Alamosaurus is a genus of titanosaurian sauropod dinosaurs containing a single known species, Alamosaurus sanjuanensis, from the Maastrichtian age of the Late Cretaceous period in what is now southwestern North America. It is one of the only known sauropods to have inhabited North America after the nearly 30-million-year absence of sauropods from the continent's fossil record and probably represents an immigrant from South America or Asia.