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Homo rudolfensis
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Homo rudolfensis
Homo rudolfensis is an extinct species of archaic human from the Early Pleistocene of East Africa about 2 million years ago (mya). Because H. rudolfensis coexisted with several other hominins, it is debated what specimens can be confidently assigned to this species beyond the lectotype skull KNM-ER 1470 and other partial skull aspects. No bodily remains are definitively assigned to H. rudolfensis. Consequently, both its generic classification and validity are debated without any wide consensus, with some recommending the species to actually belong to the genus Australopithecus as A. rudolfensis or Kenyanthropus as K. rudolfensis, or that it is synonymous with the contemporaneous and anatomically similar H. habilis.
H. rudolfensis is distinguished from H. habilis by larger size, but it is also argued that this species actually consists of male H. habilis specimens, assuming that H. habilis was sexually dimorphic and males were much larger than females. Because no bodily remains are definitely identified, body size estimates are largely based on the stature of H. habilis. Using this, male H. rudolfensis may have averaged about 160 cm (5 ft 3 in) in height and 60 kg (130 lb) in weight, and females 150 cm (4 ft 11 in) and 51 kg (112 lb). KNM-ER 1470 had a brain volume of about 750 cc (46 cu in). Like other early Homo, H. rudolfensis had large cheek teeth and thick enamel.
Early Homo species exhibit marked brain growth compared to Australopithecus predecessors, which is typically explained as a change in diet with a calorie-rich food source, namely meat. Though not associated with tools, dental anatomy suggests some processing of plant or meat fiber before consumption, though the mouth could still effectively chew through mechanically challenging food, indicating tool use did not greatly affect diet.
The first fossils were discovered in 1972 along Lake Turkana (at the time called Lake Rudolf) in Kenya, and were detailed by Kenyan palaeoanthropologist Richard Leakey the following year. The specimens were: a large and nearly complete skull (KNM-ER 1470, the lectotype) discovered by Bernard Ngeneo, a local; a right femur (KNM-ER 1472) discovered by J. Harris; an upper femur (proximal) fragment (KNM-ER 1475) discovered by fossil collector Kamoya Kimeu; and a complete left femur (KNM-ER 1481) discovered by Harris. However, it is unclear if the femora belong to the same species as the skull. Leakey classified them under the genus Homo because he had reconstructed the skull fragments so that it had a large brain volume and a flat face, but did not assign them to a species. Because the horizon they were discovered in was, at the time, dated to 2.9–2.6 million years ago (mya), Leakey thought these specimens were a very early human ancestor. This challenged the major model of human evolution at the time where Australopithecus africanus gave rise to Homo about 2.5 mya, but if Homo had already existed at this time, it would call for serious revisions. However, the area was redated to about 2 mya in 1977 (the same time period as H. habilis and H. ergaster/H. erectus), and more precisely to 2.1–1.95 mya in 2012. They were first assigned to the species habilis in 1975 by anthropologists Colin Groves and Vratislav Mazák. In 1978, in a joint paper with Leakey and English anthropologist Alan Walker, Walker suggested the remains belong in Australopithecus (and that the skull was incorrectly reconstructed), but Leakey still believed they belonged to Homo, though they both agreed that the remains could belong to habilis.
Homo family tree showing H. rudolfensis and H. habilis at the base as offshoots of the human line:
KNM-ER 1470 was much larger than the Olduvai remains, so the terms H. habilis sensu lato ("in the broad sense") and H. habilis sensu stricto ("in the strict sense") were used to include or exclude the larger morph, respectively. In 1986, English palaeoanthropologist Bernard Wood first suggested these remains represent a different Homo species, which coexisted with H. habilis and H. ergaster/H. erectus. Coexisting Homo species conflicted with the predominant model of human evolution at the time which was that modern humans evolved in a straight line directly from H. ergaster/H. erectus which evolved directly from H. habilis. In 1986, the remains were placed into a new species, rudolfensis, by Russian anthropologist Valery Alekseyev (but he used the genus Pithecanthropus, which was changed to Homo three years later by Groves). In 1999, Kennedy argued that the name was invalid because Alekseyev had not assigned a holotype. Pointing out that this is in fact not mandatory, Wood the same year nevertheless designated KNM-ER 1470 as the lectotype. However, the validity of this species has also been debated on material grounds, with some arguing that H. habilis was highly sexually dimorphic like modern non-human apes, with the larger skulls classified as "H. rudolfensis" actually representing male H. habilis. In 1999, Wood and biological anthropologist Mark Collard recommended moving rudolfensis and habilis to Australopithecus based on the similarity of dental adaptations. However, they conceded that dental anatomy is highly variable among hominins and not always reliable when formulating family trees.
In 2003, Australian anthropologist David Cameron concluded that the earlier australopithecine Kenyanthropus platyops was the ancestor of rudolfensis, and reclassified it as K. rudolfensis. He also believed that Kenyanthropus was more closely related to Paranthropus than Homo. In 2008, a re-reconstruction of the skull concluded it was incorrectly restored originally, though agreed with the classification as H. rudolfensis. In 2012, British palaeoanthropologist Meave Leakey described the juvenile partial face KNM-ER 62000 discovered in Koobi Fora, Kenya; noting it shares several similarities to KNM-ER 1470 and is smaller, she assigned it to H. rudolfensis, and, because prepubescent male and female bones should be indistinguishable, differences between juvenile H. rudolfensis and adult H. habilis specimens support species distinction. She also concluded that the jawbone KNM-ER 1802, an important specimen often used in classifying other specimens as H. rudolfensis, actually belongs to a different (possibly undescribed) species, but American palaeoanthropologist Tim D. White believes this to be premature because it is unclear how wide the range of variation is in early hominins. The 2013 discovery of the 1.8 Ma Georgian Dmanisi skulls which exhibit several similarities with early Homo have led to suggestions that all contemporary groups of early Homo in Africa, including H. habilis and H. rudolfensis, are the same species and should be assigned to H. erectus. There is still no wide consensus on how rudolfensis and habilis relate to H. ergaster and descendent species.
Beyond KNM-ER 1470, there is disagreement on which specimens actually belong in H. rudolfensis as it is difficult to assign with accuracy remains that do not preserve the face and jaw. No H. rudolfensis bodily elements have been definitively associated with a skull and thus to the species. Most proposed H. rudolfensis fossils come from Koobi Fora and date to 1.9–1.85 mya. Remains from the Shungura Formation, Ethiopia, and Uraha, Malawi, are dated as far back as 2.5–2.4 mya, which would make it the earliest identified species of Homo. The latest potential specimen is KNM-ER 819 dating to 1.65–1.55 mya.
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Homo rudolfensis
Homo rudolfensis is an extinct species of archaic human from the Early Pleistocene of East Africa about 2 million years ago (mya). Because H. rudolfensis coexisted with several other hominins, it is debated what specimens can be confidently assigned to this species beyond the lectotype skull KNM-ER 1470 and other partial skull aspects. No bodily remains are definitively assigned to H. rudolfensis. Consequently, both its generic classification and validity are debated without any wide consensus, with some recommending the species to actually belong to the genus Australopithecus as A. rudolfensis or Kenyanthropus as K. rudolfensis, or that it is synonymous with the contemporaneous and anatomically similar H. habilis.
H. rudolfensis is distinguished from H. habilis by larger size, but it is also argued that this species actually consists of male H. habilis specimens, assuming that H. habilis was sexually dimorphic and males were much larger than females. Because no bodily remains are definitely identified, body size estimates are largely based on the stature of H. habilis. Using this, male H. rudolfensis may have averaged about 160 cm (5 ft 3 in) in height and 60 kg (130 lb) in weight, and females 150 cm (4 ft 11 in) and 51 kg (112 lb). KNM-ER 1470 had a brain volume of about 750 cc (46 cu in). Like other early Homo, H. rudolfensis had large cheek teeth and thick enamel.
Early Homo species exhibit marked brain growth compared to Australopithecus predecessors, which is typically explained as a change in diet with a calorie-rich food source, namely meat. Though not associated with tools, dental anatomy suggests some processing of plant or meat fiber before consumption, though the mouth could still effectively chew through mechanically challenging food, indicating tool use did not greatly affect diet.
The first fossils were discovered in 1972 along Lake Turkana (at the time called Lake Rudolf) in Kenya, and were detailed by Kenyan palaeoanthropologist Richard Leakey the following year. The specimens were: a large and nearly complete skull (KNM-ER 1470, the lectotype) discovered by Bernard Ngeneo, a local; a right femur (KNM-ER 1472) discovered by J. Harris; an upper femur (proximal) fragment (KNM-ER 1475) discovered by fossil collector Kamoya Kimeu; and a complete left femur (KNM-ER 1481) discovered by Harris. However, it is unclear if the femora belong to the same species as the skull. Leakey classified them under the genus Homo because he had reconstructed the skull fragments so that it had a large brain volume and a flat face, but did not assign them to a species. Because the horizon they were discovered in was, at the time, dated to 2.9–2.6 million years ago (mya), Leakey thought these specimens were a very early human ancestor. This challenged the major model of human evolution at the time where Australopithecus africanus gave rise to Homo about 2.5 mya, but if Homo had already existed at this time, it would call for serious revisions. However, the area was redated to about 2 mya in 1977 (the same time period as H. habilis and H. ergaster/H. erectus), and more precisely to 2.1–1.95 mya in 2012. They were first assigned to the species habilis in 1975 by anthropologists Colin Groves and Vratislav Mazák. In 1978, in a joint paper with Leakey and English anthropologist Alan Walker, Walker suggested the remains belong in Australopithecus (and that the skull was incorrectly reconstructed), but Leakey still believed they belonged to Homo, though they both agreed that the remains could belong to habilis.
Homo family tree showing H. rudolfensis and H. habilis at the base as offshoots of the human line:
KNM-ER 1470 was much larger than the Olduvai remains, so the terms H. habilis sensu lato ("in the broad sense") and H. habilis sensu stricto ("in the strict sense") were used to include or exclude the larger morph, respectively. In 1986, English palaeoanthropologist Bernard Wood first suggested these remains represent a different Homo species, which coexisted with H. habilis and H. ergaster/H. erectus. Coexisting Homo species conflicted with the predominant model of human evolution at the time which was that modern humans evolved in a straight line directly from H. ergaster/H. erectus which evolved directly from H. habilis. In 1986, the remains were placed into a new species, rudolfensis, by Russian anthropologist Valery Alekseyev (but he used the genus Pithecanthropus, which was changed to Homo three years later by Groves). In 1999, Kennedy argued that the name was invalid because Alekseyev had not assigned a holotype. Pointing out that this is in fact not mandatory, Wood the same year nevertheless designated KNM-ER 1470 as the lectotype. However, the validity of this species has also been debated on material grounds, with some arguing that H. habilis was highly sexually dimorphic like modern non-human apes, with the larger skulls classified as "H. rudolfensis" actually representing male H. habilis. In 1999, Wood and biological anthropologist Mark Collard recommended moving rudolfensis and habilis to Australopithecus based on the similarity of dental adaptations. However, they conceded that dental anatomy is highly variable among hominins and not always reliable when formulating family trees.
In 2003, Australian anthropologist David Cameron concluded that the earlier australopithecine Kenyanthropus platyops was the ancestor of rudolfensis, and reclassified it as K. rudolfensis. He also believed that Kenyanthropus was more closely related to Paranthropus than Homo. In 2008, a re-reconstruction of the skull concluded it was incorrectly restored originally, though agreed with the classification as H. rudolfensis. In 2012, British palaeoanthropologist Meave Leakey described the juvenile partial face KNM-ER 62000 discovered in Koobi Fora, Kenya; noting it shares several similarities to KNM-ER 1470 and is smaller, she assigned it to H. rudolfensis, and, because prepubescent male and female bones should be indistinguishable, differences between juvenile H. rudolfensis and adult H. habilis specimens support species distinction. She also concluded that the jawbone KNM-ER 1802, an important specimen often used in classifying other specimens as H. rudolfensis, actually belongs to a different (possibly undescribed) species, but American palaeoanthropologist Tim D. White believes this to be premature because it is unclear how wide the range of variation is in early hominins. The 2013 discovery of the 1.8 Ma Georgian Dmanisi skulls which exhibit several similarities with early Homo have led to suggestions that all contemporary groups of early Homo in Africa, including H. habilis and H. rudolfensis, are the same species and should be assigned to H. erectus. There is still no wide consensus on how rudolfensis and habilis relate to H. ergaster and descendent species.
Beyond KNM-ER 1470, there is disagreement on which specimens actually belong in H. rudolfensis as it is difficult to assign with accuracy remains that do not preserve the face and jaw. No H. rudolfensis bodily elements have been definitively associated with a skull and thus to the species. Most proposed H. rudolfensis fossils come from Koobi Fora and date to 1.9–1.85 mya. Remains from the Shungura Formation, Ethiopia, and Uraha, Malawi, are dated as far back as 2.5–2.4 mya, which would make it the earliest identified species of Homo. The latest potential specimen is KNM-ER 819 dating to 1.65–1.55 mya.
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