Fossils of a species of dinosaur that lived 160 million years ago in China may help explain why birds have toothless beaks.

The two-legged Limusaurus inextricabilis was born with teeth but the ostrich-like creature eventually become toothless when it got older. As a result of this drastic transition, the creature, characterized by short arms, long and slender legs, and down-like feathers switched from being an omnivore to becoming herbivore by adulthood.

First Evidence Of Ontogenetic Edentulism In Fossil Record

The growth-related loss of teeth known as ontogenetic edentulism has been seen in some animals that live today. The platypus, for instance, is born with teeth but loses them as it becomes an adult. The phenomenon also occurs in some species of fish and amphibians but this is the first time researchers found evidence of the phenomenon in the fossil record.

Limusaurus belongs to the theropod dinosaur group from which the modern-day birds evolved. The drastic transformation of the prehistoric animal during its lifespan feeding on insects and small vertebrates as a juvenile and eventually thriving on plants as an adult may help shed light on the evolution of beaks.

Researchers said that the dinosaur's development from babies to adults can help show how theropods such as birds lost their teeth.

"The discovery of ontogenetic edentulism in the theropod Limusaurus is potentially significant in understanding the development and evolution of the beak, an important feeding structure present in several tetrapod clades, including modern birds," the researchers wrote in their study

"Early signaling pathways involved in odontogenesis remain inducible in modern birds; the fully developed dentition present in early postnatal ontogenetic stages of Limusaurus indicates that the complete signaling pathways responsible for odontogensis are present and viable in at least one fully beaked theropod."

Earliest Birds Have Teeth

Birds first appeared about 150 million years ago and evolved from small and feathered dinosaurs. The earliest birds are known to have teeth but over a period of tens of millions of years, many evolved to have toothless beaks just like the ones seen in modern-day birds. The last birds who have teeth died with the dinosaurs about 66 millions years ago.

"Species close to the origin of birds may have gone through a similar development, and tooth loss may have been gradual during the evolutionary origin of birds," said James Clark, a paleontologist from George Washington University.

"This is important in showing that growth and development in dinosaurs was more complex than previously suspected, and it provides a model for a stage that birds may have gone through in evolving their beak."

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