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Palaeontology: The sister of the Tyrannosaurus rex
One of the most intriguing mysteries surrounding the most famous of all dinosaurs, the dreaded Tyrannosaurus rex, concerns its origins. However, according to a recent study published in the scientific journal Scientific Reports, at least one related species of T. rex existed in the same region six to seven million years before it. The twelve-metre-long, six-tonne animal appeared seemingly out of nowhere at the end of the Cretaceous period in what is now North America. Despite intensive searches, no fossils of ancestors have yet been found that could explain the evolution of the T. rex.
Origins of tyrannosaurs in what is now North America
The newly discovered species was named Tyrannosaurus mcraeensis, and although it was not a direct ancestor of T. rex according to the palaeontologists, they did share a common ancestor. In their report, the researchers refer to T. mcraeensis as the sister of T. rex, but do not comment on the sex of the giant lizard fossil they analysed. The findings are based on the analysis of a fossilised dinosaur skull that was found in New Mexico in 1983 and was previously mistaken for the skull of a Tyrannosaurus rex.
The research team led by Sebastian Dalman from the New Mexico Museum of Natural History and Science identified differences between the two species that were minimal but clear. In particular, the shape of the skull bones of T. mcraeensis differed from those of T. rex. Another research group contributed to the confirmation by redetermining the age of the sediment layer in which the skull was found. This layer is therefore around 71 to 73 million years old, which is too early for the existence of a T. rex, which according to current knowledge lived several million years later.
The discovery of T. mcraeensis supports the hypothesis that the origins of tyrannosaurs lie in what is now North America, which was divided by a sea into the eastern region called Appalachia and the western region called Lamidia. According to the study in Scientific Reports, the root of the tyrannosaurs originated in southern Lamidia. Although the alternative theory that Tyrannosaurus originated in Asia and later migrated to North America has not yet been ruled out, it now seems less likely. Dinosaur fossils have also been found in Asia that are closely related to Tyrannosaurus rex, such as Tarbosaurus bataar and Zhuchentyrannus magnus, but which were somewhat smaller and lighter than T. rex.
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