New Mexico Unearths T rex's Prehistoric Giant Cousin
Newly discovered in New Mexico, T mcraeensis, previously mistaken for a T rex, unveils evolutionary mysteries This newfound species, shedding light on why tyrannosaurs evolved into colossal giants, provides groundbreaking insights
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A new study released Thursday has identified a previously unknown relative of the legendary Tyrannosaurus rex, providing paleontologists with an important clue in understanding the evolutionary chain that led to the massive predatory dinosaur.
DTGN0M Megalosaurus jaw
Natural History Museum/Alamy Stock Photo
Megalosaurus, the first ever dinosaur discovery
The creature called Tyrannosaurus mcraeensis likely roamed the Earth up to 7 million years before the emergence of T. rex. Its bones, which have been dated to 72-73 million years old during the late Campanian-early Maastrichtian Period, were discovered decades before the creature officially received its scientific name. About one-quarter of its fossilized skull was found in the 1980s and early 90s in what is now known as Elephant Butte, New Mexico. The bones were initially classified as T. rex by the New Mexico Museum of Natural History & Science due to their size, with T. rex being known to grow up to 39 feet (12 meters) long and weigh up to 10 tons.
T. rex vs. its relative
There were two big differences between T. rex and T. mcraeensis.
"The lower jaw in a Tyrannosaurus rex is notably strong. Our jaw is certainly large and full of teeth, but it is slimmer compared to the robust jaw of a Tyrannosaurus rex," explained Anthony R. Fiorillo, coauthor of the study published Thursday in the journal Scientific Reports. The robust jaw of T. rex allowed it "freedom to do whatever it pleased. A slimmer jaw, despite its large teeth, would result in less biting force."
A mandible fossil from the newly discovered Tyrannosaurus mcraeensis. Its jaw was more slender than that of the robust Tyrannosaurus rex.
Courtesy NMMNHS
T. rex had a prominent ridge over its eyes, believed to help attract mates, much like antlers on deer or elk, while T. mcraeensis had a much more subtle ridge.
The authors wrote that giant tyrannosaurs most likely appeared as an evolutionary response to the presence of large herbivores. However, the study still considers the evolution of giant plant-eating dinosaurs as an unexplained mystery.
On April 1, 2014, the Field Museum of Natural History in Chicago, Illinois displayed Sue, one of the largest, most extensive, and best-preserved Tyrannosaurus rex specimens ever found, as part of its permanent collection. The image was captured by Brett T. Roseman for The Washington Post/Getty Images.
New research on T. rex fossils challenges the belief that the king of dinosaurs was misunderstood. Fiorillo pointed out that this idea is currently highly speculative, but also noted that, unlike the pygmy tyrannosaur found in the Arctic called Nanuqsaurus hoglundi, T. mcraeensis likely did not experience extreme changes in temperature and light in southern North America, allowing it to continue growing. While Arctic conditions may have contributed to N. hoglundi's small size, overall, other tyrannosaurids from the same era were much smaller than T. mcraeensis.
The research team will revisit the rock formation where the specimen was discovered in hopes of uncovering more bones. They also plan to shift their focus towards studying the paleoecology and environment in which the animal lived, in order to understand why it adapted to grow so large in New Mexico. According to Fiorillo, this will provide insight into what made the region special for the animal's evolution.
A tyrannosaur sleuth
When the lower jaw was first found, there werent many T. rex specimens out there, Fiorillo said.
Sebastian G. Dalman, an associate researcher at the museum and a paleontological consultant with the Springfield Science Museum in Massachusetts, finally uncovered the identity of T. mcraeensis decades later.
About one-quarter of a fossilized skull from Tyrannosaurus mcraeensis was found in an area known as Elephant Butte, New Mexico.
Spencer Lucas/Courtesy NM Department of Cultural Affairs
Dalman was the first to suggest in 2013 that while studying the bones, they "might be something different," according to Fiorillo.
T. rex, as the largest apex predator of its time, has garnered continuous attention from the paleontological community, both professional and amateur, for many years. The creature's portrayal in popular films such as "King Kong" and "Jurassic Park" has increased the excitement of scientists and amateur fossil hunters alike in their quest for more T. rex bones, Fiorillo noted.
"He said that our sample size had increased, which set the stage for Sebastian to notice that our specimens did not resemble the famous Tyrannosaurus rex specimens from places like Montana."
