Alamosaurus was a massive plant-eater (herbivore) that lived in the late Cretaceous period, between about 70 and 65 million years ago, in North America - in the region that is today the southwestern part of the United States.
Alamosaurus was usually around 69 feet (21 meters) long, and probably weighed around 33 tons.
The first fossils of Alamosaurus were found by Charles W. Gilmore in 1922. He found a pelvic bone ("ischium") and a shoulder bone ("scapula"). Later in 1946, Gilmore discovered further fossils, including a complete tail, a nearly complete right forelimb, and both pelvic bones ("ischia"). Various other Alamosaurus fossils have also subsequently been found in the southwestern US, but no skull material (other than a few teeth) have yet been found.