就像懶人坐在容易拿到高熱量食物的地方，恐龍的巨大尺寸很可能起源于可獲得的資源的豐富程度,，再加上低能量開支,?？铸埵欠裢ㄟ^新陳代謝,、內(nèi)溫性或者外部溫度——這些因素可能影響它們的身體尺寸——維持穩(wěn)定的體溫，長久以來這是古生物學(xué)家的一個問題,。
Brian McNab提出,，能獲取多少食物資源比熱生物學(xué)在決定各種恐龍的尺寸方面更加重要。McNab開發(fā)了一個描述了脊椎動物的能量開支的模型,，它考慮到了生物的體重和進(jìn)食習(xí)慣,。McNab指出，他的模型可以解釋現(xiàn)存和滅絕的哺乳動物的身體尺寸,，包括須鯨,、一種古代犀牛和今天的象。這個模型還考慮了哺乳動物和大型爬行動物的差別,。McNab指出熱生物學(xué)差異很容易在小型生物中見到，他提出恐龍既非變溫動物也非恒溫動物,，而是維持了一種處于哺乳類和爬行類之間的中間溫度,，這是它們的龐大體重帶來的一種技巧。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
