Biggest, Baddest Dinos Had Fanciest Head Bling

A recreation of Spinosaurus, one of the largest carnivorous dinosaurs. It was eye-catching from head to tail.

Carnivorous dinosaurs that rapidly evolved large bodies also tended to evolve bony skull ornaments, according to a new study.

An open habitat likely favored both big bodies and conspicuous head features on meat-eating dinosaurs, helping to explain why these two seemingly disconnected characteristics so often appeared in tandem. The findings are reported in a paper published this week in the journal Nature Communications.

"Head ornaments are very effective because they are on the major communication center of the dinosaurs," lead author Terry Gates of North Carolina State University's Department of Biological Sciences, told Discovery News.

Gates and colleagues Chris Organ and Lindsay Zanno investigated the relationship between body size and skull ornamentation across theropod dinosaurs, meaning dinos like T. rex that had short forelimbs, two larger hind limbs for walking or running and a hunger for meat.

The researchers show that evolution of large body size in dinosaurs was accelerated in lineages with bony skull structures known as ornaments.

"Ornaments we defined as any structure that was extraneous," Gates said, explaining that they "came in varieties of crests, knobs, rugosites (wrinkled thick skin), and horns."

Crests are thin sheets of bone that rise above the skull. In many dinosaurs, such as Dilophosaurus, they probably looked a bit like an elaborate hairdo from a distance.

As for hairdos on humans, the ornaments probably served as unique identifiers. During displays, these features might have communicated information about the individual's sex, age, health and other factors.

"Animals today use signals other than size to communicate with one another," Gates explained, offering the rhinoceros as a living example. "Rhinos are large, but use their horns for maintaining social structure."

He and his colleagues are not sure when ornaments first evolved on carnivorous dinosaurs, and what initial function they might have held. They suspect that the features started out small before becoming larger and more varied across different dinosaur species.

Oviraptors -- a type of theropod that had claws, a toothless muscular jaw, slender limbs and other bird-like characteristics -- might have initially used their head ornaments for heat control. Later they were probably co-opted for visual communication, which is critical for today's birds.

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