Researchers have discovered a 380-million-year-old heart, the oldest ever found, along with a separate fossilized stomach, intestines and liver in an ancient jawed fish, shedding new light on the evolution of our own bodies.
The new study, published today in Science, found that the position of the organs in the body of arthrodirs – an extinct class of armored fish that flourished during the Devonian period from 419.2 million years ago to 358.9 million years ago – Anatomy is similar to the modern shark and offers important new evolutionary clues. Lead researcher John Curtin Distinguished Professor Kate Trinajstic of Curtin’s School of Molecular and Life Sciences and the Western Australian Museum said the discovery is remarkable considering that soft tissues of ancient species have rarely been preserved and it is even rarer to see a 3D find preservation.
“As a paleontologist who has been studying fossils for more than 20 years, I was truly amazed to find a three-dimensional and beautifully preserved heart in a 380-million-year-old ancestor,” said Professor Trinajstic.
“Evolution is often thought of as a series of small steps, but these ancient fossils suggest there was a larger leap between jawless and jawless vertebrates. These fish literally have their hearts in their mouths and under their gills – just like sharks do today.”
This research presents – for the first time – the 3D model of a complex S-shaped heart in an arthrodir composed of two chambers, with the smaller chamber sitting on top.
Professor Trinajstic said these traits were advanced in such early vertebrates and offer a unique window into how the head and neck region began to change to accommodate jaws, a critical stage in our own bodies’ evolution.
“For the first time we can see all the organs together in a primitive jawed fish, and we were particularly surprised to learn that they weren’t that different from us,” said Professor Trinajstic.
“However, there was one crucial difference – the liver was large and allowed the fish to remain buoyant, just like today’s sharks. Some of today’s bony fish, such as lungfish and bircher, have lungs that evolved from swim bladders, but it was significant that we found no evidence of lungs in any of the extinct armored fish we studied, suggesting that they evolved in the bony fishes at a later date.”
The Gogo Formation in the Kimberley region of Western Australia where the fossils were collected was originally a large reef.