The origin of the bird's beak: new insights from dinosaur incubation periods

The toothless beak of modern birds was considered as an adaption for feeding ecology; however, several recent studies suggested that developmental factors are also responsible for the toothless beak. Neontological and palaeontological studies have progressively uncovered how birds evolved toothless...

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Bibliographic Details
Published in:Biology letters (2005) 2018-05, Vol.14 (5), p.20180090-20180090
Main Authors: Yang, Tzu-Ruei, Sander, P. Martin
Format: Article
Language:English
Subjects:
Animals
Beak - embryology
Beaks
Biological effects
Biological Evolution
Birds
Birds - embryology
Developmental Biology
Dinosaurs
Dinosaurs - embryology
Ecological effects
Ecological monitoring
Edentulism
Embryos
Fossils
Gene expression
Gene regulation
Hypotheses
Incubation
Incubation Periods
Opinion Piece
Palaeontology
Phylogeny
Teeth
Tooth - embryology
Tooth Formation
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Summary:The toothless beak of modern birds was considered as an adaption for feeding ecology; however, several recent studies suggested that developmental factors are also responsible for the toothless beak. Neontological and palaeontological studies have progressively uncovered how birds evolved toothless beaks and suggested that the multiple occurrences of complete edentulism in non-avian dinosaurs were the result of selection for specialized diets. Although developmental biology and ecological factors are not mutually exclusive, the conventional hypothesis that ecological factors account for the toothless beak appears insufficient. A recent study on dinosaur incubation period using embryonic teeth posited that tooth formation rate limits developmental speed, constraining toothed dinosaur incubation to slow reptilian rates. We suggest that selection for tooth loss was a side effect of selection for fast embryo growth and thus shorter incubation. This observation would also explain the multiple occurrences of tooth loss and beaks in non-avian dinosaur taxa crownward of Tyrannosaurus. Whereas our hypothesis is an observation without any experimental supports, more studies of gene regulation of tooth formation in embryos would allow testing for the trade-off between incubation period and tooth development.
ISSN:1744-9561
1744-957X
DOI:10.1098/rsbl.2018.0090