Current consensus regarding Brachycarcharias and Tethylamna

[Othniel C. Marsh]

I have been utilising this guide by @Doctor Mud to identify a Brachycarcharias-like tooth from the Ouled Abdoun Basin in Morocco. According to the guide, there are two rather distinct Brachycarcharias teeth known from the formation: the large, robust, broad-cuspleted B. lerichei and the smaller, more gracile, long-cuspleted B. atlasi. However, on websites such as elasmo.com I have seen the name B. lerichei applied to teeth which look much more like those of B. atlasi. To confuse matters further, it appears that Tethylamna twiggsensis, which the Wikipedia article states is sometimes referred to as being nested within Brachycarcharias, is extremely similar to B. lerichei.
This raises the question of what exactly is the current consensus surrounding sharks with this tooth type. Have both Brachycarcharias species been condensed into a single species, B. lerichei? Are B. atlasi-like teeth now referred to as B. lerichei, and have B. lerichei teeth been moved to T. twiggsensis? Or were the labels in my guide correct?

 

Thanks in advance for any information
Othniel

 

I should add that I only just realised a "Q&A" section existed, and up until this point have been putting all my questions in the "General Fossil Discussion" section. Should the moderators of the forum wish to transfer my incorrectly placed questions, they can be found here, here, here, here, and here.

[DD1991]

Cappetta and Case (2016) referred Brachycarcharias twiggsensis to their new genus Tethylamna, but Ebersole et al. (2019) disputed this generic assignment and followed Underwood et al. (2011) in classifying this species as a member of Brachycarcharias. Although the recorded stratigraphic range of the type species of Brachycarcharias, B. lerichei, is similar to that recorded for B. atlasi, both B. lerichei and B. atlasi are distinct taxa (e.g. Cappetta and Case 2016 as well as Ebersole et al. 2019), and the Bartonian-Priabonian age of B. twiggsensis might indicate that twiggsensis could be a new genus derived from both Brachycarcharis and Tethylamna. 

 

Cappetta, H., and Case, G.R. 2016. A selachian fauna from the middle Eocene (Lutetian, Lisbon Formation) of Andalusia, Covington County, Alabama, USA. Palaeontographica Abteilung A 307 (1–6): 43–103.

 

Ebersole, J.A., Cicimurri, D.J., and Stringer, G.L., 2019. Taxonomy and biostratigraphy of the elasmobranchs and bony fishes (Chondrichthyes and Osteichthyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Claiborne Group in Alabama, USA, including an analysis of otoliths. European Journal of Taxonomy 585: 1–274. doi:10.5852/ejt.2019.585.

 

Underwood C.J., Ward D.J., King C., Antar S.M., Zalmout I.S. & Gingerich P.D., 2011. Shark and ray faunas in the middle and late Eocene of the Fayum Area, Egypt. Proceedings of the Geologists’ Association 122 (1): 47–66. https://doi.org/10.1016/j.pgeola.2010.09.004 

[Othniel C. Marsh]

Much appreciated, @DD1991.

Edited May 26 by Othniel C. Marsh