Two young brothers and their cousin were wandering through a fossil-rich stretch of the North Dakota badlands when they made a discovery that left them "completely speechless": a T. rex bone poking out of the ground.

Based on the size of the tibia, experts estimate the dino was 13 to 15 years old when it died and likely weighed around 3,500 pounds (1,587.57 kilograms)—about two-thirds of the size of a full-grown adult.

Ultimately, a Black Hawk helicopter airlifted the plaster-clad mass to a waiting truck to drive it to the Denver museum.

Lyson said more than 100 individual T. rex fossils have been unearthed, but many are fragmentary. It is unclear yet how complete this fossil is. So far, they know they have found a leg, hip, pelvis, a couple of tailbones and a good chunk of the skull.

The public will get to watch crews chip away the rock, which the museum estimates will take about a year.