Sergey Krasovki/Courtesy of the New Mexico Museum of Natural History and Science
The display shows Tyrannosaurus mcraeensis, a newly discovered relative of Tyrannosaurus rex. This creature likely roamed the Earth up to 7 million years before Tyrannosaurus.
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A previously unknown relative of the most famous dinosaur, Tyrannosaurus rex, has been newly identified, according to a study released Thursday. The discovery adds new evidence that could help paleontologists uncover another step in the evolutionary chain that ended with the massive predatory dinosaur, T. rex.
This creature is called Tyrannosaurus mcraeensis, and it likely roamed the Earth for up to 7 million years before the appearance of T. rex. The bones have been dated to between 72 million and 73 million years ago during the late Campanian and early Maastrichtian period.
But the bones of Tyrannosaurus mcraeensis were discovered decades before the creature officially got its scientific name. About a quarter of his fossilized skull was found over the course of the 1980s and early 1990s in an area now known as Elephant Butte, New Mexico. Due to the size of the specimens, the bones were originally classified by the New Mexico Museum of Natural History and Science as a T. rex, which measured up to 39 feet (12 m) in length and weighed 10 tons.
There were two major differences between T. rex and T. mcraeensis.
“The lower jaw in Tyrannosaurus rex is actually very strong. Our jaw is clearly large and serrated, but it is much thinner than what we typically see in Tyrannosaurus rex,” said Anthony R. Fiorello, co-author of the study published Thursday in the journal T. rex. Scientific reports. The T. rex's powerful jaw means it “can do whatever it wants.” A more slender jaw, even with larger teeth, means it will have less bite force.
Newly discovered dinosaur lower jaw fossil. Its jaw was much thinner than that of a powerful dinosaur.
Another big difference was that, unlike T. rex, T. mcraeensis did not have a prominent ridge above its eyes. Fiorello, who is executive director of the New Mexico Museum of Natural History and Science in Albuquerque, said scientists believe the T. rex's edge was used to help attract mates, such as the antlers of a deer or elk. In T. mcraeensis, the ridges are much finer.
The researchers wrote that large dinosaurs may have emerged as an evolutionary adaptation to the availability of large herbivores. However, why giant plant-eating dinosaurs evolved remains an unexplained mystery, according to the study.
Fiorillo stressed that it is a “highly speculative” idea at the moment, but added that, unlike the dwarf dinosaur found in the Arctic – it is called Nanoxaurus hoglondi — T. mcraeensis probably did not experience the drastic changes in temperature and light in southern North America, so it was able to continue growing. Arctic conditions may have played a role in N. hoglundi's apparent small size, but in general other dinosaurs from the same time period were much smaller than T. mcraeensis.
The research team will now return to the rock formation where the sample was extracted to see if they can find more bones.
“Then, because it's so large, we actually need to shift some of our investigations to try to understand the paleoenvironment and the environment in which this animal lived so that we can begin to understand what was so special in New Mexico that this animal adapted to life,” Fiorello said. It's about getting big.”
When the lower jaw was first found, there weren't many T. rex specimens, Fiorello said.
The identity of T. mcraeensis has been revealed after all these decades thanks to Sebastian J. Dahlmann, first author of the study and a museum research associate and paleontology consultant at the Springfield Science Museum in Massachusetts.
Spencer Lucas/Courtesy of New Mexico Department of Cultural Affairs
About a quarter of a fossilized skull of Tyrannosaurus mcraeensis has been found in an area known as Elephant Butte, New Mexico.
While studying the bones starting in 2013, Dallman was the first person to suggest they “might be something different,” Fiorello said.
As the largest predator of its time, Tyrannosaurus rex has received near-constant attention from the paleontological community, both professional and amateur, for decades. According to Fiorello, a fascination with this ferocious giant and outsized roles in popular films like “King Kong” and “Jurassic Park” has fueled scientists and amateur fossil hunters alike in their search for more T. rex bones.
“This improved our sample size,” he said. “That set the table when Sebastian started looking at our specimen and saying, 'Hey, these don't actually look like the famous T. rex specimens from places like Montana.'
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