Microstructural characterization and growth dynamics in Notosuchus terrestris, a Mesoeucrocodylia crocodyliform from the Upper Cretaceous of Northern Patagonia, Argentina

Abstract

The clade Notosuchia was the most successful lineage of Crocodyliformes during the Cretaceous in Gondwana, and was particularly diverse during the Late Cretaceous of South America. The clade has been extensively analyzed in terms of their morphology and phylogenetic relationships, but studies on their paleobiology from a paleohistological viewpoint are still scarce. In this contribution we take this approach in order to infer different paleobiological aspects of Notosuchus terrestris, such as the relative growth rate, growth strategies, intraskeletal and intraspecific variation, as well as evaluation of maturity and age assessment. We conducted paleohistological studies on long bones of six individuals assigned to Notosuchus terrestris from the Upper Cretaceous of Northern Patagonia, Argentina. The cortical bone in N. terrestris is mainly formed by well vascularized woven fibered bone/parallel fibered bone. With the exception of the smaller individual, cyclical growth marks are recorded in all individuals but their number and distribution are variable. N. terrestris experienced a high growth rate interrupted by periods of decreased or even arrested growth. This growth strategy clearly differs from the reported for other advanced notosuchians as Adamantinasuchus, revealing important variation with regard to this parameter in the clade. The sexual maturity in N. terrestris was reached before complete fusion of the caudal vertebrae. There is not a clear correlation between body size and ontogenetic stage in N. terrestris. This inconsistency could be due to sexual dimorphism and/or, more probably, developmental plasticity.