The Tyrannosaurus rex, Giganotosaurus and the Allosaurus were among the biggest and most fearsome carnivorous dinosaurs when they walked the earth in prehistoric times. These Jurassic predators also happen to have strange bony structures that stick out of their skulls.
Now, findings of a new research have revealed that the large ornamented heads of these Jurassic predators may have something to do with their gigantic bodies and their rapid growth.
In a new study, researchers from the North Carolina State University analyzed the evolution of the body sizes of theropods, a group of mostly meat-eating bipedal dinosaurs, and found that those whose lineages have ornamented heads got bigger faster.
The theropod species whose large heads have horns, knobs and crests evolved to have enormous body size 20 times faster compared with those that lack such embellishments. The large species that lack ornamentation such as the Acrocanthosaurus did not grow to gigantic sizes as fast as their counterparts with head ornaments.
"We were surprised to find such a strong relationship between ornaments and huge body size in theropods," said study researcher Terry Gates, from the Department of Biological Sciences of the North Carolina State University. "Something about their world clearly favored bling and big bods."
Analysis of 111 fossils of theropod species suggests that the species with ornamented heads got bigger and bigger overtime while those without head ornamentation remained small. When a species of theropod evolved to have some style of head display, the subsequent species would take big leaps toward gigantic body sizes every 4 to 6 million years.
Of the 22 largest theropod species that the researchers looked into, 20 are characterized by heads with bony lumps or crests.
"We explore correlative evolution of osseous cranial ornaments with large body size in theropod dinosaurs using a phylogenetic comparative framework," the researchers wrote in their study, which was published in the journal Nature Communications on Sept. 27.
"Body size evolved directionally toward phyletic giantism an order of magnitude faster in theropod species possessing ornaments compared with unadorned lineages."
Paleontologists have long hypothesized that the bony protrusions on dinosaur skulls are used by dinosaurs for socio-sexual display mechanism using them to defend and communicate, intimidate and possibly send signal which individuals were socially dominant or sexually mature. The study hints these features are also associated with evolution of body size.
The researchers noted that it remains unclear if the bony structures were directly caused by growth or these were just associated with another factor that prompted growth in these prehistoric creatures.