Longirostrine crocodylians from the Bartonian of Morocco and Paleogene climatic and sea level oscillations in the Peri-Tethys area

ABSTRACT

The Eocene–Oligocene transition was a period of high faunal and floral turnover, often correlated with climatic deterioration. Crocodyliforms are climate sensitive, and they have been often used for reconstruction of paleoclimates. The description of crocodylian material from the Bartonian of Aaiun-Tarfaya Basin (Morocco) allows the recognition of at least two longirostrine crocodylians, including a gavialoid. This identification is important, because the migration of gavialoids to South America probably occurred during the late Eocene. Close relationships between late Eocene–early Oligocene Eogavialis africanum from Egypt, Argochampsa krebsi from the Paleocene of Morocco, and the South American gavialoid clade suggests that Morocco could have had a particular place in the gavialoid dispersal route to South America. The resemblance between Moroccan material described herein and E. africanum is thus important in this context. Analysis of the distribution of longirostrine crocodylians in the Peri-Tethys area through the Eocene–Oligocene shows a strong difference in the evolution of the distribution between longirostrine crocodylians and Diplocynodon. Whereas the freshwater Diplocynodon has a continuous distribution in western Europe, the mainly marine longirostrine crocodylians have a northern maximal expansion that moves southward during the middle Eocene, being restricted to North Africa during late Eocene–early Oligocene. European freshwater Asiatosuchus-like taxa also disappear during the late Eocene. Climatic deterioration, helped by sea level oscillations, may have strongly impacted the diversity and latitudinal distribution of the crocodylians, but we highlight a possible differential tolerance in range of climatic conditions between crocodylians. This could help to refine the use of crocodylians as paleoclimatic proxies.

ACKNOWLEDGMENTS

S.J. thanks L. Steel (Natural History Museum, London) and M. Rabi and Z. Szentesi (both Hungarian Natural History Museum) for their help, hospitality, and access to collections and material. We are grateful to two anonymous reviewers for their comments and to S. Salisbury for the editing process. S.J. received support from the SYNTHESYS Project (www.synthesys.info), which is financed by the European Community Research Infrastructure Action under the FP7 ‘Capacities’ Program (HU-TAF-4866; GB-TAF-3366). Fieldwork research was supported by GRANT #9765-15 from the National Geographic Society.

ORCID

Stéphane Jouve http://orcid.org/0000-0002-0420-8648