Hi, littlemissattitude (love the handle!), and welcome to Comparative Religion!
I absolutely agree with you about modern perceptions of our ancestor's talent, imagination, and ability. One of my peeviest of pet peeves is Eric van Daniken and his ilk, who blithely declare that since modern technology would be hard pressed to reproduce such wonders as the pyramids, Teotihuacan, Baalbek, or the Easter Island statues, they MUST therefore have been built by aliens from outer space. Nonsense! We don’t give our ancestors nearly enough credit! As for their ability to make up imaginary critters, well, mythology is richly populated by everything from Cyclopes to snake-tailed sons of Athena to hundred-headed, hundred-handed giants who threw mountains at the gods. If anything, our modern age has LOST some abilities in this arena.
I certainly didn’t intend to use the carvings on the Ishtar Gate as proof of the survival of dinosaurs, nor was it my intent to suggest that the Babylonians couldn’t make up imaginal beasties. What I find interesting is the fact that of the three critters portrayed, one is real, one WAS real at the time, though it later became extinct, and one . . . well, at the very least, it suggests that the Babylonians themselves thought the thing was flesh and blood, an idea supported by popular urban legends at the time (which even made it into the Biblical Apocrypha) that the Neobabylonians had a living pet "dragon" hidden in the palace basement. I find the sirrush evocative and interesting, something to make us think and wonder, but NOT proof, certainly.
I’d like to address the bird- and animal-headed figures on the cave walls, if I may. We have very few examples of human representation in cave art. Those figures we have found all seem to depict magical themes—such as the popular image of a hand print superimposed over game animals, an apparent attempt to gain control over them or their spirits. (The single exception I can think of is an oft-reproduced picture of an exquisitely rendered wounded bison apparently goring a crude human stick figure, which is falling over backwards while a bird looks on. The human figure is so simply rendered it’s tough to tell even if it’s meant to be a man or some kind of man-beast fusion. I often wonder if it represents magic, religious belief—with the bird being the dying man’s soul, or a memorial to someone killed in the hunt.)
A fair guess at the animal-headed pictures, though, is that they represent shamanic rites. There’s a famous cave wall painting that seems to show a human wearing furs and an elk’s head and antlers, which is assumed to be the image of a shaman invoking animal spirits. It’s called “the Sorcerer” for that reason. The practice of becoming one with the spirits of the animals we hunt or fear in order to control or summon them or to placate them is very, very old, and almost certainly reaches back several tens of thousands of years into our remote past. I find this a wonderful and startlingly unexpected window into our origins as spiritual beings.