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.
Diplodocus
"Diplodocus hallorum", known from partial remains, was even larger, and is estimated to have been the size of four elephants. When first described in 1991, discoverer David Gillette calculated it may have been up to 52 m (171 ft) long, making it the longest known dinosaur (excluding those known from exceedingly poor remains, such as "Amphicoelias"). Some weight estimates of this time ranged as high as . The estimated length was later revised downward to and later on to based on findings that show that Gillette had originally misplaced vertebrae 12–19 as vertebrae 20–27. The nearly complete "Diplodocus carnegii" skeleton at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, on which size estimates of "D. hallorum" are mainly based, also was found to have had its 13th tail vertebra come from another dinosaur, throwing off size estimates for "D. hallorum" even further. While dinosaurs such as "Supersaurus" were probably longer, fossil remains of these animals are only fragmentary.