A Terror of Tyrannosaurs

Trent Ernst, Editor

 

Anyone who has seen Jurassic Park knows that having a Tyrannosaurus chase you is a Very Bad Thing.

But what if three Tyrannosauruses were chasing you?

Well that would be terrifying. Or rather, it would be terror-fying, as the official name for a group of tyrannosaurs is a terror.

While scientists have debated whether Tyrannosaurs hunted solo or in groups, local guide outfitter may have stumbled across the answer while out hunting back in the fall of 2011.

Aaron Fredlund came across a track that belonged to a rather large creature while out guiding a hunt in 2011. The tracks were amazingly well preserved, but Fredlund just about gave them a miss. He is, after all, a hunter, not a fossil hunter. But he went back and took some pictures before continuing on.

And that was just about that, until wife Jessica noticed the photos. She posted them to Facebook, asking if anyone knew what kind of footprint it was. People encouraged her to send the pictures on to the Peace River Paleontological Research Centre (PRPRC).

The pictures were passed on to Rich McCrea, who was in Australia at the time. As soon as he returned, he and his team went out to study the tracks and make casts before snow fell. (The trouble with finding exposed fossils is as soon as they are exposed, they begin to weather.)

The next year, the researchers returned to the site, a slab of rock at the base of a cliff about 4 metres wide and 60 metres long. As they excavated the area, they found a series of other tracks, including a Hadrosaur track. some made by smaller theropods called Saurexallopus cordata, and, most excitingly, other tracks made by tyrannosauruses, parallel to the original.

The findings were recently published at plosone.org, a peer-reviewed, open-access online publication put out by the Public Library of Science. “The skeletal record of tyrannosaurids is well-documented,” begins the paper, written by Rich McCrea, Lisa Buckley, and a team of five other scientists. “Whereas their footprint record is surprisingly sparse. There are only a few isolated footprints attributed to tyrannosaurids and, hitherto, no reported trackways.”

“The trackways were covered with a layer of bentonite, which is ancient compressed volcanic ash,” says Charles Helm. “The tracks were not made by T. rex, but by a smaller tyrannosaur, possibly Albertosaurus.”

But that’s up for debate. The tracks are unique enough that they have been assigned their own ichnotaxon—a taxonomic unit assigned based on the fossilized work of a creature, as opposed to the remains of the creature itself—named after Fredlund. The working name for the tyrannosaurs that made these tracks is the Bellatoripes fredlundi, which translates, very roughly from Latin into “Warlike Foot of Fredlund.”

While everyone thinks about the king of all predators, the T-Rex, when referring to tyrannosaurus, there are a number of smaller species in the same family, including the Albertosaurus, the Gorgosaurus, and the Tarbosaurus. However, without any skeletal remains, the new designation remains simply that: a designation.

The findings seem to support that Tyrannosaurs may have been pack hunters, which is something that Phillip Currie has been arguing for years. In 2011, the very year these tracks were first discovered, Currie wrote the book Dino Gangs, proposing the idea. Not surprisingly, Currie is a co-author of the paper with McCrea and Buckley.

In the movie Jurassic Park, Doctor Alan Grant (Sam Neil) sees the dinosaurs for the first time and says “They’re moving in herds. They do move in herds.”

The movie went on to present the velociraptors (based on the real-world Deinonychus) as cooperative predators, but in that movie, the T-Rex stood alone.

But in 1998, five years after the movie and eight years after the book, Currie located an old excavation site in Dry Island Buffalo Jump Provincial Park where a smattering of fossils had been excavated. Currie and his time fully excavated the site, discovering the remains of at least a dozen Albertasuarus, a member of the Tyrannosaur family.

In 2000, he wrote the first paper suggesting “gregarious behavior in tyrannosaurids”. In that paper, he speculated that the creatures moved in a social group with complex hunting behaviors.

Dino Gangs picks up on that idea, using new findings of 68 Tarbosaurus—another member of the Tyrannosaurus family—along the Korea-Mongolia border.

The idea of Tyrannosaurus hunting in packs has received much opposition in the scientific community, with opponents arguing that bones alone are not enough to reconstruct dinosaur behavior. In an article published on the Guardian website, science writer Brian Switek (one of those doubters), says that ““bones alone are not enough to reconstruct dinosaur behaviour… I would be thrilled if palaeontologists discovered compelling evidence that tyrannosaurs were social hunters. A trackway preserving the footsteps of several individuals moving in the same direction at the same time would be excellent. But until then, tableaus of tyrannosaur families dining together must remain tantalisingly speculative parts of prehistory.”

That was on July 25, 2011. Less than three months later, that trackway was found by Fredlund.

Rich McCrea was in Australia when he got the email from Fredlund showing a picture of Fredlund’s foot, dwarfed by a giant track. When he returned, he went out to explore the trackway. It was even better than he was expecting. “On a scale of one to ten? These are a nine, going on ten.”

He says the situation in which the tracks were made was near perfect. “Picture yourself walking across a muddy area,” he says. “The sediment would squish up between your toes, pressure bulges would form around your foot. Even though humans are small, if you step into mud that was mostly sand and silt and some organic, it would be really messy. There’d be these extra morphology features.

“These creatures weighed three to four tonnes. But their footprints didn’t disturb the sediment. It’s punched down into it like a pencil into playdough. It just compressed the sediment, it didn’t displace it. In that way, it’s perfect. We get a true reflection of the foot of the animal. Footprints and trackways don’t usually record this one time record of the foot, it’s the interaction with the substrate; there’s a fourth dimension, of time, where the foot comes down, then the weight bearing phase, then the take-off phase, which causes the track to get messy.”

McCrea says that trackways provide much stronger evidence than bones for a variety of reasons. “The main objection to using bones overmuch for interpreting behavior is they can be transported and concentrated,” says McCrea. “The Dry Island bone bed is a Point Bar deposit. A whole bunch of animals got caught up in what basically amounts to a log jam. There’s a lot of tyrannosaurs there, but did they succumb as a group in a flood, or were they washed up to the same place.

“The strength in trackways is they can’t be moved. When you find a bone, you don’t know if the dinosaur lived there, you don’t even know if they died there.”

McCrea says he found Currie’s interpretation of the bones compelling. “There were a lot of people seeing evidence of gregariousness in dinosaurs. When you’re doing science, what you’re doing is looking at the evidence for and against a particular idea. You’re not trying to go in any one direction, you’re just looking at the evidence. And that evidence was mounting.”

The trackway, says McCrea, brings another line of evidences and it strengthens the whole case.

The trackway consists of six tracks showing three parallel trackways of creatures. While six tracks between three dinosaurs doesn’t seem to be many, the finding doubles the number of known footprints from tyrannosaurs. “We’ve had one in BC, but it was on an isolated block,” says McCrea. That fossil was found in 2004 east of Tumbler Ridge, also by hunters. “There are a few in Alberta, some in the US and one in Mongolia.”

More importantly, this is the first ever trackway from a tyrannosaur. “It’s very compelling that when we had this discovery. It was three, moving in the same direction, in the area at the same time,” says McCrea.

He says that people will no doubt ask if the tracks were made at the same time. To which the answer is yes. “The passage of time is recorded on tracksites. When you have a freshly deposited sediment, it’s quite waterlogged. When the first animals go across, they sink down more deeply. As time goes by, maybe a few hours, a few days, the sediment begins to dewater and becomes more resistant. If you have a tyrannosaur that weighs three or four tonnes walk across a few hours later, the sediment will have becomes more compact, and the print won’t be as deep.”

McCrea says there are about thirty other tracks in the same area, including hadrosaur tracks. While that creature weighs about the same as the tyrannosaur, their footprints are very shallow.

McCrea says that often times, creatures will be funneled through the same area by a natural barrier, like a lake or a cliff. But, he says, the trackways of the other dinosaurs are going every which way. “They weren’t constrained,” he says. “There was no geographic barrier present.”

McCrea admits that what they are doing is interpreting the facts that are present, and there’s a chance that they are wrong. “We have this thing in science called parsimony. That states that the simplest answer is usually correct. This is the strongest case we have; this is the most parsimonious explanation. But it doesn’t mean its correct. There are no witnesses, and all the evidence has been left out in the rain for 70 million years. We see what’s left, and we make inferences. There’s always the chance for inferences. But there’s not likely to be any better evidence unless someone invents time travel.”

McCrea says they did a simple mental exercise. Assuming that there was no natural barrier to the direction of travel, then the dinosaurs could travel whichever way they wanted to. “We divided the full compass into ten degree slices. So there are 36 directions the animals could have gone or a one in 36 chance of them travelling any one direction. If there’s two going the same direction, you have a one in 1296 chance. If there’s three, that increases to a one in 46,000 chance of them going in the same direction randomly. We didn’t put that in the paper, but it wasn’t chance is what I’m getting at. The trackways don’t cross. If they came a minute after each other, they could go whatever direction they wanted. But they didn’t.”

The trackway is currently on a slab or rock about four metres wide by six long. The exposed end of the surface has eroded away. The leading edge disappears under a cliff. McCrea wonders if the trackway continues. But for now, he’ll have to keep wondering. “It’s at the base of a cliff, and we don’t have the resources and equipment to excavate it. But maybe this media interest will draw focus to the whole issue of museum funding.”

While the museum has been trying to get funding for a new major display around the discovery, that hasn’t come through, so a new, smaller display will be going up in a few weeks as a stop-gap. “We’re at this cusp where we could take a big step forward,” says McCrea. “Ideally, what I’d like to do is add another gallery or two on to the museum. Then we’d have three main exhibits from BC, researched in BC and discovered by local residents. That starts to take us away from being an attraction and being a destination.”

Charles Helm says the publication of the article is the culmination of work of the past three years by the Peace Region Palaeontology Research Centre and Tumbler Ridge Museum Foundation.  Helm says the museum was unable to publicly announce this site until it had been formally published in the scientific literature. The site is fragile, and public tours are not envisaged; instead, he says, an exhibit will be developed in the Dinosaur Discovery Gallery to interpret this globally significant site, along with replicas.

“The timing of this announcement is fortuitous from the perspective of the Tumbler Ridge Aspiring Geopark Society,” says Helm, “We are preparing to travel to Stonehammer in New Brunswick in September for the International Conference of the Global Geoparks Network, supported by UNESCO. There we will learn if our proposal to become a member of this network is successful. If so, we would become the first Global Geopark in the west and the second in North America. The tyrannosaur trackway site is within the boundary of the proposed Geopark.