Histovariability and fossil diagenesis of Pissarrachampsa (Pseudosuchia, Notosuchia, Baurusuchidae) from the Upper Cretaceous of Southeast Brazil.

Notosuchians were key components of western Gondwanan Cretaceous ecosystems in terrestrial predator niches and exhibited remarkable taxonomic and ecological diversity. Previous research has explored their physiology, metabolism, and histology, revealing varied growth patterns and life history strategies. While significant advancements have been made in recent years, there is much to unveil about the evolution of growth rate strategies within this clade. Here, we analyzed the histological variability of Pissarrachampsa sera, a baurusuchid from the Upper Cretaceous Adamantina Formation in Southeast Brazil, to investigate its growth dynamics and ecological adaptations. Thin sections from the femur, tibia, and fibula revealed fibrolamellar bone tissue with varied vascularization patterns, including radial, reticular, plexiform, laminar, and longitudinal canals. These patterns indicate differential growth rates among skeletal elements, with the tibia growing the fastest and the fibula the slowest. External Fundamental System and multiple Lines of Arrested Growth suggest somatic maturity in this young adult specimen. Limited diagenetic artifacts ensured reliable preservation for paleohistological interpretation. This study provides valuable information about notosuchian physiology and their evolutionary success in Gondwanan terrestrial ecosystems during the Mesozoic. Future investigations should aim to expand histological sampling across diverse taxa to refine our understanding of notosuchian growth strategies and ecological roles.