It's primitive symbolic artwork of cave dwellers enslaved by the dinosaurs. That's why the humans are carrying the dinos on their backs. It represents the fact that they supported their reptile overlords and metaphorically carried them everywhere.
Turns out the Ark is actually created by the reptiloids as both a haven for their less evolved ancestors and a study into human nature. The constant infighting of all the survivors simply proves what the reptiloids already knew: humanity is by nature aggressive, illogical, overly emotional, backstabbing and traitorous. After studying the survivors of the Ark, the reptiloids have decided the only course of action is to destroy humanity