The fossils of the first dinosaur¹ fossil from Washington State were collected along the shores of Sucia Island State Park in the San Juan Islands, and described in a study published May 20, 2015 in the open-access journal PLOS ONE by Brandon Peecook and Christian² Sidor from the Burke Museum of Natural History and Culture at the University of Washington. The fossils were discovered while collecting ammonite fossils (a nautilus-like creature) from a marine³ rock unit known as the Cedar⁴ District Formation. The authors of the study describe the fossil as the partial left femur of a theropod dinosaur, the group of two-legged, carnivorous dinosaurs⁵ that includes Velociraptor, Tyrannosaurus rex, and modern birds. The fossil is 16.7 inches long and 8.7 inches wide, but would have been over three feet long when complete. The dinosaur is from the Late Cretaceous period and is approximately 80 million years old. 

 

Although incomplete, the authors believe it is a theropod dinosaur femur due to the hollow middle cavity of the bone, where marrow⁶ was present, which is unique to theropods during this time period. The authors also point to a feature on the surface of the bone, the fourth trochanter, that is prominent and positioned relatively⁷ close to the hip⁸, which is a combination of traits known only in some theropods among dinosaurs. 

 

"This fossil won't win a beauty contest," lead author Dr. Sidor said. "But fortunately it preserves enough anatomy⁹ that we were able compare it to other dinosaurs and be confident of its identification." "The fossil record of the West Coast is very spotty when compared to the rich record of the interior of North America," said Peecook. "This specimen¹⁰, though fragmentary, gives us insight into what the West Coast was like 80 million years ago, plus it gets Washington into the dinosaur club!" 

 

Because the fossil is incomplete, paleontologists aren't able to identify the exact family or species it belonged to. However, Drs. Sidor and Peecook compared the fossil to other specimens¹¹ and were able to calculate and estimate that the complete femur would have been over a meter in length (1.17m)--slightly smaller than T. rex. 

 

Fossilized prehistoric¹² clams¹⁴ were also found inside the hollow part of the bone, which indicates the dinosaur fossilized in marine rock. These additional fossils are a rare occurrence, and provide scientists with a snapshot of other lifeforms that were present where the dinosaur fossilized. The accompanying fossilized clams are so well-preserved that Burke paleontologists were able to identify the clam¹³ species, Crassatellites conradiana. These clams lived in shallow water, so the authors suggest that it's likely the dinosaur died near the sea, was tossed by the waves, and eventually came to rest among the clams.

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