Does this Thread belong here? If not, where? In SciFi and mythology (Centaurs), there are large mammals and/or reptiles with more than 4 limbs. There are biophysical reasons why large SciFi insects cannot exist. Ignoring reptiles, is there any reason why large 6 or 8 legged mammals cannot exist? As a side issue, what about large animals with 2 or 3 heads as the norm? I cannot think of any biophysical argument against them. I believe that there are evolutionary arguments against them. I assume that bipeds evolved from quadrupeds. It seems like a reasonable assumption, and the fossil record indicates that it is an historical fact, suggesting that it might be the only path to the primate-like design. Assuming the above, evolutionary analysis of 6 or 8 legged mammals seems like the first step in answering this question. An extra pair of legs does not seem to provide much advantage in speed (if any) for running in a straight line. It does not seem to add much, if anything, to maneuverability when dodging a predator or changing direction to pursue prey. It requires a more complex brain & nervous system to supply the necessary motor nerve signals. It also requires extra resources to maintain the extra body mass. It looks like an evolutionary dead end or never was from a cost effectiveness point of view. It is my understanding that evolution results in cost effective design. Any thoughts on the above? BTW: I always thought that a Centaur was a cool creature. I think I would rather have a sleeker quadruped design (panther or tiger), but the idea of 4 legs for running and arms/hands for using tools looks great. I would not mind having a tail. That could be handy if properly designed.
