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They Want To Divide T. Rex Into 3 Species. paleontologists


They found some samples difficult to classify. But the 26 appeared to be grouped in three types, Mr. Paul said: a solid form with two sets of incisors on their lower jaws from the head of Hell Creek, and a later robust and graceful form with only one incisor.

Mr. Paul and his colleagues concluded that these three forms were probably sufficiently different from each other that they had emerged for long enough to warrant separate names. Hence, the earliest, cumbersome Tyrannosaurus to appear in Hell Creek was named Tyrannosaurus imperator (“emperor tyrant lizard”), and later – for one million to two million years – the robust Tyrannosaurus rex and the newly named relatively slender Tyrannosaurus regina (tyrannosaurus) lizard queen).

This proposed evolutionary trajectory – from one tank-like population to the next relatively agile – matches ecosystems dominated by Tyrannosaurus relatives in the early Cretaceous period, Mr. Paul said. At that time, bruises like Daspletosaurus coexisted with long-legged predators like Gorgosaurus.

Dr. According to Holtz, such an idea is perfectly plausible—but proving it will require support from future findings.

Dr. “It’s a testable hypothesis, as any statement of species identity should be,” Holtz said. “With additional new samples, we can see if the samples they don’t include or that we haven’t found yet are consistent with this recommendation or if they reject it.”

Dr. Holtz noted that the authors’ case would be more convincing if the different species they described were arranged more chronologically in certain rock strata, while the Hell Creek Formation contained other examples of species diversity. Dr. Other fossils found there lead to general agreement that there was more than one species of triceratops, Holtz said. And it’s possible that the hadrosaurs at the top of the formation and the dome-headed Pachycephalosaurus were significantly different from those at the bottom.

Dr. “At the same time, in the same place, classes of organisms of the same size cross over a number of species,” Holtz said. “It’s not inconceivable that Tyrannosaurus did that too.”



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