The new research found that the position of the organs in the body of arthrodires -- an extinct class of armoured 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. The researchers said that 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 palaeontologist 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,” one of the researchers 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.