Evolutionary success of theropod-like crocodiles (Sebecosuchia) in the aftermath of the end-Cretaceous mass extinction – SEBEK

The end-Cretaceous biological crisis, 66 myr ago, affected both marine and continental environments at a global scale. Crocodilians are emblematic for their survival across this crisis, which could be partly explained by their peculiar physiology and adaptations to the aquatic environment. However, another group of crocodilians, the Sebecosuchia, is supposed to be adapted to a fully terrestrial lifestyle and their survival across this event challenges interpretations about the influence of abiotic factors on biodiversity. In fact, sebecosuchians are interpreted as morphological analogues of non-avian theropod dinosaurs but why sebecosuchians survived whereas non-avian theropod dinosaurs did not, remains unsolved.
The Sebecosuchia are represented by diverse forms, recovered in continental deposits of the Cretaceous and Cenozoic. They are essentially distributed in Gondwana, i.e. southern landmasses with principal fossil occurrences in South America and Africa. During their evolutionary history, sebecosuchians also transpired into Laurasia, as evidenced from the European fossil record. Phylogenetic relationships of the Sebecosuchia are fluctuating but depending on the results, the main lineages include the Baurusuchidae (Cretaceous), the Peirosauridae (Cretaceous) and the Sebecidae (Cenozoic). Although sebecosuchian specimens are represented by fairly complete individuals in southern landmass deposits, those from Europe are fragmentary in comparison. However, Europe represents a unique “hotspot” for sebecosuchians because it holds, in a spatially restricted area, several fossiliferous outcrops from both sides of the Cretaceous–Paleogene boundary. Thus, new sebecosuchian discoveries from Europe represent an opportunity to stabilize their internal phylogenetic relationships and unlock the evolutionary transition of the group during a major extinction event. As part of the SEBEK project, our team will investigate fossiliferous localities from southern France with known occurrences of sebecosuchians.
The main objective of the project will be, through a multidisciplinary approach using geochemical and anatomical evidence, to test the terrestrial hypothesis of the Sebecosuchia and re-evaluate evolving links between the biosphere and abiotic factors before and following the end Cretaceous mass extinction. Thanks to international collaborative work, samples from South America, North Africa and Europe will be analysed as part of the SEBEK project. Light and non-traditional isotopes will be measured in tooth enamel of sebecosuchians and associated faunas to assess their lifestyle and living environment (oxygen and strontium isotopes) and their dietary preferences (calcium and carbon isotopes). Anatomical evidence for their lifestyle and behaviour will be gathered from X ray micro-computed tomography of skull specimens, comparative anatomy of the appendicular skeleton and comparative histology. These approaches will provide an opportunity to train a PhD student and recruit a postdoctoral researcher. Altogether, our results will provide, for the first time, an unprecedented understanding into the palaeobiology of the Sebecosuchia, a group with no modern analogues.