Cranial ornaments associated with large body size in theropod suborder.
T. rex and other theropod dinosaurs that sported bony bumps and crests on their heads evolved their massive body sizes 20 times faster than species lacking those cranial ornaments, according to a study published in Nature Communications.
Researchers compared the body sizes of 111 theropod dinosaurs, some with fancy headwear, and others lacking it. Those weighing in below a threshold of 36 kilograms (80 pounds) showed no signs of the ornamentation that was present in 20 of the 22 largest species.
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For most of the species, these bony head structures were likely used in displays, but for some, they may have been physiological adaptations for controlling body heat.
"We were surprised to find such a strong relationship between ornaments and huge body size in theropods," study lead author Terry Gates, from the North Carolina Museum of Natural Sciences explains in a press release.
The authors suggest that whatever social or sexual functions the bony ornaments served was likely also driving mass increases among theropod dinosaurs. "Something about their world clearly favored bling and big bods," says Gates.
The relationship between body size and ornaments did not extend to the lineage that led to modern birds, which included species like the Velociraptor — even the dinosaurs in this group that were above the body weight threshold did not gain bumps or crests on their heads. The researchers believe the feathers in these species may have been a more flexible substitute for the bony displays.
"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," says study co-author Lindsay Zanno, also from the museum.
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