Evrim Yazgin
Cosmos science journalist
Two new species have been identified from fossils found at the Hell Creek Formation in the northern US. The ancient bones belong to the oldest predatory birds ever found.
Hell Creek is famous for its fossils of some of the most beloved dinosaurs like Tyrannosaurus rexand Triceratops horridus. These creatures lived right at the end of the “Age of Dinosaurs” which came to a close with a mass extinction 66 million years ago.
Not all the dinosaurs died out at this time. The ones that lived on are birds – among them predatory birds.
Palaeontologists report in the journal PLOS ONE that they have discovered the earliest evidence of predatory birds. At 68 million years old, the new species lived alongside T. rex and the other dinosaurs of the late Cretaceous period.
“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,” says lead author Alex Clark, a PhD student at the Field Museum and the University of Chicago. “While they might not be the first birds of prey to ever evolve, their fossils are the earliest known examples of predatory birds.”
Clark and his colleagues studied 3 fossil foot bones collected over recent years.
“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,” says Clark.
The foot bones showed a bump called a tubercle where muscles attach.
“When we see tubercles this large and this far down in modern birds, they’re in birds of prey like owls and hawks,” says Clark. “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.”
Comparing the biomechanics of the fossil foot bones with modern birds. They determined that the hawk-sized ancient birds could have picked up small mammals or even baby dinosaurs.
“These discoveries have effectively doubled the number of bird species known from the Hell Creek Formation and 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 described here,” says co-author Jingmai O’Connor, the Field Museum’s associate curator of fossil reptiles in the Negaunee Integrative Research Center.
