Article: The 'dwarf' crocodiles of the Purbeck Formation, Dorset: a reappraisal
Nannosuchus gracilidens and Theriosuchus pusillus were described by Owen, who believed that they were dwarf goniopholid crocodiles, adapted for preying on the contemporary small mammals. Several skull characters, which are now known to alter during life in modern crocodiles, were investigated in these 'dwarfs'. A number of these characters in Nannosuchus indicate that it is merely a juvenile form. Furthermore, since a larger form from the same beds, Goniopholis simus, exhibits several specific features found also in Nannosuchus, it is concluded that the latter is the juvenile of G. simus. Both the skull morphology of Theriosuchus and the presence of similar, larger remains in the same bed, indicate that it, too, is a juvenile. Reappraisal of its characters shows that it belongs to the family Atoposauridae and not to the Goniopholidae. The goniopholids have been suggested as possible ancestors of the later, eusuchian crocodiles. However, signs of progression towards eusuchian characters are unknown in the goniopholids, but are found in such atoposaurids as Theriosuchus and a recently discovered form from Texas. The Atoposauridae therefore appear to merit investigation as possible ancestors of the Eusuchia. The meaning and usage of the term 'dwarf' are briefly discussed.