Sinotyrannus lived about 60 million years before T. rex, a time when every other tyrannosaur we knew of could fit in the back of a pickup truck. Could this one find really rewrite tyrannosaur history? I had the sinking feeling that this fossil would remain a problem for a long time. This happens all too often in the field of dinosaur research: a single fossil emerges that hints at a major evolutionary story—the oldest member of a major group, or the first fossil to exhibit a really important behavior or feature of the skeleton—but it’s too broken or incomplete or poorly dated to be certain.
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