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:

Discriminating diets of meat-eating dinosaurs
A big problem with dinosaurs is that there seem to be too many meat-eaters.
Jurassic dinosaurs trotted between Africa and Europe
Dinosaur footprints found in several European countries, very similar to others in Morocco, suggest that they could have been dispersed between the two continents by land masses separated by a shallow sea more than 145 million years ago.
In the shadow of the dinosaurs
Research published this Wednesday in Scientific Reports describes Clevosaurus hadroprodon, a new reptile species from Rio Grande do Sul state in southern Brazil.
When the dinosaurs died, lichens thrived
When the asteroid hit, dinosaurs weren't the only ones that suffered.
Dinosaurs were thriving before asteroid strike that wiped them out
Dinosaurs were unaffected by long-term climate changes and flourished before their sudden demise by asteroid strike.
Did volcanoes kill the dinosaurs? New evidence points to 'maybe.'
Princeton geoscientists Blair Schoene and Gerta Keller led an international team of researchers who have assembled the first high-resolution timeline for the massive eruptions in India's Deccan Traps, determining that the largest eruption pulse occurred less than 100,000 years before the mass extinction that killed the (non-avian) dinosaurs.
Want to learn about dinosaurs? Pick up some Louisiana roadkill
Scientists are able to learn about an animal's ecosystem by studying the chemical makeup of its body, whether the animal died recently or millions of years ago.
How did alvarezsaurian dinosaurs evolve monodactyl hand?
An international research team led by XU Xing from the Institute of Vertebrate Palaeontology and Palaeoanthropology announced the discovery of two new Chinese dinosaurs: Bannykus and Xiyunykus, in the journal Current Biology, which shed light on how alvarezsaurian dinosaurs reduced and lost their fingers.
Those fragrances you enjoy? Dinosaurs liked them first
The compounds behind the perfumes and colognes you enjoy have been eliciting olfactory excitement since dinosaurs walked the Earth amid the first appearance of flowering plants, new research reveals.
What the asteroid that wiped out dinosaurs meant for birds
Sixty-six million years ago, an asteroid struck the earth and wiped out non-avian dinosaurs.
More Dinosaurs News and Dinosaurs Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab