Wear patterns and dental functioning in an Early Cretaceous stegosaur from Yakutia, Eastern Russia

Abstract

Isolated stegosaurian teeth from the Early Cretaceous high-latitude (palaeolatitude estimate of N 62°- 66.5°) Teete locality in Yakutia (Eastern Siberia, Russia) are characterized by a labiolingually compressed, slightly asymmetrical and mesiodistally denticulated (9–14 denticles) crown, a pronounced ring-like cingulum, as well as a “complex network of secondary ridges”. The 63 teeth (found during on-site excavation in 2012, 2017–2019 and screen-washing in 2017–2019) most likely belong to one species of a derived (stegosaurine) stegosaur. Most of the teeth exhibit a high degree of wear and up to three wear facets has been observed on a single tooth. The prevalence of worn teeth with up to three wear facets and the presence of different types of facets (including steeply inclined and groove-like) indicate the tooth-tooth contact and precise dental occlusion in the Teete stegosaur. The microwear pattern (mesiodistally or slightly obliquely oriented scratches; differently oriented straight and curved scratches on some wear facets) suggest a complex jaw mechanism with palinal jaw motion. Histological analysis revealed that the Teete stegosaur is characterized by relatively short tooth formation time (95 days) and the presence of a “wavy enamel pattern”. Discoveries of a “wavy enamel pattern” in the Teete stegosaur, in a Middle Jurassic stegosaur from Western Siberia, and in the basal ceratopsian Psittacosaurus, suggest that this histological feature is common for different ornithischian clades, including ornithopods, marginocephalians, and thyreophorans. A juvenile tooth in the Teete sample indicates that stegosaurs were year-round residents and reproduced in high latitudes. The combination of high degree of tooth wear with formation of multiple wear facets, complex jaw motions, relatively short tooth formation time and possibly high tooth replacement rates is interpreted as a special adaptation for a life in high-latitude conditions or, alternatively, as a common stegosaurian adaptation making stegosaurs a successful group of herbivorous dinosaurs in the Middle Jurassic–Early Cretaceous and enabeling them to live in both low- and high-latitude ecosystems.

Multi-proxy dentition analyses reveal niche partitioning between sympatric herbivorous dinosaurs

“…To our knowledge, tooth formation time has only been reported in one other thyreophoran, a taxonomically indeterminate stegosaur tooth from the Early Cretaceous of eastern Siberia 36 . This small tooth crown (height ~ 4 mm) possesses 95 VEIB with a mean width of 16.24 μm (measured on the basis of 36 . Skutschas et al .…”

“…Skutschas et al . 36 interpreted these observations as indicative of a short tooth formation time (95 days) and suggested a high tooth replacement rate. However, comparing these values with those of the above mentioned ankylosaurs, it seems that the Siberian stegosaur tooth was quite similar with respect to tooth formation.…”

“…Its tooth size is almost identical to that of Pinacosaurus grangeri 34 and the mean width of VEIB is also very similar (15.7 μm in the latter). Due to the more extensive, and perhaps faster, wear compared to that inferred in ankylosaurs 36 , a faster tooth replacement rate cannot be excluded, but further evidence from replacement teeth of this unnamed stegosaur taxon will be required to test this issue.…”

“… Pinacosaurus 34 IGM 100/3186 ? 3.5* 75 15.7 Transverse Teete stegosaur 36 ZIN PH 41/246 ? 4.0* 95 16.24 Longitudinal Mochlodon MTM VER 2016.2551.…”

“…1 – 20 ). Ornithopods exhibit some of the most elaborate dentitions and jaw mechanisms 11 , 21 – 27 , but it is now clear that thyreophorans also had varied ways of processing food 28 – 36 . In both groups, complex jaw mechanisms, distinct from the simple orthal jaw closure that was symplesiomorphic for the clade, were present in numerous taxa, and allowed more efficient chewing (and subsequent digestion) of the food consumed.…”