The Mastodon is a species that went extinct during the past few pole shifts, primarily when the grasslands they browsed in Siberia were drawn rapidly into the new polar circle. But where drawn into water and drown, and then far enough north, the Mastodons were flash frozen. If the Mastodons were not flash frozen, they would be in some sort of state of decay - perhaps the skin preserved, but the internal organs a mush. This is not the case, as your recent documentaries on the frozen state of these preserved beasts shows! So if flash frozen, and frozen steadily since that date, then how did the Mastodons get green grass and buttercups in their stomachs? A fast trot to the Arctic Circle? Does anyone presume they ate snow? These were herbivors! Their grasslands were moved during poles shifts. The remains of Mastodons that were not far enough into the polar circle to be completely frozen are bones and the ivory that has been harvested from the Ivory Islands for centuries. The bodies rotted, the Ivory did not. A wealth of ivory, with no flesh to disturb those shipping the tusks off to become piano keys. The permafrost only goes so deep, and just as in temperate areas, frost goes only so many inches of at most feet deep. There is soil, and mud, and decaying matter where decay proceeded with or without oxygen, just as it does in your gut where methane gas is generated daily.