WAPITIODIDAE, Mutter & Blanger & Neuman, 2007

Mutter, Raoul J., Blanger, Keith De & Neuman, Andrew G., 2007, Elasmobranchs from the Lower Triassic Sulphur Mountain Formation near Wapiti Lake (BC, Canada), Zoological Journal of the Linnean Society 149 (3), pp. 309-337 : 326-328

FAMILY WAPITIODIDAE FAM. NOV.

GEN. ET SP. INDET.

Type stratum: From within the Vega-Phroso Siltstone Member of the Sulphur Mountain Formation , Wapiti Lake , British Columbia .

Age:?Smithian–?Spathian.

Referred specimens: TMP 83.205.62, UALVP 46530 (thin sections UALVP 46530- T 1/ T 2) and UALVP 46534. Isolated teeth: TMP 88.98.51 (thin section - T 1), UALVP 17933–17935, UALVP 46537 and UALVP 46538.

Description: Specimen UALVP 46530 represents a partial posterior body portion including the proximal part of the caudal fin. From front to back the specimen measures 330 mm in length. The anteriormost portion consists of a set of dorsally reclining interdorsal elements with associated basiventrals. The interdorsals are reduced in size posteriad and recline at an angle of 31° to the longitudinal axis of the body. The first visible fin supports (elements 1–6) are only partially preserved – the lower section connecting to the neural spines is missing. The vertebral column curves upwards at the anterior end of the caudal fin elements. There are 17 visible supporting elements. The posteriormost section of the fin is not preserved. The smallest caudal element is 17 mm in length (from the base of the preserved interdorsal) and the largest is 30 mm in length. Although incompletely preserved, it is clear that these radials are far larger and wider in the anterior portion of the caudal fin than the posterior supporting elements. The basiventrals lie at equal but opposite angles to the longitudinal axis of the body compared with the interdorsals, and extend into the lower fin supporting elements. The lower elements lie at an angle of 46° to the longitudinal axis of the body. All lower elements lack the lower portion, and the amount that is missing increases posteriad in each element.

The dermal denticle morphology is similar to that seen in specimen UALVP 46527 ( W. aplopagus gen. et sp. nov.). Although incompletely preserved, the caudal peduncle also yields denticles found in W. aplopagus gen. et sp. nov., but is also similar in its slender body shape to W. homalorhizo sp. nov. However, there are no diagnostic features preserved to identify the species.

Specimen UALVP 46534 probably represents an anal fin ( Fig. 16 ), and may be referred to as Wapitiodus gen. nov., because its shagreen of denticles shows a structure similar to holotype TMP 97.74.10 ( W. aplopagus gen. et sp. nov.) and matches the overall size and shape of that anal fin. Yet the internal structure of the anal fin is not visibly preserved in any specimen (other than UALVP 46534) clearly referable to Wapitiodus gen. nov. All three specimens discussed here resemble each other closely in denticle morphology, which justifies their inclusion in the same group (although they are not identifiable at either the genus or species level). The structure and arrangement of seven slender/acuminate radials suggest that the entire series of distal radials in the anal fin may not be preserved. The outline and arrangement of basiventrals closely matches the pattern observed in W. aplopagus gen. et sp. nov., however. The denticles on the anal fin also closely resemble those found covering the dorsal fin of TMP 97.74.10. The internal structure of the anal fin is either not preserved or only poorly preserved ( TMP 97.74.10) in all other specimens assigned to Wapitiodus gen. nov., and the avail- able material does not allow the identification and comparison of species-specific features.

Specimen TMP 83.205.62 is a partial tail including the anal fin and measures about 300 mm in length. We found that 25 of at least 29 calcified elements are visibly preserved in the upper lobe of the tail, and the anal fin is quite deep but short ( Fig. 17 ). The caudal fin is composed of a very short lower lobe, somewhat deeper than the anal fin. The upper lobe is only partly preserved, but seems to have been long and well developed with respect to the extent of calicification in the preserved hypochordal elements.

Furthermore, isolated teeth have been recovered from the scree (see list in referred specimens). In concert with their crown morphology they can be unequivocally assigned to Wapitiodidae fam. nov.

Several isolated wapitiodid or polyacrodontid teeth were found and are all partly embedded in matrix ( Fig. 18A, B ). Many of these teeth may possess lateral cusps or cusplets, but the teeth in general conform to a polyacrodontid type with more or less asymmetric crown morphology. None of the teeth are further identifiable. Tooth ultrastructure reveals a rather primitive condition with the variably thick enameloid layer (referred to as ‘single-crystallite-enamel’ by some authors) covering the partly orthodont/osteodont crown and the osteodont root ( Fig. 18 ). In tooth histology, wapitiodid teeth appear indistinguishable from polyacrodontid teeth (see below and Fig. 18 ).

CLASS CHONDRICHTHYES HUXLEY, 1880 SUBCLASS ELASMOBRANCHII BONAPARTE, 1838 SUPERFAMILY HYBODONTOIDEA OWEN, 1846 FAMILY POLYACRODONTIDAE GLIKMAN, 1964 ? POLYACRODUS JAEKEL, 1889 SP. INDET.

Type stratum: From within the Vega-Phroso Siltstone Member of the Sulphur Mountain Formation , Wapiti Lake , British Columbia .

Age:?Smithian–?Spathian.

Referred specimens: TMP 88.98.51 (thin section - T 1), UALVP 19191 (but see Material and Methods; some fragmentary teeth that are listed and referred to Elasmobranchii appear polyacrodontid, but cannot be identified with certainty).

Tentatively referred specimens: TMP 88.98.52,

TMP 88.98.60, TMP 89.127.42, TMP 89.127.45, TMP 89.127.52 and TMP 2001.21.17.

Description: Specimen UALVP 19191 comprises a few long thin skeletal elements (probably ribs), a few unidentifiable pieces of scattered cartilages and one partially preserved tooth. These elements are not associated but are simply preserved on the same slab. All three of the long thin skeletal elements have a longbow shape, but two of them have an abbreviated shape and an opposite curvature at the end forming an ‘S’ shape. None of the elements have the distal end preserved, but the shape suggests that the distal end would taper to a point in some elements. The longest element measures 88 mm from end to end, with the other two being 66 mm and 47 mm, respectively. It is the two shorter ones that have S-shaped ends. Assuming these elements are ribs belonging to the same specimen, and if compared with similar-sized elements in Hybodus (Agassiz, 1837) , this shark would have measured at least 1.4–1.5 m in total length.

The tooth conforms to the general Polyacrodus (not Palaeobates , see the Discussion) morphology. It is 6 mm in length, but is only partially preserved and was probably about 10 mm in length originally. The crown is 2 mm long (assessed, because the apex of the main cusp is missing) and the root is approximately 2 mm deep. The tooth is probably seen in labial view because the crown projects out at the bottom creating a slight overhang over the base. The main cusp is pyramidal and is either vertical or very slightly posteriorly reclining. There is only one ridge descending from the main cusp that extends into a projection on the (labial and/or lingual) face of the cusp. Besides this ridge the main cusp is free of ornamentation. Only one side of the crown is preserved. On this side there are five visible lateral cusplets, each getting progressively smaller in size. There may be several other very small secondary cusplets at the far end giving a serrated structure to the extreme ends of the teeth. Each of the secondary cusplets also has one ridge descending from it and forming progressively smaller pegs. The crown is otherwise free of ornamentation.

In the centre of the base there appears to be a single long row of regular foramina. By the second lateral cusplet these foramina cease to be single, clear and long, and degenerate into a series of seemingly randomly placed circular foramina. The lower, randomly placed foramina appear to be bigger than the upper ones.

Specimen TMP 88.98.51 (see Fig. 18B ) is a single, isolated tooth. In outline, the tooth is fairly short and has a slightly elevated central cusp. As can be seen from the thin section, the centre of the crown shows an intermediate condition between orthodont (at the apex) and osteodont (root). In the literature, polyacrodontid teeth are described as ‘mainly orthodont’ ( Jaekel, 1889; Stensiö, 1921; Rieppel, 1981).

CLASS CHONDRICHTHYES HUXLEY, 1880 SUBCLASS ELASMOBRANCHII BONAPARTE, 1838 SUPERORDER?CTENACANTHOIDEA ZANGERL, 1981

Figures

Figure 16. Indetermined?Wapitiodus gen. nov.: almost complete anal fin as preserved in specimen UALVP 46534. Anterior is to the left.

Figure 17. Wapitiodus aplopagus gen. et sp. nov. (specimen TMP 83.205.62): photograph (A) and drawing (B) of the partially preserved caudal fin showing the number and arrangement of?interventrals (iv) and radials (rad) in the tail. Anterior is to the left. See the Appendix for the abbreviations.

Figure 18. Morpho-histology of teeth (cf. Fig. 2). A, Wapitiodus aplopagus gen. et sp. nov.: an isolated tooth in labial view (holotype specimen TMP 97.74.10). B, Polyacrodontidae gen. et sp. indet.: vertical section through an isolated tooth, specimen TMP 88.98.51. Note that the root and most of the crown is osteodont. C–E, Polyacrodontidae gen. et sp. indet.: various scanning electron microscopy (SEM) magnifications of the SLE in specimen TMP 88.98.51 (white asterisks mark the same position in B–E). Abbreviations: ORT, orthodentine; OST, osteodentine; SLE, single layer enameloid.