These dinosaurs lost their teeth as they grew up

December 22, 2016
As Limusaurus grew from adolescent to adult, it lost its teeth and did not grow a new set. Credit: George Washington University

By comparing the fossilized remains of 13 ceratosaurian theropod dinosaurs known as Limusaurus inextricabilis collected from the Upper Jurassic Shishugou Formation of northwestern China, researchers have been able to reconstruct the dinosaur's growth and development from a young hatchling of less than a year to the age of 10. The findings, reported in Current Biology on December 22, uncovered something unexpected: the dinosaurs had teeth as young juveniles that were gradually lost as they grew up.

"We found a very rare, very interesting phenomenon in a ceratosaurian dinosaur whereby toothed jaws in juvenile individuals transition to a completely toothless beaked jaw in more mature individuals during development," says Shuo Wang of Capital Normal University in Beijing, China.

The findings make Limusaurus the first known reptile with the characteristic known as ontogenetic edentulism (meaning tooth reduction or loss in development). Together with other evidence, they led the researchers to conclude that the toothed juveniles were probably omnivorous meat-eaters. The beaked adults most likely transitioned to a plant-based diet.

Wang and colleagues first reported on this ceratosaurian back in 2001. At that point, they had collected just one fossilized juvenile, and they didn't yet know what it was. Over the course of the next several years, more specimens were found. But it wasn't clear that they all belonged to the same species.

"Initially, we believed that we found two different ceratosaurian dinosaurs from the Wucaiwan Area, one toothed and the other toothless, and we even started to describe them separately," Wang says.

Image of Limusaurus. Credit: Yu Chen

As they started to code the dinosaurs' characteristics for phylogenetic analysis, they began to realize that they looked remarkably similar—all except for the teeth. With more careful study, the researchers concluded that in fact the specimens did represent the same dinosaur. It's just that those dinosaurs lost their teeth over time.

The researchers identified 78 developmental changes in Limusaurus in all, with being the most surprising. They say that the discovery has significant implications for understanding the evolution of the beak, an important feeding structure in many dinosaurs of the past, as well as modern birds.

Wang says that tooth loss isn't so unusual in animals alive today. There are fish and an amphibian that lose teeth as they grow. Platypuses lose their too. But the discovery is still a first for the fossil record and for reptiles.

The findings suggest that the dietary habits and needs of some changed over the course of their development, most likely along with shifts in their digestive systems. Wang and colleagues will continue studying changes to the digestive system and skeleton in greater detail.

Explore further: Dinosaurs' rise was 'more gradual,' new fossil evidence suggests

More information: Current Biology, Wang et al.: "Extreme Ontogenetic Changes in a Ceratosaurian Theropod" http://www.cell.com/current-biology/fulltext/S0960-9822(16)31269-6 , DOI: 10.1016/j.cub.2016.10.043

Related Stories

Beaked, bird-like dinosaur tells story of finger evolution

June 17, 2009

James Clark, the Ronald B. Weintraub Professor of Biology in The George Washington University's Columbian College of Arts and Sciences, and Xu Xing, of the Chinese Academy of Science's Institute of Vertebrate Paleontology ...

Big dinosaur discoveries in tiny toothy packages

August 7, 2015

Researchers have examined one of the smallest parts of the fossil record—theropod teeth—to shed light on the evolution of dinosaurs at the end of the Cretaceous. Findings published in the prestigious journal Acta Palaeontologica ...

Did dinosaurs have lips?

June 2, 2016

Can a crocodile's smile reveal whether dinosaurs had lips? What if lips and gums hid most of dinosaur's teeth?

Recommended for you

Fossils reveal unseen 'footprint' maker

January 17, 2017

Fossils found in Morocco from the long-extinct group of sea creatures called trilobites, including rarely seen soft-body parts, may be previously unseen animals that left distinctive fossil 'footprints' around the ancient ...

Study finds links between swearing and honesty

January 16, 2017

It's long been associated with anger and coarseness but profanity can have another, more positive connotation. Psychologists have learned that people who frequently curse are being more honest. Writing in the journal Social ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.