Nav: Home

Chew on this: Two new studies reveal secrets of early dinosaur and mammal tooth evolution

November 07, 2018

The studies, involving Professor Robert Reisz, a paleontologist at the University of Toronto Mississauga, appear in the latest issues of PLOS ONE and the Proceedings of the Royal Society B.

In the first paper, Reisz and his colleagues at Jilin University in China examined the teeth of Changchunsaurus parvus, a small herbivorous dinosaur from the Cretaceous period.

Ornithischian ("bird-hipped") dinosaurs developed an incredible diversity of teeth, including the complex dental batteries of derived ornithopods (like the famous duck-bill dinosaurs), but little is known about how these intricate arrangements arose from the simple tooth arrangements of early dinosaurs. Changchunsaurus parvus belongs to a branch at or near the origins of the ornithopods, and thus may provide insight into early ornithopod tooth development.

In this study, Reisz and his colleagues found a unique method of tooth replacement that allowed Changchunsaurus to recycle teeth without disrupting the continuous shearing surface formed by its tooth rows. The authors also found that the teeth feature wavy enamel, a tissue type formerly thought to have evolved only in more modern ornithopods. The authors suspect these features may have arisen early on as this group of dinosaurs became specialized for eating plants.

The whole tooth: how mammals evolved their unique tooth anchoring system

In the second study, published in the Proceedings of the Royal Society B, Reisz worked with his students who are now at the University of Alberta and the University of British Columbia, as well as collaborators at the University of Washington in Seattle, and the Unidad Ejecutora Lillo in Argentina.

Any person who has worn braces knows that your teeth can slowly be pushed and pulled into their proper spots. What you may not know is that this movement is made possible by a special ligament that holds each tooth in its socket. This ligament also serves to cushion each tooth as we chew our food. The origins of this ligament, however, have been a mystery.

This study, led by former University of Toronto Mississauga PhD student Aaron LeBlanc, has solved the mystery surrounding how mammals evolved their complex tooth-anchoring system. For over a hundred years, scientists thought that this ligament evolved with the earliest mammals when they first began to chew, but this new paper shows that this system appeared first in the extinct relatives of mammals, called the therapsids.

By examining CT scans and making thin sections of fossil therapsid teeth and jaws for microscopic study, LeBlanc and his colleagues found that mammal teeth are not as unusual as we once thought. "We found evidence for this ligament system in several groups of extinct therapsids, telling us that it evolved before the first mammals were chewing their food," says LeBlanc.

The researchers also think they've figured out how our therapsid ancestors evolved this ligament anchoring system. They found that in many of the fossil synapsid jaws, the teeth were rapidly fused in place by this encroaching bone, but in some therapsids, the surrounding bone grew more slowly.

"We found that some therapsids, like mammals, must have evolved this ligament anchoring system not by developing brand new tissues, but by delaying the growth of the surrounding bone," says Reisz. "We've re-framed how we view the mammalian condition. We don't think that mammals are more 'advanced' than the other extinct therapsids, but instead mammal teeth are frozen in an earlier state of development compared to animals that have teeth fused to the jaws."

Both studies undertaken at the University of Toronto Mississauga involve teeth that are not firmly anchored to the jaws, but rather held in place by ligaments. There is now clear evidence that ligaments are present in both carnivorous and herbivorous dinosaurs and mammals, and these ligaments are not necessarily related to the evolution of chewing, as previously thought. Reisz hopes that ongoing research will continue to reveal a better understanding of this interesting enigma.
-end-


University of Toronto

Related Dinosaurs Articles:

Volcanic eruptions triggered dawn of the dinosaurs
Huge pulses of volcanic activity are likely to have played a key role in triggering the end Triassic mass extinction, which set the scene for the rise and age of the dinosaurs, new Oxford University research has found.
Dinosaurs: Juvenile, adult or senior?
How old were the oldest dinosaurs? This question remains largely unanswered.
How the darkness and the cold killed the dinosaurs
66 million years ago, the sudden extinction of the dinosaurs started the ascent of the mammals, ultimately resulting in humankind's reign on Earth.
These dinosaurs lost their teeth as they grew up
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.
Dinosaurs' rise was 'more gradual,' new fossil evidence suggests
Researchers have discovered two small dinosaurs together with a lagerpetid, a group of animals that are recognized as precursors of dinosaurs.
Dinosaurs of a feather flock and die together?
In the paleontology popularity contest, studying the social life of dinosaurs is on the rise.
Unique skin impressions of the last dinosaurs discovered in Barcelona
Researchers from the Universitat Autònoma de Barcelona in collaboration with the Institut Català de Paleontologia Miquel Crusafont, have discovered in Vallcebre an impression fossil with the surface of the skin of a dinosaur from the Late Cretaceous, a period right before their extinction.
What dinosaurs' color patterns say about their lives
After reconstructing the color patterns of a well-preserved dinosaur from China, researchers have found that the long-lost species called Psittacosaurus was light on its underside and darker on top.
The success of the plant-eating dinosaurs
Plant-eating dinosaurs had several bursts of evolution, and these were all kicked off by innovations in their teeth and jaws, new research has found.
Soot may have killed off the dinosaurs and ammonites
A new hypothesis on the extinction of dinosaurs and ammonites at the end of the Cretaceous Period has been proposed by a research team from Tohoku University and the Japan Meteorological Agency's Meteorological Research Institute.

Related Dinosaurs Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...