These spawn during the turkey trial event, you can usually find them at beaches

They always spawn at level 250 and have high damage resistance, so brute-forcing with something other than a giga or carchar isn't recommended

They aren't immune to the bleeding effect of carnos, allosaurus, thyla, etc which deals % damage, and I heard non-melee attacks from dinos (wyvern breath for example) are immune to the resistance

Or you could use a high damage shotty and aim for the head