University of Cambridge discovery overturns more than a century of understanding about the origin of modern birds

Scans of fossilised fragments of a skeleton inside a rock have overturned more than a century of understanding about the origin of modern birds.

Researchers from the University of Cambridge and the Natuurhistorisch Museum Maastricht discovered one of the key skull features characterising 99 per cent of modern birds – their mobile beak – evolved before the mass extinction event 66 million years ago that killed all large dinosaurs.

The finding also suggests that the skulls of ostriches, emus and their relatives evolved ‘backwards’, meaning they reverted to a more primitive condition after modern birds arose.

The Cambridge team used CT scanning to identify bones from the roof of the mouth - the palate - of a newly-found species of a large ancient bird that they named Janavis finalidens, which lived at the end of the age of dinosaurs. One of the last toothed birds to live, the arrangement of the palate bones of this ‘dino-bird’ showed it had a mobile, dexterous beak that was almost indistinguishable from that of most modern birds.

It had been assumed for more than a century that birds’ mobile beaks evolved after the extinction of the dinosaurs.

That arose after British biologist Thomas Huxley - known as ‘Darwin’s Bulldog’ for his vocal support of Charles Darwin’s theory of evolution - divided all living birds in 1867 into either ‘ancient’ or ‘modern’ jaw groups, based on the arrangement of their palate bones.

Today, all of the 11,000 or so species of birds on Earth today remain classified into these groups. Ostriches, emus and their relatives are classified into the palaeognath, or ‘ancient jaw’ group, which means their palate bones are fused together into a solid mass, like humans’.

All other bird groups are classified into the neognath, or ‘modern jaw’ group, as their palate bones are connected by a mobile joint making their beaks much more dexterous, which is useful for nest-building, grooming, gathering food and defence.

Huxley assumed the ‘ancient’ jaw configuration was the original condition for modern birds, and that the ‘modern’ jaw arising later.

“This assumption has been taken as a given ever since,” said Dr Daniel Field from Cambridge’s Department of Earth Sciences, senior author of a paper published in Nature. “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.”

In the 1990s, a 66.7 million-year-old fossil - Janavis - was found in a limestone quarry near the Belgian-Dutch border and it was first studied in 2002.

But encased in a grapefruit-sized rock, they could only describe what they saw outside.

Then nearly 20 years later, the fossil was loaned to Dr Field’s group in Cambridge, and Dr Juan Benito, then a PhD student, studied it again.

Dr Benito, now a postdoctoral researcher at Cambridge, and the paper’s lead author, said: “Since this fossil was first described, we’ve started using CT scanning on fossils, which enables us to see through the rock and view the entire fossil.

“We had high hopes for this fossil – it was originally said to have skull material, which isn’t often preserved, but we couldn’t see anything that looked like it came from a skull in our CT scans, so we gave up and put the fossil aside.”

But during lockdown, Dr Benito took the fossil out again.

“The earlier descriptions of the fossil just didn’t make sense – there was a bone I was really puzzled by. 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 meeting, and he passed the mystery fossil bone to me,” said Dr Field, the curator of ornithology at Cambridge’s Museum of Zoology. “I could see it wasn’t a shoulder bone, but there was something familiar about it.”

Dr Benito continued: “Then we realised we’d seen a similar bone before, in a turkey skull, and because of the research we do at Cambridge, we happen to have things like turkey skulls in our lab, so we brought one out and the two bones were almost identical.”

This led the researchers to conclude that the unfused ‘modern jaw’ condition, that turkeys share, evolved before the ‘ancient jaw’ condition of ostriches and their relatives.

The fused palates of ostriches and kin must have evolved at some point after modern birds were already established, for unknown reasons.

A toothless beak and a mobile upper jaw distinguish modern birds from dinosaurs.

Janavis finalidens had teeth, meaning it was a pre-modern bird, but its jaw structure is that of the modern, mobile kind.

Pei-Chen Kuo, a co-author of the study, a PhD student in Dr Field’s lab, said: “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.”

Co-author Klara Widrig, a fellow PhD student in the lab, added: “Surprisingly, the bird palate bones that are the least similar to that of Janavis are from ostriches and their kin.”

Dr Field explained: “Evolution doesn’t happen in a straight line. 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.”

It does not mean that the whole bird family tree needs to be redrawn, but it does rewrite our understanding of a key evolutionary feature.

Janavis finalidens, like the large dinosaurs and other toothed birds, did not survive the mass extinction event at the end of the Cretaceous period - possibly because of its size. It was around 1.5kg and the size of a vulture.

It it thought likely that smaller animals – like the ‘wonderchicken’, which was identified by Dr Field, Dr Benito and colleagues in 2020, which lived alongside Janavis – benefitted from the fact that they had to eat less to survive after an asteroid struck Earth and disrupted food systems.

The research was supported in part by the American Ornithological Society, the Jurassic Foundation, the Paleontological Society, and UK Research and Innovation (UKRI).