Researchers have discovered a 380 million-year-old heart – the oldest ever – along with a separate fossilized stomach, intestines and liver in an ancient-jawed fish, shedding new light on the evolution of our bodies.
The new research, published today in Sciencesfound that the location of organs in the body of arthropods – an extinct class of armored fish that thrived during the Devonian period from 419.2 million years ago to 358.9 million years ago – is similar to the anatomy of a modern shark, providing new biological evolution clues.
Principal investigator John Curtin, Distinguished Professor Kate Triangstick, of Curtin’s School of Molecular and Life Sciences and the Western Australian Museum, said the discovery was remarkable because the soft tissues of ancient species are rarely preserved, and 3-D preservation was rare to find.
“As a paleontologist who has studied fossils for more than 20 years, I was truly amazed to find a beautifully preserved 3D heart of a 380 million year old ancestor,” Professor Tringstik said.
“Evolution is often thought of as a series of small steps, but these ancient fossils suggest there was a greater leap between jawless vertebrates and jaws. These fish literally have their hearts in their mouths and under their gills – just like sharks today.”
This research presents – for the first time – a 3D model of a complex S-shaped heart in a two-chamber hinge with a smaller chamber located on top.
Professor Tringstik said these features were developed in such early vertebrates, providing a unique window into how the head and neck region changed to accommodate the jaws, a crucial stage in the evolution of our bodies.
“For the first time, we can see all the organs together in a prokaryotic fish, and we were particularly surprised to learn that they weren’t very different from ours,” Professor Tringstik said.
“However, there was one fundamental difference – the liver was large and enabled the fish to stay afloat, just like today’s sharks. Some bony fish today like lungfish and birch have lungs that developed from swimming bladders but it was important that we found no evidence on the presence of lungs in any of the extinct armored fish we examined, suggesting that they evolved independently in later bony fish.”
The Gogo Formation, in the Kimberley region of Western Australia where the fossils were collected, was originally a large reef.
With the help of scientists at the Australian Organization for Nuclear Science and Technology in Sydney and the European Synchrotron Radiation Facility in France, the researchers used neutron and synchrotron beams to scan the samples, which are still embedded in the limestone concrete, and build 3D images of the soft tissue within them based on the different densities of the minerals they contain. It is deposited by bacteria and the surrounding rock matrix.
This new discovery of mineralized organs, combined with previous discoveries of muscles and embryos, makes the jojo arthropods the most well-understood of all jawed stem vertebrates and illustrates the on-line evolutionary transition to living jawed vertebrates, which includes mammals and humans.
Co-author Professor John Long, of Flinders University, said: “These new discoveries of soft organs in these ancient fish are truly the stuff of paleontologists’ dreams, as they are undoubtedly the best-preserved in the world for this age. They demonstrate the value of Gogo fossils for understanding the great strides in our distant evolution.” Gogo gave us the world’s first, from the origins of the genus to the oldest vertebrate core, and is now one of the most important fossil sites in the world. It is a time when the site was seriously considered as a World Heritage Site.”
Co-author Professor Per Ahlberg, from Uppsala University, said: “The really exceptional thing about the gogo fish is that its soft tissues are preserved in three dimensions. Most cases of soft tissue preservation are found in flatfossils, where the soft anatomy is little more than a spot on the rock. We We are also very fortunate that modern scanning techniques allow us to study these fragile soft tissues without destroying them. Two decades ago, the project would have been impossible.”
The research Curtin led was a collaboration with Flinders University, the Western Australian Museum, the European Synchrotron Radiation Facility in France, the Australian Nuclear Science and Technology Organization Nuclear Reactor, Uppsala University, the Australian Institute of Regenerative Medicine at Monash University, and the South Australian Museum.