LONG BONE HISTOLOGY OF MUSSAURUS PATAGONICUS, A BASAL SAUROPODOMORPH DINOSAUR FROM THE EARLY JURASSIC OF ARGENTINA

IGNACIO A. CERDA; ANUSUYA CHINSSAMY; DIEGO POL

Jornada; Jornadas Argentinas de Paleontología de Vertebrados; 2014

The growth pattern of the Early Jurassic basal sauropodomorph Mussaurus patagonicus Bonaparte and Vince is inferred from long bone histology. Several skeletal elements (including humeri, femora and fibulae) of five individuals of M. patagonicus (MPM-PV 1813/10, MLP 61-II-20-26, MLP 61-III-20-22, 68-II-27-1, 61-III-20-23) of different sizes (femora mid-shaft circumferences, fmsc: 5.2, 16, 20, 28 and 32 cm respectively) were sampled. All the specimens were collected from the Laguna Colorada Formation (Laguna Colorada locality, Santa Cruz Province, Early Jurassic). The ontogenetic pattern of bone histology in M. patagonicus is similar to that of other dinosaurs (i.e. early deposition of fibro-lamellar bone, which grades progressively into a less vascularized parallel fibred bone; presence of growth marks which become more closely spaced toward the outer cortex). However, these histological features are poorly correlated with body size. For example, the histology of MLP 68-II-27-1 (fmsc of 28 cm) corresponds to that of an earlier ontogenetic stage than MLP 61-II-20-26 (fmsc of 16 cm). The observed histological variation indicates intraspecific variation with regard to the final body size in M. patagonicus. This variation has been previously observed in the basal sauropodomorph Plateosaurus, and could be related to factors such as sexual dimorphism and phenotypic plasticity.