- It is far more likely they belong to a known group supposedly extinct than something which nobody has every heard of.
- They are part of the larger "sea serpent" phenomenon. The rule of parsimony would suggest that it is more likely that some unknown animals from the high seas have managed to get into freshwater lakes than that the sea serpents and lake monsters are two completely different phenomena. However, their presence in an enclosed lake raises issues not present in the open sea, as we shall see.
As we all know, this is the most all-time popular interpretation. The popular image of a plesiosaur matches the popular image of the Loch Ness monster, which has been largely generated by the famous Surgeon's Photo. It's a pity, because there are serious doubts about the authenticity of this photo, even if we discount the mini-submarine story, which has a lot of problems of its own. If you take a census of lake monster sightings, you will discover that long necks protruding from the surface like a periscope make up a very small proportion of them - but they do exist. What cannot be denied is that they make up a large proportion of "sea serpent" reports. And to make things more interesting, some of them have large eyes, and some extremely small, if not invisible eyes. However, identifying them as plesiosaurs raised a number of problems.
First of all, the major consensus is that plesiosaurs could not stick their necks above the surface in the manner in which they are popularly portrayed. Their vertebral spines would have prevented this. All right, it is possible that they have evolved the skill in the 66 million years since they supposedly became extinct, but we're drawing a long bow.
More importantly, they were reptiles, and so, presumably, "cold blooded". Yes, it is generally accepted now that a lot of the dinosaurs were at least partly "warm blooded", so it is possible that plesiosaurs followed suite. The problem is, there wouldn't be any need for them to be so. Indeed, it would have been a hindrance. In the tropics during parts of the Cretaceous, the sea temperature was like a hot tub - 33º to 42º C. That's blood heat, or higher. A marine reptile would operate at optimal body temperature by simply being in the water. On the other hand, a human being would be most uncomfortable in such water, because he would be unable to lose the heat his own body generated. Admittedly, it wasn't always as hot during the whole of the Cretaceous, or the whole of the world. Just the same, when the asteroid ended the Cretaceous - and allegedly, the plesiosaurs - the sea was pretty hot. However, from the data provided by Dr Heuvelmans, long-necked sea serpents have been reported in quite high latitudes, where sea temperatures are rather chilly. And nobody would claim that Loch Ness is warm.
Both these factors should rule out plesiosaurs as the origin of sea serpent sightings. But there is one crucial factor which should rule them out completely as lake monster candidates.
They have to breathe. And large aquatic animals which rise to the surface to breathe at regular intervals tend to get noticed frequently. But how frequently are lake monsters seen? Tim Dinsdale calculated that he spent a thousand hours watching Loch Ness between his first sighting and his second. I suppose, of course, it is theoretically possible for the animal to just poke its nostrils above the surface, by why would any long necked animal do that? It would serve no practical purpose. Dr. Roy Mackal pointed out that the sonar results are consistent with a creature which moves up and down in the middle depths, but only occasionally rises to the surface. (And incidentally, perhaps the debunkers would like to provide an explanation for the sonar results.)
Archaeocetes were the most primitive group of whales, and the operative family for this discussion is the Basilosauridae, which allegedly went extinct about 35 million years ago, for they were elongated and serpentine in appearance. Now, there are innumerable reports of elongated sea serpents swimming with vertical undulations, which Zoology 101 will teach you is a feature of mammals, and only of mammals. Dr Mackal suggested them as a possible identification of what he calls "naitakas", the monsters of the western Canadian lakes. (Naitaka was the Indian name for the monster of Lake Okanagan, which the whites call Ogopogo.) In fact, one Ogopogo witness even cited a whale-like horizontal tail fluke.
It all makes perfect sense - except that not matter how long a whale can hold its breath, it has to come up breathe and spout at very frequent intervals. Although a sign at Lake Okanagan declares that it is the home of Ogopogo, you know you would have to be incredibly lucky to see it. And let's be realistic: how long would it take for even a single whale to exist in even a large lake before its presence became of regular occurrence for every boat-user on the waters, it acquired a pet name, its movements were tracked in the local press, and tourists were setting out with a reasonable expectation of sighting it?
This, of course, was the theory of Antoon Oudemans and, if you don't mind my saying so, one of the silliest. To be fair, he proposed it for sea serpents, not lake monsters, but even then there are problems. For a start, seals have to come to shore to bear and raise their young. Secondly, seals are mammals, and mammals possess only seven neck vertebrae. Even a giraffe has only seven. Yes, there are a few exceptions. Manatees have only six, two-toed sloths five, and three-toed sloths nine. So it is possible for mutations to have a minor effect but, by and large, mammals appear to lack the genetic ability to change the number of their neck vertebrae. It is pushing the odds a bit to propose that one branch of the seal lineage has not only grown huge, found a way to bear its young at sea, and multiplied its neck vertebrae such that the neck is as flexible as it appears, and as flexible as is needed to chase fish underwater. A stiff, giraffe-like neck would be counterproductive under the circumstances.
And, of course, in a lake seals still have to breathe.
So, what are they?
I don't know. This essay is only intended to dispel misconceptions, not explain the whole topic. I think that basilosaurids are still the best candidates for many sea serpent sightings. I have no idea what long necked sea serpents might be. But I am convinced that lake monsters, to the extent that they actually exist, do not belong to any order of animals which has lungs.
In an earlier post, I suggested that the Lake Labynkyr monster (which is known only from a single sonar reading) is probably a large sturgeon. It appears to me, having due regard to possible misperceptions, that some of the "lake monsters" in Quebec, such as Memphré in Lake Memphrémagog and Ponik in Lake Pohénégamook, or Mocking Lake, are also consistent with large sturgeons. Nevertheless, I would hesitate to apply that hypothesis to every single lake monster. And, of course, it would not apply to anything south of the Equator.
So there the mystery rests.