Evolution “backwards”: the discovery overturns more than a century of knowledge about the origin of modern birds

Artist's reconstruction of Janavis finalidens

Artist’s reconstruction of the last known toothed bird, Janavis Finalidens, in its original environment surrounded by the concurrent ‘wonder chicken’, 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 It was a very large sea bird, with long wings and teeth in its jaws. It would have hunted fish and squid-like creatures in the tropical sea. Credit: Philip Krzeminski

The fossilized remains of a skeleton found inside a small rock have challenged a long-held belief about the evolution of modern birds.

A team of researchers from the University of Cambridge and the Natuurhistorisch Museum Maastricht found that a crucial feature of the skull of modern birds, the mobile beak, had developed before the mass extinction that wiped out the dinosaurs 66 million years ago.

This finding also suggests that the skulls of ostriches, emus and their relatives evolved “backward”, 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 end of the Age of Dinosaurs and was one of the last toothed birds to live. The arrangement of the palate bones shows that this ‘dinobird’ had a mobile and dexterous beak, almost indistinguishable from that of most modern birds.

Video showing the spinal pterygoid (a palate bone) of Janavis finalidens, which is very similar to that of living duck- and chicken-like birds. The bone was found as two matching fragments, which have been digitally joined. The bone is hollow and was probably filled with air in life, as shown by the large opening in its side. Credit: Dr. Juan Benito and Dr. Daniel Field, University of Cambridge

For more than a century, it was assumed that the mechanism that enabled a mobile beak evolved after the extinction of the dinosaurs. However, the new discovery, published in the journal Naturesuggests that our understanding of how the modern bird skull arose needs to be reassessed.

Each of the roughly 11,000 bird species on Earth today falls into one of two general groups, based on the arrangement of the palate bones. Ostriches, emus and their relatives are classified in the paleognathous or ‘old jaw’ group, which means that, like humans, the palate bones are fused together into a solid mass.

pterygoid comparison

palate of Janavis Finalidens compared to that of a pheasant and an ostrich. The anatomy of the palate Janavis probably 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 such as ostriches and emus, which were previously he thought they exhibited the status of an ancestral bird. . Credit: Juan Benito and Daniel Field, University of Cambridge

All other groups of birds are classified in the neognath, or ‘modern jaw’ group, which means that their palate bones are connected by a movable joint. This makes their beaks much more dexterous and useful for nest building, grooming, food gathering, and defense.

The two groups were originally classified by Thomas Huxley, the British biologist known as ‘Darwin’s Bulldog’ for his vocal support for Charles Darwin’s theory of evolution. In 1867, he divided all living birds into “ancient” or “modern” jaw groups. Huxley’s assumption was that the ‘ancient’ jaw configuration was the original condition of modern birds, and that the ‘modern’ jaw arose later.

“This assumption has been taken for granted ever since,” said Dr Daniel Field of Cambridge’s Department of Earth Sciences, lead author of the paper. “The main reason this assumption has endured is that we have not had any well-preserved fossil bird palates from the period when modern birds originated.”

janavis bird

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 seabirds such as gulls and petrels. Janavis it was a large seabird with long wings and teeth in its jaws and would have hunted fish and squid in the warm seas of the Late Cretaceous. Credit: Philip Krzeminski

the fossil, Janavis, was found in a limestone quarry near the Belgian-Dutch border in the 1990s and first studied in 2002. It dates to 66.7 million years ago, during the last days of the dinosaurs. Since the fossil is encased in rock, scientists at the time could only base their descriptions on what they could see from the outside. They described the chunks of bone that protruded from the rock as fragments of skull and shoulder bones and put the nondescript-looking fossil back into storage.

Nearly 20 years later, the fossil was loaned to Field’s group in Cambridge, and Dr. Juan Benito, then a Ph.D. student, began to give him another look.

“Since this fossil was first described, we started using CT scans on fossils, which allows us to see through the rock and see the whole fossil,” said Benito, now a postdoctoral researcher at Cambridge and lead author of the paper. “We had high hopes for this fossil – it was originally said to have skull material, which is not usually preserved, but we couldn’t see anything that looked like it came from a skull on our CT scans, so we gave up and leaves the fossil to a side.

During the first days of the confinement by the Covid-19, Benito took out the fossil again. “Previous descriptions of the fossil just didn’t make sense – there was a bone that really puzzled me. I couldn’t see how what was first described as a shoulder bone could actually be a shoulder bone,” he said.

“It was my first in-person interaction in months: Juan and I had a socially distanced outdoor gathering, and he passed me the mysterious bone fossil,” said Field, who is also curator of ornithology at the Cambridge Museum of Zoology. “I could see it wasn’t a shoulder bone, but there was something familiar about it.”

“Then we realized that we had seen a similar bone before, in a turkey skull,” Benito said. “And because of the research that we do at Cambridge, we have things like turkey skulls in our lab, so we pulled one out and the two bones were almost identical.”

The realization that the bone was a skull bone, and not a shoulder bone, led the researchers to conclude that the unfused “modern jaw” condition, which turkeys share, evolved before the “ancient jaw” condition. “Ostriches and their relatives. For an unknown reason, the fused palates of ostriches and relatives must have evolved sometime after modern birds were already established.

Two of the key features we use to differentiate modern birds from their dinosaur ancestors are a toothless beak and a movable upper jaw. Time Janavis Finalidens it still had teeth, making it a pre-modern bird, its jaw structure being of the modern, movable type.

“Using geometric analyses, we were able to show that the shape of the fossil palate bone was extremely similar to that of living chickens and ducks,” said Pei-Chen Kuo, co-author of the study. Added co-author Klara Widrig: “Surprisingly, the palate bones of birds that are less similar to those of Janavis They are from ostriches and their relatives.” Both Kuo and Widrig have Ph.D. students in Field’s laboratory at Cambridge.

“Evolution doesn’t happen in a straight line,” Field said. “This fossil shows that the mobile beak, a condition we had always thought of postdate the origin of modern birds, actually evolved before modern birds existed. We have been completely behind in our assumptions of how the modern bird skull evolved for more than a century.”

The researchers say that while this discovery doesn’t mean the entire bird family tree needs to be redrawn, it does rewrite our understanding of a key evolutionary feature of modern birds.

and what happened to Janavis? Like the great dinosaurs and other toothed birds, it did not survive the mass extinction event at the end of the[{” attribute=””>Cretaceous period. The researchers say that this may be because of its large size: Janavis weighed around 1.5 kilograms and was the size of a modern vulture. It’s likely that smaller animals – like the ‘wonderchicken’, identified by Field, Benito, and colleagues in 2020, which comes from the same area and lived alongside Janavis – had an advantage at this point in Earth’s history since they had to eat less to survive. This would have been beneficial after the asteroid struck the Earth and disrupted global food chains.

Reference: “Cretaceous ornithurine supports a neognathous crown bird ancestor” by Juan Benito, Pei-Chen Kuo, Klara E. Widrig, John W. M. Jagt and Daniel J. Field, 30 November 2022, Nature.
DOI: 10.1038/s41586-022-05445-y

The study was funded by the by the American Ornithological Society, the

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