New species may have hunted like modern hawks and owls

The Hell Creek Formation, in what is now Dakota, Montana, and Wyoming, was once home to some of the world’s most beloved dinosaurs, like Triceratops and Tyrannosaurus rex (including SUE, one of the T. rex the largest, most complete and best preserved). specimens never found).

But these giant dinosaurs were not alone in their ecosystem, and according to an article published in the journal PLOS ONEscientists describe two new species of birds that lived alongside these dinosaurs 68 million years ago. The researchers were able to name these new species from a single bone each: the powerful foot bone, suggesting that these birds could have captured and carried off prey.

“Based on clues found in their foot bones, we believe that these birds would have been able to catch and carry prey, in the same way that a modern hawk or owl does,” explains Alex Clark , holds a Ph.D. student at the Field Museum and the University of Chicago and lead author of the study.

“While they may not have been the first birds of prey to evolve, their fossils are the earliest known examples of predatory birds.”

The three fossils Clark studied in this paper had been collected in recent years by researchers at other institutions, but little work had been done on them.

Clark remembers that when he first saw the fossils, they weren’t particularly dazzling: They were all one foot bone to which the toes attach, called the tarsometatarsus, and they had been found alone, without other flashier body parts like skulls and claws. And although the bones were large for a bird tarsometatarsi, they were still only the size of an adult human thumb. However, these isolated bones proved to be a treasure trove of information.

“Every nook, cranny, and bump that occurs on a bone can tell us something about where the muscles or tendons are attached and how big they are,” Clark says.

On these bones, there was a particularly notable bump: a muscular attachment point called a tubercle. On each bone it was larger and lower than in most birds. “When we see tubercles this large and this deep in modern birds, they are birds of prey like owls and hawks,” Clark says.

“This is because when they hunt and gather prey with their feet, they lift proportionately heavy objects and hold them close to their body to remain as aerodynamically efficient as possible. These fossil ankle bones appear to have were built to do something similar.

Clark and his colleagues conducted a series of biomechanical analyzes comparing fossil foot bones to those of a variety of modern birds.

“The muscles and bones of the ankle work like a lever, and by comparing the distance the muscle attaches to the bone, we can get a good idea of ​​how it would have moved and how strong it would have been,” Clark explains.

The calculations supported the researchers’ hypothesis that these legs would have been strong enough for these hawk-sized birds to catch small mammals and even baby dinosaurs.

Using the bones of the three feet, Clark and his team described two new species to science: Avisaurus darwini, named after Charles Darwin, and Magnusavis ekalakaenis, in honor of the town of Ekalaka, Montana, where the fossil was found. (The third bone could be another new species, but the fossil’s degraded condition made it difficult to be sure.)

All of these birds are part of a group called the avisaurids. They belong to a larger group of birds called enantiornithines, which disappeared along with most of their dinosaur relatives when the asteroid hit 66 million years ago.

“These discoveries have effectively doubled the number of known bird species in the Hell Creek Formation and will be critical in helping us better understand why only some birds survived the mass extinction that wiped out T. rex and the Avisaurids described here,” said Jingmai O. ‘Connor, associate curator of fossil reptiles at the Field Museum at the Negaunee Integrative Research Center, advisor to Clark and co-author of the paper.

“‘I’m really proud and very impressed by what Alex was able to do with these specimens. They’re each just one bone. But he brings his experience as an ecologist into his paleontological work to say more than the paleontologist what an animal’s life would have been like,” says O’Connor. “Alex has done a superb job of being able to extract so much incredible ecological information from a single bone.”