Plesiosaurs from the fluvial Kem Kem Group (mid-Cretaceous) of eastern Morocco and a review of non-marine plesiosaurs

Georgina Bunker, David M. Martill, Roy Smith, Samir Zouhri, Nick Longrich

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Abstract

Plesiosaurs were a long-lived and widespread group of marine reptiles, with a worldwide distribution and a temporal range from the Late Triassic to the Late Cretaceous. Most occur in marine deposits, but some occur in low-salinity, brackish to freshwater environments. We report plesiosaurs from the freshwater fluvial deposits of the mid-Cretaceous (?Albian-Cenomanian) Kem Kem Group of Morocco. Remains include numerous shed teeth, vertebrae, and a humerus. The humerus represents a young juvenile; vertebrae likely belong to sub-adults. Teeth show heavy wear, similar to teeth of co-occurring spinosaurids. While coeval plesiosaurs from the Bahariya Formation of Egypt are members of Polycotylidae, the Kem Kem fossils show features of Leptocleididae, small-bodied plesiosaurs that were widely distributed in nearshore and non-marine settings in the Early Cretaceous. These fossils are the first freshwater plesiosaurs from Morocco, and are among the youngest representatives of Leptocleididae. The Kem Kem leptocleidids could have been infrequent visitors from the sea, freshwater-tolerant, or even freshwater-adapted, as in modern river dolphins. The abundance of shed teeth in the Kem Kem Group supports the hypothesis that they had some degree of freshwater tolerance. Furthermore, leptocleidids occur almost exclusively in shallow nearshore, brackish, or freshwater environments, suggesting adaptation to shallow, low-salinity environments. Other plesiosaur groups and other Mesozoic marine reptiles, including teleosaurids and mosasaurids, also occur in freshwater settings, suggesting plesiosaurs and other marine reptiles frequently exploited non-marine environments.
Original languageEnglish
Article number105310
JournalCretaceous Research
Volume140
Early online date21 Jul 2022
DOIs
Publication statusPublished - 31 Dec 2022

Bibliographical note

Funding Information:
We are indebted to our Moroccan colleagues for their assistance in the field. DMM thanks Mr Mohammed Segaoui of Atlas Geotours for assistance in the field and introducing the geology of Saf Saf, and to Chris Moore (Charmouth) for access to juvenile plesiosaur specimens. NRL thanks Mr. Mohammed Ben Sekkou for hospitality in Erfoud and Nathalie Bardet for discussions. Thanks to Julian Kiely for drawing Fig. 7, to Andrey Atuchin for Fig. 12. We also thank Richard Hing and Thomas Beevor for assistance with specimen photography. We acknowledge the anonymous reviewers for their time and effort reviewing the manuscript.

Keywords

  • Freshwater
  • Kem Kem Group
  • Leptocleididae
  • Morocco
  • Palaeoecology
  • Plesiosauria

ASJC Scopus subject areas

  • Palaeontology

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