New fossil finds suggest dino-era birds hunted like modern raptors

By Stephen Beech via SWNS

Predatory birds that lived at the same time as the dinosaurs may have hunted like today's hawks and owls, suggests new research.

New hawk-sized species identified from the same American fossil formation as T.rex and other giant beasts had "unusual" foot bones that indicate they may have carried heavy prey, just like modern raptors.

The most diverse birds during the Cretaceous Period were a now-extinct group called enantiornithines, known to live all over the world at the time.

The newly discovered birds were part of a smaller group called the avisaurids which went extinct with most of the dinosaurs when an asteroid hit 66 million years ago.

Scientists say the newly discovered species date to the latest Cretaceous Period 66- to 68-million years ago, shortly before the mass extinction.

Two are new species named Magnusavis ekalakaensis and Avisaurus darwini while the research team says the third bone may be another new species, but the fossil’s degraded condition made it difficult to tell for sure.

Avisaurus darwini was named after Charles Darwin, and Magnusavis ekalakaenis, in honor of the town of Ekalaka, Montana, where the fossil was found.

The birds are all larger than Early Cretaceous enantiornithines, with Avisaurus darwini estimated to have weighed over one kilo (2.2lbs), roughly the size of a large hawk.

Analysis of the leg bones of Avisaurus and its relatives reveals proportions and adaptations similar to hawks and owls, indicating powerful leg muscles and feet that could grip and potentially carry proportionally large prey, similar to some modern raptors.

They were found in the Hell Creek Formation in what is now Montana the Dakotas and Wyoming and was once home to Triceratops and T.rex - including Sue, one of the largest, most complete, and best-preserved Tyrannosaurus specimens ever found.

Scientists described the new species of birds that lived alongside those dinosaurs 68 million years ago in the journal PLOS One .

They were able to name the new species from just one bone each: the powerful foot bone that suggests the birds could have captured and carried off prey.

Study lead author Alex Clark, a PhD student at Chicago's Field Museum and the University of Chicago, said: “Based on clues in their foot bones, we think these birds would have been able to catch and carry prey, similar to what a modern hawk or owl does.

“While they might not be the first birds of prey to ever evolve, their fossils are the earliest known examples of predatory birds.”

He said that when he first saw the fossils, they weren’t especially dazzling - they were all a foot bone that the toes attach to, called the tarsometatarsus, and they’d been found on their own, without other, "flashier" body parts such as skulls and claws.

While the bones were large for bird tarsometatarsi, they were still only about the size of an adult human thumb.

But the bones proved to be a treasure trove of information.

Clark said: “Every nook and cranny and bump that occurs on a bone can tell us something about where the muscles or tendons attached and how big they were."

He says that on the bones, there was an especially noteworthy bump - a muscle attachment point called a tubercle.

On each bone, it was larger and farther down than in most birds.

Clark said: “When we see tubercles this large and this far down in modern birds, they're in birds of prey like owls and hawks.

“That’s because when they hunt and pick up their prey with their feet, they're lifting proportionally heavy things and holding them close to their bodies to stay as aerodynamically efficient as possible.

"These fossil ankle bones look like they're built to do something similar.”

Clark and his colleagues conducted a series of tests comparing the fossil foot bones to those of a range of modern birds.

He said: “The muscles and bone of the ankle work like a lever, and by comparing how far down on the bone the muscle attaches, we can get a good idea of how it would have moved and how strong it would have been."

The findings corroborated the researchers’ hypothesis that the feet would have been strong enough for the birds to pick up small mammals and even baby dinosaurs.

Study co-author Dr. Jingmai O’Connor, the Field Museum’s associate curator of fossil reptiles, said: “These discoveries have effectively doubled the number of bird species known from the Hell Creek Formation.

"They will be critical for helping us to better understand why only some birds survived the mass extinction that wiped out T. rex and the avisaurids."

Dr. O'Connor, who is Clark's advisor, added: “​​'I’m really proud and very impressed with what Alex was able to do with these specimens.

"They're each just a single bone. But he brings his background as an ecologist into his paleontological work to tell more than the average paleontologist about what an animal’s life would have been like.

“Alex has done a superb job with being able to extract so much incredible ecological information from just a single bone.”