PACIFIC NW MAGAZINE: ‘Spirit Whales & Sloth Tales’ tracks Washington fossils and their stories
With more than a half-billion years of history, Washington state has an enviable diversity of fossils. Each is unique. Each is interesting. Each tells a story of natural and human history. Here are two such stories.
The Sea-Tac Sloth (Megalonyx jeffersonii)
THE WASHINGTON CONNECTION to Megalonyx began Feb. 14, 1961, at Seattle-Tacoma International Airport with the first known discovery of giant sloths in the state. Workers excavating a hole for a lighting tower saw bones in the bottom of their work pit. Alerted to the discovery, the Burke Museum sent a paleontologist and an archaeologist to investigate. Although flooding and collapsing walls made the dig difficult, the construction crew and scientists extracted the skeleton, which rested in a peat layer 13 feet thick, representing what was once a marshy wetland.
Most of the skeleton was intact, except for the skull, which was crushed and mostly missing. Based on the shape of the pelvis, which was 45 inches wide, as well as the limb bones and claws, the Burke paleontologist determined that the bones came from the extinct giant sloth, Megalonyx jeffersonii, or Jefferson’s ground sloth. Since the initial discovery, other isolated bones and claws of Megalonyx have been found in Eastern Washington Scablands’ megaflood deposits and dated at 12,100 years before present. Bones and teeth of a considerably older sloth, Megalonyx leptostomus, also have been found in Pliocene sediments in Eastern Washington, dated around 4.9 million years old.