A nondescript gravel pit in rural Alberta has been a boon for paleontologists.
In Big Stone, about 380 kilometers southeast of Edmonton, paleontologists have found rare fossils of prehistoric camels and horses from 1.5 to 4.5 million years ago.
By studying these fossils, researchers are getting a glimpse into Alberta's prehistory.
Kelsey Martin, aggregates manager at the Alberta Special Areas Board, noticed that in 2019, the rocks they were removing from a particular gravel pit looked different from other locations.
Martin wanted to know how old the rocks were and contacted the Royal Alberta Museum for help.
Cristina Baron-Ortiz, a paleontologist at RAM, hoped they would be able to find fossils that would help date the site.
But he did not have high expectations.
“It's usually really hard to find fossils in gravels,” he said.
“We've visited many gravel pits in the province and often find nothing.”
Gravel beds are what's left of ancient rivers, he said, and rivers break animal bones into small fragments.
The Big Stone site far exceeded Barron-Ortiz's expectations.
When they visited in 2019, his colleague Catherine Bramble discovered a complete and well-preserved premolar tooth from the upper jaw of a prehistoric horse, much to Baron-Ortiz's delight.
Martin said it was a day where many elected officials and administrative staff visited the site.
“So — lo and behold — when they got off the bus, Christina and Catherine said, ‘Hey, that looks unique.' And they picked up the horse tooth fossil just as everyone was getting off the bus,” Martin recalled.
“Kudos to them for going out and looking because there's a hundred to a thousand to one chance you're going to find the material,” said Duane Fross, a professor in the Department of Earth and Atmospheric Sciences. University of Alberta specializing in ice ages and the past 2.5 million years.
According to Fross, the Big Stone site is likely a rich source of fossils.
“The fact that people have found them just walking around tells you there's probably a lot out there,” he said.
The bones provide clues about the prehistoric environment
Baron-Ortiz said the tooth they found is about 1.5 to 4.5 million years old, and fossils from this period are “extremely rare.”
Paleontologists have been returning to the Big Stone site since 2019 and have visited it twice this year. In addition to horse bones and teeth, they also found camel bones in a large stone pit.
Both horses and camels evolved and diversified in North America about four million years ago and became extinct about 10,000 years ago.
Prehistoric camels, like horses, migrated to Asia, where they evolved into the modern Bactrian and dromedary camels. They also migrated to South America, where they evolved into modern llamas and alpacas.
Until now, paleontologists have mostly found camel and horse bones because of how abundant they were at the time. They were grazers, well adapted to Alberta's dry, grassy steppe between 1.5 and 4.5 million years ago, Frozey said.
“We're thinking about what's probably living in the grasslands. It's consistent with what we think about the environment at the time.”
But RAM scientists are also looking for other fossils that have yet to be identified.
This September, for example, a fragment of the lower jaw of an unknown animal. The teeth are broken, but the roots are still there.
“This could give us evidence that will help us identify what it is,” Baron-Ortiz said.
He said it was not a horse to which the jaw belonged, and RAM scientists do not believe it was a camel. Potential candidates include peccaries, which are related to pigs, but it could also be a predator, he said.
“We haven't had time to sit down and take measurements and start comparing it to other fossils to really understand what it might be,” he said.
Scientists are also working on dating the fossils more precisely.
At the moment, they only have a range that spans millions of years. The fossils are too old to be carbon dated, so paleontologists and geologists working on them have to use different methods.
“We collected samples to see if there were any dust grains that would give us an understanding of the vegetation that lived in the area,” said Dale Leckie, a geologist who specializes in reconstructing ancient environments.
They are looking for remnants of volcanic ash at the site, which will allow them to date the site more precisely.
Many volcanic eruptions have been studied, and linking ash to a particular eruption will allow scientists to determine the age of the site.
They also discuss dating deposits using paleomagnetism. At irregular intervals, the north and south poles reverse, and this change in Earth's polarity is imprinted in the rocks.
Paleontologists plan to return to the boulder again, Baron-Ortiz said, and Martin is optimistic about the possibility of finding more fossils there.
“We definitely plan to come back next year,” Baron-Ortiz said.
“Hopefully there will be more erosion in the winter and some of the bones that are just exposed will be exposed.”