Thursday, January 9, 2014

The color of an extinct critter

Artist's depiction of a leatherback turtle (top), an ichthyosaur
(middle), and a mosasaur (bottom).
Credit: Stefan Sølberg.  Image source.
In any artist's illustration of an extinct creature, a great deal of interpretation and outright creativity is used to assemble an entire organism from bones.  Soft tissues are typically not preserved, so muscle mass, skin texture and color, and extra fleshy features (like a turkey's gobbler or an elephant's trunk) are left to the whim of the artist.  However, on rare occasions some of the softer organs are preserved, allowing a glimpse of previously unknown characteristics of extinct animals, such as the "head comb" of the Edmontosaurus discovered late last year.  Fossilized skin has revealed the texture of several dinosaurs and marine reptiles, but the process of fossilization removes the color from the skin.

Nevertheless, a group of scientists have claimed to have figured out the approximate shade of some extinct marine reptiles.  Their report, published online yesterday by Nature, reveals that they analyzed fossilized melanin within the cells of fossilized skin.  Melanin is an organic chemical that produces color in most organisms, including humans.  More specifically, eumelanin, the brown/black pigment, was found by the scientists in high concentrations in the analyzed fossilized skins, implying a very dark coloration.  The study involved the fossilized skin of three animals: a leatherback turtle (a large marine turtle that is still around today), an ichthyosaur (an extinct and vaguely dolphin-like marine reptile), and a mosasaur (a large extinct marine lizard).  The preserved melanin indicates that all three had dark coloration on at least a portion of their bodies.

Though it is not explicitly stated, there seems to be an implication that the mosasaur and turtle were countershaded; that is, they had dark backs and light bellies, as pictured in the image above.  This would be consistent with many modern marine creatures, including whales and modern leatherback turtles.  The dark back is useful for basking in the sun near the surface while reflecting harmful UV radiation.  Additionally, when seen from above, a dark back is difficult to distinguish from the dark depths of the ocean, while a white belly is less noticeable when viewed against the bright sunlight at the surface.  This marine camouflage scheme is useful for both predators and prey.

The ichthyosaur, on the other hand, apparently had dark coloring all over its body.  The authors liken this to the sperm whale, which spends much of its time in very deep waters, where any light coloring would make it more noticeable to both predators and prey.  It is inferred, then, in combination with their very large eyes, that ichthyosaurs were likewise deep divers.

Although there is some amount of interpretation involved with this study, the science is quite sound here.  The preserved melanin was identified by its chemistry rather than by the wishes of the scientists.  The effect of the melanin on the animal is observed in modern creatures, and there is no reason to think it might differ for extinct ones.  So, while the color was not directly observed, it is supported by observations and logic.  This study was dominated by operational and observational science, rather than interpretive origins science, so I commend the authors on their methods.  Studies like these demonstrate that paleontology need not rely on assumptions and interpretations to be scientific.  The science shows that melanin is abundant in the remains of these animals, which then allows for the unscientific (but likely and logical) interpretation that these animals were darkly colored for purposes similar to modern analogues.  The objective of science is to gather data currently available, which can then be used to build a picture of the past based on a framework outside of a scientific context.  Once science attempts to extend into the realm of interpretation, misinformation will readily join in.

3 comments:

  1. I would just like to say that I enjoy your blog posts and appreciate your work. Thank you.

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    1. I'm glad you like it! Feel free to share with anyone else who might appreciate it!

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