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Artist's rendering of Alamosaurus sanjuanensis - Giant Sauropod DinosaurAlamosaurus sanjuanensis
Giant Sauropod Dinosaur

Humerus TMM 41398-2
Femur TMM 41541-1
Javelina Formation, Cretaceous
Big Bend National Park
Brewster County, Texas

Alamosaurus sanjuanensis was first discovered in San Juan County, New Mexico. The rock unit in which it was found, the Ojo Alamo Formation, was named for a local trading post, the Ojo Alamo. Alamosaurus roamed over much of southwestern North America during the latest part of the Cretaceous.  It became extinct at the very end of the Mesozoic Era, during the mass extinction episode that wiped out many other species at the same time.  Alamosaurus was one of the very last of the non-avian dinosaurs in Texas. 

Alamosaurus was a member of the sauropod dinosaur lineage.  The sauropods were not only the largest dinosaurs but also the largest land animals ever to evolve.  Only some of today’s baleen whales are larger.  The largest sauropods may have weighed around 50 tons.  This is about 10 times more than African elephants, who are the largest land-living animals alive today. 

The earliest members of the lineage were small and walked on their hind legs, leaving their hands free for other purposes.  But during the course of the Mesozoic, the sauropods evolved to giant size, and had to drop to all fours in order to support their gigantic weight.  At the same time, they evolved almost unbelievably long necks but retained relatively small heads.  Of all the dinosaurs, they had the smallest brains compared to their body size. 

Alamosaurus and the other huge sauropods were herbivores.  They had small blunt teeth, which they used for cropping and stripping vegetation.  The discovery of polished stones inside the ribcage in several skeletons suggests that they had a large muscular gizzard containing stones to mechanically break down fibrous plants.  The stones accomplished the grinding of food instead of the teeth!

The two huge bones of Alamosaurus buried in the Dino Pit were cast from specimens collected from Big Bend National Park in 1971 and 1973 by Dr. Wann Langston, Jr. and a crew from the Vertebrate Paleontology Laboratory of the Texas Memorial Museum.  One bone is the humerus (upper arm bone), which lies between the shoulder and elbow joints.  The other is the femur (thigh bone), which extends from the hip to the knee joint.  These two bones came from different individuals of about the same size.


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