Protomammals continued to butt their heads until the end of the Triassic Period, when dinosaurs took over the roles of large herbivore and carnivore on land. (animatronic dinosaur factory)The dinosaurs’ approaches to sex and intimidation ran the entire gamut from elaborate dorsal displays to head-butting and perisexual symphonies. Largest of the dinosaurs resorting to display was the appropriately named Spinosaurus, the “spine lizard,” a forty-foot predator probably related distantly to Allosaurus. All specimens of Spinosaurus are frustratingly fragmentary, but it’s clear a tall sail decorated its back, rising six to eight feet above the backbone.(animatronic dinosaur) A strutting Spinosaurus must have been a singular sight striding on its long hind legs, its head twenty feet above the ground, turning broadside to dare its rival to test its potency. Sex also probably explains the tails of duckbill dinosaurs. Those tails were very deep from top to bottom and well suited for conveying messages. Some duckbills even evolved true sails constructed from vertebral spines over the base of their tail.
Torso and tail were not the only sites of sexual adornment. The Early Jurassic carnivore Dilophosaurus evolved a striking cranial profile: two tall crests, very thin from side to side, rose from the edges of its skull from snout to forehead. (dinosaur costume)Lower, thicker crests in the same location decorated the heads of the Late Jurassic Allosaurus and Ceratosaurus and the tyrannosaurs of the Cretaceous. Dilophosaur crests were so thin that they could have been only for visual effect. But the bony crests of the later meat-eaters were heavy and covered by stout layers of horny skin. Allosaurus and its relatives probably butted heads during confrontations on the field of sexual valor.
To be sure, a pair of male allosaurs, driven by their hormones, could have bitten each other to death. But I suspect such terminal contests were relatively rare. Evolution tends to favor the sexual soldier who can win multiple contests and who therefore, by implication, does not run the risk of being dismembered in his first bout. Less than lethal horns would confirm this general theory. The allosaurs’ ancestors possessed little in the way of crests or horns but they did have dangerously sharp teeth and quick-biting jaws. (dinosaur factory)These earlier carnivores could have resorted to biting to settle mating contests, but they were probably restrained by genes that programmed for less dangerous encounters. And the success of genetic changes that increased the disposition toward head-butting among the later, larger carnivores indicates that but-ting, not biting, was the best strategy for maximizing success in mating. Big mammals show the same pattern clans with dangerous teeth often evolve nonlethal horns.