Fig. 5

Summary of the results of the bone histological analysis: Eusauropterygia and Pachypleurosauria revealed similar trends within their branches, which are indicated by arrows. The pachypleurosaurids decrease the (1) organisation of the crystallites (bone tissue organisation), as well as the (2) bone compactness values with stratigraphical age (Hugi et al. 2011). Bone compactness values only decrease slightly with stratigraphical age based on the greater number of simple vascular canals in the cortex (vascularisation pattern). The orientation of the vascularisation (vascularisation pattern) changes from predominantly longitudinally orientated ones in S. mirigiolensis to predominantly radially orientated ones in the cortex of N. edwardsii (Hugi et al. 2011). A similar trend is observed in Nothosauria: the cortex of C. calcagnii shows an overall higher organisation of the bone matrix with a higher number of radially orientated simple vascular canals and primary osteons, whereas C. lanzi shows a higher amount of less organised bone matrix (pfb) with a greater number of longitudinally orientated primary osteons and simple vascular canals of wider diameter. The bone compactness value of ontogenetically young C. calcagnii and C. lanzi is slightly higher in the latter in relation to the bone samples of the former. The compactness values of Nothosaurus are lower based on a wider diameter of the medullary cavity and a higher abundance of vascularisation in the cortex (simple vascular canals, primary osteons and secondary osteons). The bone matrix of the cortex additionally consists of fibrolamellar bone tissue type in relation to the exclusive presence of lamellar-zonal bone tissue type in the other eosauropterygians from Monte San Giorgio