Homo rudolfensis is an extinct species of hominin that lived in East Africa during the Pleistocene.
History[]
The first H. rudolfensis were found in 1972 at Lake Turkana (called Lake Rudolf at the time), Kenya, detailed by Richard Leakery the next year. KNM-ER 1470 was discovered by Bernard Ngeneo and assigned lectotype, KNM-ER 1472 was discovered by J. Harris, KNM-ER 1475 was discovered by Kamoya Kimeu and KNM-ER 1481 was discovered by Harris. However, the femora recovered may not be the same species as the skull. They were classified as Homo since the reconstructed skull fragments indicated a large brain and flat face, but were not assigned to a species. They were dated to 2.9-2.6 million years based on the locality, and Leakey thought they were a very early hominin ancestor. This challenged the major human evolution model, that Australopithecus evolved into Homo ~2.5 million years ago, but it would call for serious revision since H. rudolfensis existed when supposedly no Homo existed. However, in 1977, the area was redated to 2 million years and 2.1-1.95 million years in 2012. Colin Groves and Vratislav Mazák (1975) assigned the remains to Homo habilis. Leaker and Alan Walker (1978) suggested they were Australopithecus, incorrectly reconstructing the skull, but Leaker still believed they were Homo. However, both agreed on the Homo habilis classification.
KNM-ER 1470 is much larger compared to the the Olduvai remains. In the terms of Homo habilis in the broad sense and Homo habilis in the strict sense were used to include/exclude the larger morph (respectively). Bernard Wood (1986) suggested the remains were of a different species. Coexisting Homo conflicted the predominant model of human evolution at the time, that derived humans evolved in a straight line from Homo erectus, which evolved directly from Homo habilis. Valery Alekseyev (1986) erected rudolfensis, but assigned the genus Pithecanthropus. Kennedy (1999) had argued it was invalid, since no holotype was assigned, with Wood finding a holotype was unnecessary, assigning KNM-ER 1470 as the lectotype. However, others argue it was invalid since Homo habilis could have been high dimorphic (like extant non-Homo hominids), arguing "H. rudolfensis" were male Homo habilis. Wood and Mark Collard (1999) thought Kenyanthropus was an ancestor of rudolfensis based on similar dental adaptations, but concluded dental anatomy is variable in hominins and not always a reliable source to sort family trees.
David Cameron (2003) concluded Kenyanthropus was an ancestor of H. rudolfensis, naming K. rudolfensis. He also thought Kenyanthropus was closer to Paranthropus than to Homo. In 2008, it was agreed the skull was incorrectly restored, but H. rudolfensis remained valid. Meave Leakey (2012) described KNM-ER 62000 from Koobi Fora, Kenya: finding it was similar to KNM-ER 1470 and smaller. She assigned it to H. rudolfensis since prepubescent male and females should be the same, but Homo habilis and H. rudolfensis have many distinctive traits. She also concluded KNM-ER 1802, a specimen used to classify other H. rudolfensis, may be a different (undescribed?) species, but Tim D. White believes it is too premature to find the range of variation in early hominins. The discovery of the Dmanisi Man have led to suggestions of early contemporaneous African Homo, including Homo habilis and H. rudolfensis, to be lumped into Homo erectus. There is no wide consensus on how rudolfensis and habilis relate to Homo erectus and descendants.
Aside from KNM-ER 1470, authors disagree on which specimens are H. rudolfensis because it is difficult to assign remains lacking a face and jaw. No bodily elements have been definitively assigned. Most H. rudolfensis are from Koobi Fora and Shungura, Ethiopia and Uraha, Malawi (the earliest of the genus Homo). The latest potential specimen is KNM-ER 819. However, both species are widely considered valid, but many now believe Homo evolved from Australopithecus at an ever-changing date. Many Australopithecus have been seen as candidates for H. rudolfensis' ancestor. LD 350-1 shows Homo split is around 2.8 million years, and shows this specimen may be an H. rudolfensis or H. habilis. Based on 2.1 million-year-old stone tools from Shangchen, China shows a possible ancestor species dispersed across Asia.
Description[]
Leakey (1973) reconstructed KNM-ER 1470 with a flat face and a cranial capacity of 800 cc³ (49 inches³). Ralph Holloway (1983( revised the base of the skull, calculating a volume of 752-753 cc (45.9-46 inches³). Timothy Bromage et al. revised the face, finding a 5° angle rather than fully flat, being slightly prognathic. The nasal was pushed directly under the frontals. He said it was possible to predict cranial capacity based on the face, finding 526 cc (32.1 inches³), chalking Leakey's errors up to a lack of research in facial anatomy and confirmation bias (as a flat face aligned with the model of human evolution at the time). John D. Hawks refuted this due to the skull's base remaining virtually unchanged except for an outwards 5° rotation. Bromage et al. (2008) once more revised the skull reconstruction, finding a cranial capacity of 700 cc (43 inches³).
Fossils assigned H. rudolfensis are generally classified due to their large size, flat and broad face, borad cheek teeth, thicker enamel than Homo habilis and complex tooth crowns and roots. Early Homo are characterized by their larger teeth. The cheek teeth of KNM-ER 60000 are on the lower scale for early Homo, not including the third molar, who is within range. The molars increase in size nearer to the posterior of the mouth. UR 501, the oldest H. ruldolfensis (2.5-2.3 million years old), has a tooth enamel thickness the same as early Homo, with molar enamel nearly as thick as Paranthropus molars. Such a wide variation is not seen in KNM-ER 1802, which indicates a regional difference amongst populations.
Size estimates of H. rudolfensis typically find a smaller size similar to australopithecines, usually relying on OH 62 (Homo habilis). H. rudolfensis may have been larger than Homo habilis, but it is unclear how large since bodily material have been definitively referred. Based on KNM-ER 1470 skull, male H. rudolfensis were 160 centimeters (5 feet 3 inches) tall and 60 kilograms (130 pounds) heavy and females 150 centimeters (4 feet 11 inches) tall and 51 kilograms (112 pounds) heavy.
For possible H. rudolfensis: KNM-ER 1472 was estimated to be 155.9 centimeters (5 feet 1 inches) tall and 41.8 kilograms (92 pounds) heavy, KNM-ER 1473 162.9 centimeters (5 feet 4 inches) and 47.1 kilograms (104 pounds), KNM-ER 1481 156.7 centimeters (5 feet 2 inches) and 41.8 kilograms (92 pounds), KNM-ER 3228 165.8 centimeters (5 feet 5 inches) and 47.2 kilograms (104 pounds) and KNM-ER 3728 153.3 centimeters (5 feet) and 40.3 kilograms (89 pounds). It is typically assumed pre-Homo erectus, including H. rudolfensis and H. habilis, had sexual dimorphism (males being larger). However, female weight is unknown in both species.
Early hominins, including H. rudolfensis, probably had thick body hair (like extant non-human hominids) since they appear to have lived in cooler regions and could have had a less active lifestyle than post-erectus, who are presumed hairless, likely requiring thick body hair to keep warm. KNM-ER 62000, a juvenile partial face, has identical age landmarks as a 13-14 year old derived human child, but likely died at around the age of 8 because of presumed faster growth in early hominins (based on a dental development rate).
Classification[]
H. rudolfensis is known to have had distinguished sexual dimorphism, and even separate morphs, the former only known in non-human apes. KNM-ER 1470, KNM-ER 60000 and KNM-ER 62000 have noticeably rectangular tooth rows. However, specimens like NM-ER 1802 are shaped like the letter U. Some think this represents a differentiated species, while others speculate this is the range of individual variation within the species.
Paleoecology[]
Diet[]
It is often thought the diet of early Homo had a greater portion of meat than Australopithecus, which led to lesser brain growth. The two main hypotheses are: meat is energy and meat allows the large, calorie-expensive hominid gut to decrease and allow for brain growth. However, it has also been suggested a drying climate led to scarce food, relying on subterranean items such as tubers and cooperative sharing, which led to social bonding amongst members. H. rudolfensis was likely incapable of endurance sprinting and hunting, and were likely arboreal (to a degree). Additionally, organized hunting and gathering is thought to have emerged in Homo erectus, but gathering may explain brain growth (which may increase possible travelling distance). The larger incisor implies this species may have relied on them more, and large, Australopithecus-like molars may indicate food which is mechanically harder to process. The mandibular bodies are thicker than later species and living apes, comparable to Australopithecus, unusually resisting torsion and producing powerful stresses during feeding.
Technology[]
H. rudolfensis is not associated with tools, but the greater molar cusp suggests they used tools to fracture tough foods, such as pliable plant and animal material. This is assumed, since the cusps would have been more worn. Still, their jaw being adapted to tough foods suggests technological advancement did not impact their diets. Large stone tool concentrations from Koobi Fora emerge alongside Homo erectus, but may have been produced by H. rudolfensis, Homo habilis and Paranthropus boisei. LD 350-1, the oldest Homo, is associated with the Oldowan industry, which may have been utilized by H. rudolfensis near-to emergence. Since H. rudolfensis and Paranthropus have very thick molars and coincides with a cooling and aridity trend (~2.5 million years ago), they may have been influenced by climate change. In East Africa, tropical forests and woodlands persisted through drought. H. rudolfensis was contemporaneous with Homo habilis, Homo erectus and Paranthropus boisei.