Bony injuries in a Late Triassic forerunner of mammals from Brazil

Abstract

Traversodontidae is a clade of non-mammaliaform cynodonts within the Cynognathia lineage, representing the most successful herbivorous/omnivorous group of the Triassic period. Here, we describe bony injuries in the ribs of a ~ 228–million–year–old traversodontid from Brazil. The specimen, assigned to Exaeretodon riograndensis, was discovered in Upper Triassic strata of the Santa Maria Supersequence, Paraná Basin. Macroscopic analysis, supported by micro-computed tomography, revealed the presence of bony calluses in the ribs, indicative of a transverse traumatic fracture, likely caused by a fall or an interaction (either intra- or interspecific) during the individual’s lifetime. Such trauma would have likely hindered its locomotion, impacting foraging efficiency and predator evasion. However, this species was possibly gregarious, which may have helped mitigate the injury’s impact on survival through group behavior. This finding represents a rare documented case of paleopathology in non-mammaliaform cynodonts, contributing to discussions on their behavior and paleoecology during the Triassic.