Dental evolution in non-coelurosaur theropods

Christophe Hendrickx^1,2
1Dinosauria Lab, Fundación Miguel Lillo, Miguel Lillo 251, San Miguel de Tucumán 4000, Tucumán, Argentina.
²Unidad Ejecutora Lillo, CONICET-Fundación Miguel Lillo, Miguel Lillo 251, San Miguel de Tucumán 4000, Tucumán, Argentina.
Corresponding author e-mail: christophendrickx@gmail.com

Non-coelurosaur theropods are best known for comprising most carnivorous dinosaurs such as the iconic Allosaurus, Ceratosaurus, Dilophosaurus, and Spinosaurus. Even though the dentition of most non-coelurosaur theropods retained the blade-shape denticulated teeth of their dinosaur ancestors, a few carnivorous clades such as spinosaurids and noasaurids deviated from this plesiomorphic morphology whereas some herbivorous taxa evolved leaf-shaped teeth and even lost their teeth entirely. The discovery and study of theropod teeth are closely tied to the earliest discoveries and research on dinosaurs themselves and despite the numerous studies on theropod teeth, none have addressed the evolution of their external dentition in detail. This study comprehensively explores dental evolution in non-coelurosaur theropods based on a data matrix of 44 external dental characters scored in 80 saurischian taxa and mapped onto six topological trees representing alternative hypotheses of theropod relationships. Results of this study show that zero to one dental apomorphy diagnoses most major non-coelurosaur theropod clades whose dentition typically evolved through minor dental changes in a mainly carnivorous group. The early dental evolution of theropods is characterized by an enlargement of mesial dentary teeth in neotheropods and the anterior displacement of the upper tooth at the level of the lachrymal in non-coelophysoid neotheropods. The first important dental change in early theropods, which likely resulted from a consumption of larger prey items, occurred during the radiation of the clade encompassing Dilophosaurus and averostrans, which is marked by a reduction in dentary and maxillary tooth count, an increase in crown height, and an enlargement of distal denticles in lateral teeth. Among ceratosaurs, ceratosaurids developed particularly tall maxillary crowns, some noasaurids acquired strongly procumbent fluted mesial teeth, and abelisaurids evolved a weaker variation of the crown size along the maxillary tooth row, with the tallest crowns positioned in the middle part of the maxilla. Dental evolution in Carnosauria was primarily marked by changes in premaxillary, maxillary, and dentary tooth count but a few clades also evolved apomorphic dental features such as teeth with a notable difference in size between mesial and distal denticles in piatnitzkysaurids and tall, poorly recurved crowns with pronounced marginal undulations in carcharodontosaurines. The most significant shifts in theropod dental evolution took place during the radiation of “chilesaurs” and spinosaurids in the Middle or Late Jurassic. Both lineages exhibit numerous apomorphic dental features, including a fully procumbent folidont dentition with unserrated teeth in “chilesaurs” and a strongly heterodont dentition made of fluted, conical crowns bearing minute denticles or non-denticulated carinae in spinosaurids. Both dental transitions are explained by a shift in dietary habit, from a strictly faunivorous to an herbivorous diet in “chilesaurs” and from an occasionally piscivorous to a primarily ichthyophagous feeding ecology in spinosaurids.

Dentition, Teeth, Theropoda, Ceratosauria, Megalosauroidea, Allosauroidea.