Bone histology on Koreaceratops hwaseongensis (Dinosauria: Ceratopsia) from the Lower Cretaceous of South Korea

Abstract

Koreaceratops hwaseongensis is a basal ceratopsian dinosaur found in the Lower Cretaceous Sihwa Formation (Albian), South Korea. It was found only with the lower part of the body. The right tibia and fibula exhibit poor histological preservation due to microbial degradation. They are characterized by signs of extensive tunneling by microorganisms, which rendered the bone cortex into an amalgam of microscopical globules and foci. Such signs of biodegradation may support the hypothesis that the Lower Cretaceous Korean peninsula had a semi-arid and seasonal wet-dry climate. However, a few remaining traces of histological features like the vasculature and absence/presence of growth marks indicate that the growth pattern of Koreaceratops is very similar to that of a subadult Protoceratops andrewsi. Both species exhibit zonation with some bone remodeling in their tibiae and lines of arrested growth with an extensive bone remodeling in their fibulae. The only histological similarity between Koreaceratops and the more basal ceratopsians Psittacosaurus is the longitudinal and reticular vasculature in their fibulae. These suggest that Koreaceratops is much closer to Protoceratops than Psittacosaurus in terms of phylogeny. The fibula of Koreaceratops shows a constant osseous drift that initially drifted toward the medial axis but abruptly changed to the anterior axis in the final growth interval. In addition, the right tibia's final growth exhibiting an anteromedial osseous drift suggests that Koreaceratops experienced a change in its right hindlimb's biomechanics before death. The number of growth zones in the tibia indicates that Koreaceratops was approximately eight years old when it died.