The answer lies in two associated differences among the species, in their digestive systems and bodysizes.
答案在于两个相关的物种之间的差异，它们的消化系统和体型。
2
In an unrelated recent experiment with insect bodysizes, scientists discovered that a more oxygen-rich atmosphere supports super-giant insects, so this could be the case with giant mammals too.
As it happens, the patent offices have agreed upon a fairly tightly constrained set of permitted image formats and sizes for embedding into the XML application body.