The bizarre snouted fish scientists say could explain how our arms and legs evolved

PUBLISHED: 05:40 EST, 8 August 2012 UPDATED: 05:45 EST, 8 August 2012

It is one of the oddest animals on the planet, with a giant snout and eggs harvested for caviar.

Yet scientists have found that the American paddlefish, one of the oldest fish on the planet, could explain why we developed our arms and legs.

Scientists found the fish duplicated its entire genome about 42 million years ago, according to a new study published in the journal Genome Biology and Evolution. 

A paddlefish in Chattanooga, Tennessee. Researchers believe the primitive fish could hold the key to how our limbs evolved.

A paddlefish in Chattanooga, Tennessee. Researchers believe the primitive fish could hold the key to how our limbs evolved.


They believe the unique trait could help explain how fins eventually evolved 

‘We found that paddlefish have had their own genome duplication,’ said Karen Crow, assistant professor of biology at San Francisco State University. 

‘This creates extra genetic material that adds complexity to comparative studies. 

‘It may change the way we interpret studies on limb development.’

In order to study how human limbs develop, scientists compare the limb-building genes found in mice with fin-building genes found in fishes.

Previous research on paddlefish has suggested that fishes possessed the genetic toolkit required to grow limbs long before the evolution of the four-limbed creatures (tetrapods) that developed into reptiles, birds, amphibians and mammals.


Crow and colleagues sequenced chromosomal regions containing 19 Hox genes in the American paddlefish. Hox genes determine body shape and limb development, and have become prime candidates for detecting whole genome duplications.

Whole genome duplications are described by researchers as ‘game-changing events’ in evolutionary history that give rise to new species or novel features within a species.

They occur when a series of unlikely circumstances coincide, resulting in twin copies of every gene. 

When this happens, one scenario that could take place is that one gene in the pair keeps its designated function while the other is either lost or takes on a new purpose.

‘This extra genetic material provides the canvas for evolution to paint with,’ said Crow, who studies the evolution of novelty and diversity.

Two milestone genome duplications are believed to have taken place before the evolution of jawed vertebrates. 

Additional whole genome duplications have also taken place further down the evolutionary tree, in specific lineages or branches, but it is a phenomenon more common in plants than animals.

‘Our findings on the paddlefish suggest that whole duplication is not as uncommon in animals as previously thought,’ Crow said.

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