摘要The complete mitochondrial NADH dehydrogenase subunit 2 (ND2)gene sequences of two species of Thermophis,T.baileyi and T zhaoermii,were sequenced and compared to those of 86 sequences from other snakes (74 from Caenophidia and 12 from Henophidia).By using Bayesian inference (BI)and maximum likehood (ML)approaches,Thermophis was demonstrated as the sister group to the North American relicts of Dipsadinae,and rooted in Central and South American members of this subfamily.The results suggest that the closest relatives of Thermophis are the North American relicts,and thus support the hypothesis for an Asian-North American origin of xenodontine snakes as suggested by Vidal et al.(2000).Extensive sampling of Asian snakes and American dipsadines is needed to further test this hypothesis in the future.