Evolution ‘backwards’ – The discovery overturns more than a century of knowledge about the origin of modern birds

Reconstruction of the artist Janaves finalidens

An artist’s reconstruction of the last known toothed bird, Janavis final, in its native environment surrounded by the common “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 seabird, with long wings and teeth in its jaw. He would hunt fish and squid-like creatures in the tropical sea. Credit: Philip Krzyminski

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

A team of researchers from Cambridge University The Natuurhistorisch Maastricht Museum has discovered that a crucial cranial feature of modern birds, the movable beak, evolved before the mass extinction event that wiped out the 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 state after the advent of modern birds.

Using computed tomography techniques, the Cambridge team identified the bones of the palate, or roof of the mouth, of a new species of large ancient bird, which they named Janavis final. It lived at the end of the age of the dinosaurs and was one of the last birds ever to live. The arrangement of the palatal bones shows that this “dinosaur bird” had a dexterous movable beak, almost indistinguishable from that of most modern birds.

Video showing the pterygoid rotator (palatine bone) of Janavis finalidens, which is very similar to that of living duck- and chicken-like birds. The bone was found as two identical fragments, which were digitally fitted together. The bone is hollow and was likely filled with air in life, as evidenced by the large opening on 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 moving beak had evolved after the extinction of the dinosaurs. However, the new discovery, which was reported in the journal natureindicates that our understanding of how the skull of modern birds appeared needs to be re-evaluated.

Each of the 11,000 species of birds on earth today is classified into one of two overlying groups, based on the arrangement of the palatal bones. Ostriches, emus, and their relatives are classified in the Palaeognath, or “ancient jaw” group, which means that, like humans, the palatal bones are fused together into a solid mass.

Wing comparison

palate Janavis final Compared to a pheasant and an ostrich. palate anatomy Janavis It likely approximates the most recent common ancestor of all living birds and is more similar to chicken- and duck-like birds, such as pheasants, than to birds such as ostriches and ostriches, which were previously thought to display ancestral bird status. Credit: Juan Benito and Daniel Field, University of Cambridge

All other groups of birds are classified into the Neognath group, or “modern jaw” group, which means that the palatal bones are connected by a movable joint. This makes their beaks 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 of Charles Darwin’s theory of evolution. In 1867, he divided all living birds into the “ancient” or “modern” jaw group. Huxley’s assumption was that “ancient” jaw formation was the original condition for modern birds, with “modern” jaws coming later.

“This assumption has been taken for granted ever since,” said Dr Daniel Field of the Department of Earth Sciences, Cambridge, senior author of the paper. “The main reason this assumption persists is that we haven’t had any well-preserved fossil bird tastes from the period when modern birds arose.”

Janavis Bird

An artist’s reconstruction of the world’s last known toothed bird, Janavis final. This reconstruction is based on the original fossil bones of Janavis and comparisons to its close relative Ichthyornis, as well as inspiration from modern seabirds such as gulls and egrets. Janavis It was a large seabird with long wings and teeth in its jaw and would have hunted fish and squid in the warm late Cretaceous seas. Credit: Philip Krzyminski

fossil JanavisIt was found in a limestone quarry near the Belgian-Dutch border in the 1990s and first studied in 2002. It dates back 66.7 million years, during the last days of the dinosaurs. Because the fossil is covered in rock, scientists at the time could only base their descriptions on what they could see from the outside. They described the fragments of bone protruding from the rock as fragments of cranial and shoulder bones and returned the seemingly unremarkable fossil to storage.

Nearly 20 years later, the fossil was loaned to Fields’ collection at Cambridge, and to Dr. Juan Benito, who had a PhD at the time. Student, he started to give him another look.

“Since this fossil was first described, we’ve started using computed tomography on fossils, which enables us to see through rocks 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 contain skull material, which isn’t often preserved, but we couldn’t see anything that looked like it came from a skull on our CT scans, so we gave up and put it down.” fossil aside.”

During the early days of the Covid-19 lockdown, Benito took up the fossil again. “Previous descriptions of the fossil didn’t make sense — there was a bone I was confused about. I couldn’t see how what was first described as a shoulder bone could actually be a shoulder bone,” he said.

“This was my first personal interaction in months: Juan and I had a socially distanced meeting outdoors, and he passed me the mysterious fossil bone,” said Field, who is also Curator of Ornithology at Cambridge Zoological Museum. “I could see that it wasn’t a shoulder bone, but there was something familiar about it.”

“Then we realized we’d seen a similar bone before, in a turkey skull,” Benito said. “And because of the research we did in Cambridge, we have things like turkey skulls in our lab, so we brought one in and the two bones were almost identical.”

The realization that the bone was a skull bone, not a shoulder bone, led the researchers to conclude that the unused “modern jaw” condition, which turkeys shared, had evolved before the “ancient jaw” condition of ostriches and their relatives. For some unknown reason, the fused palates of ostriches and their relatives must have evolved at some point after modern birds were already established.

Two of the main characteristics we use to distinguish modern birds from their dinosaur ancestors are the toothless beak and the movable upper jaw. While Janavis final It still has 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 very similar to that of living chickens and ducks,” said Pei Chen Kuo, a co-author of the study. Added co-author Clara Widrig: “Surprisingly, the palatal bones of birds are the least similar to those of birds. Janavis of ostriches and their relatives.” Both Kuo and Widrig are Ph.D. students in the Field Laboratory in Cambridge.

“Evolution does not happen in a straight line,” Field said. “This fossil shows that the movable beak—a condition we always thought had a posthistoric origin in modern birds, actually evolved before modern birds appeared. We’ve been completely backward in our assumptions about how the skull of modern birds evolved for more than a century.”

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

What happened Janavis? It, like other large dinosaurs and toothed birds, did not survive the eventual mass extinction event[{” 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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