Australian fish fossils get to the heart of vertebrate evolution

Scientists in Australia have unearthed beautifully preserved fossilized hearts and other internal organs of ancient armored fish in a discovery that provides insight into the evolution of the bodies of vertebrates – including humans.

The researchers on Thursday described the heart, the organ that pumps blood through the body’s circulatory system, in fish called placoderms that inhabited a tropical reef about 380 million years ago during the Devonian Period. The fossils were 250 million years older than any previously known fish heart.

The fossilized liver, stomach and intestine from these placoderms helped give a fuller view of the internal anatomy at a pivotal time in the history of vertebrates – backboned animals including fish, amphibians, reptiles, birds and mammals.

The fossils were found in a locale called the Gogo Formation in Western Australia’s Kimberley region near the town of Fitzroy Crossing. They are remarkable because soft tissue, unlike hard stuff such as bones and teeth, is rarely preserved as fossils and even less often preserved in a robust three dimensions, as these are, rather than flattened.

“The site is without a doubt one of the world’s most important fossil sites for understanding the early evolution of backboned animals, including the origins of the human body plan,” said vertebrate paleontologist Kate Trinajstic, Curtin University and the Western Australian Museum, lead author of the study published in the journal Science.

The newly described fossils are of two species, named Compagopiscis croucheri and Incisoscutum ritchieiboth about 10 inches (25 cm) long with shark-like asymmetrical tail fins, jaws bearing teeth and blade-like cutting edges, and broad, blunt-nosed heads.