Alamosaurus fossil map
Where fossils of Alamosaurus have been found, shown on the Earth as it looked about 66 million years ago and on today’s map.
Dots are fossil collections recorded in the Paleobiology Database. The “then” view moves today’s fossil sites back to their positions 66 million years ago (the time slice nearest the median age of the fossils) using the Merdith et al. (2021) plate model; positions are approximate. Open on the timeline map →
| Group | Sauropods & prosauropods |
|---|---|
| Lived | 83.6–66 million years ago (Campanian to Maastrichtian) |
| Periods | Cretaceous |
| Family | Saltasauridae |
| Named by | Gilmore 1922 |
| Fossil records | 38 occurrences at 25 locations (PBDB) |
| Found in | United States, Mexico |
| Rock formations | Ojo Alamo, Javelina, North Horn, Kirtland, txn:64335, Black Peaks |
About Alamosaurus
Alamosaurus (; meaning "Ojo Alamo lizard") 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 ("sauropod hiatus") and probably represents an immigrant from South America or Asia.
Adults would have measured around 26 metres (85 ft) long, 5 metres (16 ft) tall at the shoulder and weighed up to 30–35 tonnes (33–39 short tons), though some specimens indicate a larger body size. Isolated vertebrae and limb bones suggest that it could have reached sizes comparable to Argentinosaurus and Puertasaurus, which would make it the absolute largest dinosaur known from North America. Its fossils have been recovered from a variety of rock formations in the southwestern United States that were dated to the latest Maastrichtian age.
Text in “About” is quoted from the Wikipedia article Alamosaurus (revision 1380985809), licensed under CC BY-SA 4.0; introduction excerpted verbatim, formatting removed. Ages, family, authority and fossil records: Paleobiology Database, accessed 22 October 2026. Ages are those of the rock layers the fossils were found in.
