In 1861, as debates about evolution were brewing among naturalists, two important skeletons were discovered from the Late Jurassic limestone quarries of Germany. Both would be relevant to ideas about how birds evolved. Although not recognized as such until the late 20th century, Archaeopteryx was the first feathered dinosaur ever discovered and was a confirmation that birds had evolved from reptiles. The other creature, Compsognathus, represented a small, exceptionally bird-like dinosaur, and the anatomist T.H. Huxley took it as a proxy for the kind of animal from which birds originated. "There is no evidence that Compsognathus possessed feathers," Huxley said during his 1877 American lecture tour, "but, if it did, it would be hard indeed to say whether it should be called a reptilian bird or an avian reptile."

Now another feathered dinosaur has been discovered from the famous German limestone quarries. Named Juravenator starki in 2006, this dinosaur was a close relative of Compsognathus which lived just a little bit earlier on the same prehistoric archipelago. It is one of the most complete dinosaurs from these limestone deposits. From the tip of the snout to very nearly the end of the tail, the whole skeleton was preserved, but there was something special about this animal that could only be seen in the right light.

Earlier this year David Hone and colleagues published a paper showing how examining fossils under ultraviolet light can illuminate soft-tissue structures—like feathers—that would otherwise be hidden. Paleontologists Luis Chiappe and Ursula Göhlich applied the same technique to the Juravenator skeleton, and near the middle of the dinosaur's tail they found an area of preserved soft tissue. The most easily seen parts of the soft tissue were patches of tiny bumps consistent with the skin impressions of other dinosaurs. Yet there were wispy protofeathers, too. Thanks to high-resolution photography, the remains of downy feathers were also detected, and these were similar to the structures that covered the body of a relative of Juravenator from China called Sinosauropteryx.

The presence of both scaly skin and filamentous feathers makes Juravenator unique among feathered dinosaurs. This combination has not been seen before, but it is consistent with laboratory models of how feathers evolved from scaly skin. Furthermore, it appears that Juravenator was not wholly covered by a coat of fluffy feathers like baby chicks, perhaps indicating that feathery structures appeared on some parts of the bodies of dinosaurs before others. Frustratingly, the extent of soft-tissue preservation on the first Juravenator specimen is extremely limited, but further discoveries of this animal may help us better understand the origins of feathered dinosaurs.

References:

Chiappe, L., & Göhlich, U. (2010). Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen, 258 (3), 257-296 DOI: 10.1127/0077-7749/2010/0125