While we know quite a bit about dinosaurs and their time on earth, there are still many unknowns.

One of the things scientists assume is that the diversity of dinosaurs co-existed on the planet by dividing up the landscape and food sources. It’s been their assumption that horned dinosaurs stuck to coastal areas, while duck-billed dinosaurs preferred inland habitats. 

However researchers from Western University in London, Ont., the Field Museum in Chicago and Toronto’s Royal Ontario Museum set out to challenge these assumptions — using dinosaur teeth. Lead researcher Thomas Cullen started the project as his PhD thesis at Western University, continuing his work into a post-doctoral fellowship at the Field Museum. 

“There’s been a long-standing pattern observed in the biodiversity and ecology of dinosaurs,” says Cullen. “There were a ton of supposedly co-existing large dinosaurs … North America at the time was a relatively thin splint of land.”

That’s very different from how different species live further apart today, which has resulted in many theories about why dinosaur species may have lived so close together. 

“There could have been limits or restrictions of their ranges,” says Cullen. “There hasn’t been a lot of direct testing of these theories.” 

To find some clues, researchers looked at stable carbon and oxygen isotope compositions of dinosaur teeth, measured using a technology called laser gas chromatography isotope ratio mass spectrometry. Without the scientific jargon, Cullen says this type of analysis of dinosaur teeth and bones could show how the creature consumed its environment. 

“All the cells in us show the raw environment, they’re reflective of food stuffs or elements in the ecosystem.” says Cullen. “That’s what we were trying to measure.”