I don't think any domesticated animals were around, a few half feral wolves might tolerate being around familiar humans.
If you introduce Mammoths, that would be in the realm of hunting, rather than combat. In that regard I would see mammoths as a side of their own with a Herd Leader, rather than a human (Cr/Ne/He) directed force. A 3 player scenario. Most times the Mammoths would be directed by the Mammoth player but the other 2 sides would try to panic the Mammoths into a stampede against the other human side. A Mammoth Wave would be a sight to see, though.
Moving through woods or brush might be risky, so a DR for a Random Animal Attack each turn, each side having a RAA counter like ASL's Sniper. A subsequent dr of 1 a big cat, 2 a wolf and 4-6 startled rabbits (NE).
Snake Pits would be the equivalent of Mines, but only 1 or 2 FP and start HIP. If you blunder (Assault Move/Advance gives a +1 to effects DR) into one and survive then you back away slowly (AM or Adv away) or attempt to Capture the Snakes. Capture is done by allowing an additional attack by the snakes and if no IFT effect the Snakes are possessed by the attacked unit (a passed MC does not result in capture). A Shaman/Southern Preacher counter gives a +2 DRM to the 2nd (capture) attack die roll. A Snakes may be placed/thrown like a DC but with a FP of only 4/8 (4 for an original 1 FP Snakes counter, 8 for an original 2). Once placed the Snakes remain in the same location with their higher FP and never move or be recaptured, they're really, really pissed off now.
Torches, as seen recently in Charlottsville, would be treated like MOL but with a -1 DRM for any attack using torches against He. No more than 1/2 (FRU) Torch attacks may be made for each squad equivalent during a game. Only by SSR, use the PF counter to keep track of usage.
Snake Pits and Torches may be allocated to any human side (Cr, Ne, He).
I've been thinking about
Homo Floresiensis. Hf would suffer a +1 in HtH CC but also get a beneficial +1 DRM to any other attack including non-HtH CC (basically small target).