How A 50 Million Year Old Fossil Could Shed Light On The Origins Of Certain Mammals

May 11, 2018

CT scan imagery taken at Ivinson Memorial Hospital & Foundation shows what is potentially the complete foot, ankle, and lower leg bone structure of the tapiromorph specimen discovered near Kemmerer, Wyoming. Modern tapirs have four toes on their front feet and three on their back feet. If modern analogies are representative of this specimen, this image shows what appears to be a four-toed front foot.
Credit Wyoming State Geological Survey

On a bright, cloudless day in southwest Wyoming, Rick Hebdon, a commercial fossil collector, drove over a steep dirt road to one of his quarries within the Green River Formation. He’s been uncovering fossils for most of his life, but it still holds a thrill for him.

"Like… what my dad said, ‘It’s like digging in the crackerjacks looking for the prize'," he said, laughing.

Hebdon stepped into the crater-like formation and pointed to small black fish imprints on the ground. He explained the Green River Formation used to be covered in big lakes. 50 million years ago, Wyoming had a climate closer to Florida, so Hebdon is used to uncovering fish fossils.

"99 out of a 100 times you’re going to find a fish. And then sometimes you get a little insect or a leaf, something that gives you a little surprise. But to find a mammal," Hebdon said, "it’s crazy rare to even have them out here."

One of Rick Hebdon’s state-leased quarry where the tapiromorph fossil was originally found.
Credit Cooper McKim

Finding a mammal is so rare because 50 million years ago mammals were just taking off. They were evolving to become the modern animals we know today, albeit a little smaller. So, when Hebdon found one, he was excited.

"Up in this layer, right there. And that’s where this new mammal was found. And it was right here," he said, pointing to a rectangle on the ground.

Hebdon found well-preserved hooves, a long femur bone, a tooth, and a mostly put together rear-half. He reached out to a paleontologist nearby who couldn’t find a match for the species. But, Hebdon did find out it might be the largest mammal ever found in the Green River formation.

Hebdon’s quarry was state-leased. Soon after he found the fossil, it went to the Wyoming State Geological Survey (WSGS) in Laramie. A paleontologist in North Carolina narrowed down what it could be based off of a molar image, finding it was likely a tapiromorph - the group that gave rise to modern rhinos and tapirs.

The exact location where the tapiromorph fossil was found.
Credit Cooper McKim

Mark Clementz, director of the University of Wyoming’s Geological Museum, said this fossil could help answer long-held questions about where tapiromorphs came from.

"Which continent was their home is a big question and there’s a lot of debate surrounding it because their fossils are found all over those different continents," he said. "It may be it’s a North American origin for either tapirs, rhinos or tapirs and rhinos based on this fossil."

An advisory board organized a search for a preparator, someone who frees a fossil from the rock. Many, like Hebdon, have been anxious for the preparation to find out what animal it is. Now, that person has been chosen: Mike Eklund.

Eklund is a specialist located in Illinois. He’s just begun preparing the specimen.

"The pieces I’m working on today, according to the X-ray, has a very nice articulated leg with all of the footbone and everything," Eklund said.

He said the bones look almost black and are encased in tan colored rock. He uses small needles, mini air jackhammers, and hand tools to remove the bone. But he’s also been setting up technology to see what the naked eye cannot.

"I’ve been working on using fluorescent illumination and getting images of the specimen before work has begun, but also I’ve spent a fair bit today getting the time-lapse photography set up," he said.

Time-lapse photography, special lighting, extra magnification -- those are all special skills Wyoming’s small advisory board wanted in a preparator, because they can help Eklund find biological information that might otherwise be lost.

"There’s a lot more tissues and other things present that get missed very often that we just need to look closer for to have a chance of finding them," he said.

Soft tissue is the name of the game, here. It’s pretty rare, but Eklund and WSGS expect to find it given how well the fossil has been preserved. Soft tissue can shed light on how the animal looked, the size of its snout, shape of its ears, or its diet.

It’s not guaranteed to find all that information, but it could, "put a better picture together of the environment it was from as well as the actual biologic details of this mammal,” Eklund said.

He said he's still around two months away from fully removing the fossil from its rock surroundings. Once it’s prepared, the specimen will be housed within the Wyoming State Geological Survey in Laramie with the chance to be on loan for display or research elsewhere.

Rick Hebdon at his quarry.
Credit Cooper McKim

Back at the quarry in the Green River Formation, Rick Hebdon stood by the site where this special fossil was originally discovered. He’s found crocodiles, bats, and palm leaves in his lifetime of fossil hunting. But he says this is something brand new, and that’s exciting. Both for him and for science.

"It opens a whole other chapter in mammals. It does."