The leg bone weighs 15 pounds, is 16.7 inches and is the first dinosaur fossil found in Washington. Much of the region was under water during that era 80 million years ago.

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The fossil has the very sexy name of UWBM 96770, but at the Burke Museum, they’re pretty excited.

The fossil is not that big — 16.7 inches long, weighing maybe 15 pounds.

But it is the first dinosaur bone ever found in this state.

It was a leg bone from an animal from the T. rex family, but smaller by tyrannosauroid standards — around 36 feet long.

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Still, think of a transit bus to imagine its size. Think of a carnivorous transit bus with bone-crunching teeth.

The fossil is a rarity in this state because it goes back 80 million years.

Much of the land mass that encompasses our region didn’t exist in those days. It was mostly under water; obviously, not a place for land-roaming big guys.

That’s why our official state fossil is much younger.

The Columbian mammoth, with its big, curved tusks, was found in Western Washington until as recently as 10,000 years ago.

In fossil research, excitement is measured in a different way than how you and I might measure excitement.

This fossil was found in April 2012. Three years later, we have the big unveiling.

“It’ll be a point of civic pride for this state. We’re now the 37th state to have found a dinosaur fossil,” says Brandon Peecock, a University of Washington graduate student and co-author of the paper about the find.

As can happen with such discoveries, it was by accident.

The fossil was found along the shore — at the high-water mark — at Sucia Island State Park in the San Juans.

UW researchers were collecting fossils of extinct marine invertebrates called ammonites. Those fossils look like spiral shells.

But then the researchers came upon an unusual sight: “A slightly discolored, whitish lump, and they could see spongy bone texture. It was different from the surrounding rock where it was embedded,” says Christian Sidor, Burke Museum’s curator of vertebrate paleontology.

The fossil was chiseled out over a period of hours. It came out in three pieces, later reassembled with epoxy glue.

“For a long time, we thought very little of the specimen,” says Sidor, the other co-author on the paper. “We didn’t think we could identify it, other than as a large piece of bone. Then we found a critical piece of anatomy.”

Welcome to CSI: Dinosaurs.

The fossil they had found was part of a femur.

The way the researchers could tell it was from a land animal and not an aquatic one was from the large muscle scars on the bone.

A dinosaur would have pronounced scars because it was using a lot of muscle to move around. The fossil chunk they had, concluded the researchers, was from a femur more than 3 feet long.

Given that we’re talking about a 1½-foot fossil from 80 million years ago, the scenarios about how it got there are best guesses.

This state is a result of a lot of land movement.

At one point, there was an inland sea separating North America into two large land masses.

Because the region rock-and-rolled to its present physical state, “and various geological processes smashed up,” says Sidor, geologists have debates about what happened.

Maybe something like the fossil found in the San Juans was from a dinosaur that had lived around here. That would mean that maybe this region wasn’t as covered by water as previously thought, says Sidor.

Or maybe the bone made its way up from Oregon, Northern California or as far south as Baja California. The latter would have meant 2,000-plus-miles of travel, says Sidor.

The fossil will be on display at the Burke beginning Thursday.

And, oh, in case you were considering going to the San Juans to look for your own fossils: The answer is, no, at least on state land.

Permits are issued only for “legitimate scientific research,” and a souvenir for your fireplace mantel doesn’t count.