APRIL 20, 2016
by Brett Smith
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.
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.
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