 (1), 141 (2), 151 (1), 160* (1), 231* (1),
237* (1). Runs 2, 5 and 6 are identical; runs 3
and 4, and 7 and 8, add character 156 (1) to that
list. Run 2: bootstrap support, 72%; decay index
= 2. Run 4: bootstrap support, 76%; decay index
= 2.
(Pachyrhachis, Macrostomata): 47* (1), 50 (3),
157 (0), 158 (0), 233* (2), 238* (1), 239* (1).
Run 2 is identical; runs 3 and 4 add character 120
(0) to that list; runs 5 through 8 delete character
157. Run 2: bootstrap support, 97%; decay index
= 4. Run 4: bootstrap support, 98%; decay index
= 4.
The most parsimonious result obtained in this
analysis is run 8, which is based on the assump-
tion that Dinilysia lacks a jugal (character 12 re-
tained, character 140 excluded) and had all mul-
tistate characters unordered, all characters so des-
ignated deleted, and was rooted on the ancestor.
The result is ((Heloderma (Mosasauroidea (Lan-
thanotus (Varanus))) (Sineoamphisbaena ((Am-
phisbaenia, Dibamidae) (Scolecophidia (Dinilysia
(Anilioidea (Pachyrhachis, Macrostomata)))))))
(Fig. 17). Note, however, that the bootstrap sup-
port for the node linking mosasauroids or vara-
noids (including mosasauroids) to the amphisba-
enian-dibamid-snake clade was consistently less
than 50%; the decay index for that node is 1.
The Phylogenetic Relationships of
Pachyrhachis, Dinilysia, and Dibamus
Our analysis of snake interrelationships recog-
nizes five terminal taxa, viz. Scolecophidia, Din-
ilysia, Anilioidea, Pachyrhachis, and Macrosto-
mata. The monophyly of macrostomatans is well
Fig. 17. Cladogram of the interrelationships of
snakes ohtained hy rcanalysis of the data of Lee (1998).
For further discussion, sec text.
corroborated (Rieppel, 1988), but the same cannot
be said for scolecophidians or anilioids (Cundall
et al., 1993). The test of the monophyly of Sco-
lecophidia is beyond the scope of this paper and
it is tentatively accepted here, but the monophyly
of the Anilioidea has been corroborated in an in-
dependent study (Zaher & Rieppel, unpublished
data), which is why we retain this taxon. One
character that supports the monophyly of the An-
ilioidea in this latter work is the configuration of
the perilymphatic foramen (Rieppel, 1979b).
Our analysis indicates that, among the terminal
taxa used in this context. Pachyrhachis is the sis-
ter taxon of Macrostomata (Zaher, 1998). This re-
sult is very robust, as it was obtained in all ana-
lyses performed, with or without inclusion of the
newly added characters 231 through 239 (240).
Indeed, four unequivocal synapomorphies diag-
nose the clade including Pachyrhachis and Ma-
crostomata, viz. supratemporal at least half of
maximum skull width (47, 1 ), posterior dentiger-
ous process of the dentary enlarged (233, 2),
tooth-bearing anterior process of the palatine pre-
sent (238, 1). and suprastapedial process of the
quadrate absent (239, 1). This corroborates Za-
her's (1998) earlier findings and removes Pachy-
rhachis from the position of a link between mo-
sasauroid squamates and snakes (contra Carroll,
1988; Caldwell & Lee, 1997; Lee & Caldwell,
1998). The significance of the presence of poste-
rior limbs in Pachyrhachis remains elusive at the
present time. Either the limb was redeveloped
from a rudimentary stage, as is still retained in
basal alethinophidians, or relatively complete hind
limbs were retained in a variety of fossil alcthin-
ophidian snakes that remain unknown (Zaher,
1998). Arguments for the position of Pachyrhach-
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
61
is that rely on the presence of hind limbs are ad
hoc and ignore all the other data.
The relationship of Dinilysia as the sister taxon
of alethinophidian snakes (Rieppel, 1988) is also
well corroborated. Only by deletion of the newly
added characters 231-239 (240) does Dinilysia
fall into an unresolved trichotomy with the Ani-
lioidea and the Pac/ryr/iac/i/s-Macrostomata
clade. Although there is a substantial list of char-
acters supporting this hypothesis of relationships
of Dinilysia, only one character is an unequivocal
synapomorphy: surangular extends far into lateral
surface of dentary and terminates in a point ( 1 30,
3). In other words, Dinilysia shares the alethino-
phidian intramandibular joint.
Another sister-group relationship that we find
well supported is the clade that comprises dibamids
and amphisbaenians. The bootstrap support for the
node linking dibamids to amphisbaenians is 95%
(runs 2 and 4), and its decay index is 6 (runs 2 and
4). These two taxa are linked by an impressive list
of characters (DELTRAN character optimization;
run 1): 1 (1), 15 (1), 27 (1), 32 (1), 70 (1), 77 (2),
82 (0), 83 (1), 91 (1), 96 (1), 103 (1), 104 (1), 108
(1), 113 (0), 120 (1), 144 (1), 146 (1), 147 (0), 173
(0), 180* (1), 185 (0), 186 (0), 187 (1), 188* (1),
202 (3). Run 2 is identical; runs 3 and 4 add char-
acters 102 (1) and 126 (0) to that list and delete
characters 120, 146, and 185; runs 5 and 6 delete
characters 103, 104, and 202; runs 7 and 8 add 126
(0) and delete 103, 104, 146, and 185. The two
unequivocal synapomorphies linking these two taxa
are caudal transverse processes project anterolater-
ally ( 1 80, 1 ), and proximal end of rib with poster-
oventral pseudotuberculum (188, 1). This clade was
also obtained by Lee (1998) and other authors
(Caldwell, 1999; Evans & Barbadillo, 1998; Haller-
mann, 1998). We feel less confident, however, ac-
cepting other aspects of the cladogram(s) obtained
in the present analyses, for reasons discussed below.
Discussion: Snake Origins, and
Homology Versus Convergence
Based on his analysis, Lee (1998) concluded
that the elongate fossorial ecomorph evolved in-
dependently in nonophidian squamates (e.g., di-
bamids and amphisbaenians) and in snakes. Al-
though he recognized a suite of derived characters
shared by snakes, dibamids, and amphisbaenians,
he attributed these to miniaturization of fossorial
forms (Lee, 1998, p. 415). Characters that diag-
nose the fossorial ecomorph were judged to be
correlated, and a case was made that such char-
acters need to be downweighted in order to avoid
a "cascade of effects that lead to apparently
strong support for a (probably spurious) phylo-
genetic hypothesis" (Lee, 1998, p. 417). This pro-
cedure was justified by reference to the claim that
independent a priori evaluation of the potential
phylogenetic information content of characters
(on the basis of functional anatomy, for example)
may be necessary to avoid mistaken conclusions
(Lee & Doughty, 1997). That way, a phylogenetic
hypothesis is reconstructed that is believed to be
better in line with an evolutionary scenario sup-
ported, for example, by functional anatomical ex-
planations (of the burrowing ecomorph in this ex-
ample).
In our view, and contrary to Lee (1998; see also
Lee & Doughty, 1997), this procedure is circular
because empirically empty a priori assumptions
about an evolutionary process are allowed to in-
fluence the phylogenetic analysis, when informa-
tion about evolutionary processes, including func-
tional anatomical explanations, should flow from
the reconstructed phylogeny (e.g., Lauder &
Liem, 1989). However, we agree with Lee (1998)
that there is a serious potential for convergence in
the evolution of the fossorial ecomorph owing to
structural constraints that correlate with miniatur-
ization and that affect not only dibamids, amphis-
baenians, and snakes but also members of other
"lizard" families as well, such as Anniella (Riep-
pel, 1984b). However, it remains unclear from
Lee's (1998) arguments why a clade grouping di-
bamids with amphisbaenians should be retained
and even named, although it is supported by char-
acters of the fossorial ecomorph, while the same
characters are claimed to support "spurious" phy-
logenetic relationships of snakes and hence have
to be downweighted if snakes are included in the
analysis. We acknowledge, however, that the di-
bamid-amphisbaenian clade survives even more
severe downweighting of these characters than is
necessary to break the snakes away from that
clade.
But just as snakes might group with amphis-
baenians and dibamids on the basis of convergent
characters correlated with fossorial habits, char-
acters that are correlated with the evolution of the
intramandibular joint might lend unjustified sup-
port to the snake-mosasaur link. As shown in our
analysis of the intramandibular joint, there are
enough structural differences in varanoids, mo-
sasaurs, and snakes to justify at least the suspicion
62
FIELDIANA: GEOLOGY
that this functional complex evolved convergently
in snakes and nonophidian squamates (Gauthier,
1982).
Several of the characters used in support of a
monophyletic Pythonomorpha by Lee (1997,
1998) and Lee and Caldwell (1998) reflect the dif-
ferentiation of an intramandibular joint. Estes et
al. (1988, p. 253) recognized the problem of po-
tential character correlation in association with the
differentiation of an intramandibular joint such as
the limited posterior extent of the splenial (L97:
char. 72; LC98: char. B14). Lee (1997) lists a total
of nine mandibular characters that group aigialo-
saurs, mosasaurs, and snakes. Of these, at least
four are correlated with the development of an
intramandibular joint: (L97: char. 68, 1; LC98:
char. B8) mobile mandibular symphysis; (L97:
char. 72, 1 ) posterior end of the splenial anterior
to coronoid process; (L97: char. 73, 1; LC98: char.
B12) splenial-angular contact abutting, straight,
mobile; (L97: char. 75, 1; LC98: char. B14) cor-
onoid not sutured to splenial. Characters used by
Lee (1998) to analyze squamate interrelationships
include even more potential synapomorphies that
are correlated with the differentiation of an intra-
mandibular joint (our dp-characters in the discus-
sion of the character evidence above). But in con-
trast to the characters that diagnose the fossorial
ecomorph, no attempt or recommendation was
made by Lee (1998) to investigate the influence
of potential character correlation related to the in-
tramandibular joint on his phylogenetic analysis
by downweighting or deleting those. In essence,
however, we believe the strategy of downweight-
ing characters to be misguided. In the absence of
testability, some kind of correlation (ontogenetic,
allometric, functional, etc.) can be invoked for
any number of characters, which renders it im-
possible to establish objective criteria for justifi-
able degrees of downweighting.
As Lee (1998) postulates convergence of the
burrowing ecomorph in the dibamid-amphisba-
enian clade and in snakes, the phylogenetic link
of snakes to marine mosasaurs becomes essential
because it alone documents that snakes could
have had a marine origin (Caldwell & Lee, 1997;
Lee & Caldwell, 1998; Scanlon et al., 1999) and,
consequently, that fossorial habits evolved inde-
pendently within snakes. The phylogenetic rela-
tionships of Pachyrhachis thus becomes a key is-
sue in this controversy, and Lee (1998) goes to
great lengths to refute Zaher's (1998) conclusion
that Pachyrhachis is not the most basal snake but
the sister group of Macrostomata (i.e., of relative-
ly advanced snakes) instead.
However, by treating Serpentes as only one ter-
minal taxon, Lee's (1998) analysis did not test
Zaher's (1998) hypothesis, because Pachyrhachis
had nowhere else to go other than being the sister
taxon of Serpentes. Breaking up Serpentes as a
terminal taxon is therefore important, not only to
eliminate polymorphism in this terminal taxon but
also to properly test the phylogenetic position of
Pachyrhachis. Lee (1998) might have thought it
unimportant to further test the relationships of Pa-
chyrhachis in the context of a global analysis of
squamate interrelationships because the position
of this genus as the most basal snake had previ-
ously been obtained by Lee and Caldwell (1998).
Yet the previous analysis of snake relationships
conducted by Lee (1997) again constrained the
search for the sister group of snakes to varanoid
squamates, and many of the characters found in
support of a monophyletic Pythonomorpha were
used in the subsequent placement of Pachyrhachis
(Lee & Caldwell, 1998). To provide as broad a
basis as possible for the test of the phylogenetic
relationships of Pachyrhachis, we added to the
global squamate analysis presented above those
characters that were used by Caldwell and Lee
(1997), Lee and Caldwell (1998), and Zaher
(1998), but were not included in Lee (1998).
Our discussion of Lee's (1998) evidence above
indicates that many of his character definitions are
flawed. For some of them, we propose new defi-
nitions, for others different codings; some we pro-
pose to delete from the analysis; others, which
would not seem to directly affect the position of
Pachyrhachis and the relationships of snakes to
the amphisbaenian-dibamid clade, we simply re-
tain. On the basis of only revising character def-
initions and/or codings as indicated above but
without deletion of any character or addition of
new characters, Pachyrhachis is already found to
be the sister taxon of Macrostomata instead of be-
ing a link between mosasaurs and snakes, irre-
spective of whether multistate characters were or-
dered or unordered. At the same time, snakes
group with the dibamid-amphisbaenian clade in-
stead of with mosasaurs and varanoids. The rele-
vant part of the cladogram reads as (varanoids (mo-
sasaurs ((dibamids, amphisbaenians) snakes))).
Upon deletion of the problematic characters listed
above, mosasaurs cluster within a monophyletic
Varanoidea, which in turn forms the sister group
of a clade that includes ((dibamids, amphisbaeni-
ans) snakes). This result, although only very
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
63
weakly supported, is interesting, as it corresponds
partly to the cladogram obtained by Evans and
Barbadillo (1998). However, we believe that dif-
ferent dichotomies of this hierarchy have to be
evaluated at different levels of confidence.
The position of Pachyrhachis as sister group of
Macrostomata is here considered to be very ro-
bust. It had been obtained by critical reassessment
(Zaher, 1998) of another data matrix previously
used by Caldwell and Lee (1997); it is obtained
in this study by a critical review of the character
evidence used by Lee (1998); and it is corrobo-
rated by an independently compiled data set fo-
cusing on cranial characters and the interrelation-
ships of basal snakes (Zaher & Rieppel, unpub-
lished data).
With Pachyrhachis nested within snakes as sis-
ter taxon of Macrostomata, the hypothesis that
snakes had an aquatic origin (Caldwell & Lee,
1997; Lee & Caldwell, 1998) loses its empirical
basis. The taxa Ophidia and Serpentes as defined
by Lee and Caldwell (1998) become redundant.
The name to be retained for reasons of priority is
Serpentes Linnaeus, 1758 (Linnaeus included cae-
cilians within his Serpentes; as pointed out by
Kuhn [1967], the name Serpentes can already be
found in the writings of Albertus Magnus). Unless
another intermediate fossil is found to relate
snakes to mosasauroids, the hypothesis of a ter-
restrial origin of snakes is more parsimonious.
Given our currently poor understanding of the sis-
ter-group relationships of snakes within squa-
mates, there is no good basis on which to try to
optimize a terrestrial versus an aquatic origin of
snakes, however.
In light of our discussion of characters related
to squamate dentition (Zaher & Rieppel, 1999),
braincase structure (Rieppel & Zaher, in press),
and intramandibular joint structure, the putative
relationship of snakes with mosasauroids appears
to have a weak morphological basis. It is certainly
not supported after critical assessment of the data
set used by Lee (1998). Conversely, the corrected
data set still shows mosasauroids (or varanoids
inclusive of mosasauroids) to be pulled into a sis-
ter-group relationship with the amphisbaenian/di-
bamid-snake clade, which indicates similarities
shared at some level of the analysis. Corrobora-
tion of the monophyly of Pythonomorpha (Lee,
1997) will require new and additional morpholog-
ical characters but still remains a possibility be-
cause molecular data do support a sister-group re-
lationship of snakes and varanoids (Reeder, 1995;
Forstner et al., 1995). The same is true of some
soft anatomy characters (McDowell & Bogert,
1954; McDowell, 1972; Schwenk, 1988).
Critical reassessment of the data matrix com-
piled by Lee (1998) results in snakes being the
sister clade to dibamids and amphisbaenians. This
clade is very robust in our analysis and conflicts
with Lee's (1998) argument for convergence. It is
interesting to note that the only total evidence ap-
proach to the phylogenetic relationships of snakes
reported so far found the same result, i.e., snakes
grouping with dibamids and amphisbaenians, al-
though the separate analysis of the same DNA
data yielded a grouping of snakes with varanoids
(Reeder, 1995). This finding in itself suggests that
the morphological data may be subject to conver-
gence, and structural constraints resulting from
miniaturization may provide a reasonable expla-
nation for such rampant homoplasy of morpho-
logical characters (Rieppel, 1984b). However, the
acceptance of convergence cannot be an a priori
(and hence empirically empty) assumption but
must follow from phylogenetic analysis. The dif-
ficulty here is that convergence, if indeed in-
volved in this case, may result in such a strong
signal that the node linking snakes to the dibam-
id-amphisbaenian clade cannot be broken on an-
atomical grounds. The solution cannot be an ar-
bitrary weighting or ordering of characters. In-
stead, the analysis of snake relationships among
squamates would seem to be a classical case call-
ing for a combination of molecular and morpho-
logical data (Reeder, 1995). In addition, it should
be noted that almost all of the morphological data
that have so far been brought to bear on this ques-
tion are osteological characters, many of which
are particularly subject to structural constraints
correlated with miniaturization. In addition to mo-
lecular data, it would seem that the inclusion of
soft anatomy characters may help to resolve the
question of homoplasy versus homology in the
comparison of snakes, dibamids, and amphisba-
enians (Senn & Northcutt, 1973). Hallermann
(1998), for example, used the ethmoidal region
(nasal capsule and associated structures) in the
analysis of phylogenetic relationships of squa-
mates, and found a sister-group relationship of
snakes with the dibamid-amphisbaenian clade on
the basis of a character complex that would seem
to be less subject to structural constraints resulting
from miniaturization than would be the braincase
and surrounding structures.
Indeed, the long list of characters shared by Si-
neoamphisbaena, amphisbaenians, dibamids, and
snakes (see above, primarily run 1) includes, for
64
FIELDIANA: GEOLOGY
the most part, characters that appear to be related
to miniaturization and/or paedomorphosis in fos-
sorial or burrowing squamates. However, there are
also some shared characters that would not seem
to be related to fossorial or burrowing habits. Rec-
ognizing that the interpretation of morphological
characters in terms of putative adaptations is
fraught with difficulties, we propose the following
loose groupings of the characters shared by Si-
neoamphisbaena, amphisbaenians, dibamids, and
snakes.
Characters that appear to be related to paedo-
morphosis coupled with miniaturization in fosso-
rial or burrowing squamates are loss of the lacri-
mal (8); loss of the jugal (12); loss of the post-
frontal (23); postfrontal (postorbitofrontal), where
present, not forked medially (25); incomplete pos-
terior orbital margin (29); loss of posterolateral
processes of the parietal (37); incomplete upper
temporal arch (38); loss of squamosal (40); re-
duction of crista prootica (66).
Characters that are coupled with structural re-
modeling of the skull in miniaturized fossorial or
burrowing squamates, resulting primarily from an
increased relative size of the braincase, are jaw
adductor muscles invading the dorsal surface of
the parietal (35); quadrate suspension mainly from
opisthotic (49); parietal downgrowths prominent
(56); alar process on prootic absent (58); otic cap-
sule expanded laterally (71); stapes robust, foot-
plate large (72); closure of the posttemporal fos-
sae (80, 84); neurocranium and dermatocranium
positioned at same level (81).
Characters potentially directly related to fos-
sorial or burrowing habits are pineal foramen ab-
sent (33); tympanic crest on quadrate absent (51);
neural spines are low ridges (168); elongation of
trunk (172); scapulocoracoid reduced (190); clav-
icle absent (194); interclavicle absent (197); fore-
limbs small or absent (204); pelvis reduced (206);
hind limbs rudimentary or absent (211, 235, 236).
Finally, characters that do not appear to be re-
lated to miniaturization and/or paedomorphosis
nor to fossorial or burrowing habits are frontal
with straight or weakly concave orbital margin
(19); palatine as long as vomer (98); intramandi-
bular septum of dentary does not approach pos-
teriormost tooth position (116); compound bone
in lower jaw present (129); tooth crowns closely
spaced (149); medial premaxillary tooth enlarged
(155); lymphapophyses present (189); scleral os-
sicles absent (222); cartilaginous processus ascen-
dens of supraoccipital absent (232). At an early
date, Rage (1982) proposed a cladistic relation-
ship of snakes with amphisbaenians and dibamids;
this hypothesis continues to be worth testing. A
relation to fossoriality does not, after all. preclude
any character a priori from being homologous in
a clade comprising amphisbaenians, dibamids.
and snakes. Although the potential for conver-
gence certainly exists, there exists also the pos-
sibility that this clade evolved from a fossorial
ancestor, from which the descendants inherited the
characters of the fossorial ecomorph.
At this point, we refrain from comments on
other parts of the hierarchy obtained by the revi-
sion of Lee's (1998) data matrix. The primary rea-
son is that we critically reassessed characters and
character states for dibamids, amphisbaenians.
varanoids, mosasaurs, Pachyrhachis, and other
snakes only, in order to test the relative relation-
ships of these key taxa. In order to comment on
other aspects of this phylogeny, critical reassess-
ment of the character evidence would have to cov-
er all other nonophidian squamate families, as was
pointed out above (problems of varanoid codings
have also been highlighted by Gao & Norell.
1998). In this context, we note that a tree only
one step longer than the most parsimonious re-
construction results in a dramatic loss of resolu-
tion already outside the Sineoamphisbaena-axtx-
phisbaenian/dibamid-snake clade. and a tree four
steps (run 2) or three steps (run 4) longer results
in a loss of all resolution outside the latter clade.
As discussed in more detail above, the coding of
nonophidian squamates at the family level only
by Lee (1998) calls for greater scrutiny. This
opens an avenue to a long-term project. When a
new data matrix is built to investigate squamate
interrelationships, the basic topology or the rela-
tive support for the different nodes discussed in
this paper may change dramatically. At this point,
it may suffice to point out that the conclusions
reached by Lee (1998) — namely, that Pachy-
rhachis is the most basal snake, linking this group
to mosasauroids (Caldwell & Lee, 1997; Lee &
Caldwell, 1998); that snakes (therefore) may be
inferred to have had a marine origin (Scanlon et
al., 1999); and that the fossorial ecomorph (there-
fore) evolved convergently in dibamids plus am-
phisbaenians as opposed to snakes — do not pass
the test of critical examination of the character
evidence he used in their support.
Notes Added in Proof
While this paper was in press, Lee, Bell, et al.
(1999) presented a gradualistic model for the evo-
RIEPPEL AND ZAHER: INTRAMANDIBULAR JOINT IN SQUAMATES
65
lution of the ophidian feeding mechanism from
the ancestral mosasauroid condition, with Pachyr-
hachis as an intermediate stage. Mediolateral flex-
ion of the mandible in mosasaurs (previously de-
scribed by Telles Antunes [1964, pp. 156 ff. and
Fig. 22], in a monograph overlooked by Lee, Bell,
et al. [1999]) was interpreted as the starting point
for the evolution of ophidian jaw mechanics.
However, both the description of the intramandi-
bular joint in squamates given above and the ma-
crostomatan affinities of Pachyrhachis invalidate
this scenario.
Lee, Caldwell, et al. (1999) also redescribed
Pachyophis woodwardi Nopcsa (1923) from the
Cretaceous of Bosnia-Herzegovina. In order to
analyze its relationships, Lee, Caldwell, et al.
(1999) used the data matrix in Lee (1998), which
we reviewed above, to which they added two
characters: pachyostosis of mid-dorsal vertebrae
and ribs, and the laterally compressed body.
Pachyophis was found to be the sister taxon of
Pachyrhachis on the basis of these two characters,
and the two taxa were classified in a family of
their own, the Pachyophiidae, again placed as sis-
ter taxon to all other snakes.
We were unable at this time to inspect the holo-
type of Pachyophis, but based on the description
by Lee, Caldwell, et al. (1999), we doubt the
ophidian status of this taxon (see also Rage,
1984). With an estimated 120 presacral vertebrae,
the vertebral count is lower in Pachyophis. The
posterior part of the preserved vertebral column
appears to us to closely approach the sacral or
cloacal region. Pachyophis shows a greater degree
of pachyostosis than Pachyrhachis, and pachyos-
tosis persists into the posterior dorsal region in-
stead of remaining restricted to the midtrunk as in
Pachyrhachis. The latter taxon also shows elon-
gated, nonpachyostotic ribs shortly in front of the
"pelvic" region, before the last three or four ribs
become abruptly shortened. In Pachyophis, the
ribs gradually decrease in length in the posterior
dorsal region, which accordingly would not have
been laterally compressed as it was it in Pachy-
rhachis.
More important, Lee, Caldwell, et al. (1999)
interpret a fragmentary bone as part of the right
dentary. Their rendering of this fragment in their
Figure 3b shows the anteriorly convex angular be-
ing received by the posteriorly concave splenial.
We understand from Nopcsa's (1923) description
that this element is difficult to identify, but if the
interpretation given by Lee, Caldwell, et al. (1999,
Fig. 3b) is correct, Pachyophis shares the mosa-
sauroid intramandibular joint, which is different
from that of snakes and also different from that
of Pachyrhachis (Lee & Caldwell, 1998, Fig. 4).
Given the incompleteness of the material, we be-
lieve the best solution is to retain Pachyophis
(Pachyophiidae) as incertae sedis among squa-
mates.
Acknowledgments
We would like to thank N. E. Arnold and C.
McCarthy (bmnh), Harold Voris and Alan Resetar
(fmnh), Eitan Tchernov (huj), and Guiseppe Puor-
to (Instituto Butantan) for permission to study the
collections under their care. N. C. Fraser, M.
Kearney, and R. Etheridge kindly read an earlier
draft of this paper, offering much helpful advice
and criticism. The research of the junior author
was supported by grants from fapesp (Fundacio
de Amparo Persquisa de Sao Paulo, Brasil).
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69
A Selected Listing of Other Fieldiana: Geology Titles Available
Status of the Pachypleurosauroid Psilotrachelosaurus toeplitschi Nopcsa (Reptilia: Sauropterygia), from
the Middle Triassic of Austria. By Olivier Rieppel. Fieldiana: Geology, n.s., no. 27, 1993. 17 pages,
9 illus.
Publication 1448, $10.00
Osteology of Simosaurus gaillardoti and the Relationships of Stem-Group Sauropterygia. By Oli\ior
Rieppel. Fieldiana: Geology, n.s., no. 28, 1994. 85 pages, 71 illus.
Publication 1462, $18.00
The Genus Placodus: Systematics, Morphology, Paleobiogeography, and Paleobiology. By Olivier
Rieppel. Fieldiana: Geology, n.s., no. 31, 1995. 44 pages, 47 illus.
Publication 1472, $12.00
Pachypleurosaurs (Reptilia: Sauropterygia) from the Lower Muschelkalk, and a Review of the
Pachypleurosauroidea. By Olivier Rieppel and Lin Kebang. Fieldiana: Geology, n.s., no. 32, 1995.
44 pages, 28 illus.
Publication 1473, $12.00
A Revision of the Genus Nothosaurus (Reptilia: Sauropterygia) from the Germanic Triassic, with
Comments on the Status of Conchiosaurus clavatus. By Olivier Rieppel and Rupert Wild. Fieldiana:
Geology, n.s., no. 34, 1996. 82 pages, 66 illus.
Publication 1479, $17.00
Revision of the Sauropterygian Reptile Genus Cymatosaurus v. Fritsch, 1 894, and the Relationships of
Germanosaurus Nopcsa, 1928, from the Middle Triassic of Europe. By Olivier Rieppel. Fieldiana:
Geology, n.s., no. 36, 1997. 38 pages, 16 illus.
Publication 1484, $11.00
The Status of the Sauropterygian Reptile Genera Ceresiosaurus, Lariosaurus, and Silvestrosaurus from
the Middle Triassic of Europe. By Olivier Rieppel. Fieldiana: Geology, n.s., no. 38, 1998. 46 pages,
21 illus.
Publication 1490, $15.00
Sauropterygia from the Middle Triassic of Makhtesh Ramon, Negev, Israel. By Olivier Rieppel.
Jean-Michel Mazin, and Eitan Tchernov. Fieldiana: Geology, n.s., no. 40, 1999. 85 pages, 58 illus.
Publication 1499, $25.00
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