While scientists have drawn a strong evolutionary bridge between dinosaurs and birds, they have been at a loss as to why the former had teeth but the latter does not – however, a newly-published study could shed some light on how, when and why beaks originally began to develop.
The paper, published Thursday in the journal Current Biology, details the discovery of a species of dinosaur called Limusaurus inextricabilis that lived in northwestern China approximately 150 million years ago and which appears to have been born with teeth that it lost as it grew older.
According to Reuters and BBC News reports, scientists from the Capital Normal University in Beijing and their colleagues discovered 19 individual specimens of Limusaurus, ranging in age from less than one year to 10 years old, at a site in Xinjiang Province. It appears as though they became trapped in a mud pit and were unable to free themselves before it was too late.
These dinosaurs lost their teeth as they grew up (Credit: Yu Chen)
The discovery provided a rare opportunity for the researchers to examine fossils from the same species of dinosaur across various stages of maturation, and revealed that these tiny, two-legged creatures apparently had small, sharp teeth as juveniles but lost them upon entering adulthood.
“At first we thought they were different dinosaurs – one with teeth and one without – and we started to study them separately,” study co-author Wang Shuo, an evolutionary biologist at the Beijing university, told CNN. “But they were largely identical and we found solid evidence that teeth were lost. There were empty tooth sockets in their jaw bones.”
Dinosaur development ‘more complex’ than previously thought
In light of the evidence of this transition, Shuo and his colleagues believe that Limusaurus likely went from being omnivores that would eat meat (primarily insects) to exclusively eating plants. The phenomenon is common in some species of fish and amphibians, but according to CNN, this marks the first time such changes have been found in a reptile.
This type of tooth-loss is known as ontogenetic edentulism, Reuters explained, and in addition to the empty tooth sockets, the authors also found gastroliths (stones swallowed by some herbivores to help grind up plant material) in the stomachs of some of the adult Limusaurus. However, none of the juvenile stomachs contained any gastroliths, providing additional evidence of tooth loss and dietary changes in members of the species as they grew older.
Limusaurus is a member of the theropod group from which birds evolved, and James Clark, a paleontologist at George Washington University and a co-author on the study, told Reuters that the findings indicate that “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.”
It also shows 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,” Clark added. He also told CNN that the study “suggests a mechanism that arrests the development of teeth – an immediate pathway for the origin of beaks.”
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Image credit: Yu Chen
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