When J.B Reeside discovered Alamosaurus in 1921, it was North America's first Late Cretaceous sauropod, albeit one known from scrappy remains. Funnily enough, a hip bone and shoulder blade also made Alamosaurus North America's best-known titanosaurian sauropod, mainly because the land of the free has yet to yield another. But despite laying claim to a steady stream of discoveries since then the most attention has been drawn through a misinterpretation of its name (see etymology).
After a 2011 review of two enormous vertebrae (SMP VP-1850, collected in 2004 and SMP VP-2104, collected in 2006) from "Willow Wash" and a 30% complete femur (collected in 2003) from "De-na-zin" Wash, Alamosaurus gained some real notoriety by catapulting itself into the big league of dinosaurs. Pound-for-pound it's genuinely comparable to the likes of Puertasaurus, Futalognkosaurus, and the mighty Argentinosaurus. In fact, the new specimens are so much bigger than the original fossils it seems likely that all studies prior to 2011 had been based on the study of unreliable juveniles. But at least we can now add Alamosaurus to the ever increasing ranks of confirmed armoured titanosaurs.
On June 15th 1937, George B. Pearce discovered a partial Alamosaurus skeleton on the southwest toe of Utah's North Horn Mountain that was catalogued as USNM 15660, and in 2009 Michael Brett-Surman realised that a single armour plate bearing an identical catalogue number was hidden away in the Smithsonian. Based on style and hand, it seems likely that the same person created both hand-written labels, and probably at the same time, suggesting the armour and skeleton represent one individual.
Alamosaurus lived in North America in the dying days of the dinosaurs (but never ventured north of Central Utah) and shared its yard with Tyrannosaurus rex. So it's quite fitting that its remains were eventually discovered in Texas, where General Custer also made his last stand.
The species epithet, sanjuanensis, is a reference to San Juan, the county in which it was discovered. "Ensis" is a genus of edible saltwater clam (known as "razors" in England and "spoots" in Scotland), and also means "sword" in Latin, but when used as a Latin suffix for a place name it means "pertaining to", "originating in", or just "from". Genus name and epithet were coined by Smithsonian paleontologist Charles W. Gilmore in 1922.