Scyliorhinotheca goederti, Kiel & Peckmann & Simon, 2013

Kiel, Steffen, Peckmann, Jörn & Simon, Klaus, 2013, Catshark egg capsules from a Late Eocene deep-water methane-seep deposit in western Washington State, USA, Acta Palaeontologica Polonica 58 (1), pp. 77-84 : 80

Scyliorhinotheca goederti gen. et sp. nov.

Figs. 1–3 .

Etymology: For James L. Goedert, who discovered these fossils.

Holotype: Almost complete internal mold USNM 544321 ( Fig. 1A ).

Paratypes: Internal and external molds; all figured specimens are deposited in the USNM (numbers 544322 to 544328); additional specimens are deposited at SMF ( P9796 to P9798 ), UWBM (95285 to 95287) and at GMUG ( GZG.IF.11020) .

Type locality: The Bear River seep deposit, southwestern Washington State, USA (46°19.943 N, 123°55.964 W). This is LACM locality number 5802 and UWBM locality number C1459 .

Type horizon: Siltstone of Cliff Point, latest Eocene (nannofossil zone CP15b of Okada and Bukry 1980), based on the presence of Isthmolithus recurvus ).

Diagnosis.—The egg capsules have an inflated fusiform shape and a slightly constricted waist; the maximum dimensions are: length = 50 mm, width = 15 mm, thickness = 11 mm. The surface shows at least 12 rough ridges and two thin secondary ridges. The lateral edges extend to narrow lateral flanges along the entire length of the egg case. The anterior border is slightly concave, with two well−developed respiratory fissures but apparently no horns; the posterior end is tapering after a slight constriction, and the horns are short and pointing at, or twisting around, each other.

Discussion.—We have seen no tendrils on either end of the egg capsules, but this may be a preservational artefact. The most similar egg capsules produced by modern catsharks are those of the scylorhinid genus Apristurus : many have a similarly tapering posterior end, and some show coarse ribs on the surface ( Sato et al. 1999; Iglésias et al. 2002, 2004; Flammang et al. 2007). Fossil teeth attributed to the genus Apristurus are known from the Late Eocene of European Tethys ( Adnet et al. 2008), which agrees with the stratigraphic age of the egg capsules reported here. The only other extant scylorhinid with a fossil record ranging into the Eocene, including the Pacific Northwest of the United States, is Scyliorhinus ( Welton 1972; Adnet et al. 2008); although the egg capsules of this genus resemble those of Apristurus in general shape ( Rusaouën et al. 1976; Ebert et al. 2006), they are apparently smooth (cf. Treude et al. 2011). Similar in outline are the egg capsules of two species of the genus Schroederichthys ( S. tenuis and S. maculatus ), but on their surfaces the egg capsules show only tortuous longitudinal striations ( Springer 1966; Gomes and de Carvalho 1995) instead of strong ribs as in the Bear River specimens.

Figures

Fig. 1. The Late Eocene Bear River egg capsule Scyliorhinotheca goederti gen. et sp. nov. in different states of preservation. A. Steinkern showing the anterior and posterior ends (USNM 544321). B. Posterior half of a steinkern, showing the tapering end with a horn (USNM 544322). C. Deformed steinkern with spindle−like shape (USNM 544323). D. Steinkern with faint wrinkles on the surface, perhaps due to shrinkage (USNM 544324). E. Two specimens: the lower, main specimen shows the anterior constriction and the flattened anterior end (left) and remnants of the ribbed capsule wall (right); the upper specimen (arrow) is just a cast of a ribbed capsule surface; note relics of worm tubes on the right side of the block (USNM 544325) (image from Treude et al. 2011). F. Steinkern showing indentation on lower left (USNM 544326). G. Cast (external mold) showing ribbing on capsule surface (USNM 544327).

Fig. 2. Silicon rubber casts of external molds of the Late Eocene Bear River egg capsule Scyliorhinotheca goederti gen. et sp. nov. A. USNM 544327 (the same specimen as in Fig. 1). B. USNM 544328.

Fig. 3. Thin section micrographs of the capsule wall of the Late Eocene Bear River egg capsule Scyliorhinotheca goederti goederti gen. et sp. nov. A, B. Two sections of a capsule wall with several ribs, dark, micritic seep carbonate on the outside, and several diagenetic carbonate phases in the interior; plane−polarized light. C, D. Close−up on the middle rib in A, rotated ca. 90° clockwise. Note that the capsule wall consists of microsparite, enclosing globular calcite crystals; plane−polarized light (C) and UV light (D). E. Detail of the capsule wall; laser scanning microscope image generated by linear unmixing using the spectra of the globules versus that of the wall matrix.F. Detail of capsule wall, showing extinction of some of the globules; crossed−polarized light.