Alamosaurus sanjuanensis, a sauropod from the Late Cretaceous of New Mexico, USA.
Nobumichi Tamura/Stocktrek Images/ Stocktrek Images/ Getty Images


Alamosaurus (Greek for "Alamo lizard"); pronounced AL-ah-moe-SORE-us


Woodlands of North America

Historical Period:

Late Cretaceous (70-65 million years ago)

Size and Weight:

Up to 60 feet long and 50-70 tons



Distinguishing Characteristics:

Long neck and tail; relatively long legs

About Alamosaurus

Although there may be other genera whose fossils have yet to be discovered, Alamosaurus is one of the few titanosaurs known to have lived in late Cretaceous North America, and possibly in vast numbers: According to one analysis, there may have been as many as 350,000 of these 60-foot-long herbivores living in Texas at any given time. Its closest relative appears to have been another titanosaur, Saltasaurus.

A recent analysis has shown that Alamosaurus may have been a bigger dinosaur than originally estimated, possibly in the weight class of its more famous South American cousin Argentinosaurus. It turns out that some of the "type fossils" used to reconstruct Alamosaurus may have come from adolescents rather than full-grown adults, meaning that this titanosaur may well have attained lengths of over 60 feet from head to tail and weights in excess of 70 or 80 tons.

By the way, it's an odd fact that Alamosaurus wasn't named after the Alamo in Texas, but the Ojo Alamo sandstone formation in New Mexico. This herbivore already had its name when numerous (but incomplete) fossils were discovered in the Lone Star State, so you might say that everything worked out in the end!