Archosauromorpha: the Crocodylomorpha
Résumé
The Crocodylomorpha, one of the three main archosaurian clades, form a large and diversified group spanning from the early Late Triassic (Carnian) to the present. During its long evolutionary history, Crocodylomorphs developed three broad adaptations: terrestrial and cursorial in the earliest taxa (the Sphenosuchia) and the Cenozoic Notosuchia; amphibious in many taxa since the Middle Jurassic, especially the Eusuchia and marine in the Mesozoic Thalattosuchia and Tethysuchia. Bone microstructures in crocodilian are relatively consistent among taxa. At a microanatomical level, long bones are tubular and robust, with high corticodiaphyseal index and compactness values. However, in the most specialized Thalattosuchia, the Metriorhynchids, the bones are much more cancellous. Histologically, periosteal cortices in all groups, except the Notosuchia, consist of lamellar-zonal tissue with very conspicuous cyclical growth marks. This tissue generally displays abundant, geometrically variable vascular networks and is submitted to active Haversian remodeling that can locally create dense Haversian bone. Conversely, bone cortices of the Notosuchia are made of poorly vascularized parallel or lamellar tissues void of significant Haversian remodeling. After describing in detail the microstructures of crocodilian bones, this chapter considers the issue in terms of habitat and ecophysiological adaptations.