I agree that in one way 150 or 70 million years is quite a moot point. Long gone in this context, is long gone. Which, as I think we agree, is that of romantic imaginings. If though it really was a question of whether an animal had really survived, then it'd become significant. Again though in general conversation, you're quite right.
Modern alligator and crocodilians in general did first arise in the Cretaceous, and their appearance hasn't changed that much. In terms of their earlier ancestors and relatives though, again as you say, they've changed radically. Although at various times similar forms to today's have existed in the deep past. Mokele mbembe though changes depending on who you ask. The version that's stuck here in the west though, is that of a sauropod, which lives in the wetlands of the Likouala Aux Herbs and especially in and around Lake Tele. All the sort of habitat that seemed to be ideal back in the days when the stories were first popularised, and when we though dinosaurs were big bulky things that needed water to support themselves.
But these days we realise that such an environment is completely unsuitable. And that the animals themselves were in life, very different to how we then imagined them.
It's a tale that's dated now and evaporates when you look into it. Which is sad in a way, because it's by far the most romantic of all the cryptids. More worryingly though, the logging roads are now within about 15-20KM of the lake, so belief in it may be set to last just last as long as its supposed habitat. The World is getting smaller.
As to a fossil being the inspiration, so far stegasours are only known from the U.S and Portugal, so it's unlikely I'd say
I doubt it's a chameleon, it's quite away out of their distribution range. And good point about the size of the head.
I agree it's a mammal of some sort, or a creature inspired by one. I have to say though, due to the depth of the carving and the way the 'plates' are distributed along its back, I think they are supposed to be part of the animal. Whatever it is.
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