Archaeopteryx wore black

Analysis compares microscopic structures with modern birds?

Web edition : Tuesday, January 24th, 2012

It may be time to hatch a new crop of those colorful illustrations of early feathered creatures spreading their wings amid the branches of Late Jurassic trees. In life, a new study suggests, the fossil feather whose discovery gave rise to the name Archaeopteryx more than 150 years ago was actually black.

Longtime celebrities among fossils, Archaeopteryx lithographica specimens have until last year been largely accepted as the most ancient bird species known. Whether or not they end up retaining their claim as early birds, their feathers had small pigment-bearing structures that closely matched those found in today?s birds, Ryan Carney of Brown University in Providence, R.I., and his colleagues report January 24 in Nature Communications.

Archaeopteryx got its name in 1861 based on a lone fossil feather. Modern articles about the creature often show one of the daintily preserved fossils of a spread-out skeleton, but not until 2011 was any skeletal fossil designated as an official example of the species.

To examine that original dark trace of feather, Carney and his colleagues turned to a specialized scanning electron microscope in Germany. Checking points along the feather revealed evidence of rod-shaped nubbins like the structures that hold pigments called melanins inside the cells of modern feathers.

In a procedure that has identified colors on several dinosaurs as well as fossil penguins, the researchers compared dimensions of the pigment-carrying structures, called melanosomes, against measurements of melanosomes of known color from 87 kinds of modern birds. The Archaeopteryx melanosomes grouped with modern birds? black ones instead of the brown or gray ones, or the oddball melanosomes found in penguins.

The findings fit with results reported last September by another research group that detected trace metals in fossils, indicating the presence of melanin pigments in Archaeopteryx feathers.

?I absolutely buy that this Archaeopteryx feather was black, but it?s hard to say what the rest of the animal was like,? says vertebrate paleontologist Lawrence Witmer of Ohio University in Athens, who was not part of either feather study but has worked with Archaeopteryx fossils.

Melanosomes add strength to plumage, and Witmer notes that there have been questions about whether Archaeopteryx feathers would have been strong enough for the early bird to fly. ?This new finding shows that the substance of the feather material was pretty tough stuff due to the melanin,? he says, ?but it doesn?t necessarily follow that the feather as a whole had the aerodynamic stiffness for sustained, powered flight.? Most scientists, he says, have thought that Archaeopteryx was probably a pretty clumsy flier or glider.

Carney, who has the feather?s image tattooed on his arm, also proposes a rethink of what kind of wing feather the fossil represents. It?s been assumed to be one of the long feathers, called primaries and secondaries, along the outer edge of the wing. Yet a bird sized to go with the fossil as a primary or secondary wing ?would be super, super small,? he says.

Looking back at the original 1861 description, though, Carney realized that the measurements given indicate a longer stemlike shaft at the base of the feather than is visible in today?s trace. The signs of the longer stem have worn away, so Carney and his colleagues propose that the original trace was for one of the feathers called coverts, which grow above the long feathers on the edge. That gets the size of the creature back in the range of known skeletal fossils.

Details of the feather probably won?t influence the current debate over whether to call Archaeopteryx a bird, says vertebrate paleontologist Mark Norell of the American Museum of Natural History in New York. The creature had reptilian traits such as a long tail and teeth but was long described as the earliest known bird.

In 2011 a research team argued that so many feathered dinosaurs have now turned up that a strict accounting of traits would transfer Archaeopteryx out of the birds and into the non-avian dinosaurs. As analyses duel on this point, Norell says he only uses the word bird for living species. ?It?s kind of a movable word,? he says.

Found in: Life

Source: http://www.sciencenews.org/view/generic/id/337887/title/Archaeopteryx_wore_black

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