A new primitive alligatorine from the Eocene of Thailand: relevance of Asiatic members to the radiation of the group

Despite the report of fragmentary remains from China, the fossil record of primitive Alligatorinae is unbalanced with most of its members reported from North America and Europe. Here, we describe cranial, mandibular, and some postcranial elements of a new alligatorine taxon from the Late Eocene of Krabi Basin, southern Thailand. Krabisuchus siamogallicus gen. et sp. nov. was a small animal probably not surpassing 2 m in total length. Despite deformation, the remains show a dorsally elevated cranium similar to Arambourgia gaudryi and Osteolaemus tetraspis. The new alligatorine is characterized by a very short snout and a blunt dentition in the posterior region. Krabisuchus siamogallicus is the first fossil alligatorine from Asia to be incorporated into cladistic analysis. Results indicate a close relationship of the newtaxon to Procaimanoidea, Arambourgia gaudryi, and Allognathosuchus polyodon, all of them being sister groups to the Alligator clade. Alligatorine were widespread as early as the Late Eocene across the northern hemisphere. Scenarios of alligatorine dispersal during the Palaeogene are discussed in comparison with the European and North American alligatorine fossil record. Basal alligatorines were probably land-dwelling animals contrary to modern-day crocodylians. Such a mode of life may have allowed this group to colonize vast territories, especially during periods of global warm climates. (C) 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158, 608-628.