The oldest heart ever discovered in a 380-million-year-old fossil: it has an atrium and a ventricle
An extraordinary three-dimensional, S-shaped heart with an atrium and ventricle was discovered in the fossil of an armored fish that lived in the Devonian.
In the fossil of a prehistoric fish that lived 380 million years ago, scientists have identified an incredible detail: the presence of a heart oldest ever discovered. To make this paleontological find even more extraordinary, the fact that soft tissue has been preserved (mineralized) in three dimensions and not as a flat spot, as often happens in these already very fortunate circumstances.
Thanks to modern and sensitive scanning technologies, scientists were able to observe the incredible details of this organ that pulsed hundreds of millions of years ago, shedding new light on the evolutionary biology of vertebrates (to which we also belong).
Discovering and describing the oldest heart ever discovered was an international research team led by Australian scientists from the Curtin University of Bentley, who collaborated closely with colleagues from Flinders University's College of Science and Engineering, European Synchrotron Radiation Facility of Grenoble (France), of the Department of Organismal Biology, Evolutionary Biology Center of the University of Uppsala (Sweden), of the Australian Nuclear Science and Technology Organization (ANSTO) and many other institutes.
The scientists, led by Professor Kate Trinajstic, a lecturer at the Australian University's School of Molecular and Life Sciences, discovered the fish fossil in the Gogo training, located in the North Kimberly region of Western Australia. It is one of the most important paleontological sites in the world related to Devonianothe's so-called "age of fish" between 419.2 and 358.9 million years ago.
Other fossils of fish with mineralized soft tissues in three dimensions had already been found in this formation, but as indicated this is the oldest known case of a fossilized heart in the world. The fish was part of the arthrodiri ancient armored fish of the class of placoderms which became extinct at the very end of the Devonian, after having dominated it for tens of millions of years.
The fossil in question was subjected to neutron beams e X-ray scans (synchrotron microtomography) which allowed to bring out all the details of the soft tissues. The heart is an S shape and comes with two superimposed chambers, one lobby it's a ventricle, with the smallest placed at the top. The researchers also detected a blood outflow channel. Also identified are the fish's stomach, intestines, and liver, which help to better understand its overall biology.
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“As a paleontologist who has been studying fossils for more than 20 years, I was truly amazed to find a well-preserved, 3D heart in a 380 million-year-old ancestor,” Professor Trinajstic said in a press release. Evolution is often thought of as a series of baby steps, but these ancient fossils suggest that there has been a larger leap between jawless and jawed vertebrates.
These fish have hearts in their mouths and under their gills, just like today's sharks, "added the scientist, underlining that for the first time it was possible to see all organs together in a primitive fish with jaws. “We were particularly surprised to learn that they weren't that different from us,” said the expert.
Despite these similarities, there is still one fundamental difference, namely the presence of a large liver that allowed the buoyancy of fish (as occurs in sharks), while some modern bony fish have lungs that evolved from swim bladder. "Significantly, we found no evidence of lungs in any of the extinct armored fish we examined, which suggests that they evolved independently in bony fish at a later time," she concluded. The details of the research "Exceptional preservation of organs in Devonian placoderms from the Gogo lagerstätte" have been published in the authoritative scientific journal Science.