Paleozoic The Mesozoic Mailbag

A Cold, Little Fossil: The World’s Oldest Chambered Heart

Can 380-million-year-old fossilized organs last into the present? A new discovery suggests they can…

Modern technology has allowed paleontologists to view prehistory in ways never thought imaginable.

Look no further than a brand-new study of a 380-million-year-old fossilized fish from the Devonian Period of Australia. Published on September 15th by a research team under paleontologist Kate Trinajstic, the study utilized x-ray and neutron beams to peer within the remains of a Gogo fish, a member of an extinct lineage of armoured fishes known as the placoderms. What they found was incredible: its organs weren’t just intact but also preserved in three dimensions.

A 380-million-year-old fossilized heart. ©Trinajstic et al

The Gogo’s heart was the most spectacular feature preserved in the fossil. The researchers determined it was located near the base of the jaw, was S-shaped, comprised of two chambers, and vertically oriented. The two-chambered heart may seem primitive compared to the four-chambered hearts of bony fishes, but its orientation may have aided efficiency[i][ii]. While the hearts of more primitive vertebrates like Lampreys have three horizontal chambers[iii], the vertical heart of the Gogo enabled more active behaviours in the Devonian seas.

The heart wasn’t the only organ found within the Gogo Fish. The liver, intestines, and stomach were also preserved. The liver had two lobes and was proportionately large, which researchers believe may have aided buoyancy like in sharks[iv]. The stomach had thick and muscular walls, suggesting it utilized stomach acids to digest food[v]. Paleontologists were surprised at how developed these traits were given the fossil’s age, which may demonstrate that advanced internal systems appeared early in vertebrate evolution.

The skull of Dunkleosteus, the largest and most famous of the placoderms. ©The Field Museum

Placoderms like the Gogo Fish are an interesting lineage in earth’s history. They were vertebrates and amongst the first organisms with developed jaws, making them more derived than animals like lampreys and hagfish. These jaws weren’t like those of ray-finned and cartilaginous fishes, as they were comprised of numerous plates that worked together to give placoderms strong bite forces[vi]. There was another difference between the placoderms and ray-finned fishes: they lacked lungs.

We can look to our Gogo Fish for evidence of this absence. While the organs of the Gogo are preserved in exquisite detail, lungs are noticeably absent[vii]. This isn’t a strange coincidence or new revelation as paleontologists believe lungs evolved in bony fishes after they diverged from placoderms[viii]. The absence of lungs in the Gogo may confirm this, which could explain why placoderms struggled at the end of the Devonian while bony fish thrived. Mind you, sharks don’t have lungs either and were around in the Devonian too, so maybe not…

The Gogo Fish, ©

The presence of organs in any fossil is incredible. To find them on a 380-million-year-old specimen is ground-breaking. The Gogo Fish’s internal anatomy shows that early vertebrates already had advanced organs and that lungs aren’t ancestral to jawed fishes. As the utilization of technology continues to radiate throughout paleontology, discoveries like this will only become more common.

Thank you for reading today’s article! If you’re interested in animals like the placoderms, I suggest you read about – and visit – the Royal Ontario’s Dawn of Life Exhibit. Featuring beautiful art, stunning centrepieces, and more fossils than you can get your hands on, Dawn of Life is a must-see exhibit about life before the dinosaurs!

I do not take credit for any images found in this article.

Header image courtesy of Brian Choo & Kate Trinajstic, found here

Works Cited:

[i] Randall, D. J. “Functional Morphology of the Heart in Fishes.” American Zoologist, vol. 8, no. 2, 1968, pp. 179–189.,

[ii] Ghosh, Pallab. “World’s Oldest Heart Found in Prehistoric Fish.” BBC News, BBC, 15 Sept. 2022,

[iii] De Luliis, Gerry, and Pulerà Dino. The Dissection of Vertebrates: A Laboratory Manual. Elsevier/Academic Press, 2019.

[iv] Pappas, Stephanie. “The Oldest 3-D Heart from Our Vertebrate Ancestors Has Been Discovered.” Scientific American, Scientific American, 15 Sept. 2022,

[v] Trinajstic, Kate, et al. “Exceptional Preservation of Organs in Devonian Placoderms from the Gogo Lagerstätte.” Science, vol. 377, no. 6612, 2022, pp. 1311–1314.,

[vi] Benton, M. J. Vertebrate Palaeontology. Wiley-Blackwell, 2014.

[vii] Trinajstic, Kate, et al. “Exceptional Preservation of Organs in Devonian Placoderms from the Gogo Lagerstätte.” Science, vol. 377, no. 6612, 2022, pp. 1311–1314.,

[viii] Goujet, Daniel. “‘Lungs’ in Placoderms, a Persistent Palaeobiological Myth Related to Environmental Preconceived Interpretations.” Comptes Rendus Palevol, vol. 10, no. 5-6, 2011, pp. 323–329.,

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