A beautifully preserved fossil of a 150-million-year-old megalosaurus called Sciurumimus albersdoerferi has once again transformed our notions of what dinosaurs must have looked like. This newly discovered species shows that the early ancestors of all dinosaurs were feathered — and that's a strong indication that feathers were a common characteristic of all dinosaurs that followed, including large predators.
Paleontologists had found theropod fossils with feathers before, but only within a class of dinosaurs closely related to birds — a diverse group that includes the Tyrannosaurus rex. What makes Sciurumimus particularly interesting is that its lineage lies deep within the evolutionary tree of dinosaurs, far removed from those creatures that would eventually branch off and become birds.
Analysis of the exquisite fossil was made by Mark Norell, chair of the Division of Palaeontology at the American Museum of Natural History, along with researchers from Bayerische Staatssammlung für Paläontologie und Geologie and the Ludwig Maximilians University.
The fossil itself was of a baby Sciurumimus, which was found in the limestones of Northern Bavaria. The detailed sample shows a filamentous plumage, an indication that the entire body was covered with feathers. Adult megalosaurs grew to a size of 20 feet in length and often weighed more than a ton. Paleontologists speculate that the baby Sciurumimus hunted for insects and other small prey given its pointed teeth in the tip of the jaws.
Writing in Nature, Brian Switek offers some insights into the discovery:
Megalosauroids were a group of archaic sharp-toothed dinosaurs near the base of the theropod family tree, and greatly removed from the various types of feathered dinosaur and early birds recognized so far. According to...Oliver Rauhut...this means that simple feathers were a very ancient dinosaur trait. The filaments of Sciurumimus, Rauhut says, are very similar to the simple structures seen in Psittacosaurus, Tianyulong and even pterosaurs - extinct flying reptiles that were the closest cousins that dinosaurs had. The wide evolutionary spread of this characteristic means that protofeathers are probably as old as the Dinosauria itself.
Palaeontologist Paul Barrett of London's Natural History Museum agrees that the structures on Sciurumimus are probably protofeathers. Although additional geochemical work is needed to study the features' details, Barrett says, the fossilized wisps are very similar to the fuzz seen on other dinosaurs. But he notes that the presence of these filaments among all dinosaurs is "speculation". Feathery structures might be a common feature of dinosaurs, but it's also possible that they evolved multiple times. "We need more examples in both non-coelurosaurian theropods, and particularly in the other big dinosaur groups, before we can really speculate that these features are a character of dinosaurs as a whole," Barrett says.
As the researchers note, it's very likely that all dinosaurs had a simple, hair-like feathery coat — and that it appears to be a deep-rooted ancestral dinosaurian trait. The trick now will be to find more fossils that reaffirm this fascinating conclusion.
The details of their study can be found at PNAS.
Image courtesy of Helmut Tischlinger, the Eichstätt Museum of the Jurassic.