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posted by janrinok on Monday September 19, @03:25PM   Printer-friendly [Skip to comment(s)]
from the hope-is-the-beat-in-the-oldest-heart dept.

Oldest vertebrate fossil heart ever found tells a 380 million-year-old story of evolution:

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 fertilization 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 fossilized muscle were identified in placoderms.

With the advent of an X-ray method called "synchrotron microtomography"—first used on the Gogo fossils in 2010—more muscles were revealed from the Gogo placoderms, including neck and abdominal muscles.

Our work used this same technology to show, for the first time, the presence of a liver, stomach and intestines in a Devonian fish. Some of the specimens even showed remnants of their last meal: a crustacean.

We found the soft organs fossilized in an order of placoderms called arthrodires. These were the most common and diverse of all known placoderms, characterized by a unique joint between their head and trunk armor.

The most exciting find for us was the heart. We found our first placoderm heart using synchrotron imagining.

Then while experimenting with a technology called neutron imaging, we discovered a second heart within a different specimen.

[...] Today, 99% of all living vertebrates have jaws. Arthrodires provide the first anatomical evidence to support the hypothesis that, in jawed vertebrates, the repositioning of the heart to a more forward position was linked to the evolution of jaws and a neck.

Journal Reference:
Kate Trinajstic, John A. Long, Sophie Sanchez, et al., Exceptional preservation of organs in Devonian placoderms from the Gogo lagerstätte, Science, 377, 2022. DOI: 10.1126/science.abf3289

Original Submission

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