Okay, so I took a closer look at that plains level screenshot of the dam. Because of the JPeg degradation, it's not easy to see, but there are indeed shadows. And actually, that image is much brighter than the version of the image I have so the shadows aren't showing up as good.
If you take a look at the area near the Stego and the skinny tree, you can see the shadows easier. It's still not that easy to see, but you'll see it a lot better than in the above screenshot. This was indeed taken ingame. Probably from the no AI period of production. The dinosaur models are just static models that they put in for the purpose of the screenshot. There's actually an early Trespasser video that uses a static brown raptor that's set to land onto the player. (definitely made for a good prerelease jumpscare that's for sure)
What I'd like to know though is what level that was. It looks like it might be the Plains as well. If it's not, then it's a very early version of Tres's test level. Here's a picture from roughly the same spot as said Teaser video:
This Yellow Grass/sand texture is similar to the Desert style texture the Test level uses, but it also looks like Savannah grass as well, which is why I'm unsure.
This area would kinda fit the transition to PV from PL as you can see by the pine trees in the background.
Another image, possibly from the same location. The ground foliage does kinda match up with the .max file. From what little we know, the level was probably very flat in most places since the idea was that you were supposed to be able to see for miles in all directions. You'd come out of the town and be out in the open and need to get the battery for the floodgates on the dam to be able to pass. after that you'd start making your way up into the higher altitude parts of the island (PV and later)