Histovariability and lifestyle in Proterochampsidae Romer, 1966 (Archosauriformes) from the Chañares Formation (Late Triassic), northwestern Argentina

This present work reports new data on the palaeohistology of Chañares Formation (early Carnian) proterochampsids based on appendicular bones, particularly Chanaresuchus bonapartei Romer, 1971 (i.e., PULR-V 116, femur, tibia and fibula) and Tropidosuchus romeri Arcucci, 1990 (i.e., PVL-4606, femur), and provides new insights into their paleobiology, histovariability, as well as lifestyle. Chanaresuchus bonapartei presents intraspecific and interelemental histovaribility with collagen fibers organized from lamellar to woven fibered bone tissue, and degree of vascular density from sparse to dense. Both specimens appear to have attained sexual and skeletal maturity, but somatic maturity could not be inferred. Tropidosuchus romeri presents intraspecific histovaribility with collagen fibers organized from parallel-fibered to woven fibered bone tissue, and dense vascularization. The lifestyle analysis for T. romeri, using a statistical model that employs anatomical and microanatomical data, suggests a terrestrial habit. The Proterochampsidae Romer, 1966 recovered from the Chañares Formation exhibits a large disparity in growth strategies among individuals of the same taxa, and with respect to other contemporaneous Archosauriformes.