an expansion of genus Canis from out of Eurasia led to the dire wolf. In 1974 RobertA.Martin proposed that the large North American wolf C.armbrusteri (Armbruster's wolf) was C.lupus. Nowak, Kurtén, and Annalisa Berta proposed that C.dirus was not derived from C.lupus. In 1987, a new hypothesis proposed that a mammal population could give rise to a larger form called a hypermorph during times when food was abundant, but when food later became scarce the hypermorph would either adapt to a smaller form or go extinct. This hypothesis might explain the large body sizes found in many Late Pleistocene mammals compared to their modern counterparts. Both extinction and speciationa process by which a new species splits from an older onecould occur together during periods of climatic extremes. Gloria D. Goulet agreed with Martin, proposing further that this hypothesis might explain the sudden appearance of C.dirus in North America and, judging from the similarities in their skull shapes, that C.lupus had given rise to the C.dirus hypermorph due to an abundance of game, a stable environment, and large competitors. The three paleontologists Xiaoming Wang, Richard H. Tedford, and Ronald M. Nowak propose that C.dirus evolved from Canis armbrusteri, with Nowak stating that both species arose in the Americas and that specimens found in Cumberland Cave, Maryland, appear to be C.armbrusteri diverging into C.dirus. Nowak believed that Canis edwardii was the first appearance of the wolf in North America, and it appears to be close to the lineage which produced C. armbrusteri and C. dirus. Tedford believes that the early wolf from China, Canis chihliensis, may have been the ancestor of both C.armbrusteri and the gray wolf C.lupus. The sudden appearance of C.armbrusteri in mid-latitude North America during the Early Pleistocene 1.5 million years ago along with the mammoth suggests that it was an immigrant from Asia, with the gray wolf C.lupus evolving in Beringia later in the Pleistocene and entering mid-latitude North America during the Last Glacial Period along with its Beringian prey. In 2010 Francisco Prevosti proposed that C.dirus was a sister taxon to C.lupus. C. dirus lived in the Late Pleistocene to the early Holocene (125,000–10,000 years before present or YBP) in North and South America. The majority of fossils from the eastern C.d.dirus have been dated 125,000–75,000YBP, but the western C.d.guildayi fossils are not only smaller in size but more recent; thus it has been proposed that C.d.guildayi