The finding is based on a fossil dubbed Sciurumimus albersdoerferi, a description of which has been published in the journal Proceedings of the National Academy of Sciences.
Sciurumimus sits deep within the evolutionary tree of dinosaurs, researchers said.
"All of the feathered predatory dinosaurs known so far represent close relatives of birds," said paleontologist Oliver Rauhut of the Bayerische Staatssammlung fur Palaontologie und Geologie in Munich, Germany. "Sciurumimus is much more basal [deep] within the dinosaur family tree and thus indicates that all predatory dinosaurs had feathers."
The fossil of a baby Sciurumimus was found in northern Bavaria and preserves remains of a filamentous plumage, indicating feathers covered the whole body, researchers said.
"Everything we find these days shows just how deep in the family tree many characteristics of modern birds go, and just how bird-like these animals were," study author Mark Norell, a paleontologist at the American Museum of Natural History in New York, said. "At this point it will surprise no one if feather-like structures were present in the ancestors of all dinosaurs."