就像懒人坐在容易拿到高热量食物的地方，恐龙的巨大尺寸很可能起源于可获得的资源的丰富程度，再加上低能量开支。恐龙是否通过新陈代谢、内温性或者外部温度——这些因素可能影响它们的身体尺寸——维持稳定的体温，长久以来这是古生物学家的一个问题。
Brian McNab提出，能获取多少食物资源比热生物学在决定各种恐龙的尺寸方面更加重要。McNab开发了一个描述了脊椎动物的能量开支的模型，它考虑到了生物的体重和进食习惯。McNab指出，他的模型可以解释现存和灭绝的哺乳动物的身体尺寸，包括须鲸、一种古代犀牛和今天的象。这个模型还考虑了哺乳动物和大型爬行动物的差别。McNab指出热生物学差异很容易在小型生物中见到，他提出恐龙既非变温动物也非恒温动物，而是维持了一种处于哺乳类和爬行类之间的中间温度，这是它们的庞大体重带来的一种技巧。（生物谷Bioon.com）
生物谷推荐原始出处：
PNAS July 6, 2009, doi: 10.1073/pnas.0904000106
Resources and energetics determined dinosaur maximal size
Some dinosaurs reached masses that were ≈8 times those of the largest, ecologically equivalent terrestrial mammals. The factors most responsible for setting the maximal body size of vertebrates are resource quality and quantity, as modified by the mobility of the consumer, and the vertebrate's rate of energy expenditure. If the food intake of the largest herbivorous mammals defines the maximal rate at which plant resources can be consumed in terrestrial environments and if that limit applied to dinosaurs, then the large size of sauropods occurred because they expended energy in the field at rates extrapolated from those of varanid lizards, which are ≈22% of the rates in mammals and 3.6 times the rates of other lizards of equal size. Of 2 species having the same energy income, the species that uses the most energy for mass-independent maintenance of necessity has a smaller size. The larger mass found in some marine mammals reflects a greater resource abundance in marine environments. The presumptively low energy expenditures of dinosaurs potentially permitted Mesozoic communities to support dinosaur biomasses that were up to 5 times those found in mammalian herbivores in Africa today. The maximal size of predatory theropods was ≈8 tons, which if it reflected the maximal capacity to consume vertebrates in terrestrial environments, corresponds in predatory mammals to a maximal mass less than a ton, which is what is observed. Some coelurosaurs may have evolved endothermy in association with the evolution of feathered insulation and a small mass.
