Researchers have discovered a 380-million-year-old heart preserved in 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 a backbone, including humans.
The heart belonged to a fish known as the Gogo, which is now extinct.
The “stunning” discovery, published in the journal Science, was made in Western Australia.
The lead scientist, Prof Kate Trinajstic of Curtin University in Perth, told BBC News about when she and her colleagues realized they had made the biggest discovery of their lives.
“We sat around the computer recognizing that we had a heart and could hardly believe it! It was incredibly exciting,” she said.
Usually they’re bones rather than soft tissues that turn into fossils — but at this Kimberley location known as the Gogo Rock Formation — minerals have preserved many of the fish’s internal organs, including the liver, stomach, gut and heart. .
“This is a pivotal moment in our own evolution,” says Prof. Trinajstic.
“It shows the body plan that we developed very early on, and we see this for the very first time in these fossils.”
Her collaborator, Prof. John Long of Flinders University in Adelaide, described the find as “a mind-boggling, breathtaking discovery”.
“We have never known anything about the soft organs of such ancient animals until now,” he said.
The Gogo fish is the first of a class of prehistoric fish called placoderms. These were the first fish with jaws and teeth. Before them, fish were no larger than 30 cm, but placoderms could grow up to 9 m in length.
Placoderms were the dominant life form on the planet for 60 million years and existed more than 100 million years before the first dinosaurs roamed the Earth.
Scans of the Gogo fish fossil showed that the 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 this made the animal’s heart more efficient and was the crucial step that transformed it from a slow-moving fish into a fast-moving predator.
“This was how they could raise the bar and become a voracious predator,” said Prof. Long.
The other important observation was that the heart was much more forward in the body than that of more primitive fish.
This position is thought to have been associated with the development of the neck of the Gogo fish and has allowed for the development of lungs further down the evolutionary line.
dr. Zerina Johanson of the Natural History Museum, London, who is a world leader in placoderms and independent of Prof. Trinajstic’s team, described the research as a “very important discovery” that helps explain why the human body is the way it is. . Today.
“A lot of the things you see we still have in our own bodies; jaws and teeth, for example. We first have the front fins and the back fins, which eventually evolved into our arms and legs.
“There are many things going on in these placoderms that we see evolving into ourselves today, such as the neck, the shape and arrangement of the heart, and its position in the body.”
The discovery marks 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 from the Australian research team.
“It’s really exciting to see this result,” he told BBC News.
“The fish that my colleagues and I study 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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