In 1917, Harold Cook, a rancher and geologist from Nebraska, unearthed one molar tooth in Pliocine deposits in western Nebraska. In 1922, he sent the tooth to Dr. Henry Osborn of Columbia University, head of the American Museum of Natural History, who claimed that it belonged to an early hominid and determined that the tooth had characteristics of chimpanzee, Pithecanthropus (Java man), and man. He wrote Cook saying: "I sat down with the tooth and I said to myself: 'It looks one hundred per cent anthropoid'" (Osborn, Henry Fairfield, 1922, "Hesperopithecus, the first anthropoid primate found in America," American Museum Novitates, 37, p. 2 ). One month later, Osborn announced that Hesperopithecus haroldcookii was the first anthropoid ape from America; a missing link in human evolution.
Sir Grafton Elliot Smith, F.R.S., Professor of Anatomy of Manchester, England, supported Osborn saying, "I think the balance of probability is in favour of the view that the tooth found in the Pliocene beds of Nebraska may possibly have belonged to a primitive member of the Human Family" (Smith, The Evolution of Man 1927).