A controversy that has stirred the world of paleontology for three decades could end. In 1988, a paleontologist by the name of Robert Bakker claimed that a dwarf species of tyrannosaurs existed. He reclassified a specimen discovered in 1942, exhibited at the Cleveland Natural History Museum and named Nanotyrannus .
A fossil from another small tyrannosaurus was discovered in 2001 this time in Montana. Named Jane, the animal was quickly described as a juvenile Tyrannosaurus rex. But a minority of specialists claimed that it belonged to this "pygmy" species, Nanotyrannus , based on the morphology of the skull and bones, different from that of adult T-Rex. Finally, in a study published Wednesday by Science Advances , paleontologists confirmed that this fossil and another, called Petey, were immature individuals, not adults. By extension, they therefore consider the existence of Nanotyrannus unlikely.
13 and 15 year old T-Rex
For their study, paleontologists performed a microscopic analysis of the interior of the tibia and femur bones. "Fossils are really cool because bones fossilize down to the microscopic level," says Holly Woodward of Oklahoma State University. "We can infer the growth rate, the age and the level of maturity". The researchers were 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 the still limited knowledge of the 20 years that separate the hatching of tyrannosaurs from their adulthood. Jane, who was only supposed to weigh one ton, died just before the exponential growth phase, which would have brought her to the adult mass of around 9.5 tons. "Everyone loves T-Rex, but we don't know much about how they grow," said Holly Woodward. "It is probably the most famous dinosaur in the world, but we mainly have only very large skeletons". Only five to seven young T-Rex fossils are today preserved worldwide, some of which are in private collections and inaccessible to researchers.
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