Old T-Rex Ancestor is New Discovery for Paleontologists

Jan 22, 2024

Dinosaur fans, say hello to your newest obsessionTyrannosaurus mcraeensis.

An ancestor to the famed T. rex, a dinosaur that had tiny arms and huge jaws, mcraeensis dates to the late Campanian-early Maastrichtian Period. This puts its peak about 7 million years before T. rex ruled the forests and plains of North America.  

Paleontologists in New Mexico dug up a quarter of a mcraeensis skull in the mid 1980s. At first, they mistook it for that of a T. rex. The skull piece was placed in the New Mexico Museum of Natural History and Science. It was classified there for decades as a T. rex. But recently a team of researchers took a second look at the skull. What they saw convinced them they were looking at a new, older species.

“The lower jaw in a Tyrannosaurus rex is (really) quite robust. Our jaw is (clearly) big and toothy, but it’s more slender than what we see in a (T. Rex),” Anthony R. Fiorillo told CNN. He's the museum's director. He also noted that the new species lacked the T. rex's striking brow line. The new species had no big, broody ridge over its eye. This new species, mcraeensis, takes its name from the rock structures where it was found. 

Fiorillo’s team published their findings this month. They're still searching New Mexico’s McRae foothills for more samples. They hope to piece together the story of how T. rex spread across North America. They want to know how it evolved into the biggest (and baddest?) apex land predator of all time. 

Photo from Unsplash courtesy of Jon Butterworth.

Reflect: How might studying different species of dinosaurs be important for scientists and our understanding of Earth's history?

How does the author organize the information in the story? (Common Core RI.5.5; RI.6.5)
a. by listing facts in chronological order
b. by comparing and contrasting two different dinosaur species
c. by explaining how the Tyrannosaurus rex evolved into the biggest apex land predator of all time
d. by providing a step-by-step explanation of the scientific discovery process
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