Sharon Hill, geologist, skeptic, and Sounds Sciencey columnist, has given the boot (boot? Hill? Get it?) to the claims that prehistoric survivors are still roaming around causing cryptozoologists to get all excited. She has a number of major points, one being that the coelacanth is not enough to make a logical link with any claims of living plesiosaurs. (Actually, I'm almost getting tired of Old Fourlegs, a marvelous discovery, but one that apparently be trotted out forever in arguments over cryptozoology.) Hill notes that neither Central Africa nor any other spot on Earth is unchanged since the Mesozoic era, a point hammered home in the African case by Louis Jacobs in his book Quest for the African Dinosaurs.
She dismisses two of the most famous corpses in sea serpent history, noting they were in advanced stages of decay. I had to push back a little there: the 1937 Naden Harbor "Cadborosaurus," while clearly beat up, was not described in the contemporary accounts as being in "an advanced state of decomposition." There's still something odd about that damned thing: while it does resemble a decayed basking shark, it puzzles me that the vertebral column would have stayed intact for so long while the whale was digesting it, given the combination of chemical and muscular processes going on.. (While I wrote in 2006 that there are no accounts of sperm whales swallowing basking sharks, Richard Ellis mentions one in his book on the sperm whale, a 14-foot shark to be precise, so we can agree such a swallowing can happen.) It probably was a known creature of some sort, and Bousfield and LeBlond overreached in making it the type specimen of a new reptile. It's just not resolved quite as definitely as I'd like.
The article raises and interesting question: if there is a decent body of sightings of a large animal, is it more likely to be a survivor which has left no fossil remains for a very long time, or a more recent development which has somehow left no remains at all?