Complete mitochondrial DNA sequence of Chinese alligator, Alligator sinensis, and phylogeny of crocodiles

The 16746-neucleotide (nt) sequence of mitochondrial DNA (mtDNA) of Chinese alligator, Alligator sinensis, was determined using the Long-PCR and primer walking methods. As is typical in vertebrates, the mtDNA encodes 13 proteins, 2 rRNA, 22 tRNA genes, and a noncoding control region. The composition of bases is respectively 29.43% A, 24.59% T, 14.86% G, 31.12% C. The gene arrangement differs from the common vertebrate gene arrangement, but is similar to that of other crocodiles. DNA sequence data from 12S rRNA, 16S rRNA, protein-coding genes and combined sequence data were used to reconstruct the phylogeny of reptiles with the MP and ML, methods. With this large data set and an appropriate range of outgroup taxa, the authors demonstrate that Chinese alligator is most closely related to American alligator among three crocodilian species, which suppors the traditional viewpoint. According to the branch lengths of ML tree from the combined data set, the primary divergence between Alligator and Caiman genus was dated at about 74.9 Ma, the split between Chinese alligator and American alligator was dated at 50.9 Ma.