Revision of the Late Jurassic deep-water teleosauroid crocodylomorph Teleosaurus megarhinus Hulke, 1871 and evidence of pelagic adaptations in Teleosauroidea

Author:

Foffa Davide12,Johnson Michela M.2,Young Mark T.2,Steel Lorna3,Brusatte Stephen L.12

Affiliation:

1. Department of Natural Sciences, National Museums Scotland, Edinburgh, United Kingdom

2. School of GeoSciences, University of Edinburgh, Edinburgh, United Kingdom

3. Department of Earth Sciences, Natural History Museum, London, United Kingdom

Abstract

Teleosauroids were a successful group of semi-aquatic crocodylomorphs that were an integral part of coastal marine/lagoonal faunas during the Jurassic. Their fossil record suggests that the group declined in diversity and abundance in deep water deposits during the Late Jurassic. One of the few known teleosauroid species from the deeper water horizons of the well-known Kimmeridge Clay Formation is ‘Teleosaurus megarhinus Hulke, 1871, a poorly studied, gracile longirostrine form. The holotype is an incomplete snout from the Aulacostephanus autissiodorensis Sub-Boreal ammonite Zone of Kimmeridge, England. The only other referred specimen is an almost complete skull from the slightly older A. eudoxus Sub-Boreal ammonite Zone of Quercy, France. Recently, the validity of this species has been called into question. Here we re-describe the holotype as well as the referred French specimen and another incomplete teleosauroid, DORCM G.05067i-v (an anterior rostrum with three osteoderms and an isolated tooth crown), from the same horizon and locality as the holotype. We demonstrate that all specimens are referable to ‘Teleosaurusmegarhinus and that the species is indeed a valid taxon, which we assign to a new monotypic genus, Bathysuchus. In our phylogenetic analysis, the latest iteration of the ongoing Crocodylomorph SuperMatrix Project, Bathysuchus megarhinus is found as sister taxon to Aeolodon priscus within a subclade containing Mycterosuchus nasutus and Teleosaurus cadomensis. Notably Bathysuchus has an extreme reduction in dermatocranial ornamentation and osteoderm size, thickness and ornamentation. These features are mirrored in Aeolodon priscus, a species with a well-preserved post-cranial skeleton and a similar shallow and inconspicuous dermal ornamentation. Based on these morphological features, and sedimentological evidence, we hypothesise that the Bathysuchus + Aeolodon clade is the first known teleosauroid lineage that evolved a more pelagic lifestyle.

Funder

Small Grant Scheme ‘2015 Wood Award’

Palaeontographical Society

Natural Sciences and Engineering Research Council of Canada grant

Palaeontographical Society and Small Grant Scheme ‘Sylvester Bradley Award’

Leverhulme Trust Research Project grant

Marie Curie Career Integration Grant

Royal Commission for the Exhibition of 1851

Publisher

PeerJ

Subject

General Agricultural and Biological Sciences,General Biochemistry, Genetics and Molecular Biology,General Medicine,General Neuroscience

Reference86 articles.

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4. Beiträge zur Kenntnis der Krokodilier des schwäbischen oberen Lias;Berckhemer;Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, Beilagenband,1929

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