Tyrannosaurus rex might have been three species of dinosaur instead of one. Fresh analysis of Tyrannosaurus skeletons has revealed physical differences in the femur* and dental structures across specimens* that could indicate the mighty king of dinosaurs should be reclassified* as three distinct species.
Published in Evolutionary* Biology*, the research suggests that the larger specimens should be attributed* to a new species called Tyrannosaurus imperator (tyrant lizard emperor) and the smaller, more slender specimens should be attributed to a species called Tyrannosaurus regina (tyrant lizard queen).
Tyrannosaurus rex is currently the only recognised species of the group. Previous research has acknowledged variation across Tyrannosaurus skeletal remains in the femur and specimens with either one or two slender incisor teeth on each side of the front ends of the jaw.
Researcher Gregory Paul and colleagues* analysed the bones and dental remains of 37 Tyrannosaurus specimens. The authors compared the robustness* of the femur in 24 of the specimens, with length and circumference* helping to indicate the strength of the bone. They also measured the diameter* of the base of teeth or space in the gums to assess if specimens had one or two slender incisors.
The authors found that the femur varied across specimens, with two times more robust femurs than thin ones across specimens – suggesting the difference was not between males and females, which would likely result in a more even split.
The authors argued that the variation was not related to age either, as robust femurs were found in some juvenile specimens and slim femurs were found in some full-size adults.
Dental structure also varied across specimens.
“We found that the changes in Tyrannosaurus femurs are likely not related to the sex or age of the specimen,” lead author Mr Paul said. “We propose that the changes in the femur may have evolved over time from a common ancestor* who displayed more robust femurs to become more gracile* in later species.
“The differences in femur robustness across layers of sediment* may be considered distinct enough that the specimens could potentially be considered separate species.”
But there are difficulties trying to assign fossil vertebrates to potential new species and researchers could not rule out extreme individual differences as the cause of variation. They nonetheless concluded that the level of variation found in the Tyrannosaurus specimens, combined with their relative position in sediment layers, could signify the two new species.
Argentinian scientists have meanwhile unearthed the remains of a previously unknown species of another meat-eating dinosaur that lived about 70 million years ago. It had such little arms that it may have used its powerful head to ram its prey.
The fossil skull of the Cretaceous Period dinosaur, named Guemesia ochoai, was discovered in Argentina’s northwest. The researchers said it likely belonged to a carnivorous* group of dinosaurs called abelisaurs, which walked on two legs and had stumpy arms even shorter than the Tyrannosaurus rex.
“It’s so unique and so different from other carnivorous dinosaurs, which allows us to understand that we’re dealing with a totally new species,” said lead author of the study Federico Agnolin.
The animal, possibly a juvenile, lived just a few million years before an asteroid* wiped out about three-quarters of Earth’s species, including dinosaurs, about 66 millions years ago.
“We know it had a very sharp sense of smell and was shortsighted,” said Mr Agnolin, noting that it would have walked upright on its large feet, with its solid cranium* leading the way.
“Some scientists think that could mean the animal hunted its prey by charging them with its head.”
The discovery adds to Argentina’s reputation as a treasure trove of fossils of dinosaurs and other prehistoric creatures.
GLOSSARY
- femur: thighbone, upper bone of the leg or hind leg
- specimen: plant or animal of a particular species or type examined by scientists
- reclassified: assign to a different class, category or group
- evolutionary: relating to the gradual change and development of species
- biology: study of living organisms including plants and animals
- attributed: assigned, ascribed, allocated
- colleagues: associate, co-worker, teammate
- robustness: quality of having strength and health
- circumference: outer boundary, perimeter, line around a circle
- diameter: a line through the centre of a circle or sphere from one side to the other
- ancestor: earlier animal, plant or person from which others have come, forebear, predecessor
- gracile: slender, slight, thin, slim
- sediment: solid matter that settles at the bottom of liquid, especially earth and rock
- carnivorous: any meat-eating species
- asteroid: small, rocky objects that orbit the sun
- cranium: the skull, head, particularly the part enclosing the brain
EXTRA READING
New dino study is nothing to sneeze at
Young dinosaur was crocodile’s last meal
Case of mistaken dino identity
QUICK QUIZ
- What does “Tyrannosaurus imperator” mean?
- What does “Tyrannosaurus regina” mean?
- Researchers studied bones and dental remains of how may Tyrannosaurs?
- What wiped out the dinosaurs and when did it happen?
- What makes researchers think the Argentinian dinosaur used its head to ram prey?
LISTEN TO THIS STORY
CLASSROOM ACTIVITIES
1. Tyrannosaurus traits
Compare and contrast similarities and differences between the original Tyrannosaurus rex with the two new Tyrannosaurus species researchers think they have discovered by drawing two intersecting circles. Use the evidence provided in the Kids News article to complete your diagram.
Time: allow 20 minutes to complete this activity
Curriculum Links: English; Science; Critical and Creative Thinking
2. Extension
New dinosaur species are still being found around the world, including Argentina. Why is it important to continue this scientific research of what species did exist and how they lived?
Why do you think Argentina is a treasure trove?
Time: allow 10 minutes to complete this activity
Curriculum Links: English; Science; Critical and Creative Thinking
VCOP ACTIVITY
Adjectives
An adjective is a describing word. They are often found describing a noun. To start with, look at the words before the nouns.
Search for all the adjectives you can find in the article.
Did you find any repeat adjectives or are they all different?
Extension:
Pick three of your favourite adjectives from the text and put them in your own sentences to show other ways to use them.
Have you used any in your writing?
