North America is a hotspot for dinosaur fossils. Not only is it among the world leaders in terms of the amount of specimens found, but it’s actually produced the highest number of different species. Some areas have been jackpots, like Alberta in Canada, or Montana in the United States. But not all states have been fruitful; 14 have been dry of dinosaurs, including Washington. And to make Washington state feel even more left out of the dinosaur discovery party, specimens had been recovered in neighboring Idaho and Oregon, and also nearby Montana and California.
Researchers were therefore understandably overjoyed when a long-overdue fossil finally turned up recently, discovered on the shores of Sucia Island State Park in the San Juan Islands archipelago, northwestern Washington. Before you get too excited, it’s only a portion of a leg bone, so scientists don’t know to what species it belonged. Regardless, in a collaborative effort, scientists from Burke Museum and the University of Washington have been scrutinizing the specimen in search of every detail they can find, and their report has now been published in the journal PLOS ONE.
The newly described, 42-centimeter-long (16.7-inch-long) bone fragment was happened upon by a bunch of Burke Museum researchers whilst they were scouring marine rocks in the Cedar District Formation. After noticing the fossil poking out through the surface of a rock, the team carefully excavated it and returned it to the museum for further examination.
Although it doesn’t give us enough information to be classified, researchers were able to determine that it was a chunk of a left femur that would have been around a meter in total length, or just over three feet. They were also able to give it an approximate age of 80 million years old, which places it from the Late Cretaceous period.
But what was perhaps more impressive is that this fragment had enough tell-tale signs for the researchers to conclude that it once belonged to a theropod, the two-legged, “beast-footed” carnivores such as the T. rex. The features that gave away the creature’s group were the presence of a hollow middle cavity that housed the bone marrow and a prominent surface feature that would have been near the animal’s hip. According to the researchers, this particular combination of characteristics has only so far been described in theropods.
Interestingly, the researchers also found ancient, prehistoric clams inside the bone cavity, suggesting that the animal’s skeleton fossilized in marine rock. Given the fact that all dinosaurs lived on land, rather than in the sea, this is quite a rare and unexpected find. This is also the reason that the West Coast has been rather scantily clad in terms of dinosaur fossils when compared with other areas of North America, since much of it was submerged during the dinosaur era.
So how did this fossil end up in the San Juan Islands? Although the researchers can’t be sure, it has been speculated that the rocks that form this archipelago today may have been deposited further south around the time that the animal died. Geological processes could have therefore caused the rocks to shuffle around and end up further along the coast.