We generally perceive Tyrannosaurus rex as a ferocious animal always seething with rage. However, a new study has indicated that the presence of two mysterious holes on its skull might have helped in controlling the temperature inside its head. The work appears in The Anatomical Record.
Earlier these holes also termed as dorsotemporal fenestra were considered to be only occupied by muscles which helped in the operation of its jaw. Casey Holliday, an anatomist from the University of Missouri said that it was strange for a muscle to extend from the jaw till the top of the skull. But now enough evidence has been gathered from alligators and other reptiles which suggest the presence of blood vessels in this region. Similar fenestra has been observed in the skulls of animals collectively termed as diapsids. It includes crocodilians, birds, lizards, and tuatara. It is estimated that the holes evolved nearly 300 million years ago. Fenestra can be found in tyrannosaurs and pterosaurs. The team analyzed several diapsid skulls to find out which animals had fenestra resembling T.rex; the closest one was crocodilians.
Holliday and his team members, William Porter, Lawrence Witmer from Ohio University and Kent Vliet, University of Florida used thermal cameras for studying alligators at St Augustine Alligator Farm Zoological Park. The body temperature of alligators is dependent on the temperature of the surroundings since they are cold-blooded. As a result of which their thermoregulation processes are different from the warm-blooded or endothermic animals.
“We noticed when it was cooler and the alligators are trying to warm up, our thermal imaging showed big hot spots in these holes in the roof of their skull, indicating a rise in temperature,” Vliet said.
“Yet, later in the day when it’s warmer, the holes appear dark, like they were turned off to keep cool. This is consistent with prior evidence that alligators have a cross-current circulatory system – or an internal thermostat, so to speak.”
It is not sure if dinosaurs were endothermic or ectothermic and this is a topic of heavy debate. Some scientists think they were in between the two categories i.e a feature called mesothermy. Previous research suggested that armoured ankylosaur had tunnels in the skull for keeping the brain at optimum temperatures.
It is suggested that T.rex use few thermoregulation tactics of the ectotherms. It can, however, be confirmed that there are no osteological features on the skull of tyrannosaurus which shows that fenestra were extensions of muscle attachment. They can also infer, based on modern alligators that Fenestra could have been used for controlling the temperature in the skull of T.rex by warming or cooling the blood flowing through blood vessels.
Witmer said that similar to T.rex, alligators have holes on their skull-tops which are filled with blood vessels. But still, muscles have been grouped with dinosaurs. The anatomy and physiology of the present-day animals can be used to discard the early hypotheses.
Journal Reference: The Anatomical Record.