Limusarus Inextricabilis: This Unusual Dinosaur Shed Teeth As It Aged

In an unusual new discovery, one species of dinosaur shed teeth as it grew older, making it the first of its kind in fossil records, and the first of its kind among reptiles.

Limusaurus inextricabilis lived about 160 million years ago, and based on researchers’ findings, babies were most probably omnivorous or carnivorous, sporting sets of pointy teeth. Live Science stressed how this made L. inextricabilis a rather peculiar species – by the time young dinosaurs of this species had turned about 3-years-old, the ostrich-like creatures had lost all their teeth, and wouldn’t grow them back again, thus making them toothless herbivores for the rest of their lives.

Live Science added that the research is based on years of trips to the Gobi Desert in China, as study authors James Clark and Xu Xing made regular travels to the area from 2001 to 2011, digging up Jurassic-era fossils, including Limusaurus inextricabilis. During those trips, the authors found specimens from 19 separate L. inextricabilis skeletons, which included those of babies less than a year old, and adults who were at least 10 years of age. The dinosaurs had most probably died when they got stuck in mud pits, the researchers noted.

When time came to analyze the dinosaurs, teeth were found in the baby L. inextricabilis specimens, but adults of the species did not have any. That left the researchers wondering whether they were dealing with two separate species, but as they found out, the babies and adults belonged to one and the same.

“It’s pretty unlikely that you would have just the juveniles of one species hanging around with the adults of another,” said Clark, a biology professor at George Washington University. “They share all of these features; they’re nearly identical in everything but the teeth.”

Clark noted some of the physical features of Limusaurus inextricabilis, which is believed to be an ancestor of modern birds. The creature was a theropod whose babies measured about one foot in length, but grew to about eight feet as adults. While it was a bipedal dinosaur with an ostrich-like body, short arms, a long tail, and claws on its fingers, it’s still unsure whether it had feathers like other theropods.

Fellow researcher Josef Stiegler, a paleontology candidate at George Washington University, said that L. inextricabilis was such a fascinating specimen because it showed dinosaurs lost their teeth through evolution multiple times across various species.

“We usually think about the evolution of toothlessness in terms of animals having fewer and fewer teeth as a lineage evolves. This finding suggests that the evolution of toothlessness may often involve the interplay between the development of individuals and long-term evolutionary changes.”

Regarding the change in diet from carnivorous in early youth to herbivorous in adulthood, the researchers believe that the answer lies in the adult dinosaurs’ gullets, which contain rocks called gastroliths. These rocks are a feature of modern birds, and serve as an aid for mechanical digestion, the Christian Science Monitor wrote, and in order to have gastroliths, animals would have to literally swallow rocks.

Illustration of Limusaurus inextricabilis. [Image by Nobu Tamura/Wikimedia Commons]
Illustration of Limusaurus inextricabilis. [Image by Nobu Tamura | Wikimedia Commons | Cropped and resized | CC BY 3.0]

But, as SlashGear pointed out, it wasn’t rocks that L. inextricabilis babies ate – instead, they chomped on leftover bones to work around the fact that they were losing their teeth over time.

“Instead, it is as if these dinosaurs had teeth whilst in their first six months of life, lost their teeth, and used the bone left over to continue eating. From that point on, gastroliths started to appear in the guts of these dinosaurs.”

This example of dinosaur teeth disappearing over time as a creature aged marks the first time it was found in dinosaur fossils, and the main takeaway, according to Stiegler, is how tooth loss doesn’t just happen through evolution.

“Limusaurus shows us is that we have to not only think about the evolutionary component, or the phylogenetic component, but also the ontogenetic (growth) component. How does the development of the animal figure into tooth loss?”

[Featured Image by FunkMonk/Wikimedia Commons/Cropped and Resized/CC BY-SA 2.0]