Theropod dinosaurs – such as dilophosaurus – had bumps, knobs and crests on their head. Science Photo Library / Getty Images

The biggest dinosaurs, including famous Tyrannosaurus rex, often sported crests and horns on their heads – and a new study says this correlation between size and horns may not be a coincidence.

A paper published in Nature Communications connects the evolution of ornamental head structures with an increase in body size across larger theropods – a group of two-legged land-dwelling dinosaurs.

Ornamental bone structures such as crests and horns have several functions in the animal kingdom, including attracting a mate, but the evolution of dinosaur ornaments isn’t well understood.

A US research team led by Terry Gates at North Carolina State University set out to track the enormous increases in body size throughout the evolution of some large dinosaurs, and the presence of these ornaments.

Their findings show that the bodies of dinosaurs with crests and horns increased at a faster rate than those without ornaments on their heads, suggesting a strong genetic link, and possibly shining a light on the habitats of these species.

“Our analysis finds a significantly positive correlation between large body mass and the evolution of osteological cranial ornamentation in theropod dinosaurs,” the researchers state in their paper.

This finding suggests that sexual preference and environment may have something to do with the enormity of these theropod species.

For instance, the researchers hypothesise, larger horned dinosaurs living in open habitats may have been more conspicuous in their environments, and sexually selected over time to increase in size.

This wasn’t the case for all dinosaurs, though.

The findings point to a size threshold for the development of ornamental horns.

Animals below a certain body mass did not develop head gear like their larger counterparts, and possibly stayed small in order to avoid predators in their open habitats.

The researchers acknowledge that their findings should be taken with a grain of salt, given their low sample size of 38 species, but the correlation between these two traits is a first-time find among reptile and bird species.

The research also points to a group of dinosaurs exempt from this rule. Feathered dinosaurs known as Maniraptoriformes, some of which had feathered crests, do not demonstrate this evolutionary link.

The researchers say future theropod discoveries will help to more accurately calculate the body mass threshold that impacts the development of size and horns, as well as any other potential genetic links.