Laser-Based Imaging Technique Uncovers the Origin of Feathers

If you think that feathers are for the birds, you may be interested to know that Earth’s first feathered creature was actually a reptile that lived about 230 million years ago. A new imaging technique shows that pterosaurs — close relatives of the dinosaurs — had at least four types of feathers in common with the dinosaurs, thus pushing back the origin of feathers by some 70 million years. The discovery was made by researchers at Nanjing University and the University of Hong Kong (HKU) using laser-stimulated fluorescence, a technique developed by HKU’s Michael Pittman and Tom Kaye of the Foundation for Scientific Advancement.

Laser-stimulated fluorescence (LSF) image of pterosaur specimen NJU-57003 shows extensive soft tissue preservation in black, demonstrating that the feathers were preserved in place. Courtesy of Michael Pittman and Thomas G Kaye.

The researchers removed tissue samples from the specimen and collected 10 spectra using an IR microscope. Selected areas with extensive soft tissue preservation were photographed using a microscope with a digital camera and fluorescence illuminator attached.

Laser-stimulated fluorescence images were collected using a protocol developed by the researchers. The specimen was imaged with a 405-nm, 500-mW laser that was projected into a vertical line, which was swept repeatedly over the specimen during the exposure time for each image in a dark room. Images were captured with a digital single-lens reflex camera fitted with a long-pass blocking filter to prevent image saturation by the laser.

Pterosaurs had at least four feather types: filaments, filament bunches, tufted filaments, and down feathers. Scale bars in photos a-d are: 100 μm, 200 μm, 500 μm, and 1 mm. Courtesy of Zixiao Yang.

The study revealed that pterosaurs had at least four types of feathers. These feather types are known from two major dinosaur groups — the plant-eating ornithischians and the theropods, which include living birds.

Pittman said, “These exceptional pterosaur specimens were imaged by myself and Tom Kaye using laser-stimulated fluorescence, a technique we co-developed. The LSF images vividly revealed the form of the wing membrane, demonstrating that its generally ginger-colored feathers were preserved in place.”

The team was unable to find any anatomical evidence that the four pycnofiber types identified were in any way different from the feathers of dinosaurs, including those of birds. Thus, they came to the conclusion that they must share an evolutionary origin with dinosaurs of around 250 million years ago.

The research was published in Nature Ecology & Evolution (https://doi.org/10.1038/s41559-018-0728-7).