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. 2014 Oct 29;9(10):e110806.
doi: 10.1371/journal.pone.0110806. eCollection 2014.

New Early Eocene basal tapiromorph from southern China and its phylogenetic implications

Bin Bai  1 , Yuanqing Wang  2 , Jin Meng  3 , Qian Li  2 , Xun Jin  2
Affiliations

New Early Eocene basal tapiromorph from southern China and its phylogenetic implications

Bin Bai et al. PLoS One. .

Abstract

A new Early Eocene tapiromorph, Meridiolophus expansus 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. Meridiolophus is morphologically intermediate between basal Homogalax-like taxa and derived tapiromorphs (such as Heptodon). Phylogenetic analysis indicates Equidae is more closely related to Tapiromorpha than to Palaeotheriidae, although the latter is only represented by a single species Pachynolophus eulaliensis. 'Isectolophidae', with exception of Meridiolophus and Karagalax, has the closest affinity with Chalicotherioidea. Furthermore, the majority rule consensus tree shows that Meridiolophus is closer to Karagalax than to any other 'isectolophid', and both genera represent stem taxa to crown group Ceratomorpha.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Left lower jaw and dentition of Meridiolophus expansus gen. et sp. nov. (IVPP V 20125) from the Sanshui Basin, Guangdong Province, China.
(A–C), occlusal, buccal and lingual views of lower jaw; (D–F), occlusal, buccal, and lingual views of lower dentition from p2-m3. Abbreviations: co, cristid obliqua; end, entoconid; med, metaconid; prd, protoconid.
Figure 2
Figure 2. Log-ratio diagram comparing the value of lower dentition of Meridiolophus and other early tapiromorphs (for raw data see Table S1).
Figure 3
Figure 3. Bivariate plots of m1 and m2 length-width proportion (100× width/length) in some early perissodactyls (for raw data see Table S2).
Red, Meridiolophus; Blue, Homogalax-like taxa from North America and Asia; Green, three representatives of most primitive perissodactyls from Eurasia and North America; Yellow, ‘isectolophids’ from Indo-Pakistan.
Figure 4
Figure 4. Lower dentitions of Meridiolophus and other basal tapiromorphs.
A, Cymbalophus cuniculus (casts of IRSNB M 167 and BMNH M 29710, p3-m2 from AMNH FM 13759, m3 from AMNH FM 119191 and reversed); B, Orientolophus hengdongensis (cast of IVPP V 5789.1, AMNH FM 144353); C, Meridiolophus expansus gen. et sp. nov. (IVPP V 20125); D, Gandheralophus minor (GSP–UM 6770, reversed); E, Homogalax protapirinus (AMNH FM 15371); F, Karagalax mamikhelensis (H–GSP 5139, reversed); G, Chowliia laoshanensis (p3-m2 from IVPP V 10740.7, m3 from IVPP V 10740.11 and reversed); H, Heptodon calciculus (AMNH FM 294, reversed); I, Cardiolophus radinskyi (UM 78915, p4-m3 reversed).
Figure 5
Figure 5. Strict (A) and majority rule (50%) (B) consensus of 55 equally most parsimonious trees (for data matrix see Text S1).
The indices on the strict consensus show Bremer Support, and the question mark indicates values larger than 9. Pink, palaeotheriid Pachynolophus eulaliensis from Europe; Orange, four representatives of Equidae from Europe and North America; Green, ‘isectolophids’ excluding Meridiolophus and Karagalax from Eurasia and North America. Blue, Chalicotherioidea from Asia and North America; Red, crown group ceratomorph Heptodon and stem taxa Meridiolophus and Karagalax from Asia and North America.
Figure 6
Figure 6. Four different hypotheses of phylogenetic relationships among Meridiolophus, Karagalax, Heptodon and Pappomoropus based on 55 MPTs.
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