Size and Weight:
Protoceratops is one of those dinosaurs that people think was a lot bigger than it actually was: today, it's often mistakenly pictured as a giant, but this horned dinosaur was only about three feet high (in its quadrupedal stance) and weighed in the neighborhood of 400 pounds--meaning Hulk Hogan might have been able to wrestle one to the ground. It's believed that large herds of these pig-sized ceratopsians roamed the plains and woodlands of late Cretaceous Asia, where they were preyed on by hungry tyrannosaurs and raptors. (See also 10 Facts About Protoceratops.)
As tiny as it was compared to later herbivorous dinosaurs, Protoceratops lay near the trunk of a mighty dinosaur evolutionary tree, giving rise to the giant ceratopsians of the late Cretaceous period--including such famous and familiar dinosaurs as Triceratops, Centrosaurus and Styracosaurus. However, Protoceratops wasn't the most "basal" ceratopsian; that honor probably belongs to the much earlier Psittacosaurus, if not an even earlier genus (a bewildering array of ceratopsians have been discovered over the last decade, in Eurasia and North America, dating to both the beginning and the end of the Cretaceous period.
Protoceratops has earned a place in the paleontology hall of fame because of a rare fossil find: the tangled skeletons of a Protoceratops and a Velociraptor, who were presumably in mid-combat when they were both buried together by a sudden sandstorm. (See Protoceratops vs. Velociraptor - Who Wins? for an analysis of this battle.) It's not surprising that Protoceratops should be on the receiving end of a raptor's sharp claw, since this not-especially-intelligent dinosaur must have been a popular menu item for the hungry theropods of central Asia.