Dinosaurs, Fossils, and Feathers

144 million years ago, the beginning of the Cretaceous Period. South America, Antarctica, Australia, Africa and India are starting to break away from the supercontinent Gondwana. Consequent changes in climate plunge the world into a cold period. Only a few flowering plants grow in the temperate forests of coniferous trees and the plains of ferns that cover the northern and southern parts of the globe, and there are correspondingly few pollinating insects. During this period, dinosaurs apparently grew feathers.

Finding feathers on dinosaurs is now becoming a relatively common occurrence. In China's Liaoning Province, fine-grained sedimentary rocks often contain fossils of dino-feathers with exquisite details still intact. But all of these feathered fossils have been of the bipedal, carnivorous lineage, which includes Tyrannosaurus and Velociraptor. Tyrannosaurs are actually closer cousins to birds than they are to the large plant-eating Diplodocus and Brachiosaurus. A few years ago, there was even a movement to make T. rex the state bird of Montana.

Dinosaurs are divided into two main orders: saurischians, which have forward-pointing pubic bones, and ornithischians, which have backward-pointing pubic bones. "Ornithischian" literally means "bird-hipped," but the resemblance is in fact superficial and confusing, as birds actually descended from the saurischians, and all feathered dinosaurs discovered to date have belonged to the saurischian order. Only one ornithischian fossil has suggested the presence of anything that even approximates feathers: Psittacosaurus, which has bristle-like structures on its tail that have been hotly debated.

However, Chinese paleontologists have recently discovered a dinosaur fossil in Liaoning that has long feather-like structures sticking up from its body. The species has been identified as a heterodontosaurid, an ornithischian from the Early Cretaceous period. This in itself is remarkable, as heterodontosaurids are exceptionally rare, and previously unknown from Asia. They were most widespread during Late Triassic times, more than 65 million years earlier, and animal groups rarely survive for such long periods of geological time. This fossil confirms that heterodontosaurids, one of the oldest groups of dinosaurs, survived into the Cretaceous. Dubbed Tianyulong confuciusi, it was likely small, active, and agile based on the bones found, and probably ate a mix of insects, small vertebrates and plants.

The feathery structures found on T. confuciusi are not like those found on modern birds or even on some of the smaller, more bird-like dinosaurs. Whereas modern feathers are flexible and have a central shaft with vanes that run off either side at angles, the feathers on T. confuciusi are all relatively stiff and lack vanes.

The fossil supports the idea of a single evolution of feathers. If both saurischians and at least some ornithischians had feather-like structures, the origin of feathers must have occurred back in the Triassic, when the saurischian and ornithischian lineages split. There are still gaps in the fossil record between T. confuciusi and the feathered dinosaurs, but future discoveries may fill these gaps. If so, then many dinosaurs may once have sported feather-like structures, with descendant species losing the characteristic later on.

At present, no one is sure of the function of the protofeathers. If they were indeed protofeathers, then they were not related in any way to flight. The fact that the filaments over the tail are so long and stiff suggests a possible display function, not unlike the peacock.

Dinosaurs were clearly highly visual animals that not only modified their skeletons for show, but exaggerated their effect through external structures. It doesn't take that much to imagine dinosaurs as colorful as birds, their evolutionary descendants.