Fossil sheds light on evolutionary journey from dinosaur to bird

Scientists have reconstructed the skull of an Ichthyornis dispar, a very early bird species that still had the sharp teeth of a dinosaur

It was one of the fossils Darwin hailed as evidence of evolution. Now scientists have unveiled four skulls of an ancient toothed seabird in a study experts say reveals the face of early birds.

Thought to have lived between 66 and 100m years ago the gull-like bird, known as Ichthyornis dispar, was first written about in the 19th century by American palaeontologist Othniel Marsh after fossil remains were unearthed in the US.

These revealed that the animal’s body was similar to modern birds in many respects. But there was a startling difference: it had jaws which housed sharp teeth.

The findings astonished experts who recognised that the creature offered crucial insights into how today’s birds came to be. However the skull was far from complete.

Now a team of researchers from the UK and US have produced a clear picture of what the head of the animal looked like, after analysis of four more skulls of the bird. Experts say the findings help to unpick how modern birds evolved from their dinosaur ancestors.

“The famous bird archaeopteryx and a lot of the fossils in the early history of bird evolution, they had wings, but their skulls basically looked like little baby dinosaur skulls,” said Dr Bhart-Anjan Bhullar, a co-author of the research from Yale University. “Ichthyornis, it turns out, is just at this transitional moment,” he said, adding that the results “show the order of appearance of modern bird features.”

While three of the new skulls were discovered in museum collections, where the fragments had lain unanalysed for years, the fourth was only discovered in a rock in Kansas in 2014.

The team CT-scanned the new skulls and the 19th century specimen – the latter of which was found to contain important bones surrounding the eye socket and nostrils that had not previously been recognised. Together, the data was used to produce a three-dimensional, virtual reconstruction of the skull of the ancient bird.

The findings, published in the journal Nature, reveal that the creature was unlike modern birds in having jaws replete with sharp, curved teeth and a skull with space for large jaw muscles.

What’s more, a particular type of bone that largely makes up beaks in modern birds was confined to the very end of the animal’s jaws – as found in many dinosaurs, and even in animals today. However, like modern birds, this tiny beak was covered in a fingernail material called keratin and was toothless and hooked. Bhullar said, this beak was used like a hand after wings evolved, and was probably used for preening, grabbing and pecking – functions likely helped by the fact the animal was able to raise its upper jaw, like modern birds can.

“It was flying around eating probably fish, shellfish and other things, plucking them out of the water with its abbreviated little pincer-tip beak and then tossing them back into its mouth and crunching down on them with its powerful dinosaur-like jaws,” said Bhullar.

The animal’s brain meanwhile was relatively large compared to its body size, a feature found in birds today. That, said Bhullar, scotches the idea that a large brain evolved at the expense of space for jaw muscles. “I think the reason the bird brain is large basically is to deal with the demands of flight,” he said.

“This discovery is a great example of the necessity of the fossil record for solving evolutionary puzzles,” said Dr Daniel Field, a co-author of the research from the University of Bath.

Dr Stephen Brusatte, a palaeontologist at the University of Edinburgh who was not involved in the study, described the work as exceptional.

“It shows us the face of the earliest birds. And it’s a bit different than I would have expected,” he said, describing the creature as almost looking like it was half bird, half velociraptor. “The earliest birds had Frankenstein creature heads and it was only through a long and gradual period of evolution that the fully modern bird skull – beak, no teeth, huge brain, tiny jaw muscles – evolved,” he said.


Nicola Davis

The GuardianTramp

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