|Skeleton of Terrestrisuchus, an early crocodylomorph|
They were originally small, lightly built, active land animals. These were supplanted during the early Jurassic by various aquatic and marine forms. The later Jurassic, Cretaceous, and Tertiary saw a wide diversity of terrestrial and semi-aquatic lineages. Modern crocodilians do not appear until the Upper Cretaceous.
The crocodylian lineage (clade Crurotarsi) were a very diverse group of reptiles. Not only are they an ancient group of animals, at least as old as the dinosaurs, they also evolved into a great variety of forms.
The earliest forms, the sphenosuchians, evolved during the Upper Triassic. They were slim land animals built like greyhounds. During the Jurassic and the Cretaceous, marine forms evolved forelimbs that were paddle-like and had a tail similar to modern fish.
The group had a wider range of habitats and behaviours than it does at presenr. Dakosaurus andiniensis, a species closely related to Metriorhynchus, had a skull adapted for eating large marine reptiles. Several terrestrial species during the Cretaceous evolved herbivory. A number of lines during the Tertiary and Pleistocene became wholly terrestrial predators.
- Irmis, R. B.; Nesbitt, S. J.; Sues, H. -D. (2013). "Early Crocodylomorpha". Geological Society, London, Special Publications. 379 (1): 275–302. Bibcode:2013GSLSP.379..275I. doi:10.1144/SP379.24. S2CID 219190410.
- Nesbitt S.J. 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History. 352: 1–292. [permanent dead link]