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Jmmv19783905.Pdf https://doi.org/10.24199/j.mmv.1978.39.05 7 July 1978 DETAILED COMPARISONS OF THE DENTITIONS OF EXTANT HEXANCHID SHARKS AND TERTIARY HEXANCHID TEETH FROM SOUTH AUSTRALIA AND VICTORIA, AUSTRALIA (SELACHII: HEXANCHIDAE) By Noel R. Kemp Tasmanian Museum, G.P.O. Box 1164M, Hobart, 7001, Australia Abstract In extant hexanchid sharks except for (usually) a bigger primary cusp, isolated teeth of a given size of the smaller species Hexanchus vitulus (Springer and Waller) may be confused with those of H. griseus (Bonnaterre). This specific size difference has significance in the fossil record. Heptranchias perlo (Bonn.) differs in its more slender and relatively larger primary cusp with basal denticles (not serrations as in Hexanchus) on its mesial margin and fewer crownlets increasing and then decreasing in size distally. Notorynchus cepedianus (Peron) differs mainly in its more robust primary cusp and crownlets which are fewer in number than in Hexanchus and which decrease evenly in size distally, like Hexanchus. Cali- fornian specimens of Notorynchus are included in the monotypic TV. cepedianus until the taxonomic significance of the variability of the upper medial teeth is established and defined. N. cepedianus is recorded from the fossil record for the first time. Heptranchias haswelli Ogil- by is regarded as a species inquirenda. Hexanchus agassizi Cappetta is expanded to include the Eocene Hexanchus teeth from South Australia. Heptranchias howellii (Reed) from the South Australian Eocene and Notorynchus primigcnius (Agassiz) from the Victorian Mio- cene are recorded and described from Australia for the first time. Introduction Compagno (1973) lists two families in the suborder Hexanchoidei; Hexanchidae, with The sixgill and sevengill sharks of the family two genera, Hexanchus and Notorynchus and Hexanchidae, although a relatively small group, Heptranchidae with the monotypic genus Hep- are well represented in the fossil record, es- tranchias. He based this separation of Hep- pecially outside Australia, for example Wood- tranchias into its own family on a suggestion ward (1886), Jordan (1907), Leriche (1910, by Dr Shelton P. Applegate 'because of many 1927, 1957) and are common in modern seas, differences in cranial and external morphology for example Garman (1913), Bigelow and between it and the other hexanchoids {Hexan- Schroeder (1948), Whitley (1968), Bass, D'- chus and Notorynchus)' (Compagno, 1973:33). Aubrey and Kistnasamy (1975). Taxonomic- Recently Bass et al. (1975) suggest that more ally, however, they are not a stable group (see detailed anatomical studies of the six- and below). sevengill sharks may show that the smaller Less than a dozen fossil hexanchid teeth species of Hexanchus, H. vitulus, may have have been described from the Australian fossil more in common with Heptranchias perlo than (Pledge, 1967; Kemp, 1970). Three record with the larger species, Hexanchus griseus. H. teeth and several fragments from the Eocene of griseus, on the other hand, may have more in were assigned by Pledge (1967) South Australia common with Notorynchus cepedianus. Until 'Notidanus' serratissimus Ag., cf. serra- to W these suggestions are confirmed or repudiated serritissimus. The three tissimus and W? by further detailed work the suprageneric clas- the Miocene of Victoria were fragments from sification adopted here is that of Patterson described Kemp (1970) as Notorynchus cf. by (1967). primigenius. In light of recent publications (Welton, 1974; Cappetta, 1976) and with the Terminology recovery of further specimens from the South Australian Eocene during the last decade, the The tooth types medials, laterals and pos- present study shows that the three extant gen- teriors are used in the sense of Applegate termed la- era are represented in the South Australian and (1965a). The faces of a tooth are Victorian Tertiary material. bial and lingual and the margins mesial and 61 62 NOEL R. KEMP basal primary cusp entire denticles \ crow nlets ma T crown root LABIAL LINGUAL serrations ingual thickening mesial + distal MESIAL LABIAL Figures 1-4—Terminology. Abbreviations 1-3. Notarynchus cepedianus (Peron), The following abbreviations are used: AMS, lower right second lateral tooth (Figs. 1, 2, x2;Fig. 3, xl-5). Australian Museum, Sydney; AUGD, Univer- 4. Hexanchus agassizi Cappetta, lower left sity of Adelaide, Department of Geology; CM, lateral of about fourth, fifth or sixth row Canterbury Museum, Christchurch, New Zea- (xl-5). land; MUGD, University of Melbourne, De- partment of Geology; NMV, National Museum distal as defined by Hoojier (1954). In the of Victoria, Melbourne; NZNM, National Mu- cockscomb-like dentition of the hexanchids the seum of New Zealand, Wellington; RJFJ, pri- larger primary cusp is followed by a number of vate collection of Dr R. J. F. Jenkins, South crownlets (Applegate, 1965b). The mesial mar- Australia; SAMD, South Australian Depart- gin of the primary cusp may be serrated, or, if ment of Mines; SAM, South Australian Mu- the serrations are relatively large, they are seum, Adelaide; TFF, private collection of Mr termed basal denticles. A character of the T. F. Flannery, Beaumaris, Victoria; USNM, family is the presence of one series of func- United States National Museum, Washington. tional teeth in both jaws except for the upper Systemalics medials which have two or three and the Order HEXANCHIFORMES posteriors of both jaws which have two Suborder HEXANCHOIDEI to four functional series. The description of dentition of Hexanchus griseus is given in de- Family HEXANCHIDAE tail as a datum for the diagnoses of the other The Hexanchidae are characterized by six species. or seven gill-openings and heterodont denti- SOUTH-EASTERN AUSTRALIAN HEXANCHID SHARKS 63 tion, that is the teeth are of dissimilar shape Genera both within and between the two jaws. Except Rafinesque (1810) erected two genera, Hex- for another two families all other sharks have anchus and Heptranchias, based on six- and only five gill openings. sevengill sharks respectively. Cuvier (1817, The Chlamydoselachidae, or frill shark, of fide Bigelow and Schroeder, 1948) included which only one specimen has been recorded both of these genera in his new genus Noti- from Australian waters, in 1976 (J. R. Paxton, danus. This genus also came to include an- pers. comm.), has a terminal mouth compared other sevengill shark, Notorynchus, both before with the subterminal mouth of all other sharks and after Ayres (1855) described it as a new and six gill openings with the first opening con- genus. Subsequent studies showed that the tinuous across the throat. The remaining five three genera of Rafinesque and Ayres were openings are interrupted on the ventral sur- valid and Cuvier's Notidanus has not been face. The dentition of Chlamydoselachus, the used for extant sharks for more than half a single genus of the family, is homeodont, that century. Palaeontologists have until recently is all the teeth are of similar shape both within used Notidanus as an encompassing genus, for and between the two jaws. example Leriche (1957), Casier (1966), Cap- The Pristiophoridae, or saw sharks, has a petta et al. (1967) (fide Cappetta 1970), sixgill genus, Pliotrema, which has yet to be Pledge (1967), as it was widely held that sep- found in Australian waters. It is easily sepa- aration of the genera of hexanchids was only rated from the sixgill hexanchid species by possible on the basis of the anatomy of their its two dorsal fins, rostral snout with barbells soft parts. A number of authors, however (Ap- and marginal teeth, homeodont dentition and plegate 1965b; Waldman 1970; Welton 1974; no anal fin. The hexanchids have only one dor- Cappetta 1975) have noted some of the sa- sal fin, no rostral snout and possess an anal lient dental differences, mainly in the lower fin. lateral teeth, between these three genera. An- Main characters tunes and Jonet (1969), in describing Miocene teeth from Portugal, include in the family Hex- One dorsal fin, always posterior to pelvics; anchidae only two genera, Hexanchus Rafines- anal fin present; caudal fin with a definite lobe que and Heptranchias Rafinesque. They in- and well marked subterminal notch pre- ; clude Notorynchus Ayres in the latter genus caudal pit absent; six or seven gill-openings but give no reason for this. not connected ventrally, last gill opening in As set out in the key below the sixgill genus front of and extending below pectoral origin; is readily separated from the two sevengill spiracle present but small; nictitating mem- genera which differ from each other in the brane absent; upper labial furrow absent, lower shape and size of their snouts. The descriptions labial furrow present, developed to varying de- under each genus further differentiates them on grees. their dental characteristics. Dentition heterodont: upper jaw, teeth with slender primary cusp and a variable number KEY TO LIVING GENERA of small crownlets; small medial tooth present (After Bigelow and Schroeder, 1948). or absent; lower jaw, teeth basically trapezoi- dal in outline and multicusped; small medial 1 A Six gill-openings Hexanchus tooth present. Small undifferentiated posterior IB Seven gill-openings 2 teeth present in both jaws. As all species of hexanchids possess a simi- 2A Head narrow; snout tapering; hori- lar pavement-like dentition formed by the zontal diameter of eye considerably posteriors in both jaws and as they are rarely greater than distance between nos- recognized in the fossil record, teeth of this trils Heptranchias type are omitted in the following descriptions 2B Head broad; snout broadly rounded; and diagnoses. horizontal diameter of eye consider- 64 NOEL R. KEMP ably smaller than distance between bulge forward exactly as shown by the South nostrils Notorynchus African H. vitulus (Bass et al, 1975, PI. 3B). In one specimen of H. vitulus (USNM 1 12600) Genus HEXANCHUS Rafinesque, 1810 the upper medials do protrude but only slightly, Hexanchus Rafinesque, 1810:14; type species much less so than in the Victorian H. griseus. Squalus griseus Bonnaterre, 1788.
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