Oh, this is fantastic! This story… I love this. Now, go read it so I don’t have to tell the story all over again.
OK. So! Haha. The Creationists have a bombshell! There’s a carving of a Stegosaurus! 
From a thousand years ago! Which proves that humans and dragons coexisted (creationists call dinosaurs “dragons,” for the same reason that they call little people “leprechauns”). Only it doesn’t look anything like a stegosaurus. Stegosauruses have tiny little heads and no horns.

Hell. O. Tiny Head. No Horns.
That thing has horns — or something growing off the top of its head there. Well, so what? We’re going to pick nits here when we’re talking about a stone carving of a creature with PLATES on its back! So, scientists say that stegosauruses didn’t live in Cambodia — who cares? They have an agenda that does not include eye-witnesses carving images of stegosauruses into walls.
And then the evolution people have to say something! No, they can’t just let the creationists have their moment. This must be handled. So, they say that the plates are just ornament — which I really think is most likely and realistic, not because I’m a true believer (who can prove to me that we’re not slipping in and out of dimensions and realities, and falling into wormholes all the damn time? Blinking in and out of existence, like quarks? Hmm? I thought so…), but because it looks like ornament to me, and the other animals represented there have ornament on and around them, too. Plus, it seems like the logical ornament for the job. What else is an artist going to do with a big boring round back, but put a frill around it?
So, they photoshop the ornament off the creature to get a better look at it, and they make a few other adjustments, and decide that it’s either a chameleon or a rhinoceros — one or the other. The thing is that when you take the ornament off, it looks more like a triceratops than anything extant.

Big Head. Horns. No Plates.
Look, there are no horns on its nose! The single distinctive characteristic of a rhinoceros are the horns on its nose, and there are no horns on this nose. Why is a rhinoceros even called a rhinoceros if not for the dang horns on its nose?
And a chameleon? Grazing? With big fat legs? (Though I do concede that chameleons have big fat sticky feet; so that much works.) No crazy eyeballs and a tail that only a mother could love? Look at the tail on that carving. If you were going to carve a chameleon into a temple, would you say, “Oh, fuck the tail. What Ever!” You wouldn’t. You would start with the tail.

Chameleon?
Also, the veiled chameleon, which might account for the horn thing, is not from Cambodia. Look, that is not a chameleon. And if you say it’s a chameleon it’s because you secretly want the creationists to win. It looks way more like ANY dinosaur than a chameleon. And I have a 7 year old son, so I know from dinosaurs.

No, Chameleon.
I thought it might be a water buffalo, but I changed my mind. I think it’s a Kouprey — an animal that oughta make both the creationists and the cryptozoologists very happy! It’s a great compromise for this situation we have here. It’s got the horns (and I imagine it would be tricky to carve curved horns into the wall), the humped back, the tail, the bovine grazing thing, also the elusiveness, the utter uniqueness to Cambodia — and I read that they like the sun, which might account for the design work, which could be sun rays (Hey, maybe it’s a sun bear, which they also have in Cambodia). Also, since it’s underneath another ungulate, it seems to be logically placed.

kouprey!
The puzzle is mostly those plates. I was looking around to see if I could find some ancient Cambodian rendering of the sun, but I didn’t have any luck. What I did find, though, is very interesting.
OK, picture this: way back when these images were carved into the temple walls, Angkor Wat was new, and it is spectacular. Perhaps what we have in this image is an homage to Things Cambodian. The Koupray is unique to Cambodia, and Angkor Wat is a Cambodian masterpiece. If you were an artist at the beginning of the 12 century in Cambodia, wouldn’t you think to pair the two distinctly Cambodian treasures? The Koupray in the shadow of Angkor Wat:

Voila! Angkor Wat
The spires on this opulent temple are very similar in shape to the ornament around the triceratops, and the temple slightly predates the carvings. So, what we have here, it seems, is a case of sylization. This “plate” shape has a precedent. If I were an early 12th century Cambodian artist, I would so totally create a kouprey silhouetted against the Angkor Wat. You’d have to be an idiot not to.
In any event, I don’t blame the artist for not producing an immediately recognizable creature. I mean, have a look at Blake’s rendering of The Tyger:
It looks like a lump fish. Fearful symmetry? I think not. It doesn’t even look like a cat.
Anyway, what really concerns me about this carving is the sea creature coiled around it. Am I the only one whe sees that? Or is that just too crazy?