TYRANNOSAURS IN TANDEM? FOOTPRINTS SUGGEST PACK HUNT

Dinosaurs may have coordinated

About 90 million years ago, three carnivorous dinosaurs sloshed through the mud, leaving footsteps still visible today. Researchers have found clues hinting at the intent: dinner, in the form of a fellow dinosaur.

If this idea is correct — and it’s far from confirmed — the tracks could provide valuable evidence for cooperative hunting by tyrannosaurs, the family of meat-eating, hind-leg-walking reptiles headed by the mighty T. rex.

Scientists found fossils and other tracks suggesting dinosaurs hunted cooperatively, but evidence for dinosaur behavior “is still relatively rare, because we’re talking about something we can’t see,” says Brent Breithaupt, a Wyoming-based regional paleontologist for the U.S. Bureau of Land Management. Whatever happened at this spot one day in the Cretaceous, “tracks are the first good step — excuse the pun — into learning about what animals were there.”

The predator tracks were discovered a decade ago in a rugged corner of New Mexico overseen by the land management bureau. The researchers found 13 prints left by three meat-eating dinosaurs.

The proportions and shape of the three-toed prints point to tyrannosaurs as the culprits, says Douglas Wolfe of the White Mountain Dinosaur Exploration Center, who found the tracks. Fossils of a tyrannosaur-like dinosaur lie nearby, bolstering the case that the tracks are the footwork of tyrannosaurs.

Many of the tracks parallel each other, indicating “a family group, maybe moving in concert,” Wolfe says. What stumped him was the pattern. The prints march across the ground in a relatively straight line. They sud- denly change direction.

A few years ago, Douglas Wolfe’s wife, Hazel, noticed something no one else had seen: a round footprint exactly where the tyrannosaur tracks swerve. Piles of sediment hint that the roundfooted animal kicked up sand as it scrambled away.

The maker of the round track probably was a plant-eating horned dinosaur of the Triceratops family, Douglas Wolfe says. One candidate is Zuniceratops, a smallish horned dinosaur. Wolfe says he thinks the tyrannosaurs closed in on the horned dinosaur’s right side before their quarry fled. The Wolfes reported their findings at a recent meeting of the Society of Vertebrate Paleontology.

A joint tyrannosaur attack may seem far-fetched, but dinosaurs were not the loners of popular imagination. At one Canadian site, fossils from tyrannosaurs of different ages suggest the animals died together, says James Kirkland of the Utah Geological Survey. “These were sophisticated animals,” he says.

Breithaupt calls the site “intriguing ” but wonders whether the meat-eaters and the planteater actually crossed paths, rather than trekking across the same spot days or weeks apart.

Wolfe says it’s useful simply to find prints of tyrannosaur-like animals. The tracks indicate tyrannosaurs stalked this patch of ground in the Cretaceous and did so in a herd.

The set of tracks also “shows there are many, many unique sites still out there” waiting to be discovered, Breithaupt says.

“Tracks are the first good step — excuse the pun — into learning about what animals were there.” Brent Breithaupt, paleontologist

HAZEL WOLFE, PICASA A round footprint was left by some kind of vegetarian dinosaur, most likely a Zuniceratops. These and other footprints suggest a pack of three carnivores chased the vegetarian.

WILLIAM MONTELEONE The Zuniceratops was a horned dinosaur related to Triceratops. This creature was a good candidate for the dinosaur that left the round footprint discovered by researchers in what was probably a predatory chase.