These Dinosaurs Traded Teeth For Beaks As They Grew

What was thought to be two different dinosaurs turned out to be a single species at different stages of development.

AsianScientist (Dec. 30, 2016) – Like platypuses, Limusaurus inextricabilis dinosaurs lose their baby teeth and never get replacements. These findings, based on an analysis of the fossilized remains of 13 specimens collected from the Upper Jurassic Shishugou Formation of northwestern China, have been published in Current Biology.

Limusaurus is the first reptile to show this characteristic known as ontogenetic edentulism, meaning tooth reduction or loss in development. Based on this finding, researchers to concluded that the toothed juveniles were probably omnivorous meat-eaters while the beaked adults most likely transitioned to a plant-based diet.

The researchers 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,” said study corresponding author Wang Shuo of Capital Normal University.

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; juvenile dinosaurs just lost their teeth over time.

The researchers identified 78 developmental changes in Limusaurus in all, with tooth loss being the most surprising. They said 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 added 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 teeth 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 dinosaurs 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.

The article can be found at: Wang et al. (2016) Extreme Ontogenetic Changes in a Ceratosaurian Theropod.


Source: Cell Press; Photo: Yu Chen.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Asian Scientist Magazine is an award-winning science and technology magazine that highlights R&D news stories from Asia to a global audience. The magazine is published by Singapore-headquartered Wildtype Media Group.

Related Stories from Asian Scientist