Ornamented heads drove arms race of giant dinosaur bodies

RALEIGH, N.C., Sept. 27 (UPI) -- Which came first, giant dinosaur heads or massive dino bodies? New research suggests large ornamented heads triggered the rapid increase in body mass among Jurassic predators.

When researchers at North Carolina State University analyzed the evolution of body size among theropods, they found lineages with ornamented heads -- large heads with crests, horns or nobs -- got bigger faster.

The heads of 20 of the largest 22 theropod species are marked by bony lumps or crests. The group includes some of the most famous predators, like Tyrannosaurus rex and Allosaurus.

Analysis of fossils of 111 ornamented and unornamented theropod species suggests species that evolved head ornamentation got bigger and bigger over time, while unornamented species remained small.

"We were surprised to find such a strong relationship between ornaments and huge body size in theropods," researcher Terry Gates, a biological scientist at North Carolina State, said in a news release. "Something about their world clearly favored bling and big bods."

The new research was published in the journal Nature Communications.

The correlation didn't extend across the entirety of the theropod family tree. The lineages most closely related to modern birds -- Velociraptor, Ornithomimus and Falcarius -- all were large but without head ornamentation. Researchers believe their feathers served as ornaments, minimizing the pressure to draw attention to themselves with unique head shapes.

"Our work supports the idea that vaned feathers were great communication tools from the get-go and may have helped large bird-like theropods sidestep the bother of skeletal bells and whistles," Gates says.