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Crocodiles are a close living relatives of birds, but compared to their feathered cousins, they are stuck in the past, scientists claim.

Both groups of animals share a common ancestor that lived around 240 million years ago, and also gave rise to the dinosaurs.

But while birds quickly evolved after the demise of dinosaurs, the evolution of crocodilians has crawled along slowly.

Crocodiles are a close living relatives of birds, but compared to their feathered cousins, they are stuck in the past, scientists claim. The reptiles evolved at a slow rate after the demise of dinosaurs and their 'body plan' has remained largely unchanged for millions of years, experts claim

Crocodilians make up the group of creatures that includes crocodiles, caimans, alligators and gharials.

Now, new genetic studies have revealed their unusually slow rate of genetic evolution.

The sluggish progress of the reptiles has helped scientists build up a genetic picture of the archosaurs that predated dinosaurs, pterosaurs, birds and crocodilians.

Dr Richard Green, from the University of California at Santa Cruz, said: 'The ticking of the molecular clock in the crocodilians is much slower than in other lineages we're used to looking at, like mammals, which means we can see back into their past more cleanly.

Both crocodiles and birds share a common ancestor called archosaurs (illustrated) that lived around 240 million years ago. This ancestor also gave rise to the dinosaurs

'We know from fossils that the body plan of crocs has remained largely unchanged for millions of years.'

The team sequenced the genomes, or genetic blueprints, of three crocodilian species: the American alligator, the saltwater crocodile, and the Indian gharial.

The study, published in the journal Science, suggests that the ancestor of all archosaurs had an extremely slow rate of molecular evolution, which sped up in the bird lineage.

After the meteor strike, which is thought to have wiped out the dinosaurs 66 million years ago, surviving birds experienced a rapid burst of evolution.

After the meteor strike, which is thought to have wiped out the dinosaurs 66 million years ago, surviving birds experienced a rapid burst of evolution. This led to nearly all the species of birds seen on Earth today including Snow geese (pictured), of which there are more than 10,000

This led to nearly all the species of birds seen on Earth today, of which there are more than 10,000.

In related studies, also reported in Science, researchers compared the genomes of 48 bird species selected from all major avian groups, including the woodpecker, owl, penguin, hummingbird and flamingo.

They discovered that birdsong evolved independently at least twice.

Birds were also found to have lost their teeth around 116 million years ago, when the dinosaurs still ruled. 

PREHISTORIC CROCODILES 'RAN LIKE DOGS' TO ESCAPE PREDATORS

Prehistoric crocodiles were able to run around like dogs to escape the jaws of predatory dinosaurs.

This is according to a study published last year that showed, for the first time, how the reptiles evolved in a dinosaur dominated world.

Today, most modern crocodiles live in freshwater habitats and feed on mammals and fish, but their ancestors ran around on land like dogs while others adapted to life in the open ocean, imitating the behaviour of whales.

Today, most modern crocodiles live in freshwater habitats and feed on mammals and fish. But their ancestors (pictuerd) were very different creatures, with some running around on land like dogs while others adapted to life in the open ocean, imitating the behaviour of whales

The study, by Bristol University, revealed how the jaws of the ancient crocodiles evolved to enable the fierce animals to survive in vastly different environments.

The team examined variation in the shape and biomechanics function of the lower jaws in over 100 ancient crocodiles during the Mesozoic - a period which began 251 million years ago and covered over 170 million years.

The study revealed that ancient crocodiles invaded the Jurassic seas and evolved jaws built primarily for water efficiency to capture agile prey, such as fish. 

Sample of jaws from the Mesozoic crocodile record

The research also found that variation peaked again in the Cretaceous period- 142 million years ago - where ancient crocodiles evolved a great variety of lower jaw shapes as they adapted to a diverse range of food.

The research also found that variation peaked again in the Cretaceous period- 142 million years ago - where ancient crocodiles evolved a great variety of lower jaw shapes as they adapted to a diverse range of food.

After the devastating end-Triassic extinction event, crocodile ancestors invaded the seas and evolved jaws primarily built to efficiently swim in the water to catch agile prey such as fish.

They also evolved a great variety of lower jaw shapes during the Cretaceous Period - about 145 million to 65 million years ago - as they adapted to a diverse range of niches and environments alongside the dinosaurs, including eating plants.

Surprisingly, the lower jaws of Cretaceous crocodiles did not have a huge amount of variation.

Instead, the fossil record points towards novel adaptations in other areas of their anatomy, such as armadillo-like body armour.