robust P. boisei (a hypothesis notably argued by palaeoanthropologist in 1985) by establishing the boisei lineage as beginning long before robustus had existed. In 1989, palaeoartist Walter Ferguson recommended KNM WT 17000 be classified into a different species, walkeri, because the holotype of aethiopicus comprised only the jawbone and KNM WT 17000 preserves no jaw elements. Ferguson's classification is almost universally ignored, and is considered to be synonymous with P. aethiopicus. Several more lower and upper jaw specimens have been unearthed in the Shungura Formation, including a juvenile specimen, L338y-6. In 2002, a 2.7–2.5 Ma maxilla, EP 1500, from Laetoli, Tanzania, was assigned to P. aethiopicus. Also found was the upper portion of a tibia, but it cannot definitively be associated with EP 1500 and thus with P. aethiopicus. Classification The genus Paranthropus (from Ancient Greek παρα para beside or alongside, and άνθρωπος ánthropos man, otherwise known as "robust australopithecines") typically includes P. aethiopicus, P. boisei, and P. robustus. P. aethiopicus is the earliest member of the genus, with the oldest remains, from the Ethiopian Omo Kibish Formation, dated to 2.6 million years ago (mya) at the end of the Pliocene. It is possible that P. aethiopicus evolved even earlier, up to 3.3 mya, on the expansive Kenyan floodplains of the time. P. aethiopicus is only confidently identified from the skull KNM WT 17000 and a few jaws and isolated teeth, and is generally considered to have been ancestral to P. boisei which also inhabited East Africa, making it a chronospecies. Because of this relationship, it is debatable if P. aethiopicus should be subsumed under P. boisei or if the differences stemming from archaicness should justify species distinction. The terms P. boisei sensu lato ("in the broad sense") and P. boisei sensu stricto ("in the strict sense") can be used to respectively include and exclude P. aethiopicus from P. boisei when discussing the lineage as a whole. It is also debated if Paranthropus is a valid natural grouping (monophyletic) or an invalid grouping of similar-looking hominins (paraphyletic). Because skeletal elements are so limited in these species, their affinities with each other and to other australopithecines is difficult to gauge with accuracy. The jaws are the main argument for monophyly, but such anatomy is strongly influenced by diet and environment, and could in all likelihood have evolved independently in P. boisei and P. robustus. Proponents of monophyly consider P. aethiopicus to