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A new study led by Carthage College paleontologist Dr. Thomas D. Carr finds that size and weight don’t determine the age of Tyrannosaurus rex.

“Evolutionary change often comes about by changing growth,” Carr said. “We can now compare this high-resolution growth series for T. rex with other tyrannosaurs to see how growth was pulled from one direction to another, resulting in new species.”

Over the course of the study, Carr analyzed 1,850 features resulting in the most complete growth series ever obtained for the iconic beast. The study included 31 specimens, from pint-sized juveniles to multi-ton adults.

The most significant outcome show big and heavy doesn’t mean old; size and mass turn out to be poor evidence for estimating age among adult T. rex. For example, Scotty, the largest and heaviest T. rex, was found to be a youngster among adults.

“The scariest result is that the trademark powerful skull and teeth of T. rex grew in by the time it was only half-sized, around 15 years old,” Carr said. “The monstrous killing equipment that we associate with T. rex was in play before it reached its mammoth size, which made subadults as dangerous as full-sized adults.”

Two to three years after that, T. rex passed the 3-tonne mark, exceeding its closest relatives in mass, putting it into a zone of destructive power all to itself.

Carr’s work also finds that the specimens thought to belong to the controversial species Nanotyrannus, are really juveniles that form a transitional series between the smallest juveniles and the much larger, and imposing subadults.

Another significant outcome found that the skeleton of T. rex does not show evidence of sexual dimorphism, although life males and females may have been distinguished by differences in soft tissue structures or pigmentation.

T. rex might have been dimorphic in terms of size, like living crocodiles, but without a good sample size of slam-dunk females or males, we’ll be in the dark about that for quite some time.”

Carr’s research sets the stage for deeper questions regarding the influence of growth and development upon the evolution of the tyrannosaurs, of which T. rex was the ultimate and most threatening expression.

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