Researchers have discovered a 380-million-year-old heart preserved inside a fossilized prehistoric fish.
They say the specimen captures a key moment in the evolution of the blood pumping organ found in all animals with backbones, including humans.
The heart belonged to a fish known as the Gogo, which is now extinct.
The “astounding” discovery, published in the journal Science, was made in Western Australia.
Lead scientist, Prof. Kate Trinajstic of Curtin University in Perth, told BBC News of the moment when she and her colleagues realized they had made the biggest discovery of their lives.
“We were crammed around the computer and we recognized that we had a heart and we pretty much couldn’t believe it! It was incredibly exciting,” he said.
Usually, it is the bones rather than the soft tissues that are turned into fossils, but at this location in Kimberley, known as the Gogo rock formation, 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.
“It shows the body plan that we evolved very early, and we see it for the first time in these fossils.”
His collaborator, Professor John Long of Flinders University in Adelaide, described the discovery as “an astounding and astounding discovery.”
“We have never known anything about the soft organs of such old animals until now,” he said.
The Gogo fish is the first of a class of prehistoric fish called placoderms. These were the first fish to have jaws and teeth. Before them, the fish were no larger than 30 cm, but the placoderms could grow up to nine meters in length.
Placoderms have been the dominant life form on the planet for 60 million years, existing more than 100 million years before the first dinosaurs walked the Earth.
Scans of the Gogo fish fossil showed that its heart was more complex than expected for these primitive fish. It had two chambers one above the other, similar in structure to the human heart.
The researchers suggest that this made the animal’s heart more efficient and was the fundamental shift that transformed it from a slow-moving fish to a fast-moving predator.
‘This was how they could up the ante and become a voracious predator,’ said Professor Long.
The other important observation was that the heart was much further forward in the body than that of the more primitive fish.
This position is thought to have been associated with the development of the neck of the Gogo fish and made room for the development of the lungs further down the evolutionary line.
Dr Zerina Johanson of the Natural History Museum in London, a world leader in placoderms and independent of Professor Trinajstic’s team, described the research as an “extremely important discovery” that helps explain why the human body is the way it is. today.
“Many of the things you see still have in our body; jaws and teeth, for example. We have the first appearance of the front and rear fins, which eventually evolved into our arms and legs.
“There are many things happening in these placoderms that we see evolving for 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 is really exciting to see this result,” he told BBC News.
“The fish that my colleagues and I are studying are part of our evolution. This is part of the evolution of humans and other animals that live on land and the fish that live in the sea today.”
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