I knew I had to enter the All Yesterdays contest, but I couldn't figure out what I would like to explore. I though of many obvious and unoriginal things, like wacky and extravagant courtship displays and interspecies cooperation. I even went as far as to design a hadrosaur which head pattern mimicked its tail's to confuse predators, but nothing striked me as a good entry. Finally I though of something that could be nicely explored, although I guess it is not immediately recognizable by the picture: homosexual behaviour in dinosaurs.
Same-sex copulation, bonding and parenting is well-documented in many animals, especially birds and mammals. The exact reason why these behaviour exists, which by an evolutionary standpoint would be rather disadvantageous, is not really known. But the fact is that it is much more common in nature than most people would think, with unusually high rates of homosexual pairing in species like giraffes, bonobos, ducks and penguins, and in many cases leading to the adoption and successful raising of surrogate offspring.
In my entry, a male pair of caenagnathid oviraptorosaurs engage in mutual courtship - something that would definitely not be preserved in the fossil record. Their colouration is inspired by black swans, of wich an estimated 25% of pairings are male-male.