These are the facts:
The giant beaver was a real creature, but it is now, luckily for us, extinct. It had incisors as long as your forearm, towered 2.5 meters tall and weighed over 200 kilos. This enabled it to gnaw down the gigantic trees that formed the largest part of its diet.
They built lodges, but do not appear to have built dams. They coexisted with humans until the ice age wiped them out.
The part where they threaten to snap off a caveman's head in a single bite is pure conjecture on my part. It would explain all those headless skeletons in the Canadian fossil record, though.
