The postcranial skeleton of <i>Cerrejonisuchus improcerus</i> (Crocodyliformes: Dyrosauridae) and the unusual anatomy of dyrosaurids

Dyrosauridae is a clade of neosuchian crocodyliforms that diversified in terrestrial and aquatic environments across the Cretaceous-Paleogene transition. The postcranial anatomy dyrosaurids has long been overlooked, obscuring both their disparity locomotive adaptations. Here we thoroughly describe remains an unusually small dyrosaurid, Cerrejonisuchus improcerus , from middle-late Paleocene Cerrejón Formation Colombia, provide wealth new data concerning key dyrosaurids: Congosaurus bequaerti Hyposaurus rogersii . We identify series autapomorphies (an elliptic-shaped odontoid laterally wide, ulna possessing double concavity, fibula bearing widely flattened proximal end, pubis showing large non-triangular distal surface) as well functionally-important traits such relatively (85% humerus’ length), short forelimb (83% hindlimb’s or thoracic vertebra comparatively lateral process (with widened parapophysis diapophysis) along with strongly arched ribs allowing more sturdy cylindrical rib cage. These indicate lifestyle for compared to derived members clade. also built dataset 187 on 27 taxa, extensively samples cranial architectures exemplar crocodyliforms. analyze these via Principal Coordinate Analysis (PCoA) visualize morphospace occupation Dyrosauridae, Thalattosuchia, Crocodylia. Our reveal existence distinctive markedly distinct crocodylians. As result, modern crocodylians are probably not good functional analog extinct crocodyliformes. Postcranial should be used phylogenetic analyses Crocodyliformes.