Dinosaurs, dragons, and dwarfs: The evolution of maximal body size

Among local faunas, the maximum body size and taxonomic affiliation of the top terrestrial vertebrate vary greatly. Does this variation reflect how fo od requirements differ between trophic levels (herbivores vs. carnivores) a nd with taxonomic affiliation (mammals and birds vs. reptiles)? We gathered data on the body size and food requirements of the top terrestrial herbivo res and carnivores, over the past 65,000 years, from oceanic islands and co ntinents. The body mass of the top species was found to increase with incre asing land area, with a slope similar to that of the relation between body mass and home range area, suggesting that maximum body size is determined b y the number of home ranges that can fit into a given land area. For a give n land area, the body size of the top species decreased in the sequence: ec tothermic herbivore > endothermic herbivore > ectothermic carnivore > endot hermic carnivore. When we converted body mass to food requirements, the foo d consumption of a top herbivore was about 8 times that of a top carnivore, in accord with the factor expected from the trophic pyramid. Although top ectotherms were heavier than top endotherms at a given trophic level, lower metabolic rates per gram of body mass in ectotherms resulted in endotherms and ectotherms having the same food consumption. These patterns explain th e size of the largest-ever extinct mammal, but the size of the largest dino saurs exceeds that predicted from land areas and remains unexplained.