A 380-million-year-old fish heart found embedded in a piece of Australian sediment is making scientists’ hearts beat faster. Not only is this organ in remarkable condition, but it could provide clues to the evolution of jawed vertebrates, of which you and I are a part.
The heart belonged to an extinct class of armored jawfish called Arthrodire, which thrived in the Devonian between 419.2 million and 358.9 million years ago — and the ticker predates the jawfish heart, which currently has the “oldest” title, by a good 250 million years. But despite the fish being so archaic, the positioning of its S-shaped, dual-chambered heart led researchers to observe surprising anatomical similarities between the ancient swimmer and modern-day sharks.
“Evolution is often thought of as a series of small steps, but these ancient fossils suggest there was a larger leap between jawless and jawed vertebrates,” said Professor Kate Trinajstic, a vertebrate paleontologist at Australia’s Curtin University and co-author of a new study on the insights. “These fish literally have their hearts in their mouths and under their gills — just like sharks do today,” Trinajstic said.
The study appeared in Science magazine on Wednesday.
Scientists were able to get a closer look at the exact location of the organ because they were able to observe it in relation to the fish’s fossilized stomach, intestines and liver, which is rare.
“I can’t tell you how amazed I was to find a three-dimensional and beautifully preserved heart and other organs in this ancient fossil,” Trinajstic said.
The white ring shows the spiral valves of the intestine, but the heart is not visible here. “I was absolutely blown away by the fact that we could actually see the soft tissue preserved in such an ancient fish,” says John Long, professor of paleontology at Flinders University in Australia and co-author of a new study on the find. “I knew immediately that this was a very important find.”
John Long/Flinders University
Paleontologists stumbled upon the fossil during a 2008 expedition in the GoGo Formation, and it adds to a wealth of information gathered from the site, including the origins of the teeth and insights into the fin-to-limb transition. The GoGo Formation, a sedimentary deposit in the Kimberley region of Western Australia, is known for its rich fossil record that preserves reef life from the Devonian period of the Paleozoic, including relics of such delicate tissue as nerves and umbilical cord embryos.
Anatomy of an Arthrodian.
“Most instances of soft-tissue preservation are found in flattened fossils, where the soft anatomy is little more than a speck on the rock,” said study co-author Professor Per Ahlberg of Sweden’s Uppsala University. “We are also very fortunate that modern scanning techniques allow us to examine these fragile soft tissues without destroying them. A few decades ago, the project would have been impossible.”
These techniques include neutron beams and X-ray microtomography, which creates cross sections of physical objects that can then be used to recreate virtual 3D models.
Recent fish fossil finds have enlightened like “dinosaur fish”, an endangered species, stand on their heads and how much the prehistoric fish lizard looked like flipper the dolphin.
But for those who might not think such discoveries significant, study co-author Ahlberg has a reminder: that at its most basic level, life is an evolving system.
“That we ourselves and all other living organisms with which we share the planet evolved through an evolutionary process from a common ancestry is no accidental fact,” Ahlberg said. “It’s the deepest truth of our existence. We’re all related, in every sense of the word.”
