Archaeopteryx: The Embargoed Tattoo

A fair number of scientists like to get a tattoo to celebrate their research. Ryan Carney, a biologist at Brown University has taken the practice one step further. He's gotten a tattoo that shows the key finding of a paper he and his colleagues have just published today. They studied a fossil feather from Archaeopteryx, the iconic bird (or almost-bird). They conclude it looked just like this tattoo. Carney collaborated on the research with a team of scientists who have developed a method to reconstruct colors from fossils. One source of colors in animals is a cellular structure called a melanosome. Depending on the size, shape, and spacing of melanosomes, they can produce a range of hues. It turns out that melanosomes are incredibly rugged, sometimes enduring for millions of years. As I wrote in the New York Times in 2009, the scientists first found melanosomes in the ink sac of a fossil squid and then went on to look at a 47-million-year-old bird feather. Then they went on to look at the feathers and feather-like structures of dinosaurs, reconstructing some of the colors of their plumage. The color pattern, which included stripes and tufts, hints that dinosaurs may have been using their feathers to show off to each other long before they evolved flight. (More details can be found in this story I wrote for National Geographic last year.) No examination of feather evolution would be complete, of course, without Archaeopteryx. For over 150 years, it's been at the center of debates about the history of birds--not to mention evolution itself. The first fossil of Archaeopteryx was a single feather--the one that Carney has turned into a tattoo. It was discovered in 1861 in a limestone quarry near the town of Solnhofen and brought to Hermann von Meyer, one of Germany’s leading paleontologists at the time. As scientists would later determine, this exceptional feather was 145 million years old. Despite its antiquity, the feather looked much like the feathers on the wings of living birds. The fossil was so extraordinary that Von Meyer wondered if some forger had etched it. After all, Solnhofen limestone was prized for making finely detailed lithographic prints. But then von Meyer compared the slab and the counterslab and found them to be identical. “No draughtsman could produce anything so real,” he declared. Even as von Meyer was studying the feather, the quarry at Solhofen yielded another spectacular fossil: an entire animal cloaked in feathers. Word of the fossil spread fast, but only a few scientists got to glimpse the fossil in person. Its owner, a local doctor, was carefully managing the access to his fossil to fuel a bidding war for his entire fossil collection. Those few glimpses were enough to electrify scientists across Germany and beyond. The animal looked in some ways like a bird. It had wing feathers draped from its arms, for example. But other parts of its body looked more like a reptile’s, such as its long bony tail. It was unlike anything alive today. At the end of 1861, Von Meyer came up with a name to describe both fossils: Archaeopteryx lithographica—the lithographic first bird. The debut of Archaeopteryx 150 years ago was a case of beautiful timing. Just two years earlier, Charles Darwin had published The Origin of Species, in which he claimed that living animals had evolved from transitional ancestors. “Had the Solenhofen quarries been commissioned – by august command – to turn out a strange being a la Darwin – it could not have executed the behest more handsomely – than in the Archaeopteryx,” wrote the paleontologist Hugh Falconer. Darwin agreed. “It is a grand case for me,” he confided to a friend. In later years, more fossils of Archaeopteryx emerged, and it became even more of a chimera. Like a bird, it had feathers on its entire body. But unlike living birds, it had teeth in its mouth and claws on its wings. Darwin’s followers continued to argue that it marked a transition in the origin of birds. But opponents of Darwin and his followers argued that a single species—especially one with feathers no different than those on living birds—did not establish a full-blown transition. “Their views must be at once rejected as fantastic dreams,” the German paleontologist Andreas Wagner declared. Wagner turned out to be wrong. A number of bird-like dinosaurs have come to light in the years since the discovery of Archaeopteryx, and researchers have been able to work out many of their relationships to each other. There's still plenty of debate about just how well Archaeopteryx itself could fly, as well as its precise place in the dinosaur-bird tree of life. Last July fellow Discover blogger Ed Yong wrote about a new study suggesting other dinosaurs were more closely related to living birds than Archaeopteryx. In a study funded by the National Geographic Society, Carney and his colleagues were able to sample tiny bits of the original, lone Archaeopteryx fossil, housed in a museum in Germany. They examined its melanosomes, comparing them to the melanosomes in 115 living birds. As they report today, the feather was most likely straight black, as you see it in Carney's tattoo. While a single feather isn't enough to reconstruct Archaeopteryx's entire appearance, it does provide some interesting clues about the animal. The feather was what's known as a covert, meaning that it was sandwiched in the middle of the wing, covering the primary flight feathers but covered in turn by the feathers at the wing's leading edge. As a result, it was mostly hidden from sight. So its black color couldn't have served to attract the opposite sex or to camouflage it from enemies. It's possible that the whole wing was black, and this particular covert just went along on the evolutionary ride. It's also possible, Carney and his colleagues speculate, that the melanosomes were serving another function in this particular feather. In living birds, melanosomes can block bacterial infections, and they can also make feathers hard, preventing them from breaking under the forces of flight. As for the function of black pigmentation on the shoulders of biologists--well, that's another story. Reference: R.M. Carney et al, "New evidence on the colour and nature of the isolated Archaeopteryx feather." Nature Communications 2012 doi: 10.1038/ncomms1642