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.
Choristodera
The neochoristoderan taxa Champsosauridae and Simoedosauridae are found from the Late Cretaceous to the middle Eocene, indicating that the group survived the Cretaceous–Paleogene extinction event. "Champsosaurus" teeth, vertebrae, and other bones are common fossils in Cretaceous deposits such as the Dinosaur Park Formation of Alberta and the Lance Formation of Wyoming. The presence of champsosaurs as far north as the North Slope of Alaska implies warmer temperatures during the Cretaceous. The Paleocene species, "Champsosaurus gigas", is the largest known champsosaur. The most complete skeleton was found at the Wannagan Creek site in North Dakota, but is found throughout North American Paleocene strata in the Dakotas, Wyoming, and Montana. "C. gigas" is unusual among Paleocene reptiles in that it is far larger than known Mesozoic ancestors, at about 3 meters in length (10 ft) versus 1.5 meters (5 ft) for the largest Cretaceous champsosaurs.