Ancient bird reveals clues about the evolution of flight: 75 million year old fossil shows how creatures evolved stronger muscles and bones in order to fly

  • Modern birds are the only group to survive the extinction of the dinosaurs 
  • It has remained a mystery as to why these animals survived and others did not   
  • The latest fossil has a range of features that are similar to modern birds  
  • This animal was an expert flyer and well adapted for flight and scientists do not know why it went extinct but others survived 
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Mystery surrounding the ancestry of modern birds has deepened after the discovery of a rare fossil dating back to the age of the dinosaurs.

Scientists analysed the almost perfectly intact fossil skeleton of a bird the size of a turkey vulture that lived 75 million years ago.

They discovered that the creature, Mirarce eatoni, must have been an expert flyer and was well adapted for flight as modern birds with stronger muscles and specific bone structures.

The fossil has bones from virtually all parts of the skeleton, except the skull, allowing a clear idea of the animal’s complete form.

Previous fossils of the Cretaceous creatures were single bones from the feet, so experts didn’t accurately know what they looked like in 3D. 

Imagined: Previous fossils of enantiornithines were single feet bones, so experts didn’t accurately know what they looked like in 3D, but the fossil helped create this impression

This type of bird and other members of its family group, the enantiornithines, vanished in the mass extinction that wiped out the dinosaurs 65 million years ago.

Only one group of birds, whose descendants are still living today, survived the cataclysm that followed a massive meteor impact off the coast of Mexico.

It has long remained a mystery why this one particular group survived the Armageddon when many other groups did not. 

The advanced traits seen on this latest fossil compounds the mystery, experts claim.    

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US researcher Jessie Atterholt, from the University of California at Berkeley, said: ‘We know that birds in the early Cretaceous, about 115 to 130 million years ago, were capable of flight but probably not as well adapted for it as modern birds.

‘What this new fossil shows is that enantiornithines, though totally separate from modern birds, evolved some of the same adaptations for highly refined, advanced flight styles.’

Despite having the appearance of a modern bird, the fossil probably had teeth in the front of its beak and claws on its wings as well as its feet, said the scientists.

The fossil, housed at the University of California Museum of Palaeontology at Berkeley, was discovered in Utah in 1992 but has only now undergone analysis. The findings are published in the journal PeerJ.

All birds evolved from feathered two-legged ‘theropod’ dinosaurs, the large group of meat-eaters that included Tyrannosaurus rex.

Explaining how modern avialans came to be: The so-called ‘opposite birds’ were a group that existed during the geologic period, where they existed alongside dinosaurs

Evolution in progress: By the late Cretaceous period, they had separately evolved adaptations for advanced flight, similar to what we see on birds today


Dinosaurs ruled and dominated Earth around 66 million years ago, before they suddenly went extinct. 

The Cretaceous-Tertiary extinction event is the name given to this mass extinction.

It was believed for many years that the changing climate destroyed the food chain of the huge reptiles. 

In the 1980s, archaeologists discovered a layer of iridium.

This is an element that is rare on Earth but is found  in vast quantities in space.  

When this was dated, it coincided precisely with when the dinosaurs disappeared from the fossil record. 

A decade later, scientists uncovered the massive Chicxulub Crater at the tip of Mexico’s Yucatán Peninsula, which dates to the period in question. 

Scientific consensus now says that these two factors are linked and they were both probably caused by an enormous asteroid crashing to Earth.

With the projected size and impact velocity, the collision would have caused an enormous shock-wave and likely triggered seismic activity. 

The fallout would have created plumes of ash that likely covered all of the planet and made it impossible for dinosaurs to survive. 

Other animals and plant species had a shorter time-span between generations which allowed them to survive.

There are several other theories as to what caused the demise of the famous animals. 

One early theory was that small mammals ate dinosaur eggs and another proposes that toxic angiosperms (flowering plants) killed them off.  

Enantiornithines were ‘very, very common’ and could be found all over the world, said PhD student Ms Atterholt.

M. eatoni had a deeply keeled breast bone, implying large and powerful flight muscles.

It also had anchor points known as ‘quill knobs’ on its forearm bones.

In modern birds quill knobs help to strengthen the wing feathers for active flight.

‘This is the first discovery of quill knobs in any enantiornithine bird, which tells us that it was a very strong flyer,’ said Ms Atterholt.

A possible reason for the extinction of enantiornithines is that they were mostly forest dwellers, according to the researchers.

Many experts believe the meteor strike that ended the dinosaurs’ reign sparked a global fire storm that destroyed much of the world’s forests.

The name Mirarce combines the Latin word for wonderful with the mythical Greek character Arce, the winged messenger of the Titans.

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