Pteranodon
"Pteranodon" was the first pterosaur found outside of Europe. Its fossils first were found by Othniel Charles Marsh in 1870, in the Late Cretaceous Smoky Hill Chalk deposits of western Kansas. These chalk beds were deposited at the bottom of what was once the Western Interior Seaway, a large shallow sea over what now is the midsection of the North American continent. These first specimens, YPM 1160 and YPM 1161, consisted of partial wing bones, as well as a tooth from the prehistoric fish "Xiphactinus", which Marsh mistakenly believed to belong to this new pterosaur (all known pterosaurs up to that point had teeth). In 1871, Marsh named the find ""Pterodactylus oweni"", assigning it to the well-known (but much smaller) European genus "Pterodactylus". Marsh also collected more wing bones of the large pterosaur in 1871. Realizing that the name he had chosen had already been used for Harry Seeley's European pterosaur species "Pterodactylus oweni" in 1864, Marsh re-named his giant North American pterosaur Pterodactylus occidentalis, meaning "Western wing finger," in his 1872 description of the new specimen. He also named two additional species, based on size differences: Pterodactylus ingens (the largest specimen so far), and Pterodactylus velox (the smallest).
Nothronychus
The first fossil evidence later attributed to "Nothronychus" was discovered by a team of paleontologists working in the Zuni Basin of New Mexico at the Haystack Butte site. A therizinosaur ischium (a hip bone) had originally been mistaken for a squamosal, a part of the skull crest of the newly discovered ceratopsian "Zuniceratops". However, closer examination revealed the true identity of the bone, and soon more parts of the skeleton were found. The New Mexico team, led by paleontologists Jim Kirkland and Doug Wolfe, published their find in the "Journal of Vertebrate Paleontology" on 22 August 2001, making it the type specimen of the new species "Nothronychus mckinleyi". The "Arizona Republic" newspaper, however, was first to announce the name on 19 June 2001, in a column by R.E. Molnar. The generic name is derived from Greek νωθρός, "nothros", "heavy" or "slothful", and ὄνυξ, "onyx", "claw". The specific name honours rancher Bobby McKinley on whose land the find was made. The holotype, specimen MSM P2106, consists of two skull fragments, a braincase, some vertebrae and parts of the shoulder girdle, forelimbs, pelvis and hindlimbs.
A second, more complete therizinosaur specimen, UMNH VP 16420, was discovered from the Tropic Shale formation (dating to the early Turonian stage) of southern Utah in 2000 by Merle Graffam, a resident of Big Water, Utah. The area around Big Water had been subject to several expeditions by teams from the Museum of Northern Arizona (MNA), and was known for its abundance of marine reptile fossils, especially plesiosaurs. During part of the late Cretaceous period, the region had been submerged under a shallow sea, the Western Interior Seaway, and preserves extensive marine deposits. Graffam's initial discovery (a large, isolated toe bone) came as a surprise to scientists, as it clearly belonged to a land-dwelling dinosaur, rather than a plesiosaur. However, the location of the bone at the time would have been nearly 100 kilometers from the Cretaceous shoreline. An excavation of the area by an MNA crew revealed more of the skeleton, and the scientists found that it was a therizinosaur, and the first example of that group to be found in the Americas. All previous therizinosaur fossils had come from China and Mongolia. It is the most complete therizinosaurid specimen known but lacks the skull.