The divergence and dispersal of early perissodactyls as evidenced by early Eocene equids from Asia.

The earliest perissodactyls are represented by some basal equoid fossils from Euramerica near the Paleocene/Eocene boundary. Unequivocal early equoids have yet to be reported from the early Eocene of Asia, although other groups of early perissodactyls were indeed present in Asia. Here we report the earliest Eocene Asian equid, Erihippus tingae gen. et sp. nov., based on partial specimens initially assigned to the ceratomorph Orientolophus hengdongensis, from the Hengyang Basin of Hunan Province, China. The specimens previously assigned to 'Propachynolophus' hengyangensis from the same Lingcha fauna are split and now reassigned as an ancylopod Protomoropus? hengyangensis and a brontothere Danjiangia lambdodon sp. nov. The nearly simultaneous appearance of equids, ceratomorphs, ancylopods, and brontotheres in the Hengyang Basin suggests that the four main groups of perissodactyls diverged as early as, or no later than, the beginning of the Eocene (about 56 Ma), and displayed different dispersal scenarios during the early Eocene.