People do not normally think of fishes with rippling abdominal muscles, but that’s exactly what palaeontologists working in the remote north of Western Australia have found.
Published in the journal Science, a team of palaeontologists headed by Associate Professor Kate Trinajstic from Curtin University have uncovered that 380 million year old armour-plated fishes from the Kimberley, called placoderms, preserve the oldest muscles ever discovered in a vertebrate.
Professor Trinajstic said the preservation of soft tissues within fossils was extremely rare as normally only the fossil skeletons were found. Researchers previously relied on scars on the bone to restore muscles in fossils and now they were able to prove these older reconstructions were not accurate.
“We were stunned to find that our ancient fossil fishes had abs!” Professor Trinajstic said.
“Abdominal muscles were thought to be an invention of animals that walked onto the land but this study revealed that these muscles appeared much earlier in our evolutionary history.”
The study used specialist synchrotron scanning at the European Synchrotron Radiation Facility in Grenoble, France, to also show tendons arranged in a helix-like pattern that connected the tail skin to the muscles and helped propel the fish through the water like a modern shark.
The team conducted their study on fossils found in rocks of the Gogo Formation of north Western Australia, where previous work by Professor Trinajstic had identified 3-D preserved soft tissues including nerve and muscle cells in these fossil fishes, a remarkable discovery because such tissues almost never fossilise.
Corresponding author Professor Per Ahlberg from Uppsala University in Sweden said this time the team decided to go beyond identifying soft tissues, to mapping out the musculature of the entire fishes.
“We have managed to produce something close to a dissection guide for placoderms, nothing like this has ever been possible for such early vertebrates,” he said.
Professor Philippe Janvier of the Natural History Museum in Paris, who was not associated with the work, said it was a milestone in early vertebrate studies, which saw scientists at last very close to the actual anatomy of what was probably the root of the jawed vertebrates.
Co-author Professor John Long from Flinders University who found some of the specimens used in the work said this new research showed that palaeontology still held an important role in modern science.
He said the next stage is to understand how soft tissues evolved in the big evolutionary steps from early fishes to humans.