Call it The Mystery of Oblong Blobs.
In the prevailing scientific view, they are microscopic remains of ancient pigment granules, offering clues to the colors of winged dinosaurs.
But a new study proposes a different explanation one that has ruffled a few academic feathers.
Alison Moyer, a doctoral student at North Carolina State University, says the cigar-shaped microbodies, just one-millionth of a meter long, might simply be impressions left by very old bacteria. Their size and shape, among other attributes, do not rule out either interpretation, she said.
You have these little structures that look very similar, and so we have to be careful, said Moyer, lead author of the paper published this month in the journal Scientific Reports.
The study has prompted a heated social media reaction from one researcher who favors the interpretation that the shapes are melanosomes, or pigment granules. Others in the field have been more accepting of Moyers work, acknowledging it as a helpful challenge to established views.
Such give-and-take is perhaps more prevalent in paleontology than in some other fields of science, as the only surefire way to answer certain questions about the ancient world would be to travel back in a time machine.
Failing that, Moyer found a living time machine: a chicken.
Remnants of bacteria?
Paleontologists consider birds to be modern dinosaurs, so Moyer took chicken feathers and grew bacteria on them. She compared the bacteria with the pigment granules inside the feathers, as well as with the oblong impressions found in fossilized feathers from winged dinosaurs.
The size, shape and distribution of the fossil impressions suggested bacteria, though it is still possible that they were pigment granules, she said.
Her work was overseen by prominent N.C. State paleontologist Mary Schweitzer. Among her co-authors was Ken Lacovara, associate professor of paleontology and geology at Philadelphias Drexel University.
Matthew Shawkey, an associate professor in the integrated bioscience program at the University of Akron, said on Twitter that the new research was bad science.
Shawkey, who was involved in a 2012 study that determined the feathers of the winged dinosaur Archaeopteryx were black, had several objections to Moyers paper.
Chief among them was the juxtaposition of two images one showing cigar-shaped bacteria on a chicken feather, the other depicting similar-shaped impressions found in a fossil feather from Archaeopteryx.
At a glance, the dark shapes in the two images look about the same size. Shawkeys beef is that the images are reproduced at different scale (as indicated in the fine print) and that the bacteria on the chicken feathers are actually four times as long as the impressions in the fossils.
Thats not a good way to give confidence in your paper, Shawkey said.
Moyer counters that the bacteria are closer to twice the length of the fossil impressions. (To the untrained eye, the graininess of the image makes it a bit hard to tell who is right.)
In any event, the size of the purported melanosomes falls well within the range of the sizes of known bacteria, Moyer said. Its hard to shut the door on either interpretation.
Another reason the matter remains up in the air: Chemical analysis of the fossil feathers has been inconclusive, Moyer said.
While Shawkey fired off more than a dozen tweets objecting to the paper, another scientist who has interpreted the shapes as pigment granules had a more receptive attitude to the work of Moyer and her colleagues.
Need for more data
Its always good to take one step back, said Johan Lindgren, an associate professor at Lund University in Sweden. What theyre saying is we need more data, and I think thats fair.
So how did the other scientists conclude anything about the color of dinosaur feathers, if all that remained of the purported pigment granules was their fossilized imprints?
The key was their shape. By looking at what granule shapes were associated with which colors in modern birds, the scientists concluded that various winged dinosaurs were black, gray or brown.
Or maybe not. Said Moyer, Theres a ton of work that needs to be done.