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.
St. Louis Museum
A museum specimen of particular note was a fossil, the Zeuglodon, which the Complete Guide to the St. Louis Museum called "the greatest fossil in the world." The Zeuglodon was discovered in 1848 in a field in Alabama. After it was extricated from the rock in which it was found, Dr. Koch purchased the fossil for the St. Louis Museum. The fossilized animal was amphibious and resembled a whale, alligator, and serpent. Only one other fossil of this animal was known to exist at the time, which was owned by the King of Prussia. Previously a Mastodon fossil was the largest one discovered, at 20 feet. The Zeuglodon measured 96 feet. Though some doubted the authenticity of the specimen, Professor Joseph Leidy, M.D. of the University of Pennsylvania and Curator of the Academy of Natural Sciences of Philadelphia and Professor Silliman of Yale College both attested to the authenticity of the fossil.