The scientists who collected it are pretty sure it’s from a big carnivorous theropod in the T. rex lineage, such as Daspletosaurus torosus (illustrated below), Gorgosaurus libratus, Teratophoneus curriei, or Bistahieversor sealeyi. They found it at the shore of Sucia Island State Park in the San Juan Islands.
The fossilized fragment of the animal’s left femur is about 17 inches long and 9 inches wide. Its full length would have been more than three feet – fitting a theropod the size of Albertosaurus, Daspletosaurus, or Acrocanthosaurus, but smaller than Tyrannosaurus, according to Brandon Peecook and Christian Sidor from the Burke Museum of Natural History and Culture at the University of Washington.
Inside the hollow part of the bone, they found fossilized clams, which suggests that the Late Cretaceous beast died near the sea 80 million years ago and was swept by waves to decompose in a lagoon or inlet.
The photograph above shows a posterior view of the fossil paired with a drawing of the complete left femur modeled after that of Daspletosaurus torosus. (Credit: Peecook and Sidor [CC-BY])
In Oregon, there is only one Mesozoic dinosaur fossil on record, and the record is sadly sketchy. The single bone, the sacrum, is from some kind of hadrosaurid, or duck-billed dinosaur. A paleontologist named David Taylor collected the fossil from a sandstone outcrop above the surf at Cape Sebastian in 1995. Although the find was documented by a television crew, it seems Taylor never formally described the fossil and nor did he place it in a public repository. Peecook and Sidor could find no such records and neither could I.
The First Dinosaur from Washington State and a Review of Pacific Coast Dinosaurs from North America. Peecook BR, Sidor CA PLoS ONE (2015)