Hynobiidae origin in middle Cretaceous corroborated by the new mitochondrial genome of Hynobius chinensis.

Hynobius chinensis was first described by Günther in the nineteenth century. At present, the origins of the extinct Hynobius chinensis on the Zhoushan Island (Hynobius chinensis-ZI) remain a mystery. It is the only species of family Hynobiidae on the Zhoushan Island. However, there is very little empirical evidence regarding Hynobius chinensis-ZI phylogenetic relationship, and when or how did its ancestors colonized the island. Here, we used mitochondrial genome data to recover the phylogeny of family Hynobiidae. Results suggested that the origin of Hynobiidae was most likely in Middle Cretaceous (~112.9 Mya), and some Hynobius species of Taiwan and Japan diverged earlier than that of the mainland of China. Hynobius chinensis-ZI diverged from its closest living relative (Hynobius yiwuensis) around 6.5 Mya, and Hynobius chinensis-ZI was isolated on Zhoushan Island since the postglacial transgression in Holocene period.