The strongest argument against these legendary animals is often the unlikeliness of such large animals existing so long without even a dead specimen, in reasonable condition for study, being discovered.
Although mainstream biologists believe that a large number of animal species are still unknown, these are generally small species (e.g. insects) that require a trained eye to distinguish from known species, and are not fantastic enought to arouse the curiosity of the cryptozoologist, whose interests lie in large animals that would generate great publicity.
Cryptozoologists often defend their pursuits by citing the capture of such previously undescribed animals as the giant squid, the coelocanth, the okapis, and mountain gorillas. However, it should be mentioned that sea creatures such as the giant squid and the coelocanth have the vastness of the ocean in which dead specimens will easily vanish and live creatures can easily evade detection. Additionally, the skeletal remains of mountain gorillas and the okapis are not so extraordinary that an untrained eye would find anything unusual and they might be overlooked whereas the skull of a creature such as sasquatch would be so out of place in the North American woodlands that it would certainly arouse suspicion if found.