Size and Weight:
Sometimes, the dinosaurs with the longest names are the ones about that paleontologists know the least about. That's the case with Archaeornithomimus, an ornithomimid ("bird mimic") from the middle Cretaceous period that was probably ancestral to the more well-known Ornithomimus. As you might expect, given their evolutionary relationship, Archaeornithomimus was comparatively less specialized than its famous descendant, with a much more slender build. Like other ornithomimids, Archaeornithomimus was probably omnivorous, fast enough to both chase down small animals and avoid larger predators.