We found the oldest ever vertebrate fossil heart. It tells a 380 million-year-old story of how our bodies evolved

Scientists found a three-dimensionally preserved heart of a 380 million-year-old jawed vertebrate in Australia.

In the limestone ranges of Western Australia’s Kimberley region, near the town of Fitzroy Crossing, you’ll find one of the world’s best-preserved ancient reef complexes.

Here lie the remnants of myriad prehistoric marine animals, including placoderms, a prehistoric class of fish that represents some of our earliest jawed ancestors.

Placoderms were the rulers of the ancient seas, rivers and lakes. They were the most abundant and diverse fishes of the Devonian Period (419-359 million years ago) - but died out at the end in a mass extinction event.

Studying placoderms is important as they provide insight into the origins of the jawed vertebrate body plan (vertebrates are animals with backbones). For instance, placoderms have revealed when the first jaws, teeth, paired skull bones and paired limbs evolved. They’ve also taught us about the origins of internal fertilisation and live birth in vertebrate evolution.

Now, in a paper published in Science, we detail our findings of the oldest three-dimensionally preserved heart from a vertebrate - in this case a jawed vertebrate. This placoderm heart is about 380 million years old, and 250 million years older than the previous oldest vertebrate heart.

Fish fossils from near Fitzroy Crossing were first reported from Gogo Station in the 1940s. But it wasn’t until the 1960s that beautiful 3D preservations were revealed, using a technique that removes rock from bones with weak acetic acid.

However, this technique proved to be a double-edged sword. While the fine details of the bony skeleton were uncovered, soft tissues in the fossils dissolved away. It wasn’t until 2000 that the first pieces of fossilised muscle were identified in placoderms.