Reconstructed and restored skeletons of Tyrannosaurus rex harassing an Alamosaurus sanjuanensis. CC BY 2.0
Alamosaurus sanjuanensis is estimated to have grown to approximately 30 m (98 ft) long and to have weighed up to 80 tons. That is a just a little more than 4 fully loaded school busses (we can call it 4 and a half just to be safe). If one were curious about length, that is about 10.6 m (8 ft) longer than two school busses; we can make that 2.2 school busses in length. Living immediately prior to the K-Pg (Cretaceous - Paleogene) boundary, notable because of the extinction event that eradicated the non-avian dinosaurs, Alamosaurus was one of the last of the sauropods and, more generically, the non-avian dinosaurs to have evolved and to have lived. Remains from multiple specimens represent differently aged animals. This means that we have, we think, a good representation of this dinosaur species across a large portion of its lifespan from juvenile to adult (also known as ontogeny). Named in 1922 by Charles Whitney Gilmore, a paleontologist at the United States National Museum, now the National Museum of Natural History (commonly referred to at large as "The Smithsonian"), Alamosaurus was originally discovered in New Mexico during 1921 in the Ojo Alamo Formation and not, as the name immediately may appear to suggest, in Texas. It was named by Gilmore for the formation, not for the more widely famous Alamo in San Antonio, TX. The specific name refers to the New Mexico county (San Juan County) where the holotype remains were originally discovered. Remains have been found, since that time, all across the southwestern United States of America and are housed in different institutions from California to Washington D.C. When considering its estimated size, we can say that Alamosaurus is a titanosaur (a group of large sauropod dinosaurs) that is nearly the same weight as the titanosaurs Argentinasaurus and Puertasaurus; both are large sauropods known mainly from Argentina.