Ab-solutely fascinating fish fossil found
The extinct placoderm had armour and abdominal muscles. Credit: Eastman and Compago
Fish do not normally have rippling abdominal muscles, but that’s exactly what palaeontologists working in the remote north of Western Australia have found - in fossil form.
A team of palaeontologists headed by Curtin University's Associate Professor Kate Trinajstic and including Monash University's Dr Catherine Boisvert, have uncovered the oldest preserved muscles ever found in a vertebrate. The details of the rare find were published today in Science.
The surprise abdominals, found on 380 million year old fossils of armour-plated, extinct fishes from the Kimberley, called placoderms, re-write a chapter of evolution.
Associate Professor Trinajstic said the preservation of soft tissues within fossils was extremely rare - normally only the fossil skeletons are found.
Previously researchers have relied on scars on the bone to restore muscles in fossils but the placoderm find proves 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.
Dr Boisvert from the Australian Regenerative Medicine Institute at Monash University was part of the fossil collecting expedition and worked on the comparative anatomy of sharks for this project.
"This study shows how important fossils are in our understanding of evolution," Dr Boisvert said.
"Fishes are often assumed to be primitive but this shows that abdominal muscles like ours evolved a very long time ago.”
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.