A team of researchers has discovered a 380-million-year-old heart, the oldest ever found, along with a fossilized stomach, intestine and liver in a jawed fish, shedding new light on the evolution of our own bodies.
The new research published in the magazine Science, has found that the position of organs in the body of arthropods, an extinct class of jawed fish that flourished during the Devonian period, between 419.2 million and 358.9 million years ago, is similar to the anatomy of modern sharks, which offers new and vital evolutionary clues.
Lead researcher Professor Kate Trinajstic, from Curtin University’s School of Molecular and Life Sciences and the Western Australian Museum, stresses that the discovery is remarkable given that the soft tissues of ancient species are rarely preserved and that it is even rarer to find a 3D conservation.
“As a paleontologist who has studied fossils for more than 20 years, I was surprised to find a beautifully preserved, 3D heart in a 380-million-year-old ancestor,” says Trinajstic. “Evolution is often thought of as a series of small steps. , but these ancient fossils suggest that there was a larger jump between jawless and jawless vertebrates. These fish literally had their hearts in their mouths and under their gills, like sharks today.”
Critical stage in evolution
This research presents for the first time, the 3D model of a complex “S” shaped heart in an arthropod that is made up of two chambers with the smaller one at the top.
Professor Trinajstic points out that these features were advanced in such early vertebrates, offering a unique window into how the head and neck region began to change to accommodate the jaws, a critical stage in the evolution of our own bodies.
“For the first time, we can see all the organs together in a primitive jawed fish, and we were especially surprised to learn that They weren’t that different from us.” highlights Trinajstic.
“However, there was one fundamental difference: the liver was large and allowed the fish to remain buoyant, just like today’s sharks,” he continues. Some of the extant bony fishes, such as lungfishes and birches, have lungs that evolved from swim bladders, but it was significant that we found no evidence of lungs in any of the extinct armored fishes we examined, suggesting that independently evolved in bony fishes at a later date”.
With neutrons and x-rays
The Gogo Formation in the Kimberley region of Western Australia, where the fossils were collected, was originally a great reef.
With the help of scientists from the Australian Organization for Nuclear Science and Technology in Sydney and the European Synchrotron Radiation Facility in France, the researchers used synchrotron beams of neutrons and X-rays to scan the specimens, still embedded in the limestone concretions, and constructed three-dimensional images of the soft tissues inside them based on the different densities of the minerals deposited by the bacteria and the surrounding rocky matrix.
This new discovery of mineralized organs, in addition to previous findings of muscles and embryos, makes Gogo’s arthropods most complete jawed vertebrates and elucidates an evolutionary transition in the line of living jawed vertebrates, which includes mammals and humans.
An exceptional site
One of the co-authors, Professor John Long of Flinders University, said: “These new discoveries of soft organs in these ancient fish are really the stuff of paleontologists’ dreams, as these fossils are undoubtedly the best preserved in the world for this time”.
“They demonstrate the value of Gogo fossils in understanding the great steps of our distant evolution,” he adds. “Gogo has provided us with world firsts, from the origins of sex to the oldest vertebrate heart, and is now one of the most important fossil beds in the world. It is high time that the possibility of declaring this site a world heritage site was seriously considered,” he stresses.
Another co-author, Professor Per Ahlberg, from Uppsala University (Sweden), points out that “what is really exceptional about Gogo fish is that its soft tissues are preserved in three dimensions. Most cases of soft tissue preservation are found in flattened fossils, where the soft anatomy is little more than a speck in the rock. We are also very fortunate that modern scanning techniques allow us to study these fragile soft tissues without destroying them. A couple of decades ago, the project would have been impossible,” concludes.