When Robert Sullivan, a research associate at the New Mexico Museum of Natural History and Science in Albuquerque, found some dinosaur bones in 67-million year-old Cretaceous rocks in New Mexico's San Juan Basin, in 2008, he had little idea they belonged to a new raptor species. More significantly, the feathered dinosaur roamed southern North America just prior to the mass extinction event, when most raptors had already disappeared from the fossil record.
The Dineobellator notohesperus ("Navajo warrior from the Southwest") belonged to a group of dinosaurs known as dromaeosaurids — the same family as the Asian Velociraptor. However, unlike the massive raptors depicted in the Jurassic Park movie franchise, this one stood about 3.5 feet (about 1 meter) tall, 6 to 7 feet (about 2 meters) long, and weighed no more than 50 pounds (22.7 kilograms). The quill nobs — small bumps on the surface where feathers would be attached by ligaments — on its forearm bones led the researchers to conclude that the Dineobellator was covered in feathers.
Its diminutive size probably made it hard for the raptor to battle larger predators single-handedly. However, Steven Jasinski, head of the Paleontology and Geology Section at the State Museum of Pennsylvania, who led the study, believes that similar to other raptors, these dinosaurs probably lived in packs. According to the researchers, the hypercarnivore's upper arm bones allowed muscles to be attached from a different angle, providing more strength, while its massive claws gave it excellent grip and grasping power.
"Combining the large claws with the stronger arms and grasping ability suggests Dineobellator could have used this combination to jump on and attack much larger dinosaurs than themselves, and this would have been especially useful if a pack went after dinosaurs several times their size," Jasinski said.
The Dineobellator's combative lifestyle was apparent from the injury scars on the fossil's rib and a cut on its sickle-shaped claws. The researchers speculate that the former was probably the result of a battle with a larger predator, while the latter was a remanent of a skirmish with a fellow Dineobellator. "It is interesting to find out new things about a species of dinosaur, but it's especially surprising when you can understand a bit more about the life of a single individual," Jasinski said.
One of the dinosaur's most unique features was its tail bone. Raptors were known for having long, stiff tail bones that helped provide balance and allowed for higher speed. However, the Dineobellator's tail vertebrae appeared to be curved inwards, suggesting extreme agility as well. Jasinski believes this enabled the dinosaurs to not only run at rapid speeds in a straight line but also quickly change directions when needed.
The researcher says, "Think of a cheetah chasing a gazelle. The tail is held straight, but when the gazelle changes direction, the cheetah whips its tail around to counterbalance its change of direction. This increases the cheetah's agility by having the tail act as a counterbalance for the sudden changes in direction." These qualities probably meant that the Dineobellator excelled in pursuit, making it a formidable predator despite their small size.
However, David Evans, deputy head of the Department of Natural History at the Royal Ontario Museum in Canada, who was not involved in the study, believes the researchers' conclusions of the creature's strength and agility based on just 20 bones, is premature.
"Ultimately, the specimen is still very fragmentary and leaves a lot of questions, including the strength of the functional inferences in the study," Evans told Live Science in an email. "Although the bones suggest Dineobellator may have had a suite of special adaptations that could be related to predation, for instance, the scrappy nature of the fossils makes it difficult to evaluate the significance of the seemingly unique shapes of its bones." The researcher believes more complete fossils of the raptor need to be found to confirm the conclusions.
Fortunately, that is precisely what Jasinski and his team, who published the results of their study in the journal Scientific Reports on March 26, 2020, plan on doing next. "It was with a lot of searching and a bit of luck that this dinosaur was found weathering out of a small hillside," Jasinski says. "We do so much hiking, and it is easy to overlook something or simply walk on the wrong side of a hill and miss something. We hope that the more we search, the better chance we have of finding more of Dineobellator or the other dinosaurs it lived alongside."
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