Presence of ossified ethmoidal elements in Peirosauridae (Mesoeucrododylia): First record of these structures in Crocodyliformes

BARRIOS, F.; PAULINA CARABAJAL, A.; BONA, P.

VIRTUAL

Jornada; Jornadas Argentinas de Paleontologia de Vertebrados; 2021

Mendoza

In vertebrates, the ethmoid complex is a series of bones (e.g., sphenoethmoid, mesethmoid, and ectoethmoid) that ossify from nasal cartilages at the olfactory region, anterior and dorsal to the interorbital septum, and surround the olfactory tracts and bulbs. Among the extant and extinct archosaurs, these elements may be ossified or remain cartilaginous in advanced ontogenetic states. Ossified ethmoidal elements are frequent in non-avian theropod and ornithischian dinosaurs (such as tyrannosaurids, carcharadontosaurids, abelisaurids, and ceratopsids) and in birds, where the sphenoethmoid and mesethmoid are recognized as ethmoidal complex. On the other hand, the extinct Crocodyliformes lack ossified ethmoidal elements, and the living Crocodylia have a completely cartilaginous internasal and interorbital septum throughout the life of the individual. From computed tomography performed on two specimens of extinct crocodyliforms of the family Peirosauridae (Lomasuchus palpebrosus -MOZ-Pv 4084- and Gasparinisuchus peirosauroides -MOZ-Pv 1750-), ossified ethmoidal elements were recognized. These elements are located posterior to the nasal cavity and in front of the olfactory bulbs, and would correspond to the mesethmoid (medial and articulated to the frontal) and the ectoethmoid (lateral and articulated to the mesethmoid and containing the foramen for the olfactory nerve). This contribution presents the first record of ossified ethmoidal elements in Crocodyliformes, a potential synapomorphy of Peirosauridae. The functional significance of these ossifications is unknown, but they would have implications in terrestrial and predatory habits (associated with olfaction) of these peirosaurids.