Here’s some added fuel for the speculation.
In about 600 B.C., Nebbuchadnezzar had bas reliefs fashioned for the brickwork on the Ishtar Gate of Babylon. They show three species of animals, large numbers of each in each brick row. The rows alternate between depictions of lions, the rimi, and the sirrush.
Lions, of course, are real animals. The rimi was extinct in Mesopotamia at this time, but may have been remembered or known through specimens brought in from Eurasia. We know them today as urus or aurochs, and they became extinct only in 1627.
So what is a sirrush?
The bas reliefs show a slender, scaled body; a long, slender, and snaky tail; clawed feet that appear almost birdlike; a serpent’s or dragon’s head with a forked tongue; flaps of skin attached to the back of the head; and a single straight horn. Archeological commentary calls them “dragons” and assumes them to be mythological. So why have two real animals and one imaginary one?
In the apocryphal Book of Bel and the Dragon, the writer relates how the priests of Nebuchadnezzar kept “a great dragon or serpent, which they of Babylon worshipped.” They challenged Daniel to dispute this god, “who liveth and eateth and drinketh; you canst not say that he is no living god; therefore worship him.” According to the story, Daniel poisoned the beast.
And then there is Behemoth, mentioned in the Book of Job. Modern scholars assume it refers to the hippopotamus, but . . .
“Behold now Behemoth . . . he eateth grass as an ox. Lo now his strength is in his loins and his force is in the navel of his belly. He moveth his tail like a cedar: the sinews of his stones are wrapped together. His bones are as strong as pieces of brass, his bones are like bars of iron . . . He lieth under the shady trees, in the cover of the reed, and fens. The shady trees cover him with their shadow . . . His nose pierceth through snares.”
That comparison of the hippo’s tail to a cedar makes me wonder.
The guy who discovered the Ishtar Gate openly wondered if the Sirrush was a real animal, now unknown. There are other depictions of the beast across a span of centuries. Unlike other fantastic beasts of Babylonian mythology, however, these depictions remain anatomically consistent.
The idea that our ancestors gathered fossils and speculated about them is a good one. Scholar Adrienne Mayor has written, “Reliable ancient sources relate that, when fossils were discovered in antiquity, they were transported with great care, identified, preserved, and sometimes traded. Reconstructed models or remains of ‘unknown’ species were displayed in Greece and Rome.” She adds that ancient writings seem to indicate that “some representations and descriptions of crypto-animals in antiquity were based on reconstructions from skeletons of living or extinct animals.” [Mayor, Adrienne. “Paleocryptozoology: A Call for Collaboration Between Classicists and Cryptozoologists.” Cryptozoology 8 (1989): 12 – 26.]
Along this same idea, there is good reason to believe that Chinese ideas about dragons were at least partially born of the discovery of fossilized remains. There was until quite recently a rather horrifying trade in the pulverized fossil teeth, bones, and horns of "dragons," "giants," and other mythological beasts to cure various maladies . . . and the practice may not be ended yet.
So, what was the sirrush? A creature based on recovered fossils? It’s possible, though we should remember that there are no dinosaur remains in Mesopotamia. Wrong geology, wrong period. They would have had to have found them elsewhere. Also, many of the details from the bas reliefs--skin flaps, tongue, scales--could not be recovered or guessed at from fossil remains.
Another possibility; Babylonians are known to have penetrated parts of Africa in search of gold and ivory, and we have the modern-day reports from natives of a small sauropod surviving in the Congo, called mokele-mbembe.
Makes you wonder, doesn’t it?