Washington, 1 Jan 2020 (AFP) – For three decades, a controversy has stirred the world of paleontology: was there a dwarf species of tyrannosaurs?
A paleontologist named Robert Bakker had stated this in 1988 when reclassifying a specimen discovered in 1942.
Exhibited at the Cleveland Museum of Natural History, this specimen became the first member of a species named Nanotyrannus (dwarf tyrannosaurus).
In 2001, another team discovered the nearly complete fossil of another small tyrannosaurus near Ekalaka, Montana, in the famous Hell Creek formation.
The animal, named Jane, slightly larger than a draft horse, was quickly described as a juvenile Tyrannosaurus rex.
But a minority of experts continued to claim that it belonged to this "pygmy" species, Nanotyrannus, based on the morphology of the skull and bones, unlike that of the adult T-Rex.
In a study published Wednesday by Science Advances, paleontologists performed a microscopic analysis of the inside of the tibial bones and Jane's femur and another less complete fossil called Petey.
From this technique, paleohistology confirmed that both were immature individuals, not adults.
By extension, the authors consider the existence of Nanotyrannus unlikely.
"These fossils are really very useful because bones fossilize to the microscopic level," Holly Woodward of Oklahoma State University, who conducted the study, told AFP.
"We can infer growth rate, age and maturity level," he detailed.
Researchers were also able to count femur rings and spines, as they do on a tree trunk to determine their age: 13 years for Jane and 15 years for Petey.
Jane died shortly before the exponential growth phase, which would have led her to an adult mass of about 9.5 tons. It was believed that it weighed "only" a ton.
"Everyone loves the T-Rex, but we don't know much about how they grow," said Holly Woodward.
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