Soft tissue preservation in the Barremian Montsecosuchus depereti (Neosuchia: Atoposauridae)

Crocodylomorpha (crocodilians and their extinct relatives) have an extensive fossil record that extends from the Late Triassic to the present day. Nevertheless, fossilized soft tissues (e.g. skin and cartilage) are virtually unknown for most clades, with the exception of the marine thalattosuchians. Here, with the assistance of ultraviolet light, we identify and describe a variety of cartilaginous and non-ossified epidermal tissues in the Early Cretaceous (Barremian) putative atoposaurid Montsecosuchus depereti from Spain, which is among the most complete and oldest preserved skin among Crocodylomorpha, with scale architecture varying along its body. Although broadly similar to the integument of extant representatives, Montsecosuchus lacks the deep caudal ‘fin’ and deeply keeled scales on the limbs characteristic of modern crocodylians. Additional features include possible integumentary sensory organs and evidence of banded coloration along the tail. The restricted presence of possible integumentary sensory organs on scale inclusions on the body periphery suggests that such organs first evolved as small, specialized scales prior to assuming a more widespread distribution on basement scales along the body. Preserved cartilaginous tissues (uncinate processes and cartilaginous ribs) in the thoracic region show adaptations in Montsecosuchus for increased respiratory efficiency. These discoveries help to fill gaps in the evolution of the crocodylomorph integument and respiratory apparatus.