A 380-million-year-old fish heart found embedded in a section of Australian sediment has scientists’ pulses racing. Not only is the organ in remarkable condition, but it may also provide clues about the evolution of jawed vertebrates, which includes you and me.
The heart belonged to an extinct class of armored, jawed fish called arthrodires that thrived in the Devonian period between 419.2 million and 358.9 million years ago – and the ticker is a good 250 million years older than the jawed fish heart that currently holds the “oldest” title. But despite the fish being so archaic, the placement of its S-shaped, two-chambered heart led scientists to observe surprising anatomical similarities between the ancient swimmer and modern sharks.
“Evolution is often seen as a series of small steps, but these ancient fossils suggest there was a bigger 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 findings. “These fish literally have their hearts in their mouths and under their gills — just like sharks today,” Trinajstic said.
The study appeared in the journal Science on Wednesday.
Scientists got an extra good look at the organ’s exact location because they were able to observe it in relation to the fish’s fossilized stomach, intestines and liver, a rare occurrence.
“I can’t tell you how truly amazed I was to find a 3D and beautifully preserved heart and other organs in this ancient fossil,” Trinajstic said.
Paleontologists encountered the fossil during a 2008 expedition at the GoGo Formation, and it adds to a wealth of information gleaned from the site, including the origin of the teeth and insights into the transition between fin and limb. The GoGo Formation, a sedimentary deposit in the Kimberley region of Western Australia, is known for its rich fossil record that has preserved reef life from the Devonian to the Paleozoic era, including relics of tissues as delicate as nerves and embryos with umbilical cords.
“Most cases of soft tissue preservation have been 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 Uppsala University in Sweden. “We are also very fortunate in that modern scanning techniques allow us to study these fragile soft tissues without destroying them. A couple of decades ago, the project would have been impossible.”
These techniques include neutron beam and X-ray microtomography, which create cross-sections of physical objects that can then be used to recreate virtual 3D models.
Recent fish fossil discoveries have shed lightand how much the prehistoric fish lizard .
But for those who may not consider such discoveries important, study co-author Ahlberg has a reminder: that life at its most basic level is an evolving system.
“That we ourselves and all the other living organisms with which we share the planet have evolved from a common ancestor through an evolutionary process is not an accidental fact,” said Ahlberg. “It is the deepest truth of our existence. We are all related, literally.”