Growth and limb bone histology of aetosaurs and phytosaurs from the Late Triassic Krasiejów locality (sw Poland) reveals strong environmental influence on growth pattern

Abstract The growth pattern of the Polish phytosaur Parasuchus cf. arenaceus and aetosaur Stagonolepis olenkae (both Krasiejów; Norian) was studied. Results were compared to published data other members these two groups a new sample German (Heslach; Nicrosaurus sp. All three herein studied taxa display lamellar-zonal bone consisting predominately parallel-fibred tissue on average low moderate vascular density. Towards outer cortex thickness annuli increases in most samples becomes distinctly wider than zones. Therefore, appositional adults achieved during phases prolonged slow growth. bones show diffuse pattern, without well demarcated zones annuli. Distinct lines arrested ( lag ) are not identified Krasiejów sample, only femur shows one distinct as do outside Krasiejów. Instead, multiple rest sub-cycles. Thus, identification count annual cycles remains difficult, finally counted range (two six) is quite large despite size samples. A correlation between age length identified, indicating developmental plasticity. Although both archosaurs, phylogenetically closely related, however, they very similar different life styles (terrestrial vs. semi-aquatic). Based data, previously histological studies from Krasiejów, local environmental conditions special had strong influence pattern.