One thing to keep in mind; these creatures were possibly still extant during the last ice age, when men were venturing into the North American continent.
While it is untenable to suggest that men encountered dinosaurs, it is entirely possible that men had to deal with dire wolves, and short-face bears, and giant beavers, giant prairie dogs, and other things that are not dreamed of or even mentioned in your philosophies, Horatio.
Interesting article on the giant beavers, here:
https://earthsky.org/earth/why-giant-beavers-went-extinct
As they were aquatic plant eaters, I suspect the oversize beavers had more to fear from Man than Man did from the beavers.
Still, it is interesting to consider that there was evidently a big enough change to a dryer* climate around 10k years ago to knock out the giant beavers, which were not local ecosystem engineers, as are modern beavers. (The article contradicts itself regarding temperatures, so I’ll not speculate about such.)