Tyrannosaurus rex Had ‘Thermostat’ in Its Head

Tyrannosaurus rex, a species of carnivorous dinosaur that lived about 68 million years ago, had an internal thermostat in its head, according to a study published in the journal Anatomical Record.

A graphic thermal image of a T. rex with its dorsotemporal fenestra glowing on the skull. Image credit: Brian Engh.

T. rex had two large holes — called the dorsotemporal fenestra — in the roof of its skull.

In the past, paleontologists believed these holes were filled with muscles that assist with jaw movements.

The new study suggests blood vessels in the dorsotemporal fenestra acted as an internal thermostat, much like alligators have today for body temperature control.

“It’s really weird for a muscle to come up from the jaw, make a 90-degree turn, and go along the roof of the skull,” said University of Missouri’s Professor Casey Holliday, lead author of the study.

“Yet, we now have a lot of compelling evidence for blood vessels in this area, based on our work with alligators and other reptiles.”

Using thermal imaging, Professor Holliday and colleagues examined alligators at the St. Augustine Alligator Farm Zoological Park in Florida.

A graphic thermal image of a T. rex skull. Image credit: Brian Engh.

“An alligator’s body heat depends on its environment,” said co-author Dr. Kent Vliet, a researcher in the Department of Biology at the University of Florida.

“Therefore, 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.”

“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.”

The scientists then took their thermal imaging data and examined fossilized remains of dinosaurs and crocodiles to see how these holes in the skull changed over time.

“We know that, similarly to the T. rex, alligators have holes on the roof of their skulls, and they are filled with blood vessels,” said Ohio University’s Professor Larry Witmer, co-author of the study.

“Yet, for over 100 years we’ve been putting muscles into a similar space with dinosaurs.”

“By using some anatomy and physiology of current animals, we can show that we can overturn those early hypotheses about the anatomy of this part of the T. rex’s skull.”

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Casey M. Holliday et al. The Frontoparietal Fossa and Dorsotemporal Fenestra of Archosaurs and Their Significance for Interpretations of Vascular and Muscular Anatomy in Dinosaurs. Anatomical Record, published online July 1, 2019; doi: 10.1002/ar.24218