Live Science By Mindy Weisberger, Senior
Writer, October 20, 2017
Preserved soft tissue in Tasbacka danicai
held traces of pigments, hinting that the turtle's shell was patterned with
dark regions.
Credit: Johan Lindgren
An extraordinarily well-preserved fossil of a
baby sea turtle that lived 54 million years ago contains traces of dark
pigments that would have acted as built-in sunscreen, protecting the animal
from the sun's harmful ultraviolet (UV) radiation.
The specimen, which is among the
best-preserved fossils of sea turtles in the world, includes soft tissue, and
analysis identified molecules linked to color, muscle contraction and oxygen
transport in the blood, researchers reported in a new study.
One molecule in particular — eumelanin, a
pigment linked to dark skin color in humans — hinted that the ancient turtle's
shell contained dark colors, perhaps in patterns such as those found in sea
turtles alive today, the study authors wrote.
Found in 2008 entombed in fine-grain
limestone in a marine deposit in Denmark, the fossil is very small — about 3
inches (74 millimeters) long, and many of the bones retain their original shape
in three dimensions. The reason the fossil is in such good condition is likely
that the turtle's remains were trapped within a hard, rocky mass of sediment
very early in the fossilization process, the
study's lead author, Johan Lindgren, a senior lecturer with the Department of
Geology at Lund University in Sweden, told Live Science in an email.
After much of the fossil mineralized,
protecting remnants of soft tissue, the absence of extreme heat or cold would
have prevented any remaining soft tissue from degrading further, Lindgren
explained.
The scientists evaluated five samples of soft tissue from a
sublayer in the turtle's shoulder area, which was revealed during a second
stage of fossil cleaning and preparation in 2013. When the researchers probed
the tissue samples, they noted "a dark, well-defined film" containing
structures that were carbon-rich, and which may have held organic compounds,
they reported in the study.
The researchers analyzed the film using a
combination of imaging and chemical techniques, which allowed them to identify
molecules and determine their precise locations within the fossil —
specifically, in organic material that once made up the turtle's skin and
shell, Lindgren told Live Science.
Molecules of eumelanin revealed to the
scientists that the turtles were pigmented with dark patches, much like the
dark patterns seen on the backs of modern sea turtles, the study authors wrote.
Patterns with dark coloration are known to protect sea turtles from UV rays and
also help young turtles retain heat, which can enable them to grow faster. This
biological feature is known as adaptive melanism — coloration that improves the
turtles' chances for survival — and the researchers' findings suggest that this
adaptation may have emerged in the turtle lineage as early as
54 million years ago, according to the study.
Scientists have examined fossilized plants
and animals for centuries, yet there is still much to be discovered about how
living organisms are preserved for millions of years, and how much of their
biological makeup may be retained after fossilization, Lindgren told Live
Science.
"Despite many years of research, we
still have an incomplete understanding of what can be retained in the fossil
record and exactly how the fossilization process works,"
Lindgren said.
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