Size and Weight:
Just as a running coach can judge an Olympic hopeful by the size and shape of her legs, so a paleontologist can infer the relative speed of an ornithomimid ("bird mimic") dinosaur by analyzing these same features. Judging by its short legs, Garudimimus must have been a relatively undistinguished sprinter, especially compared to the speedier ornithomimids (like Struthiomimus and Dromiceiomimus) that imhabited North America during the late Cretaceous period.
For a long time, Garudimimus was believed to be the only ornithomimid to have had a decorated skull--namely, a short crest in between its eyes. New research, though, shows that this "crest" didn't actually exist; the paleontologists who originally reconstructed the skeleton put a small bone in the wrong place!