A psittacosaurid-like basal neoceratopsian from the Upper Cretaceous of central China and its implications for basal ceratopsian evolution.

Wenjie Zheng,Xingsheng Jin,Xing Xu

doi:10.1038/srep14190

Abstract

Psittacosauridae (parrot-beaked dinosaurs) represents the first major radiation of ceratopsians (horned dinosaurs). However, psittacosaurids are divergent from the general morphology found in other ceratopsians, and this has resulted in their uncertain systematic position among ceratopsians. Here we describe a new basal neoceratopsian dinosaur, Mosaiceratops azumai gen. et sp. nov. based on a partial semi-articulated skeleton recovered from the Upper Cretaceous Xiaguan Formation of Neixiang County, Henan Province, China. Although our phylogenetic analysis supports this taxon as the most basal neoceratopsian, Mosaiceratops exhibits many features previously considered unique to the Psittacosauridae among the basal Ceratopsia. These include a relatively highly positioned external naris, a proportionally large premaxilla, the nasal extending ventral to the external naris, slender postorbital and temporal bars, a large notch between the basal tubera, and the edentulous premaxilla. Thus, the discovery of Mosaiceratops reduces the morphological disparity between the Psittacosauridae and other basal ceratopsians. Character optimization suggests that basal neoceratopsians have re-evolved premaxillary teeth; a major reversal previously unknown in any dinosaur clade. The new specimen also highlights the mosaic nature of evolution among early ceratopsians and supports the phylogenetic hypothesis that the Psittacosauridae is a relatively derived clade, rather than the most basal group of the Ceratopsia.

Highlights

Psittacosauridae represents the first major radiation of ceratopsians
This new species can be placed in the Neoceratopsia based on the presence of several derived features known only in neoceratopsians: a rostral with a well-developed lateral process and a strongly ventrally curved ventral edge; a quadratojugal more prominent in occipital view than lateral view; a spherical occipital condyle; a predentary with a beveled dorsal margin; a predentary that is relatively long and keeled, and has an acutely pointed and strongly upturned anterior tip; shortened post-dentary mandibular elements; a reduced retroarticular process; and the hemispherical humeral head extending onto the posterior surface of the humerus
Mosaiceratops possesses several plesiomorphic features that are previously unknown in other basal neoceratopsians

Summary

Introduction

Psittacosauridae (parrot-beaked dinosaurs) represents the first major radiation of ceratopsians (horned dinosaurs). We report a new basal neoceratopsian based on a specimen recovered from the Upper Cretaceous Xiaguan Formation of Neixiang County, Henan Province, China. The horizon lacks radiometric dates, but is believed to fall between the early-middle Turonian and the middle Campanian of the Late Cretaceous, based on the plant and invertebrate fossils[17] This new specimen displays a mosaic combination of features, some of which were previously considered diagnostic of a certain ceratopsian clade, notably the Psittacosauridae. This specimen represents a significant discovery for understanding the early evolution of ceratopsian dinosaurs. The new information provided by this specimen reshapes our hypotheses of the evolution of several features in ceratopsian evolution

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Conclusion