Palaeobiology of the early sauropodomorph Mussaurus patagonicus inferred from its long bone histology

We present here a detailed histological study of long bones from an ontogenetic series of Mussaurus patagonicus, an early sauropodomorph from the Early Jurassic of Argentina. Twenty long bones, including humeri, femora and fibulae, obtained from thirteen individuals of different body sizes were sampled for histological analysis. In general terms, the cortical bone is formed by a well vascularized fibrolamellar and parallel fibred bone. Except for the smaller individuals, cyclical growth marks (CGMs) are well recorded in all the specimens, but their number and relative position is highly variable. Mussaurus exhibits marked variation regarding relative growth rates, with some individuals growing much faster than others. Such variation affects the size of the adult individuals, which results in a poor correlation between the body size and the age/ontogenetic stage for this taxon. These discrepancies may be related to sexual dimorphism and/or developmental plasticity. Intraspecific variatio...