Wednesday, September 30, 2015

[Paleontology • 2015] Mosaiceratops azumai • A Psittacosaurid-like Basal Neoceratopsian from the Upper Cretaceous of central China and Its Implications for Basal Ceratopsian Evolution

Mosaiceratops azumai
  Zheng, Jin & Xu, 2015

Figure 1: Holotype and skeletal reconstruction of Mosaiceratops azumai, gen. et sp. nov (ZMNH M8856).   (a) photograph and line drawing of ZMNH M8856;  (b) skeletal reconstruction showing preserved elements in white. Scale bar 10 cm.

Abbreviations: a, astragalus; boc, basioccipital; c, calcaneum; cav, caudal vertebra; ch, chevron; cv, cervical vertebra; dr, dorsal rib; dv, dorsal vertebra; f, frontal; fem, femur; fl, fibula; h, humerus; il, ilium; is, ischium; L, left; mt, metatarsal; ph, phalanx/phalanges; po, postorbital; R, right; sk, skull; sq, squamosal; t, tibia; td, tendon; ?, undiagnostic remains.

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.

Systematic palaeontology

Dinosauria Owen, 1842
Ornithischia Seeley, 1887

Ceratopsia Marsh, 1890
Neoceratopsia Sereno, 1986

Mosaiceratops azumai gen. et sp. nov.

Etymology: The generic name Mosaiceratops (“mosaic ceratopsian”) is a contraction of the Latin terms “mosaicus” and “ceratops” in reference to the specimen’s unique (mosaic) combination of characters that were previously considered diagnostic of basal ceratopsians, psittacosaurids, or basal neoceratopsians. The specific name honors Dr. Yoichi Azuma from Fukui Prefectural Dinosaur Museum, who co-organized and participated in several dinosaur expeditions in China. One of those expeditions led to the discovery of the basal neoceratopsian Archaeoceratops.

Figure 3: Temporal calibration of the single most parsimonious tree produced by phylogenetic analysis.

Locality and horizon: Upper Cretaceous (lower-middle Turonian—middle Campanian), Xiaguan Formation, Neixiang County, Henan Province, China.

Wenjie Zheng, Xingsheng Jin and Xing Xu. 2015. A Psittacosaurid-like Basal Neoceratopsian from the Upper Cretaceous of central China and Its Implications for Basal Ceratopsian Eevolution. Scientific Reports. 5, 14190. doi: 10.1038/srep14190