Fossilized skin pigments from an 85 million-year-old mosasaur, a 193 million-year-old ichthyosaur and a 55 million-year-old leatherback turtle have revealed the skin color of these extinct marine reptiles.
This is an artist’s impression of a dark-colored ichthyosaur, mosasaur, and prehistoric leatherback turtle:
mosasaurs and leatherback turtles had a dark back and light belly, whereas ichthyosaurs, similar to the modern deep-diving sperm whale, were uniformly dark-colored. Image credit: Stefan Sølberg.
Previously, paleontologists could only guess what colors huge reptiles such as mosasaurs and ichthyosaurs had.
However, pigments preserved in fossilized skin of these prehistoric animals have now revealed that they were, at least partially, dark-colored in life. This feature probably contributed to more efficient thermoregulation, as well as provided means for camouflage and protection against harmful UV radiation.
The fossils are composed of skeletal remains, in addition to dark skin patches containing masses of micrometer-sized, oblate bodies. These microbodies were previously interpreted to be the fossilized remains of those bacteria that once contributed to the decomposition and degradation of the carcasses.
However, by studying the chemical content of the soft tissues, a team of researchers from Europe and the United States was able to show that they are in fact remnants of the animals’ own colors, and that the bodies are fossilized melanosomes, or pigment-containing cellular organelles.
“Our results really are amazing. The pigment melanin is almost unbelievably stable. Our discovery enables us to make a journey through time and to revisit these ancient reptiles using their own biomolecules,” said Dr Per Uvdal of the Lund University’s MAX IV Laboratory, a co-author of the study published in the journal Nature.
“Now, we can finally use sophisticated molecular and imaging techniques to learn what these animals looked like and how they lived.”
Top: skin fossil of a 55 million-year-old leatherback turtle; scale bar – 10 cm. Center: scales from an 85 million-year-old mosasaur; scale bar – 10 mm. Bottom: a tail fin from a 193 million-year-old ichthyosaur; scale bar – 5 cm. Image credit: Bo Pagh Schultz / Johan Lindgren / Johan A. Gren.
Mosasaurs (98–66 million years ago) are giant marine lizards that could reach 15 m in body length, whereas ichthyosaurs (250–94 million years ago) could become even larger. Both ichthyosaurs and mosasaurs died out during the Cretaceous Period, but leatherback turtles are still around today.
A noticeable feature of the living leatherback turtle, Dermochelys coriacea, is that it has an almost entirely black back, which probably contributes to its worldwide distribution. The ability of leatherback turtles to survive in cold climates has mainly been attributed to their huge size, but it has also been shown that these animals bask at the sea surface during daylight hours. The black color enables them to heat up faster and to reach higher body temperatures than had they instead been lightly colored.
“The fossil leatherback turtle probably had a similar color scheme and lifestyle as does Dermochelys,” explained lead author Dr Johan Lindgren of Lund University.
“Similarly, mosasaurs and ichthyosaurs, which also had worldwide distributions, may have used their darkly colored skin to heat up quickly between dives.”
______
Johan Lindgren et al. Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles. Nature, published online January 08, 2014; doi: 10.1038/nature12899
