Phylogeny And Divergences Of Crocodilia Based On The Complete Mitochondrial Genomes Sequences

Two complete mitochondrial genomes of crocodiles were sequenced and analyzed with the Long-PCR and Primer Walking in this research. The two genomes have similar gene order with that of crocodiles determined, neither contains the pseudo control region. The lengths of intergenic spacers and overlap genes, as well as the start codon and stop codon usage in the two crocodiles are special in some species.The results of phylogenesis indicate that the Crocodilia consist of a monophylogey. And it composed a sister group with Aves. It can be deduced that Crocodilia is divided into two groups: Alligatoridae and Crocodylidae. The Crocodylidae includes Crocodylinae and Gavialinae. The Gavialinae includes Genus Tomistoma and Genus Gavialis.According to the divergence time of crocodiles based on three calibration points, we found that primary crocodiles had started to diverge with the splitting apart of ancient continent. This time is about 150 million years before present (the Jurassic period). One enters America to be Alligatoridae, then dividing into Genus Alligator and Genus Caiman, the time is about 110 million years before present. Another branch divided into Crocodylidae and Gavialidae. The time is about 80 million years before present (the Cretaceous period). With the geography presumption, they should enter Africa by North America. One part enters Asia, from Southern Asia enter Australia.