Raptorex, the tiny T. rex

Tyrannosaurus rex had a "murderous 'mini-me' in its family tree," said Alan Boyle in MSNBC. Paleontologists long thought that the massive T. rex, with its gigantic, powerful jaws marked the end the line in evolution's quest to create the perfect killing machine. A study in the journal Science says that a fossil unearthed in China proves that a T. rex-like predator dubbed Raptorex Kriegsteini, which was barely larger than a human, "had virtually all the lethal weapons brandished tens of millions of years later" by the massive T. rex.

Scientists are truly shocked, said Lizzie Buchen in Nature, to learn that "T. Rex's notoriously massive head, sharp teeth, and piddly-diddly arms first evolved in a runty ancestor one hundredth its size." It was accepted wisdom for years that T. rex's limbs withered into tiny things as the head and body expanded. (Read the Chicago Tribune's account of the Raptorex fossil's sketchy history.)

Raptorex's mouth was "most likely a primary weapon," said Michael D. Lemonick in Time, but "that alone wasn't enough of an advantage to let it evolve into the predator that would ultimately dominate North America and Asia." Larger predatory dinosaurs probably went extinct for other reasons, "allowing Raptorex-like creatures to begin growing." When T. rex arrived, with it's size, speed, and "bone-crushing" jaws, it reigned unchallenged until—as paleontologist Paul Sereno, a co-author of the Raptorex research, put it—"the comet hit."

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