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

Shuo Wang, Josef Stiegler, Ping Wu, Cheng Ming Chuong, Dongyu Hu, Amy Balanoff, Yachun Zhou, Xing Xu

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

Beaks are innovative structures characterizing numerous tetrapod lineages, including birds, but little is known about how developmental processes influenced the macroevolution of these important structures. Here we provide evidence of ontogenetic vestigialization of alveoli in two lineages of theropod dinosaurs and show that these are transitional phenotypes in the evolution of beaks. One of the smallest known caenagnathid oviraptorosaurs and a small specimen of the Early Cretaceous bird Sapeornis both possess shallow, empty vestiges of dentary alveoli. In both individuals, the system of vestiges connects via foramina with a dorsally closed canal homologous to alveoli. Similar morphologies are present in Limusaurus, a beaked theropod that becomes edentulous during ontogeny; and an analysis of neontological and paleontological evidence shows that ontogenetic reduction of the dentition is a relatively common phenomenon in vertebrate evolution. Based on these lines of evidence, we propose that progressively earlier postnatal and embryonic truncation of odontogenesis corresponds with expansion of rostral keratin associated with the caruncle, and these progenesis and peramorphosis heterochronies combine to drive the evolution of edentulous beaks in nonavian theropods and birds. Following initial apomorphic expansion of rostral keratinized epithelia in perinatal toothed theropods, beaks appear to inhibit odontogenesis as they grow postnatally, resulting in a sequence of common morphologies. This sequence is shifted earlier in development through phylogeny until dentition is absent at hatching, and odontogenesis is inhibited by beak formation in ovo.

Original languageEnglish (US)
Pages (from-to)10930-10935
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume114
Issue number41
DOIs
StatePublished - Oct 10 2017

Keywords

  • Beak evolution
  • Caenagnathidae
  • Ontogenetic edentulism
  • Sapeornis
  • Tooth reduction

ASJC Scopus subject areas

  • General

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