Mysterious Large Carnivore Is First Dinosaur Discovered in Washington State

A large carnivore that lived on what’s now the San Juan Islands probably had many distinguishing characteristics that we don’t know about. But for now, it can claim at least one important distinction: the first fossil dinosaur ever to be found in Washington State.

Somewhat smaller than T. rex — and likely a relative of the famous predator — the dinosaur was a large theropod, the type of bipedal meat-eaters that include raptors and tyrannosaurs.

But beyond that, not much more is known about Washington’s first known dinosaur, because all that’s been found of it, at least so far, is a chunk of its thigh bone.

“This fossil won’t win a beauty contest,” said Dr. Christian Sidor, of the Burke Museum of Natural History and Culture, in a press statement.

“But fortunately it preserves enough anatomy that we were able compare it to other dinosaurs and be confident of its identification.”

Though only about 42.5 centimeters long, the fossil fragment was in tact enough to produce a few important clues.

Among them were a hollow center cavity where marrow was once present — a trait unique to theropods among dinosaurs at the time, Sidor said — and also a telltale flange of bone, called a trochanter, that flared out to meet the hip bone in a way that indicated the animal stood on two legs.

Multiple views show the fragment of a femur belonging to an unknown type of theropod found in Washington’s San Juan Islands. (Photo courtesy Peecook et al.)

Based on the size of the fragment, Sidor and his colleague, Burke paleontologist Brandon Peecook, estimate that the entire thigh bone of the animal probably measured about 1.2 meters, which would put the Washington dino just under the average height of Tyrannosaurus rex, which stood from 4.5 to 6 meters tall. [Read about a recent related discovery: “New Tyrannosaur Species, ‘King of Gore,’ Reveals Origins of T. Rex“]

Indeed, the paleontologists believe that the newfound specimen was probably a member of T. rex‘s broader family, a group known as tyrannosaurids.

This “seems likely given its size and the widespread occurrence of the group” throughout the American West, they write, in their paper announcing the find.

Researchers discovered the fossil along the shoreline of Sucia Island State Park in the San Juan Islands, while initially searching for some of Washington’s more prevalent fossil specimens: the nautilus-like molluscs known as ammonites.

Although Washington has produced a wealth of fossils, most have been either of ancient marine creatures — like ammonites and trilobites — or of Ice Age fauna, such as mastodons and Columbian mammoths, which roamed the region until 10,000 years ago.

But Washington has never produced a dinosaur until now, partly because, for most of the era when dinosaurs ruled the land, known as the Mesozoic, western Washington was under water.

The site where the specimen died some 80 million years ago was clearly a marine environment, Sidor and his colleagues noted, because ancient saltwater clams had made a home for themselves inside the cavities of the dead dinosaur’s bone before they, too, fossilized.

The new specimen’s discovery indicates that there are more dinosaurs waiting to be discovered in Washington and elsewhere throughout the Pacific Northwest, Sidor and Peecook said, and it’s further evidence of the animals’ wide diversity and distribution.

A map shows the known assemblages of fossil dinosaurs found along what was the Pacific Coast during the Late Cretaceous. (Map by Peecook et al.)
[See how far tyrannosaurs really ranged: “‘Cool’ New Arctic Tyrannosaur Discovered in Alaska Fossil“]

“The Washington theropod represents one of the northernmost occurrences of a Mesozoic dinosaur on the west coast of the United States and one of only a handful from [what was] the Pacific Coast … during the Cretaceous,” the pair writes.

“The fossil record of the West Coast is very spotty when compared to the rich record of the interior of North America,” Peecook added in a press statement.

“This specimen, though fragmentary, gives us insight into what the West Coast was like 80 million years ago.

“Plus it gets Washington into the dinosaur club.”

Sidor and Peecook report their find in the open-access online journal PLOS.

Peecook, B., & Sidor, C. (2015). The First Dinosaur from Washington State and a Review of Pacific Coast Dinosaurs from North America PLOS ONE, 10 (5) DOI: 10.1371/journal.pone.0127792

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