Life history and growth dynamics of a peirosaurid crocodylomorph (Mesoeucrocodylia; Notosuchia) from the Late Cretaceous of Argentina inferred from its bone histology.

Notosuchia were a successful lineage of Crocodyliformes that achieved a remarkable diversity during the Cretaceous of Gondwana, particularly in South America. Although paleohistology has expanded our knowledge of the paleobiology of notosuchians, several clades of this lineage remain poorly understood in this aspect. Here we help to address this gap by conducting the first histological analysis of appendicular bones of a peirosaurid. To increase our knowledge about growth dynamics and examine intraeskeletal and interspecific histological variation, we analyze the microstructure of a tibia, fibula, phalanx, fragment of ornamented element (possible osteoderm or skull bone) and a possible long bone of an individual assigned to Peirosauridae indet. (MAU-Pv-437). The peirosaurid studied here appears to have reached sexual but not somatic maturity and the minimum age inferred from appendicular bones results in a lower estimated than the age inferred from osteoderms in a previous study on the same individual. The cortical bone in MAU-Pv 437 is formed by vascularized parallel fibered bone/lamellar bone which indicates that this individual experienced a moderate growth rate. This indicates different growth dynamics from what has been observed for other notosuchians specimens, suggesting a lack of a uniform growth pattern for this clade.