Dr Sam Giles has paper published in 'Nature'

Dr Sam Giles, Junior Research Fellow in Biological Sciences at Christ Church, has had a paper published in the international scientific journal Nature. The paper, entitled 'Early members of ‘living fossil’ lineage imply later origin of modern ray-finned fishes’, focuses on the use of CT scanning to examine fossils and improve understanding of the evolution of ray-finned fishes.

For every species of mammal, bird, reptile and amphibian on land, there is a species of bony fish in the ocean. In fact, this group--the ray-finned fishes--represent about half of all backboned animals on the planet.

Ray-finned fishes and their land-living cousins share an ancestor deep in evolutionary history. Tracing the origin of one group also provides insights into the origin of the other. Diverse lines of evidence from paleontology, genetics, and anatomy have revealed a great deal about the early stages of land vertebrate evolution. However, initial events in the ray-finned fish half of the family tree remain obscure in comparison. Now, an international team of researchers have started to pull back the curtain on the hidden early history of ray-finned fishes by revealing unexpected fossil relatives of what have long considered the most ‘primitive’ of the living ray-finned fishes, an enigmatic group known as polypterids..

These bizarre fishes dwell in African freshwaters, and display a head-scratching combination of features: thick scales, lungs and fleshy fins. They are so strange, in fact, that it took over a century after they were discovered before the ray-finned fish identity of polypterids was deciphered.

Placement of polypterids in the fish family tree solved one conundrum but raised a more glaring one: the oldest fossils of the group are over a quarter of a billion years younger than the supposed origin of the group. Even more intriguingly, living polypterids appear to be more primitive than a host of ancient fossils.

In this new analysis, spearheaded by Dr Sam Giles, researchers used CT scanning—exploiting the same techniques involved in getting an x-ray to check for a broken bone—to take a fresh look at 250 million-year-old fossils, and discovered that polypterids aren’t as primitive as they might at first seen.

“Polypterids appear to have undergone several reversals in their evolution, which has clouded the view of their position in the fish family tree.” Dr Giles explained “It’s like if your brand-new smartphone came with a rotary dialler and without WiFi; we know it’s the latest handset, but its characteristics might lead us to thinking it’s an older model.”

Seeing the outwardly ‘primitive’ characters for what they were, the new analysis found polypterids nestled neatly back within the ray-finned fish tree.

“With this new analysis, we were able to iron out a lot of the wrinkles in our understanding of the sequence of evolutionary events.” Dr Giles reflected, “These results change our understanding of when the largest living group of vertebrates evolved, and tell us that ray-finned fishes dominated the seas following a major mass extinction that eradicated their closest rivals.

“Analyses like these are powerful tools, and go to show that palaeontology doesn’t always rely on the discovery of new fossils; re-examination of old fossils using new techniques is just as important for revitalising our understanding of vertebrate evolution.”

The full paper is available to read on the Nature website.

 

 

 

 

 

 

 

The skull of a 250 million year old fossil fish and a virtual model of its internal skeleton, along with a life reconstruction. 

Image credit: Andrey Atuchin