Seattle's airport was once the site of a 12-foot giant sloth skeleton discovered near a runway

• A construction crew was working at the Seattle-Tacoma Airport in 1961 when they came across bones.
• The bones, which dated back 12,700 years, belonged to an extinct giant ground sloth.
• The giant sloth would've weighed more than a ton and towered around 12 feet.

Some airports in the United States see thousands of passengers a day but have stories largely unknown to travelers.

Take the Seattle-Tacoma International Airport - which, today, is a destination for planes, passengers, and pilots. But about 12,700 years ago, the area in Washington state was home to giant sloths the size of Mini Cooper cars.

Six decades ago, researchers unearthed bones of a giant ground sloth - an extinct animal that roamed the earth around the time of the most recent Ice Age - at the airport, according to Evan Bush of The Seattle Times.

In February 1961, a construction crew was working in a bog near one of the airport's runways, according to The Seattle Times.

Their work was put on pause when a crew member discovered some bones in the bog. Paleontologist Stan Mallory and archaeologist Robert Greengo from Seattle's Burke Museum were called in to excavate the bones, and a team discovered that they belonged to a Megalonyx, or giant ground sloth, according to HistoryLink, the online encyclopedia of Washington state history.

The majority of the sloth's 12-foot skeleton was found in the bog, with only its skull, and some neck and limb bones missing, The Seattle Times reported.

Professor Howard Coombs, the chair of the University of Washington geology department at the time of the excavation, told The Seattle Times that the skeleton was in excellent condition.

"You can even see the tiny scars left by muscles," Coombs said. "All we have to do to clean them is to put them under the faucet. Usually, you have to chip old bones out of hardened soil."

After some research and carbon dating, it was determined that the giant sloth skeleton dated back 12,700 years, The Seattle Times reported. According to The Seattle Times, it would've weighed about a ton. So it would have been about the size and weight of a Mini Cooper, according to HistoryLink.org.

The skeleton was determined to be the Jefferson ground sloth - or Megalonyx jeffersonii - and this was the first evidence that this species had been in Washington state, according to The Seattle Times.

According to the Burke Museum in Seattle, Megalonyx jefersonii and other types of giant sloths roamed North America during the Pleistocene era. This is when the most recent Ice Age occurred, Live Science reported.

Over the next 16 years, the museum created casts for the missing bones from other Megalonx specimens, which have been found across the country, according to The Seattle Times.

Using the casts, a complete skeleton was put on display at Seattle's Burke Museum. The Highline Heritage Museum in Burien, Washington, also has a re-creation of the giant 12-foot skeleton, where visitors can learn about the airport's surprising past.

The Burke Museum and the Highline Heritage Museum did not immediately respond to Insider's request for comments.