In FO2 they say Deathclaws come from iguanas. The doctor in Vault 13, Joseph, says:
"Well, let's see... Deathclaws appear to be mutated Jackson's Iguanas, the horned variety. There are a lot of similarities still present, but an even greater number of differences. The mutation factor is quite high. This species is highly intelligent, about the equivalent of an eight-year-old, with some individuals reaching human normal level. Their learning capacity is very high and they are capable of abstract thought and reasoning."
Which is misleading, really. IRL there is no "Jackson's Iguana". There is a Jackson's Chameleon, though. Apparently the "iguana" bit is used as an alternate name in the game- or, equally likely (given the alternate-timeline nature of the game setting) an entirely new creature not found in reality.
Supposing they meant the Jackson's chameleon, though... Polar bears and moose would be ridiculously scary enemies if equally mutated. Thanks to the interwebs, I now know the Jackson's chameleon gets between 8 and 15 inches long (counting tail) and weighs between two and four pounds. If that turns into a Deathclaw which appears in game to be as tall as a human and much bulkier... Picture a 50 foot tall, upright-walking polar bear, with 20" claws. Or a similar moose, with antlers the size of a large truck.
If they were in a Canada edition of Fallout... I'd move my character to Mexico.