A diagram of the dimetrodon, with an empasis on the internal bone structure of the face.

Carleton’s Hillary Maddin Helps Identify Canada’s Second Oldest Vertebrate Fossil

Carleton University’s Hillary Maddin, assistant professor in the Department of Earth Sciences, is part of a team that has made important discoveries about a Canadian fossil.

The fossil, originally discovered in Prince Edward Island and long mistaken for that of a dinosaur, has been shown to have steak-knife-like teeth. Maddin joined with researchers from the University of Toronto (Mississauga) and the Royal Ontario Museum in identifying the fossil. The group has changed its name from Bathygnathus borealis to Dimetrodon borealis, marking the first occurrence of a Dimetrodon fossil in Canada.

“This greatly expands our knowledge of these early relatives of modern mammals, as well as the history of life in Canada,” said Maddin. “As the second oldest vertebrate fossil known from Canada, it is an important part of understanding our natural heritage.”

The study was published today in the Canadian Journal of Earth Sciences.

“It’s really exciting to discover that the detailed anatomy of the teeth has finally allowed us to identify precisely this important Canadian fossil,” says Kirstin Brink, lead author on the study and a graduate student of Biology at the University of Toronto (Mississauga). “Dimetrodon is actually more closely related to mammals than it is to dinosaurs.”

In fact, it is believed that Dimetrodon went extinct some 40 million years before the dinosaurs.

The fossil was collected in 1845 while a farmer was digging a well on his property near French River, PEI. As there were no natural history museums in Canada at the time, it was sold to the Academy of Natural Sciences in Philadelphia, where paleontologist Joseph Leidy studied and named it.

Leidy named the fossil Bathygnathus (meaning deep jaw) borealis (from the north) because he mistook it as the lower jaw of a dinosaur, similar to the large bipedal species that were being collected in Europe at the time.

The Bathygnathus specimen was the second vertebrate fossil named from Canada. Dendrerpeton, an extinct amphibian from Nova Scotia, was named by Sir Richard Owen two months earlier. Several paleontologists have studied the Bathygnathus specimen since it was first named, but its precise identity was unknown. For example, it was unclear whether it had Dimetrodon’s signature dorsal sail – created by tissue stretched between spines sticking up from its backbone – or lacked a sail like its smaller cousin Sphenacodon.

Using family trees and imaging techniques to see the internal anatomy of the fossil, researchers found that the eight preserved teeth linked the fossil to the Dimetrodon family – the first terrestrial animal to have “ziphodont” teeth.

“These are blade-like teeth with tiny serrations along the front and back of the teeth, similar to a steak knife,” says Robert Reisz, professor of Biology at University of Toronto (Mississauga). “The roots of these teeth are very long, around double the length of the crowns. This type of tooth is very effective for biting and ripping flesh from prey.”

Fossils of Dimetrodon have now been found in the USA, Canada and Germany.

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