therefore later Gastornis). Additional fragmentary specimens were found in Wyoming in 1911 and assigned in 1913 to the new species Diatryma ajax (also now considered a synonym of G. gigantea). In 1916, an American Museum of Natural History expedition to the Bighorn Basin (Willwood Formation) of Wyoming found the first nearly complete skull and skeleton, which was described in 1917 and gave scientists their first clear picture of the bird. Matthew, Granger, and Stein (1917) classified this nearly complete specimen as yet another new species, Diatryma steini. After the description of Diatryma, most new European specimens were referred to this genus instead of Gastornis. However, after the initial discovery of Diatryma, it soon became clear that it and Gastornis were so similar that the former could be considered a junior synonym of the latter. In fact, this similarity was recognized as early as 1884 by Elliott Coues, but this was debated by researchers throughout the 20th century. Meaningful comparisons between Gastornis and Diatryma were made more difficult by Lemoine's incorrect skeletal illustration, the composite nature of which was not discovered until the early 1980s. Following this, several authors began to recognize a greater degree of similarity between the European and North American birds, often placing both in the same order (Gastornithiformes) or even family (Gastornithidae). This newly recognized degree of similarity caused many scientists to tentatively accept their synonymy, pending a comprehensive review of the anatomy of these birds. Consequently, the correct scientific name of the genus is Gastornis. Description Gastornis is known from a large amount of fossil remains, but the clearest picture of the bird comes from a few nearly complete specimens of the species G. gigantea. These were generally very large birds, with huge beaks and massive skulls superficially similar to the carnivorous South American "terror birds" (phorusrhacids). The largest known species, G. gigantea could grow to the size of the largest moas, and reached about in maximum height. The skull of G. gigantea was huge compared to the body and powerfully built. The beak was extremely tall and compressed (flattened from side to side). Unlike other species of Gastornis, G. gigantea lacked characteristic grooves and pits on the underlying bone. The 'lip' of the beak was straight, without a raptorial hook as found in the predatory phorusrhacids. The nostrils were small and positioned close to the front of the eyes about midway up the skull. The