This is a sirrush, a curious creature that keeps turning up in Babylonian art. Basically it’s a dragon with a cat’s forelegs and an eagle’s talons. Strangely, it was depicted that way consistently for centuries, while other mythological animals went through sometimes drastic evolutions.
The German archaeologist Robert Koldewey, who discovered this bas-relief on the Ishtar Gate in 1902, believed that the sirrush might have been a real animal. For one thing, he pointed out, it’s depicted among ordinary animals, including lions and aurochs. For another, a biblical text refers to a “great dragon or serpent, which they of Babylon worshiped.”
After some research, Koldeway decided the best match was the iguanodon, a dinosaur with birdlike hind feet. Ancient civilizations are known to have unearthed fossils, so possibly the Babylonians had found the remains of an iguanodon or of a monitor lizard. Or, much more speculatively, perhaps some dinosaur lines still survived 2400 years ago in Central Africa — where bricks have been found similar to those in the Ishtar Gate.