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.
Highlights
The findings of polar dinosaurs have changed our understanding of dinosaurs as warm climate animals, and have raised a number of questions
The studied stegosaur teeth were collected from the Batylykh Formation, Sangar Series (Lower Cretaceous, Berriasian–Barremian) at the Teete locality in Suntar Ulus, Yakutia, Eastern Siberia, Russia
Taking into account the “en echelon” arrangement of maxillary and dentary teeth in stegosaurs, the confluence or overlapping of wear facets in the Teete stegosaur, and only orthal and palinal movements of the mandibles, we suggest that two or even three wear facets are the result of a consistent contact of the functional tooth with opposite teeth of different ages
Summary
The findings of polar dinosaurs have changed our understanding of dinosaurs as warm climate animals, and have raised a number of questions. Were these dinosaurs perennial polar residents or did they migrate south with the beginning of the polar night? Maidment et al, 2008 [17] did not agree with the assignment of the Teete teeth to stegosaurs They noted that “the large denticles that are confluent with striations extending from the base of the crown to the tip are unlike those seen on other stegosaurian dinosaurs” and referred them to an indeterminate ankylosaur [17]. A preliminary study of newly collected material has shown that the supposed thyreophoran teeth from Teete exhibit stegosaurian dental features (for details see “Affinities of Teete stegosaur” below) and Averianov et al, 2018 [9] identified a number of isolated teeth from Teete as Stegosauria indet
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