discovered in 2013, dated to 2.8 Mya, has been argued as being transitional between the two. It is also disputed whether H. habilis was the first hominin to use stone tools, as Australopithecus garhi, dated to c. 2.5 Mya, has been found along with stone tool implements. Fossil KNM-ER 1470 (discovered in 1972, designated Pithecanthropus rudolfensis by Alekseyev 1978) is now seen as either a third early species of Homo (alongside H. habilis and H. erectus) at about 2 million years ago, or alternatively as transitional between Australopithecus and Homo. Wood and Richmond (2000) proposed that Gray's tribe Hominini ("hominins") be designated as comprising all species after the chimpanzee-human last common ancestor by definition, to the inclusion of Australopithecines and other possible pre-human or para-human species (such as Ardipithecus and Sahelanthropus) not known in Gray's time. In this suggestion, the new subtribe of Hominina was to be designated as including the genus Homo exclusively, so that Hominini would have two subtribes, Australopithecina and Hominina, with the only known genus in Hominina being Homo. Orrorin (2001) has been proposed as a possible ancestor of Hominina but not Australopithecina. Designations alternative to Hominina have been proposed: Australopithecinae (Gregory & Hellman 1939) and Preanthropinae (Cela-Conde & Altaba 2002); Species At least a dozen species of Homo other than Homo sapiens have been proposed, with varying degrees of consensus. Homo erectus is widely recognized as the species directly ancestral to Homo sapiens. Most other proposed species are proposed as alternatively belonging to either Homo erectus or Homo sapiens as a subspecies. This concerns Homo ergaster in particular. One proposal divides Homo erectus into an African and an Asian variety; the African is Homo ergaster, and the Asian is Homo erectus sensu stricto. (Inclusion of Homo ergaster with Asian Homo erectus is Homo erectus sensu lato.) There appears to be a recent trend, with the availability of ever more difficult-to-classify fossils such as the Dmanisi skulls (2013) or Homo naledi fossils (2015) to subsume all archaic varieties under Homo erectus. Subspecies Homo sapiens subspecies The recognition or nonrecognition of subspecies of Homo sapiens has a complicated history. The rank of subspecies in zoology is introduced for convenience, and not by objective criteria, based on pragmatic consideration of factors such as geographic isolation and sexual selection. The informal taxonomic rank of race is variously considered equivalent or subordinate to the rank of subspecies, and the division