In the summer of 2004, study author Jaelyn Eberle, a paleontologist and associate professor of geological sciences at the University of Colorado at Boulder, ventured out with her research team to Banks Island, which is Canada’s westernmost Arctic island. The researchers were hoping to find fossils of mammals, but after spending about a week there, they had not found any. Moreover, the weather was cold and the researchers’ tents were covered with snow, Eberle said.
This really is the pits, Eberle remembers thinking at the time.
But then the team started finding the teeth of ancient sharks.
“Probably the biggest surprise, at least at first, was that most of them — literally thousands of these things — belong to just two shark genera, and they are both within the sand [tiger] type of sharks,” Eberle said. The two genera are Striatolamia and Carcharias, according to the paper.
The researchers went back to the island in 2010 and 2012 to collect more shark teeth. They estimate that the teeth date to the late-early or middle Eocene epoch, or about 53 to 38 million years ago, according to the study, published in the November issue of the Journal of Vertebrate Paleontology.
The modern relatives of the two genera identified by the researchers live in warm, tropical waters, Eberle told Live Science.
Two of the teeth the researchers found belonged to an extinct species of sand shark, Odontaspis winkleri. And about 1 percent of the teeth belonged to species within the genus Physogaleus, related to sharpnose and tiger sharks, according to the study.
The researchers wondered why the diversity of the shark teeth they found was so low. “We have got four genera so it is not a lot of diversity, and yet we know during this time, the early Eocene, the climate was warmer than at any other time since the extinction of dinosaurs, and we know the Arctic was much warmer in the early Eocene [than it is now],” Eberle said. The warmer water would be expected to hold a higher diversity of shark species than what the researchers found.