The first dinosaur fossil described from Washington state (left) is a portion of a femur leg bone (full illustration right) from a theropod dinosaur. Theropods are a group of meat-eating, two-legged dinosaurs, including T. rex and Velociraptor. The fossil was discovered by Burke Museum paleontologists at Sucia Island State Park in the San Juan Islands. (Illustration courtesy of PLOS ONE, modified by the Burke Museum.)

Washington just became the 37th state to find a confirmed dinosaur fossil -- and it may be the last.

Burke Museum Curator of Vertebrate Paleontology Christian Sidor, one of the leaders of the new study published Wednesday in PLOS ONE that announces the find, didn't think his team would ever be able to identify the bone in question. The fossil, found in hard inter-tidal rock in Sucia Island State Park in 2012, was big enough to get noticed at nearly 17 inches long -- but it was just one fragment of one bone.

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"In the year and a half that it waited in the museum queue to be prepared, I was pretty dubious about our being able to identify it as anything more than a large bone," Sidor said.

But then he saw the side of the bone that the attached rock had been hiding, and he changed his tune.

The part of the bone that had been embedded in rock has a muscle ridge found in land animals. Most of Washington state was covered in water at the time of the dinosaurs, which is probably why none had been found before. But if the fossil wasn't part of a marine creature, that meant there was a chance. And when Sidor and his team realized that the bone was hollow -- a trait that birds inherited from their dinosaur ancestors -- it was time to go compare it with known dinosaur bones.


Christian Sidor, Burke Museum curator of vertebrate paleontology, and Brandon Peecook, University of Washington graduate student, show the size and placement of the fossil fragment compared to the cast of a Daspletosaurus femur. (Burke Museum)

"We went to museums with fossils of the same age and compared them," Sidor said, "And that's when I became really convinced that what we had was the upper part of a carnivorous dinosaur's thigh."

Because the fossil is such a tiny piece of the dinosaur, any further identification is impossible for now. Sidor is certain it's a theropod -- the group that includes carnivorous dinosaurs like T. rex -- and it lived during the Late Cretaceous, about 80 million years ago. But that's all we can say.

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According to Sidor, his team's big first may be the nation's last. Washington was pretty much the last state with a reasonable hope of dinosaur fossils that hadn't had any turn up yet. The remaining 13 all have pretty good excuses. Hawaii, for example, is only 6 million years old, which is way past dino time. Other states, like Florida and Louisiana, were probably totally underwater at the time. And in a lot of Northeastern states, Sidor explained, all the rocks from the dinosaur era were scraped away by glaciers long ago.

"We may actually be the last state to find its first dinosaur," he said.

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