The postcranial skeleton ofCerrejonisuchus improcerus(Crocodyliformes: Dyrosauridae) and the unusual anatomy of dyrosaurids

Abstract

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

Limited convergence in the postcranium of aquatic Crocodylomorpha

“…2016, 2019b; Jouve & Jalil 2020a; Jouve et al . 2021; Scavezzoni & Fischer 2021) and its significance in understanding crocodylomorph relationships (Pol et al . 2012; Godoy et al .…”

“…2016; Mannion et al . 2019; Scavezzoni & Fischer 2021). Fortunately, recent works have started to incorporate more postcranial anatomy in both descriptions and character building, which has brought to light the rich morphological disparity of Crocodylomorpha (Pol et al .…”

Form and function of the pelvic girdle of Thalattosuchia and Dyrosauridae (Crocodyliformes)

“…Hyposaurus natator, Dyrosaurus maghribensis, and Anthracosuchus balrogus). Considering the potential existence of a respiration involving pubic movements, such an enlarged pubic apron presumably enabled to displace consequent visceral masses (Scavezzoni & Fischer, 2021). In parallel, the overall size of the pubic apron, and subsequent pubic symphysis, presumably impacted the angle of pubic rotation compared to extant crocodylians (Claessens, 2004).…”

Architecture of the bronchial tree in Cuvier's dwarf caiman (Paleosuchus palpebrosus)

“…Reconstructions of pulmonary anatomy in extinct taxa have been of great interest over the last 20 years to paleontologists and biologists (Farmer, 2006;O'Connor, 2006O'Connor, , 2009O'Connor & Claessens, 2005;Schachner et al, 2011;Sereno et al, 2008;Wedel, 2003Wedel, , 2009. However, the details of crocodilian lung evolution have rarely been the focus of these analyses aside from discussions of the hepatic-piston ventilation mechanism and how it relates to dinosaurian ventilation or the ancestral archosaurian respiratory system (Brocklehurst et al, 2020;Radermacher et al, 2021;Scavezzoni & Fischer, 2021). More data on a variety of extant taxa are required to properly understand the origin and evolution of the crocodilian bronchial tree, including the origin of the hepatic-piston system.…”