(A.sanjuanensis TMM 41541-1)

Alamosaurus ("Ojo Alamo [New Mexico] lizard") named after a trading post in New Mexico Ojo Alamo where it was first found was the last giant, sauropod dinosaur in North America. Its remains have been found in Texas, New Mexico, and Utah. The trading post got its name after a large cottonwood tree, called alamo in Spanish, that grew next to the spring where the trading post was located.

The one continent on which titanosaurids were rare is North America, but, ironically, this continent has produced the most complete articulated skeleton (one quarter complete) yet found. Partial postcranial skeleton, isolated postcranial remains.

The Dallas Museum of Natural History (in partnership with Big Bend National Park and the University of Texas-Dallas) excavated a large concentration of Alamosaurus bones in Upper Cretaceous Javelina Formation of Big Bend National Park after a first discovery made by members of a dinosaur class from the University of Texas at Dallas in the spring of 1995.

The rocks containing these bones are approximately 65 million years old making Alamosaurus one of the last dinosaurs in the world. The site has produced the disarticulated remains of possibly three individuals, one adult and two juveniles that are approximately half the adult size. Excavation of this site has thus far shown this accumulation of material to be monospecific.

Scientists think that Alamosaurus was probably a "re-entrant" into North America from South America, where its closest relatives have been found.