An international team coordinated by the Broad Institute, a research center affiliated with the Massachusetts Institute of Technology (MIT) and Harvard University, announced they have completed the sequencing of the genome of a coelacanth (Photo ©Alberto Fernandez Fernandez), a fish that was thought to be extinct until 1938, when a living specimen was found.

To be precise, coelacanths constitute an order called technically Coelacanthiformes. They are among the oldest vertebrates with jaws and the remains found of fishes similar to them date back to the beginning of the Devonian, a geological period that started about 410 million years ago. Judging by the fossils found, they were widespread especially in the Mesozoic and some species exceeded three meters in length.

In the past it was believed that coelacanths had disappeared during the great extinction that happened 65 million years ago, the one that also led to the extinction of the dinosaurs. The species discovered in 1938 in the Mozambique Channel was named Latimeria chalumnae while another species was discovered in 1999 near the coast of Indonesia, called Latimeria menadoensis.

The coelacanths are considered living fossils. This expression was coined by Charles Darwin to indicate species of living creatures that have characteristics very similar to species known only through fossil findings. Today’s coelacanths are very similar to some species that lived in the Cretaceous period.

The coelacanths live in deep waters, where it’s difficult for fossils to be brought to the surface and this may explain why they were considered extinct. It’s therefore likely that only the ancient species that lived in shallow water become completely extinct.

The fact that the coelacanths have changed very little compared to their ancestors that lived many millions of years ago has made them very interesting to biologists and evolutionists. Probably their habitat has remained fairly stable over time so they didn’t have great evolutionary pressures to force them to change.

The sequencing work wasn’t easy because it required fresh tissue. Today’s coelacanths die quickly when they’re brought to the surface because of the changes in pressure and temperature compared to their natural environment and their DNA rapidly degrades. The needed tissue samples were obtained in 2003 but only in 2011 the researchers were able to start the sequencing work, when they obtained the funds and the necessary equipment.

The sequencing is only the first stage of the job. In fact, now the scientists can analyze the coelacanths DNA and thanks to the fact that its changes were limited, they’ll try to get more information on the evolution of vertebrates.

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