Alamosaurus
Alamosaurus (; meaning "Ojo Alamo lizard") is a genus of titanosaurian sauropod dinosaurs, containing a single known species, Alamosaurus sanjuanensis, from the late Cretaceous Period of what is now southern North America. Isolated vertebrae and limb bones indicate that it reached sizes comparable to "Argentinosaurus" and "Puertasaurus", which would make it the largest dinosaur known from North America. Its fossils have been recovered from a variety of rock formations spanning the Maastrichtian age of the late Cretaceous period. Specimens of a juvenile "Alamosaurus sanjuanensis" have been recovered from only a few meters below the Cretaceous-Paleogene boundary in Texas, making it among the last surviving non-avian dinosaur species.
Sauropoda
Their body structure did not vary as much as other dinosaurs, perhaps due to size constraints, but they displayed ample variety. Some, like the diplodocids, possessed tremendously long tails, which they may have been able to crack like a whip as a signal or to deter or injure predators, or to make sonic booms. "Supersaurus", at long, was the longest sauropod known from reasonably complete remains, but others, like the old record holder, "Diplodocus", were also extremely long. The holotype (and now lost) vertebra of "Amphicoelias fragillimus" may have come from an animal long; its vertebral column would have been substantially longer than that of the blue whale. However, a research published in 2015 speculated that the size estimates of "A. fragillimus" may have been highly exaggerated. The longest dinosaur known from reasonable fossils material is probably "Argentinosaurus huinculensis" with length estimates of to .