Insights into iguanodontian dental architecture from an Early Cretaceous Chinese basal hadrosauriform maxilla (Ornithischia: Iguanodontia)

Abstract

Basal hadrosauriform iguanodontian dinosaurs have been invaluable towards understanding the evolution of the complex and highly efficient advanced hadrosauriform tooth battery dental system. Here we report a new basal hadrosauriform maxilla specimen -IVPP V22529 -from the Dashuiguo Formation of Maortu, Nei Mongol, China that preserves a corrugated middle ventrolateral margin that differs from the straight and undulating ventral margins found in most iguandontian and non-iguanodontian dinosaurs. The uniqueness of this ventrolateral margin relates to a new dental structure -cementum 'jackets' that wrap about the labial sides of the teeth. To our knowledge this is the first time that cementum has been described migrated onto the tooth crowns of iguandontians (and other dinosaurs), but this trait is common amongst mammals. This dental morphology -seen in a similar form in the basal hadrosauriform Equijubus -therefore broadens our knowledge of iguanodontian maxillary anatomy and shows that the basal hadrosauriform dental system was more morphologically complex than previously thought. IVPP V22529 resembles maxillae specimens of Probactrosaurus gobiensis, a contemporaneous taxon known from the same locality in North China, in sharing an inferred subtriangular shape, a relatively flat lateral surface bearing a low row of foramina as well as similar-looking teeth.However, the presence of a unique corrugated middle ventrolateral margin in IVPP V22529, a low row of foramina on its lateral surface that also open anteriorly and increase in size posteriorly as well as a prominent medial shelf suggests that this specimen does not belong to P. gobiensis. However, these differences could conceivably be related to ontogenetic and sexual variation, which have not been fully documented in P. gobiensis. Basal hadrosauriform iguanodontian dinosaurs have been invaluable towards understanding the evolution of the complex and highly efficient advanced hadrosauriform tooth battery dental system. Here we report a new basal hadrosauriform maxilla specimen -IVPP V22529 -from the Dashuiguo Formation of Maortu, Nei Mongol, China that preserves a corrugated middle ventrolateral margin that differs from the straight and undulating ventral margins found in most iguandontian and non-iguanodontian dinosaurs. The uniqueness of this ventrolateral margin relates to a new dental structure -cementum 'jackets' that wrap about the labial sides of the teeth. To our knowledge this is the first time that cementum has been described migrated onto the tooth crowns of iguandontians (and other dinosaurs), but this trait is common amongst mammals. This dental morphology -seen in a similar form in the basal hadrosauriform Equijubus -therefore broadens our knowledge of iguanodontian maxillary anatomy and shows that the basal hadrosauriform dental system was more morphologically complex than previously thought. IVPP V22529 resembles maxillae specimens of Probactrosaurus gobiensis, a contemporaneous taxon known from the same locality in North China, in sharing an i...