Styracosaurus

You might be excused for thinking Styracosaurus was all head: this dinosaur's broad, flat face extended upward into a massive frill, which was itself topped by no less than six dangerous-looking spikes. As if all that weren't enough, this plant-eater had a two-foot-long horn extending from its snout, two smaller horns jutting out from its cheeks, and (for some obscure reason) unusually large nostrils.

Why would nature have allowed this otherwise gentle ceratopsian to evolve such an elaborate (and fearsome) display? There are three possible explanations. First, it may have been a sexual adaptation (that is, male Styracosaurus with bigger frills and sharper spikes had a better chance of mating with females); and second, it may have been a means of defense, either to actively gore hungry raptors and tyrannosaurs or make this dinosaur look larger and more threatening.

There's also an interesting third possibility. The enormous frill of Styracosaurus may have helped dissipate heat from its body, like the floppy ears of an African elephant. If so, this would lend support to the theory that dinosaurs had warm-blooded metabolisms and needed to occasionally shed excess heat.