Also, there has been a lot of water under the bridge, scientifically speaking, since the B-movie dinosaurs of yore. While tyrannosaurs and allosaurs are still the top threats, there are a lot more dinosaurs available to choose from for our prehistoric bestiary. Some are as small as chickens, but since many species may have hunted in packs even relatively "small" critters could become a problem. There were lots of man-sized or cow-sized killers, and all sorts of aquatic horrors, not to mention the large and/or armored herbivores, who may have been as testy as modern bulls and rhinos. Escaping a T-Rex only to be confronted by a horde of hungry Chihuahua-sized predators might not be comforting for hapless PC explorers.