Ancient predators grew 'steak-knife' teeth

As the meat it ate came in bigger and bigger packages, an ancient predator found a solution it evolved serrated teeth similar to steak knives, a Canadian study has found.

Dimetrodon was a lizard-like carnivore with a huge, sail-like fin on its back. It stalked its prey in the hot, swampy, equatorial forests of the Permian period of the Paleozoic Era, about 298 million to 272 million years ago before the Age of Dinosaurs.

Dimetrodon arose at a time when its ecosystem was dominated by small amphibians and most animals were carnivores, said Kirstin Brink, lead author of the study published recently in Nature Communications.

No such carnivore-heavy ecosystems exist today, leading scientists to wonder how so many meat-eaters co-existed, she told CBC's Quirks & Quarks in an interview that aired Saturday.

• Hear the full interview on Quirks & Quarks

Brink, a graduate student in biology at the University of Toronto Mississauga, said that over the time that Dimetrodon lived, its ecosystem developed into something more like the kinds we recognize ones with more herbivores than carnivores, and much larger herbivores than before.

In a study conducted with her supervisor, University of Toronto Mississauga professor Robert Reisz, Brink tried to see what she could learn about those changes by looking at Dimetrodonteeth.

The teeth they studied were from the collection of the Royal Ontario Museum and were so well-preserved that "you'd look at them and think that maybe it just fell out of the mouth of Dimetrodon," she recalled.

The researchers peered closely at the teeth, which had been discovered in what is now Texas, with an electron microscope, cutting some open to reveal their internal structure. They observed and recorded changes over 25 million years of evolution, from the time that Dimetrodons were small predators hunting among small amphibiansto when they grew to be larger than tigers and had much larger herbivores to eat.

They discovered that early Dimetrodons had teeth with smooth edges, but in later species "the edges of the teeth are serrated like a steak knife," Brink said.

Similar adaptation in later dinosaurs

That adaptation, which allows a predator to slice up prey more efficiently, had been previously seen in later meat-eating dinosaurs, but Dimetrodon is now the earliest-known animal with teeth like that.

The change in tooth shape suggests that Dimetrodon's prey was changing, Brink said.

In a statement, Reisz noted that serrated teeth would have allowed Dimetrodon to grab, rip and dismember larger prey, which were becoming increasingly available.

Brink said the researchers are interested next in how Dimetrodon's changing body size fits into the picture.

"What I would like to know is if we can actually figure out if there was kind of an evolutionary arms race can we tell ifthere was an increase in body size in Dimetrodon because the prey items it's eating are also getting very large?"

Dimetrodon is considered the ancestor of mammals and in fact the study uncovered another interesting evolutionary change it was the first animal to develop cusps or points on the crowns of its teeth, like the ones found in humans.