First-ever fossilized heart found in prehistoric fish fossil
While paleontologists have regularly found fossilized bones, locating well-preserved soft tissue has been much, much harder.
In a recent edition of the journal eLIfe, researchers announced the first-ever discovery of a fossilized heart, found in the 113-119 million-year-old fossilized remains of a fish known as Rhacolepis.
In 2000, a group of US researchers said they discovered a heart preserved in a dinosaur known as Thescelosaurus. However, a recent study debunked this claim, revealing the cavity of the dinosaur body was actually filled by sediment and iron-rich minerals to make the cavity inside appear heart-like under CT scanning.
The new study imaged a fossil with synchrotron X-ray tomography. The heart was then modeled out slice by slice with computer software to image the organ’s features digitially
This technique has now been used in paleontology to show many detailed soft tissue structures in fossils, including the preserved brain of a 300 million-year-old fish from North America.
What does this digital reconstruction tell us?
The Rhacolepis heart was digitally restored to reveal clear details of the conus arteriosus, a bulb on top of the heart, with five rows of valves in it.
Left: Scan of the fossil showing the heart. Right: Cross section of the heart showcasing valves. (Credit: Maldanis et al.)
The fossilized heart is noteworthy in that it reveals the valves in an initial member of the ray-finned fish group, the biggest group of vertebrates today with almost 30,000 species. Some species, such as the African reedfish, have nine rows of valves. However, the current most diverse group of ray-fins, the teleosts, has a single outflow valve in the heart.
Rhacolepis is associated with a completely extinct family, the Pachyrhizodontidae, and is named after the extinct fish Pachyrhizodus. The valve pattern revealed by the fossil appears to represent an intermediate condition between the most ancient pattern and the most modern type. In biology, simple patterns often hold more detail, the researchers said.
The find shows the enormous possibility for the discoveries of more fossilized organs, which would add to discussions of the comparative anatomy in extinct organisms and how they have evolved over the years.
With more discoveries like this one and more detailed understanding of the organs of extinct animals, we will understand more about the progression of the first back-boned animals, the researchers claimed.
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Image credit: Dr John Maisey, American Museum of Natural History
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