Bone microstructure of Lewisuchus admixtus Romer, 1972 (Archosauria,Dinosauriformes)

Lewisuchus admixtus is a basal dinosauriform coming from Late Triassic outcrops of NW Argentina. Although this taxon was recently anatomically restudied, histological data is still wanting. The microstructure of the long bones (femur and two tibie) reveals a relatively fast rate of growth, comparable with that seen in other basal Dinosauriformes and basal dinosaurs. Cortical bone is comprised of fibro-lamellar complex in one femur and tibia, but parallel-fibered matrix are observed in the other tibia. The secondary remodelling of bone is poor and there is not growth marks. The vascularization is relatively dense, longitudinal, laminar and reticular. There are some features that indicate slowdown of the growth at late age of the specimens. The fast growth of L. admixtus implies a relatively high metabolic rate. This is probably related with environmental conditions.