Bone microstructure in terrestrial Mesozoic Crocodylomorpha: Neuquensuchus and notosuchians

The bone histology of different taxa of terrestrial Crocodylomorpha, specifically the Cretaceous non-mesoeucrocodylian Neuquensuchus universitas and three mesoeucrocodylian notosuchians, were studied. In order to better understand their growth pattern, we analysed the bone histology of the femora and humerus of Neuquensuchus universitas, two specimens of Notosuchus terrestris, one specimen of Mariliasuchus amarali, and one specimen of Adamantinasuchus navae. Neuquensuchus exhibits an important inter-elemental histovariability (the humerus constituted by crossed parallel-fibred bone tissue and without growth marks, while the femur possesses fibrolamellar bone tissue and growth marks). The Mariliasuchus cortex presents a parallel-fibred bone tissue, as well as a moderate density of longitudinal vascular canals and 4 LAGs (lines of arrested growth). Adamantinasuchus exhibits in its cortex a parallel-fibred bone tissue, and a moderate density of longitudinal vascular canals. The specimens of Notosuchus present a cortex with parallel-fibred bone tissue, with vascularization densities from moderate to dense, and from longitudinal to reticular vascular patterns. The evidence presented here does not support an endothermic metabolism for the analysed specimens; it reinforces the previous hypothesis about the uncoupling between terrestrial life habits and a high growth rate; and the environmental influence on growth patterns is remarkable. This study suggests that the high growth tissues described in some specimens could be related to a plesiomorphic condition shared with other early archosaurs.