Scyliorhinus weemsi, Cicimurri & Knight & Ebersole, 2022

Cicimurri, David J., Knight, James L. & Ebersole, Jun A., 2022, Early Oligocene (Rupelian) fishes (Chondrichthyes, Osteichthyes) from the Ashley Formation (Cooper Group) of South Carolina, USA, PaleoBios 39 (1), pp. 1-38 : 5-8

publication ID	https://doi.org/ 10.5070/P939056976
publication LSID	lsid:zoobank.org:pub:13E6A6E9-DE0F-4C71-BE40-2957F48D9F70
persistent identifier	https://treatment.plazi.org/id/FE30E586-6874-4FE4-ACE8-2A9535A59CC2
taxon LSID	lsid:zoobank.org:act:FE30E586-6874-4FE4-ACE8-2A9535A59CC2
treatment provided by	Felipe
scientific name	Scyliorhinus weemsi
status	sp. nov.

Treatment

SCYLIORHINUS WEEMSI N. SP.

FIG. 4 View Figure 4

Type species — Squalus canicula Linnaeus, 1758 ;

Recent, Mediterranean Sea.

2009a Bythaelurus sp. ;Cicimurri and Knight, p. 634–635, fig. 5M.

Diagnosis —Diminutive teeth measuring just over 1 mm in total height and 1 mm in crown width. Two morphotypes occur, including one with robust longitudinal ridges on the labial and lingual faces, and one exhibiting longitudinal ridges on the lingual face but having a smooth labial face. When present, labial ridges extend from one-third to three-quarters of the crown height. Lingual ridges always extend nearly to the apex of the main cusp. Cusplets are small or may be lacking altogether.

Holotype —SC2007.36.133 ( Fig.4A–D View Figure 4 ), from locality 2 of Fig. 1B

Paratype —SC2015.29.7 ( Fig. 4E–G View Figure 4 ), from locality 3 of Fig. 1B.

Referred specimens (n=9) —SC2007.36.6 ( Fig. 4 View Figure 4 K- M), SC2007.36.160 ( Fig. 4Q–S View Figure 4 ), SC2007.36.203 ( Fig. 4T–V View Figure 4 ), SC2007.36.204 ( Fig. 4W–Y View Figure 4 ), SC2007.36.205 ( Fig. 4 View Figure 4 Z-BB), SC2007.36.206, SC2007.36.207, SC2015.29.6 ( Fig. 4N–P View Figure 4 ), SC2015.29.8 ( Fig. 4H–J View Figure 4 ).

Etymology —This species is named in honor of Robert E. Weems to recognize his contributions to our understanding of the stratigraphy and paleontology of the Atlantic Coastal Plain, and specifically for his extensive work on the Ashley Formation of South Carolina.

Description —Specimen SC2007.36.133 ( Fig. 3A–D View Figure 3 ) is designated as the holotype because of its completeness. This tooth measures 1.1 mm in height and 0.9 mm in mesiodistal width. The specimen exhibits a tall, distally inclined main cusp that sharply tapers apically. In profile view the crown curves labially. A single pair of lateral cusplets occurs low on the crown, and the mesial cusplet is conspicuously wider than the distal one. The labial crown face is very weakly convex, and numerous coarse ridges occur on its lower one-third.The crown foot clearly overhangs the root and is medially concave but drawn into projections on the mesial and distal sides. The lingual crown face is very convex, and coarse longitudinal ridges nearly reach the apices of the main cusp and lateral cusplets. The cutting edge is smooth and continuous to the lateral side of the cusplets. The lingual root boss is large, and although the root lobes are both rather short, the mesial lobe is slightly wider. A large margino-lingual foramen occurs on each side of the boss.

SC2015.29.7 ( Fig. 4E–G View Figure 4 ) is designated as a paratype. This specimen is morphologically similar to the holotype ( Fig. 4A–D View Figure 4 ) and appears to represent a similar tooth file. SC2015.29.7 differs from the holotype by having a labio-lingually thinner crown ( Fig. 4E View Figure 4 ), lower but wider lateral cusplets, and a smooth labial face ( Fig. 4G View Figure 4 ). As on the holotype, robust longitudinal ridges extend nearly to the apex of the main cusp and lateral cusplets ( Fig. 4E View Figure 4 ).

SC2007.36.6, SC2007.36.160, SC2015.29.6 and SC2015.29.8 are comparable to each other, and to the type specimens, by having a rather straight but distally inclined main cusp, as well as coarse longitudinal ridges that extend nearly to the apex of the main cusp and lateral cusplets. However, there are slight differences among these teeth. For example, SC2007.36.6 ( Fig. 4K–M View Figure 4 ) compares well to the paratype ( Fig. 4E–G View Figure 4 ) but has a labio-lingually thicker crown, larger lateral cusplets, and robust plications at the labial crown foot, whereas SC2007.36.160, SC2015.29.6 and SC2015.29.8 are similar to the holotype by having coarse labial and lingual crown ornamentation. Specimen SC2007.36.160 has a very broad main cusp compared to the other specimens ( Fig. 4R View Figure 4 ), and the preserved distal cusplet is broad but poorly differentiated from the main cusp ( Fig. 4S View Figure 4 ). SC2015.29.6 differs by having a mesio-distally wider crown ( Fig. 5O View Figure 5 ), that lacks a mesial cusplet but bears a diminutive distal cusplet ( Fig. 5P View Figure 5 ), and the labial face is more apico-basally concave ( Fig. 4N View Figure 4 ). SC2015.29.8 is unusual by having an elongated mesial shoulder that is sub-perpendicular to the main cusp, and a short distal shoulder that merges with the cusp ( Fig.4I View Figure 4 ). The shoulders lack lateral cusplets, but the mesial shoulder appears weakly serrated due to the intersection of the crown ornamentation with the cutting edge ( Fig. 4J View Figure 4 ).

Like the holotype, SC2007.36.204 and SC2007.36.205 have course labial and lingual crown ridges.SC2007.36.204 is unique among the sample by having a narrow crown with erect cusp that is only weakly distally curved, and there is a single pair of small, diverging lateral cusplets ( Fig. 4W–Y View Figure 4 ). Although SC 2007.36.205 has a rather low but very wide main cusp like that of SC2007.36.160 (compare Fig. 4R View Figure 4 to 4AA), it differs significantly by having two pairs of large lateral cusplets, with the first pair being tall and needle like, but the second pair is diminutive and located at the very base of the crown ( Fig. 4 View Figure 4 BB). Specimen SC 2007.36.203 exhibits a cusplet arrangement similar to that of SC2007.36.205, but the crown of the former is comparatively higher and narrower ( Fig. 4U View Figure 4 ), and the labial ornamentation is restricted to the crown foot ( Fig. 4V View Figure 4 ) .

Remarks — Herman et al. (1990) identified five tooth groups within scyliorhinid sharks that they differentiated largely by the root morphology. At the time of their report, the genera discussed therein were regarded as “catsharks” and subdivided into one of four subfamilies within Scyliorhinidae . However, it has since been shown that “catsharks” are a complex paraphyletic group consisting of several families and subfamilies ( Iglésias et al. 2005, Weigmann et al. 2018). With respect to the tooth root, although this structure is poorly preserved on nearly all the South Carolina Oligocene specimens, the lobes are rather narrow, and the basal attachment surface is flat. These features would preclude their assignment to genera like Atelomycterus Garman, 1913 and Aulohalaelurus Fowler, 1934 , both of which have rather broad root lobes, and to Cephalurus Bigelow and Schroeder, 1941 , which has a root with a concave attachment surface. Pollerspöck and Straube (2017) noted the possible taxonomic utility of enameloid ornamentation on catshark teeth, which can occur as reticulated ridges at the base of the labial face on the genera Apristurus Garman, 1913 , Bythaelurus Compagno, 1988 , Galeus Cuvier, 1816 , Haploblepharus Garman, 1913 , and Holohalaelurus Fowler, 1934 ( Herman et al. 1990, Weigmann et al. 2016, Weigmann et al. 2018), and on taxa like Scyliorhinus ( Herman et al. 1990) .

The specimens in our sample are strikingly similar to the teeth of various Scyliorhinus species illustrated by Soares and de Carvalho (2019), and we therefore assign the Oligocene specimens to this genus. The teeth of the 11 species of extant Scyliorhinus shown by Soares and de Carvalho (2019) exhibit a wide range of morphologies that reflect both interspecific (among species) and intraspecific (monognathic, dignathic, gynandric heterodonty within species) variation. It can be said that the Scyliorhinus dentition exhibits gradual monognathic heterodonty and can be sorted into anterior, lateral, and, in the lower jaw, parasymphyseal files. Anterior teeth may be erect (roughly symmetrical) to slightly distally inclined, cusplets may be poorly developed or well-developed (generally one pair), and labial ornamentation may be absent, limited to the lower part of the crown, or extend more than halfway to the apex. Lateral teeth are typically lower crowned but broader, with a vertical (generally lower jaw, but sometimes upper) to distally inclined main cusp (generally in the upper jaw but sometimes both). These teeth also bear two or more pairs of lateral cusplets, and crown ornamentation is more conspicuous than on anterior teeth. With respect to dignathic heterodonty, crown ornamentation is usually more extensive on upper teeth when compared to lowers, and lateral cusplets of upper teeth are generally taller but narrower than those of lower teeth. Development of gynandric heterodonty has not been evaluated for all Scyliorhinus species, but for those species where it has been documented, female teeth are often more coarsely ornamented, the main cusps are lower but broader, and the cusplets are better developed compared to male teeth of the species ( Herman et al. 1990, Soares and de Carvalho 2019).

The morphological variation within the dentitions of the various extant Scyliorhinus species makes it difficult to accurately interpret the Ashley formation sample (n=11). However, the generalities observed in the genus lead us to conclude that our sample reflects heterodonty within a single species rather than multiple taxa and allow us to make informed hypotheses with respect to the dentition of the Oligocene species. For example, SC2007.36.204 ( Fig. 4W–Y View Figure 4 ) has a narrow, rather symmetrical crown and extensive labial and lingual ornamentation, indicating it was located within an upper anterior tooth file. The holotype, SC2007.36.133 ( Fig. 4A–D View Figure 4 ) is slightly inclined, has very robust labial and lingual ornamentation, and bears a single pair of rather narrow lateral cusplets. These features indicate it was from an upper anterior/antero-lateral file. In contrast, SC2015.29 (paratype, Fig. 4E–G View Figure 4 ) has a similar main cusp shape to the holotype, but labial crown ornamentation is restricted to the crown foot, and the (single pair of) lateral cusplets are rather low but broad, indicating it is from a lower anterior/antero-lateral position. Specimen SC 2007.36.203 ( Fig. 4T–V View Figure 4 ) has an erect main cusp, ornamentation is limited to the crown foot, and two pairs of lateral cusplets (which are only preserved on the distal side), suggesting it is a lateral tooth, possibly from the lower dentition. Similarly, SC 2007.36.2005 ( Fig. 4Z View Figure 4 – BB) appears to be a lateral tooth based on the presence of two pairs of lateral cusplets, but it may be representative of a female dentition based on the low but very broad main cusp and greater development of labial ornamentation and lateral cusplets (compare Fig. 4 View Figure 4 BB to 4 V). Specimens SC 2015.29.8 ( Fig. 4H–J View Figure 4 ) and SC2015.29.6 ( Fig. 4N–P View Figure 4 ) could represent male anterior and lateral teeth, respectively, as they have tall and narrow main cusps and lack lateral cusplets. In contrast, SC2007.36.160 ( Fig. 4Q–S View Figure 4 ) has a very wide main cusp, more robust labial ornamentation, and larger lateral cusplet (which is only preserved on the distal side), indicating a female individual .

Although roughly the same size as the Chattian Scyliorhinus biformis Reinecke (2014) , S. weemsi n. sp. teeth differ by having a much less medially concave labial crown base, the main cusp is broader, the cusplets are shorter, and the lingual ornamentation is more extensive. Among teeth with conspicuous labial ornamentation, those of S. weemsi n. sp. differ from S. biformis by having more robust ridges that extend higher on the crown. In addition, S. biformis exhibits one or two pairs of rather large cusplets, whereas S. weemsi n. sp. lacks or has only diminutive cusplets. Regarding teeth having much reduced ornamentation, those of S. weemsi n. sp. have a shorter main cusp, less convex labial crown foot, and smaller cusplets than S. biformis ,

Teeth of Chattian Scyliorhinus suelstorfensis Reinecke, 2014 are two-thirds larger than those of S. weemsi n. sp., and they have a more gracile crown and much more medially concave labial crown foot. Also, vertical labial ridges on S. suelstorfensis are restricted to the lower one-third to one-half of the crown, whereas labial ridges can extend up to two-thirds or more of the crown height on S. weemsi n. sp. Finally, S. weemsi n. sp. differs from the Oligocene Scyliorhinus kannenbergi Leder, 2015 by being smaller in overall size and more gracile in appearance, having higher labial longitudinal ridges,and having fewer and smaller lateral cusplets.

Specimen SC2007.36.160 ( Fig. 4Q–S View Figure 4 ) is nearly identical to the specimen identified as Bythaelurus sp. by Cicimurri and Knight (2009a: fig. 5M) from the Chattian Chandler Bridge Formation (overlying the Ashley Formation). Although both specimens are imperfectly preserved, together they show that only a single pair of lateral cusplets was developed in this jaw region. Hovestadt and Hovestadt-Euler (1995) were the first to identify Bythaelurus in the fossil record when they reassigned teeth formerly identified as Scyliorhinus aff. coupatezi (i.e., Steurbaut and Herman 1978, Génault 1993) to their new taxon, B. steurbauti . Cicimurri and Knight (2009a) considered their singular specimen as conspecific with Bythaelurus . However, teeth of extant Bythaelurus , like B. canescens ( Günther, 1878) (see Herman et al. 1990), B. giddingsi McCosker et al., 2012 , B. bachi Weigmann et al., 2016 and B. stewarti Weigmann et al., 2018 have one or more pairs of very large lateral cusplets. This contrasts strikingly with the teeth of the South Carolina Oligocene taxon, which have rather small cusplets or lack them altogether. The teeth of Pachysyllium sp. described earlier differ from those of S. weemsi n. sp. by being approximately twice the size, having larger lateral cusplets compared to crown size, and labial and lingual ornamentation is restricted to the crown foot.