Alamosaurus

Alamosaurus (/ˌæləmɵˈsɔrəs/; meaning "Ojo Alamo lizard") is a genus of titanosaurian sauropod dinosaurs, containing a single species, Alamosaurus sanjuanensis, from the late Cretaceous Period of what is now southern North America. It was a large quadrupedal herbivore. 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.[1] Its fossils have been recovered from a variety of geological formations spanning the Maastrichtian stage (late Edmontonian-Lancian land vertebrate ages) of the Late Cretaceous. 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.

Description
The vertebrae from the middle part of its tail had elongated centra.[3] Alamosaurus had vertebral lateral fossae that resembled shallow depressions.[4] Fossae that similarly resemble shallow depressions are known from Saltasaurus, Malawisaurus, Aeolosaurus, and Gondwanatitan.[4] Venenosaurus also had depression-like fossae, but its "depressions" penetrated deeper into the vertebrae, were divided into two chambers, and extend farther into the vertebral columns.[4]

Alamosaurus had more robust radii than Venenosaurus.[5] Long thought to have been unarmored, recent discoveries indicate that Alamosaurus was armored like other lithostrotians, including Saltasaurus.

Classification
Alamosaurus is undoubtedly a derived member of Titanosauria, but relationships within that group are far from certain. One major analysis unites Alamosaurus with Opisthocoelicaudia in a subfamily Opisthocoelicaudinae of the family Saltasauridae [7] A major competing analysis finds Alamosaurus as a sister taxon to Pellegrinisaurus, with both genera located just outside Saltasauridae.[8] Other scientists have also noted particular similarities with the saltasaurid Neuquensaurus and the Brazilian Trigonosaurus (the "Peiropolis titanosaur") which is used in many cladistic and morphologic analyses of titanosaurians.