[Deinonychus] is usually considered a small dinosaur. But the largest individual was an eleven-foot-long animal whose head approached half a yard lon… - Gregory S. Paul

The dinosaur world I grew up in was classical. They were universally seen as scaley herps that inhabited the immobile continents. There was no hint that birds were their direct descendents. Being reptiles, dinosaurs were cold-blooded and rather sluggish except perhaps for the smaller more bird-like examples. They all dragged their tails. Forelimbs were often sprawling. Leg muscles were slender in the reptilian manner. Intellectual capacity was minimal, as were social activity and parenting; the Knight painting of a Triceratops pair watching over a baby threatened by the Tyrant King was a notable exception. Hadrosaurs and especially sauropods were dinosaurian hippos, the latter perhaps too titanic to even emerge on land, and if they did so were limited by their bulk to lifting one foot of the ground at a time. Suitable only for the lush, warm and sunny tropical climate that enveloped the world from pole to pole before the Cenozoic, a cooling climate and new mountain chains did the obsolete archosaurs in, leaving only the crocodilians. Dinosaurs and the bat-winged pterosaurs were merely an evolutionary interlude, a period of geo-biological stasis before things got really interesting with the rise of the energetic and quick witted birds and especially mammals, leading with inexorable progress to the apex of natural selection: Man. It was pretty much all wrong. Deep down I sensed something was not quite right. Illustrating dinosaurs I found them to be much more reminiscent of birds and mammals than of the reptiles they were supposed to be. I was primed for a new view.

What gave archosaurs the edge as large predators at this time, and therapsids the edge as smaller ones? Frankly, I am not sure. Both seem to have had heightened metabolic rates and fur or feather insulation... Perhaps the chief advantage enjoyed by thecodonts centered around their big, slashing attack jaws. These may have made them better big-game hunters, while the more precise cutting teeth of therapsids were more suitable for smaller prey.

Put a leopard and a [Deinonychus] together and the former would be in trouble.