Heterochronic truncation of odontogenesis in theropod dinosaurs provides insight into the macroevolution of avian beaks

We identified truncation of tooth development during postnatal ontogeny in two theropod dinosaurs, a caenagnathid oviraptorosaur and the Early Cretaceous bird Sapeornis. Developmental and paleontological evidence each suggests dental reduction and beak evolution are coupled, and a sequence of common morphologies is identified that characterizes the multiple transitions to toothless beaks in theropod dinosaurs and birds. Shifts toward earlier cessation of postnatal tooth development can be identified in fish, amphibians, and mammals that are edentulous as adults; therefore the identification of similar transitions in multiple Mesozoic theropod dinosaur lineages strongly implies that heterochronic truncation of odontogenesis played an important role in the macroevolution of beaks in modern birds.