The oldest heart ever discovered was found inside a jawed fish of 380 million years ago along with fossilized stomach, intestines, and liver.
Researchers have discovered the oldest heart ever found alongside fossilized stomachs, intestines, and livers in an ancient jawed fish, shedding new light on our own bodies’ evolution. This new research, published in Science today, suggests that the position of the organs in arthrodires is similar to that of modern shark anatomy, revealing crucial evolutionary clues about the extinct class of armored fish that flourished from 419.2 million to 358.9 million years ago.
It is remarkable that soft tissues of ancient species were preserved and even rarer that they are preserved in 3D, said lead researcher John Curtin Distinguished Professor Kate Trinajstic, from Curtin’s School of Molecular and Life Sciences and the Western Australian Museum.
Professor Trinajstic, a paleontologist who has examined fossils for over 20 years, said she was amazed to discover a 3D heart preserved for 380 million years. The evolution of jawless and jawed vertebrates is commonly viewed as a series of small steps. However, these ancient fossils suggest that there was a larger leap between the two. Basically, they had their hearts under their gills and in their mouths like sharks do today.
A complex s-shaped heart comprising two chambers, with the smaller one sitting above the larger, is presented here for the first time in a 3D model in an arthrodire. Trinajstic said such advanced features offered a unique insight into how early vertebrates began to evolve to accommodate jaws, a crucial stage in our evolution.
Professor Trinajstic explained how they were surprised to see that primitive jawed fish were not so different from us in terms of the organs they possessed.
There was, however, one key difference – the fish had a large liver that enabled them to stay buoyant, just like sharks do today. While some of today’s bony fish are derived from swim bladders, we found no evidence of lungs in any extinct armored fishes that we examined, suggesting that they evolved independently in the bony fishes at a later date. This fossil was found in the Kimberley region of Western Australia’s Gogo Formation, which was once a large reef.
Researchers used neutron beams and synchrotron x-rays to scan the specimens, still embedded in limestone concretions, enlisting the help of scientists at the Australian Nuclear Science and Technology Organization in Sydney and the European Synchrotron Radiation Facility in France. As a result of the differences in mineral density deposited by the bacteria and the surrounding rock matrix, the researchers constructed three-dimensional images of the soft tissues within.
As a result of this discovery of mineralized organs, as well as previous discoveries of muscles and embryos, the Gogo arthrodires is now more fully understood than any other jawed stem vertebrates and have a clear evolutionary transition to the living jawed vertebrates, which include humans and mammals.
“These fossils are without doubt the best preserved in the world for an ancient fish of this age, in part because of the new discoveries of soft organs in these ancient fishes,” said co-author Professor John Long of Flinders University. They demonstrate the importance of Gogo fossils for understanding our distant evolutionary history. It is one of the world’s most significant fossil sites because it has given us world firsts, including the origins of sex and the oldest vertebrate heart. A world heritage designation is long overdue for this site.”
Moreover, the Gogo fish’s soft tissues can be preserved in three dimensions, according to co-author Professor Per Ahlberg of Uppsala University. Soft tissues are usually preserved in flattened fossils, where they are hardly more than stains on rocks. We are also very fortunate to be able to study soft tissues without having to destroy them using modern scanning techniques. It would have been impossible to accomplish this project a couple of decades ago.”
Click here to view the full paper titled “Exceptional preservation of organs in Devonian placoderms from the Gogo lagerstätte.”
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