The New Look in dinosaurs is that they were endothermic, or "warm-blooded," like mammals. It is an extreme response to the pedantic tradition that because dinosaurs are classified as reptiles, they ought to have been cold-blooded and sluggish, and because they were so monstrously large, they were "overspecialized" and doomed to extinction.
Actually, dinosaurs enjoyed enormous biological success, living all over the earth for about 140 million years, more than twice the time that has elapsed since they became extinct. The active nature and biological success of dinosaurs have been repeatedly demonstrated since their distinctive anatomy was first recognized 150 years ago. But it was not necessary for the dinosaurs to be endothermic to be successful. Ectothermic, or "cold-blooded," animals are neither sluggish nor slow most of the time, as anyone knows who has played footsie with a rattlesnake, and they do very well in competition with mammals to this day, given the proper environments. We must note, as the author of this book does not, that the dinosaurs with their erect method of walking and their great size, in addition to other advantages they enjoyed, were quite adequate to outstrip the competition, without postulating endothermy to account for their success.
McLoughlin has great fun blowing away the wheezy old model of dinosaurs as sluggish monsters, but in doing so he promulgates some absurdities of his own and refers indiscriminately to those with whom he disagrees as "great fossil lizard" enthusiasts as though everyone who wrote before 1970 regarded dinosaurs as overgrown lizards.
The reasoning behind dinosaur endothermy seems to be that since mammals are active, successful and endothermic, the dinosaurs, which were active and successful, must also have been endothermic. Such oversimplification masks the fundamental features in which dinosaurs are unique, and perpetuates yet another stereo-type, that of dinosaurs as surrogate mammals.
In fact dinosaurs are not similar to mammals in details of limb structure and function. All dinosaurs, irrespective of size, walked on erect limbs, but only some of the largest mammals do so; most mammals use a crouching pose. The dinosaur hip joint lacks the lateral play that all mammals have, and dinosaurs were probably unable to run as fast as many mammals. That does not mean they were sluggish, only that they were as different from mammals as from conventional reptiles. (Limb, joint and pelvic structure suggest that they may have been very effective long-distance walkers.)
McLoughlin suggests that erect posture led to endothermy, as muscles generate more heat as they worked to keep the legs straight. Not so: animals burn little more energy standing quietly erect than they do sprawling, and mammalian endothermy gets its heat from the viscera, not from muscle action. Pointing out that many dinosaurs were small, McLoughlin ridicules the classic idea that large size may have served for temperature control by reducing the rate of heat exchange with the environment. What he misses here is that the chicken size of the smallest dinosaur is larger than 80 percent of all the mammals that ever lived. Conversely, no more than 2 percent of mammals have attained sizes in the range of the larger half of dinosaurs.
Large size is as distinctive of dinosaurs as erect posture, and the two appear to have evolved in concert. This suggests that they were inter-related, possibly with respect to temperature control. Because erect limb posture implies more continuous general activity, it implies more continuous heat production, with large size the means of keeping body temperature constant between periods of activity. In this way dinosaurs could have achieved an independence of the environment approaching that of many mammals, but they would have done so by an energy-conservative process very different from the energy-intensive process of mammals. Since the "great dying" at the end of the age of dinosaurs may well have involved world-wide temperature changes, the different means of temperature regulation of dinosaurs and mammals may help to explain the extinction of one group and the survival of the other.
McLoughlin advocates the idea that the Archosauria, which include dinosaurs, should be separated from other reptiles because they were warm-blooded. Whether they were or not, the classification is trivial. It makes no more sense to separate archosaurs from reptiles because of the single character of endothermy, than it does to separate bats from mammals because of the single character of wings.
McLoughlin's advocacy of dinosaur endothermy is unfortunate, not only because the theory is weak, but also because it is not necessary to any attempt to bring the dinosaurs to life. Dinosaur heat-conserving mechanisms would have provided a constancy and scope of activity comparable in many ways to those of mammals. Their effectiveness as walkers may have given the big dinosaurs a migratory ability such as no land mammal ever attained. Dinosaur function was no doubt spectacular in its own right, and these exotic animals are sold short when presented as surrogate mammals.