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Limusaurus inextricabilis: Strange new dinosaur species lost their teeth as adults

A team of researchers  from George Washington University has published a paper in Current Biology that details their discovery of a new species of dinosaur, which could explain why birds have beaks but no teeth. The dinosaur, Limusaurus inextricabilis, was discovered in the Xinjiang province of China. The team studied 19 skeletons that were found in an ancient “death pit,” where they had become stuck in mud and were unable to escape.

The dinosaurs ranged in age from babies to adults, exhibiting a pattern of tooth loss over time. This age range was important to the researchers for two reasons, as Dr. James Clark outlines, “First, it’s very rare to find a growth series from baby to adult dinosaurs. Second, this unusually dramatic change in anatomy suggests there was a big shift in Limusaurus inextricabilis diet from adolescence to adulthood.”

The baby skeleton had small, sharp teeth, while the adult skeletons had no teeth at all and did not appear to grow another set as adults. This may indicate that the young Limusaurus were carnivores or omnivores, while the adults were herbivores. Generally, a change in tooth structure or loss of teeth is indicative of a diet change as well. The chemical makeup of the dinosaurs’ bones also supports the team’s theory of a diet change between babies and adults.

Limusaurus is a part of the theropod group of dinosaurs, which are the evolutionary ancestors of birds. Scientists believe that these fossils may help show how theropods such as birds lost their teeth, initially going through anatomical changes during development from infancy to adulthood.

Josef Stiegler, a co-author on the paper, reiterates the importance of these fossil findings, “For most dinosaur species we have few specimens and a very incomplete understanding of their developmental biology. The large sample size of Limusaurus allowed us to use several lines of evidence including the morphology, microstructure, and stable isotopic composition of the fossil bones to understand development and dietary changes in this animal.”

Limusaurus inextricabilis fossil. Credit: GWU

Limusaurus inextricabilis fossil. Credit: GWU

Credit: author Connor Ertz/George Washington University

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