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Novtatesamerican MUSEUM PUBLISHED by the AMERICAN MUSEUM of NATURAL HISTORY CENTRAL PARK WEST at 79TH STREET, NEW YORK, N.Y NovtatesAMERICAN MUSEUM PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2878, pp. 1-39, figs. 1-19 June 5, 1987 Cranial Anatomy of the Lower Jurassic Shark Hybodus reticulatus (Chondrichthyes: Elasmobranchii), with Comments on Hybodontid Systematics JOHN G. MAISEY1 ABSTRACT Hybodus reticulatus Agassiz, from the LowerJu- species ofHybodus. Some differences are noted in rassic of England, is considered to be the type the detailed arrangement ofthe lateral otic process, species ofHybodus. It is founded on skeletal frag- cephalic spines, and ethmopalatine articulation in ments and associated teeth. The cranial anatomy H. reticulatus and H. basanus. These differences is described from several incomplete specimens, are considered to be of systematic importance; H. including some of the type material. Two speci- basanus and H. fraasi are placed in a new genus, mens from the Upper Lias ofGermany are referred Egertonodus, on the basis of several differences to H. cf. reticulatus. Comparisons are made with from H. reticulatus. The genus Hybodus remains the Lower Cretaceous Hybodus basanus, whose an assemblage of nominal species, but increased cranial morphology is more completely known. anatomical data will gradually alleviate this situ- The neurocranium and jaws are similar in these ation. A list of genera retained within the Hybo- species, suggesting that many of the anatomical dontidae is given. Hybodontid tooth histology is peculiarities noted in the ethmoid and otico-oc- reviewed, and forms the basis of a phylogenetic cipital regions of H. basanus characterize a larger hypothesis which is open to falsification by other group of hybodontid sharks, including the type anatomical data. INTRODUCTION Hybodus is a species-rich genus of Meso- upon isolated teeth and fin-spines. A few zoic elasmobranchs. Most of these nominal species are known from more complete skel- taxa are dubious, however, being founded etal material, such as H. reticulatus, H. de- I Associate Curator, Department of Vertebrate Paleontology, American Museum of Natural History. Copyright C American Museum of Natural History 1987 ISSN 0003-0082 / Price $4.00 2 AMERICAN MUSEUM NOVITATES NO. 2878 labechei, and H. hauffianus from the Lower Hybodus reticulatus is one ofseveral species Jurassic (Agassiz, 1837; Charlesworth, 1839; occurring in the Lower Lias of Lyme Regis Day, 1864; Woodward, 1889a, 1889b; Fraas, in Dorset, England. There are also some early 1889, 1896; Brown, 1900; Jaekel, 1906; Ko- references to H. reticulatus from the Upper ken, 1907), H.fraasi from the Upper Jurassic Lias of Germany; fin spines and a fragment (Koken, 1907; Maisey, 1986), and H. ba- of mandible with teeth from Ohmden were sanus from the Lower Cretaceous (Egerton, described by Quenstedt (1858, p. 222, pl. 27, 1845; Woodward, 1889a, 1916, 1919; Mai- fig. 1; 1885, p. 274, pl. 21, fig. 1). Woodward sey, 1982, 1983). (1889a, p. 268) also noted "an undetermined There are a number ofproblems surround- species allied to Hybodus reticulatus" from ing the nomenclature and type species ofHy- the Upper Lias of Boll, Wiirtemberg, repre- bodus. The name first appears in Alberti sented by BM(NH) P5880. According to Fraas (1834), where H. plicatilis is quoted without (1896), all these German specimens are re- description from a then-unpublished Agassiz ferable to another species, H. hauffianus. The manuscript. The species name is thus un- latter has since become known from magnif- available as an indicator for the genus in that icent complete specimens (Brown, 1900; Ko- work. Hybodus was first defined (along with ken, 1907; Hauff and Hauff, 1981), and is 20 nominal species, including H. plicatilis) widely envisioned as a "typical" shark ofthe by Agassiz (1837), but a type species was not Mesozoic (e.g., Romer, 1945; Gregory, 1951; designated. Some authors have subsequently Schaeffer, 1967). Fraas (1896) distinguished regarded H. plicatilis as the type species (e.g., H. hauffianus from H. reticulatus on strati- Glikman, 1967), but Woodward's (1916, p. graphic grounds and on differences in the teeth 4) designation ofH. reticulatus takes priority. and fin spines. Hybodus reticulatus is consequently retained A recently acquired specimen at the Staat- here as the type species of Hybodus. liches Museum fur Naturkunde (Stuttgart; Of the 20 original Hybodus species de- catalog no. 52460) has more gracile and acu- scribed by Agassiz (1837), 17 are founded minate teeth than H. hauffianus from the same partly or entirely upon teeth or partial den- stratigraphic horizons (see latter part of this titions. The remaining three species were paper). The teeth of this specimen are rem- based on fin spines; none ofthese species are iniscent of H. reticulatus in having vertical considered taxonomically reliable (Wood- lingual and labial striations confined to the ward, 1889a, p. 250; Maisey, 1978). lower two-thirds of the crown (cf. H. hauffi- Koken (1907, p. 4) commented that H. re- anus teeth which are more extensively striat- ticulatus was widely regarded as the type ed and have relatively shorter cusps; Fraas, species of Hybodus, and was extremely crit- 1896). Other Hybodontidae with similar teeth ical of Jaekel's (1889) proposal to relegate to H. reticulatus include H. plicatilis (Mu- Hybodus to a form genus of fin spine, partic- schelkalk of Germany and France) and H. ularly since Jaekel's (op. cit.) new genus Or- basanus (Wealden of Southern England). thybodus supposedly included Hybodus retic- Fortuitously, H. reticulatus is represented ulatus (see comments on taxonomy in the by a number of incomplete skeletons and latter part of this work). Thus the grounds skeletal fragments associated with teeth, all for regarding H. reticulatus as the type species from Lyme Regis (the type locality). Only of Hybodus are well established. material having teeth identical with Agassiz's From a pragmatic viewpoint, Woodward's original specimens has been included in the (1916) proposal is highly justified: (1) the present hypodigm. species has page priority over others founded upon teeth; (2) it is one of the three original species known both from teeth and fin spines; ACKNOWLEDGMENTS (3) it is represented by skeletal material (in- I thank Drs. Patterson and Forey for per- cluding some of the original specimens), un- mitting preparation and study of H. reticu- like the majority of other Hybodus spp.; and latus specimens in the British Museum (Nat- (4) it is the first Hybodus species to be reliably ural History), and for allowing me to borrow figured (in de la Beche, 1822). material for closer examination. My thanks 1987 MAISEY: CRANIAL ANATOMY OF HYBODUS RETICULATUS 3 are also extended to Dr. Powell (Oxford), Dr. crm mesial crest M. D. Crane (Bristol City Museum and Art crp posterior crest Gallery), and Ms. Alison Longbottom (Brit- csp cephalic spine ish Museum) for their efforts in tracking down ebr epibranchial ect pr ectethmoid process actual and purported Agassiz type specimens. end f endolymphatic fossa Dr. R. Wild kindly allowed me to study the ethp pr ethmopalatine process Holzmaden sharks in the Stuttgart collection feha foramen for efferent hyoidean artery including the new specimen resembling H. fica foramen for internal carotid artery reticulatus, and Dr. P. Wellnhofer generously fm foramen magnum allowed me access to the holotype ofH.fraasi fora foramen for orbital artery in Munich. Preparation of BM(NH) and glda groove for lateral dorsal aorta Stuttgart specimens was undertaken at the hbr hypobranchial American Museum by Walter Sorensen and hym VII hyomandibular branch of facial nerve Ed Pederson. Illustrations were prepared by hyp 1 hypotic lamina Ellen Garvens, Peter Goldberg, and Frank hy r hyoid rays jc jugular canal Ippolito. The manuscript was typed by Ale- lab labial cartilage jandra Lora and edited by Brenda Jones. This 11 lateral lobe work is an integral part of a project concern- lm mesial lobe ing Mesozoic Hybodontidae, and is funded lot pr lateral otic process by the National Science Foundation (Award lp posterior lobe no. BSR 8308419). I thank Drs. G. Johnson Mc Meckel's cartilage (University of South Dakota) and B. Schaef- mil lateral marginal indentation fer (AMNH) for critically reviewing the MS, mim mesial marginal identation and Drs. L. Herman and P. Meylan (AMNH) not c notochordal canal for discussing the nomenclatural situation. not f notochordal foramen oc ar occipital arch oc cot occipital cotylus ABBREVIATIONS olfc olfactory canal Institutional ot cap otic capsule pbr pharyngobranchial AMNH American Museum ofNatural History po pr postorbital process BCM Bristol City Museum, England pq palatoquadrate BM(NH) British Museum (Natural History) pr cf precerebral fontanelle MCZ Museum of Comparative Zoology, prf com prefacial commissure Harvard q con quadrate concavity OUM Oxford University Museum, England q fl quadrate flange SMNS Staatliches Museum fuir Naturkunde in rb rostral bar Stuttgart sc scapulocoracoid sof spino-occipital foramen Anatomical sp c spinal canal acl accessory lateral cusp sub s suborbital shelf acm accessory mesial cusp sup cr supraorbital crest add f adductor fossa t teeth afsp anterior fin spine vgf vagus-glossopharyngeal fossa art cot articular cotylus II optic nerve art k articular knob V trigeminal nerve art pr articular process VII facial nerve ba barb IX glossopharyngeal nerve bh basihyal X vagus nerve bp basal plate c crown Orientation (teeth) cbr ceratobranchial ch ceratohyal lab labial cik caudal internasal
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