Janavis finalidens — an extinct bird species that lived 66.7 million years ago and was one of the last toothed birds to ever live — had a mobile, dexterous beak, almost indistinguishable from that of most modern birds. The discovery shows that such mobile beak, one of the key skull features that characterizes 99% of modern birds, evolved before the end-Cretaceous mass extinction. It also suggest that the skulls of ostriches, emus and their relatives evolved backwards, reverting to a more primitive condition after modern birds arose.
Life reconstruction of Janavis finalidens. Image credit: Phillip Krzeminski.
Each of the roughly 11,000 species of birds on Earth today is classified into one of two over-arching groups, based on the arrangement of their palate bones.
Ostriches, emus and their relatives are classified into Palaeognathae (‘ancient jaws’), meaning that, like humans, their palate bones are fused together into a solid mass.
All other groups of birds are classified into Neognathae (‘modern jaws’), meaning that their palate bones are connected by a mobile joint. This makes their beaks much more dexterous, helpful for nest-building, grooming, food-gathering, and defense.
The two groups were originally classified by the British biologist Thomas Huxley.
In 1867, he divided all living birds into either the ‘ancient’ or ‘modern’ jaw groups. His assumption was that the ‘ancient’ jaw configuration was the original condition for modern birds, with the ‘modern’ jaw arising later.
“This assumption has been taken as a given ever since,” said Dr. Daniel Field, a researcher in the Department of Earth Sciences and the Museum of Zoology at the University of Cambridge.
“The main reason this assumption has lasted is that we haven’t had any well-preserved fossil bird palates from the period when modern birds originated.”
Janavis finalidens lived in what is now Belgium approximately 66.7 million years ago and, like non-avian dinosaurs and other toothed birds, did not survive the mass extinction event at the end of the Cretaceous period.
Its partial skeleton was found the 1990s in the CBR-Romontbos Quarry near the Belgian city of Liège.
Janavis finalidens weighed around 1.5 kg and was the size of a modern vulture.
While it still had teeth, making it a pre-modern bird, its jaw structure is that of the modern, mobile kind.
“Using geometric analyses, we were able to show that the shape of the fossil palate bone was extremely similar to those of living chickens and ducks,” said Pei-Chen Kuo, a Ph.D. student in the Department of Earth Sciences at the University of Cambridge.
“Surprisingly, the bird palate bones that are the least similar to that of Janavis finalidens are from ostriches and their kin. Evolution doesn’t happen in a straight line,” added Klara Widrig, a Ph.D. student in the Department of Earth Sciences at the University of Cambridge.
“This fossil shows that the mobile beak — a condition we had always thought post-dated the origin of modern birds, actually evolved before modern birds existed.”
“We’ve been completely backwards in our assumptions of how the modern bird skull evolved for well over a century.”
The findings appear in the journal Nature.
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J. Benito et al. 2022. Cretaceous ornithurine supports a neognathous crown bird ancestor. Nature 612, 100-105; doi: 10.1038/s41586-022-05445-y
