\r\. 590.5 Fl N.S. A0.100 DeG 31. 200g Biology Zoology NEW SERIES, NO. 100 Osteology of the Extant North American Fishes of the Genus Hiodon Lesueur, 1818 (Teleostei: Osteoglossomorpha: Hiodontiformes) Eric J. Hilton December 31, 2002 Publication 1520 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY Information for Contributors to Fieldiana General: is pnmarii; i for Field Museum staff members and r. aciaies. although iiianuscripts from nonaffiliated authors may be considered as space permits. The Journal carries a page charge of S65.00 per printed page or fraction thereof. Pa>Tnent of at least 50% of pr.oe charges qualifies a paper for expedited processing, which reduces the publication time. Contributions from staff. research associates, and invited authors will be considered for publication regardless of ability to pay page charges, however, the full charge is mandatory for nonaffiliated authors of unsolicited manuscripts. Three complete copies of the text (including title page and abstract) and of the illustrations should be submitted (one original copy plus two review copies which may be machine copies). No manuscripts will be considered for publication or submitted to reviewers before all materials are complete and in the hands of the Scientific Editor. Manuscripts should be submitted to Scientific Editor. Fieldiana^ Field Museum Illinois 60605-2496, U.S.A. Text: Manuscripts must .. double-spaced on standard-weight, margins on all four sides. If typed on an IBM-compatible computer using MS-DOS, also submit icxi on 5:4-iiuh diskette (WordPerfect 4.1, 4.2, or 5.0, MultiMate, Displa>'write 2, 3 & 4. \\'an>i PC. Samna. Nficrosoft Word. \b!k?- w liter, or WordStar programs or ASCII). For papers over 100 manuscript pages, authors are requester .-. .. Illustrations," and a "List of Tables" immediately following title page. In most cases, the text si by an '".Abstract" and should conclude with "Acknowledgments" (if any) and "Literature Cited " All measurements should be in the metric system (periods are not used after abbreviai. format and style of headings should follow that of recent issues of Fieldiana. For more detailed style information, see The Chicago Manual of Style i published i of Chicago Press, and also recent issues of Fieldiana. References: In "Literature Cited," book and journ ui full. Where abb;^ desirable (e.g., in citation of synon>TTiies). authors consistently should follow Botanico-Pehodicum-Huniianum aiiu TL-2 Taxonomic Literature by F A. Stafleu & R. S. Cowan (1976 et seq.) (botanical papers) or Serial Source^ frr- ihe Biosis Data Base (1983) published by the BioSciences Information Sen-dce. Names of botam. follow the "Draft Index of Author Abbreviations, Royal B-— ' .^r.i,>n. w.-v. " iQs;-i ,-,lltion or T References should be typed in the following form: Croat, T. B. 1978. Flora of Barro Colorado Island, biaiilord L ni\erMty l^icss. Maniora. l am., v-t.^ pp. Grubb, p. J., J. R. Lloyd, and T. D. Pennington. 1963. A comparison of montane and lowland rain \ Ecuador. I. The forest structure, physiognomy, and floristics. Journal of Ecology, 51: 567-601. 1 \NGr>ON, E. J. M. 1979. Yage among the Siona: Cultural patterns in visions, pp. 63-80. In Browina: md R. A. Schwarz, eds.. Spirits, Shamans, and Stars. Mouton Publishers. The Hague, Netherlands. .1. 1946. The historic tribes of Ecuador, pp. 785-821. M Steward J. H.. ed.. Handbook of South American Indians. Vol. 2. The Andean Civilizations. Bulletin Smithsonian Institution, Washington. DC. R. G. 1981, Ferns and fer ' ' . ., .. poiypoa,ace:.-- mc./ 522. Illustrations: Illustrations are referred to as "figures" in liie text (not as "plates"). Figures must be acconipaiiicu by some indication of scale, normally a reference bar. Statements in figure captions alone, such as "v-o.8." are not acceptal ed double style. All illustrations should be marked on the reverse with author's name, figure niunber(s), and "top. " Figures as submitted should, whenever practicable, be 8V^ by 11 inches (22 X 28 cm) and may not by 1 6Vi inches (30 X 42 cm). Illustrations should be mounted on boards in the arrangement to be obtained in the printed work. This original set should be suitable for transmission to the printer as follows: Pen and ink drawings may be originals (preferred) or photostats; shaded drawings must be originals, but within the size limitation; and photostats must be high-quality, glossy, black and white prir " ... .. . . . o ._ sponding author upon publication unless otherwise specified Authors who wish to publish figu quire costl> .-.pccial . .productio arrangements with the Scientific Editor Page Proofs: Fieldiana employs a two-step correction system. The corresponding author will normally recene a copy of the edited manuscript on which deletions, additions, and changes can be made and queries answered. Only one set of page proofs will be sent. All desired corrections of type must be made on the single set of page proofs. Changes in page proofs (as opposed to corrections) are very e>"^"-'^ -^ ^,,Il„^r...,.n.-r5t,-,^ . i-, m^^,-.. ,n n.i>.,' nronf-. can only be made if the author agrees in advance to pay for them @ This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper). FIELDIANA Zoology NEW SERIES. NO. 100 Osteology of the Extant North American Fishes of the Genus Hiodon Lesueur, 1818 (Teleostei: Osteoglossomorpha: Hiodontiformes) Eric J. Hilton Department of Geology Field Museum of Natural History 1400 South Lake Shore Drive Chicago. Illinois 60605-2496 U.S.A. BIOLOGY LIBRARY Accepted January 10, 2002 ,q^ BUmil HALL Published December 31, 2002 Publication 1520 J/^^ g g 20B3 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY © 2002 Field Museum of Natural History ISSN 0015-0754 PRINTED IN THE UNITED STATES OF AMERICA Table of Contents List of Illustrations Abstract 1 Introduction 1 Methods 3 Specimen Preparation 3 Study, Photography, and Illustration 6 Meristic Data, Measurements, and Skele- tal Landmarks 6 Materials Examined 7 List OF Abbreviations 10 Anatomical 10 Measurements and Meristic Data 12 Institutional 12 Systematic Description of Hiodon 12 Hiodon Lesueur, 1818 12 Hiodon tergisus Lesueur, 1818 14 Hiodon alosoides (Rafinesque, 1819) 16 OSTEOLOGICAL DESCRIPTIONS 18 Skull Roof and Dorsal and Lateral Eth- moid Region 18 Sensory Canals 30 Posterior and Ventral Portions of the Braincase and Ventral Ethmoid Re- gion 31 Temporal Fossae 52 Membranous Labyrinth, Otoliths, and Auditory Fenestrae 64 Infraorbital Bones and Sclerotic Ring .... 65 Oral Jaws and Suspensorium 66 Opercular Series 79 Ventral Portions of the Hyoid Arch and Gill Arches 83 Vertebral Column 89 Caudal Fin and Supports 99 Dorsal and Anal Fins and Pterygio- phores 1 07 Pectoral Girdle, Fin, and Supports 108 Pelvic Girdle, Fin, and Supports 118 Scales 123 Conclusions 127 Future Study of Hiodontid Osteology 127 Ontogeny and the Establishment of Pri- mary Homology 128 Remarks on Phylogenetic Fusion 129 Remarks on the Study of Individual Vari- ation 132 Acknowledgments 1 34 Note Added in Proof 1 34 Literature Cited 1 35 1. Hiodon, living taxa 2 2. Ranges of extant Hiodon taxa 4 3. Hiodon, nominal fossil taxa 5 4. Counts and measurements, body and skull 8 5. Counts and measurements, median fins 9 6. Neotypes for Hiodon tergisus and H. alosoides 14 7. Hiodon alosoides, skull, dorsal view ... 33 8. Hiodon alosoides, neurocranium and associated dermal bones, dorsal view, extrascapulars in situ 34 9. Hiodon alosoides, neurocranium and associated dermal bones, dorsal view, extrascapulars removed 35 10. Hiodon alosoides, skull, anterior and posterior views 36 1 1 . Hiodon alosoides, neurocranium and associated dermal bones, anterior view 37 12. Hiodon alosoides, neurocranium and associated dermal bones, posterior view 38 13. Hiodon alosoides, skull, lateral view; infraorbitals and extrascapulars re- moved 39 14. Hiodon alosoides, skull and pectoral girdle from a growth series, lateral view 40 15. Hiodon alosoides, cephalic sensory ca- nals 41 16. Hiodon alosoides, skull roof and other skull elements of small juvenile, dorsal view 42 17. Hiodon alosoides, neurocranium, dorsal view 43 18. Hiodon alosoides, neurocranium, later- al view 44 19. Hiodon alosoides, neurocranium, ven- tral view 45 20. Hiodon alosoides, neurocranium and associated dermal bones, lateral view; extrascapulars in situ 46 21. Hiodon alosoides, neurocranium and associated dermal bones, lateral view; extrascapulars removed 47 22. Hiodon alosoides, neurocranium and associated dermal bones, ventral view 48 m 23. Hiodon alosoides, transverse histologi- cal sections through ethmoid region .... 51 24. Hiodon alosoides, camera lucida draw- ing of occipital region 52 25. Hiodon alosoides, transverse and fron- tal histological sections through otic and occipital regions 53 26. Hiodon alosoides, posterior neurocra- nia in dorsal view, and membranous labyrinth 54 27. Hiodon alosoides, otoliths 55 28. Hiodon alosoides, disarticulated skull roof, mostly in dorsal view 56 29. Hiodon alosoides, disarticulated skull roof, mostly in ventral view 57 30. Hiodon alosoides, disarticulated neuro- cranium and ventral dermal skull bones, dorsal view 58 31. Hiodon alosoides, disarticulated neuro- cranium and ventral dermal skull bones, ventral view 59 32. Hiodon alosoides, ventral ethmoid re- gion of two juvenile specimens 60 33. Hiodon tergisus and H. alosoides, comparison of orbitosphenoids 61 34. Hiodon alosoides, posterior region of the neurocranium and skull roof, anter- oventral and anterodorsal views 62 35. Hiodon alosoides, skull, ventral view .. 63 36. Hiodon alosoides, infraorbital bones ... 64 37. Hiodon alosoides, cleared and stained eye ball 64 38. Hiodon alosoides, oral jaws of an adult male, lateral and medial views 68 39. Hiodon alosoides, oral jaws, oral view 69 40. Hiodon tergisus and H. alosoides, comparison of maxillae 70 41. Hiodon alosoides, disarticulated lower jaw, lateral view 71 42. Hiodon alosoides, disarticulated lower jaw, medial view 72 43. Hiodon tergisus and H. alosoides, comparison of lower jaws 73 44. Hiodon alosoides, lower jaw of small individual, medial and ventral views ... 73 45. Hiodon alosoides, suspensorium and opercular elements, lateral view 74 46. Hiodon alosoides, disarticulated sus- pensorium and opercular elements, lat- eral view 75 47. Hiodon alosoides, suspensorium and opercular elements, medial view 76 48. Hiodon alosoides, disarticulated sus- pensorium and opercular elements, lat- eral view 77 49. Hiodon alosoides, suspensorium and lower jaw from juvenile specimen, in medial view 78 50. Hiodon alosoides, skull and gill arches in lateral view, gill arches in situ 79 51. Hiodon alosoides, ossifications of dor- sal gill arches, dorsal and ventral views 80 52. Hiodon alosoides, disarticulated ossifi- cations of dorsal gill arches, dorsal view 81 53. Hiodon alosoides, ventral gill arches, dorsal and ventral views 82 54. Hiodon alosoides, disarticulated ossifi- cations of ventral gill arches, mostly in dorsal view (photograph) 84 55. Hiodon alosoides, disarticulated ossifi- cations of ventral gill arches, mostly in dorsal view (line drawing) 85 56. Hiodon alosoides, dorsal and ventral gill arches from juvenile specimen 86 57. Hiodon alosoides, ventral elements of hyoid arch from juvenile specimen 87 58. Hiodon tergisus and H. alosoides, comparison of basibranchial and basi- hyal series 87 59. Hiodon alosoides, urohyal. dorsal, lat- eral, and ventral views 88 60. Hiodon alosoides, complete skeleton ... 89 61. Hiodon alosoides, abdominal vertebral column, lateral view 90 62. Hiodon alosoides, abdominal vertebral column, lateral view, with ribs re- moved 91 63. Hiodon alosoides, abdominal vertebral centra, dorsal, lateral, and ventral views 92 64. Hiodon alosoides, isolated abdominal vertebra, anterior view 93 65. Hiodon alosoides, isolated abdominal vertebra, lateral view 94 66. Hiodon alosoides, abdominal centra, anterior view 95 67. Hiodon alosoides, caudal vertebral col- umn and fin, lateral view 96 68. Hiodon alosoides, isolated caudal ver- tebra, lateral and anterior views 97 69. Hiodon alosoides, transitional and cau- dal vertebrae, anterior view 98 70. Hiodon tergisus, posterior supraneurals, lateral view 99 IV 7 1 . Hiodon alosoides, posterior caudal ver- tebral column and fin, lateral view 100 72. Hiodon alosoides, posterior caudal skeleton, lateral view 101 73. Hiodon alosoides, disarticulated poste- rior caudal skeleton, lateral view 102 74. Hiodon tergisiis, posterior caudal skeleton from small juveniles, lateral view 103 75. Hiodon alosoides, posterior caudal skeleton from three adult specimens (photographs) 1 04 76. Hiodon alosoides, posterior caudal skeleton from three adult specimens (line drawings) 105 77. Hiodon alosoides, dorsal fin and sup- ports, lateral view 109 78. Hiodon alosoides, dorsal and anal fins and supports from juvenile specimen .. 110 79. Graphs of ratios of pre-dorsal fin length and pre-anal fin length to total length for a sample of specimens ill 80. Hiodon alosoides, anal fin and sup- ports from adult male specimen, later- al view 112 81. Hiodon alosoides, anal fin and supports from adult female specimen, lateral view 113 82. Hiodon alosoides, pectoral girdle and fin, lateral view 114 83. Hiodon alosoides, disarticulated pecto- ral girdle and fin, lateral view 115 84. Hiodon alosoides, pectoral girdle and fin, medial view 116 85. Hiodon alosoides, disarticulated pecto- ral girdle and fin, medial view 117 86. Hiodon alosoides, pectoral girdle and fin, dorsal view 118 87. Hiodon alosoides, pectoral girdle and fin, ventral view 119 88. Hiodon tergisus, pectoral girdle and ra- dials 120 89. Hiodon alosoides, pelvic girdle and fin, dorsal and ventral views, and pelvic splint 121 90. Hiodon alosoides, pelvic girdle, lateral and ventral views 122 9 1 . Hiodon alosoides, pelvic girdle from juvenile specimen, dorsal and ventral views 123 92. Hiodon alosoides, regional variation of scales 124 93. Hiodon alosoides, detail of representa- tive nape scale 125 94. Hiodon tergisus and H. alosoides, comparison of scale rows above anal fin and axillary scale 126 List of Tables 1. Hiodon tergisus and H. alosoides, body measurements of neotypes 15 2. Hiodon tergisus, sex and body mea- surements 19 3. Hiodon alosoides, sex and body mea- surements 19 4. Hiodon tergisus, head measurements and meristic data 20 5. Hiodon alosoides, head measurements and meristic data 20 6. Hiodon tergisus, meristic data and measurements for the head region 21 7. Hiodon alosoides, meristic data and measurements for the head region 21 8. Basihyal toothplate length of hiodontid fishes 22 9. Hiodon tergisus, meristic data of verte- brae and centra 22 10. Hiodon alosoides, meristic data of ver- tebrae and centra 23 1 1 . Hiodon tergisus, meristic data of verte- bral elements 23 12. Hiodon alosoides, meristic data of ver- tebral elements 24 13. Hiodon tergisus, fin measurements and ratios 24 14. Hiodon alosoides, fin measurements and ratios 25 15. Hiodon tergisus, meristic data of the caudal fin and skeleton 25 1 6. Hiodon alosoides, meristic data of the caudal fin and skeleton 26 17. Hiodon tergisus, meristic data of dorsal and anal fin and supports 26 18. Hiodon alosoides, meristic data of dor- sal and anal fin and supports 27 19. Hiodon tergisus, meristic data of paired fins 27 20. Hiodon alosoides, meristic data of paired fins 28 21. Hiodon tergisus, meristic data of scales 28 22. Hiodon alosoides, meristic data of scales 28 23. Types and sources of individual varia- tion 133 Osteology of the Extant North American Fishes of the Genus Hiodon Lesueur, 1818 (Teleostei: Osteoglossomorpha : Hiodontif ormes) Eric J. Hilton Abstract Despite the widespread use of Hiodon as a "representative" osteoglossomorph in systematic analyses of basal teleostean fishes, no previous study has thoroughly examined the skeletal anatomy of this genus as has been done recently for other groups of fishes. The goal of this study is to describe and illustrate the osteology of Hiodon, using a detailed postlarval growth series of both extant species. Large series of specimens allow the best opportunity to detect and understand potential sources of morphological variation (phylogenetic, ontogenetic, sexu- ally dimorphic, and individual). Many aspects of the osteology of Hiodon are clarified by this study (e.g., there are only seven hypurals at all stages of development) or recorded here for the first time (e.g., sclerotic ossifications are present in specimens greater than 100 mm SL). The postlarval development of the entire skeleton is described and illustrated for the first time. For example, the vomer, which is typically a single median element in the adult of Hiodon, begins development as two distinct ossification centers. Comparable ontogenetic data such as these are lacking for many basal teleostean taxa (e.g., other osteoglossomorphs and elopo- morphs). I conclude by commenting on some issues of general significance to the broader study of comparative osteology. The contribution of ontogenetic data to studies of comparative anatomy and systematics can be critical in the processes of character conceptualization and character state definition, and therefore influence ideas of homology. Similarly, hypotheses of phyloge- netic fusion between skeletal elements can influence the assessment of primary homology. Phylogenetic fusion of skeletal elements is an unobservable process that can only be hypoth- esized following an analysis of relationships, although it is often an assumption made in char- acter state definition. If undetected, individual morphological variation, also discussed in the conclusions, may compromise the unambiguous description of characters and must be a com- ponent of future morphological analyses. Introduction . . . all life is a great cliain, tire nature of wiiich is Icnown wiienever we are sliown a single link of it. Lilce all other arts, the Science of Deduction and Analysis is one which can only be acquired by long and patient study. . . . Before turning to those moral and mental aspects of the matter which present the greatest difficulties, let the inquirer begin by mas- tering more elementary problems. —Arthur Conan Doyle (1887) Hypotheses of relationships within Teleostei — and actinopterygian fishes in general — have changed continuously since Miiller first named the group in 1844 (see also Muller, 1846). Within the past 35 years, considerable attention has been paid to the systematics of various subgroups of teleosts (e.g., see papers in Greenwood et al., 1973; Stiassny et al., 1996; Kocher &. Stepien, 1997) resulting from the adoption of cladistic method- ology (e.g., Hennig, 1966; Wiley, 1981; Kitching et al., 1998) as the basis for phylogenetic recon- FIELDIANA: ZOOLOGY, N.S., NO. 100, DECEMBER 31, 2002, PP. 1-142 Mooneye Hiodon tergisus Lesueur 1818 197 mm SL Goldeye Hiodon alosoides (Rafinesque1819) 212mmSL Fig. 1 . The two living species of Hiodon. A, The mooneye. H. tergisus. B. The goldeye. H. alosoides (both from Trautman. 1957). These specimens are immature, and this is reflected in the shape of the anal fin. which resembles the anal fin in adult females. Insets below each figure show the morphology of the anal fin of a mature male. struction. The continual change in ideas regarding the systematics of teleostean fishes is demonstrat- ed by the many changes in the classifications pre- sented in the various editions of J. S. Nelson's Fishes of the World (1976, 1984, 1994; see also Eschmeyer, 1998). Integrated analysis of fossil and living actinopterygians has become common (e.g., Wiley, 1976; Patterson & Rosen. 1977; Lau- der & Liem, 1981; Grande & Bemis, 1991. 1998; Arratia, 1997, 1999), yet the detailed anatomical knowledge of living taxa needed for interpretation of fossils is lacking for many groups, including some that are commonly included in broad phy- logenetic studies. As clearly articulated by Riep- pe! and Zaher (2(XX): 510). "A high degree of character congruence in itself says nothing about the quality of a phylogenetic hypothesis if it is based on . . . questionable statements of primary homology" (also see Patterson & Johnson, 1997a.b). Sound statements of (morphological) primary homology can only result from rigorous analysis of morphology. Comparative morpholo- gy, often regarded as an outdated science (see, however, Janvier. 1998). is enjoying a renaissance and has become increasingly vital for modem morphological phylogenetic analyses. In this paper, I describe the osteology of the two living species of the genus Hiodon (Fig. 1). FIELDIANA: ZOOLOGY Hiodontiformes {sensu Li & Wilson, 1999) con- tains four genera: fPlesiolycoptera Chang and Chou, 1976 (Middle Cretaceous, Asia), ■\Yanbi- ania Li, 1987 (Early Cretaceous, Asia), tEohio- don Cavender, 1966 (1966a; Eocene, western North America), and Hiodon Lesueur, 1818 (Eo- cene to present. North America). Fossil fishes of the family tLycopteriformes (Cretaceous, Asia) often are allied to Hiodontiformes, an interpreta- tion stemming mainly from the work of Green- wood (1970). However, the flycopterids have most recently been considered the sister-group to all other osteoglossomorphs (Li & Wilson. 1996a, 1999). The genus Hiodon is known only from North America (Fig. 2). The genus contains two living species (Fig. 1): the mooneye, H. tergisus Lesueur, 1818, and the goldeye, H. alosoides (Raf- inesque, 1819). A single valid fossil species, t-f/- consteniorum Li and Wilson, 1994, is known from two specimens from the Eocene of Montana (Fig. 3A-E). Fragmentary material (i.e., pieces of low- er jaws and vertebrae) referred to Hiodon has been recovered from the Pliocene and Pleistocene of Nebraska (e.g.. Fig. 3E G; G. R. Smith & Lundberg, 1972; Bennett, 1979; G. R. Smith, 1981). The genus 'fEohiodon Cavender, 1966 ( 1 966a), includes three described species from the Eocene of western North America (see Li, Wil- son, & Grande, 1997). A new study of the anat- omy of this fossil genus is currently in progress (Hilton & Grande, in prep.). Species of Hiodon are used often as represen- tative osteoglossomorphs in analyses of basal tel- eostean relationships. Despite this, no study has thoroughly and critically examined and illustrated their skeleton, as has been done recently for groups of sarcopterygians (e.g., Actinistia — For- ey, 1998), nonteleostean actinopterygians (e.g., Polyodontidae— Grande & Bemis, 1991; Lepisos- teidae — Wiley, 1976; Amiidae — Grande & Be- mis, 1998), and certain groups of teleosts (e.g., Characidae — Weitzman, 1962; Elopiformes — For- ey, 1973; Clupeomorpha — Grande, 1985; Sal- monidae — Sanford, 2000). Various portions of the skeleton of Hiodon have been described in a scat- tered literature (e.g., Ridewood, 1904; Boulenger, 1922; Gregory, 1933; Gosline, 1960; G. J. Nel- son, 1968a, 1969a,b; Greenwood, 1970, 1973; Schultze & Arratia, 1988; Arratia & Schultze, 1991; Li & Wilson, 1994), and it was not until Taverne (1977, 1978, 1979) published a series of monographs concerning osteoglossomorph oste- ology and relationships that the entire skeleton of Hiodon was described and illustrated. These pa- pers became important contributions to the mor- phology of osteoglossomorphs, and of basal tele- osts in general. However, only few and relatively small individuals were examined in Taverne's studies (four specimens of H. alosoides and three of H. tergisus), and only a single specimen served as the basis for most of his figures. This sort of description and illustration cannot control for in- dividual variation, which has proved to be impor- tant in understanding the comparative osteology of actinopterygians (e.g., Arratia, 1983; Grande & Bemis, 1991, 1998; Arratia & Cloutier, 1996; Cloutier, 1997; Hilton & Bemis, 1999; Poyato-Ar- iza, 1999; Davis & Martill, 1999). Also, it is dif- ficult, if not impossible, to understand ontogenetic variation when specimens of a single or even a few life history stages (e.g., juvenile or adult) are studied. Methods Specimen Preparation The skeletal materials studied consisted of both dried and cleared and stained specimens. All new- ly prepared dry skeletons were made from fresh (i.e., not preserved) specimens using dermestid beetles or water maceration. After a series of stan- dard body measurements was taken (see Counts and Measurements; Fig. 4A), specimens were dis- sected to confirm or determine, if possible, the sex of the individual (see Anal Fin). The branchial arches and the ventral portions of the hyoid arch were removed as a single unit. Specimens to be prepared by beetles (Dermestidae) were air-dried in a fume hood and placed in a dermestarium. After beetle preparation, any remaining tissue was removed by hand. Some dry skeletons were pre- pared by water maceration and stored as disartic- ulated elements. Clearing and staining for study of bone (stained with alizarin red S) and cartilage (stained with alcian blue 8GX) was based on the protocol of Dingerkus and Uhler (1977) as mod- ified by Hanken and Wassersug (1981; see also Hildebrand, 1968; Wassersug, 1976). Two specimens of Hiodon alosoides were pre- pared as histological sections. I used the low-vis- cosity nitrocellulose (LVN; Nikolas Co., Bell- wood, 111.) embedding method for preparing thick histological sections, as described by Thomas (1983). Most sections were cut at 30 jjim using a sledge microtome, and approximately every 10th HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 ■ Hiodon tergisus I I Hiodon alosoides H range overlap Fig. 2. Ranges of the two living species of Hiodon (the mooneye, H. tergisus, in blue; the goldeye. H. alosoides. in green; overlap between the two in gray). Ranges adapted from Page and Burr (1991); biogeographic provinces based on Burr and Mayden (1992; see also Hocutt & Wiley, 1986, and papers therein). Base map adapted from MapArt Geopolitical Deluxe v2.0 software (© 1998 Cartesia Software). FIELDIANA: ZOOLOGY ^rr^ r 1 1 1 1 1 1 nu. ."•«&.-■ ■ ' . - •.T^s:as«it,'vtit.'«f^m«B Fig. 3. Nominal fossil Hiodon. A-E, \H. consteniorum Li and Wilson, 1994, from the Eocene of Montana (A- C, UALVP 38875, holotype; D and E, ualvp 24200, paratype and only other known specimen). F and G, ^H. lirellus Bennett, 1979, from the Pleistocene of Nebraska; this taxon is considered here a nomen dubium. '\Hiodon lirellus is known only from isolated angulars and dentaries (specimen shown here is a dentary in F, medial and G, dorsal views; kuvp 31 139). A-E, scale bars in millimeters; F and G, scale bars = 2 mm. Anterior facing right in all. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 section was stained with Ehrlich hematoxylin and counterstained with picric-ponceau (Humason, 1979) and mounted on glass microscope slides us- ing Eukitt mounting reagent (Calibrated Instru- ments. Inc.. Hawthorne, N.Y.). Slides were ex- amined and photographed under a Zeiss Axioskop compound microscope. The head and pectoral gir- dle of one specimen (uamz 4041 A, 63 mm SL) were sectioned in the transverse plane. For the second specimen (uma F 10595, 55 mm SL), the head and pectoral girdle were cut in frontal sec- tions and the abdominal cavity was cut in sagittal sections. Study, Photography, and Illustration In general, names of bones and cartilages fol- low those of Grande and Bemis (1998) where ap- plicable; exceptions are noted in the text. Termi- nology for portions of the scales follows Lagler (1947). Terminology for skeletal tissues and sys- tems follows the outline of Hilton and Bemis (1999: table 1), which is based on Patterson (1977a), M. M. Smith and Hall (1990, 1993), and Grande and Bemis (1998). Although a description of the soft tissue anatomy (e.g., muscles, nerves, and blood vessels) is beyond the scope of this study, specimens stored in alcohol were dissected to examine soft tissue anatomy in relationship to the skeleton (e.g., points of muscle attachment or determination of foramina). However, many de- tails of the nervous system in particular remain unclear, and future confirmation must be derived from the focused study of these soft tissue sys- tems. Names of muscles follow Winterbottom (1974). Skeletons were examined under a Wild M5 dis- secting microscope equipped with fiber-optic lights. Specimens were photographed using either 9 X 16 cm black-and-white Polaroid Type 55 pos- itive-negative film or 35 mm color slide film. Small specimens were photographed using a Wild M8 monocular microscope with substage illumi- nation, fiber-optic lights, and a camera attach- ment. Cleared and stained specimens were pho- tographed in an 4:1 solution of glycerin:water. Scales stored in alcohol were submerged and pho- tographed under water. Photographs and slides were scanned and illustrations were created elec- tronically using Adobe Illustrator software. Some images were digitally captured using a Nikon Cool-Pix 990 digital camera attached to a Nikon or Wild dissecting microscope. Meristic Data, Measurements, and Skeletal Landmarks All specimens were visually examined, and a sample of ten specimens of each species was se- lected for counts and measurements. This sample represents the ontogenetic range of specimens ex- amined in this study. I used staining of elements to recognize the presence of particular elements in small specimens; this method, however, has in- herent problems (e.g., bones may not stain owing to decalcification during fixation, preservation, or preparation). Most cranial elements found in adult specimens were found to be present in the small- est individuals studied (2 1 mm SL for H. tergisus and 24 mm SL for H. alosoides): any that were found to develop later are noted in the text. In- terspecific differences in the earliest appearance of ossification in an element were noted between small individuals of equal sizes. Given the small number of specimens of these early stages, and the fact that they were all museum specimens of wild-caught individuals (subject to different tem- peratures, feeding regimes, etc.), it is unclear whether these differences are phylogenetic or due to extrinsic factors (see discussion under Future Study of Hiodontid Osteology). Where such dif- ferences were detected, I have so noted in the text. Body Measurements — Figures 4 and 5 show the measurements recorded and summarized in 20 tables for ten specimens of each species. In gen- eral, these measurements are adapted from Hubbs and Lagler (1958) and Grande and Bemis (1998). All whole-body measurements were recorded to the nearest millimeter except for specimens that were less than 35 mm standard length (SL). which were measured using digital calipers and were re- corded to the nearest 0. 1 mm. Any sort of prep- aration may influence the overall size of a speci- men, and because many of the specimens pre- pared during the course of this study were ac- quired from museum collections (i.e.. already preserved), it was impossible to determine actual lengths; no calculations were made to determine "live" lengths of the specimens (e.g., Mabee et al., 1998). All body measurements were made on fresh or fixed specimens before preparation by ei- ther clearing and staining or by dermestid beetles; skeletal structures were measured after prepara- tion. Meristic Data — All meristic data (i.e., counts of serial structures) were collected with the aid of a dissecting microscope. In general, serial struc- tures are numbered anterior to posterior or medial FIELDIANA: ZOOLOGY to lateral; exceptions (e.g., preural vertebrae) are indicated below and in the text. Teeth — Following Grande and Bemis (1998), counts of teeth (Fig. 4B) include all teeth associ- ated with the margin of the jaw (even if only con- nected to a socket by soft tissue, as in young in- dividuals or replacement teeth) as well as empty sockets from which teeth had fallen out (e.g., in dry skeletons). This method allows reasonable comparisons to be made with fossil material, from which teeth often are missing. PosTCRANiAL AxiAL SKELETON — The axial skel- eton is divided into an abdominal region and a caudal region. The first caudal vertebra is the an- teriormost vertebra to possess a complete haemal arch. Posterior abdominal vertebrae, in which the left and right haemal arches are not fused, are termed transitional vertebrae. Preural caudal ver- tebrae (e.g.. Fig. 5A) are numbered posterior to anterior (e.g., preural 1 is the first vertebra ante- rior to the ural caudal region). The parhypural is the posteriormost element that surrounds the dor- sal aorta. Ural centra are defined as those that sup- port hypurals. Median Fins and Pterygiophores — A ptery- giophore consists of a single series of radials (i.e., proximal, middle, and distal, if present; Grande & Bemis, 1998); sequential pterygiophores are num- bered anterior to posterior. I distinguish between segmented and rudimentary fin rays (Fig. 5B, C; note that this distinction applies to all fin rays of all fins, not just those of the median fins). Seg- mented rays are defined as all fin rays that are divided into two. or more lepidotrichia, whereas rudimentary rays are defined as all unsegmented rays (Grande & Bemis, 1998) and are typically restricted to the leading edge of the fin. Patterson (1992: 147) defined supernumerary fin rays as those which "lie in front of the ray serially as- sociated with the first radial." Rudimentary rays, as defined above, compose a subset of the super- numerary fin rays of a fin (i.e., all rudimentary rays are supernumerary, but not all supernumer- ary rays are rudimentary). I further distinguish be- tween branched and unbranched fin rays (Fig. 5). This scheme of fin ray classification differs from the recognition of "principal fin rays" (e.g., Hubbs & Lagler, 1958). Because I found that the last two fin rays of the dorsal and anal fins were separate in small specimens, the last "double fin ray" characteristic of adults was counted as two fin rays, also differing from the convention of Hubbs and Lagler (1958: fig. 3). Caudal Fin and Supports — The lengths of the upper and lower lobes of the caudal fin were mea- sured as the length of the longest fin ray (Fig. 5 A). Hypurals are defined as cartilaginous or ossified elements supported by a ural centrum or the no- tochord posterior to the centrum that supports the parhypural (pul; see above). By convention, hy- purals are numbered from anterior to posterior. The condition of the neural spine of pul was ex- amined and recorded as rudimentary (less than half the length of the next-anterior neural spine, i.e., nspu2), moderately developed (more than half the length but not the full length of nspu2) or well-developed (equivalent in length to nspu2). Scale Morphology and Counts — Scales were sampled from six locations on the body (see Scales). Scales were removed from the dermis with forceps, rinsed clean under warm water, and placed into 70% ethanol. Scales were lightly stained by placing a drop of alizarin red S dis- solved in 0.05% potassium hydroxide into the al- cohol. Once stained, the scales were returned to clean 70% ethanol. Scale counts (Fig. 4A) follow those of Hubbs and Lagler (1958) and Grande and Bemis (1998). All scale counts reported in the ta- bles were made on whole specimens stored in al- cohol and not prepared as skeletons. Counts of scale rows above and below the lateral line do not include the lateral line, and the counts of those above the lateral line include the single median scale row along the dorsal margin of the body. The scales of Hiodon are deciduous, and a few scales are likely to have fallen out of preserved specimens, particularly older material that was not well fixed at the time of collection. However, a missing scale could be counted by probing the scale pocket to confirm the presence of a pocket as well as by correlation with adjacent scale rows. If such "presence" of a missing scale could not be justified, the specimen was not included in the tables of scale counts. Materials Examined Thirty-nine skeletal specimens of Hiodon ter- gisus and 81 skeletal specimens of H. alosoides were examined during the course of this study. My descriptions and illustrations are based pri- marily on H. alosoides, although postlarval growth series of both species were examined and compared. Ossification was well under way in the smallest of my specimens (21 mm SL for H. ter- gisus; 24 mm SL for H. alosoides), so I can com- HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 Pre-Dorsal Fin Length (POOR) Dorsal Fin Base Length Lower Jaw Length Basihyal Toothplate Length Fig. 4. Illustrations showing how some of the counts and measurements were taken. A. Body measurements. Drawing of H. teri^isiis (modihed from Goode. 1884). B. Cranial measurements and meristic counts. Lateral dentary teeth are highlighted in blue: arrows point to empty tooth sockets. ment only on the sequence of later ossifications. More specimens and a more complete growth se- ries were available for H. alosoides than for H. tergisus, although earlier developmental stages were available for H. tergisus than for H. alo- soides. Differences I discovered between the two species are described and illustrated. Following is a list of the specimens of Hiodon- FIELDIANA: ZOOLOGY Dorsal Caudal Fin Length Ural Centrum 1 Ventral Rudimentary Fin Rays Ventral Segmented Fin Ray 1 Ventral Branched Fin Ray 1 B Segmented Fin Ray 1 Branched Fin Ray 1 Rudimentary Fin Ray 1 Branched Fin Rays 1-31 Rudimentary ''i" f^^y^ Segmented Fin Ray 1 Fig. 5. Illustrations showing how some of the postcranial measurements and meristic counts were taken. A, Caudal fin and skeleton. B, Dorsal fin and skeleton. C, Anal fin and skeleton. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 tidae (Hiodon and iEohiodcm) that I prepared and/or examined during the course of this study. Specimens are described as stored in alcohol (a), serially sectioned (sec), cleared and double stained (c&s), or dry skeleton (ds). Specimens of nonhiodontid taxa that were used during this study are referred to in the text where relevant. All taxa known exclusively as fossils are preceded by a dagger (t). All fossils listed below are com- plete specimens unless otherwise noted. Hiodon tergisiis: 66 specimens total; 21 mm to 230 mm SL, including: ansp 108903 (1 a), ansp 114175 (1 a), ANSP 169010 (1 a), fmnh 100590 (1 c&s), FMNH 109186 (1 ds), FMNH 109187 (1 ds), JFBM 22746 (1 c&s), jfbm 22748 (3 c&s), JFBM 22747 (3 c&s), jfbm 24760 (3 c&s), jfbm 27508 (1 a), jfbm 11262 (1 a), mcz 40888 (1 a), MCZ 17906 (2 a), mcz 17694 (1 a), mcz 23824-23829 (6 a), mcz 17714-17716 (3 a), tu 1681 1 (4 a, 6 c&s), tu 108145 (1 a), tu 108166 (5 c&s), UAic 10473.02 (1 c&s), uf 31651 (1 ds), uf 78537 (1 a), uf 78879 (1 c&s), uma F10379 (1 a), uma F10599 (1 a), uma F10607- F 106 13 (4 ds, 3 c&s), uma F10635-F 10640 (4 ds, 2 c&s). Hiodon alosoides: 104 specimens total; 24 mm to 294 mm SL, including: ansp 149441 (2 a, 1 c&s), ansp 159095 (1 ds), aum 5169 (1 a, 2 c&s), FMNH 109173-109185 (12 ds, 1 c&s), MCZ 17908 (3 a), mcz 54926 (1 c&s), mcz 157462 (1 a), nmc 75-1553 (1 a, 1 c&s), tu 108118 (5c&s), TU 113117 (5 c&s), TU 113236 (3 c&s), UAic 10473.01 (5 a, 2 c&s), uamz 4041 (5 c&s), UAMZ 4043 (2 c&s, 1 sec), UF 65838 (1 a), UMA F10149 (2 a), uma F10150 (1 ds), UMA F 10380 (1 a), uma F10580-F 10598, uma F10600-F 10606 (19 ds, 5 c&s, 1 a, 1 sec), uma F 10634 (1 ds), UMA F 1 064 1-F 10653 (11 ds, 2 c&s), UMA Fl 1259 (1 ds); usnm 007529 (3 a). ''(Hiodon lirellus: KU 31134-31140 (isolated par- tial dentaries). KU 31 155 (isolated articular), KU 31156 (isolated articular), KU 31158 (isolated articular). '\Hiodon constenionun: ualvp 38875 (holotype), UALVP 24200 (paratype, only other known spec- imen). tEohiodonfolcatus: fmnh PF9878, fmnh PF9880, FMNH PF9881, fmnh PF 10424 (holotype), fmnh PF 10630, fmnh PF 10637, fmnh PF12516, FMNH PF 13065a & b, fmnh PF15167, fmnh PF15174, FMNH PF15175; uma F10614, uma F 10650, UMA F 10651. iEohiodon woodruffi: fmnh PF12996 (partial specimen), fmnh PF14331; ualvp 13227 (ho- lotype), UALVP 41213, UALVP 22905a & b. fEohiodon rosei: amnh 8059 (paratype), amnh 8059a (paratype, head only), amnh 8060 (para- type, partial specimen); fmnh PF 12991 (partial specimen), fmnh PF12995. List of Abbreviations Anatomical abbtp, anterior basibranchial toothplate (= basi- branchial 1-3 toothplate, G. J. Nelson, 1968a; Taverne, 1977); ac/pm, posterior opening of aor- tal canal and posterior myodome; af, auditory fe- nestra; afd, anterior field of scale (Lagler, 1947); afon, anterior fontanelle; ag, aortal groove on ventral surface of basioccipital (Allis, 1919); ahh, anterior head of hyomandibula; ama, ampullae of anterior duct of membranous labyrinth; ame, am- pullae of external (= horizontal) duct of membra- nous labyrinth; amp, ampullae of posterior duct of membranous labyrinth; ang-rar, anguloretroar- ticular; ao. antorbital; aon, aortic notch of the par- asphenoid; aor, aorta; ap, pars autopalatina, car- tilage of palatoquadrate that ossifies as autopala- tine bone in other teleosts (Arratia & Schultze, 1991); apr, anterior process of parasphenoid; ar, articular (= endosteal articular; Ridewood, 1904); arp, ascending ramus of parasphenoid; as, pelvic axillary scale; asd, anterior duct of membranous labyrinth (= anterior vertical canal); asmxp, ar- ticulating surface on premaxilla for anterior pro- cess of maxilla; bb, basibranchial; bfr, branched fin ray; bhtp, basihyal toothplate; bo, basioccipi- tal; br, branchiostegal; bsp, basisphenoid; bspt, basipterygium of pelvic girdle; c, vertebral cen- trum; cama, chamber for ampulla of anterior duct of membranous labyrinth; cb, ceratobranchial; cc, caudal vertebral centrum; cesd. chamber for an- terior bend of external (= horizontal) semicircular duct; cf, caudal fin; cfpm, cartilaginous floor of posterior myodome; eg, longitudinal groove on ventral surface of abdominal vertebral centra; cha, anterior ceratohyal; chp, posterior ceratohy- al; cl, cleithrum; elf, foramen on dorsolateral sur- 10 FIELDIANA: ZOOLOGY face of horizontal arm of cleithrum (function un- known); cl-cofn, fenestra formed between ventro- medial edge of cleithrum and dorsal edge of cor- acoid; cm, coronomeckelian (= sesamoid articular, Ridewood, 1904); co, coracoid; cof, small vascular foramen in posterior portion of coracoid; clot, chamber in basioccipital for lagen- ar otolith; cpl, cheek pit line (G. J. Nelson, 1972b); cpsd, chamber for ventral bend of pos- terior semicircular duct; crc, crus commune of membranous labyrinth; csoc, supraoccipital crest, bony extension of supraoccipital that forms in vertical epaxial septum; csp, process on antero- ventral part of preural haemal arches and hypurals of caudal skeleton; cut, chamber in prootic for utricule; d, dentary; dpi, dermopalatine; dr, distal radial of dorsal and anal fin pterygiophores; dsp, dermosphenotic (= posteriormost infraorbital bone); eb, epibranchial; ecp, ectopterygoid; ecs, extracranial space dorsal to spinal cord; enp, en- dopterygoid (= entopterygoid, Arratia & Schul- tze, 1991); ep, epural; epl, ethmoidal pit line (G. J. Nelson, 1972b); epn, epineural; epo, epioccip- ital (following rationale of Patterson, 1975: 425; = epiotic, Ridewood, 1904; Taverne, 1977; Li & Wilson, 1994); es, extrascapular (= scale bone, Ridewood, 1904; = supratemporal); esd, external duct of membranous labyrinth {- horizontal ca- nal); etc, triangular portion of ethmoid cartilage exposed between supraethmoid and frontals; exo, exoccipital; facv, foramen for anterior cephalic vein; fepa, foramen for efferent pseudobranchial artery (Taverne, 1977); fht, foramen for antero- ventral lateral line nerve; fie, foramen for internal carotid aitery (Taverne, 1977); fjc, common fo- ramen for jugular canal and trigeminal and facial nerves; fm, foramen magnum; fo, focus of scale; for, foramen for the otic lateral line nerve (North- cutt & Bemis, 1993); fpsd, foramen for posterior duct of membranous labyrinth; fr, frontal (= pa- rietals of JoUie, 1962); fson, foramen for a spino- occipital nerve; fll; foramen for optic nerve; fill, foramen for oculomotor nerve; fV+VII, foramen for trigeminal and facial nerves; fV+VII(op), fo- ramen for ophthalmic portions of the anterodorsal lateral line nerve; fVI, foramen for abducent nerve; fIX+X, foramen for glossopharyngeal and vagal nerves; gr, gill rakers; h, hyomandibula; ha, haemal arch; hb, hypobranchial; hcl, haemal ca- nal; hhd, dorsal hypohyal; hhv, ventral hypohyal; hmf, foramen for compound facial and antero- ventral lateral line nerves (Northcutt & Bemis, 1993); hp, opercular head of hyomandibula; hs, haemal spine; by, hypural; hyfa, anterior fossa for dorsal head of hyomandibula; byfp, posterior fos- sa for dorsal head of hyomandibula; ic, intercalar; iby, interhyal (cartilaginous); io, infraorbital; iocn, infraorbital sensory canal; iop, interopercle; ipb, infrapharyngobranchial (G. J. Nelson, 1968a, following rationale of G. J. Nelson, 1968b); jf, opening of jugular canal; le, lateral ethmoid; lem, membranous lateral extension from lateral eth- moid (= antorbital, Patterson, 1977a; Taverne, 1977; Li & Wilson, 1994); lexo, membrane bone wall of exoccipital lateral to spinal cord; Ifd, lat- eral field of scale (Lagler, 1947); lig, ligament connecting dorsal limb of posttemporal to epioc- cipital; Ilcn, lateral line sensory canal (= trunk canal, Liem et al., 2001); lot, lagenar otolith (Nolf, 1985; = asterisk); Iptp, lower (ventral) pharyngeal toothplates; Is, ligamentous sheath separating the intra- and extracranial spaces dorsal to spinal cord; maf, membrane closing auditory fenestra; mc, Meckel's cartilage; men, mandibular sensory canal; mco, mesocoracoid; mcp, mandib- ular canal pore; mf, meckelian fossa; met, mes- ethmoid; mpl, middle pit line (G. J. Nelson, 1972b; Northcutt, 1989); mpt, metapterygoid; mx, maxilla; mxp, anterior process of maxilla; n, nasal; na, neural arch; nacn, nasal sensory canal; neap, nasal capsule; ncf, notochord foramen; ncn, neural canal; ncp, concavity on posterior face of basioccipital that marks anterior extent of noto- chord; nf, facets on dorsal surface of centra for articulation of neural arches; not, notochord; ns, neural spine; nspul, neural spine of preural ver- tebrae 1 ; occ, cartilage of occipital region extend- ing posteriorly over foramen magnum; op, oper- cle; ops, posterodorsal spine of opercle; ors, or- bitosphenoid; otcn, otic sensory canal; pa, parie- tal (= postparietal of Jollie, 1962); parp, postarticular process (G. J. Nelson, 1973a,b; = retroarticular process); pap, pectoral axillary pro- cess (Arratia, 1997); pas, parasphenoid; pb, pel- vic bone (Grande & Bemis, 1998; = ossified por- tion of basipterygium of Sewertzoff, 1934) (note that Grande and Bemis (1998) use basipterygium to include both the cartilage and its ossification, which together form most of the pelvic girdle); pbbtp, posterior basibranchial toothplates (= bas- ibranchial 4 toothplates, G. J. Nelson, 1968a); pcf, pectoral fin rays; pel, postcleithrum; pf, prootic foramen allowing contact between utricule and perilymphatic sac (= foramen utriculo-vesiculaire du prootique of Taverne, 1977); pfd, posterior field of scale (Lagler, 1947); pfon, posterior fon- tanelle; pg, groove in ethmoid cartilage for the anterior process of parasphenoid; phh, posterior HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 11 head of hyomandibula; phy, parhypural: pla. an- terior pit line (G. J. Nelson, 1972b; Northcutt. 1989): plf. pelvic fin rays: plm. middle pit line (G. J. Nelson. 1972b: Northcutt. 1989): pm. pos- terior myodome; pmcn. preoperculomandibular sensory canal: pmo, posterior opening of poste- rior myodome: pmx. premaxilla: pop. preopercle; pope, opening of preopercular sensory canal: popcn. preopercular sensory canal: pp. parapo- physis (= ossification of basiventral portion of ab- dominal vertebrae): ppb. postpelvic bone: pr. proximal radial: pro. prootic: pt. posttemporal: ptcn. posttemporal sensory canal: pt(d). dorsal arm of posttemporal: pt(l). ventrolateral arm of posttemporal: pt(m). ventromedial arm of post- temporal: pto. pterotic (Patterson. 1973: = fused dermopterotic and autopterotic): pts. pterosphen- oid: ps. pelvic splint (Gosline. 1961): pu. preural centrum: q. quadrate: qg. groove where quadrate rests against preopercle: r, rib; ra. radial: rad. ra- dii of scale (Lagler. 1947); rar. retroarticular ( = ectosteal articular of Ridewood. 1904); rfr. rudi- mentary (= unsegmented) fin rays of dorsal and anal fins; ri. ridges (= circuli) of scale (Lagler. 1947); sac. saccule; sc, scapula (= hypercleithrum of Taverne. 1977); sea. anterior supracarinalis muscle: sef. scapular foramen: sel. supracleith- rum: set. supraethmoid; sfr. segmented fin rays (as opposed to rudimentary fin rays); sle. supra- dorsal ligament canal: sn, supraneural; soc, supra- occipital; seen, supraorbital sensory canal: sop. subopercle: sot. saccular otolith (Nolf. 1985): spc. spinal cord: spo. sphenotic; sr. sclerotic ring; sten. supratemporal sensory canal; swb. cranial diverticula of swim bladder; sym, symplectic; tf. temporal fossa; tp. transverse process of an ab- dominal centrum; tv. transitional vertebrae: u. ural centrum: uh. urohyal: un. uroneural (= uro- dermal of Monod. 1968): uos. unossified posterior portion of posterior field of a scale; uot. utricular otolith (Nolf. 1985; = lapillus); uptp. upper (= dorsal) pharyngeal toothplate; vppb. process on ventral surface of the pelvic bone; vrfr, ventral rudimentary fin rays of caudal fin: X. tenth ( = vagal) cranial nerve. Measurements and Meristie Data D. dorsal: FL. fork length: L, left side; PAN. pre- anal fin length; PDOR. pre-dorsal fin length: FOR. pre-orbital length: PFEC. pre-pectoral fin length: FFEL. pre-pelvic fin length: R. right side; SL, standard lensth: TL. total lensth: V. ventral. Institutional AMNH, American Museum of Natural History (New York. N.Y.); ansp. Academy of Natural Sci- ences of Philadelphia (Philadelphia. Penn.): aum. Auburn University Museum Fish Collection (Au- burn, Ala.); BMNH. The Natural History Museum (London): fmnh. Field Museum of Natural His- tory (Chicago. 111.); JFBM. James Ford Bell Mu- seum of Natural History. University of Minnesota (St. Paul. Minn.): ku. University of Kansas Mu- seum of Natural History (Lawrence. Kan.); MCZ. Museum of Comparative Zoology. Harvard Uni- versity (Cambridge. Mass.): mnhn. Museum Na- tional d'Histoire Naturelle (Paris. France); nmc, Canadian Museum of Nature (Ottawa. Canada); TU. Tulane University Museum of Natural History (Belle Chasse. La.); uaic. University of Alabama Ichthyology Collection (Tuscaloosa. Ala.); UAMZ. Museum of Zoology, University of Alberta (Ed- monton. Canada): ualvp. Laboratory for Verte- brate Paleontology. University of Alberta (Ed- monton. Canada): uf. Florida Museum of Natural History. University of Florida (Gainesville. Fla.): UMA. University of Massachusetts Museum of Natural History (Amherst, Mass.): USNM. Smith- sonian Institution. National Museum of Natural History (Washington. D.C.). Systematic Description of Hiodon Teleostei Miiller, 1844 Osteoglossomorpha Greenwood et al., 1966 Hiodontiformes Taverne, 1979 Hiodontidae Cuvier and Valenciennes, 1846 Hiodon Lesueur, 1818 Rejected Synonyms — Glossodon (Rafinesque. 1818). Amphiodon (Rafinesque. 1819). Clodalus (Rafinesque. 1820), Elottonistius (Gill & Jordan, in Jordan & Bean. 1877). Type Species — Hiodon tergisiis Lesueur. 1818. Type by subsequent designation (Eschmeyer. 1998). Species Included as Valid — Hiodon tergisus Lesueur. 1818: Hiodon alosoides (Rafinesque. 1819); f Hiodon consteniorum Li and Wilson. 1994. Distribution — Fossil and living species of Hiodon are known only from North America, and as a genus. Hiodon is found throughout much of the continent, from the northernmost portion of FIELDIANA: ZOOLOGY continental Canada to the northern coast of the Gulf of Mexico (Fig. 2). The single valid fossil species, t^- consteniorum, is known from two specimens collected in the Eocene-Oligocene Kishenehn Formation of Montana. Other fossil material referred to Hiodon is known from the Miocene, Pliocene, and Early Pleistocene of Ne- braska (G. R. Smith & Lundberg, 1972; Bennett, 1979; G. R. Smith, 1981). Discussions of fossil hiodontids and their allies can be found in Cav- ender (1966a, 1986), Greenwood (1970), Chang and Chou (1976), Chang (1999), Wilson (1977, 1978, 1980), Grande (1979), Ma (1980, 1987), Patterson (1981b), Li (1987, 1994), Shen (1989, 1996), Su (1991), Jin (1991), Wilson and Wil- liams (1993), Jin, Zhang, and Zhou (1995), Li, Wilson, and Grande (1997), and Li and Wilson (1999). Emended Generic Diagnosis — Hiodon differs from all other teleostean fishes by possessing a postpelvic bone. Remarks — An additional fossil species, -\Hio- don lirellus Bennett, 1979, was described based on isolated and fragmentary lower jaws from the Pliocene of Nebraska. The characters used by Bennett (1979) to distinguish this material from other Hiodon were found in one or both of the living species. Given also the fragmentary nature of these specimens, this taxon is here considered Hiodon lirellus Bennett, 1979, nomen dubium. Other characteristics of the genus Hiodon in- clude 6-10 branchiostegals (usually 8); 11-13 branched pectoral fin rays (usually 12); 7 pelvic fin rays (rarely, 6 or 8); 16 (8 dorsal and 8 ventral) branched (rarely, 15) caudal fin rays. In Jordan and Bean (1877: 67), D. S. Jordan wrote, "Prof. Gill and myself, therefore, propose the new subgeneric term Elattonistius . . . ." This term, intended to include only Hiodon chrysopsis (a synonym of H. alosoides, see below) was sub- sequently raised to generic status (e.g., Jordan & Thompson, 1910) and given the authorship "Gill and Jordan, 1877." Jordan (1923) commented that Rafinesque used Amphiodon because the word Hiodon sounded too much like Diodon, a genus of Tetraodontiformes (Rafinesque, 1820: 41). Hy- odon is commonly seen as the spelling of the ge- nus in older literature and is considered invalid, although perhaps more proper etymologically. Jordan and Evermann (1896: 412) noted, "It is not certain which of these two names, Hiodon and Glossodon, has precedence of date. Hiodon is in common use and was accompanied by a much better description than Rafinesque usually fur- nished. We therefore retain it." Members of the genus Hiodon in general are referred to as "mooneyes" (Hiodon tergisus) or "goldeyes" {Hiodon alosoides; Jordan & Ever- mann, 1896; Scott & Grossman, 1973). Another vernacular name for members of the genus col- lectively is "false herring" (Rafinesque, 1820). The living species of Hiodon are sometimes considered (informally, at least) living fossils, al- though this term is often used ambiguously and nonchalantly (Patterson, 1984). True enough, Hio- don is a member of a largely fossil group of fishes (Hiodontiformes) that is believed to have separat- ed from other teleosts at least by the Early Cre- taceous (based on the oldest putative members of this clade), and portions of its anatomy closely resemble those of other early groups of teleosts (i.e., it possesses many plesiomorphies) that are known only as fossils. However, one meaning of the term living fossil is that the taxon is experi- encing a state of arrested evolution (Eldredge & Stanley, 1984: 1). This is certainly not true for Hiodon, as members of the genus possess many derived features (i.e., autapomorphies) as well; merely because a taxon is plesiomorphic does not necessarily make it a living fossil. As Eldredge and Stanley (1984: 3) observed, taxa "cannot qualify [as living fossils] simply because they are primitive — by such a yardstick, virtually every- thing is a living fossil." Forey (1998) posed four questions in consid- ering whether or not the coelacanth, Latimeria chalumnae, is a living fossil (a question that he ultimately answered negatively): (1) Is it a "miss- ing link"? (2) Is it anatomically close to the ear- liest members of its group? (3) Does it signify a long unrepresented fossil record? (4) Does it have a very restricted range? Although Hiodon pos- sesses many plesiomorphic features, it is not a "missing link" at any level of comparison (e.g., within neopterygians, teleosts, or osteoglosso- morphs). Hiodon does closely resemble the ear- liest members of its group (e.g., ^Eohiodon and iYanbiania). The fossil record of hiodontiform fishes is relatively continuous from the Early Cre- taceous. The description of the range of Hiodon as "relictual" (Li & Wilson, 1999: 371) is some- what misleading, as there is no evidence to sug- gest that the present range of Hiodon is restricted relative to a more widespread ancestral taxon (i.e., tEohiodon and other fossil hiodontids do not have a wider range that encompasses that of living Hio- HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 13 A. Hiodon tergisus Lesueur 1818 / L^ -t7 ^H MCZ 17910 (neotype) Fig. 6. Neotype specimens of A. H. tergisus (mcz 17910). and B. H. alosoides (mhnh 3607). Body measurements of these specimens are given in Table 1. (See also Note Added in Proof, p. 134.) don). By these criteria, therefore, Hiodon is only weakly, if at all. supported as a living fossil. Etymology — Hyoeides (Greek), shaped like the letter upsilon (Y, v), referring to the hyoid arch; odontos (Greek), tooth, referring to the large teeth on elements of the gill arches (Jordan & Ev- ermann, 1896). Hiodon tergisus Lesueur, 1818 1818 Hiodon tergisus Lesueur: 366 1818 Hiodon clodalus Lesueur: 367. pi. XIV: figs. 1-3 1818 Glossodon harengoides Rafinesque: 354 1818 1820 1820 1823 1836 1836 1846 1847 1868 1877 Glossodon heterurus Rafinesque: 354 Hyodon vernalis Rafinesque: 43 Hyodon {Clodalus) Clodalus Rafinesque: 43 Hiodon clodalis Richardson: 716 Cyprinus (Abramisl) smithii Richardson: lio ("fig. faulty," Gunther, 1868: 376) Hiodon chrysopsis Richardson: 232 Hyodon claudalus Cuvier and Valenci- ennes: 313 Hiodon tergissus Kirtland: 338-339. pi. 28, figs. 1 and 2 (a misspelling of H. ter- gisus) Hyodon tergisus Gunther: 375 Hiodon selenops Jordan and Bean: 67 HOLOTYPE — No holotype exists for Hiodon ter- 14 FIELDIANA: ZOOLOGY .-IH in IT) ,^; in o 2! "^ ~ 00 E -^ E -^ s ^ E '^' o JC^; (N 2 E^ E .: E ^ E 00 ^,3 5 -> •? O E- S o^ E -J :| g S r^ P S o " -:: sO ^ 3 r<~, IT) gisus (Eschmeyer, 1998). I designate mcz 17910 as a neotype. This specimen (Fig. 6A, Table 1) is an alcohol-stored specimen collected by C. M. Warren in Buffalo, New York, probably in Lake Erie. This specimen was received by the mcz in 1854. (See also Note Added in Proof, p. 134.) Type Locality and Distribution — Lake Erie at Buffalo, New York, U.S.A. (Lesueur, 1818). Hiodon tergisus is found in eastern and central North America in five of Burr and Mayden's (1992) faunal provinces (Hudson Bay, Great Lakes, Mississippi, Central Appalachian, and Southeastern; see Fig. 2). Diagnosis — Differs from other members of the genus by possessing irregular pattern of scale rows above insertion of anal fin; fleshy keel pres- ent from pelvic fin to anus only; a groove on an- terodorsal portion of orbitosphenoid; smaller oral teeth; basihyal toothplate more than 65% of man- dibular length (>35 mm SL); 53-57 preural ver- tebrae; 13-16 branched dorsal fin rays; 24-27 branched anal fin rays. Natural History — Relatively less is known about the natural history of H. tergisus than of H. alosoides (see below), and much of what is known was summarized by Scott and Grossman (1973). Glenn and Williams (1976) studied a pop- ulation of H. tergisus in Manitoba. Canada, and concluded that individuals began to mature in the fourth year of life, and that all individuals over the age of 6 years in their sample were mature. However, age at maturity is likely to vary across the range of the species (Scott & Grossman, 1973), and males generally mature 1 year before females (Glenn & Williams, 1976). Hiodon ter- gisus migrates upstream in spring (April-June) to spawn in fast waters of large clear rivers. The buoyant eggs of H. tergisus presumably are car- ried downstream from the spawning site by the current (Scott & Grossman, 1973). Glenn and Williams (1976) estimated the relative fecundity of H. tergisus as 2,000-4,000 ova per 100 g of body weight (5,000-9,000 ova per female in their study), and concluded that there was a steady in- crease in fecundity over the life of the fish until the age of 8 years, when fecundity began to de- crease. Glenn and Williams (1976) further con- cluded that males have a shorter life span (8 years) than females (10 years). Scott and Grossman (1973) listed the food of H. tergisus as aquatic and terrestrial invertebrates (primarily insects, but also including crayfish and mollusks) and small fishes. Boesel (1938; cited in Wallus 1990: 165) found that "Summer stomach HILTON: OSTEOLOGY OF HIODON LESUEUR, contents of 16 mooneye, 25-133 mm, were in- sects and crustaceans; some Cladocera in 106- 146 mm specimens, but terrestrial insects were the most abundant food." Glenn (1975) found similar gut contents in his sample, and that corixids were the major component of the diet. Glenn (1975) also found that there were vernal and autumnal peaks in feeding in a population of H. tergisus in Manitoba, Canada. Trautman (1957) concluded that H. tergisus is found only in the clearest and largest waters with- in Ohio. Trautman (1957) also stated that Ohio riverine populations of H. tergisus have declined since the mid- 1800s because of an increase in the turbidity of the waters in which it lives (see also Scott & Grossman, 1973). This statement was based primarily on catch records and general early accounts. Roberts (1989: 140), however, found H. tergisus to be abundant in turbid water systems in Alberta, Canada, and suggested that "an increase in turbidity is probably the most visible, but not the only change that occurred in Ohio." Hiodon tergisus is rare or extirpated in many areas of its range (e.g.. New York: Smith, 1985, http://www.dec.state.ny.us/website/dfwmr/wildlife/ endspec/etsclist.html [visited September 2000]; Pennsylvania: Cooper, 1983; Michigan: http:// www.dnr.state.mi.us./pdfs/wildlife [visited Septem- ber 2000]; Missouri: Pflieger, 1997; North Caroli- na: Rhode et al., 1994, 1998), although in other areas it is stable or common (e.g., Tennessee: Et- nier & Stames. 1993; Alabama: Mettee, O'Neil, & Pierson, 1996). Etymology — Tergisus (Greek), polished, refer- ring to its silver color (Scott & Grossman, 1973). Remarks — Other characteristics of H. tergisus include 11-25 premaxillary tooth positions; 8-17 maxillary tooth positions; 19-40 dentary tooth positions; 55-59 scales along lateral line; and in- sertion of dorsal fin anterior to that of anal fin (plesiomorphic: also present in t//. consteniorum, iEohiodon, and fYanbiania). General morpho- metric and meristic measures of a sample of ten specimens from a growth series of H. tergisus are presented in Tables 2, 4. 6, 9. 11, 13, 15, 17, 19, and 21 (see p. 19 j^). When Lesueur (1818: 367-368) described H. tergisus, he also described the species H. cloda- lus, but suggested that this might be the other sex of H. tergisus, a hypothesis he "had not the op- portunity of settling by an examination of the sex- ual organs, as [his] stay at the places where they are found was very short, and [he] was enabled to procure but two solitary individuals." Hiodon clodalus was formally recognized as the female of H. tergisus by Kirtland (1847: 339), who gave full credit to Lesueur: "but it is due to him [Le- sueur] to say that he suggested that such might be the fact" (see also Storer, 1846). Vernacular names of H. tergisus include "mooneye" (this is the most common), "toothed herring." "larger herring," "toothed herring of the lakes," "summer false herring," "spring false herring," "May false herring," "lake false her- ring," "river whitefish," "notch-fin Hiodon," "fresh water herring," and "laquaiche argentee" (Rafinesque, 1820; Kirtland, 1847; Jordan & Ev- ermann, 1896; Scott & Grossman, 1973). References on Anatomy of Soft Tissues — Allis, 1919 (eye muscles, swim bladder, cranial nerves, and cranial blood vessels); Moore, 1944; Moore and McDougal, 1949 (retinae); Haedrich, Winterberg, and Nelson, 1973 (optic septum); H.- J. Wagner and AH, 1978 (retinae); Zyznar, Gross, and Nicol, 1978 (retinae). References on Early Ontogeny — Snyder and Douglas (1978); Wallus (1986); Wallus and Buch- anan (1989); Wallus (1990). Hiodon alosoides (Rafinesque, 1819) 1818 Clupea alosoides Rafinesque: 354 ("Ap- peared first as name only ["C/- alosoides R."; Rafinesque, 1818: 354] and not avail- able . . ."; Eschmeyer, 1998: 76) 1819 Amphiodon alveoides Rafinesque: 421 (al- veoides is regarded as a misspelling of alosoides) 1820 Hyodon amphiodon Rafinesque: 42 1820 Hyodon heterurus Rafinesque: 42 1836 Cyprinus {Abramisl) smithii Richardson: 110 ("fig. faulty," Gunther, 1868: 376) 1836 Hiodon chrysopsis Richardson: 232, 311, pi. 94, fig. 3 1842 Glossodon smithii Meckel: 1033 1877 Elattonistius chrysopsis Gill and Jordan, in Jordan and Bean: 67 1883 Hyodon alosoides Jordan and Gilbert: 259 HoLOTYPE — No type specimen exists for Hio- don alosoides (Eschmeyer. 1998). I designate MNHN 3.607 as a neotype. This specimen (Fig. 6B, Table 1) is a dried specimen collected by Le- sueur in 1828 from the Ohio River at Cincinatti, Ohio. This specimen was referred to as a "non- type Lesueur specimen" of H. tergisus by Esch- meyer (1998: 1664); however, this specimen is H. 16 FIELDIANA: ZOOLOGY alosoides (Fig. 6B). (See Note Added in Proof, p. 134.) Type Locality and Distribution — Lee et aL (1980) reported the type locality of H. alosoides as the Ohio River, U.S.A., probably at Louisville, Kentucky. Although H. alosoides is found in only three of Burr and Mayden's (1992) faunal prov- inces (Yukon-Makenzie, Hudson Bay, and Mis- sissippi; see Fig. 2), it has a much broader range across North America than does H. tergisus, which is found in five provinces. Of all North American freshwater fishes, H. alosoides has one of the widest latitudinal ranges, rivaled only by few other species (e.g., Aplodinotus gniniens. Page & Burr, 1991). Hiodon alosoides is known from the Early Pleistocene of Nebraska (G. R. Smith & Lundberg, 1972). Diagnosis — Differs from other members of ge- nus by having dorsal fin insertion above or pos- terior to anal fin insertion; a fleshy keel from pec- toral girdle to anus; no groove on anterodorsal portion of orbitosphenoid (unknown in '\H. con- steniorum); larger oral teeth; basihyal toothplate more than 55%-60% of mandibular length (>35 mm SL); 56-61 vertebrae; 9-10 branched dorsal fin rays; 30-31 branched anal fin rays. Natural History — Scott and Grossman (1973: 329) stated that H. alosoides is typically found in "quiet, turbid waters of large rivers, the small lakes, ponds, and marshes connected to them, and the muddy shallows of larger lakes." In the Scioto River in Ohio, Trautman (1957) found that H. alo- soides was most abundant in deep pools with a swift current. Hendrickson and Power (1999: 414) found that H. alosoides "followed the general pat- tern of increases in abundance, followed by de- clines and stabilized abundances" after creation in 1953 of Lake Sakakawea, a reservoir in north- western North Dakota. These authors further not- ed that favored conditions for H. alosoides "were prevalent during the early years of impoundment, and the increase in goldeye between 1990 and 1994 was attributable to good recruitment caused by very turbid conditions in the upper portion of the reservoir during the recent drought" (Hen- drickson & Power, 1999: 414). Based on studies by Kennedy and Sprules (1967) and others, Scott and Grossman (1973) list as the food of H. alosoides aquatic and terrestrial invertebrates (primarily insects, but also including crayfish and mollusks), small fishes, and other vertebrates, including green frogs, shrews, and mice. Hiodon alosoides appears to be an oppor- tunistic feeder, with prey reflecting local, season- al, and annual changes in availability (Donald & Kooyman, 1977a). Moon, Fisher, and Krentz (1998) found that Gorixidae, Goleoptera, Gopep- oda, and Gladocera form the bulk of the diet dur- ing peak abundance of H. alosoides in two back- waters of the Missouri River in North Dakota, and that larval fishes are not an important part of their diet. Donald and Kooyman (1977b) studied the mi- gration patterns of immature and adult H. alo- soides in the Peace River system in northern Al- berta, Ganada. They found that adults migrated from the Peace River into the Peace-Athabasca Delta following ice breakup in late April, al- though individuals were caught near the delta in early March. Spawning took place in mid-May and hatching occurred in early June. Both juve- niles and adults were caught in the delta through August, although they found that the migration back to the Peace River peaked during the last week of July and the first week of August, and that juveniles tended to remain in the delta longer. The migration of the young of the year did not begin until mid-July and lasted until November, with no consistent peak during the study (3 years). In this study, some animals were estimated to mi- grate up to 800 km between wintering and spawn- ing habitat. Moon et al. (1998) found H. alosoides in peak abundance in backwaters of the Missouri River in North Dakota during July. Hiodon alosoides seems to be faring better than H. tergisus (e.g., Pflieger, 1997; Etnier & Starnes, 1993; Robinson & Buchanan, 1988), although it has declined at the margins of its range (e.g., Al- abama: Mettee et al., 1996; Pennsylvania: Gooper, 1983). Etymology — Alosa (Glassical Latin), a shad; -oides (New Latin), denoting likeness of form (Jaeger, 1978), referring to the superficial resem- blance to members of the clupeid genus Alosa. Remarks — Other characteristics of H. alo- soides include 11-17 premaxillary tooth posi- tions; 15-30 maxillary tooth positions; 22-30 dentary tooth positions; 58-63 scales along the lateral line. General morphometric and meristic measures of a sample of ten specimens from a growth series of H. alosoides are presented in Ta- bles 3, 5, 7, 10, 12, 14, 16, 18, 20, and 22. The misspelling of the species name (alveoides) by Rafinesque (1819) is considered a misprint (Jordan & Evermann, 1896), although, as Scott and Grossman (1973: 332) remark, "There seems little reason for this decision of later authors." However, it seems clear, both etymologically and HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 17 based on the name alosoides given in Rafinesque (1818), that alosoides was Rafinesque's (1819) in- tent. Vernacular names of H. alosoides include '■goldeye" (this is the most common), "toothed false herring.'" 'ia Quesche." "naccaysh," "yel- low herring." "shad mooneye." "weepicheesis," and "laquaiche aux yeux d"or" (Rafinesque. 1 820: Jordan & Evermann. 1 896; Scott & Cross- man. 1973). References on Anatomy of Soft Tissues — Moore and McDougal, 1949 (retinae); Green- wood. 1971 (ventral gill arch and hyoid muscu- lature); G. J. Nelson. 1972a (stomach and intes- tine); Haedrich et al., 1973 (optic septum); H.-J. Wagner and AH. 1978 (retinae); Zyznar et al., 1978 (retinae); Best and Nicol. 1979 (eye); Brae- kevelt. 1982a.b. 1985 (retinae); Hilton, 2001 (ven- tral gill arch and hyoid musculature). References on Early Ontogeny — Battle and Sprules (1960). Pankhurst (1985), Pankhurst, Sta- cey. and Van Der Kraak (1986). Wallus (1986. 1990). Osteological Descriptions Skull Roof and Dorsal and Lateral Ethmoid Region Ten paired dermal bones, including extrasca- pulars. parietals. frontals. pterotics. and nasals, and the median supraethmoid form the skull roof of Hiodon. The median chondral supraoccipital also comprises a significant part of the posterior skull (discussed under Posterior and Ventral Por- tions of the Braincase and Ventral Ethmoid Re- gion). The dorsal and lateral ethmoid region is comprised of four bones: the median supraeth- moid (dermal) and mesethmoid (chondral), and the paired lateral ethmoid (chondral with a large membrane-bone flange, see below). All of the skull bones in Hiodon are smooth, unomamented, and. with the exception of the extrascapulars. lie mostly below a thick layer of dermis and adipose tissue. The skull roof and ethmoid region are il- lustrated in Figures 7 to 14. 16, 28. and 29. De- tails of the posterior skull roof and braincase in fossil hiodontids are not well known, in part be- cause of the large, superficial extrascapulars, which often are preserved covering the deeper el- ements. The thin, concave extrascapulars (es. Fig. 8) lie above the epaxial musculature that inserts on the temporal and occipital regions of the skull. These elements are the most superficial bones of the skull roof and develop initially as simple tubular ossifications of the supratemporal sensory canal (Fig. 14), but become roughly triangular in the adult (e.g.. Fig. 28) and cover much of the dorsal surface of the parietals and the supraoccipital, as well as the portions of the epioccipitals and pter- otics that border the temporal fossae. In some specimens, the extrascapulars may extend forward to contact the frontals. Contrary to Taveme (1977). the left and right extrascapulars do not meet in the midline, even in the largest individuals examined. Thin, expanded extrascapulars are found in several basal teleost taxa, both within (e.g., Petrocephaliis, fPalaeonotopterus, and Monnyrops, Cavin & Forey, 2001: fig. 10) and outside (e.g.. Megalops, Forey, 1973: fig. 26) of Osteoglossomorpha. The parietals (pa. Figs. 7 and 9) occupy the central portion of the skull roof and form the an- terior borders of the temporal fossae (see discus- sion under Temporal Fossae). These bones lie dor- sal to the posterior fontanelles and the portion of the neurocranial cartilage that carries the anterior semicircular canals. Anteriorly, there is a tight su- ture between the parietals and frontals. Often the left and right parietals share a tight suture for a small length in the midline of the skull, although the degree of this contact is variable (compare the specimens illustrated in Figs. 7 and 9). The pari- etals overlap the dorsal surface of the supraoccip- ital posterodorsally and the pterotics laterally. An elongate posterior process of the parietal contacts the epioccipital and forms a "bridge" over the ventral margin of the supraoccipital (here termed the "parietal bridge"). A similar-shaped parietal is present in fEohiodon rosei (amnh 8059). The parietals variably support a small segment of the supraorbital canal that runs toward the posterior midline of the skull (Figs. 14. 15D, E, and 16; see discussion under Sensory Canals). This is in con- tradiction to Li and Wilson (1999, character 12; also Li, Grande. & Wilson. 1997). who coded Hiodon as having the supraorbital canal ending in the frontal bone (versus ending in the parietal). The frontals (fr. Figs. 7-9) lie anterior to the parietals and are the largest elements of the der- mal skull roof. These elements form early as sim- ple ossifications surrounding the supraorbital sen- sory canal (already present in the smallest avail- able specimens of both species; Fig. 14), but be- come roughly trapezoidal by 39 mm SL (e.g., UAMZ 404 IB; see also Fig. 16); the posterior mar- FIELDIANA: ZOOLOGY Table 2. Sex and body measurements for a growth series of Hiodon tergisus. Specimen SL FL PPEC PPEL PDOR PAN POR (TL) Sex* (%TL) (%TL) (%TL) (%TL) (%TL) (%TL) (%TL) JFBM 22748 7 21.0 mm 25.0 mm 6.0 mm 10.0 mm 13.0 mm 14.0 mm 2.0 mm (26.0 mm) (80.8%) (96.2%) (23.1%) (38.5%) (50.0%) (53.8%) (7.7%) JFBM 22747C 7 24.0 mm 26.0 mm 7.0 mm 11.0 mm 14.0 mm 15.0 mm 2.0 mm (28.0 mm) (85.7%) (92.9%) (25.0%) (39.3%) (50.0%) (53.6%) (7.1%) TU 108166E 7 34 mm 38 mm 8.0 mm 15.0 mm 19.0 mm 20.0 mm 1.7 mm (40 mm) (85.0%) (95.0%) (20.0%) (37.5%) (47.5%) (50.0%) (4.3%) TU 108166D 7 49 mm 55 mm 11.0 mm 21.0 mm 28.0 mm 29. mm 2.6 mm (58 mm) (84.5%) (94.8%) (19.0%) (36.2%) (48.2%) (50.0%) (4.5%) UMA F 10608 7 57 mm 62 mm 13.0 mm 24.0 mm 31 mm 33 mm 3.1 mm (66 mm) (86.4%) (93.9%) (19.7%) (36.4%) (47.0%) (50.0%) (4.7%) UMA F 10609 F 160 mm 174 mm 33 mm 65 mm 93 mm 100 mm 7.0 mm (194 mm) (82.5%) (89.7%) (17.0%) (33.5%) (47.9%) (51.5%) (3.6%) UMA F10610 M 183 mm 200 mm 39 mm 77 mm 107 mm 1 17 mm 9.0 mm (222 mm) (82.4%) (90.1%) (17.6%) (34.7%) (48.2%) (52.7%) (4.1%) UMA F10611 M 210 mm 229 mm 45 mm 85 mm 121 mm 134 mm 8.0 mm (246 mm) (85.4%) (93.1%) (18.3%) (34.6%) (49.2%) (54.5%) (3.3%) UMA F10612 M 215 mm 235 mm 41 mm 89 mm 126 mm 137 mm 9.0 mm (263 mm) (81.7%) (89.4%) (15.6%) (33.8%) (47.9%) (52.1%) (3.4%) UMA F10613 F 230 mm 256 mm 44 mm 98 mm 130 mm 144 mm 10.0 mm (280 mm) (82.1%) (91.4%) (15.7%) (35.0%) (46.4%) (51.4%) (3.6%) M, male; F, Female. Table 3. Sex and body measurements for a growth series of Hiodon alosoides. Specimen SL FL PPEC PPEL PDOR PAN POR (TL) Sex* (%TL) (%TL) (%TL) (%TL) (%TL) (%TL) (%TL) TU 113117E 7 24.3 mm 27.5 mm 6.4 mm 10.9 mm 16.0 mm 13.8 mm 1.5 mm (29.3 mm) (82.9%) (93.9%) (21.8%) (37.2%) (54.6%) (47.1%) (5.1%) TU 1081 18A 7 30.0 mm 35 mm 7.0 mm 14.0 mm 20.0 mm 19.0 mm 1.3 mm (37 mm) (81.1%) (95.6%) (18.9%) (37.87o) (54.1%) (51.4%) (3.5%) UAMZ 404 IB 7 38 mm 40 mm 9.0 mm 17.0 mm 26.0 mm 24.0 mm 2.0 mm (47 mm) (83.0%) (91.5%) (19.1%) (36.2%) (55.3%) (51.1%) (4.3%) UMA F 10600 7 52 mm 57 mm 12 mm 21.0 mm 31 mm 29.0 mm 2.5 mm (61 mm) (85.2%) (93.4%) (19.7%) (34.4%) (50.8%) (47.5%) (4.1%) UMA F 10601 7 107 mm 122 mm 23 mm 43 mm 71 mm 63 mm 4.0 mm (122 mm) (81.1%) (92.4%) (17.4%) (32.6%) (53.8%) (47.7%) (3.0%) UMA F 10604 F 184 mm 207 mm 36 mm 76 mm 122 mm 1 13 mm 6.0 mm (225 mm) (81.8%) (92.0%) (16.0%) (33.8%) (54.2%) (50.2%) (2.7%) UMA F 10588 M 252 mm 274 mm 47 mm 104 mm 164 mm 154 mm 6.0 mm (305 mm) (82.6%) (89.8%) (15.4%) (34.1%) (53.8%) (50.5%) (2.0%) UMA F 10606 M 254 mm 282 mm 50 mm 1 12 mm 169 mm 165 mm 7.0 mm (308 mm) (82.5%) (91.6%) (16.2%) (37.7%) (54.9%) (53.6%) (2.3%) UMA F 10605 F 279 mm 309 mm 50 mm 1 16 mm 189 mm 180 mm 7.0 mm (335 mm) (82.3%) (92.2%) (14.9%) (34.6%) (59.1%) (53.7%) (2.1%) UMA F 10634 F 300 mm 330 mm 46 mm 120 mm 195 mm 190 mm 7.0 mm (360 mm) (83.3%) (91.7%) (12.8%) (33.3%) (54.2%) (52.8%) (1.9%) M, male; F Female. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 19 Table 4. Head measurements and meristic data for a growth series of Hiodon tergisus. L, R mandibular sensory Head Lower jaw canal Specimen length Head width Frontal length length openings (SL) (%SL) (%SL) (%SL) (%SL) (in dentary) JFBM 22748 6.0 mm 2.5 mm Not fully 3.3 mm 5,4 (21.0 mm) (28.6%) (11.9%) ossified (15.7%) JFBM 22747C 7.0 mm 2.3 mm 2.1 mm 3.6 mm 5,5 (24.0 mm) (29.2%) (9.6%) (8.8%) (15.0%) TU 108166E 8.0 mm 3.3 mm 2.8 mm 5.4 mm 5,5 (34 mm) (23.5%) (9.7%) (8.2%) (15.9%) TU 108166D 12.0 mm 4.4 mm 4.1 mm 7.0 mm 5,5 (49 mm) (24.5%) (9.0%) (8.4%) (14.3%) UMA F 10608 14.0 mm 4.6 mm 4.4 mm 7.5 mm 5,6 (57 mm) (24.6%) (8.1%) (7.7%) (13.2%) UMA F 10609 32 mm 1 1.6 mm 1 1 .0 mm 19.5 mm 5,6 (160 mm) (20.0%) (7.3%) (6.9%) (12.2%) UMA F10610 40 mm 13.6 mm 16.3 mm 21.0 mm 5,6 (183 mm) (21.9%) (7.4%) (8.9%) (11.5%) UMA F 106 11 46 mm 14.4 mm 17.9 mm 23.6 mm 4,5 (210 mm) (21.9%) (6.9%) (8.5%) (11.2%) UMA F 106 12 47 mm 14.8 mm 17.6 mm 25.0 mm 5,5 (215 mm) (21.4%) (6.9%) (8.2%) (11.6%) UMA F 106 13 49 mm 13.9 mm 18.4 mm 26.4 mm 7,7 (230 mm) (21.3%) (6.0%) (8.0%) (11.5%) Table 5. Head measurements and meristic data for a growth series of Hiodon alosoides. L, R mandibular sensory Head Frontal Lower jaw canal Specimen length Head width length length openings (SL) (%SL) (%SL) (%SL) (%SL) (in dentary) TU 113117E 5.7 mm 2.7 mm 2.2 mm 3.8 mm 6,6? (24.3 mm) (23.5%) (11.1%) (9.1%) (15.6%) TU 1081 18A 7.0 mm 3.1 mm 2.7 mm 5.4 mm 7,6 (30.0 mm) (23.3%) (10.3%) (9.0%) (14.6%) UAMZ 404 1 B 9.0 mm 3.8 mm 2.9 mm 5.5 mm 6,6 (39 mm) (23.1%) (9.7%) (7.4%) (14.1%) UMA F 10600 13.0 mm 4.7 mm 3.6 mm 6.7 mm 6.6 (52 mm) (25.0%) (9.4%) (6.9%) (12.9%) UMA F 10601 23.0 mm 7.7 mm 7.8 mm 14.3 mm 7,6 (107 mm) (21.57f) (21.5%) (7.3%) (13.4%) UMA F 10604 36 mm 1 1.4 mm 11.2 mm 21.7 mm 8,6 (184 mm) (19.6%) (6.2%) (6.1%) (11.8%) UMA F10588 48 mm 16.3 mm 14.6 mm 28.7 mm 7.8 (252 mm) (19.0%) (6.5%) (5.8%) (11.4%) UMA F 10606 51 mm 16.5 mm 17.8 mm 30.7 mm 7,8 (254 mm) (20.1%) (6.5%) (7.0%) (12.1%) UMA F 10605 55 mm 17.9 mm 17.5 mm 3 1 .9 mm 7.7 (279 mm) (19.7%) (6.47^) (5.2%) (11.4%) UMA F 10634 52 mm 17.2 mm 18.3 mm 31.7 mm 7,7 (300 mm) (17.3%) (5.7%) (6.1%) (10.6%) 20 FIELDIANA: ZOOLOGY Tabi^e 6. Meristic data and measurements for the head region of a growth series of Hiodon tergisus. Basihyal L, R L, R L, R Basihyal toothplate dentary premaxillary maxillary L, R toothplate length as a Specimen tooth tooth tooth branchio- length % of lower (SL) positions positions positions stegals (%SL) jaw length JFBM 22748 19,20 14, 11 9,8 8,8 2.0 mm 60.6% (21 mm) (9.5%) JFBM 22747C 21, 17 14, 14 8,9 9,8 2.1 mm 58.3% (24 mm) (8.8%) TU 108166E 31,31 16, 15 11, 11 8,7 3.4 mm 63.0% (34 mm) (10.0%) TU 108166D 30,31 19, 19 13, 12 8,8 4.8 mm 68.6% (49 mm) (9.8%) UMA F 10608 36,29 21,20 16, 17 8,8 5.4 mm 72.0% (57 mm) (9.5%) UMA F 10609 32,37 23, 19 15, 16 7,8 14.1 mm 72.3% (160 mm) (8.8%) UMA F10610 35,32 ?*,24 16, 14 8,8 15.5 mm 73.8% (183 mm) (8.5%) UMAF10611 36, 35 25,22 12, 11 8,7 17.3 mm 73.3% (210 mm) (8.2%) UMA F10612 39,40 22,22 14, 13 8,8 17.7 mm 70.8% (215 mm) (6.7%) UMA F10613 36,36 25,22 11, 13 8,8 18.0 mm 68.2% (230 mm) (7.8%) * The left premaxilla of this specimen was broken, and the anterior piece is missing. Table 7. Meristic data and measurements for the head region of a growth series of Hiodon alosoides. Specimen L, R dentary tooth L, R premaxillary tooth L, R maxillary tooth L, R branchio- Basihyal toothplate length Basihyal toothplate length as a % of lower (SL) positions positions positions stegals (%SL) jaw length TU 113117E 23,23 12, 14 18, 17 8,8 2.5 mm 65.8% (24.3 mm) TU 1081 18A 30,28 15, 15 24,20 9,9 (10.3%) 2.8 mm 51.8% (30.0 mm) UAMZ 404 1 B 30,28 17, 13 15, 14 8,8 (9.3%) 3.1 mm 56.4% (39 mm) UMA F 10600 30,26 14, 12 21,21 8,8 (7.9%) 4.2 mm 62.7% (52 mm) UMA F 10601 22,24 11, 13 18,22 9,8 (8.1%) 8.2 mm 57.3% (107 mm) UMA F 10604 27,29 13, 13 27,30 8,8 (7.7%) 12.1 mm 58.5% (184 mm) UMA F10588 27,30 14, 13 27,30 8,8 (6.6%) 15.9 mm 55.4% (252 mm) UMA F 10606 27,28 13, 14 27,27 8,7 (6.3%) 16.3 mm 53.1% (254 mm) UMA F 10605 25,27 11, 10 30,28 8,8 (6.4%) 17.5 mm 54.5% (279 mm) UMA F 10634 25,27 14, 13 26,25 9,8 (6.3%) 18.8 mm 59.3% (300 mm) (6.3%) HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 21 Table 8. Average basihyal toothplate length of hiodon- tid fishes reported as a percentage of lower jaw length. Basihyal toothplate length (as Taxa % of lower (n) jaw length) -\Eohiodon 49% FMNH PF 10637, UMA F 106 14 (2) Hiodon tergisus 70% (10) "^Hiodon consteniorum 60% UALVP 38875 (1) Hiodon alosoides 53% (10) Note: Adult specimens of Hiodon tergisus and Hiodon alosoides other than those recorded in Tables 6 and 7 were used for calculating means; n is the number of specimens used to retrieve the average. Table 9. Meristic data of vertebrae and centra for a growth series of Hiodon tergisus. Specimen (SL) Total centra Total preural Total abdominal centra centra Transitional vertebrae Total preural caudal centra JFBM 22748 (21.0 mm) JFBM 22747C (24.0 mm) TU 108166E (34 mm) TU 108166D (49 mm) UMA F 10608 (57 mm) UMA F 10609 (160 mm) UMA F10610 (183 mm) UMA F10611 (210 mm) UMA F106I2 (215 mm) UMA F10613 (230 mm) 1 0 0 0 0 3* 2 0 0 0 57 55 30 1 25 57 55 31 1 24 56 54 30 0 24 57 55 31 1 24 56 54 30 1 24 54 54 30 1 24 57 55 30 1 25 52t 53t 29t 1 24 Note: Numbers in italics indicate lower than typical counts because of early stage of development. * cl, c2, and u2 are the only centra that have completely formed (i.e., completely surrounded the notochord). Other centra have started to form, although most are only a spot of bone in the ventral midline and thus are not included in this count. t These counts are lower than average because of the pathological fusion of the first five centra (cl-5). This is counted as a single centrum because it occupies the space of a single centrum, although it is recognized as a fusion because the associated five neural arches are not fused to one another (i.e., they are distinguishable). The neural arches are fused to this pathological centrum. 22 FIELDIANA: ZOOLOGY Specimen (SL) Table 1 0. Meristic data of vertebrae and centra for a growth series of Hiodon alosoides. Total preural Total abdominal Transitional Total preural Total centra centra centra vertebrae caudal centra TU 113117E (24.3 mm) TU 1081 18A (30.0 mm) UAMZ 404 IB (39 mm) UMA F 10600 (52 mm) UMA F 10601 (107 mm) UMA F 10604 (184 mm) UMA FI0588 (252 mm) UMA F 10606 (254 mm) UMA F 10605 (279 mm) UMA F 10634 (300 mm) 59* 57 32 It 25 60 58 31 27 60 58 33 25 59* 57 32 25 59 57 32 25 59 57 32 25 59 57 32 25 59 57 33 2 24 58 56 31 0 25 60 58 33 1 25 * Some centra are not complete rings. t The left and right portions of the anterior haemal arches of this specimen may not be fused to one another to form a haemal spine because of the early stage of development, but do curve toward one another to approximate the adult condition. The left and right sides of the haemal arch of the transitional vertebra do not show this morphology. Table 1 1. Meristic data of vertebral elements for a growth series of Hiodon tergisus. Specimen (SL) Total preural neural arches (excluding pul) Autogenous neural arches Supraneurals L, R epineural bones JFBM 22748 54 Centra not formed 24 None ossified (21.0 mm) (None ossified) (None ossified) JFBM 22747C 55 Centra not formed 24 10, W (24.0 mm) TU 108166E 54 55 24 26,25 (34 mm) TU 108166D 54 31 25 27,28 (49 mm) UMA F 10608 53 31 25 27,27 (57 mm) UMA F 10609 54 31 25 28,27 (160 mm) UMA F10610 53 29 24 27,26 (183 mm) UMA F10611 53 27 ? 25,27 (210 mm) UMA F10612 54 29 26 27,27 (215 mm) UMA F10613 53 24 26 27,27 (230 mm) Note: Numbers in italics indicate higher or lower than typical counts because of early stage of development HILTON: OSTEOLOGY OF ///6>D0A^ LESUEUR, 1818 23 Table 12. Meristic data of vertebral elements for a growth series of Hiodon alosoides. Specimen (SL) Total preural neural arches Autogenous neural (excluding pul) arches Supraneurals L, R epineural bones TV 113117E (234.3 mm) TU 1081 18A (30.0 mm) UAMZ 404 1 B (39 mm) UMA F 10600 (52 mm) UMA F 10601 (107 mm) UMA F 10604 (184 mm) UMA F10588 (252 mm) UMA F 10606 (254 mm) UMA F 10605 (279 mm) UMA F 10634 (300 mm) 56 31? 58 58 57 57 56 ? 56 31 56 31 57 31 56 31 56 31 57 32 27* 31 31 30 30 31 30 7 30 30 30. 30 29.29 31.31 29. 30 30.31 30. 30 29. 29 30. 30 30. 29 30.31 Note: Numbers in italics indicate higher or lower than typical counts because of early stage of development. * Only the anterior 17 supraneurals of this specimen stained with alcian. The remaining are assumed to be precar- tilaginous. Table 13. Fin measurements and ratios for a growth series of Hiodon tergisus. Dorsal to Dorsal lobe Ventral lobe Specimen Dorsal fin base Anal fin base anal fin base caudal fin caudal fin (SL) (%SL) (%SL) ratio (%SL) (%SL) JFBM 22748 3.2 mm 5.5 mm 1 : 1.7 4.8 mm 5.2 mm (21.0 mm) (15.2%) (26.2%) (22.9%) (24.8%) JFBM 22747C 3.2 mm 5.6 mm 1 : 1.8 4.8 mm 5.3 mm (24.0 mm) (13.3%) (23.2%) (20.0%) (22.1%) TU 108166E 3.8 mm 7.5 mm 1 :2.0 7.2 mm 8.0 mm (34 mm) (11.1%) (22.1%) (21.27r) (23.5%) TU 108166D 6.1 mm 1 1 .0 mm 1 : 1.8 11.1 mm 12.5 mm (49 mm) (12.4%) (22.4%) (22.7%) (25.5%) UMA F 10608 7.1 mm 13.3 mm 1 : 1.9 13.5 mm 14.3 mm (57 mm) (12.4%) (23.3%) (23.7%) (25.1%) UMA F 10609 20.3 mm 37 mm 1 : 1.8 47 mm 44 mm (160 mm) (12.7%) (23.2%) (26.2%) (27.2%) UMA F10610 22.9 mm 43 mm 1 : 1.9 50 mm 52 mm (183 mm) (12.5%) (23.3%) (27.3%) (28.4%) UMA F10611 21.4 mm 39 mm 1 : 1.8 56 mm 60 mm (210 mm) (10.2%) (18.4%) (26.9%) (28.5%) UMA F10612 24.0 mm 42 mm 1 : 1.7 56 mm 60 mm (215 mm) (11.2%) (19.1%) (25.9%) (27.9%) UMA F10613 25.5 mm 46 mm 1 : 1.8 63 mm 62 mm (230 mm) i\\.\%) (19.9%) (27.2%) (27.0%) 24 FIELDIANA: ZOOLOGY Table 14. Fin measurements and ratios for a growth series of Hiodon alosoides. Dorsal to Dorsal lobe Ventral lobe Specimen Dorsal fin base Anal fin base anal fin base caudal fin caudal fin (SL) (%SL) (%SL) ratio (%SL) (%SL) TU 113I17E 2.3 mm 7.4 mm .3.2 5.4 mm 6.8 mm (24.3 mm) (9.5%) (30.5%) (22.2%) (28.0%) TU 1081 18A 2.9 mm 8.2 mm :2.8 6.8 mm 7.1 mm (30.0 mm) (9.7%) (22.2%) (22.7%) (23.7%) UAMZ4041B 4.1 mm 10.4 mm :2.5 7.0 mm 7.7 mm (39 mm) (10.5%) (26.7%) (17.9%) (19.7%) UMA F 10600 5.0 mm 14.8 mm :3.0 1 1.6 mm 13.0 mm (52 mm) (9.6%) (28.5%) (22.3%) (25.0%) UMA F 10601 10.7 mm 30 mm :2.8 7* 31 mm (107 mm) (10.0%) (28.1%) (?) (28.7%) UMA F 10604 16.7 mm 51 mm :3.0 43 mm 46 mm (184 mm) (9.1%) (27.4%) (23.5%) (25.2%) UMA F 10588 22.2 mm 70 mm :3.2 50 mm 55 mm (252 mm) (8.8%) (27.9%) (19.9%) (21.9%) UMA F 10606 19.8 mm 68 mm :3.4 57 mmt 62 mmt (254 mm) (7.8%) (26.8%) (22.4%) (24.2%) UMA F 10605 24.9 mm 69 mm :2.8 62 mm 69 mm (279 mm) (8.9%) (24.6%) (22.4%) (24.7%) UMA F 10634$ 26.5 mm 72 mm :2.7 66 mm 71 mm (300 mm) (8.8%) (24%) (22.0%) (23.7%) * All fin rays of the dorsal lobe of the caudal fin are damaged on this specimen; no estimate was possible. t Estimated measurement because the distal tip of the leading fin ray is broken. t Estimated measurements because the median fins and their pterygiophores, although complete, are disarticulated. Table 15. Meristic data of the caudal fin and skeleton of Hiodon tergisus. Dorsal Hypurals (ventral) Specimen (no. segmented (SL) ossified) Epurals caudal rays Dorsal (ventral) branched caudal rays Condition of nspul Neural arches on L, R ul uroneurals JFBM 22748 (21.0 mm) JFBM 22747C (24.0 mm) TU 108166E (34 mm) TU 108166D (49 mm) UMA F 10608 (57 mm) UMA F 10609 (160 mm) UMA F10610 (183 mm) UMA F10611 (210 mm) UMA F10612 (215 mm) UMA F10613 (230 mm) 7 (7) 7 (7) 7 (7) 7 (7) 7 (7) 7 (7) 7 (7) 7 (7) 7 (7) 7 (7) viii, 9 (V, 10) vi, 12 (vi, 12) vii, 13 (V, 14) vi, 14 (V, 15) vii, 14 (vi, 14) iv, 16 (i, 17) ii, 17 (i, 18) iv, 15 (ii, 16) ii, 16 (iv, 15) iii, 16 (ii, 16) (5) (5) 8 (7) 8 (8) 8 (8) 8 (8) 8 (8) 8 (8) 8 (8) 8 (8) 8 (8) Rudimentary Rudimentary Rudimentary Rudimentary Rudimentary Rudimentary Rudimentary Rudimentary Rudimentary Rudimentary Centrum not ossified 3 1 2 3 2 2 2 2 2 3,4 3,4 3,2 3,2 3,3 3,3 3,2 4,3 2,2 3,3 Note: Lowercase Roman numerals indicate the number of unsegmented fin rays. Numbers in italics indicate lower than typical counts because of early stage of development. HILTON: OSTEOLOGY OF ///ODOA^ LESUEUR, 1818 25 Table 16. Meristic data of the caudal fin and skeleton of Hiodon alosoides. Dorsal Dorsal (ventral) Hypurals (ventral) branched Neural Specimen (no. segmented caudal Condition of arches on L, R (SL) ossified) Epurals caudal rays rays nspul ul uroneurals TU 113117E 7 viii 12 8 Rudimentary 1 3,3 (24.3 mm) (7) (vii 12) (8) TU 1081 18A 7 ix 12 8 Rudimentary 2 3,3 (30.0 mm) (7) (vii 12) (8) UAMZ 404 IB 7 viii 12 8 Full 2 3,4 (39 mm) (7) (V 13) (8) UMA F 10600 7 viii 12 8 Rudimentary 3 2,3 (52 mm) (7) (vi 13) (8) UMA F 10601 7 viii 13 7 Rudimentary 2 3,2 (107 mm) (7) (iv 14) (8) UMA F 10604 7 vi 13 8 Moderate 2 3,3 (184 mm) (7) (ii 14) (8) UMA F10588 7 vii 13 8 Rudimentary 2 2,3 (252 mm) (7) (iii 14) (8) UMA F 10606 7 V 14 8 Rudimentary 2 2,3 (254 mm) (7) (iv 15) (8) UMA Fl 0605 7 vi 13 8 Rudimentary 1* 3,2 (279 mm) (7) (i 14) (8) UMA F 10634 7 iv 15 8 Rudimentary 2 2,3 (300 mm) (7) (iii 14) (8) Note: Lowercase Roman numerals indicate the number of unsegmented fin rays. * A second, more posterior neural arch may be fused to the first uroneural. Table 17. Meristic data of dorsal and anal fin rays and pterygiophores for Hiodon tergisiis. Anal Dorsal Anal prox- Specimen Dorsal Branched proximal fin Branched imal (SL) fin rays dorsal rays radials rays anal rays radials JFBM 22748 (21.0 mm) JFBM 22747C (24.0 mm) TU 108166E (34 mm) TU 108166D (49 mm) UMA F 10608 (57 mm) UMA F 10609 (160 mm) UMA F10610 (183 mm) UMA F10611 (210 mm) UMA F10612 (215 mm) UMA F10613 (230 mm) iii, 14 (none ossified) iii, 14 iii, 13 iii, 15 iii, 15 i, 16 ii, 15 iii, 14 iii, 13 ii. 13 Distal lepidotrichi are poorly developed Distal lepidotrichia are poorly developed 15 iii. 28 Dista lepidotrichia 29 (none are poorly developed ossified) 14 iii, 29 Dista lepidotrichia 29 (none are poorly developed ossified) 15 iv, 31 27 30 14 ii, 31 27 29 15 ii, 31 26 29 14 i,31 26 28 14 i,32 26 28 14 i, 30 24 28 14 o, 32 27 30 13 ii, 29 25 28 .... ... Note: Lowercase Roman numerals indicate the number of unsegmented fin rays. Numbers in italics indicate lower than typical counts because of early stage of development. 26 FIELDIANA: ZOOLOGY Table 18. Meristic data of dorsal and anal fin and supports for Hiodon alosoides. Specimen (SL) Dorsal fin rays Branched dorsal rays Dorsal proximal Anal radials fin rays Branched anal rays Anal proximal radials TU 113117E (24.3 mm) TU 1081 18A (30.0 mm) UAMz 404 1 B (39 mm) UMA F 10600 (52 mm) UMA F 10601 (107 mm) UMA F 10604 (184 mm) UMA F10588 (252 mm) UMA F 10606 (254 mm) UMA F 10605 (279 mm) UMA F 10634 (300 mm) iii. 12 ii, 13 ii. 13 h 12 9* ii, 11 ii. 12 ii, 12 iii, 11 12 Distal lepidotrichia are poorly developed 9 9 10 10 ?* 9 9 10 9 12 (none ossified) 12 iii, 35 iii, 35 Distal lepidotrichia are poorly developed 31 35 (none ossified) 36 12 iii, 34 30 35 12 iii, 35 31 34 13 i,37 31 36t 11 ii, 34 31 34 12 V, 33 31 35 11 iii, 34 31 35 12 iii, 33 31 33 11 iii, 32 30 32 Note: Lowercase Roman numerals indicate the number of unsegmented fin rays. * Posteriormost dorsal fin rays are missing from this specimen. t The first and second proximal radials of anal fin (prl and pr2) are fused in this specimen. Table 19. Meristic data of paired fins for a growth series of Hiodon tergisus. Specimen (SL) L, R pectoral fin rays (no. branched) L, R pectoral radials (no. ossified) L, R pelvic fin rays JFBM 22748 (21.0 mm) JFBM 22747C (24.0 mm) TU 108166E (34 mm) TU 108166D (49 mm) UMA F 10608 (57 mm) UMA F 10609 (160 mm) UMA F10610 (183 mm) UMA F10611 (210 mm) UMA F10612 (215 mm) UMA F10613 (230 mm) 13. 13 Distal lepidotrichia are poorly developed 14, 11 Distal lepidotrichia are poorly developed 13, 12 (12,11) 12, 13 (11,12) 13, 13 (12. 12) 14, 13 (13, 12) 13, 13 (12, 12) 12, 13 (11,12) 13, 13 (12, 12) 14, 14 (13, 13) 4,4 {0,0) 4,4 (4,4) 4,4 (4,4) 4,4 (4,4) 4,4 (4,4) 4,4 (4,4) 4,4 (4,4) 4,4 (4,4) 4,4 (4,4) 4,4 (4,4) 6,6 7,7 7,7 7,7 7,7 7,7 7,7 7,7 7,7 7,7 Note: Numbers in italics indicate lower than typical counts because of early stage of development. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 27 Table 20. Meristic data of paired fins for a growth series of Hiodon alosoides. L, R L, R Specimen pectoral fin rays pectoral radials L, R (SL) (no. branched) (no. ossified) pelvic fin rays TU 1131 17E 12, 12 4,4 7,7 (24.3 mm) (11, II) (4,4) TU 1081i8A 11, 11 4,4 7,7 (30.0 mm) (10, 10) (4,4) UAMZ4041B 12, 12 4,4 7,8 (39 mm) (11, II) (4,4) UMA F 10600 12, 12 4,4 7,7 (52 mm) (II, II) (4,4) UMA F 10601 12, 12 4,4 7,7 (107 mm) (II, II) (4,4) UMA F 10604 II, 12 4,4 7,7 (184 mm) (10, II) (4,4) UMA F 10588 II, 12 4,4 7,7 (252 mm) (10, II) (4,4) UMA F 10606 II, 11 4,4 7,7 (254 mm) (10, 10) (4,4) UMA F 10605 12, 12 4,4 7,7 (279 mm) (II, II) (4,4) UMA F 10634 12, 12 4,4 7,7 (300 mm) (II, 11) (4,4) Table 21 . Meristic data of scales for a growth series of Hiodon tergisus. Table 22. Meristic data of scales for a growth series of Hiodon alosoides. Scale Scale Scales rows rows along the above the below the Scale Scale Scales rows rows along the above the below the Specimen lateral lateral lateral Specimen lateral lateral lateral (SL) line line line (SL) line line line TU 108145 55 6 9 NMC 75-1553 58 3 6 (39 mm) (34 mm) ANSP 114175 56 7 9 ANSP 149441 59 6 9 (55 mm) (45 mm) TU 16811 56 7 9 UAic 10473.01 58 7 9 (104 mm) (53 mm) ANSP 169010 53 7 9 UMA F 10602 62 7 11 (125 mm) (92 mm) UMA F10379 58 6 9 UP 65838 62 7 11 (138 mm) (98 mm) Mcz 23825 57 7 10 UMA F 10603 60 7 11 (175 mm) (114 mm) MCZ 23827 57 7 9 MCZ 17908 59 6 9 (230 mm) (215 mm) jfbm 27508 56 7 9 UMA F10149 63 6 9 (270 mm) (280 mm) JFBM 11262* 57 7 10 UMA F 10380 60 7 U (275 mm) (285 mm) MCZ 17906 59 6 9 MCZ 157462* 62 8 11 (295 mm) (340 mm) Note: "Rows above the lateral li ines" includes the single Note: "Rows above the lateral li ines" includes the single dorsal median row. Numbers in italics indicate lower than typical counts because of early stage of development. * Scale counts were made on the right side of this specimen. dorsal median row. Numbers in italics indicate lower than typical counts because of early stage of development. * Scale counts were made on the right side of the spec- imen. 28 FIELDIANA: ZOOLOGY gin is always wider than the anterior. The left and right frontals meet each other along the midline but are never tightly sutured together, and there is a slight ridge in the midline of the anterior portion of the neurocranium formed by the suture be- tween the two frontals. The shallow concavity on either side of the midline, formed as a result of this ridge, is filled with adipose tissue. The ante- rior edges of the frontals are irregular, but there is always a roughly triangular portion of the eth- moid cartilage exposed between the frontals and supraethmoid (etc.. Figs. 7-9). Outside of Hiodon, this pattern of supraethmoid-frontal contact is seen only in '\Eohiodon and possibly '\Lycoptera (see Gaudant, 1968: fig. 5B), although more de- tailed study of '\Lycoptera is needed to confirm the arrangement of the anterior dermal skull bones. The lateral edge of the frontal is strongly arched and forms the dorsal roof of the orbit (Fig. 13). The frontals entirely cover the paired anterior fontanelles (afon. Figs. 17 and 18; see discussion under Posterior and Ventral Portions of the Brain- case and Ventral Ethmoid Region), which are large openings in the dorsal surface of the neu- rocranial cartilage separated from each other by a strut of cartilage in the dorsal midline of the neu- rocrania. Thin laminae of bone extend from the ventral surface of the frontals and follow the lat- eral margin of the fontanelles. As in tleptolepids and most living teleosts (Pat- terson, 1975, 1977a), the pterotics of Hiodon (pto, Figs. 7, 9 and 13) are compound bones formed by a dermal ossification surrounding the otic sensory canal (= dermopterotic portion) and a chondral element roofing the dorsal bend of the external ( = horizontal) semicircular duct (= autopterotic por- tion). Even in the very smallest individuals of Hiodon examined, the two components were not independent ossifications, although this bone was fairly well-developed in these specimens (Fig. 14; note that only the dermal portion of the pterotic is drawn in this figure). Patterson (1977a) dis- cussed several teleostean taxa in which fusion of the dermal and chondral components of the pter- otic is known to be ontogenetic (e.g., Salmo: de Beer, 1937; certain cyprinoids: Lekander, 1949; and certain siluroids: Bamford, 1948), as well as some in which it is thought to be phylogenetic (e.g., Esox: Jollie, 1975; Leuciscus: Lekander, 1949; and Ictalurus: Kindred, 1919). The hypoth- esis that the pterotic represents phylogenetic fu- sion of originally separate bones in Hiodon and other teleostean fishes is supported by the pres- ence of ontogenetic fusion in some taxa (but see Remarks on Phylogenetic Fusion). In Hiodon, the dermal portion of the pterotic contacts the parietal anteriorly and the intercalar posteriorly and forms much of the posterolateral margin of the skull roof. The chondral portion of the pterotic is bor- dered by the epioccipital and intercalar posteriorly and ventrally, and by the sphenotic and prootic anteriorly. A ventrally directed lamella is involved in the posterior hyomandibular fossae (hyfp. Figs. 18-22). A more anterior ventral lamella forms the wall of a fossa for the dilatator operculi muscle. In a specimen of '\Eohiodon falcatus (fmnh PF9881), the pterotic is well-preserved in ventral view, and has a morphology exactly like that of Hiodon. There is no supraorbital bone in Hiodon. Ab- sence of a supraorbital was found to be a syna- pomorphy of Osteoglossomorpha by Li and Wil- son (1996a, 1999). Ma (1987, fig. 1) figured fLy- coptera with a single supraorbital; more recent in- terpretations contend that the supraorbital is absent in this taxon as well (e.g., Jin et al., 1995). Li and Wilson (1999) described the fossil genera '\Kuyangichthys and '\Jiuquanichthys as the only osteoglossomorphs with a supraorbital, and they (along with iTongxinichthys) were found to be the sister-group to all remaining osteoglosso- morphs. Therefore, loss of the supraorbital should be viewed not as a synapomorphy of Osteoglos- somorpha but as a synapomorphy of a less inclu- sive subgroup of osteoglossomorphs. The ethmoid region of Hiodon is largely carti- laginous. The ossifications of the dorsal and lat- eral ethmoid region include the mesethmoid, the supraethmoid, and the lateral ethmoid (Figs. 16- 1 8). The perichondral mesethmoid and dermal su- praethmoid are the last of the bones of the eth- moid region to ossify, and they fuse to one an- other in the adult to form a compound bone (Fig. 28). The smallest specimen examined with these bones is a 38 mm SL specimen of H. alosoides (tu 113117B). The smallest specimen examined of H. tergisus with these bones is a 45 mm SL specimen (xu 108166B), although a slightly larger specimen of H. tergisus (UF 78879, 50 mm SL) has only the supraethmoid. These two bones are still separate in a cross-section of a 63 mm SL specimen of H. alosoides (uamz 4043A, Fig. 23A). In this specimen, the mesethmoid is shown to ossify perichondrally on the lateral surfaces of the cartilage between the left and right nasal cap- sules. The supraethmoid is well separate from the mesethmoid ossification, but it does lie on the dorsal surface of the ethmoid cartilage, below a HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 29 layer of adipose tissue. The margin of the su- praethmoid grows posteriorly and contacts the frontals along their anterolateral corners. The bone labeled by Li and Wilson (1994: fig. 2) as "mesethmoid" in t^^- consteniorum is the su- praethmoid, which has been preserved in dorsal view. Immediately anterior to the orbit lies a bone that forms in the posterolateral wall of the nasal capsule, which I interpret as the lateral ethmoid (let. Figs. 14 and 18-22) with a large, lateral membrane-bone flange (lem. Figs. 13, 18, 20. and 21). Gosline (1961: 29) remarked that this flange makes the lateral ethmoid "look like a circumor- bital" in lateral view, although he was not sug- gesting homology of the flange with a bone of the infraorbital series. The lateral ethmoid has been interpreted as a fused element (e.g.. Patterson, 1977a; Taverne, 1977; Li & Wilson, 1994), com- posed of the lateral ethmoid (chondral compo- nent) and antorbital (membrane-bone component), although, as noted by Patterson (1977a: 97), its ontogeny has never been studied. I never ob- served this bone to be two separate ossifications; thus, there is no direct evidence that it is a fused lateral ethmoid and antorbital (see Remarks on Phylogenetic Fusion). The lateral ethmoid is the first of the ethmoid bones to develop (light chon- dral mineralization was observed in a 22 mm SL specimen of H. tergisus, jfbm 22747B). Early os- sification is confined to the lateral margin of the cartilaginous wall between the nasal capsule and the orbit, and from this splint of bone, the circular chondral component grows medially and the membrane-bone flange grows anteriorly along the lateral surface of the ethmoid cartilage (Fig. 14). The posterior margin of the flange develops a troughlike appearance along its posterior margin early in its development, but does not assume its adult shape until relatively late in ontogeny (e.g., a 38 mm SL specimen of H. alosoides TU 1131 17B). In the adult, the lateral flange is tri- angular and contacts the frontals dorsally. The condition of the "antorbital" in t//. consteniorum was described as similar to that in living Hiodon (Li & Wilson, 1994: 157). However, the "antor- bital" of Li and Wilson (1994: fig. 2) is the lateral ethmoid (a circular bone lying on the posterolat- eral portion of the nasal capsule). The holotype (UALVP 38875) appears to lack the lateral flange, whereas there is an element that may correspond to the lateral flange in the paratype (ualvp 24200). The nasals oi Hiodon (n. Figs. 7-11) are simple tubular ossifications of the anteriormost portion of the supraorbital sensory canal (= nasal sensory canal; nacn. Fig. 15) that form early in ontogeny (Fig. 14). These bones bend sharply ventrolater- ally around the anterior margin of the cartilage of the nasal sac. A curved, tubular nasal was iden- tified as a synapomorphy of Hiodon by Li and Wilson (1994, 1996a, 1999), although a similarly shaped nasal is found in fEohiodon (e.g., uma F11249). Sensory Canals The cephalic sensory canal system of Hiodon was previously described or illustrated by G. J. Nelson (1972b), Taverne (1977), Arratia (1997), and Cavin and Forey (2001). Four pit lines (rows of free neuromast organs) are present in Hiodon (Fig. 15B, C; also see G. J. Nelson, 1972b: fig. 13B), but none makes any indentation or scarring in the bone, as they do in Amia calva (Grande & Bemis, 1998). Nelson (1972b) observed that the pit lines of Hiodon are reduced. Two pit lines (an- terior and middle pit lines; pla and plm, respec- tively. Fig. 15) lie on the dorsal surface of the head posterior to the orbit. The extremely short ethmoidal pit line (epl. Fig. 15) crosses the ante- rior tip of the snout. The cheek pit line (cpl. Fig. 15) is very faint, and was not clearly visible in any of my specimens. The lateral sensory canal (lien. Fig. 15) of Hio- don is single and runs the entire length of the body, but does not extend onto the caudal fin; a lateral line scale is shown in Figure 92E. The ca- nal opens to the surface through a single pore per scale. Trautman (1957: figs. 16 and 17; repro- duced here as Fig. 1 A, B, respectively) incorrectly figured the posteriormost scales of the lateral line as lacking the sensory canal. The cephalic sensory canals open to the envi- ronment through pores that are well separated from the bone-enclosed sensory canal by a long tube in soft tissue (e.g.. Fig. 15). The lateral sen- sory canal pierces both the supracleithrum and posttemporal, becoming the posttemporal sensory canal (ptcn. Figs. 14 and 15). The posttemporal canal forks, with one branch entering the extra- scapular and running medially as the supratem- poral sensory canal (stcn. Fig. 15C-E); the left and right supratemporal canals do not connect in bone. The other branch continues anteriorly to be- come the otic sensory canal (see below). A ventral branch from the posttemporal sensory canal is the preoperculomandibular sensory canal 30 FIELDIANA: ZOOLOGY (pmcn. Fig. 15B, E, F). This canal can be divided into two components: the preopercular sensory canal (popcn) and the mandibular sensory canal (men). The preopercular sensory canal closely fol- lows the anterior edge of the preopercle. It con- tinues as the mandibular sensory canal, which en- ters the angular bone along its posterolateral mar- gin, runs obliquely and ventrally, and continues into the dentary, where it terminates near the man- dibular symphysis. The posttemporal sensory canal continues an- teriorly, becoming the otic sensory canal (otcn. Fig. 15B-E). The otic sensory canal runs almost entirely through the pterotic before entering the dermosphenotic, where it becomes the infraorbital sensory canal (iocn. Fig. 15B, E). The infraorbital sensory canal runs along the orbital margin of the infraorbital bones and terminates near the end of the nasal sensory canal; the two canals remain separate. A short segment runs anteriorly in the dermosphenotic but ends before joining the su- praorbital canal (Fig. 15E). There is no connection between the infraorbital sensory canal and the supraorbital sensory canal (socn. Fig. 15B, E). There is a short posterior por- tion of the supraorbital canal in the parietal, al- though this condition is variable in Hiodon (cf. Figs. 14-16; Li & Wilson, 1994; Cavin & Forey, 2001: fig. 8 A). From the parietal, this canal runs the length of the frontal bone before leading into the nasal sensory canal (nacn, Figs. 15B-E and 23A). Li and Wilson (1999: character 12, state 1, fig. 3) found the posterior termination of the su- praorbital sensory canal in the frontal was derived independently in three different groups of osteo- glossomorphs: once in tEohiodon + Hiodon, once in Osteoglossoidei minus (fParalycoptera + fTanolepis), and once in Notopteroidei minus fThaumaturus. Because I found that the supraor- bital canal does enter the parietal in some speci- mens of Hiodon, reexamination of this character is necessary, particularly in fEohiodon. Posterior and Ventral Portions of the Braincase and Ventral Ethmoid Region Posterior to the orbit, the neurocranium of Hio- don is well-ossified and forms a nearly complete bony box surrounding part of the brain; anteriorly the neurocranium is predominantly cartilaginous, particularly dorsally (Figs. 17 and 18). On the dorsal surface of the neurocranium there are two paired fontanelles. The anterior fontanelles (afon. Fig. 17) are the smaller of the two pairs and are covered entirely by the frontals. The posterior fontanelles (pfon. Fig. 17) are large openings that are covered by portions of the frontals, parietals, and the dermal portion of the pterotics. In front of the anterior fontanelles, the dorsal surface of the neurocranium is marked by a pair of grooves, roughly marking the path of the supraorbital canal through the frontal bones. These grooves are per- haps for the superficial ophthalmic rami of the anterodorsal lateral line nerves. In Hiodon, as in most teleosts, the chondral autopterotic (part of the posterior portion of the braincase) is fused to the dermal dermopterotic (part of the dermal skull roof) to form a single pterotic bone, and was dis- cussed earlier (see Skull Roof and Dorsal and Lat- eral Ethmoid Region). In Hiodon, the paired exoccipitals (exo. Figs. 10, 30, and 31) are the only ossifications to im- mediately surround the foramen magnum (fm. Fig. 12). The left and right exoccipitals are sep- arated dorsomedially by a thin area of cartilage associated with the supraoccipital (not shown in Fig. 12). The exoccipitals contact the supraoccip- ital and epioccipitals dorsally, the intercalars lat- erally, and the basioccipital ventrally. Anteriorly, the exoccipitals meet the prootics and together de- fine the dorsal and anterior limits of the auditory fenestrae (af. Fig. 18). A large membrane-bone wall (lexo. Figs. 18, 20, and 21) lies lateral to the spinal cord as it exits the foramen magnum, and two spino-occipital nerves pass though foramina in the exoccipitals at the base of these walls (not shown). Allis (1919) found that in his sectioned specimen of H. tergisus, only the dorsal roots of the spino-occipital nerves passed through the an- terior of these foramina; the ventral root disap- peared before exiting the skull. The posterior fac- es of the exoccipitals and epioccipitals form the paired posttemporal fossae, which serve as attach- ment sites for epaxial musculature. The paired, common foramina for the vagus and glossopha- ryngeal nerves (fIX-X, Fig. 22) are entirely with- in the exoccipitals and are found on their ventral surface, dorsal to the diverticula of the swim blad- der. Anteroventrally, the exoccipitals form the roof to the recess for the lagenar otolith in the basioccipital (clot. Figs. 26 and 30); in turn, they also form the floor of the posterior part of the braincase. The basioccipital (bo. Figs. 20 and 21) contacts the exoccipital dorsally and the prootics anteriorly and forms the ventral portion of the articulation between the braincase and the first vertebral cen- HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 31 trum (Fig. I2C, D). There is a pronounced aortal groove (ag. Fig. 22) along the ventral surface of the basioccipital that is continuous anteriorly with the posterior myodome. Allis (1919: 211) provid- ed the following description of this aortal groove: [T]he groove on the ventral surface of the basioc- cipital of my 51 -mm. specimen lodges the anterior portion of the median dorsal aorta. When, proceed- ing anteriorly, the aorta begins to widen, prepara- tory to separating into a lateral dorsal aorta on ei- ther side, it recedes from the groove and is replaced by the hind ends of the musculi recti extemi: these muscles soon occupying the entire groove, the aorta lying ventral to them and outside the groove. The lateral edges of the groove give insertion to the tunica externa of the air-bladder, the tissues of the tunica forming, in the posterior, but not the anterior portion of the groove, an arched bridge beneath the aorta and so enclosing it in a canal; this being as described by Bridge ('99) in Notopterus. The no- tochord, enclosed in the basioccipital. lies directly above the bottom of the groove, separated from it by only a thin layer of bone of perichordal origin. As observed by Allis (1919: 216), the only skeletal distinction between the posterior myo- dome and the aortal groove is that the posterior myodome is "closed ventrally by the parasphen- oid and that it lies in the prootic region." Two cartilages (cfpm. Figs. 18 and 19) are continuous anteriorly with the ventrolateral ridges (= the "lateral edges" described by Allis. 1919: 211) de- marcating the aortal groove of the basioccipital. These cartilages lie against the medial surfaces of the ascending processes of the parasphenoid (arp. Fig. 30) and meet ventrally to form the floor of the posterior myodome. The dorsal surface of the basioccipital forms the floor and walls of the paired chambers for the lagenar otoliths (clot. Figs. 26 and 30), which are separated from each other by a medial lamella of bone. In Hiodon. the median basioccipital and paired exoccipitals together form a tripartite occiput ("the boundary between the skull and vertebral colunm"; Bemis & Forey, 2001: 359; Fig. 12). No vertebral centra are incorporated into the oc- cipital region of Hiodon, either ontogenetically or phylogenetically. Bemis and Forey (2001: fig. 20.4) found that incorporation of at least three neural arches and centra into the occipital region of the skull "characterized" Chondrostei + Neop- terygii. However, as these authors note (Bemis & Forey, 2001: 373), there is much variation of the condition within teleosts, and in teleosts, "up to and including osteoglossomorphs . . . both centra and neural arches are included in the skull (al- though by no means all members of the various clades may show such incorporation)." The intercalars (ic. Figs. 8 and 9) form the pos- terolateral comers of the neurocranium and con- tribute to the fossae for the posterior heads of the hyomandibulae (hyfp. Fig. 22). This condition is found also in notopteroids (Greenwood, 1973) and most members of ticthyodectiformes (Patter- son & Rosen, 1977). The intercalar is a winglike element with a strong ventrolateral concavity that contacts the exoccipital medially, the epioccipital dorsally, and the pterotic anteriorly. The intercalar develops lateral to the vagal nerve foramen in the exoccipital but does not contribute to the forma- tion of this foramen. Patterson (1973, 1975) com- mented extensively on the comparative anatomy of this bone within actinopterygians, and partic- ularly within teleosts. Patterson (1973) concluded that the condition found in teleosts, in which the intercalar is entirely a membrane bone (i.e., the endochondral component found in tcaturids, tpholidophorids, and basal tleptolepids has been lost), is a derived condition that is a "consequence of closure of the cranial fissure" (Patterson, 1973: 254). This condition was derived independently in Amia (Grande & Bemis. 1998: 61-62). The paired epioccipital bones (epo. Figs. 9, 10, and 1 2) of Hiodon lie on the posterolateral comers of the braincase and, along with the supraoccipi- tal, enclose the dorsal portion of the posterior semicircular duct (fpsd. Fig. 29). Ventrally, this canal widens into a chamber that contains the am- pullae of the posterior semicircular ducts (cpsd. Fig. 29). The center of ossification is along the posterolateral edge of this element, which begins to develop in H. tergisus at about 22 nmi SL (jfbm 22747B), but was not observed in H. alosoides until 31 mm SL (uamz 4041C, Fig. 14C, D). In the adult, these bones contact the supraoccipital medially, the exoccipitals ventrally, and the inter- calars and pterotics laterally. The posterior arm of the parietal, which forms the parietal bridge, over- laps the epioccipital dorsally but does not actually suture into the posterior neurocranium. The su- tures between the epioccipitals and all adjacent bones are smooth or cartilage-filled. An anterior extension of the epioccipital overlaps the dorsal surface of the pterotic (Figs. 17 and 24). The slightly concave anterior face of the epioccipital forms the posterior limits of the temporal fossae (see discussion under Temporal Fossae). The con- cave posterior face of the epioccipital contributes to the dorsal portion of the posttemporal fossae (Fig. 12). The posterior apex of the epioccipital 32 FIELDIANA: ZOOLOGY B pmx Dorsal view. 2 cm Fig. 7. Hiodon alosoides. A, Photograph, and B, Line drawing of skull in dorsal view of an adult (uma F10580, 270 mm SL, female). Right temporal fossa is outlined in red. Infraorbitals were removed. Anterior faces left. HILTON: OSTEOLOGY OF ///ODOA^ LESUEUR, 1818 33 2 cm B lexo Dorsal view: extrascapulars in place. 2 cm Fig. 8. Hiodon alosoides. A. Photograph, and B. hne drawing of neurocranium and associated dermal bones of an adult (uma F10581. 315 mm SL. female) in dorsal view. 34 FIELDIANA: ZOOLOGY B spo Dorsal view; extrascapulars removed. lexo 2 cm Fig. 9. Hiodon alosoides. A, Photograph, and B, line drawing of neurocranium and associated dermal bones of an adult (uma F 10581, 315 mm SL, female) in dorsal view with extrascapulars removed. Right temporal fossa is outlined in red. Anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 35 B 2 cm Posterior view; c1 and extrascapulars in place. D Posterior view; c1 and extrascapulars removed. Fig. 12. Hiodon alosoides. A and C, Photograph, and B and D, Hne drawing of neurocranium and associated dermal bones of an aduh (uma F10581, 315 mm SL. female) in posterior view. In C and D, the extrascapulars (es) and first centrum (cl) were removed. Left posttemporal fossa is outlined in red. 38 FIELDIANA: ZOOLOGY B pmx Lateral view. Fig. 13. Hiodon alosoides. A, Photograph, and B, line drawing of skull in lateral view of an adult (uma FI0580, 270 mm SL, female). Left temporal fossa is outlined in red. Infraorbitals and extrascapulars were removed. Anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 39 B Posterior view; c1 and extrascapulars In place. D Posterior view; c1 and extrascapulars removed. Fig. 12. Hiodon alosoides. A and C, Photograph, and B and D, line drawing of neurocranium and associated dermal bones of an adult (uma F 10581, 315 mm SL, female) in posterior view. In C and D, the extrascapulars (es) and first centrum (cl) were removed. Left posttemporal fossa is outlined in red. 38 FIELDIANA: ZOOLOGY B pmx Lateral view. Fig. 13. Hiodon alosoides. A, Photograph, and B, line drawing of skull in lateral view of an adult (uma F10580, 270 mm SL, female). Left temporal fossa is outlined in red. Infraorbitals and extrascapulars were removed. Anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 39 2 mm 2 mm 2 mm Fig. 14. Hiodon alosoides. A. C. and E. Photographs: B, D. and F. Hne drawings of cleared and stained skulls and pectoral girdles from a growth series in lateral view showing the development of some skull bones. A and B, XL- 113117E (24 mm SL). C and D. la.mz 4041C (31 mm SD.^E and F xu 113117B (38 mm SL). Dashed lines indicate position of sensory canals enclosed in bone. Ventral portions of the hyoid arch and all of the branchial arches were removed in the specimen illustrated in A and B. Anterior faces left. 40 FIELDIANA: ZOOLOGY to lien pmcn Fig. 15. Hiodon, sensory canals. A, Outline of an entire fish, showing the cephalic sensory and lateral sensory canal system. B and C, Close-up view of the cephalic sensory canal system in lateral (B) and dorsal (C) views. Sensory canals and tubes are drawn based largely on H. tergisus (uma F 10599, 235 mm SL, male). This alcohol specimen was patted dry and the air-filled sensory canals and tubes (blue lines) and pit lines (blue dots) became clearly visible through the dermis. Position of pit lines after Nelson, 1972b, and specimens. Black dots indicate boundaries between regions of continuous, yet distinctly defined, sensory canals. D-F, Line drawings of the skull and pectoral girdle showing the position of the cephalic sensory canals in dorsal (D), lateral (E), and ventral (F) views. Note that only the portions of the canals enclosed in bone are illustrated in D, E, and F. Dashed lines indicate portions of canals covered by more superficial dermal bones. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 41 es epo exo pt scl 2 mm Fig. 16. Hiodon alosoides. A, Photograph, and B. line drawing of skull roof and other skull elements of a small juvenile (tu 1131 17B. 38 mm SL) in dorsal view. Dashed lines indicate position of sensory canals enclosed in bone. Note that the cartilages and many of the bones visible in the photograph have been omitted from the line drawing (e.g., oral jaw elements). Anterior faces left. Scale in A in millimeters. 42 FIELDIANA: ZOOLOGY B spo lexo Dorsal view. 2 cm Fig. 17. Hiodon alosoides. A, Photograph, and B, line drawing of neurocranium of an adult (uma F 10582, 275 mm SL, male) in dorsal view. Most of the dermal bones and the anterior dermal portion of the pterotic (= dermop- terotic) bones have been removed from the left side to show underlying cartilaginous portions of neurocranium. The neurocranium of this specimen was prepared following the method of Hilton and Bemis (1999). Briefly, after soaking in hot water to remove dermal bones and soft tissue, the neurocranium was placed in 70% ethanol and all remaining soft tissue was removed by hand under a dissecting microscope. The specimen was then transferred to a 0.5% potassium hydroxide (KOH) solution to which a few drops of alizarin red S was added. After the bones were stained, the neurocranium was returned to clean 70% ethanol. In the photograph, bones appear as dark structures, and cartilage is white. Scale bar = 2 cm. In the line drawing, cartilage is shown as black with a white stipple. Dashed line indicates a portion of cartilage that was broken during preparation. Right temporal fossa is outlined in red. Anterior faces left. HILTON: OSTEOLOGY OF ///ODOA^ LESUEUR, 1818 43 B Lateral view. 2 cm Fig. 18. Hiodon alosoides. A, Photograph, and B, Une drawing of neurocranium of an adult (uma F10582, 275 mm, SL male) in lateral view. Most of the dermal bones and the anterior membrane bone portion of the pterotic ( = dermopterotic) have been removed to show the underlying cartilaginous portions of the neurocranium. In the pho- tograph, bones appear as dark structures, and cartilage is white. Scale bar = 2 cm. In the line drawing, cartilage is shown as black with a white stipple. Left temporal fossa is outlined in red. Anterior faces left. 44 FIELDIANA: ZOOLOGY ^ -!■.■* jk >/^^*-k ^*-i J-*^J^ a:^*' c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 .•:■! :* *: h::«; c11 c12 c13 c14 c15 c16 c17 c18 c19 c20 * 1 r* C21 c22 c23 c24 c25 c26 c27 c28 c29 c30 2 cm Fig. 66. Hiodon alosoides. A, Photograph, and B, line drawing of isolated abdominal centra of an adult (uma F10586, 273 mm SL, female) in anterior view. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 95 hs5 =C57 2 cm Fig. 67. Hiodon alosoides. A. Photograph, and B, line drawing of caudal vertebral column and fin of an adult (UMA F10588. 252 mm SL, male) in lateral view. The first preural vertebral centrum (= c57 in this specimen) and parhypural are highlighted in blue. Anterior faces left. oriented toward the posterior portion of the ab- dominal region (Fig. 66). The parapophyses and pleural ribs may fuse in posterior abdominal ver- tebrae. In such vertebrae it is difficult to delimit the parapophysis and rib (i.e., the vertebrae could be interpreted as possessing elongated parapo- physes rather than parapophyses that are fused to ribs). Vertebrae that display such a condition are here termed transitional vertebrae (tv. Fig. 67) and are individually variable in number (Tables 9 and 10). Because the caudal region is defined as start- ing at the anteriormost centrum that bears a com- plete haemal arch, all transitional vertebrae are by definition abdominal vertebrae. In Hiodon, all haemal arches (ha. Figs. 67-69) are completely fused with the centra and bear elongations that are fused distally to form haemal spines (hs. Figs. 67- 69). Each vertebral segment anterior to the insertion of the dorsal fin bears a chondral supraneural (sn. Figs. 61 and 62). In some specimens (e.g.. uma F 106 13) the supraneural series extends posteriorly to end among the proximal radials of the dorsal fin (Fig. 70). The first supraneural lies anterior to the first neural arch, and the succeeding supra- neural s are positioned alternately between two neural arches. For the most part, the supraneurals are slight, rodlike ossifications that form in carti- lage in the median vertical septum. Most supra- neurals possess a slight dorsal deflection or bend in the bone. A notable exception is the first su- praneural (snl. Figs. 61 and 62), which is blade- like and S-shaped. Although there is individual shape variation within this element, it never re- sembles the more posterior supraneurals. Li and Wilson (1999: character 67) described the anterior supraneurals of iTongxinichthys, fJiuquangi- chthys. and 'rKuyangichthys as being dorsally broad and leaflike, and those of fKuntiilunia and fHuasliia as being dorsally broad and platelike. 96 FIELDIANA: ZOOLOGY B D na37 2 cm na37 has 2 cm Fig. 68. Hiodon alosoides. A and C, Photographs, and B and D, Une drawings of isolated caudal vertebra (vertebra 37) of an adult (uma F10338, 255 mm SL, female) in lateral (A and B) and anterior (C and D) views. In A and B, anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 181 97 c31 c34 c35 c36 c37 c38 c39 c40 c42 c43 c44 c45 C46 C47 c48 c49 c50 { c51 c52 c53 c54 c55 c56 c57 c58 = pul 2 cm Fig. 69. Hiodon alosoides. A. Photograph, and B, line drawing of isolated caudal vertebrae of an adult (uma F 10586. 273 mm SL. female) in anterior view. Some centra (e.g.. c49, c50. c51. c52) appear slightly laterally displaced because of the parallax of the camera lens; most centra were mounted at an angle to compensate for this effect. The first preural vertebral centrum (= c56 in this specimen) and parhypural are highlighted in blue. 98 FIELDIANA: ZOOLOGY Fig. 70. Hiodon tergisiis, photograph of cleared and stained juvenile (tu 1131 17B, 38 mm SL) in lateral view, showing the posteriormost supraneural (arrow) that lies between the anterior pterygiophores of the dorsal fin. Anterior faces left. However, Li and Wilson (1999: 376) described Hiodon (among other taxa) as having anterior su- praneurals that are "not different from the pos- terior ones in shape"; other taxa that have modi- fied anterior supraneurals (e.g., Elops; uma F 10255; Forey, 1973) were similarly scored. While the anterior supraneurals in these taxa may not be similar to one another in shape, they are also not similar in shape to the more posterior supraneurals, so the definition or scoring of this character by Li and Wilson (1999) is in need of revision. The slightly flattened proximal ends of the ribs (r. Fig. 61) loosely articulate with the centra in a deep socket just dorsal to the parapophyses (Fig. 65). All ribs are approximately the same length except for the anteriormost one, which is approx- imately half the length of the others (Fig. 61). The first rib articulates with the third vertebral cen- trum, a condition that is "remarkably constant in lower teleosts" (Patterson & Johnson, 1995: 19). The last pair of pleural ribs is variably fused to the parapophyses (e.g.. Figs. 61-63), and this fu- sion was in some cases found to be bilaterally asymmetrical. The ribs are preformed in cartilage and appear to ossify proximally to distally along their length, although a cartilaginous distal tip persists into the adult. Caudal Fin and Supports The caudal skeleton of Hiodon has previously been illustrated by Gosline (1960: fig. 4), Patter- son (1968: fig. 1 1), Monod (1968: fig. 108^/i-. and ter.). Greenwood (1970: fig. 8), Taverne (1977: figs. 26 and 27), Li and Wilson (1994: figs. 3 and 4), and Li, Wilson, and Grande (1997: fig. 5-2). The development and morphology of the caudal skeleton of Hiodon were described in detail by Schultze and Arratia (1988: figs. 1-13; see also Schultze & Arratia, 1989). The caudal fin and supporting skeleton are illustrated in Figures 71 to 76; meristic data and measurements for this re- gion are presented in Tables 13 to 16. Portions of the caudal fin and skeleton (e.g., hypurals) have begun to ossify in the smallest individuals ex- amined in the present study (e.g.. Fig. 74A, B). Caudal fin rays are supported by all hypural ele- ments, as well as the epural and the neural and haemal arches of the first five preural caudal ver- tebrae (Fig. 71). Eighteen principal caudal fin rays was considered by Patterson and Rosen (1977) to be a synapomorphy of Osteoglossomorpha (this corresponds to 16 branched plus two unbranched principal caudal fin rays, Fig. 71). In one of his specimens of H. tergisus, Monod (1968) found only 15 branched caudal fin rays (eight in the dor- sal lobe and seven in the ventral lobe). The ventral HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 99 bfr16 2 cm Fig. 71. Hiodon alosoides. A, Photograph, and B, hne drawing of posterior caudal region of vertebral column and caudal fin of an adult (uma F10588, 252 mm SL, male) in lateral view. The first preural vertebral centrum ( = c57 in this specimen) and parhypural are highlighted in blue. Anterior faces left. 100 FIELDIANA: ZOOLOGY 2 cm Fig. 72. Hiodon alosoides. A, Photograph, and B, line drawing of posterior caudal region of an adult (uma F1 0588, 252 mm SL, male) in lateral view. The first preural vertebral centrum (= c57 in this specimen) and parhypural are highlighted in blue. Anterior faces left. lobe of the caudal fin is supported by elements anterior to and including hypural 2. The ventral lobe of the caudal fin is generally longer than the dorsal lobe (Tables 13 and 14). In Hiodon, two centra support hypural elements and are defined as ural centra (ul, u2; Figs. 71 and 72). Schultze and Arratia (1988) suggested that the more anterior of these represents two on- togenetically fused centra and the more posterior represents three ontogenetically fused centra (in HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 101 2 cm Fig. 73. Hiodon alosoides. A, Photograph, and B, line drawing of disarticulated posterior caudal region of an adult (UMA F 10588, 252 mm SL, male) in lateral view. The first preural vertebral centrum {- c57 in this specimen), its associated neural spine, and parhypural are highlighted in blue. Anterior faces left. 102 FIELDIANA: ZOOLOGY 2 mm 2 mm ^ 2 mm 2 mm Fig. 74. Hiodon tergisus. A and C, Photographs, and B and D, Hne drawings of cleared and stained caudal skeletons of juveniles in lateral view. A and B: jfbm 22747A, 23 mm SL. C and D: tu 108166A, 52 mm SL. Fin rays omitted from line drawings. Centrum of pul has not yet formed in specimen shown in A and B, but the neural spine and haemal arch and spine (= parhypural) that it will bear are highlighted in blue; all elements of pul are highlighted in D. Haemal spine of pu4 and hypural 2 of specimen in C and D were damaged during preparation. Distal caudal radials (dcr) are likely present in the specimen in A and B, but did not stain with alcian blue, and therefore were omitted from the drawing. There is an anomalous ossification immediately posterior to the base of the haemal .spine of pu2 in the specimen in A and B. Anterior faces left. their terminology, ul+2, and u3+4+5, respec- tively; Schultze & Arratia, 1988: figs. 4 and 7). In contrast, I found no ontogenetic evidence of this or any other pattern of fusion (e.g., Fig. 74A, B). However, the ul is often associated with two neural arches (see below), which may be hypoth- esized to each be "ancestrally" associated with independent ural centra (see Remarks on Phylo- genetic Fusion). Therefore, I refer to the ural cen- tra as "ul" and "u2" without implying specific homologies to the ural centra of other fishes. In Hiodon, the number of neural arches asso- ciated with the ural region is quite variable, with between one and three pairs of neural arches as- HILTON: OSTEOLOGY OF ///ODOA^ LESUEUR, 1811 103 Fig. 75. Hiodon alosoides, photographs of posterior caudal skeleton of three adults (A and B: uma F10593, 254 mm SL, male; C and D: uma F 10592. 292 mm SL. female; E and F: uma F 10594. 270 mm SL, female) in lateral view showing individual variation of the caudal skeleton. Left-hand column shows left side of specimen; anterior faces left. Right-hand column shows right side of specimen; anterior faces right. The "typical" condition for nspul is shown in A and B. Scale bars = 2 cm. 104 FIELDIANA: ZOOLOGY B ep un1-3 nspu1 ep un1-3 Fig. 76. Hiodon alosoides, line drawings of specimens in Figure 75. In each specimen, the first preural vertebral centrum, its associated neural spine, and parhypural are highlighted in blue. The "typical" condition for nspul is shown in A and B. Scale bars = 2 cm. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 105 sociated with ul (Tables 15 and 16). These arches are much reduced, and often do not form com- plete arches (e.g., uma F 10606 and uma F 10634). The anteriormost of the ural neural arches may lie in the intercentral space between pul and ul (e.g., TU 108166E, UMA F 106 13). A short, sticklike epural (ep. Figs. 71-76) os- sifies around a cartilaginous rod in the dorsal mid- line of the ural region. In small specimens, the proximal end of the epural appears pinched (e.g., Fig. 74A, B). I observed variation in the position of the epural. In some specimens of H. alosoides, the epural is in series with the second neural arch of ul (e.g., UMA F10600, uma F10601, tu 1131 17E, UAMZ 4041 B), whereas in others, it lines up with the anterior neural arch on ul (e.g., tu 1081 18A). This does not seem to be related to ontogeny, as the specimen in which the epural is associated with the first neural arch is nested (sizewise) within those that exhibit the other con- dition (Table 16). In Hiodon, the number and disposition of uro- neurals vary between individuals, as well as bi- laterally within an individual (un. Figs. 75 and 76, Tables 15 and 16); this sort of variation is well documented in the literature (e.g., Gosline, 1960; Patterson, 1968; Monod, 1968; Taverne, 1977; Schultze & Arratia, 1988: fig. 11). For example, Monod (1968: fig. \QWis. and ter.) found three uroneurals in his specimens of H. tergisus, al- though there was considerable shape variation in the morphology of the uroneurals between the two specimens. I found that the number of uroneurals ranged between two and four discrete bones (al- though in many specimens there is evidence of fusion between adjacent uroneurals), and that the number of uroneurals was not correlated with the size of the specimen. Schultze and Arratia (1988) concluded that the base number of uroneurals in Hiodon is four (the most of any extant teleost; Patterson & Rosen, 1 977) and that these elements were derived from the neural arches of ural centra 4 through 7. The hypural bones (hy, Figs. 71-76) are the serial homologues in the ural region of the more anterior haemal spines. These flattened bones de- crease in size from anterior to posterior. All hy- purals have started to ossify in the smallest spec- imens available to me, although their posterior portions may still be cartilaginous (e.g., TU 1131 17E). There is a small process (csp. Fig. 73) on the anteroventral extent of hypurals, as well as some of the posterior haemal arches. On hypural 2, this process contributes to the margin of the hypural foramen (Monod, 1968). Schultze and Ar- ratia (1988: 279) reported six to eight hypurals in Hiodon, and noted that eight hypurals ("without exception") are present in small (22-38 mm SL) specimens; the eighth (posteriormost) being re- sorbed during ontogeny. I found only seven hy- purals in all of my specimens of both species, even in small specimens (e.g., 21 mm SL; Tables 15 and 16) in which the cartilage is well-stained. There is a distinct diastema between the second and third hypurals (Monod, 1968) that marks the boundary between the dorsal and ventral lobes of the caudal fin (i.e., the dorsal lobe fin rays are associated with elements dorsal to the diastema and the ventral lobe fin rays are associated with elements ventral to the diastema); this diastema has been considered a synapomorphy of teleosts (de Pinna, 1996: character 3). There are distal caudal radials (dcr. Fig. 74C, D) in the caudal skeleton of Hiodon that are com- pletely surrounded by the fin rays (see Schultze & Arratia, 1989, for a discussion of these and oth- er elements of the teleostean caudal skeleton). These irregularly shaped elements, which Fujita (1989) termed "inter-haemal spine cartilages" and "post-hypural cartilages," lie distal to the posteriormost haemal spines and the first hypural, and were never found to be ossified. The neural spine of preural centrum 1 (nspu 1 , Fig. 73) is often rudimentary in Hiodon (Figs. 73, 75, and 76; Tables 15 and 16). Patterson and Ro- sen (1977) used the presence of a full neural spine on pul as a synapomorphy of Osteoglossomor- pha. Schultze and Arratia (1988), however, found this condition in only 6% of their specimens of Hiodon (my data suggest that it is even less com- mon, e.g.. Tables 15 and 16). In one of my spec- imens of H. tergisus (tu 108166E), the neural spine of pu2 is also rudimentary, and in another (tu 108166D), there are two neural arches on pul. Li and Wilson (1994) used the reduced or absent condition of the neural arch on pu 1 as a diagnostic feature of the genus Hiodon. I never observed the absent condition in my sample of H. tergisus and H. alosoides. Given the clear variation of this character (Figs. 75 and 76), I caution against its use as a diagnostic character for the genus. Included in the diagnosis of Hiodon given by Li and Wilson (1994: 155) is the character "two neural spines usually developed on the second preural" (described as "often" present by Li & Wilson, 1994: 163). This character follows from the observation that some specimens of both H. tergisus and H. alosoides have two neural arches 106 FIELDIANA: ZOOLOGY on pu2 (e.g., Monod, 1968: fig. \OSbis.; Arratia & Schultze, 1988: fig. 1 1; Li & Wilson, 1994: fig. 4); one of the specimens of iH. consteniorum also shows this condition. This condition is not present in any of my specimens of H. tergisus and H. alosoides (e.g.. Figs. 75 and 76), and I consider it an uncommon individual variation (although further research is needed to determine its fre- quency). Therefore, I also caution against using the presence of this character, or even its "poten- tial" presence (Li & Wilson, 1999: character 60), as a diagnostic character for Hiodon. Dorsal and Anal Fins and Pterygiophores The skeletal supports of the fin rays of both the dorsal and anal fins of Hiodon consist of a series of elongate proximal radials (pr. Fig. 77) and a series of small, irregularly shaped distal radials (dr. Fig. 78). All radial elements are preformed in cartilage. The distal ends of the proximal radials are enlarged and distinctly bent, and look like fused proximal and middle radials (e.g.. Fig. 78). A series of autogenous middle radials, however, was not found in even small specimens, although in some small specimens of//, alosoides (e.g., tu 113117E, 24 mm SL; tu 113117C, 28 mm SL) I did observe a constriction in the cartilage of the proximal radials, suggesting a series of cartilagi- nous medial radials fused to the cartilage of the proximal radials (the proximal radials of my small specimens of H. tergisus did not stain very well). Additionally, in slightly larger specimens, the shaft of the proximal radial is ossified and the distal tip is a cartilaginous plug, which may rep- resent elements of the middle radial series. The dorsal and anal fin of other osteoglossomorphs have various patterns of presence and absence of pterygiophore elements. For instance, the anal fins of notopterids are supported only by a series of proximal ossifications (e.g., Taverne, 1978: figs. 75, 108, 110, and 129; pers. obs.), whereas the dorsal fin is supported by a series of ossified prox- imal radials and cartilaginous distal radials (e.g., Chitala sp., uma F10341, pers. obs.). In the mor- myrid Petrocephalus simus (mcz 50113, pers. obs.), the posterior portion of both the dorsal and anal fin are supported by three separate elements (proximal, middle, and distal radials), whereas the anterior portion of the fins have only two elements (proximal and distal radials); see Taverne (1977, 1978) for the condition of other osteoglosso- morphs. In salmonids, the proximal and middle radials of the median fins ossify within the same cartilaginous element, and in the dorsal fin the "first two to three middle pterygiophores [= mid- dle radials] do not ossify and cannot be distin- guished as separate elements" (Sanford, 2000: 166). A study of specimens of earlier stages than available for the present study may help to deter- mine if a series of middle radials (fused to the proximal radials) is present in the dorsal and anal fins of Hiodon. The dorsal fin and pterygiophores of //. alo- soides are illustrated in Figures 77 and 78A, B. The predorsal fin length in //. tergisus is relatively shorter than in //. alosoides (Fig. 79A; cf. Tables 2 and 3; Trautman, 1957; Scott & Grossman, 1977; Page & Burr, 1986). Structurally, the dorsal fins of H. tergisus and //. alosoides are virtually identical, although they differ in the number of fin rays (13-16 versus 9-10, respectively) and prox- imal radials (13-15 versus 11-13, respectively; Tables 17 and 18). A prominent ridge projects from the lateral surface of each of the proximal radials and serves as the origin for fin elevator and depressor muscles. There is roughly a one-to- one correlation between the number of proximal radials and number of segmented fin rays, al- though this pattern breaks down anteriorly be- cause the supernumerary fin rays (Patterson, 1992; these include both the unsegmented rudi- mentary fin rays and the anterior unbranched seg- mented fin rays recorded here) become crowded together (Fig. 77). The series of distal radials (dr. Fig. 78A, B) are largely covered by the proximal ends of the fin rays. Meristic data concerning the anal fin are re- corded in Tables 17 and 18. The relative pre-anal fin length is virtually indistinguishable between the two species (Fig. 79B; Tables 2 and 3). As for the dorsal fin, the number of anal fin rays and pterygiophores differs between H. tergisus and //. alosoides (cf. Tables 17 and 18). The shape of the anal fin is sexually dimorphic in mature speci- mens of Hiodon (e.g., see Scott & Grossman, 1973; Roberts, 1989). The overall shape of the fin in the female is triangular, whereas in the male the anterior portion of the fin is rounded, and the anterior rays are thinner in males than in females (Figs. 80 and 81). Sexual dimorphism in the ex- ternal shape of the anal fin has also been reported in -fEohiodon (Wilson, 1978; Grande, 1979; Li & Wilson, 1994; Li, Wilson, & Grande, 1997). The proximal radials (pr. Figs. 78G, D, 80, and 81) of the anal fin also are sexually dimorphic in form in Hiodon. In both sexes there is a lateral ridge HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 107 on the anterior elements. In the males only, how- ever, these ridges are enlarged distally to form a wing that nearly overlaps the next posterior prox- imal radial (of. Figs. 80 and 81). Sexual dimorphism of anal fin morphology has been reported in many actinopterygians (e.g., po- lypterids, Britz & Bartsch, 1998). This dimor- phism is often associated with spawning, during which the "male's anal and caudal fins wrap around the female's genital opening, forming a spoon-like chamber into which released eggs fall and are fertilised by the male" (Britz & Bartsch, 1998: 328). Within nonhiodontiform osteoglos- somorphs. Brown, Benveniste, and Moller (1996) discovered internal and external sexual dimor- phism in the structure of the anal fin of two spe- cies of the mormyrid genus Brienomyrus. In male specimens, the hypertrophied bases of the fin rays cause an indentation in the dorsal margin of the anal fin. Similar external sexual dimorphism is known in other species of mormyrids. For exam- ple, Okedi (1969: 40) noted differences in the shape of the fin between the two sexes and the presence of a notched dorsal margin of the anal fin in males ("ventral flank of the body curved inwards") for members of three genera {Gnatho- nemus, Marcusenius, and Petrocephalus) from Uganda, and suggested that this is a permanent dimorphism in mature males. lies (1960), how- ever, found that in Mormyrus kannume this di- morphism is only seasonal, and that the shape of the anal fin in males returned to the "female" shape when the testes were resorbed after spawn- ing. The observed sexual dimorphism of the anal fin (internal and external) is present in specimens of Hiodon collected throughout the year. Pectoral Girdle, Fin, and Supports The pectoral girdle and fin of Hiodon are illus- trated in Figures 82 to 88 and meristic data as- sociated with the pectoral fin are presented in Ta- bles 19 and 20. Each side of the pectoral girdle is comprised of four dermal and three chondral os- sifications. The two dorsalmost dermal bones, the posttemporal (pt) and supracleithrum (scl. Figs. 82-86) form in conjunction with the lateral sen- sory canal (e.g.. Fig. 14). The ventral arm of the posttemporal is forked so that the posttemporal is triradiate (i.e., there are three arms present: a dor- sal arm, a ventromedial arm, and a ventrolateral arm). The dorsal arm (pt(d). Figs. 82-86) is more than twice as long as the ventrolateral arm (pt(l). Figs. 82, 83, 85, and 86), a condition regarded as diagnostic of Hiodontiformes (Li & Wilson, 1996a). The dorsal arm of the posttemporal is firmly connected to the epioccipital by a stout lig- ament, which attaches to the posterior peak of the epioccipital (Fig. 24). The ventromedial arm (pt(m). Figs. 84-86) is associated with a ligament that attaches to the lateral surface of the intercalar (not shown in Fig. 24 because it was not pre- served in this specimen). The ventrolateral arm of the posttemporal carries the lateral sensory canal, posterior to where it enters the pterotic and the cephalic sensory canal system. Ventral to the post- temporal is the supracleithrum, which is a flat el- ement with a slight anterior curve. Like the post- temporal, it carries a sensory canal (Figs. 82 and 83). Dorsally the supracleithrum overlaps the posttemporal, and ventrally it overlaps the cleith- rum and postcleithrum. There is a single postcleithrum (pel. Figs. 83- 85) in Hiodon. This bone is a small, diamond- shaped element that is completely covered in lat- eral view by the supracleithrum and cleithrum. It is positioned posterior to the large medial ridge on the vertical arm of the cleithrum. The large dermal cleithrum (cl, Figs. 82-87) forms much of the ventrolateral pectoral girdle in Hiodon and has distinct horizontal and vertical arms. The cleithrum is a thin bone, except for the thickened ridge that forms along the length of its medial edge. Ventromedially, the cleithrum con- tacts the coracoid, with which it forms a large, oblong fenestra (cl-cofn. Figs. 84 and 87), the me- dial edge of which serves as the origin of a di- vision of the pectoral fin adductor musclature. This muscle passes posteriorly through a canal formed by coracoid, mesocoracoid, and cleithrum (not visible in the figures), to insert on the dorsal surface of the pectoral fin rays. Another portion of this muscle originates dorsally on the medial surface of the mesocoracoid and the chondral component of the coracoid. There is a small fo- ramen of unknown function on the lateral surface of the cleithrum where the horizontal and vertical arms meet (elf, visible only in Fig. 88A, B). Three chondral elements form much of the ven- tral portion of the pectoral girdle. The coracoid (co. Figs. 82-87) begins ossification as a chondral element posteriorly, where it contacts the other chondral elements of the pectoral girdle and sup- ports the medial two radial elements. Most of the coracoid is an anterior membranous ossification that soon follows in development (Fig. 14 A, B). The left and right coracoids meet at the midline 108 FIELDIANA: ZOOLOGY Fig. 77. Hiodon alosoldes. A, Photograph, and B, line drawing of dorsal fin and pterygiophores of an adult (uma F 10592, 292 mm SL, female) in lateral view. Anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 109 B 1 cm clr4 1 cm 1 cm '■'■t*^*. Fig. 78. Hiodon alosoides. A and C. Photographs, and B and D, Hne drawings of cleared and stained dorsal (A and B) and anal (C and D) fins and supports of a juvenile (uma 10615, 102 mm SL) in lateral view. Fin rays were omitted from the drawing. Anterior faces left. of the body and form a large keel, which serves as the origin for much of the ventral pectoral ab- ductor musculature. Of living osteoglossomorphs, Hiodon is unique in that it lacks an enlarged fe- nestra within the coracoid (Cavin & Forey, 2001: fig. 12), although there is a small foramen (cof. Figs. 84, 85, and 88A, B) for a blood vessel in a position similar to the position of the fenestra of other osteoglossomorphs. Two small chondral bones, the scapula and me- socoracoid, form dorsal to the coracoid, medial to the cleithrum. The scapula (sc. Figs. 83-85 and 87) supports the lateral two pectoral fin radials (Fig. 88A, B). A dorsal winglike projection meets the ventromedial face of the cleithrum. A thin col- umn of bone from the lateral corner of the scapula extends dorsally to meet the mesocoracoid. The scapular foramen (scf. Figs. 83 and 85-87) is completely enclosed by the scapula. The hooked mesocoracoid bone (mco. Figs. 83-85) forms a bridge with the coracoid and the cleithrum that encloses the canal through which the pectoral fin adductor musculature passes. Some of the pecto- ral fin adductor musculature also originates along the posterior surface of the mesocoracoid. The pectoral fin rays of Hiodon are supported by four ossified proximal radials (ra. Figs. 83-88) and generally five distal radials (dr. Fig. 88; al- though more were found in one specimen; ?, Fig. 88C, D), some of which were found to be ossified in an adult specimen of H. tergisus (Fig. 88A, B). Among osteoglossomorphs, ossified distal radials of the pectoral fin have also been recorded in no- topterids (e.g., Taverne, 1978: figs. 72 and 107) and osteoglossids (e.g.. Taverne, 1977: figs. 57 and 86). I also observed irregularly shaped ossi- fied distal radials in Albula vulpes (e.g., amnh 88678SD, est. 300 mm SL; amnh 55998SD, est. 470 mm SL), and up to nine ossified elements in large specimens of Megalops atlanticus (e.g., uma F11023, 1741 mm SL; amnh 90905SD. est. 1400 mm SL; although they were unossified in a small- er specimen, uma F 1 0251, est. 500 mm SL). Os- sified distal radials are also found in clupeo- 110 FIELDIANA: ZOOLOGY 0.50 - t: O 0.40 o • 1^ , • Hiodon tergisus Hiodon alosoides Specimen B ^ Hiodon tergisus Hiodon alosoides 30 40 Specimen Fig. 79. Ratio of pre-dorsal fin length (A) and pre-anal fin length (B) to total length for a sample of H. tergisus and H. alosoides. The difference between the pre-dorsal fin length of the two species is greater than the difference between the pre-anal fin length. morphs (Grande, 1985; Arratia, 1997). The prox- imal pectoral radials of Hiodon are ossified in both species by 24 mm SL (Tables 19 and 20). The lateralmost proximal radial (ral) is a small, irregularly shaped block of bone, and the remain- ing proximal radials (ra2, ra3, ra4) are progres- sively longer. In H. tergisus, ra2-ra4 bear elon- gated uncinate processes that articulate with the ventral surface of the adjacent radial (Fig. 88D); in H. alosoides, only the middle two radials (ra2 and ra3) bear a well-developed uncinate process (Figs. 83 and 85). These processes are well-de- veloped in H. alosoides by 39 mm SL. The me- dialmost proximal radial (ra4) is the longest of the series and in H. alosoides is essentially a bar of bone, although there is some variation in its over- all shape (a slight medial enlargement may rep- resent an uncinate process, e.g., in the specimen illustrated in Figs. 83 and 85, but this was never as well-developed as that of H. tergisus, e.g., Fig. 88D). In Hiodon there is a thin, scalelike bony ele- ment (pap. Fig. 88E) positioned on the lateral sur- face of the pectoral girdle just dorsal to the lead- ing fin ray. Arratia (1997), who termed this struc- ture a pectoral axillary process, distinguished be- tween true and false processes. True pectoral axillary processes are defined as those that consist of an "elongated structure formed by one or more bones, scales, or a combination of both, and is firmly attached to a skin fold just above the artic- ular condyle of the upper most fin ray," and are found in fVarasichthys, Elops, Chirocentrus, Eth- midium, Lycengraulis, Dorosoma and Engraulis (Arratia, 1997: 133). False axillary processes, on the other hand, are "formed by a row of slightly elongated scales, each of which is independently attached or inserted in the skin" and were report- ed in Sardinops and Clupea (Arratia, 1997: 134). By these definitions, the elements in Hiodon are true axillary processes. Hiodon tergisus has 12-14 pectoral fin rays, whereas there are 11-12 in H. alosoides (Tables 19 and 20); some left-right asymmetry was noted in H. alosoides (Table 20). The leading fin ray of the pectoral fin is unbranched, articulates with the ventrolateral corner of the scapula, and has an en- larged base. The formation of this enlarged base is a fusion between the dermal fin ray and the chondral propterygium (Fig. 88F-H), and even in HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 111 Fig. 80. Hiodou alosoides. A, Photograph, and B, line draw ing of anal fin and plerygiophores of an adult (laia F10588. 252 mm SL. male) in lateral view. Anterior faces left. 112 FIELDIANA: ZOOLOGY rfr 1-2 2 cm Fig. 81. Hiodon alosoides. A, Photograph, and B, Hne drawing of anal fin and pterygiophores of an adult (uma F1078, 279 mm SL, female) in lateral view. Anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 113 B Fig. 82. Hiodon alosoides. A. Photograph, and B. line drawing of left pectoral girdle and fin of an adult (\rs\A F10588. 252 mm SL. male) in lateral view. Dashed lines indicate position of sensory canal enclosed in bone. Anterior faces left. 114 HELDIANA: ZOOLOGY Fig. 83. Hiodon alosoides. A, Photograph, and B, line drawing of disarticulated left pectoral girdle and fin of an adult (UMA F 10589, 275 mm SL, female) in lateral view; radials (ra) in dorsal view. Dashed lines indicate position of the sensory canal enclosed in bone. Anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 115 B Fig. 84. Hiodon alosoides. A, Photograph, and B, line drawing of left pectoral girdle and fin of an adult (uma F 10588, 252 mm SL, male) in medial view. Anterior faces right. 116 FIELDIANA: ZOOLOGY B 2 cm Mostly in medial view. Fig. 85. Hiodon alosoides. A, Photograph, and B, hne drawing of disarticulated left pectoral girdle and fin of an adult (UMA F10589, 275 mm SL. female) in medial view; radials (ra) in ventral view. Anterior faces right. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 117 Dorsal view. Fig. 86. Hiodon alosoides. A, Photograph, and B, Hne drawing of left pectoral girdle and fin of an adult (uma F 10588, 252 mm SL, male) in dorsal view. Anterior faces left. the smallest individuals examined the elements have started to fuse together; further study of the development of this association is needed. The fu- sion between the leading fin ray and a chondral element was considered a synapomorphy of tele- osts by Patterson (1977b; see also Arratia. 1999) and is widespread in teleosts. For example, in the gobiid genus Schindleha, Johnson and Brothers (1993) found that it is the medial half of the lead- ing fin ray that fuses with the chondral element; in Hiodon the propterygium fuses to the lateral half of the leading fin ray. There is an obvious foramen in the proximalmost extent of the lateral half of the first dorsal fin ray (Fig. 88H), which corresponds to the opening lessen (1972: pi. 2, figs. 1 and 2) labeled as "vorder Offnung des Kanals durchs Propterygium" in Elops saurus. Pelvic Girdle, Fin, and Supports The pelvic girdle and fin of Hiodon are illus- trated in Figures 89 to 91; meristic data associated with the pelvic fin are presented in Tables 19 and 20. The pelvic girdle consists entirely of endo- chondral elements. A pair of elongated pelvic bones (pb. Figs. 89-91), the only ossifications of the basipterygium (Sewertzoff, 1934), form most of the girdle and are tightly sutured to each other posteriorly along the midline; their anterior tips never meet. There is a large protuberance on the ventral surface of each pelvic bone (vppb. Fig. 90C, D). Taverne (1977: fig. 19) figured a single radial element in a 58 mm SL individual of H. alosoides. I observed up to three cartilaginous ra- dial elements supporting the fin rays in small ju- 118 FIELDIANA: ZOOLOGY Ventral view. Fig. 87. Hiodon alosoides. A, Photograph, and B, line drawing of left pectoral girdle and fin of an adult (uma F 10588, 252 mm SL, male) in ventral view. Anterior faces left. venile specimens (e.g., Fig. 91). The lateralmost of these was always the first to ossify, although in large individuals there may be an additional, more medial small ossification as well. A single median postpelvic bone (ppb. Figs. 89-91) articulates with the pelvic bones in a slight concavity formed by the rounded posterior edges of these elements. The thin postpelvic bone is ori- ented in the dorsoventral plane and is bladelike. This element is unique to the genus Hiodon among all teleosts known to the author. The con- ditions of t//- consteniorum and members of fEohiodon are unknown, owing to typically poor preservation of the pelvic girdle and fin. Curving dorsally along the anterior portion of the pelvic fin is a short, thin bone (ps, Fig. 89E, F) termed a pelvic splint by Gosline (1961). Gos- line (1961: 18-19) noted that "there is probably no great systematic significance to be attached to the loss of this splint" and that "it represents, when present, the holdover of a primitive teleos- tean" condition. This element is present in Amia HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 119 2 mm Fig. 88. Hiodon tergisits. A. Photograph, and B. Hne drawing of left pectoral girdle of a cleared and stained adult (JFBM 27508. 270 mm SL. female) in dorsomedial view; pectoral fin rays have been dissected away. C and D. line drawings of pectoral radials of a cleared and stained adult (uma F 10640. 184 mm SL. male) showing unknown cartilages (?) in dorsal (C) and ventral (D) view. E. Photograph of left pectoral girdle of a cleared and stained adult (UMA F10610. 183 mm SL. male) in lateral view showing pectoral axillary process (pap). F. Photograph of the proximal portion of the left pectoral fin rays of an adult (uma F10589, 275 mm SL. female) in medial view: prop- terygium fused to first fin ray (arrow). Specimen was dusted lightly with ammonium chloride. G and H. Photographs of first pectoral fin ray in an adult (uma F1 1259. 270 mm SL. female) in medial (G) and anterior (H) views showing fused propterygium (arrow). Also note opening of pectoral canal in H (unlabeled). In line drawings, cartilage shown in black. In A-D and F-H. anterior faces right; in E, anterior faces left. 120 FIELDIANA: ZOOLOGY Fig. 89. Hiodon alosoides. A and C, Photographs, and B and D, line drawings of pelvic girdle and fin of an adult (UMA F10589, 275 mm SL, female) in dorsal (A and B) and ventral (C and D) view. E, Photograph, and F, line drawing of pelvic fin rays of an adult (uma F1 1259, 270 mm SL, female) dissected away from girdle in lateral view, showing pelvic splint (ps). Anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 121 B Lateral view. 2 cm vppb Ventral view. 2 cm Fig. 90. Hiodon alosoides. A and C, Photographs, and B and D, line drawings of pelvic girdle of an adult (uma F10589, 275 mm SL, female) in lateral (A and B) and ventral (C and D) views. Anterior faces left. (Gosline, 1961; Grande & Bemis, 1998: fig. 91) and possibly in Lepisosteus (Gosline, 1961; pers. obs.), and therefore is possibly plesiomorphic at the level of Neopterygii (the presence of this element in Lep- isosteus remains debatable because of the gradation between irregular body scales immediately sur- rounding the pelvic fin and the fulcra that line the leading edge of the pelvic fin; pers. obs.). The pelvic fin of Hiodon normally has seven fin rays. The presence of a seven-rayed pelvic fin was found to be a synapomorphy of Hiodontidae by Li and Wilson (1994). In my sample, some individuals have only six pelvic fin rays, although this condition appears to be aberrant, typically oc- curring only on a single side of the specimen (al- though see Table 19). An elongate axillary scale is present on the lateral edge of the pelvic fin (as, Fig. 94C; see below). 122 FIELDIANA: ZOOLOGY 5 mm Fig. 91. Hiodon alosoides. A and C, Photographs, and B and D, line drawings of pelvic girdle of a cleared and stained juvenile (tu 1081 18E, 57 mm SL) in ventral (A and B) and dorsal (C and D) views. Scale bars in A and B in millimeters. Anterior faces left. Scales The scales of Hiodon, and of teleosts generally (although not universally), are thin and flexible and of cycloid elasmoid type (Lagler, 1947; Schultze, 1996; Grande & Bemis, 1998). There is much regional variation in the shape of the scales (Fig. 92). The scales of Hiodon possess slight ridges (ri. Fig. 93) that completely circumscribe the focus (= circuli). Arratia (1997) observed that of all osteoglossomorphs, only '\Lycoptera davidi and the species of Hiodon lack deep furrows over the entire scale. The scales have radial furrows (rad, Fig. 93; = radii) which form grooves from the focus through both the anterior and posterior fields (afd, pfd. Fig. 93; see also Arratia, 1997, fig. 97B), although those of the anterior field are more numerous and closely arranged than those of the posterior field. An unossified (unminerali- zed) extension to the posterior field of each scale (uos. Fig. 93) is continuous with the bony portion of the scale and overlaps the next posterior scale. The histology of actinopterygian scales has re- cently been reviewed by Schultze (1996; see also references therein). In my smallest specimen with scales (//. alo- soides; AUM 5169; 25 mm SL), the lateral line scale row is almost completely developed, and consists of 52 scales. The caudal peduncle of this specimen is naked. The scale row immediately ventral to the lateral line has also started to form but is not as complete as the lateral line. The com- plete anterior portion of these two scale rows sug- gests that development of the scales occurs in an anterior-to-posterior progression (a few isolated scales in the first row dorsal to the lateral line row are present at about the level of the dorsal fin insertion). The anterior- to-posterior direction of scale development is also found in Amia (Grande & Bemis, 1998); other taxa, however, show a pos- terior-to-anterior pattern of scale development (e.g., Lepisosteus, W. E. Bemis, pers. comm.). In slightly larger specimens of Hiodon, a few more rows have developed on the anterior portion of the body, although none of these is complete, in- cluding the lateral line row. The single median dorsal scale row is the last scale row to form, and by approximately 40 mm SL, squamation is com- plete. The two extant species of Hiodon are compa- rable in their scale meristics, although H. tergisus tends to have fewer scales along its lateral line (cf. Tables 21 and 22; see also Page & Burr, 1991). Hiodon tergisus also differs from H. alo- soides in the arrangement of the scales just dorsal to the anal fin. In H. alosoides, the rows of scales HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 123 Nape scale Predorsal scale Caudal fin base scale Axillary scale Lateral line scale Abdominal scales Fig. 92. Hiodon alosoides, photographs of scales of a juvenile (uma F 10598, 100 mm SL) in lateral view. A, Nape scale; B, predorsal scale: C. caudal fin base scale: D, axillary, or anterior abdominal, scale: E, mid-body lateral line scale: and F. posterior abdominal scales. Scale bars in millimeters. Anterior faces left. (Drawing of H. alosoides modified from Trautman. 1957.) 124 FIELDIANA: ZOOLOGY Fig. 93. Hiodon alosoides, photograph showing detail of a nape scale of a juvenile (uma F10598, 100 mm SL) in lateral view. Same scale as in Figure 92A. Scale bar in millimeters. Anterior faces left. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 125 Fig. 94. Scale rows above the anal fin in A, Hiodon tergisus (uma F10599, 235 mm SL, male) and B, H. alosoides (UMA F 10380, 285 mm SL, male) showing the irregular scale rows present in H. tergisus above the anal fin insertion. C, Close-up view of the pelvic axillary scale (as) in an adult H. tergisus (uma F10599, 235 mm SL, male). Specimens are shown in lateral view. Anterior faces left. 126 FIELDIANA: ZOOLOGY in this area are continuous with those of the rest of the body, whereas in H. tergisus these rows are irregular (Fig. 94A, B; Trautman, 1957). Cockerell (1910: 4) offered a brief description of the scales of Hiodon and commented, "A re- markable thing about the scales of Hiodon is their close resemblance to those of certain old world Cy- prinidae .... The Hiodontidae cannot be directly related to the Cyprinidae, but I believe that they may stand close to the ancestors of the Characini- dae." In a later paper, Cockerell (1914: 92) wrote, "If Hiodon . . . has any relationship with the Char- acinids, it must be with the Curimatines, although the Serrasalmonine scale is not without resem- blances . . . ." While it is highly unlikely that these taxa share a close common ancestor, the scales of Hiodon and characiformes are very similar in shape and form (Cockerell, 1914: pi. XXV). An elongated axillary scale is present on the lateral (leading) edge of the pelvic fin (as. Fig. 94). Arratia (1997, 1999: character 98) termed this structure a "pelvic axillary process" and identified four states, depending on its composi- tion (e.g., bone and/or modified scale). She found that an axillary process composed solely of small bones was a synapomorphy of fVarasichthyidae and that a process composed of a combination of bone and elongated scales evolved independently in {Elops + Megalops) and (Thymallus + Onco- rhynchus). An axillary process formed only by a modified scale was found independently derived in {Opsariichthys + (iGordichthys + Chanos)) and Hiodon (Arratia, 1999). These axillary scales are distinct from the pelvic splints of Gosline (1961: fig. 5; see Fig. 89E, F), which are thin bones that lie lateral to the outermost fin ray. Conclusions Although fishes are mostly hidden by the element in which they live, so tluit the Icnife of the anatomist generally first reveals new facts connected with their life, we have sufficient evidence to show that the phenomena of life are more varied in their dif- ferent groups than in any of the higher Vertebrata, and that tfieir study will form a solid basis for the solution to those general biological questions which, perhaps rather prematurely, agitate the minds of many zoologists. -Albert Gunther ( 1 870: x) After having attempted to confine our discourse to facts it is a pleasure to relax into the more genial atmosphere of opinion and hypothesis. —Henry Fairfield Osborn (1912: 276) Future Study of Hiodontid Osteology I have described and illustrated the osteology of the genus Hiodon in more detail than has been done in the past, yet many aspects of its skeletal anatomy remain incompletely known. I observed differences in timing of ossification between the two species. However, given the material that I have assembled, it is impossible to say whether these differences rep- resent actual ontogenetic differences between the species or are the result of some preservational, pre- parational, or ecological artifact particular to the available material. A large size gap exists in my specimens of H. tergisus, between 24 mm SL and 38 mm SL, and my smallest specimen of H. alo- soides was only 24 mm SL. Comparisons of my 24 mm SL H. tergisus and 24 mm SL H. alosoides showed that H. alosoides was much further along in its development than H. tergisus (e.g., all verte- bral centra were complete rings and the articular bone was present in H. alosoides, but not in H. ter- gisus). All specimens used in this study were wild- caught specimens and came from different parts of their respective ranges. Therefore, it is possible, if not likely, that the differences in development dis- covered here were induced by environmental or oth- er extrinsic influences. Most bones of the skull al- ready had mineralized in the smallest available spec- imens of both species. As well as standardizing the development of the skeleton in Hiodon by using specimens reared in controlled environments (i.e., laboratory conditions), future studies must investi- gate the very earliest ossifications in sfill smaller specimens than were available for my study. Indi- viduals of Hiodon are notoriously fragile and die easily in captivity (G. V. Lauder, pers. comm.), so this poses challenges for future collection of devel- opmental series. The inner ear and its relationship to the cranial diverticula of the swimbladder of Hiodon has been of great interest, both from a morphological stand- point and as a source for systematic characters (e.g., Ridewood, 1904; Greenwood, 1963, 1973), al- though as Greenwood (1973: 321) stated, "Taking into account the complexity of these interconnec- tions, and the modificafions to the associated skull bones, the otophysic connection in Hiodon can only be considered a derived condition." The description of the membranous labyrinth and its association HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 127 with the swimbladder presented herein is admittedly brief and should, in the future, be based on recon- struction from serial sections of specimens. Other remaining questions (e.g.. What are the intra- and extracranial spaces of the occipital region shown in Figure 25?) might further be addressed by prepara- tion and stud)' of additional sectioned material. An important study could also be made of the soft tissue systems (e.g.. the brain, cranial nerves, and circu- latory system) of Hiodon in comparison to other teleostean fishes. I identified foramina based on gross dissection and confirmation through study of serial sections (e.g.. the foramen for the anterior ce- phalic vein was confirmed to carry a blood \'essel. but the vessel itself was not completely traced; facv. Fig. 20. also Taveme. 1977). although some of these identifications may be corrected with future work. While the morphological interpretations of this study are defensible, further study and reconstruc- tion of even more detailed anatomy of Hiodon can be expected to provide further insight into the anat- omy of teleostean fishes in general. Such studies are basic to understanding systematic interrelationships, which in turn allow the formulation of hypotheses concerning the evolution of the unique morphology that characterizes Hiodon. Ontogeny and the Establishment of Primary Homolog> Homology . . . exists only in the human mind. . . . —Colin Patterson (1982: 59) Comparative developmental osteology can greatly influence the way in which scientists de- tect topographic correspondence (Rieppel. 1988: = primary homology of de Pinna. 1991: and to- pographic identity + character state identity of Brower & Schawaroch. 1996). and thereby influ- ence the way in which we discover homology (Rieppel. 1988: = synapomorphy of Patterson. 1982. secondary homology of de Pinna. 1991. and corroborated homology of Brower & Schawaroch. 1996).- The vomer in nonteleostean neopterygians - The amount of literature invested in discussion of "primary" versus "secondary" homology and the num- ber of names given to its various concepts (only a few are cited here) are indications of the importance of these concepts to the context of comparative biology: see also papers in Hall (1994). Wagner (2001). and Rieppel and Kiemey (2002). (e.g.. Amia. Lepisosteus. tpachycormids, tcatur- ids. tparasemionotids. tsaurichthyids: Patterson, 1975) consists of a paired element. In tpholido- phorids. tleptolepids. and most extant teleosts (Patterson. 1975). a single vomer has been hy- pothesized to represent a fusion of the paired el- ements of other neopterygian fishes. A character with two character states can then be conceptu- alized and described as "vomer: paired [0]: single [1]." Implicit in this definition — or. in fact, in any character scored for phylogenetic analysis — is a hypothesis that the conditions of the character (i.e.. the character states) represent "the same but different" thing (Hawkins. Hughes, and Scotland, 1997: 275: see the discussion under the heading "What is a character?" in Rieppel & Zaher. 2000: 508-51 1 ). As observed by Hawkins et al. (1997), this amounts to a transformational approach (e.g.. Patterson. 1982: Rieppel. 1988: de Pinna. 1991) to primary homology assessment. In other words, a hypothesis of phylogenetic fusion (or division, depending on character distribution and polarity resulting from an analysis: both are processes of character transformation) is implicit in the above example of the teleostean vomer (see next section. Remarks on Phylogenetic Fusion). By equating the two conditions as alternative conditions of the same structure, there is necessarily a hypothesis of change in morphology, albeit unstated. If assessment of homology follows a two-step sequence of events (called "generation and legit- imation" by de Pinna. 1991: 372: but see also Brower & Schawaroch. 1996). a distinction can be made between taxic and transformational ap- proaches to both the "generation" and the "le- gitimation" step. The above example is transfor- mational in its approach only in terms of character state identity, i.e.. "generation" of the homology statement (e.g.. the one bone in one set of taxa corresponds to the two bones in another set of taxa). and does not concern the approach toward the analysis of that correspondence (i.e.. "legiti- mation"), which also can follow either transfor- mational (e.g.. ordered and/or weighted charac- ters) or taxic (e.g.. unordered and unweighted characters) approaches. I see the "generation" stage (i.e.. the identification of different states of a character) of homology assessments as neces- sarily transformational in nature, following the "same but different" idea of Hawkins et al. (1997). Even if the topographical correspondence cri- terion for this primary homology statement be- tween the two forms of the vomer, for example. 128 FIELDIANA: ZOOLOGY is accepted (e.g., dermal ossification(s) on the ventral surface of the ethmoid region, anterior and ventral to the anterior process of the parasphen- oid), this character is much more complex. In Hiodon, I found that the single median vomer typ- ical of the adult begins its development as two distinct ossifications that ontogenetically fuse to form a single median element. To incorporate these new observations into an analysis, there are now two ways to characterize the vomer of tele- ostean fishes. The first is to define a single mul- tistate character, in which the vomer is described as "paired throughout ontogeny [0]; paired in ear- ly development and fused later in development [1]; median throughout development [2]." If the character is ordered [0] -^ [1] -^ [2], then this is a transformational approach not only to character identification and primary homology estimation but also to character analysis (if [0] is plesio- morphic), in that state [1] is recognized as an on- togenetic terminal addition of state [0] and state [2] is recognized as an ontogenetic nonterminal deletion of state [1]. As an unordered character, however, it only invokes the hypothesis of same but different (again, fundamentally transforma- tional in nature) but does not add a priori conjec- tures of character evolution. The latter (unor- dered) is, therefore, a taxic approach to character analysis. A second taxic approach would be to define a second character (beyond the original "adult con- dition" character described above) that describes the ontogeny of those taxa that possess a median vomer in the adult (e.g., "median vomer devel- ops: paired to paired [0]; paired to median [1]; always median [2]"). Its advantage is that there is no a priori hypothesis of relationship among the various character states (e.g., terminal addition or nonterminal deletion in reference to an "ances- tral" ontogeny). Ultimately, how to code such characters comes down to choice or, perhaps more accurately and importantly, justification of the coding strategy employed for dealing with mul- tistate characters in phylogenetic analyses, as re- cently reviewed by Forey and Kitching (2000). There is an unfortunate lack of comparable data for most taxa that bear on problems similar to the above example of conceptualization and analysis of the neopterygian vomer character. While this is potentially (in theory, if not in practice) a "problem" of all characters put into an analysis, it is particularly prevalent to studies that incor- porate ontogenetic data. For example, information on the early ontogeny of the vomer in fossil taxa is unlikely to be forthcoming from even the most completely and abundantly preserved taxa, and even for most relevant extant taxa the develop- ment of the skeleton remains incompletely known. Further morphological studies on basal teleostean fishes should therefore include not only descriptions of adult morphology but also evalu- ation of ontogenetic changes in morphology as complete as possible given available materials. Remarks on Phylogenetic Fusion Whatever the details of the phylogenetic process, which are not demonstrable, the overall result is called fusion here, for want of a better word. — Gareth J. Nelson (1969a: 9) In many instances, identification of topograph- ical correspondence draws links between parts of the skeleton that are separate elements in one set of taxa (plesiomorphic state) with a single element present at all ontogenetic stages in a second set of taxa (apomorphic state). Just as the study of ontogeny can greatly influence our assessment of putatively homologous characters, hypotheses of so-called "phylogenetic fusion" also may have a great impact on assessment of primary homology^ (e.g., see Westoll, 1962, and 0rvig, 1962, for dif- fering views of primary homology statements concerning some skull bones of placoderms). For example, Jarvik (1948: 68-74), in a discussion of the skull roof of species of Acipenser, listed sev- eral variations pertaining to the "lateral extras- capular" bones. Jarvik (1948) named compound bones that incorporated (= fused to) the lateral extrascapular (e.g., he labeled an "extrascapulo- supratemporo-intertemporal" bone; Jarvik, 1948: fig. 19D), so that each specimen he examined had a unique complement of skull roofing bones. For cases in which extreme individual variability of ossifications is well-known, such as in Acipenser, naming of compound elements is hard to justify (Hilton & Bemis, 1999). Such individual varia- tions in Acipenser are most likely the product of unique patterns of ontogenetic fusion, although the ontogenetic history of such variations is rare- ' Patterson and Johnson (1995: 38) discussed a situ- ation they considered analogous to phylogenetic fusion "with the added dimension or complication of serial ho- mology" in sorting the homologies of epineural and epi- central intermuscular bones of acanthomorph teleostean fishes. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 129 ly, if ever, discernible in adults. An analogous problem of structural identification arises when fusion ("for want of a better word;" G. J. Nelson, 1969a: 9) is argued to have occurred during phy- logeny. De Beer (1937: 502-512) discussed at length the difficulty of tracing the homology of bones, and cited four potential causes for observed dif- ferences in patterns of bones: (1) the bones com- pared are not homologous; (2) two or more bones are fused into a single bone; (3) a single bone was subdivided into two or more bones; and (4) of two or more bones, one has been lost and the other(s) filled its space. Each of these categories was fol- lowed by one or more examples (de Beer dis- cussed elements of the skull, but this may be ap- plicable to other regions of the skeleton as well). As an example of fused elements, de Beer (1937: 505, 508-509) discussed and compared the der- mal bones of the snout of Polypterus and Amia. In Polypterus, there are three bones that de Beer identified as the "terminale," "adnasal," and "nasal" bones. In Amia, each nasal bone develops as three ossification centers that fuse into a single element (although this was not described by Grande & Bemis, 1998: 49, fig. 11). Therefore, de Beer concluded that the nasal bone of Amia is the fused terminale, adnasal, and nasal of Polyp- terus (this represents ontogenetic fusion, an "ob- servable" process, rather than phylogenetic fu- sion). If this hypothesis is true, and if, as is gen- erally accepted, the nasal bones in Amia corre- spond to those of teleosts, then it logically follows (although not explicitly stated by de Beer) that the nasals of teleosts, which arise as a single ossifi- cation, also correspond to the terminale, adnasal, and nasal of Polypterus ("true" phylogenetic fu- sion). This example was also discussed by Moy- Thomas (1938: 313), who wrote, "The nasals of Amia develop from three rudiments round three sense organs, those of Polypterus each from a sin- gle organ. Are those oi Amia, therefore, the prod- uct of fusion or are the bones of Polypterus the results of fragmentation? . . . Unfortunately the trouble does not end with the acceptance or rejec- tion of one of these possibilities." Acceptance or rejection can only follow from an hypothesis of phylogeny and subsequent character polarization. Hypotheses of phylogenetic fusion, often much more subtle than the above example, are common in the definition of characters for phylogenetic analysis and in effect enter additional assumptions of character evolution into an analysis a priori. Phylogenetic fusion is a hypothesis about evo- lutionary process (i.e., a transformational homol- ogy statement) and may be rejected because it constructs a priori causal relationships between character states. Additionally, phylogenetic fusion cannot be distinguished from phylogenetic loss, except in four specific circumstances discussed by Patterson (1977a): (1) the primitive condition has separate elements; (2) the elements fuse in late ontogeny in "primitive" members of a group; (3) the elements fuse in early ontogeny in some mem- bers; and (4) there is a reversal in derived taxa. An important component to this line of reasoning is that it is based on phylogenies that are gener- ated independently of this data. For example, in nonteleostean neopterygians the posterior portion of the lower jaw typically has three postdentary bones (the dermal angular bone and the chondral articular and retroarticular bones). In most tele- osts, two or more of these bones appear to have fused and actually develop from a single ossifi- cation center (G. J. Nelson, 1973a; Patterson, 1977a). Patterson and Rosen (1977) demonstrated the first two "lines of evidence" of phylogenetic fusion (i.e., plesiomorphic state with separate el- ements, and elements fusing in late ontogeny in basal members of a group) in their study of tlep- tolepids and tichthyodectiformes. Here, I provide evidence for the third (i.e., early ontogenetic fu- sion in some members) during the course of de- velopment of Hiodon (Fig. 44). The fourth (i.e., a reversal) is satisfied by the presence of separate elements in the lower jaw of Heterotis and Ara- paima (G. J. Nelson, 1973a; Taverne, 1977; pers. obs.). Therefore, a "justified" hypothesis of phy- logenetic fusion can be made for taxa that have only a single ossification center for a compound (= dermal + chondral) postdentary bone (e.g., in the lower jaw of most teleosts). A distinction can be made between hypotheses of phylogenetic fusion between two (or more) dermal or two (or more) chondral bones, and phy- logenetic fusion between dermal and chondral bones. Similar "rules," as outlined by Patterson (1977a), cannot be applied to cases of phyloge- netic fusion between dermal bones or between chondral bones because there is no initial mor- phological reason for hypothesizing fusion over loss. Coalescence of ossification centers between elements of similar histogenesis does offer a mechanism through which phylogenetic fusion may occur ("at least, I can imagine no other way in which the process might come about"; Patter- son, 1977a: 93), but again, such a hypothesis is dependent on phylogeny. Patterson (1977a: 92- 130 FIELDIANA: ZOOLOGY 93) remarked on the difficulty of studying and "documenting" phylogenetic fusion of two or more dermal or chondral bones, but offered single median bones (e.g., the single median vomer of teleosts) as a possible example. The infraorbitals of Hiodon and other osteoglossomorph fishes can be regarded as another (G. J. Nelson, 1969a; Li & Wilson, 1996a). Most "basal" teleosts have six bones (exclusive of the dermosphenotic) in the in- fraorbital series, and osteoglossomorphs have only five (with the exception of Pantodon; Tav- erne, 1978; pers. obs.). A hypothesis of fusion be- tween two of the elements has generally been pre- ferred over the hypothesis of loss of one of the elements, but the actual process by which the re- duction occurred is irrelevant to the phylogenetic pattern observed (G. J. Nelson, 1969a). However, the correlation of specific infraorbital elements with number of neuromast organs offers an inter- esting mechanism of element identification be- tween taxa. Through such correlation. Nelson (1969a) argued that it was io3 and io4 that had "fused" in most osteoglossomorphs. Li and Wil- son (1996), on the other hand, argued that it is io4 and io5 that are present as a fused single el- ement, based on the position of the osteoglosso- morph infraorbital bones compared with those of other basal teleosts (e.g., Elopiformes). Without such independent lines of evidence (e.g., neuro- mast correlation, as suggested by Nelson, 1969a), however, phylogenetic fusion between elements of similar histogenesis in which there is a single ossification center is an untestable hypothesis ("a meaningless concept": Patterson, 1977a: 93; 1975). Establishing a relationship between bones and other structures offers great potential for es- tablishing statements of primary homology in in- stances where there is no direct (e.g., ontogenetic) evidence for correspondence. It seems to me that defining the infraorbital character of osteoglosso- morph fishes, for example, as a reduction, rather than specifying which elements have become fused or which element has been lost, both of which are ultimately theory-laden, is more meth- odologically sound." The process by which this reduction took place can then be hypothesized based on taxonomic relationships, character dis- tribution, and polarity. '' This discussion is written with the full realization that not every case is clear-cut. It should be emphasized, however, that clear justification of homology statements (including discussion or recognition of a priori theories of character transformation) is of the utmost importance in rigorous analyses of morphological evolution. Beyond hypothesizing phylogenetic fusion a priori, a second way of approaching such char- acters is to define two (or more) binary characters describing the presence or absence of each of the conditions that would be defined as character states if a single character were defined. This also avoids a priori judgments of character identity be- tween the two conditions (e.g., paired and single bones), so that analysis of these conditions can be treated in a taxic manner. If, for example, a single element was found to be a synapomorphy of a group nested within a larger group defined by the presence of paired elements, a reasonable hypoth- esis of the evolutionary process that resulted in that morphology (i.e., phylogenetic fusion) then could be made (O. C. Rieppel, pers. comm.). Still, following this approach of analysis, there first must be some morphological criteria (e.g., relation to other structures) that is met in order to logically connect the two characters as different conditions of the same element. For example, Grande and Bemis (1998) found that the presence of a median parietal was a synapomorphy of tSinamiidae. This bone (Grande & Bemis, 1998: fig. 397D) oc- cupies the space of the paired parietals found in other halecomorph fishes. Because tSinamiidae is nested deeply within a group characterized by paired parietals (all other halecomorphs [except anomalous specimens of Amia calva; e.g., Grande & Bemis, 1998: figs. 12F and 13F], lepisosteids, and primitive teleosts), it is reasonable to hypoth- esize that the single parietal of tsinamiids is a fusion of paired parietals (specimens studied by Grande & Bemis [1998] represented a range of sizes, so it is believed that this is indeed an on- togenetically fixed character; W. E. Bemis, pers. comm.). While Grande and Bemis (1998) did not split this character into two characters (i.e., a char- acter describing each of the conditions), the the- oretical interpretation is, at least, similar (i.e., the median parietal is a phylogenetic fusion of paired parietals). While an intuitively believable phenomenon, phylogenetic fusion strictly depends on a partic- ular phylogenetic context, because it never can be directly observed and can be used only to hy- pothesize "cause" of morphology subsequent to an analysis of relationships that is independent of the theory of process (i.e., hypotheses of phylo- genetic fusion — a process — must follow from hy- potheses of phylogeny — a pattern; Rieppel & Grande, 1994). The discussion above has been one of ideal situations, and it is acknowledged that most often character conceptualization is not HILTON: OSTEOLOGY OF HIODON LESUEUR, 131 this straightforward. However, the question ulti- mately becomes whether characters that are de- fined based on unobserved processes, even if they do show hierarchical patterns of taxonomic vari- ation (i.e., "process" characters that are phylo- genetically informative), can be used in analyses of morphological evolution? If an hypothesis of phylogenetic fusion (or other process) is invoked as part of the definition of a character state, with- out ontogenetic, corroborative or correlative sup- porting evidence (in many cases, I do not regard positional correspondence as being sufficient), then the subsequent use of this character to infer anything concerning the evolution of structure based on a phylogenetic analysis is logically cir- cular. Remarks on the Study of Individual Variation These individual differences are of the highest im- portance for us, for they afford materials for nat- ural selection to act upon and accumulate. . . . I am convinced that the most experienced naturalist would be surprised at the number of the cases of variability, even in important parts of structure. . . . —Charles Darwin (1859: 45) Individuals of a single taxon always vary in structure. In a broad sense, this simple truth is what allows us to recognize the physical differ- ences, for example, between strangers and ac- quaintances (Patterson, 1978: 5). However, even characters of seemingly great systematic "impor- tance" are known to vary from individual to in- dividual within a taxon. The recognition and de- scription of individual variation in the vertebrate skeleton has become an increasingly important component to modern systematic and morpholog- ical studies, yet is still underappreciated by many morphologists and systematists. Morphological variation can result from one of four sources (or any combination thereof): phy- logenetic, ontogenetic, sexual dimorphic, or indi- vidual (e.g., Grande & Bemis, 1998). Individual variation is defined as "variation between individ- uals of the same species at similar stages of de- velopment" (Hilton & Bemis, 1999: 69). Much of the individual variation documented in the litera- ture is variation in meristic or morphometric data (e.g., Hubbs & Hubbs, 1945; Bailey & GosHne, 1955; Hubbs & Miller, 1965) and is often corre- lated with ecological or geographic "morphs" of a taxon (e.g., Cutwa & Turingan, 2000; although see Reimchen & Nelson, 1987). These are the so- called "trophic polymorphisms" of Hanken & Hall (1993). Discrete or "natural" variation (i.e., variation in shape, form, or presence of particular elements) has received relatively little attention, and those studies that have been done concern only one or a few portions of the skeleton (e.g., cranial roofing bones of '\Chierolepis canadensis, Arratia & Cloutier, 1996; dermal and endochon- dral skull bones and scutes of Acipenser brevi- rostnim, Hilton & Bemis, 1999). Examination of large series of specimens in terms of numbers, sexes, and ontogenetic stages is essential to the detection of such variation. Various forms of individual variation are distin- guishable."^ The primary dichotomy that I recog- nize is between "correlated" and "uncorrelated" individual variation (Table 23). Correlated indi- vidual variations are the most commonly studied and documented types of individual variation, probably because they are readily observable and contingent upon factors intrinsic (e.g., a physio- logical response to environmental conditions) or extrinsic (i.e., geographic range) to the organism. Sexual dimorphism legitimately could be viewed as a subset of this category because it is found between individuals of the same taxon at the same ontogenetic stage (Hilton & Bemis, 1999) and is correlated with the sex of the individual. How- ever, in sexually reproducing organisms there nec- essarily will be some variation (e.g., morpholog- ical and physiological) between individuals of dif- ferent sexes. Sexual dimorphism, therefore, is bet- ter thought of as a type of variation in and of itself (L. Grande, pers. comm.). Uncorrelated individual variations, on the other hand, include teratological and natural variations, and have been much less well studied. In partic- ular, the level of natural variation in the mor- phology of even phylogenetically "important" taxa is relatively unknown. The sources and cod- ing of such polymorphisms are at the center of much debate in systematic methodology (e.g., Nixon & Davis, 1991; Campbell & Frost, 1993; Wiens, 1999, 2000), and, as with other "problem- atic data" (Grande & Bemis, 1998: 568-569), in- dividually polymorphic characters are treated by computer algorithms essentially as missing data. '' I have presented these terms for use in systematic morphological studies, but a similar approach is surely applicable to other research programs, such as behav- ioral or functional morphological studies. 132 FIELDIANA: ZOOLOGY Table 23. Types and sources of individual variation. Type Source Definition and example Correlated individual variation Temporal individual varia- tion Ecomorphological individu- al variation Geographic individual vari- ation* Morphological variation due to a physiological response to the en- vironment or other factors dependent on time at any scale; e.g., day, year, etc. (the dentition of male Atlantic stingrays, Dasyatis sabina, becomes pointed during the mating season and returns to a platelike dentition during the rest of the year; Kajiura & Tricas, 1996) Morphological variation in response to a particular ecological niche filled by a particular population or subset of a taxon (papilliform and molariform pharyngeal teeth of Cichlasoma minckleyi, associ- ated with herbivorous and carnivorous forms, respectively; Kom- field et al., 1982) Morphological variation between individuals from different por- tions of a taxon's geographic range (color pattern in the milk snake Lampropeltis triangulum\ Williams, 1978) Uncorrelated individual variation Teratological individual var- iation Natural individual variation Morphological variation that is drastically atypical, including that caused by disease, injury or is otherwise pathological (two-headed and two-bodied snakes; Cunningham, 1937) Morphological variation that has no apparent direct or correlative cause (skull roofing bones of Acipenser brevirostrum; Hilton & Bemis, 1999) * The distinction between geographic morphological variation and phylogenetic variation may be blurred in some instances. If geographic "morphs" or "races" are distinct (i.e., there is no overlap in frequency of a trait), then this logically can be interpreted to be the result of phylogenetic variation. True geographic individual variation must be represented by a continuous gradation of phenotypes across the range of a taxon. However, it is useful to understand the source of the "problem" so that this information can be in- corporated into character analysis once a phylog- eny has been recovered (e.g., Platnick, Griswold, & Coddington, 1991; Grande & Bemis, 1998). Natural individual variation may differ substan- tially among various components of the skeleton. For example, characters of the caudal skeleton of teleostean fishes are often included in broad anal- yses of teleost relationships (e.g., Patterson & Ro- sen, 1977; Arratia, 1991, 1997, 1999), despite the well-documented individual variation typical of this part of the skeleton (e.g., Arratia, 1983; Davis & Martin, 1999). For example, I found that the number of uroneurals present in Hiodon is highly variable, with each specimen seemingly display- ing a unique number and pattern of ontogenetic fusion among the uroneural series, including left and right asymmetry (Tables 15 and 16, Figs. 75 and 76; see also the discussion and references un- der Caudal Fin and Supports). The condition of the neural spine on preural centrum one (nspul. Figs. 75 and 76) also varies in Hiodon. Patterson and Rosen (1977) found the presence of a full neural spine on pu 1 to be a synapomorphy of Os- teoglossomorpha. Schultze and Arratia (1988), however, found this character in only 6% of their specimens of Hiodon, and my study shows that it is likely even less common (Tables 15 and 16). The "typical" condition of Hiodon clearly is to have a rudimentary neural spine on pul. The ex- treme variation of the caudal skeleton of the spe- cies of Hiodon is in contrast to the extreme sta- bility in the pattern of their infraorbitals. In my sample, less than 1 % had a pattern of infraorbitals other than the "typical" condition. However, the high prevalence of individual variation in even some regions of the skeleton underscores the need for rigorous morphological character analysis, both during construction of a data matrix and after analysis of that matrix (Patterson & Johnson, 1997a,b). Comparative morphology remains a keystone for hypotheses about interrelationships among liv- ing and fossil taxa. Clear conceptualization of characters is impossible without rigorous knowl- edge of morphological variation, whether it is within a species or at some higher taxonomic lev- el. As modern computer-aided phylogenetic anal- yses become more powerful and approaches to analyses of data become more sophisticated, it is critical not to disregard the clear and explicit ar- HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 133 ticulation of the primary data (i.e., the morphol- ogy), for if spurious morphology serves as the basis of analysis, no amount of sophistication can bring to it any significant meaning. Acknowledgments This study formed a portion of dissertation re- search conducted primarily at the University of Massachusetts Amherst (uma) under the guidance of W. E. Bemis, whose enthusiasm for compara- tive morphology of fishes served as a stimulus for this study and the growth of my interest in com- parative osteology. I am extremely grateful for the comments, suggestions, and encouragement of my entire dissertation committee: W. E. Bemis, E. L. Brainerd, P. L. Forey, L. Grande, and B. Kynard. All have served as great inspiration, and I will be forever in their debt for all they have taught me. I especially thank L. Grande for sponsoring my wonderful and productive fellowship at the Field Museum and for the kindness he has shown throughout my time as a student. For reading and commenting on portions of the manuscript, I thank O. C. Rieppel, and for critically reading the entire manuscript, I thank my committee mem- bers, G. D. Johnson and M. V. H. Wilson. This work and the ideas it is based on benefited greatly from discussion, comments, suggestions, and en- couragement of G. Arratia, R. Britz, C. Brochu, B. Chernoff, A. Filleul, P. Z. Goldstein, T Grande, S. Huber, G. D. Johnson, M. Kearney, N. J. Kley, G. V. Lauder, K. F. Liem, J. S. Nelson, A. M. Richmond, O. C. Rieppel, C. R Sanford, A. M. Simons, A. Ward, R Willink, M. V. H. Wilson, and R. Zaragueta, as well as numerous persons I have inadvertently left from this list; mistakes, in- consistencies, and misinterpretations are, of course, my own. W. B. Sillin gave much helpful advice on the production of the illustrations. For loan of specimens, permission to prepare specimens in their care, or help during museum visits, without which this work would have been impossible, I thank W. E. Bemis (uma), J. S. Nel- son and W. Roberts (uamz), D. Didier-Dagit and W Saul (ansp, retired), S. Jewett and J. Williams (usnm), S. Laframboise and D. Balkwill (nmc), K. E. Hartel and A. Everly (formerly MCZ — Fishes), C. Schaff (MCZ — Vertebrate Paleontology), G. Burgess and R. Robins (fl), A. M. Simons (jfbm), H. Bart and M. Taylor (xu), G. J. Nelson (retired) and B. Brown (amnh), B. Chernoff and M. A. Rogers (fmnh — Department of Zoology), L. Grande (fmnh — Department of Geology), J. Arm- bruster and J. Evans (aum), D. Goujet, P. Janvier, and H. Lelievre (mhnh — Paleontology), G. Du- hamel, P. Pruvost, and X. Gregorio (mhnh — Ich- thyology), and P. L. Forey (bmnh — Paleontology). For gifts of specimens, I am grateful to R. L. Mayden (formerly), B. R. Khajda, and D. A. Nee- ly (UAic), J. C. Hendrickson (North Dakota Game and Fish Department), J. La Rose (Trent Univer- sity), and P. Cieslewicz (Missouri Department of Conservation). This work was financially supported by a Na- tional Science Foundation (NSF) Doctoral Disser- tation Improvement Grant (DEB-0073066, to W E. Bemis for E. J. Hilton), NSF DEB-0075460 (to W E. Bemis and L. Grande), NSF DEB-9707705 (to L. Grande and W E. Bemis), the Jane H. Be- mis Fund for Research in Natural History, the Lester Armour and William A. and Stella Rowley Graduate Fellowships (fmnh), a Visiting Scientist Scholarship (fmnh), a Sigma Xi Grant-in-Aid-of Research, the Graduate School at the University of Massachusetts Amherst (uma), the Woods Hole Scholarship Fund (uma), the Department of Bi- ology (uma), and the Graduate Program in Organ- ismic and Evolutionary Biology (uma). Costs as- sociated with the publication of this work were defrayed in part by a grant from the David J. Klingener Memorial Fund and the Jane H. Bemis Fund for Research in Natural History. Note Added in Proof Article 75.2 of the International Code of Zoolog- ical Nomenclature (ICZN, 1999: 84) states, "A neotype is not to be designated as an end in itself, or as a matter of curatorial routine, and any such designation is invalid." Although there is no re- cent history of confusion concerning the validity of the two extant species of Hiodon, the ranges of these two species overlap, and my efforts to track down the type specimens were unsuccessful (also see Eschmeyer, 1998, vol. 1: 76; vol. 2: 1664). Therefore, the neotypes designated in this monograph serve to preserve current usage of the species names by providing specimens to refer to in my comparisons of morphometric measure- ments and meristic counts for the two species, thereby clarifying the taxonomic status of both species (in accordance with Article 75.3.1). Fur- thermore, it is imperative that type specimens of 134 FIELDIANA: ZOOLOGY the extant species be available for ongoing and future studies of fossil hiodontid taxa. Information regarding other qualifying conditions for neotype designations (Articles 75.3.2-7) is provided in the section titled Systematic Description of Hiodon. I thank Ralf Britz for pointing out this section of the Code and its potential effect on my designa- tions of these neotypes, and Bill Eschmeyer for his advice on this matter. Literature Cited Allis, E. p. 1919. The myodome and trigemino-facialis chamber of fishes and the corresponding cavities in higher vertebrates. Journal of Morphology, 32: 207- 322. Arratia, G. 1983. The caudal skeleton of ostariophysan fishes (Teleostei): Intraspecific variation in Tricho- mycteridae (Siluriformes). Journal of Morphology, 177: 213-229. . 1 99 1 . The caudal skeleton of Jurassic teleosts: A phylogenetic analysis, pp. 249-340. In Chang, M.- M., Y. H. Liu, and G. R. Zhang, eds.. Early Verte- brates and Related Problems in Evolutionary Biology. Science Press, Beijing. 1997. Basal teleosts and teleostean phylogeny. Paleoichthyologica, 7: 1-168. -. 1999. The monophyly of Teleostei and stem- group teleosts, consensus and disagreements, pp. 265- 354. In Arratia, G., and H.-P. Schultze, eds., Mesozoic Fishes. 2. Systematics and Fossil Record. Verlag Pfeil, Munich. Arratia, G., and R. Cloutier. 1996. Reassessment of the morphology of Cheirolepis canadensis (Actinop- terygii), pp. 165-197. In Schultze, H.-R, and R. Clou- tier, eds., Devonian Fishes and Plants of Miguasha, Quebec, Canada. Verlag Pfeil, Munich. Arratia, G., and H.-P. Schultze. 1990. The urohyal: Development and homology within osteichthyans. Journal of Morphology, 203: 247-282. . 1991. Palatoquadrate and its ossifications: De- velopment and homology within osteichthyans. Jour- nal of Morphology, 208: 1-81. Bailey, R. M., and W. A. Gosline. 1955. Variation and systematic significance of vertebral counts in the American fishes of the family Percidae. Miscellaneous Publications, Museum of Zoology, University of Michigan, 93: 1-44. Bamford, T. W. 1948. Cranial development of Galei- chthvs felis. Proceedings of the Zoological Society of London, 118: 364-391. Battle, H. L, and W. M. Sprules. 1960. A description of the semi-buoyant eggs and early developmental stages of the goldeye, Hiodon alosoides (Rafinesque). Journal of the Fish Research Board of Canada, 17: 245-266. Baudelot, E. 1868. Considerations relatives a la piece scapulaire des silures. Bulletin de la Societe des Sci- ences Naturelles de Strasbourg, 12: 83-84. Bemis, W. E., and p. L. Forey. 2001. Occipital structure and the posterior limit of the skull in actinopterygians, pp. 359-378. In Ahlberg, P., ed.. Major Events in Ear- ly Vertebrate Evolution: Palaeontology, Phylogeny, and Development. Systematics Association. Taylor and Francis, London. Bennett, D. K. 1979. Three Late Cenezoic fish faunas from Nebraska. Transactions of the Kansas Academy of Science, 82: 146-177. Best, A. C. G., and J. A. C. Nicol. 1979. On the eye of the goldeye Hiodon alosoides (Teleostei: Hiodon- tidae). Journal of Zoology, London, 188: 309-322. Boesel, M. W. 1938. The food of nine species of fish from the western end of Lake Erie. Transactions of the American Fisheries Society, 67: 215-223. Boulenger, G. a. 1922. Systematic account of Teleos- tei, pp. 541-727. In Harmer, S. E, and A. E. Shipley, eds., Cambridge Natural History, vol. 7. MacMillan and Co., London. Braekevelt, C. R. 1982a. Fine structure of the retinal epithelium and retinal tapetum lucidum of the goldeye {Hiodon alosoides). Anatomy and Embryology, 165: 177-192. . 1982b. Photoreceptor fine structure in the gol- deye {Hiodon alosoides) teleost. Anatomy and Em- bryology, 165: 177-192. 1985. Further observation on the presence of wandering phagocytes within the teleostean retina. Anatomische Anzeiger, 160: 45-54. Bridge, T W. 1899. The air-bladder and its connection with the auditory organ in Notopterus borneensis. Journal of the Linnean Society of London (Zoology), 27: 503-540. Britz, R., and P. Bartsch. 1998. On the reproduction and early development of Erpetoichthys calabaricus, Polypterus senegalus, and Polypterus omatipinnis (Actinopterygii: Polypteridae). Ichthyological Explo- rations of Freshwaters, 9: 325-334. Brown, B., L. M. Benveniste, and P. Moller. 1996. Basal expansion of anal-fin rays: A new osteological character in weakly discharging electric fish (Mor- myridae). Journal of Fish Biology, 49: 1216-1225. Brower, a. V. Z., AND V. ScHAWAROCH. 1996. Three steps to homology assessment. Cladistics, 12: 265- 272. Burr, B. M., and R. L. Mayden. 1992. Phylogenetics and North American freshwater fishes, pp. 18-75. In Mayden, R. L., ed., Systematics, Historical Ecology, and North American Freshwater Fishes. Stanford Uni- versity Press, Stanford, California. Campbell, J. A., and D. R. Frost. 1993. Anguid lizards of the genus Abronia: Revisionary notes, descriptions of four new species, a phylogenetic analysis, and key. Bulletin of the American Museum of Natural History, 216: 1-121. Cavender, T. 1966a. Systematic position of the North American Eocene fish, ''Leuciscus'' rosei Hussakof Copeia, 1968: 311-320. . 1966b. The caudal skeleton of the Cretaceous teleosts Xiphactinus, Ichthyodectes, and Gillicus, and its bearing on their relationship with Chirocentrus. Occasional Papers of the Museum of Zoology, 650: 1-14. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 135 . 1986. Review of the fossil history of North American freshwater fishes, pp. 699-724. In Hocutt, C. H.. and E. O. Wiley, eds.. The Zoogeography of North American Freshwater Fishes. John Wiley and Sons, New York. Cavin, L., and p. L. Forey. 2001. Osteology and sys- tematic affinities of Palaeonotopterus greenwoodi Forey 1997 (Teleostei: Osteoglossomorpha). Zoolog- ical Journal of the Linnean Society. 133: 25-52. Chang, M.-M. 1999. "Mid" -Cretaceous fish faunas from northeast China, pp. 469-480. //; Arratia, G., and H.-P. Schultze, eds., Mesozoic Fishes. 2. Systematics and Fossil Record. Verlag Pfeil, Munich. Chang, M.-M., and C. Chou. 1976. [The discovery of Plesiolycoptera from Song Liao Basin, with notes on the origin of osteoglossomorph fishes]. Vertebrata PalAsiatica, 14: 146-153. In Chinese. Cloutier, R. 1997. Morphologic et variations du toit cranien du dipneuste Scaumenacia curta (Whiteaves) (Sarcopterygii) du Devonien superieur du Quebec. Geodiversitas, 19: 61-105. CocKERELL, T D. A. 1910. The scales of the mormyrid fishes with remarks on Albula and Elops. Smithsonian Miscellaneous Collections, 56: 1-4. . 1914. The scales of the South American char- acinid fishes. Annals of the Carnegie Museum. 9: 92- 113. . 1925. The affinities of the fish Lycoptera mid- dendorfi. Bulletin of the American Museum of Natural History, 51: 313-317. Cooper, E. L. 1983. Fishes of Pennsylvania and the Northeastern United States. Pennsylvania State Uni- versity Press, University Park. Cunningham, B. 1937. Axial Bifurcation in Serpents: An Historical Survey of Serpent Monsters Having Part of the Axial Skeleton Duplicated. Duke University Press, Durham, North Carolina. Cutwa, M. M., and R. G. Turingan. 2000. Intralocality variation in feeding biomechanics and prey use in Ar- chosargus probatocephalus (Teleostei, Sparidae), with implications for the ecomorphology of fishes. Envi- ronmental Biology of Fishes, 59: 191-198. CuviER, G.. AND A. Valenciennes. 1846. Histoire Na- turelle Des Poissons, vol. 19. Societe Geologique de France, Strasbourg [1969 facsimile reprint; A. Asher and Company, Amsterdam]. Daget, J. 1964. Le crane des teleosteens. Memoires du Museum National d'Histoire Naturelle Serie A. Zool- ogie, 31: 1-341. Daget, J., and d'Aubenton. 1957. Developpement et morpologie du crane d'Heterotis nilotious Ehr. Bul- letin de ITnstitut Fran9ais d'Afrique Noire, serie A. 19: 881-936. Darwin. C. 1859. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. John Murray, London. DA SiLVA Santos, R. 1985. Laelichthys ancestralis, novo genero e especie de Osteoglossiformes do Aptianoda Formac ao Areado, estado de Minas Gerais, Brasil. Coletanea de Trabalhos Paleontologia, Sen Geol 27, sec. Paleontol. e Estratigr., 2: 161-167. Davis, S. P., and D. M. Martill. 1999. The gonorhyn- chiform fish Dastilbe from the Lower Cretaceous of Brazil. Palaeontology, 42: 715-740. DE Beer, G. R. 1937. The Development of the Vertebrate Skull. Oxford University Press, Oxford, England. DE Pinna, M. C. C. 1991. Concepts and tests of homol- ogy in the cladistic paradigm. Cladistics, 7: 367-394. . 1996. Teleostean monophyly, pp. 147-162. In Stiassny. M. L. J.. L. R. Parenti, and G. D. Johnson, eds.. Interrelationships of Fishes. Academic Press. San Diego, California. DiNGERKUs. G.. AND L. D. Uhler. 1977. Enzyme clear- ing of alcian blue stained whole small vertebrates for demonstration of cartilage. Journal of Stain Technol- ogy. 52: 229-232. Donald. D. B. 1997. Relationship between year-class strength for goldeyes and selected environmental var- iables during the first year of life. Transactions of the American Fisheries Society. 126: 361-368. Donald. D. B.. and A. H. Kooyman. 1977a. Food, feed- ing habits and growth of goldeye. Hiodon alosoides (Rafinesque), in waters of the Peace-Athabasca Delta. Canadian Journal of Zoology. 55: 1038-1047. . 1977b. Migration and populational dynamics of the Peace-Athabasca Delta goldeye population. Oc- casional Papers of the Canadian Wildlife Service, 31: 1-19. Doyle. A. C. 1887. A Study in Scarlet. Beeton's Christ- mas Annual. Eldredge. N.. and S. M. Stanley. 1984. Living fossils: Introduction to the casebook, pp. 1-3. /// Eldredge. N., and S. M. Stanley, eds.. Living Fossils. Springer- Ver- lag, New York. EsCHMEYER, W N.. Ed. 1998. Catalog of Fishes. Vols. 1-3. California Academy of Science. San Francisco. Etnier. D. a., and W C. Starnes. 1993. The Fishes of Tennessee. University of Tennessee Press, Knoxville. Fink. W. L. 1981. Ontogeny and phylogeny of tooth at- tachment modes in actinoptervgian fishes. Journal of Morphology. 167: 167-184. Forey. P. L. 1973. A revision of the elopiform fishes, fossil and recent. Bulletin of the British Museum (Nat- ural History) Geology. Supplement. 10: 1-222. . 1998. History of the Coelacanth Fishes. Chap- man and Hall, London. Forey. P. L.. and I. J. Kitching. 2(XX). Experiments in coding multistate characters, pp. 54-80. //; Scotland, R.. and R. T Pennington, eds.. Homology and System- atics: Coding Characters for Phylogenetic Analysis. Systematics Association. Special Volume 58. Taylor and Francis. London. Fujita. K. 1989. Nomenclature of cartilaginous elements in the caudal skeleton of teleostean fishes. Japanese Journal of Ichthyology. 36: 22-29. Gardiner. B. G.. J. G. Maisey. and D. T J. Little- wood. 1996. Interrelationships of basal neopterygians, pp. 1 17-146. //; Stiassny. M. L. J., L. R. Parenti. and G. D. Johnson, eds.. Interrelationships of Fishes. Ac- ademic Press, San Diego. California. Gald.\nt. J. 1968. Recherches sur I'anatomie et la po- sition systematique du genre Lycoptera (Poisson Te- leosteen). Memoires de la Societe Geologique de France (Nouvelle Serie). 109: 1-40. 136 FIELDIANA: ZOOLOGY Glenn, C. L. 1975. Seasonal diets of mooneye, Hiodon tergisus, in the Assiniboine River. Canadian Journal of Zoology, 53: 232-237. Glenn, C. L., and R. R. G. Williams. 1976. Fecundity of mooneye, Hiodon tergisus, in the Assiniboine Riv- er. Canadian Journal of Zoology, 54: 156-161. Gosline, W. a. 1960. Contributions toward a classifi- cation of modern isospondylous fishes. Bulletin of the British Museum (Natural History), Zoology, 6: 327- 365. 1961. Some osteological features of modem lower teleostean fishes. Smithsonian Miscellaneous Collections, 142: 1-42. Goode, G. B. 1884. Natural History of Useful Aquatic Animals. U.S. Commission of Fish and Fisheries. The Fisheries and Fishery Industries of the U.S., sect. I. Washington, D.C. Grande, L. 1 979. Eohiodon falcatus, a new species of hiodontid (Pisces) from the Late Early Eocene Green River Formation of Wyoming. Journal of Paleontolol- gy, 53: 103-111. . 1985. Recent and fossil clupeomorph fishes with materials for revision of the subgroups of clu- peoids. Bulletin of the American Museum of Natural History, 181: 231-372. Grande, L., and W E. Bemis. 1991. Osteology and phy- logenetic relationships of fossil and Recent paddle- fishes (Polydontidae) with comments on the interre- lationships of Acipenseriformes. Journal of Vertebrate Paleontology. Memoir 1, 11: 1-121. . 1998. A comprehensive phylogenetic study of amiid fishes (Amiidae) based on comparative skeletal anatomy: An empirical search for interconnected pat- terns of natural history. Journal of Vertebrate Pale- ontology, Memoir 4, 18: 1-690. Grande, L., and T. M. Cavender. 1991. Description and phylogenetic reassessment of the monotypic Ostarios- tomidae (Teleostei). Journal of Vertebrate Paleontol- ogy, 11: 405-416. Greenwood. P. H. 1963. The swimbladder in African Notopteridae (Pisces) and its bearing on the taxonomy of the family. Bulletin of the British Museum (Natural History), Zoology, 11: 377-412. . 1970. On the genus Lycoptera and its relation- ship with the family Hiodontidae (Pisces, Osteoglos- somorpha). Bulletin of the British Museum (Natural History), Zoology, 19: 257-285. -. 1971. Hyoid and ventral gill arch musculature in osteoglossomorph fishes. Bulletin of the British Museum (Natural History), Zoology, 22: 1-55. -. 1973. Interrelationships of osteoglossomorphs. pp. 307-332. In Greenwood, P H., R. S. Miles, and C. Patterson, eds.. Interrelationships of Fishes. Aca- demic Press, London. Greenwood, P. H., R. S. Miles, and C. Patterson, eds. 1973. Interrelationships of Fishes. Academic Press, London. Greenwood, P. H., and C. Patterson. 1967. A fossil osteoglossoid fish from Tanzania (E. Africa). Journal of the Linnean Society (Zoology), 47: 21 1-223. Greenwood, P. H., D. E. Rosen, S. H. Weitzman, and G. S. Myers. 1966. Phyletic studies of teleostean fish- es, with a provisional classification of living forms. Bulletin of the American Museum of Natural History, 131: 341-455. Greenwood, P. H., D. E. Rosen, S. H. Weitzman, and G. S. Myers. 1967. Named main divisions of teleos- tean fishes. Proceedings of the Biological Society of Washington, 80: 227-228. Gregory, W. K. 1933. Fish skulls: A study of the evo- lution of natural mechanisms. Transactions of the American Philosophical Society, 23: 75-48 1 . Gunther, a. 1868. Catalogue of the Physostomi, con- taining the families Heteroptygii, Cyprinidae, Gonor- hynchidae, Hyodontidae, Osteoglossidae, Clupeidae, Chirocentridae, Alepocephalidae, Notopteridae, Hal- osauridae, in the Collection of the British Museum. British Museum Trustees, London. 1 870. Catalogue of the Physostomi, containing the families Gymnotidae, Symbranchidae, Muraeni- dae, Pegasidae and the Lophobranchii, Plectognathi, Dipnoi, Ganoidei, Chondropterygii, Cyclostomata, Leptocardii in the British Museum. British Museum Trustees, London. HaEDRICH, R. L., J. WlNTERBERG, AND G. J. NeLSON. 1973. A septum in the eye of osteoglossoid fishes. Copeia, 1973: 594-595. Hall, B. K., Ed. 1994. Homology: The Hierarchical Ba- sis of Comparative Biology. Academic Press, San Di- ego, California. 1995. Homology and development. Evolution- ary Biology, 28: 1-37. Hanken, J., and B. K. Hall. 1993. Mechanisms of skull diversity and evolution, pp. 1-36. In Hanken, J., and B. K. Hall, eds.. The Skull. Vol. 3. Functional and Evolutionary Mechanisms. University of Chicago Press, Chicago. Hanken, J., and R. Wassersug. 1981. The visible skel- eton. Functional Photography, 1981 (July/August): 22-26, 44. Hawkins, J. A., C. E. Hughes, and R. W Scotland. 1997. Primary homology assessment, characters and character states. Cladistics, 13: 275-283. Heckel, J. J. 1842. Ichthyologie, pp. 990-1099. In von Russegger, J., ed., Reisen in Europa, Asien und Africa, mit besonderer RUcksicht auf die naturwissenschaf- tlichen Verhaltnisse der betreffenden Lander unter- nommen in den Jahren 1835 bis 1841, vol. 1. Stutt- gart, Germany. Hendrickson, J. C, AND G. J. Power. 1999. Changes in fish species abundance in a Missouri River mainstem reservoir during its first 45 years. Journal of Fresh- water Ecology, 4: 407-416. Hennig, W. 1966. Phylogenetic Systematics. University of Illinois Press, Urbana. HiLDEBRAND, M. 1968. Anatomical Preparations. Uni- versity of California Press, Berkeley. Hilton, E. J. 2001. The tongue bite apparatus of osteo- glossomorph fishes: Variation of a character complex. Copeia, 2001: 372-382. Hilton, E. J., and W E. Bemis. 1999. Skeletal variation in shortnose sturgeon (Acipenser hrevirostrum) from the Connecticut River: Implications for the compara- tive osteological studies of fossil and living fishes, pp. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 137 69-94. /// Arratia. G.. and H.-P. Schultze, eds.. Me- sozoic Fishes. 2. Systematics and Fossil Record. Ver- lag Pfeil. Munich. HoCLTT. C. H.. AND E. O. WiLEY. Eds. 1986. The Zoo- geography of North American Freshwater Fishes. John Wiley and Sons. New York. Holmgren, N., and E. A. Stensio. 1936. Kranium und Visceralskelet der Akranier. Cyclostomen und Fische. pp. 203-500. /// Bolk. L.. E. Goppert. E. Kallius. and H. Lubosch. eds.. Handbuch der Vergleichenden An- atomic. Urban and Schwarzenberg, Berlin. Hlbbs. C. L.. and L. C. Hlbbs. 1945. Bilateral asym- metry and bilateral variation in fishes. Papers of the Michigan Academv of Science. Arts and Letters, 30: 229-310. Hlbbs. C. L.. and K. F. L.\gler. 1958. Fishes of the Great Lakes Region. Bulletin of the Cranbrook Insti- tute of Science. 26: 1-213. Hlbbs. C. L.. and R. R. Miller. 1965. Studies of cy- prinodont fishes: XXIL Variation in Lucania pan'a. its establishment in western United States, and de- scription of a new species from an interior basin in Coahuila. Mexico. Miscellaneous Publications. Mu- seum of Zooloav. University of Michigan. 127: 1- 104. Hlnlason, G. L. 1979. Animal Tissue Techniques. 4th ed. W.H. Freeman and Co.. San Francisco. Hlssakoff. L. 1916. A new cyprinid fish Leuciscus ro- sei from the Miocene of British Columbia. American Journal of Science. 42: 1 8-20. Iles. R. B. 1960. External sexual differences and their significance in Monnxrus kannume Forskal. 1975. Na- ture. 188: 516. InTERN.ATION.\L COM.VIISSION ON ZOOLOGICAL NOMENCLA- TLRE. 1999. International Code of Zoological Nomen- clature. 4th ed. International Trust for Zoological No- menclature. London. J.AEGER. E. C. 1978. A Source Book for Biological Names and Terms. Charles C Thomas. Springfield, Il- linois. J.anvier. p. 1998. Bow fins and the revenge of compar- ative biology. Science, 281: 1150. J.\RViK. E. 1948. On the morphology and taxonomy of the Middle Devonian osteolepid fishes of Scotland. Kungligar Svenska Vetenskapsakademiens Handligar, 25: 1-301. Jessen. H. 1972. Schultergurtel und Pectoralflosse bei Actinopterygierm. Fossils and Strata. 1: 1-101. Jin. F. 1 99 1 . [A new genus and species of Hiodontidae from Xintai. Shandong]. Vertebrata PalAsiatica. 29: 46-54. In Chinese with an English summary. Jin, F, J. Zh.\ng. .a.nd Z. Zhou. 1995. [Late Mesozoic fish fauna from western Liaoning. China]. Vertebrata PalAsiatica. 33: 169-193. In Chinese with an English summary. Johnson. G. D.. and E. B. Brothers. 1993. Schindleria: A paedomorphic goby (Teleostei: Gobiuidei). Bulletin of Marine Science. 52: 441-471. Johnson. G. D.. and C. Patterson. 1996. Interrelation- ships of lower euteleostean fishes, pp. 251-332. In Stiassny, M. L. J., L. R. Parenti. and G. D. Johnson. eds.. Interrelationships of Fishes. Academic Press. San Diego. California. Johnson. G. H. 1951. An investigation of the mooneye (Hiodon tergisus). Abstracts of the 5th Technical Ses- sion of the Research Council, Ontario, 1951: 16. JoLLiE. M. 1962. Chordate Morphology. Reinhold Pub- lishing Corp., New York. . 1975. Development of the head skeleton and pectoral girdle in Esox. Journal of Morphology, 147: 61-88. Jordan. D. S. 1923. A classification of fishes including families and genera as far as known. Stanford Uni- versity Publication. University Series. Biological Sci- ences. 3: 77-243. Jordan. D. S.. and T Bean. 1877. Hyodontidae. In Jor- dan. D. S., Contributions to North American ichthy- ology based primarily on the collections of the United States National Museum. No. 2. A. — Notes on Cotti- dae, Etheostomatidae. Percidae. Centrarchidae, Apho- doderidae. Umbridae, Esocidae, Dorysomatidae. Cy- prinidae, Catastomidae. and Hyodontidae, with revi- sions of the genera and descriptions of new or little known species. Bulletin of the United States National Museum, 10: 67-68. Jordan, D. S., and C. H. Gilbert. 1883. Synopsis of the fishes of North America. Bulletin of the United States National Museum. 16: 1-1018. Jordan. D. S.. .and B. W. Evermann. 1896. The fishes of North and Middle America. Part 1 . Bulletin of the United States National Museum. 47: 1-1240. JoRD.AN, D. S.. and W. E Thompson. 1910. Note on the gold-eye. Amphiodon alosoides Rafinesque. or Elat- tonistius chrysopsis (Richardson). Proceedings of the National Museum, 38: 353-357. Kajiura. S. M.. and T C. Tricas. 1996. Seasonal dy- namics of dental sexual dimorphism in the Atlantic stingray Dasxalis sabina. Journal of Experimental Bi- ology. 199: 2297-2306. Kenn-edy. W. a., and W. M. Sprules. 1967. Goldeye in Canada. Bulletin of the Fisheries Research Board of Canada, 161: 1-45. Kjtching, I. J., P. L. Forey, C. J. Humpheries. and D. M. Williams. 1998. Cladistics: The Theory and Prac- tice of Parsimony Analysis. 2nd ed. Oxford University Press. Oxford. England. Kint)RED. J. E. 1919. The skull oi Amiurus. Illinois Bi- ological Monographs. 5: 1-120. Kirtl.and. J. P. 1847. Descriptions of the fishes of Lake Erie, the Ohio River, and their tributaries (continued from page 276). Boston Journal of Natural History. 5: 330-344. Kocher. T. D.. A.ND C. A. Stepien. Eds. 1997. Molecular Systematics of Fishes. Academic Press. San Diego, California. Korntield. I. L., D. C. Smith. P. S. Gagnon, and J. N. Taylor. 1982. The cichlid fish of Cuatro Cienegas, Mexico: Direct evidence of conspecificity among dis- tinct morphs. Evolution. 36: 658-664. L.AGLER, K. F 1947. Lepidological studies: 1. Scale char- acters of the families of Great Lakes fishes. Transac- tions of the American Micro.scopical Society, 66: 149-171. 138 FffiLDIANA: ZOOLOGY Lauder, G. V., and K. F. Liem. 1983. The evolution and interrelationships of the actinopterygian fishes. Bul- letin of the Museum of Comparative Zoology, 150: 1-197. Lee, D. S., C. R. Gilbert, C. H. Hocutt, R. E. Jenkins, D. E. McAllister, and J. R. Stauffer, Jr. 1980. At- las of North American Freshwater Fishes. North Car- olina Biological Survey, Raleigh. Lekander, B. 1949. The sensory line system and the canal bones of the head of some Ostariophysi. Acta Zoologica, Stockholm, 30: 1-131. Lesueur, C. a. 1818. Descriptions of several new spe- cies of North American fishes. Journal of the Acade- my of Natural Sciences of Philadelphia, 1: 359-368. Li, G.-Q. 1987. [A new genus of Hiodontidae from Luo- zigou Basin, East Jilin]. Vertebrata PalAsiatica, 25: 91-107. In Chinese with an English summary. . 1994. New osteoglossomorphs (Teleostei) from the Upper Cretaceous and Lower Tertiary of North America and their phylogenetic significance. Ph.D. diss.. University of Alberta, Edmonton, Canada. Li, G.-Q., and M. V. H. Wilson. 1994. An Eocene spe- cies of Hiodon from Montana, its phylogenetic rela- tionships, and the evolution of the postcranial skeleton in the Hiodontidae (Teleostei). Journal of Vertebrate Paleontology, 14: 153-167. . 1996a. Phylogeny of Osteoglossomorpha, pp. 163-174. //; Stiassny, M. L. J., L. R. Parenti, and G. D. Johnson, eds.. Interrelationships of Fishes. Aca- demic Press, San Diego. California. . 1996b. The discovery of Heterotidinae (Teleos- tei: Osteoglossidae) from the Paleocene Paskapoo For- mation of Alberta, Canada. Journal of Vertebrate Pa- leontology, 16: 198-209. . 1999. Early divergence of Hiodontiformes sen- sit stricto in East Asia and phylogeny of some Late Mesozoic teleosts from China, pp. 369-384. In Ar- ratia, G.. and H.-P Schultze. eds., Mesozoic Fishes. 2. Systematics and Fossil Record. Verlag Pfeil, Munich. Li, G.-Q., M. V. H. Wilson, and L. Grande. 1997. Re- view of Eohiodon (Teleostei: Osteoglossomorpha) from western North America, with a phylogenetic re- assessment of Hiodontidae. Journal of Paleontology, 71: 1109-1124. Liem, K. F, W E. Bemis, W F Walker, and L. Grande. 2001. Functional Anatomy of the Vertebrates: An Evolutionary Perspective, 3rd ed. Harcourt College Publishers, Philadelphia. Ma, F. 1980. [A new genus of Lycopteridae from Ning- xia, China.] Vertebrata PalAsiatica. 18: 286-295. . 1987. Review of Lvcoptera davidi. Vertebrata PalAsiatica. 25: 8-19. Mabee, p. M., E. Aldridge, E. Warren, and K. Helen- URM. 1998. Effect of clearing and staining on fish length. Copeia, 1998: 346-353. Maisey, J. G. 1999. The supraotic bone in neopterygian fishes (Osteichthyes. Actinopterygii). American Mu- seum Novitates, 3267: 1-52. McAllister, D. E. 1968. The evolution of branchios- tegals and associated opercular, gular, and hyoid bones and the classification of teleostome fishes, living and fossil. Bulletin of the National Museum of Canada, 221: 1-239. Mettee, M. F, R E. O'Neil, and J. M. Pierson. 1996. Fishes of Alabama and the Mobile Basin. Oxmoor House, Birmingham, Alabama. Monod, T. 1968. Le complex urophore des poissons te- leosteens. Me'moires de I'Institut Fondamental d'Afrique Noire, 81: 1-705. Moon, D. N., S. J. Fisher, and S. C. Krentz. 1998. Assessment of larval fish consumption by goldeye (Hiodon alosoides) in two Missouri River backwaters. Journal of Freshwater Ecology, 13: 317-321. Moore, G. A. 1944. The retinae of two North American teleosts, with special reference to their tapeta lucida. Journal of Comparative Neurology, 80: 369-379. Moore, G. A., and R. C. McDougal. 1949. Similarity in the retinae of Amphiodon alosoides and Hiodon ter- gisus. Copeia, 1949: 298. Moy-Thomas, J. A. 1938. The problem of the evolution of the dermal bones in fishes, pp. 305-319. In de Beer, G. R., ed.. Evolution: Essays on Aspects of Evolu- tionary Biology Presented to Professor E. S. Goodrich on His Seventieth Birthday. Oxford University Press, Oxford, England. MOller, J. 1844. Uber den Bau und die Grenzen der Ganoiden und iiber das naturliche System der Fische. Bericht iiber die zur Bekanntmachung geeigneten Ver- handlungen der Akademie der Wissenschaften, Berlin, 1844: 117-216. . 1846. On the structure and characters of the Ganoidei, and on the natural classification offish. Sci- entific Memoirs, 4: 499-558 [a published English translation of MUller, 1844]. 1847. Fossile Fische. In von Middendorff, A. T, ed., Reise in den aussersten norder und osten Si- biriens wahrend der Jahre 1843 und 1844 (Enster Band). Buchdrukerei der Kaiserlichen Akademie der Wissenschaften, St. Petersburg, Russia. Nelson, G. J. 1968a. Gill arches of teleostean fishes of the division Osteoglossomorpha. Journal of the Lin- nean Society (Zoology), 47: 261-277. . 1968b. Gill-arch structure in Acanthodes, pp. 129-144. In 0rvig, T, ed., Current Problems of Low- er Vertebrate Phylogeny. John Wiley and Sons, New York. . 1968c. Review of "Evolution of branchioste- gals and classification of teleostome fishes." Copeia, 1968: 888-889. . 1969a. Infraorbital bones and their bearing on the phylogeny and geography of osteoglossomorph fishes. American Museum Novitates, 2394: 1-37. . 1969b. Gill arches and the phylogeny of fishes. with notes on the classification of vertebrates. Bulletin of the American Museum of Natural History, 141: 475-552. . 1972a. Observations on the gut of the O.steo- glossomorpha. Copeia, 1972: 325-329. -. 1972b. Cephalic sensory canals, pitlines, and the classification of esocoid fishes, with notes on gal- axiids and other teleosts. American Museum Novita- tes, 2492: 1-49. 1973a. Relationships of clupeomorphs, with re- marks on the structure of the lower jaw in fishes, pp. 333-350. In Greenwood, R H., R. S. Miles, and C. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 139 Patterson, eds.. Interrelationships of Fishes. Academic Press, London. 1973b. Notes on the structure and relationships of certain Cretaceous and Eocene teleostean fishes. American Museum Novitates. 2524: 1-31. Nelson, J. S. 1976. Fishes of the World. John Wiley and Sons, New York. . 1984. Fishes of the World, 2nd ed. John Wiley and Sons, New York. . 1994. Fishes of the World, 3rd ed. John Wiley and Sons, New York. Nelson, J. S., and M. J. Paetz. 1992. The Fishes of Alberta, 2nd ed. University of Alberta Press, Edmon- ton. Nixon, K. C, and J. I. Davis. 1991. Polymorphic taxa, missing values and cladistic analysis. Cladistics, 7: 233-241. NoLF, D. 1985. Otolithi Piscium, pp. 1-145. In Schultze, H.-P, ed.. Handbook of Paleoichthyology. Vol. 10. Gustav Fischer Verlag, Stuttgart, Germany. NoRTHCUTT, R. G. 1989. The phylogenetic distribution and innervation of craniate mechanoreceptive lateral lines, pp. 17-78. In Coombs, S., P. Corner, and H. Miinz, eds.. The Mechanoreceptive Lateral Line: Neu- robiology and Evolution. Springer- Verlag, New York. NoRTHCUTT, R. G., AND W. E. Bemis. 1993. Cranial nerves of the coelacanth Ltitimeria chalumnae fOstei- chthyes: Sarcopterygii: Actinistia] and comparisons with other Craniata. Brain, Behavior and Evolution, 42 (suppl. 1): X -H 1-76. Okedl J. 1969. Observations on the breeding and growth of certain mormyroid fishes of the Lake Vic- toria Basin. Revue de Zoologie et de Botanique Af- ricaines, 79: 34-64. 0RV1G, T. 1962. Y a-t-il une relation directe entre les arthrodires ptyctodontides et les holocephales? Col- loques Internationaux du Centre National de la Re- cherche Scientifique, 104: 49-60. OsBORN, H. E 1912. The continuous origin of certain unit characters as observed by a palaeontologist: II. Evidences for continuity. American Naturalist, 46: 249-278. Page, L. M., and B. M. Burr. 1991. A Field Guide to Freshwater Fishes of North America North of Mexico. Houghton-Mifflin Co., Boston. Pankhurst, N. W. 1985. Final maturation and ovulation of oocytes of the goldeye, Hiodon alosoides (Rafin- esque), in vitro. Canadian Journal of Zoology, 63: 1003-1009. Pankhurst, N. W, N. E. Stacey, and G. Van Der Kraak. 1986. Reproductive development and plasma levels of reproductive hormones of goldeye, Hiodon alosoides (Rafinesque), taken from the North Sas- katchewan River during the open water season. Ca- nadian Journal of Zoology, 64: 2843-2849. Paterson, C. G. 1966. Life history notes on the goldeye, Hiodon alosoides (Rafinesque), in the North Saskatch- ewan River in Alberta. Canadian Field Naturalist, 80: 250-251. Patterson, C. 1968. The caudal skeleton in Lower Li- assic pholidophorid fishes. Bulletin of the British Mu- seum (Natural History), Geology. 16: 201-239. . 1973. Interrelationships of holosteans, pp. 233- 305. In Greenwood, R H., R. S. Miles, and C. Patter- son, eds.. Interrelationships of Fishes. Academic Press, London. -. 1975. The braincase of pholidophorid and lep- tolepid fishes, with a review of the actinopterygian braincase. Philosophical Transactions of the Royal So- ciety of London, 269: 275-597. 1977a. Cartilage bones, dermal bones, and membrane bones, or the exoskeleton versus the en- doskeleton, pp. 77-121. In Andrews, S. M., R. S. Miles, and A. D. Walker, eds.. Problems in Vertebrate Evolution. Academic Press, London. . 1977b. The contribution of paleontology to tel- eostean phylogeny, pp. 579-643. //; Hecht, M. K., P. C. Goody, and B. M. Hecht, eds.. Major Patterns in Vertebrate Evolution. Plenum Publishing Corp., New York. . 1978. Evolution. British Museum (Natural His- tory), London. . 1981a. Significance of fossils in determining evolutionary relationships. Annual Review of Ecology and Systematics, 12: 195-223. 1981b. The development of the North American fish fauna: A problem of historical biogeography, pp. 265-281. /// Forey, P. L., ed.. The Evolving Biosphere. Cambridge University Press, Cambridge, England. 1982. Morphological characters and homology, pp. 21-74. In Joysey, K. A., and A. E. Friday, eds., Problems of Phylogenetic Reconstruction. Academic Press, London. -. 1984. Family Chanidae and other teleostean fishes as living fossils, pp. 132-139. //; Eldredge. N., and S. M. Stanley, eds.. Living Fossils. Springer- Ver- lag, New York. -. 1992. Supernumerary median fin-rays in tele- ostean fishes. Zoological Journal of the Linnean So- ciety, 106: 147-161. Patterson, C, and G. D. Johnson. 1995. The inter- muscular bones and ligaments of teleostean fishes. Smithsonian Contributions to Zoology, 559: 1-85. . 1997a. The data, the matrix, and the message: Comments on Begle's "Relationships of the osmeroid fishes." Systematic Biology, 46: 358-365. -. 1997b. Comments on Begle's "Monophyly and relationships of argentinoid fishes." Copeia, 1997: 401-409. Patterson, C, and D. E. Rosen. 1977. Review of the ichthyodectiform and other Mesozoic fishes and the theory and practice of classifying fossils. Bulletin of the American Museum of Natural History. 158: 81- 172. Pflieger, W. L. 1997. The Fishes of Missouri, rev. ed. Missouri Department of Conservation. Jefferson City. Platnick. N.. C. E. Griswold. and J. A. Coddington. 1991. On missing entries in cladistic analysis. Cladis- tics. 7: 337-343. Popper, A. N., and S. Coombs. 1982. The morphology and evolution of the ear in actinopterygians fishes. American Zoologist, 22: 31 1-328. Poyato-Ariza, F. J. 1999. The elopiform fish "tAnae- thalion angustiis restored, with comments on individ- 140 FIELDIANA: ZOOLOGY ual variation, pp. 361-368. In Arratia, G., and H.-R Schultze, eds., Mesozoic Fishes. 2. Systematics and Fossil Record. Verlag Pfeil, Munich. Rafinesque, C. S. 1818. Discoveries in natural history, made during a journey through the western region of the United States. American Monthly Magazine and Critical Review, 2: 354-356. . 1819. Prodrome de 70 nouveaux genres d'animaux decouvert dans Tinterieur des Etats-Unis d'Amerique durant I'annee 1818. Journal de Physique, Paris, 88: 417-429. -. 1820. Ichthyologica Ohioensis, or Natural His- tory of the Fishes Inhabiting the River Ohio and its Tributary Streams, Preceded by a Physical Description of the Ohio and its Branches. W. G. Hunt, Lexington, Kentucky [1970 facsimile reprint, Arno Press, New York]. Reimchen. J. S., AND J. S. Nelson. 1987. Habitat and morphological correlates to vertebral number as shown in a teleost, Gasterosteus acideatus. Copeia, 1987: 868-874. Richardson, J. 1823. Notice of the fishes, pp. 705-728. In Appendix 6. Appendix to narrative of a journey to the shores of the Polar Sea in the years 1819, 1820, 1821 and 1822. J. Franklin. John Murray, London. . 1836. The Fish, pp. 1-327. In Fauna Boreali- Americana; or the zoology of the northern parts of British America: Containing descriptions of the ob- jects of natural history collected on the late northern land expeditions, under the command of Sir John Franklin, R. N., Part 3. J. Murray, London. RiDEWOOD, W. G. 1 904. On the cranial osteology of the fishes of the families Mormyridae, Notopteridae, and Hyodontidae. Journal of the Linnean Society of Lon- don (Zoology), 29: 188-217. . 1905. On the cranial osteology of the fishes of the families Osteoglossidae, Pantodontidae, and Phractolaemidae. Journal of the Linnean Society of London (Zoology), 29: 252-282. RiEPPEL, O. C. 1988. Fundamentals of Comparative Bi- ology. Birkhauser, Basel, Switzerland. RiEPPEL, O. C, AND L. Grande. 1994. Summary and comments on systematic pattern and evolutionary pro- cess, pp. 227-255. //; Grande, L., and O. Rieppel, eds.. Interpreting the Hierarchy of Nature. Academic Press, San Diego, California. RiEPPEL, O., AND M. Kearney. 2002. Similarity. Biolog- ical Journal of the Linnean Society. 75: 59-82. RiEPPEL, O. C, AND H. Zaher. 2000. The braincase of mosasaurs and Varanus, and the relationships of snakes. Zoological Journal of the Linnean Society, 129: 489-514. Roberts, W. 1989. The mooneye in Alberta. Alberta Naturalist, 19: 134-140. Robinson, H. W., and T M. Buchanan. 1988. Fishes of Arkansas. University of Arkansas Press, Fayetteville. ROHDE, F. C, R. G. Arndt, D. G. Lindquist, and J. F Parnell. 1994. Freshwater Fishes of the Carolinas, Virginia, Maryland, and Delaware. University of North Carolina Press, Chapel Hill. RoHDE, F. C, M. L. Moser, and R. G. Arndt. 1998. Distribution and status of selected fishes in North Car- olina, with a new state record. Brimleyana, 25: 43-68. Rosen, D. E., and P. H. Greenwood. 1970. Origin of the Weberian apparatus and the relationships of the ostariophysan and gonorhynchiform fishes. American Museum Novitates, 2428: 1-25. Sanford, C. p. J. 2000. Salmonid fish osteology and phylogeny (Teleostei: Salmonoidei). Theses Zoologi- cae, 33: 1-264. Schaeffer, B. 1949. A teleost from the Livingston For- mation of Montana. American Museum Novitates, 1427: 1-16. Schultze, H.-P. 1996. The scales of Mesozoic actinop- terygians, pp. 83-93. In Arratia, G., and G. Viohl, eds., Mesozoic Fishes: Systematics and Paleoecology. Verlag Pfeil, Munich. Schultze, H.-R, and G. Arratia. 1988. Reevaluation of the caudal skeleton of some actinopterygian fishes: II. Hiodon, Elops, and Albula. Journal of Morphology, 195: 257-303. . 1989. The composition of the caudal skeleton of teleosts (Actinopterygii: Osteichthyes). Zoological Journal of the Linnean Society, 97: 189-231. Scott, W. B., and E. J. Grossman. 1973. Freshwater Fishes of Canada. Bulletin of the Fisheries Research Board of Canada, 184: 1-966. Sewertzoff, a. N. 1925. The place of the cartilaginous ganoids in the system and evolution of the Ostei- chthyes. Journal of Morphology, 38: 105-145. . 1934. Evolution der Bauchflossen der Fische. Zoologische Jahrbiicher, Abteilung fiir Anatomie und Ontogenie der Tiere, 58: 415-500. Shen, M. 1989. [Eohiodon from China and the distri- bution of Osteoglossomorphs]. Vertebrata PalAsiatica, 10: 237-247. In Chinese with an English summary. . 1996. Fossil "osteoglossomorphs" from East Asia and their implications for teleostean phylogeny, pp. 261-272. In Arratia, G., and G. Viohl, eds., Me- sozoic Fishes: Systematics and Paleoecology. Verlag Pfeil, Munich. Smith, C. L. 1985. The Inland Fishes of New York State. New York State Department of Environmental Con- servation, Albany. Smith, G. R. 1981. Late Cenozoic freshwater fishes of North America. Annual Review of Ecology and Sys- tematics, 12: 163-193. Smith, G. R., and J. G. Lundberg. 1972. The Sand Draw fauna. Bulletin of the American Museum of Natural History, 148: 40-54. Smith, M. M., and B. K. Hall. 1990. Development and evolutionary origins of vertebrate skeletongenetic and odontogenetic tissues. Biological Review, 65: 277- 373 . 1993. A developmental model for evolution of the vertebrate exoskeleton and teeth, pp. 387-448. In Hecht, M. K., R. J. Macintyre, and M. T Clegg, eds.. Evolutionary Biology, vol. 27. Plenum Press, New York. Snyder, D. E., and S. C. Douglas. 1978. Description and identification of mooneye, Hiodon tergisus, pro- tolarvae. Transactions of the American Fisheries So- ciety, 107: 590-594. Starks, E. C. 1926. Bones of the ethmoid region of the fish skull. Stanford University Publications, Univer- sity Series, Biological Science, 4: 139-338. HILTON: OSTEOLOGY OF HIODON LESUEUR, 1818 141 Stewart, J. D. 1999. A new genus of Saurodontidae (Teleostei: tichthyodectiformes) from Upper Creta- ceous rocks of the western interior of North America, pp. 335-360. In Arratia, G., and H.-P. Schultze, eds., Mesozoic Fishes. 2. Systematics and Fossil Record. Dr. Friedrich Pfeil, Munich. Stiassny. M. L. J.. L. R. Parenti, and G. D. Johnson, Eds. 1996. Interrelationships of Fishes. Academic Press, San Diego, California. Storer. D. H. 1846. A synopsis of the fishes of North America. Memoirs of the American Academy, 7: 1- 298. Su. D.-Z. 1986. [The discovery of a fossil osteoglossid fish in China]. Vertebrata PalAsiatica, 24: 10-19. In Chinese with an English summary. . 1991. [A new fossil hiodontid fish from Fuxin Group of western Liaoning, China]. Vertebrata Pal- Asiatica, 29: 38-45. In Chinese with an English sum- mary. Taverne, L. 1977. Osteologie, phylogenese et syste- matique des Teleosteens fossiles et actuels du super- ordre des osteoglossomorphes. Premiere partie. Osteo- logie des genres Hiodon, Eohiodon, Lycoptera, Osteo- glossum, Scleropages, Heterotis et Arapaima. Me- moires de la Classe des Sciences, Academie Royale de Belgique. 42: 1-235. . 1978. Osteologie, phylogenese, et systematique des Teleosteens fossiles et actuels du super-ordre des osteoglossomorphes. Deuxieme partie. Osteologie des genres Phareodiis, Phareoides, Brychaetits, Musperia, Pantodon, Singido, Notopterus, Xenomystus et Papyr- ocnmus. Memoires de la Classe des Sciences, Aca- demie Royale de Belgique, 42: 1-212. -. 1979. Osteologie, phylogenese et systematique des Teleosteens fossiles et actuels du supre-ordre des osteoglossomorphes. Troisieme partie. Evolution des structures osteologiques et conclusions generales rel- atives a la phylogenese et a la systematique du super- ordre. Memoires de la Classe des Sciences. Academie Royale de Belgique, 43: 1-168. 1998. Les osteoglossomorphes marins de FEocene du Monte Bolca (Italie): Monopteros Volta, 1796, Thrissoptems Meckel, 1856 et Foreyichthys Taverne, 1979. Considerations sur la phylogenie des teleosteens osteoglossomorphes. Studi e Ricerche sui Giacimenti Terziari di Bolca, 7: 67-158. Thomas, K. 1983. A nitrocellulose embedding technique for vertebrate morphologists. Herpetological Review, 14: 80-81. Trautman, M. B. 1957. The Fishes of Ohio. Ohio State University Press, Columbus. Wagner, G. R, Ed. 2001. The Character Concept in Evolutionary Biology. Academic Press, San Diego, California. Wagner, H.-J., and M. A. All 1978. Retinal organi- zation in goldeye and mooneye (Teleostei: Hiodonti- dae). Revue of Canadian Biology, 37: 65-85. Wallus, R. 1986. Larval development of Hiodon ter- gisus Lesueur with comparisons to Hiodon alosoides (Rafinesque). Journal of the Tennessee Academy of Science, 61: 77-80. . 1990. Family Hiodontidae, pp. 153-166. In Wallus, R., T P. Simon, and B. L. Yeager, eds.. Re- productive Biology and Early Life History of Fishes in the Ohio River Drainage. Vol. 1. Acipenseridae Through Esocidae. Tennessee Valley Authority, Chat- tanooga. Wallus, R., and J. P. Buchanan. 1989. Contributions to the reproductive biology and early life ecology of mooneye in the Tennessee and Cumberland Rivers. American Midland Naturalist, 122: 204-207. Wassersug, R. J. 1976. A procedure for differential staining of cartilage and bone in whole formalin fixed vertebrates. Journal of Stain Technology, 51: 131- 134. Weitzman, S. H. 1962. The osteology of Bry con meeki, a generalized characid fish, with an osteological def- inition of the family. Stanford Ichthyological Bulletin, 8: 1-77. Westoll, T S. 1962. Ptyctodontid fishes and the ances- try of Holocephali. Nature, 194: 949-952. WiENS, J. J. 1999. Polymorphism in systematics and comparative biology. Annual Review of Ecology and Systematics, 30: 327-362. . 2000. Coding morphological variation within species and higher taxa for phylogenetic analysis, pp. 115-145. In Wiens, J. J., ed., Phylogenetic Analysis of Morphological Data. Smithsonian Institution Press, Washington, D.C. Wiley, E. O. 1976. The phytogeny and biogeography of fossil and Recent gars (Actinopterygii: Lepisosetidae). Miscellaneous Publications of the University of Kan- sas Museum of Natural History, 64: 1-111. . 1981. Phylogenetics: The Theory and Practice of Phylogenetic Systematics. John Wiley and Sons, New York. Williams. K. 1978. Systematics and natural history of the American milk snake Lampropeltis triangulum. Publications in Biology and Geology, Milwaukee Public Museum, 2: 1-258. Wilson, M. V. H. 1977. Middle Eocene freshwater fish- es from British Columbia. Life Sciences Contributions Royal Ontario Museum, 113: 1-61. . 1978. Eohiodon woodnijfi n. sp. (Teleostei, Hiodontidae) from the middle Eocene Klondike Mountain Formation near Republic, Washington. Ca- nadian Journal of Earth Sciences, 15: 679-686. 1980. Oldest known Esox (Pisces: Esocidae), part of a new Paleocene teleost fauna from western Canada. Canadian Journal of Earth Sciences, 17: 307- 312. Wilson, M. V. H., and R. R. Williams. 1992. Phylo- genetic, biogeographic and ecological significance of early fossil records of North American freshwater tel- eostean fishes, pp. 224-244. In Mayden, R., ed., Sys- tematics, Historical Ecology, and North American Freshwater Fishes. Stanford University Press, Stan- ford, California. Winterbottom, R. 1974. A descriptive synonymy of the striated muscles of the Teleostei. Proceedings of the Academy of Natural Sciences of Philadelphia, 125: 225-317. Zyznar, E. S.. F B. Cross, and J. A. C. Nicol. 1978. Uric acid in the tapetum lucidum of mooneyes Hiodon (Hiodontidae, Teleostei). Proceedings of the Royal So- ciety of London, Series B, 201: 1-6. 142 FIELD! AN A: ZOOLOGY Field Museum or 'Natural nisiory 1400 South Lake Shore Drive Chicago, Illinois 60605-2496 Telephor- '"'^^ ..-- — --