The taxonomical classification is irrelevant. Extant (presumed) related species are irrelevant. What is relevant is the physics. Is there a viable breeding population? Is there a large enough environment to support the breeding population? Can this putative population resonably avoid unequivocal detection either by accident or by intense scientific scrutiny? Etc.
Nessie has been probed relentlessly for decades with radar and sonar and other tools of science in a tiny microcosmic ecology and yes, IMFHO, it is still incredibly more likely that there is a Nessie than a Bigfoot. Water and 3-d is not our element. Since we don't master it as we do 2-d land, human hubris needs to be considered.
Do you know that 99.99...% of Pennsylvania was logged to tree stumps at least three times since it was settled? Most people don't. There are only a few hundred acres of virgin forest in PA. Cougars, coyotes, porcupines, wolverines, wolves, otters, mussels, eels and many other species (either extinct to PA or now very rare) were spread throughout Pennsylvania. Surrounding states no doubt have suffered a similar history.
It is a viewpoint of scientific ignorance to give credence to the notion of a large hominid surviving undetected in North America.
---Al
