One way to make sense of 165-million-year-old dino tracks may be to hang out with emus, say paleontologists studying thousands of dinosaur footprints at the Red Gulch Dinosaur Tracksite in northern Wyoming. Because they are about the same size, walk on two legs and have similar feet, emus turn out to be the best modern version of the enigmatic reptiles that once trotted along a long-lost coastline in the Middle Jurassic.
"We don't have any documented dinosaur bones and teeth from that period in North America, except for some very scrappy material from Mexico," said Brent Breithaupt, curator and director of the University of Wyoming's Geological Museum in Laramie, Wyo. That makes it very hard to connect the tracks to a particular dinosaur. And of course, "We unfortunately can't go out and see walking dinosaurs today. Or can we?"
After scouring the dinosaur fossil record in other parts of the world and deciding that a human-sized, meat-eating dinosaur (theropod) fit the bill for the tracks at Red Gulch, Breithaupt and his colleagues and students did something unusual. Instead of speculating about what the dinosaurs were doing, they went hunting for a modern analog animal they could study to help decipher the tracks.
Large flightless birds are the most logical choice and are, along with all birds today, thought to be descended from dinosaurs. But not all of those alive today are good choices or easy to work with. Ostriches are two-toed and have an attitude problem, so that ruled them out, says Breithaupt. Rheas have three toes, but are "like working with a bunch of kindergarteners on too much sugar," he said.
That left emus, which are perfect: three toes, the right size, and relatively easy to work with. What's more, there is an emu ranch handily located in nearby Colorado at which Breithaupt and his team could reconnoiter and learn emu "dance steps."
"So we went from walking from dinosaurs to walking with emus," he said, referring to how they first had found many of the weathered tracks at Red Gulch by simply talking steps from one to the next, just as we might walk. "The dinosaurs were people-sized and their steps and strides were in many ways similar to those that people might make," he remarked.
What emus revealed, says Breithaupt, is that many mysterious dinosaur tracks became quite easily understood when a live animal was seen in action.
Breithaupt will be presenting some of his team's emu track discoveries on Wednesday, 25 October at the Annual Meeting of the Geological Society of America in Philadelphia. Theresearch was funded by the Bureau of Land Management and National Science Foundation.
Among the emu revelations was one that helped resolve a mysterious "crossing over" track pattern seen at Red Gulch. Researchers had found that sometimes a dinosaur's tracks became crossed -- that is, the left foot crossing over the right and the right crossing over the left. That seemed pretty strange and hard to explain on the face of it. But after watching emus, it became clear that the crossing over is partially the result of the very narrow "straddle" of the trackways, meaning their legs were close together. Emus share that characteristic and can be seen crossing over feet all the time, said Breithaupt.
The rest of the mystery was solved by observing what else emus do as they walk.
"Often they are looking around as they walk," said Breithaupt of the crossed foot tracks. "Sometimes they stop in mid-stride and look around." Walking theropods appear to have been doing the same thing. So the trackways of walking dinosaurs may also represent those animals stopping in mid-stride as they observe their environment."
Tracks at Red Gulch and those at the emu ranch were carefully documented using state-of-the-art photogrammetric techniques, which allowed detailed sub-millimeter accuracy photos to be taken. These can be computer modeled and even made into physical prototypes with rapid prototyping technology.
The bigger picture is also important and telling at the Red Gulch Dinosaur Tracksite, said Breitaupt. For instance, it appears that the dinosaurs were traveling along a tidal flat, perhaps in family groups, since there are juvenile and adult tracks. If so, that could infer some sort of parental care, he said. At very least the tracks seem to support the idea that the dinosaurs were social animals, just like modern birds.
Breithaupt remains cautious about over-interpreting the tracks, however.
"Too often people will look at fossil tracks and start making interpretations," he said. "I was just very uncomfortable with all the arm-waving. We needed to just spend some time figuring it out and looking at modern animals such as emus which prove to be great modern proxies for the extinct dinosaurs."
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