Abstract

Artiodactyls diversified during the Eocene and Oligocene in North America and
Europe after their first Holarctic appearance at the beginning of the Eocene.
However, the relationships among early artiodactyls, European endemic forms,
and later derived suiforms, tylopods, and ruminants remain unclear. Early
artiodactyls are relatively rare in Asia compared to those known from North
America and Europe; thus, investigation of Eocene artiodactyls from Asia is
important to resolve these issues. Here we report two new genera and three
new species of small early artiodactyls from middle Eocene deposits of the Erlian
Basin, Inner Mongolia, China. The new materials represent a morphologically
gradational series from Asian Land Mammal Ages Irdinmanhan to Sharamurunian,
characterized by a trend towards bilophodonty in the lower molars. Morphologic
and phylogenetic analyses suggest that these new taxa have a close relationship
with the enigmatic European Tapirulus, which currently consists of five species
that range from the middle Eocene to the early Oligocene. The close relationship
between the Erlian specimens and Tapirulus suggests possible faunal exchanges
between Europe and Asia during the middle Eocene, a view that has been
supported by other mammalian groups across the two continents. The
evolution of bilophodonty in Tapirulidae and Raoellidae is probably attributable
to convergence.