Few fossils bridge the gap between a dinosaur and a bird. This may help fill in some details.
A 120-million-year-old fossil bird found in China may provide new clues about how land-based dinosaurs evolved into modern flying birds. The researchers report in the January issue of the journal Nature Ecology & Evolution, that Cratonavis zhui the size of a pigeon, it had a head similar to a dinosaur, on a body similar to the body of modern birds.
The flattened specimen comes from the Jiufotang Formation, an ancient rock in northeastern China that is home to preserved feathered dinosaurs and archaic birds. Computed tomography showed that in Kratonavis the skull was almost identical (though smaller) to that of theropod dinosaurs such as tyrannosaurus rex, paleontologist Li Zhiheng of the Chinese Academy of Sciences in Beijing and his colleagues report. This means that in Kratonavis the movable upper jaw, which is present in modern birds, has not yet developed.
It’s one of the few specimens that belong to a newly identified group of intermediate birds known as jingoforticids, said Luis Chiappe, a paleontologist at the Natural History Museum of Los Angeles County who was not involved in the study. His mix with dino-birds “is not unexpected.” According to him, most birds discovered from the age of dinosaurs had more primitive toothy heads than modern birds. But the new finding “builds on our understanding of this primitive group of birds that are at the base of the bird tree.”
Kraton canopy also had an unusually elongated shoulder blade and a hallux, or toe, that was turned backwards. Enlarged shoulder blades, rarely seen in Cretaceous birds, may have compensated for the birds’ poor flight mechanics, the researchers say. And that big toe? This counteracts the trend towards reduced metatarsals that has been observed during the evolution of birds. Lee’s team says Kratonavis could use this impressive figure for hunting, like modern birds of prey.
Given its size, Chiappe says, the dinosaur-headed bird would likely have been a small hunter that took down beetles, grasshoppers and the occasional lizard rather than terrorized the skies.
