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Abstract :
[en] Dyrosauridae is a clade of neosuchian crocodyliformes that diversified in fluviatile and marine environments across the Cretaceous-Paleogene transition. Thalattosuchia is a clade of aquatic crocodyliforms which spanned over the Jurassic period and disappeared during the Early Cretaceous. Both clades crossed extinction events (i.e. Jurassic-Cretaceous boundary for Thalattosuchia; Cretaceous-Paleogene for Dyrosauridae). The postcranial anatomy of both groups has long been overlooked in anatomical descriptions and diagnoses, obscuring their disparity and their locomotive adaptations. We surveyed the morphology of the postcranial skeleton of Dyrosauridae, Thalattosuchia, and Crocodylia, in order to identify osteological correlates for ecology and behaviour as well as test for the existence of evolutionary trends.
We thoroughly surveyed the anatomy of crocodyliformes, creating 187 morphofunctional ratios that span the entire skeleton, more than 80% of which being postcranial. Ordination techniques on this extensive dataset reveal the existence of a distinctive postcranial anatomy for both Dyrosauridae and Thalattosuchia which are both markedly distinct from that of crocodylians. As a result, modern crocodylians are likely not a good functional or ecological analogy for extinct crocodyliform groups. It also appears clear that postcranial data in an important component of crocodyliform disparity.
A focus on thoracic and pelvic girdles reveals a wide occupation of the morphospace for coastal taxa, even though Dyrosauridae, Thalattosuchia, and Crocodylia occupy clearly separated areas of the morphospace. Within Thalattosuchia, three main clusters are observed regardless of phylogenetic affinities, putatively hinting at global morphotypes within the clade. The most discriminant features between our samples appear to concern primarily the femur (e.g. posterior curvature, fourth trochanter, head protrusion, etc.) with contributions from the pubis, sacrals, and the ilium.
This work was supported by the Fonds de la Recherche Scientifique (F.R.S.-FNRS) (Grant MIS F.4511.19).
