Appendicular skeleton of Protoceratops andrewsi (Dinosauria, Ornithischia): comparative morphology, ontogenetic changes, and the implications for non-ceratopsid ceratopsian locomotion.

Justyna Słowiak,Łucja Fostowicz-Frelik,Victor S Tereshchenko

doi:10.7717/peerj.7324

Abstract

Protoceratops andrewsi is a well-known ceratopsian dinosaur from the Djadokhta Formation (Upper Cretaceous, Mongolia). Since the 1920s, numerous skeletons of different ontogenetic stages from hatchlings to adults, including fully articulated specimens, have been discovered, but the postcranial anatomy of Protoceratops has not been studied in detail. A new, mostly articulated subadult individual provides an excellent opportunity for us to comprehensively describe the anatomy of the limb skeleton, to compare to other ceratopsian dinosaurs, and to study the ontogenetic and intraspecific variation in this species. New data provided by the specimen shed light on the lifestyle of P. andrewsi. The young subadult individuals present an array of morphological characters intermediate between the bipedal Psittacosaurus and fully quadrupedal adult P. andrewsi. We compare these observations with a broad range of non-ceratopsid Neoceratopsia (of various locomotor adaptations) and Psittacosauridae (obligate bipeds), which gives us insight into the evolution of the skeletal characters informative for the postural change in ceratopsian dinosaurs.

Highlights

Protoceratops andrewsi is one of the most common dinosaurs in the Djadokhta Formation (Upper Cretaceous; Dashzeveg et al, 2005) of the Gobi Desert, Mongolia
We give particular attention to the changes of morphology occurring during ontogeny, in order to determine any age dependent morphological trends, especially related to mode of locomotion
We describe for the first time a complete appendicular skeleton of a subadult Protoceratops andrewsi, and compare its morphology and adaptations to those of non-ceratopsid ceratopsians

Summary

Introduction

Protoceratops andrewsi is one of the most common dinosaurs in the Djadokhta Formation (Upper Cretaceous; Dashzeveg et al, 2005) of the Gobi Desert, Mongolia. Appendicular skeleton of Protoceratops andrewsi (Dinosauria, Ornithischia): comparative morphology, ontogenetic changes, and the implications for non-ceratopsid ceratopsian locomotion. The postcranial skeleton of Protoceratops andrewsi was described by Brown & Schlaikjer (1940), most of their detailed descriptions concern bones of mature specimens and information about ontogenetic changes is limited. They considered the sample of Protoceratops at their disposal This may not be the case, because the sample from Bayn Dzak studied by Tereshchenko & Alifanov (2003) was implied to contain a hitherto unknown ceratopsian (Bainoceratops). We give particular attention to the changes of morphology occurring during ontogeny, in order to determine any age dependent morphological trends, especially related to mode of locomotion (see similar studies on other ornithischian genera: Norman, 1980; Heinrich, Ruff & Weishampel, 1993; Dilkes, 2001; Wosik, Goodwin & Evans, 2018)

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Conclusion