For three decades, a controversy has agitated the world of paleontology: was there a dwarf species of tyrannosaurs?
A paleontologist by the name of Robert Bakker had affirmed it in 1988 by reclassifying a specimen discovered in 1942. Displayed at the museum of natural history of Cleveland, he became the first member of a new species baptized Nanotyrannus.
In 2001, another team discovered the almost complete fossil of another small tyrannosaurus near Ekalaka, Montana, in the famous Hell Creek formation. Baptized Jane, the animal, barely larger than a draft horse, was quickly described as a juvenile Tyrannosaurus rex.
But a minority of specialists continued to claim that it belonged to this “pygmy” species, Nanotyrannus, based on the morphology of the skull and bones, different from that of adult T-Rex.
In a study published Wednesday by “Science Advances”, paleontologists performed a microscopic analysis of the interior of Jane’s tibia and femur bones, and another less complete fossil, named Petey.
This so-called paleohistology technique confirmed that the two were immature individuals, not adults. By extension, the authors consider the existence of Nanotyrannus unlikely.
“Fossils are really cool because bones fossilize down to the microscopic level,” Holly Woodward, of Oklahoma State University, who conducted the study, told AFP. “We can infer the growth rate, the age and the level of maturity”.
The most famous dinosaur in the world
The researchers were also able to count the rings of the femurs and shins as they are counted in a tree trunk to derive their age: 13 years for Jane and 15 years for Petey.
The study thus completes our still limited knowledge of the 20 years that separate the hatching of tyrannosaurs from their adulthood. Jane, who was to weigh only one ton, died just before the exponential growth phase, which would have brought her to the adult mass of about 9.5 tons.
“Everyone loves T-Rex, but we don’t know much about how they grow,” says Holly Woodward. “It is surely the most famous dinosaur in the world, but we mainly have only very large skeletons”.
This is the consequence of the frenzy of collectors and the public for the most monstrous T-Rex possible, to the detriment of smaller specimens. Only five to seven young T-Rex fossils are today preserved around the world, some of which are in private collections and inaccessible to researchers, she regrets.
(Afp / nxp)
Created: 01.01.2020, 20h53