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Nature

True color of ancient sea creatures revealed by fossilized pigment

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Lisa Winter

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clockJan 9 2014, 20:45 UTC
232 True color of ancient sea creatures revealed by fossilized pigment
Stefan Sølberg

Typically, artist depictions of ancient animals require a bit of creative license in regards to certain features that don’t fossilize. However, every now and again a discovery comes along that allows these artists to make a more accurate image of these creatures. A laboratory at Lund University has analyzed samples of fossilized skin pigment and have been able to determine the color of three different ancient marine animals for the first time. The results have been published in Nature.

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Artists typically create their pictures from the bones up. Bony landmarks indicate muscle attachment sites and can help determine amount of muscle tone. Fat content, skin texture, hair length, and color are usually approximated based on what we know about their living descendants. For an ancient leatherback sea turtle, mosasaur, and ichthyosaur, however, preserved pigment in fossilized soft tissue has allowed artists to make a more realistic portrait, as all three were very darkly colored.

Coloration of an animal can play several important roles. It can warn predators of toxicity as a form of protection, play a role in sexual selection, serve as camouflage, or even alter how the animal interacts with the sun. This seems to be most likely, according to the researchers. Dark skin may have allowed them to interact with the sun in two different ways: protection from harmful UV rays and warming up more quickly at the surface.

The leatherback turtles alive today may be utilizing the same sun-harnessing capabilities that their 55-million-year-old ancestor had. Leatherbacks today are found in ocean waters all over the world, as were their ancestors, and their dark coloring may be a prime factor to their success. Dark coloring absorbs more sunlight and allows the turtle to warm up in icy waters, while it is protected from the strongest rays while in warm waters.

The ichthyosaur and mosasaur have no living descendants, but it is likely that they had dark coloring for the same reason as the leatherback turtle, as their remains can also be found around the world. Many current marine animals, like orcas and penguins, are dark on their back and light on the front. This gives dual camouflage from predators as they look down on the animal into the darker water, or up at them against the light hitting the surface of the water. The researchers have concluded that some ichthyosaurs were completely dark, which would have been an advantage as they dive deep.

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Ichthyosaurs lived 250-94 million years ago. Though they were reptiles, they bore a very strong similarity to modern cetaceans and dolphins in particular. These similarities in traits arose from convergent evolution. Some species could grow up to 20 meters (65.6 feet) in length. Mosasaurs were present 98-66 million years ago and one species grew to lengths of 17.5 meters (57 feet). Also marine reptiles, mosasaurs do not resemble dolphins or fish as strongly as ichthyosaurs, as they lacked a dorsal fin. Their jaws were double hinged, like a snake, which allowed it to eat animals whole.


Nature
  • fossils,

  • skin,

  • leatherback turtles,

  • ichthyosaur,

  • mosasaur

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