Bone microanatomy of Pepesuchus deiseae (Mesoeucrocodylia, Peirosauridae) reveals a mature individual from the Upper Cretaceous of Brazil

Abstract

Peirosauridae is placed within Notosuchia with members found in Cretaceous deposits of Africa and South America. These crocodyliforms were considered most terrestrial predators, according to their morphological features. Our data bring contributions to infer about peirosaurids habits from the bone histology and to inform the autoecology of the Pepesuchus deiseae (MN 7466-V). We prepared thin sections of the appendicular bones and an osteoderm from MN 7466-V. Both metacarpals show a broad cortex and a tiny marrow cavity, one has seven cyclical growth marks and Haversian bone in the endosteal region. The ulnare has a highly porous bone with several resorption cavities. The osteoderm is composed of parallel-fibred bone (PFB) forming the basal and external cortex and woven-fibred bone (WFB) constituting the internal core. The tibia shows the presence of external fundamental system (EFS) and the cortex presents WFB and PFB intercalated. The metacarpals exhibit osteosclerosis and the ulnare shows osteoporotic-like bone. In the metacarpals, the occurrence of bone mass increase would have implied rather life in shallow-water environments. The ulnare shows a reduction in bone mass, providing a better maneuverability between its joints with the carpal and ulna. The tibia was the only element indicating the specimen reached the somatic maturity by the presence of EFS. Therefore, this bone was used as a proxy to the maximum growth rate. Currently, the presence of WFB in advanced ontogenetic stage indicates a peculiar feature solely recorded in eusuchian long bones. The resorption cavities in the internal core of the osteoderm probably indicate bone resorption for calcium mobilization during the eggshell formation. In addition, the Haversian bone is an indication that metacarpal A belonged to mature individual, which had accomplished some ovogenetic cycles. In conclusion, our analyses suggest that MN 7466-V was an adult and mature female individual.