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. 2016 Dec 21:6:39607.
doi: 10.1038/srep39607.

Earliest known unequivocal rhinocerotoid sheds new light on the origin of Giant Rhinos and phylogeny of early rhinocerotoids

Haibing Wang  1   2 , Bin Bai  1 , Jin Meng  1   3 , Yuanqing Wang  1   2
Affiliations

Earliest known unequivocal rhinocerotoid sheds new light on the origin of Giant Rhinos and phylogeny of early rhinocerotoids

Haibing Wang et al. Sci Rep. .

Abstract

Forstercooperiines are a group of primitive rhinocerotoids with a relatively large body size in the Eocene, and normally considered to be closely related to Giant Rhinos. Here we report a new forstercooperiine, Pappaceras meiomenus sp. nov., from the late Early Eocene Arshanto Formation, Erlian Basin, Nei Mongol, China. Pappaceras is the earliest known unequivocal rhinocerotoid, and the holotype of the new species, represented by the most complete cranium of forstercooperiines known to date, shows the earliest evidence of reduction of the first upper premolar in rhinocerotoids, and resembles paraceratheriine Juxia in basicranial features, supporting the interpretation that the forstercooperiine clade is ancestral to paraceratheriines. The new species also displays some similarities with amynodontids in craniodental structures. Phylogenetic analysis identifies P. meiomenus as a basal taxon of the monophyletic forstercooperiines. It also reveals novel phylogenetic relationships of early rhinocerotoids that indicates Uintaceras is the sister group of paraceratheriids, to which amynodontids are more closely related than to any other group of rhinocerotoids. Furthermore, the eggysodontid clade is excluded from hyracodontids and placed as the sister group of rhinocerotids. Hyracodontidae, excluding paraceratheriids and eggysodontids, is placed as the most basal group of the rhinocerotoids.

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Figures

Figure 1
Figure 1. Location of the main fossil localities in the Erlian Basin.
Blue solid star denotes the locality where IVPP V20254 was unearthed. Black solid circles mean other fossil localities of Erlian Basin, and no-solid circles denote towns and villages. Scientific Reports remains neutral with regard to jurisdictional claims in published maps. (The maps were created in Corel DRAW X3 (v. 13.0) by Haibing Wang).
Figure 2
Figure 2. Palaeogene stratigraphy, palaeomagnetic polarities, mammalian horizons and their correlation in the eastern Erlian Basin (modified from previous ref. 25).
The red arrow marks the bed (AS-5) in which the holotype specimen of P. meiomenus was discovered. (The figure was generated in Corel DRAW X3 (v. 13.0) by Haibing Wang).
Figure 3
Figure 3. Cranium of Pappaceras meiomenus.
Photographs in dorsal (a) lateral (c) and ventral (e) views, and corresponding interpretive drawings (b), (d,e) respectively. Abbreviation: bo, basioccipital; bs, basisphenoid; cac, caudal opening of alar canal; ef, ethmoid foramina; (f) frontal; hf, hypoglossal foramen; if, incisive foramen;; i of, infraorbital foramen; l, lacrimal; m, maxilla; ml, malar; n, nasal; o, occipital; oc, occipital condyle; of, optic foramen; obf, orbital foramen; ovf, oval foramen; p, parietal; pap, paroccipital process; pl, palatine; pc, postorbital crest; pgp, postglenoid process; pm, premaxilla; pof, preorbital foramen; ppf, posttympanic-paroccipital foramen; pp, postorbital process; ppp, pterygoid process of palatine; ptp, posttympanic process; s, squamosal; sc, sagittal crest; z, zygomatic; zp, zygomatic process of squamosal; C, upper canine; I1-3, the first to third upper incisor; P2-4, the second to fourth upper premolar; M1-3, the first to third upper molar.
Figure 4
Figure 4. Correlation of geographical distributions and phylogenetic relationship of early rhinocerotoids based on the single most-parsimonious tree (tree length = 430, consistency index = 0.540, retention index = 0.704).
For convenience, node A for Amynodontidae, E for Eggysodontidae, F for Forstercooperiinae, H for Hyracodontidae, P for Paraceratheriidae, R for Rhinocerotidae, U for Paraceratheriinae. Numbers by the nodes denote the Bremer values.
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