New Early Eocene <i>Basal tapiromorph</i> from Southern China and Its Phylogenetic Implications

<div><p>A new Early Eocene tapiromorph, <i>Meridiolophus expansus</i> gen. et sp. nov., from the Sanshui Basin, Guangdong Province, China, is described and discussed. It is the first reported Eocene mammal from the basin. The new taxon, represented by a left fragmentary mandible, is characterized by an expanded anterior symphyseal region, a long diastema between c1 and p1, a rather short diastema between p1 and p2, smaller premolars relative to molars, an incipient metaconid appressed to the protoconid on p3, a prominent entoconid on p4, molar metaconid not twinned, cristid obliqua extending mesially and slightly lingually from the hypoconid, inclined metalophid and hypolophid, and small hypoconulid on the lower preultimate molars. <i>Meridiolophus</i> is morphologically intermediate between basal <i>Homogalax</i>-like taxa and derived tapiromorphs (such as <i>Heptodon</i>). Phylogenetic analysis indicates Equidae is more closely related to Tapiromorpha than to Palaeotheriidae, although the latter is only represented by a single species <i>Pachynolophus eulaliensis</i>. ‘Isectolophidae’, with exception of <i>Meridiolophus</i> and <i>Karagalax</i>, has the closest affinity with Chalicotherioidea. Furthermore, the majority rule consensus tree shows that <i>Meridiolophus</i> is closer to <i>Karagalax</i> than to any other ‘isectolophid’, and both genera represent stem taxa to crown group Ceratomorpha.</p>