The Hell Creek Formation, which encompasses the area now known as the Dakotas, Montana, and Wyoming, is known for being home to some of the most famous dinosaurs. triceratops And Tyrannosaurus rex . This area in particular was home to SUE, one of the largest and most complete fossils. T. rex, has never been discovered. But these iconic dinosaurs weren’t the only creatures that lived in this prehistoric world.

Skilled birds of prey

A new study published in the journal PLoS ONEScientists have described two newly identified bird species that coexisted with these dinosaurs about 68 million years ago. Remarkably, the researchers were able to name each of these species based on just one bone, specifically an intact foot bone; This suggested that these birds were skilled predators capable of capturing and carrying prey.

“Based on clues in their leg bones, we think these birds might have captured and transported prey similar to what a modern hawk or owl does,” said lead author Alex Clark, a graduate student at the Field Museum and the University of Chicago.

“Although they were not the first birds of prey to evolve, their fossils are the oldest known examples of birds of prey.”

Rich information in foot bones

The three fossil samples Clark analyzed for this study had been collected by other researchers in recent years but had not received much attention. Clark recalls that at first glance, the fossils were unremarkable; each was a separate foot bone, known as a metatarsal, to which the bird’s toes could be attached.

These bones were found without more attractive body parts such as claws or skulls, and although considered large for bird foot bones, they were still only about the size of an adult’s thumb. But it turns out that these modest bones contain a wealth of information about the life and behavior of ancient birds.

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

Unique features of birds of prey

A particularly interesting feature of these bones was a large protrusion known as the tubercle, which was the point of attachment of the muscles. The size and location of this tubercle was unusual; It was much larger and located deeper in the bone than is common in most birds.

“When we see tubercles this size and this spaced apart in modern birds, it means that birds of prey like owls and hawks had them,” Clark said.

“This is because when hunting and catching prey with their feet, they lift proportionately heavy objects and hold them close to their bodies to remain as aerodynamic as possible. “These fossil ankle bones look like they were made to do something like this.”

Birds of prey with strong legs

To further investigate their hypothesis, Clark and his team performed a biomechanical analysis of fossilized foot bones and compared them to those of various modern birds.

“The ankle muscles and bone work like a lever, and by comparing how far down the muscle attaches to the bone we can get a good idea of ​​how it will move and how strong it can be,” Clark explained.

The findings confirmed that the leg structure of these birds may have been strong enough to capture and carry small mammals and even baby dinosaurs, similar to modern hawks and owls.

Two new bird species have been named

Clark and his team identified and named two new species from these three foot bones: Avisaurus DarwinNamed after Charles Darwin and Magnusavis ekalakaenis It takes its name from the town of Ekalaka, Montana, where one of the fossils was found.

The third bone may represent another new species, but its deteriorating condition made it difficult to draw firm conclusions. These birds belong to a group called avisaurids, which are part of a larger group of extinct birds known as enantiornithines. Like most dinosaurs, enantiornithines went extinct when an asteroid hit Earth 66 million years ago.

Various ancient bird species

Study co-author Jingmai O’Connor is assistant curator of fossil reptiles at the Field Museum and Clark’s advisor.

“These discoveries effectively double the number of bird species known from the Hell Creek Formation and will be critical in helping us better understand why only a few birds survived the mass extinction.” T. rex and the avisaurids described here, said O. “Connor.

The findings shed new light on the diversity of ancient bird species that lived alongside dinosaurs and underscore the important role that even isolated fossils can play in understanding ancient ecosystems. Although the bones seem obscure at first glance, they provide a fascinating glimpse into the lives of some of the first birds of prey.