Fossil overturns more than a century of knowledge about the origin of modern birds

Fossilized fragments of a skeleton, hidden within a rock the size of a grapefruit, have helped upend one of the longest-standing assumptions about the origins of modern birds.

Researchers from the University of Cambridge and the Natuurhistorisch Museum Maastricht found that one of the key skull features that characterizes 99% of modern birds —a mobile beak—evolved before the mass extinction event that killed all large dinosaurs, 66 million years ago. This finding also suggests that the skulls of ostriches, emus and their relatives evolved "backwards," reverting to a more primitive condition after modern birds arose. Using CT scanning techniques, the Cambridge team identified bones from the palate, or the roof of the mouth, of a new species of large ancient bird, which they named Janavis finalidens. It lived at the very end of the Age of Dinosaurs and was one of the last toothed birds to ever live. The arrangement of its palate bones shows that this "dino-bird" had a mobile, dexterous beak, almost indistinguishable from that of most modern birds.

For more than a century, it had been assumed that the mechanism enabling a mobile beak evolved after the extinction of the dinosaurs. However, the new discovery, reported in the journal Nature , suggests that our understanding of how the modern bird skull came to be needs to be re-evaluated. 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 the palaeognath, or "ancient jaw" group, meaning that, like humans, their palate bones are fused together into a solid mass.

Artist’s reconstruction of the last known toothed bird, Janavis finalidens, in its original environment surrounded by the co-occurring ‘wonderchicken’, Asteriornis. 66.7 million years ago parts of Belgium were covered by a shallow sea, and conditions were similar to modern tropical beaches in places like the Bahamas. Janavis was a very large marine bird, with long wings and teeth in its jaws. It would have hunted fish and squid-like creatures in the tropical sea. Credit: Phillip Krzeminski Read more

Palate of Janavis finalidens in comparison with that of a pheasant and an ostrich. The palate anatomy of Janavis likely approximates that of the most recent common ancestor of all living birds, and is more similar to that of chicken- and duck-like birds, such as pheasants, than to birds like ostriches and emus, which were previously thought to exhibit the ancestral bird condition. Credit: Juan Benito and Daniel Field, University of Cambridge Read more

Artist’s reconstruction of the world’s last known toothed bird, Janavis finalidens. This reconstruction is based on the original fossil bones of Janavis and comparisons with its close relative Ichthyornis, as well as inspiration from modern marine birds such as gulls and petrels. Janavis was a large marine bird with long wings and teeth in its jaws, and would have hunted for fish and squid in warm Late Cretaceous seas. Credit: Phillip Krzeminski Read more