Researchers have discovered a 380-million-year-old heart—the oldest ever found—alongside a separate fossilized stomach, intestine, and liver in an ancient jawed fish, shedding new light on the evolution of our own bodies.

The new research, published in Science, found that the position of the organs in the body of arthrodires—an extinct class of armored fishes that flourished through the Devonian period from 419.2 million years ago to 358.9 million years ago—is similar to modern shark anatomy, offering vital new evolutionary clues.

Lead researcher John Curtin Distinguished Professor Kate Trinajstic, from Curtin’s School of Molecular and Life Sciences and the Western Australian Museum, said the discovery was remarkable given that soft tissues of ancient species were rarely preserved and it was even rarer to find 3D preservation.

“As a paleontologist who has studied fossils for more than 20 years, I was truly amazed to find a 3D and beautifully preserved heart in a 380-million-year-old ancestor,” Trinajstic said.

“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. These fish literally have their hearts in their mouths and under their gills—just like sharks today.”

This research presents—for the first time—the 3D model of a complex s-shaped heart in an arthrodire that is made up of two chambers with the smaller chamber sitting on top.

Trinajstic said these…