Ossification sequences and associated ontogenetic changes in the bone histology of pachypleurosaurids from Monte San Giorgio (Switzerland/Italy)

Pachypleurosaurids from Monte San Giorgio exhibit a transition from 'terrestrial' to more 'aquatic' osteogenetic sequences, as evidenced by increasing heterochronic shifts with decreasing stratigraphic age. This study reveals that forelimb ossification precedes hind limb elements in all stages except initiation, while early phase compaction processes align with the hypothesized plesiomorphic eureptilian condition. The research analyzed bone histology and taphonomic patterns in four pachypleurosaurid species, comparing them to extant terrestrial lizards and secondarily aquatic reptiles to determine evolutionary trends in osteogenesis.

Hugi, J., & Scheyer, T. M. (2012). Ossification sequences and associated ontogenetic changes in the bone histology of pachypleurosaurids from Monte San Giorgio (Switzerland/Italy). Journal of Vertebrate Paleontology, 32(2), 315–327. https://doi.org/10.1080/02724634.2012.646376