Abstract

The genus Aztlanolagus from North America is synonymized with Pliopentalagus based on similar morphology of dental characters including (1) general form of five reentrant angles and outline of p3, (2) an enamel lake at the position of PIR, (3) general form of enamel crenulations of the anterior wall of the talonid on p4–m2, and (4) an AER on p4–m2 on some specimens. However, the species A. agilis is valid because of its much smaller size. The general morphology and size of this species, transferred to Pliopentalagus, did not change for about the last 2.5 million years. Three Asiatic species of Pliopentalagus (Pl. huainanensis, Pl. dajushanensis, and Pl. anhuiensis, from geologically older to younger) were described from the latest Miocene (ca. 6 Ma) to Late Pliocene (ca. 3 Ma) at Dajushan in Anhui Province, China. These taxa represent a gradually evolving lineage, an example of phyletic gradualism. Pliopentalagus okuyamai was recently described based on a fragmentary skull with upper dentition from ca. 3.5 Ma deposits in Japan and represents a possible ancestral form of the living type species, Pentalagus furnessi. Fossil Pliopentalagus dietrichi is known from the Early Pliocene in Europe and likely evolved from Chinese Pl. dajushanensis. However, Pl. dietrichi lacks an enamel lake on p3 and an AER on p4–m2; this assumes that the ancestral population dispersing to Europe probably did not have a gene controlling the appearance of an enamel lake on p3 and an AER on p4–m2. Thus, Pliopentalagus diversified and dispersed widely across the Holarctic region over the last 6 million years, disappeared near the end of the Pleistocene, and left a single descendant, Pentalagus furnessi in Japan.

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Abstract

In Asia, the first find of an eomyid rodent was reported almost one century after the first studies of the family Eomyidae in North America and Europe. Since then, eomyid rodents have been increasingly found in Asia particularly over the past two decades. Here, we review the Asian record of this family at the genus level. Currently, 22 species within 14 genera were reported from Asia, including seven endemic genera and rare materials of apeomyine eomyids. Eomyids emphasize the palaeogeographic importance of Asia in considering intercontinental dispersal events of small mammals. With newly compiled data for Asian eomyids, we also compare genus-level diversity trends through time among North America, Europe, and Asia. Despite data standardizations limited with respect to potential biases in the fossil record, we found that the Asian eomyid diversity closely follows ecological shifts induced by climate changes. In general, Asian eomyid genera disappeared earlier than their European counterparts. We suggest that this pattern is not dictated by differences in the quality of the fossil record and is related to the expansion of drier habitats over large areas of Asia.

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