Researchers found a 380-million-year-old heart in a prehistoric fish fossil.
They say the specimen captures a pivotal moment in the evolution of the blood-pumping organ found in all vertebrates, including humans.
The heart was found in the fossilized form of a fish known as Gogo. Now, the fish is extinct.
The “surprising” discovery took place in Western Australia and was published in the journal Science.
The scientist who led the research team, Prof. Kate Trinajstic of Curtin University in Perth, told BBC News that when she and her colleagues realized they had made the biggest discovery of their lives.
“We huddled around the computer and realized we had found a heart and couldn’t believe it! It was so much fun,” she said.
This fish is perfectly preserved in the large rocks found in the Kimberley region of Western Australia.
Usually, what turns into fossils is bone, not soft tissue. But in the Kimberley, known for its Gogo rock formations, the minerals have preserved many of the fish’s internal organs, including the liver, stomach, intestines, and heart.
‘This is a pivotal moment in our own evolution,’ said Professor Trinajstic.
“This shows that we evolved very early and for the first time we see it in these fossils.”
His colleague, Professor John Long of Flinders University in Adelaide, described the discovery as “a truly remarkable and surprising discovery.”
“We have never known anything about the soft organs of such an old animal until now,” he said.
Evolution of the heart
Gogo fish were the first fish in a prehistoric class of fish called placoderms. This was the first fish to have jaws and teeth.
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Before the presence of the Gogo fish, the size of the fish did not exceed 30 centimeters. However, the length of the fish, called placoderms, can grow up to nine meters.
Placoderms have been the dominant living things on Earth for 60 million years. There were more than 100 million years before the first dinosaurs walked the Earth.
Scans of the Gogo fish fossils show that the heart is more complex than expected for this primitive type of fish. The heart has chambers and atria, similar to the structure of the human heart.
Researchers believe this structure makes the heart of the Gogo fish more efficient and is an important factor in the transformation of the Gogo fish from slow to fast predator.
“This is how they increase their contribution and become voracious predators,” said prof. Long.
Another important observation is that the position of the heart of the Gogo fish is much more advanced than the more primitive fish.
This position is thought to be related to the neck development of the Gogo fish and to allow for further lung development along the evolutionary line.
Dr Zerina Johanson of the Natural History Museum in London, who is the world’s leading researcher in the field of placoderms and was not involved in Professor Trinajstic’s research team, described the study as a “very important discovery” that helps to explain why the human body is as it is today.
“Many of the things you see, we still have them in our bodies; jaws and teeth, for example. We have the first appearance of the front and rear fins, which eventually develop in our arms and legs.
“There is a lot to do in this placoderm, which we see developing in ourselves today, such as the neck, the shape and arrangement of the heart and its position in the body.”
The discovery takes an important step in the evolution of life on Earth, according to Dr Martin Brazeau, a placoderm expert at Imperial College London, who is also independent of the Australian research team.
“It’s great to see these results,” he told BBC News.
“The fish my colleagues and I studied were part of our evolution. This is part of the evolution of humans and other animals that lived on land and the fish that live in the ocean today.”
