Modern chemistry can fill in some ancient gaps.
“There is something fascinating about science,” Mark Twain once mused. “One gets such a wholesale return of conjecture out of such a trifling investment of fact.” Nowhere does that sentiment ring truer than in the field of paleontology. From a stray molar or a knucklebone scientists can seemingly reconstruct the size, gait, diet, age, mating habits, phylogeny, and zodiac sign of an astonishing array of creatures, many of them dead for millions of years.
About the only thing paleontologists had to leave to artistic license was, unfortunately, pretty vital—what extinct creatures actually looked like. Even in climates and circumstances favorable to fossil formation, soft tissues like skin usually degrade too quickly to leave an impression. And with the dissolution of those tissues disappear all the stripes, spots, plumes, potbellies, snouts, wattles, and other traits that make animals stand out. There’s an old paleontology joke that if elephants with their big trunks hadn’t survived until modern times, our reconstructions of “woolly mammoths” would look like giant hamsters with tusks.
Michael DiGiorgio, natureartists.com/Michael_DiGiorgio.asp
Thanks to some clever geochemistry, though, we might finally be able to lift that veil of ignorance. It turns out that a few stubborn chemicals in soft tissues can survive decay almost indefinitely, even under extreme heat and pressure. And with these new particles scientists have started to piece together the textures, shapes, and even colors of ancient creatures for the first time, including the most famous extinct creatures of all, the dinosaurs.
This work started a few years back with less glamorous beasts. In 2008 Jakob Vinther, a Yale University graduate student, was scrutinizing the ink sacs of ancient squids under a powerful microscope when he came across sausage-shaped granules of what looked like melanin. Squids and other cephalopods use melanin to blacken their ink, but other forms of melanin that come in different colors are actually nature’s Crayolas, responsible for the basic pigmentation of many, many animals. (Humans are included: melanin colors our skin, eyes, and hair.) Vinther reasoned that if melanin could survive in squid sacs, it might survive in fossil bird feathers as well. Sure enough, he found the same granules in 100 million-year-old feathers. In fact the granules were often layered in ways that would produce an iridescent blue, green, or coppery sheen, similar to that of peacocks and other modern birds.
These findings became all the more important in light of a few recent and spectacular finds in dinosaur paleontology. In China and elsewhere scores of dinosaurs have been unearthed with haloes of fuzzy fibers around their bones, fibers that a few scientists declared “proto-feathers.” (Some dinosaurs evolved into birds, after all.) Other scientists disputed this interpretation, arguing that the fibers were collagen that had petrified and turned into minerals. Even many who bought the proto-feather theory doubted that melanin itself could survive for millions of years. They saw sausage-shaped granules but explained them away as geological artifacts—mineral deposits left over from bacteria that decomposed and digested feathers way back when.
The chemistry of the granules argued otherwise. Tests revealed that they contained loads of carbon and lacked hard minerals like pyrites—proving this was organic material. Furthermore, a few fossil feathers displayed distinct bands of granules. If those granules were really traces of bacteria, it didn’t make sense that these bacteria would have digested only parts of feathers, and digested them in such neat rows. But the melanin hypothesis explained this easily: the feathers were striped. Finally, on a microscopic level the granules were oriented in parallel rows like packaged hot dogs, whereas bacteria would have scattered in all directions.
Pace Twain, this little bit of knowledge about dino feathers has gone a long way in the last few years. For one thing proto-feathers sometimes appeared on animals without wings, which suggests that feathers must have evolved before flight. Furthermore, the patterns of melanin granules on different creatures would have produced vivid colors—orange-and-white stripes, or black-and-white bands, or vicious red Mohawks. These findings provide evidence against the theory that feathers evolved to radiate body heat and regulate temperature. Feathers evolved instead for behavioral reasons, for courtship display and camouflage.
The sudden vivification of dinosaurs is the latest in a long series of reversals about their nature and behavior. Books I devoured as a kid invariably described dinosaurs as plodding, pea-brained, cold-blooded brutes—and sure enough, whenever the artist sketched them, their hides looked about as colorful as swamp mud. All those other prejudices have also been reversed recently: dinosaurs were in fact smart and quick and even nurturing creatures. And now, thanks to chemical sleuthing, scientists can swap out those drab brown dino costumes and substitute feather boas and plumed tails and the fancy crests that kids always knew the “terrible lizards” deserved.
And who knows? Melanin seems exceptionally hardy, but other soft, colorful bits might also be able to survive for tens of millions of years in a geological vault. If so, then whatever creatures are around to dig up human fossils in tens of millions of years might just get our lovely hair, eye, and skin tones right, too.