Scientists say they found Washington state’s first dinosaur fossil

Scientists at the Burke Museum in Seattle announced Wednesday that they have discovered the first dinosaur fossil found in Washington State — a 35-foot ancestor of Tyrannosaurus rex that lived here 80 million years ago.

A team of Burke researchers found the fossil along the shore of Sucia Island in the San Juan Islands, and according to paleontologists, it amounts to irrefutable evidence that dinosaurs once lived in this corner of the country.

“I want to introduce you today to Washington state’s first dinosaur,” Christian Sidor, curator of vertebrate paleontology at the Burke Museum, said at a small unveiling ceremony at the museum.

The fossil, about the size of a large loaf of bread, is part of the dinosaur’s left leg bone, or femur. It measures about 17 inches long and about 9 inches wide.

Burke paleontologists estimate the complete femur measured about 4 feet long, leading them to conclude the entire creature was about 35 feet long.

Because the fossil is incomplete, paleontologists haven’t been able to conclusively identify the family or species it belonged to.

“We know it’s a large carnivorous dinosaur, and that’s about it,” Sidor said.

However, the leg bone most likely belonged to a theropod, a group of two-legged, carnivorous dinosaurs that includes Velociraptor, Tyrannosaurus rex and modern birds, said Sidor and Brandon Peecook, a University of Washington Department of Biology graduate student.

The fossil was discovered by a group of Burke museum researchers collecting fossil shells from a marine rock formation on Sucia Island’s south shore on May 18, 2012.

“It was found almost by accident,” said Peecook, who was part of a team of paleontologists called to the site to help excavate the fossil from the rock that encased it. “We thought it would be a marine reptile.”

Back in the lab, Sidor and Peecook said, as they separated the fossil from surrounding rock, they made two discoveries that led them to conclude it was from a dinosaur.

First, the bone had a hollow middle cavity, where marrow was present. Second a prominent ridge on the bone (the fourth trochanter) was positioned relatively close to the hip, a combination of traits known only in some theropods.

Sidor and Peecook said the fact the fossil was encased in marine rock means the dinosaur probably died near the shore and was washed to the sea after being broken to pieces either by scavenging animals or tidal action.

Wednesday’s unveiling at the museum coincided with the publication of a paper by Sidor and Peecook in the scientific journal PLOS ONE.