A reconstruction of Carnotaurus, who clearly knew a thing or two about fashion. (Credit: Lida Xing and Yi Liu/Wikimedia Commons) The fancier the crown, the bigger the dinosaur, a new study suggests. Researchers from North Carolina State University conducted a statistical analysis of theropod fossils from 111 species, comparing those with head ornamentation to those without. They found a sharp divide between the two groups when it came to size, and their results indicate that theropods with impressive crowns grew into giants 20 times faster than those with unadorned heads. In other words, head bling may have been a driving force shaping their evolution.
Big and Flashy
Twenty of the 22 theropod species above 2,200 pounds possessed some kind of ornamentation on their noggins, from the spiky horns wielded by Carnotaurus to the impressive ridges atop Dilophosaurus. But there's no clear consensus on what advantage funky-looking headwear conferred for dinosaurs. They may have been used to advertise their sexual maturity, intimidate rivals or advertise their top-dog status. Among smaller theropods, under 80 pounds, this predilection for decoration is notably absent. The correlation holds for a majority of theropod species except one distinct clade, the Maniraptoriforms. These dinosaurs, too, grew to enormous sizes, but bony bulges and crests were absent in the fossils unearthed by scientists. However, Maniraptoriforms may be the exception that proves the rule. Instead of bony headwear, the Maniraptoriforms possessed feathers, which the researchers think stood in for crests and a ridges as a form of sexual signaling. Head crests or feathers, the key here seems to be that larger dinosaurs were also more ostentatious. Whether these bony structures themselves helped dinosaurs grow or if they were correlated with another factor remains to be seen. They published their research Tuesday in Nature Communications.
An artist's rendering of Dilophosaurus, who opted for a pair of stylish head ridges. (Credit: Raphael041/DeviantArt) One reason the researchers think that head ornamentation and size went together so well is that they both conferred advantages in wide-open environments. On a plain or prairie, there is an advantage to being seen and noticed — by potential mates, for example — which happens a lot more often if you're twenty feet tall with spiky ridges on your head. In the forests, even the flashiest of dinosaurs will remain hidden, pressuring those species into staying small and modest.