Fossils Show Raptors Prowled North America Late in Dinosaurs’ Era

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One day in 2008, a lethal weapon from a bygone era spilled out of a hillside in New Mexico.

“We knew that it was something interesting right away,” said Steven Jasinski, a paleontologist at the State Museum of Pennsylvania, whose colleague, Robert Sullivan, first spotted the fossil.

The relic turned out to be the claw of a dromaeosaurid, a dinosaur popularly known as a raptor after its starring role in “Jurassic Park.” After more than a decade of field work and research, Dr. Jasinski and his colleagues have now confirmed that the claw — along with 20 other fossils — represents a new species that lived some 68 to 70 million years ago, just a few million years before an asteroid doomed most dinosaurs.

They named the animal Dineobellator notohesperus, describing it Thursday in Scientific Reports. This pint-size predator is the third known North American dromaeosaurid from the dinosaurs’ twilight period, and suggests that beasts of its stature may have been abundant at that time.

“The new animal Dineobellator confirms that there is a greater diversity of raptors at the end of the Cretaceous than has been suspected up until now,” said Philip Currie, a paleontologist at the University of Alberta in Canada, who was not involved with the study. “It represents our steady progress in understanding that small dinosaurs may have been more common than large forms like the contemporary T. rex at the end of the age of dinosaurs.”

The fossil record is partly biased toward huge animals like T. rex simply because their sturdy skeletons are more likely to stay intact for tens of millions of years, resulting in an incomplete understanding of dinosaur evolution.

“Raptor dinosaurs are among the rarest of finds because their thin, airy bones don’t often preserve,” said Lindsay Zanno, head of paleontology at the North Carolina Museum of Natural Sciences, who was not involved in the study.

Dineobellator was about three feet tall — a few sizes smaller than the fictional raptors that wreaked havoc in “Jurassic Park.” Judging from its unique adaptations, this was a particularly gracile and innovative predator that possessed clawed digits primed for pouncing onto the backs of larger animals.

“This dinosaur had an enlarged area for muscle attachment to allow for a much stronger grasping or gripping ability,” Dr. Jasinski said. “A group of these dinosaurs certainly could have been able to take down very large prey, better than other members of the group seemingly could.”

The base of Dineobellator’s tail was also unusually dexterous, perhaps allowing it to dodge and weave with the movements of its prey, similar to cheetahs on today’s African savanna.

“This dinosaur would have been better than other members of the group that we are aware of, at pursuing animals in an open area,” Dr. Jasinski said.

This hunting strategy distinguished Dineobellator from the enormous tyrannosaurs — cousins of T. rex — with which it shared this Cretaceous landscape. Where Dineobellator thrived on plains, tyrannosaurs were probably ambush predators that kept close to forested areas.

A nasty gouge mark on its claw suggests the individual excavated in New Mexico scrapped with a predator its own size, perhaps a fight with another Dineobellator over resources or mates.

“The most likely guess is the sexual display process,” Dr. Jasinski said. Dineobellator possessed quills and feathers, like most known raptors, and may have performed flamboyant courtship rituals similar to some contemporary birds. The dinosaur may have sustained its injury while battling another male over a mate, or even from a female that was not ready to copulate.

Dr. Zanno said many of the study’s behavioral hypotheses “are interesting ideas,” but they “have not yet been tested.” Further examination of the specimen could challenge the researchers’ conclusions about the raptor’s life.

However it lived, the fossil evidence of Dineobellator’s sophisticated adaptations suggests that dromaeosaurids were flourishing when the asteroid hit.

“These dinosaurs were still trying out new evolutionary pathways and testing out new things to do and diversifying,” Dr. Jasinski said. “We are finding more and more of them, and then they just completely die out.”

Given their keen predatory skills and sleek frames, it’s no wonder raptors have captured the public imagination. Dineobellator is yet another example of the ingenuity that these hunters possessed, even as they lived in the shadows of much larger carnivores.