Researchers determined that a number of ancient aquatic reptiles and almost-black skin.
The researchers found melanin (a dark pigment that absorbs light) in the animal's fossilized skin, the BBC reported.
"It's amazing. Suddenly we get this idea of the [color] of animals swimming around millions of years ago," Johan Lindgren, from Lund University in Sweden, told the BBC.
The creature's dark color could have provided a number of benefits for the ancient sea-lizards, including mosasaurs which are relatives of the leatherback turtle and a "dolphin-like" creature called ichthyosaurs, LiveScience reported.
"We suggest ... that they used it not only as camouflage and UV protection, but also to be able to regulate their body temperature," Lindgren told LiveScience.
Researchers have looked at melanosomes (a structure within the skin) to determine the color; now they have gone even deeper, the BBC reported. The team used chemical testing to determine the color through melanin.
The researchers believed the vicious mosasaur was extremely dark in color.
"If you look at leatherhead sea turtles today, they have very dark skin with huge amounts of pigment," Doctor Lindgren said. "They use it to absorb the heat and light as they bask at the sea surface. And if we look at the fossil, we see masses and masses of melanin. There is a really good chance that this had a black skin or a really dark skin."
The team believes the darkly-colored creatures may have had a much lighter stomach than the rest of its body. The light belly would have provided camouflage to protect them from predators below.
The ichthyosaur was likely to have been completely black.
"If you look at the ichthyosaur, they have been inferred as deep-diving because they have huge eyes. And we can see these animals had a uniform dark [coloration] - much like the modern sperm whale's [coloration]," Lindgren told the BBC.
