Coelacanth is a deep sea fish that lives off the coast of southern Africa and Indonesia and can grow up to two meters in length. For a long time, scientists believed that they were extinct.
In a new research published in Natural Communicationwe open the best preserved coelacanth fossil ever found from the ancient period hundreds of millions of years ago when these ancient sea-dwellers first evolved. The fossils are from the Gogo Formation in Gooniyandi State in northern Western Australia.
We also study the evolution of all the hundreds of coelacanth species we know from the fossil record to find out what led to the creation of new species over the centuries.
The answer came as a surprise: the biggest influence on the evolution of the coelacanth was not sea temperature or oxygen level but tectonic activity. As the plates of the earth’s crust move, more and more new species appear.
‘living fossils’
Coelacanths are “lobed fin” fish, which means they have strong bones in their fins that are a bit like the bones in our hands. Scientists believe they are more closely related to tetrapods (animals with a backbone and four limbs, such as frogs, emus and humans) than to other fish.
Coelacanths have been around for a long time. The oldest known fossil is over 410 million years old. But because these fossils are mostly fragments, we don’t know much about what the earliest coelacanths were.
Then, during the age of the dinosaurs that started around 250 million years ago, the coelacanth became more diverse. In total, we have found traces of more than 175 fossil species from around the world.
Finally, at the end of the Cretaceous period, 66 million years ago, all traces of the mysterious coelacanths disappeared from the fossil record. For a long time, scientists considered coelacanths to be the victims of a massive asteroid impact that also signed the death warrant for the dinosaurs (along with about three-quarters of all life on Earth).
All that changed in 1938, when fishermen in South Africa pulled a huge and mysterious fish from the depths of the ocean like nothing before. A local museum employee with a keen interest in natural science, Marjorie Courtenay-Latimer, immediately knew the fish was special.
Courtenay-Latimer enlisted her friend JLB Smith, a famous South African chemist with an interest in ichthyology (the study of fish). Smith was identified and named LatimeriaThe first living coelacanth known to science.
Finding this “Lazarus fish” is like stumbling into life Triceratops dinosaurs still roam the forests of North America today. Even today, coelacanths are often described as “living fossils”.
A new fossil coelacanth
Our team from Flinders University, together with other colleagues from Australia, Canada and Europe, discovered a new fossil species of coelacanth in Gooniyandi State in northern WA. About 380 million years ago, the site was a tropical coral reef with more than 50 species of fish.
Thank youthe new coelacanth fossil, is the first fish found in the area with a name given from the Gooniyandi language. The name means “ancient fish in honor of Wirngarri”, a respected elder in the community.
Ngamugawi is the best three-dimensionally preserved coelacanth from the Devonian Period (359 million to 419 million years ago). These fossils provide great insight into the early anatomy of this lineage.
Plate tectonics drive coelacanth evolution
The study of the new species led us to analyze the evolutionary history of all known coelacanths. In doing so, we calculate the rate of evolution over the course of 410 million years of history.
We found that coelacanths generally develop slowly, with some interesting exceptions.
Furthermore, we analyzed a series of environmental factors considered as potential candidates for influencing the rate of coelacanth evolution. These include tectonic plate activity, ocean temperatures, water oxygen levels, and atmospheric carbon dioxide levels.
Of all the variables we looked at, the one that had the biggest impact on the rate of coelacanth evolution was plate tectonic activity. New species of coelacanth are more likely to develop during periods of higher tectonic activity, as seismic movements alter their habitats.
Is the coelacanth still evolving?
Along with our analysis of all fossil coelacanths, we have also looked closely at two living species, Latimeria chalumnae and Latimeria menadoensis.
At first glance, this fish looks very similar to some of its counterparts from hundreds of millions of years ago. However, on closer analysis, we can see that they are completely different from their extinct relatives.
When Latimeria has meant to stop developing new features, the proportions of the body and DNA details are still changing a little. So maybe it’s not a “living fossil” after all.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Published – 17 September 2024 14:27 IST