Agile and vicious Nanotyrannus was not just a teenage T. rex
Nanotyrannus and Tyrannosaurus are both members of a lineage of meat-eating dinosaurs called tyrannosaurs, but they are not the same genus, the researchers said.
In the twilight of the age of dinosaurs, an agile and ferocious predator named Nanotyrannus prowled across western North America, resembling a smaller version of North America. Tyrannosaurus – about one-tenth of body mass – but with a few important anatomical differences.
That’s the finding of a new study that concludes that Nanotyrannus has been at the center of a debate among paleontologists for years about whether it was merely a juvenile version of it. Tyrannosaurus – it was actually a distinctive dinosaur.
Researchers examined Nanotyrannus fossil specimens unearthed in Montana in 1942, 2001 and 2006 and dated to about 67 million years ago, and determined that the individuals were adults and not juveniles based on features in the bones, including annual growth rings.
They also found that Nanotyrannus was anatomically different from itself.older cousin Unlike the two-toed Tyrannosaurus, it had more teeth, a crest in front of its eyes, an air sinus in a specific bone at the back of the skull, and the presence of a vestigial third finger.
A handout illustration shows a herd of dinosaur Nanotyrannus attacking a juvenile Tyrannosaurus in what is now Montana 67 million years ago. (Source: Report via Anthony Hutchings/REUTERS)
carnivorous dinosaurs
Nanotyrannus and Tyrannosaurus are both members of a lineage of meat-eating dinosaurs called tyrannosaurs, but they are not the same genus, the researchers said. A genus is a group of closely related species that share similar characteristics. For example, lions, tigers, leopards, and jaguars are from the same genus, Panthera, but each represents a different species.
The genus name Tyrannosaurus means “cruel lizard”, while the species name “rex” means “king”. The genus name Nanotyrannus means “dwarf tyrant”.
“T. rex was a massive predator adapted to having incredible bite forces. Nanotyrannus was a slender, agile predator that could run circles around the tyrannical king,” said paleontologist Lindsay Zanno of North Carolina State University and the North Carolina Museum of Natural Sciences, lead author of the study published Thursday in the journal Nature.
Zanno said the new analysis puts to rest the debate about Nanotyrannus.
“It is not biologically possible to conclude that this is a juvenile T. rex,” Zanno said.
The size differences were very noticeable. Nanotyrannus had about 10% of its body mass – around 1,500 pounds (700 kg) and 15,000 pounds (7,000 kg). And it had about half the linear dimensions – about 18 feet (5.5 meters) and roughly 40 feet (12.2 meters) long and 7 feet (2 meters) and 13 feet high.
“Nanotyrannus and T. rex are extremely different,” said paleontologist and anatomist James Napoli from Stony Brook University in New York, one of the authors of the study.
Nanotyrannus was a hunter built for speed and agility, with long legs, a long snout with blade-like teeth, and strong arms to manipulate its prey. Tyrannosaurus was a massive predator built for strength, with stocky legs, an enormous head, thick, banana-shaped teeth, and greatly reduced arms.
“I suspect these two species may occasionally engage in conflict as predators do, but Nanotyrannus’ long legs and small size suggest it mostly hunted smaller, faster prey than Tyrannosaurus,” Napoli said.
The researchers also determined that the Nanotyrannus specimens had enough anatomical differences to separate them into two separate species: Nanotyrannus lancensis and the newly named Nanotyrannus lethaeus. One of the Nanotyrannus fossils was part of the famous “Dueling Dinosaurs” specimen, which fought the horned dinosaur Triceratops at the moment of its death.
Some scientific studies of how Tyrannosaurus matured were based on the idea that Nanotyrannus fossils represented T. rex juveniles; these include hypotheses that postulate that this apex predator experienced an extreme growth rate.
“For decades, paleontologists have unwittingly used Nanotyrannus specimens as a model for understanding the biology of juvenile T. rex, Earth’s most famous dinosaur. These studies need a second look,” Zanno said.
The finding that Nanotyrannus and Tyrannosaurus shared the landscape along with countless plant-eating dinosaurs provides the latest evidence that dinosaur diversity was rich before the asteroid impact 66 million years ago that ended the age of dinosaurs.
“This discovery tells us that dinosaurs continued to evolve, innovate and diversify until their reign ended. This dovetails with growing evidence that, contrary to what we once thought, dinosaurs did not decline for millions of years before going extinct,” Napoli said.
