The beak belongs to an Ichthyornis dispar from about 85 million years ago. Bhart-Anjan Bhullar, the principal investigator on the study, said this animal existed "right in the middle of the transition from something that has more of a dinosaur head to something that has a head more like that of a modern bird."
This half-bird, half-dinosaur was a seabird similar in size to a gull.
"I bet they were loud. I bet they were pretty gross," Bhullar said. "I bet they smelled like fish and squabbled all the time."
A co-author of the study, Kristopher Super, was looking for fossils in western Kansas in 2014 when he stumbled upon a rock with many bones sticking out of it. He recognized the bones belonged to ancient relatives of birds, so he and his colleagues called Bhullar.
"OK, stop there," Bhullar advised. "Put it in a CT scanner and let's see what we can see." This would allow them to view what was preserved within the rock without damaging any fragile fossils.
From that scan, the team was able to identify a "beautifully complete" 85-million-year-old Ichthyornis dispar skull inside.
Even for a non-scientist, that probably already sounds like a big deal. But this was an even bigger deal, because up until this find, such skulls were typically only found crushed, according to Bhullar.
The co-lead authors on the team, Daniel Field and Michael Hanson, were able to digitally extract the bones. The real bones remain preserved in the rock.
Combined with a few previously found specimens, they pieced together a three-dimensional recreation of the skull, featuring the first bird beak.
While the Ichthyornis dispar had modern bird qualities like a beak and a big brain, it still had dinosaur qualities like dinosaur-strength jaw muscles, and a dinosaur-like temporal region.
From this find, scientists were able to see that the brain transformed before the remainder of the skull, according to the news release.
"It totally is a combination of really, very bird-like features, and features that seem like they