THE FIRST DISCOVERY OF AN ALLIGATORID (CROCODYLIA, ALLIGATOROIDEA, ALLIGATORIDAE) IN THE EOCENE OF CHINA

摘要

The Chinese alligator (Alligator sinensis) of the Yangtze area of China is the only living alligatorid in Asia (Wermuth and Mertens, 1961; Pough et al., 2004; Jiang, 2010; Thorbjarnarson and Wang, 2010; Fig. 1). The second modern species of Alligator, the American alligator (A. mississippiensis), is restricted to the southeastern U.S.A. (Wermuth and Mertens, 1961; Pough et al., 2004). The Chinese and American alligators are the only living representatives of Alligatorinae, a group including these two species and their closest relatives (Brochu, 1999). Other living alligatorids-five to seven species of caimans that are distributed in Mesoamerica and South America-are members of Caimaninae (a group including Caiman crocodilus and all crocodylians closer to it than to A. mississippiensis; Brochu, 1999, 2011). The timing of divergence between caimanines and alligatorines was between 71 and 60 million years ago based on molecular data and the fossil record (Brochu, 2011; Oaks, 2011) and that between the extant Alligator species is ~ 58-31 million years based on molecular data (Oaks, 2011) and ~ 20-25 million years based on fossils (Brochu, 2003). If the divergence estimate based on molecular data is correct, it implies that a stock of basal members of the A. sinensis lineage would be predicted to be present in Asiatic Paleogene-aged deposits. Otherwise, if the molecular estimates have overestimated the divergence time and fossils better capture the record, then any alligatorids found in Asia during the early Paleogene would not lie within the crown Alligator clade.