''Australopithecus anamensis'' is a

hominin The Hominini (hominins) form a taxonomic tribe of the subfamily Homininae (hominines). They comprise two extant genera: ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos), and in standard usage exclude the genus '' Gorilla'' ( gorillas) ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

that lived roughly between 4.3 and 3.8 million years ago, and is the oldest known ''

Australopithecus ''Australopithecus'' (, ; or (, ) is a genus of early hominins that existed in Africa during the Pliocene and Early Pleistocene. The genera ''Homo'' (which includes modern humans), ''Paranthropus'', and ''Kenyanthropus'' evolved from some ''Aus ...

'' species, Nearly 100

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

specimens of ''A. anamensis'' are known from

Kenya Kenya, officially the Republic of Kenya, is a country located in East Africa. With an estimated population of more than 52.4 million as of mid-2024, Kenya is the 27th-most-populous country in the world and the 7th most populous in Africa. ...

and

Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...

, representing over 20 individuals. The first fossils of ''A. anamensis'' discovered are dated to around 3.8 and 4.2 million years ago and were found in Kanapoi and Allia Bay in northern Kenya. '' A. afarensis'' is normally accepted to have emerged within this lineage. However, ''A. anamensis'' and ''A. afarensis'' appear to have lived side-by-side for at least some period of time, and whether the lineage that led to extant humans emerged in ''A. afarensis'', or directly in ''A. anamensis'' is not fully settled. Fossil evidence determines that ''Australopithecus anamensis'' is the earliest hominin species in the Turkana Basin, but likely co-existed with ''afarensis'' towards the end of its existence. ''A. anamensis'' and ''A. afarensis'' may be treated as a single grouping. Preliminary analysis of the sole upper

cranial Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Thi ...

fossil indicates ''A. anamensis'' had a smaller cranial capacity (estimated 365-370 cm³) than ''A. afarensis''.

Discovery

The first fossilized specimen of the species, although not recognized as such at the time, was a single fragment of

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

(arm bone) found in

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Kanapoi region of West

Lake Turkana Lake Turkana () is a saline lake in the Kenyan Rift Valley, in northern Kenya, with its far northern end crossing into Ethiopia. It is the world's largest permanent desert lake and the world's largest alkaline lake. By volume it is the world ...

by a

Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...

research team in 1965. Bryan Patterson and William W. Howells's initial paper on the bone was published in ''

Science Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...

'' in 1967; their initial analysis suggested an ''Australopithecus'' specimen and an age of 2.5 million years. Patterson and colleagues subsequently revised their estimation of the specimen's age to 4.0–4.5 mya based on faunal correlation data. In 1994, London-born Kenyan paleoanthropologist Meave Leakey and archaeologist

Alan Walker Alan Olav Walker (born 24 August 1997) is a Norwegian DJ and record producer. His songs "Faded (Alan Walker song), Faded", "Sing Me to Sleep", "Alone (Alan Walker song), Alone", "All Falls Down (Alan Walker song), All Falls Down" (with Noah Cy ...

excavated the Allia Bay site and uncovered several additional fragments of the hominid, including one complete

lower jaw In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

bone which closely resembles that of a

common chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close relative the ...

''(Pan troglodytes)'', but whose teeth bear a greater resemblance to those of a

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

. Based on the limited postcranial evidence available, ''A. anamensis'' appears to have been habitually bipedal, although it retained some primitive features of its upper limbs. In 1995, Meave Leakey and her associates, taking note of differences between ''

Australopithecus afarensis ''Australopithecus afarensis'' is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa. The first fossils were discovered in the 1930s, but major fossil finds would not ta ...

'' and the new finds, assigned them to a new species, ''A. anamensis'', deriving its name from the Turkana word ''anam'', meaning "lake". Although the excavation team did not find hips, feet or legs, Meave Leakey believes that ''Australopithecus anamensis'' often climbed trees. Tree climbing was one behavior retained by early

s until the appearance of the first ''

Homo ''Homo'' () is a genus of great ape (family Hominidae) that emerged from the genus ''Australopithecus'' and encompasses only a single extant species, ''Homo sapiens'' (modern humans), along with a number of extinct species (collectively called ...

'' species about 2.5 million years ago. ''A. anamensis'' shares many traits with ''A. afarensis'' and may well be its direct predecessor. Fossil records for ''A. anamensis'' have been dated to between 4.2 and 3.9 million years ago, (see pp.263-265) with findings in the 2000s from stratigraphic sequences dating to about 4.1–4.2 million years ago. Specimens have been found between two layers of

volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...

, dated to 4.17 and 4.12 million years, coincidentally when ''A. afarensis'' appears in the fossil record. The fossils (21 in total) include upper and lower jaws,

fragments, and the upper and lower parts of a leg bone (

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

). In addition to this, the aforementioned fragment of

found in 1965 at the same site at Kanapoi has now been assigned to this species. Australopithecus anamensis 5476

In 2006, a new ''A. anamensis'' find was officially announced, extending the range of ''A. anamensis'' into northeast Ethiopia. Specifically, one site known as Asa Issie provided 30 ''A. anamensis'' fossils. These new fossils, sampled from a woodland context, include the largest hominid

canine tooth In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, eye teeth, vampire teeth, or fangs, are the relatively long, pointed teeth. In the context of the upper jaw, they are also known as '' fangs''. They can appear more f ...

yet recovered and the earliest ''Australopithecus''

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

. The find was in an area known as Middle Awash, home to several other more modern ''Australopithecus'' finds and only six miles (9.7 kilometers) away from the discovery site of '' Ardipithecus ramidus'', the most modern species of ''

Ardipithecus ''Ardipithecus'' is a genus of an extinct hominine that lived during the Late Miocene and Early Pliocene epochs in the Afar Depression, Ethiopia. Originally described as one of the earliest ancestors of humans after they diverged from the chim ...

'' yet discovered. ''Ardipithecus'' was a more primitive hominid, considered the next known step below ''Australopithecus'' on the evolutionary tree. The ''A. anamensis'' find is dated to about 4.2 million years ago, the ''Ar. ramidus'' find to 4.4 million years ago, placing only 200,000 years between the two species and filling in yet another blank in the pre-''Australopithecus'' hominid evolutionary timeline. In 2010, journal articles were published by

Yohannes Haile-Selassie Yohannes Haile-Selassie Ambaye (born 23 February 1961) is an Ethiopian Paleoanthropology, paleoanthropologist. An authority on pre-''Homo sapiens'' hominids, he particularly focuses his attention on the East African Rift and Middle Awash valleys. ...

and others describing the discovery of around 90 fossil specimens in the time period 3.6 to 3.8 million years ago (mya), in the Afar area of Ethiopia, filling in the time gap between ''A. anamensis'' and ''

'' and showing a number of features of both. This supported the idea (proposed for instance by Kimbel et al. in 2006) that ''A. anamensis'' and ''A. afarensis'' were in fact one evolving species (i.e. a

chronospecies A chronospecies is a species derived from a sequential development pattern that involves continual and uniform changes from an extinct ancestral form on an evolutionary scale. The sequence of alterations eventually produces a population that is p ...

resulting from

anagenesis Anagenesis is the gradual evolution of a species that continues to exist as an interbreeding population. This contrasts with cladogenesis, which occurs when branching or splitting occurs, leading to two or more lineages and resulting in separate ...

), but in August 2019, scientists from the same Haile-Selassie team announced the discovery of a nearly intact skull for the first time, and dated to 3.8 mya, of ''A. anamensis'' in Ethiopia. This discovery also indicated that an earlier forehead bone fossil from 3.9 mya was ''A. afarensis'' and therefore the two species over-lapped and could not be a chronospecies (noting that this does not prevent A. afarensis being descended from ''A. anamensis'', but would be descended from only part of the ''A. anamensis'' population). The skull itself was found by Afar herder Ali Bereino in 2016.Greshko, Michael,
'Unprecedented' skull reveals face of human ancestor
', National Geographic, August 28, 2019 Other scientists (e.g. Alemseged, Kimbel, Ward, White) cautioned that one forehead bone fossil, which they viewed as not conclusively ''A. afarensis'', should not be taken as disproving the possibility of anagenesis yet. In August 2019, scientists announced the discovery of MRD-VP-1/1, a nearly intact skull, for the first time, and dated to 3.8 million years ago, of ''A. anamensis'' in Ethiopia. The skull itself was found by Afar herder Ali Bereino in 2016. This skull is important in supplementing the evolutionary lineage of

hominins The Hominini (hominins) form a taxonomic tribe of the subfamily Homininae (hominines). They comprise two extant genera: ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos), and in standard usage exclude the genus ''Gorilla'' (gorillas), ...

. The skull has a unique combination of derived and ancestral characteristics. The cranium was determined to be older than ''A. afarensis'' through analyzing that the cranial capacity is much smaller and the face is very prognathic, both of which indicate that it is earlier than ''A. afarensis''. Known as the MRD cranium, it is that of a male who was at an "advanced developmental age" determined by the worn-down post-canine teeth. The teeth show mesiodistal elongation, which differs from ''A. afarensis.'' Similar to other australopiths, however, it has a narrow upper face with no forehead and a large midface with broad zygomatic bones. Before this new discovery, ''A anamensis'' and ''A afarensis'' were widely thought to have evolved one right after the other in a single lineage. The discovery of MRD, though, suggests that ''A. afarensis'' did not result from anagenesis, but that the two hominin species lived side-by-side for at least 100,000 years.

Environment

''Australopithecus anamensis'' was found in Kenya, specifically at Allia Bay, East Turkana. Through analysis of stable isotope data, their environment is believed to have been more closed woodland canopies surrounding Lake Turkana than are present today. The greatest density of woodlands at Allia Bay was along the ancestral Omo River. More open savanna was thought to exist in the basin margins or uplands. Similarly at Allia Bay, the environment was suggested as much wetter. While not definitive, nut or seed-bearing trees could have been present at Allia Bay, but more research is needed.

Diet

Studies of the microwear on ''A. anamensis'' molar fossils show a pattern of long striations. This pattern is similar to the microwear on the molars of gorillas, suggesting that ''A. anamensis'' had a similar diet to that of the modern gorilla. The microwear patterns are consistent on all ''A. anamensis'' molar fossils regardless of location or time. This shows that their diet largely remained the same no matter what their environment. The earliest dietary isotope evidence in Turkana Basin hominin species comes from the ''A. anamensis''. This evidence suggests that their diet consisted primarily of C3 resources, possibly with a small amount of C4-derived resources. Within the next 1.99- to 1.67-million-year period, at least two distinctive hominin taxa shifted to a higher level of C4-resource consumption. At this point, no cause for this shift in diet is known. This research does not by itself indicate a plant-based diet, because the isotopes can be ingested by eating animals and insects that fed on C3 and C4 resources. ''A. anamensis'' hominins had thick, long, and narrow jaws with their side teeth arranged in parallel lines. The thicker tooth enamel of ''A. anamensis'' suggests that it consumed harder foods than the earlier ''Ar. ramidus'', which may have been an omnivore similar to

chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of Hominidae, great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close rel ...

Relation to other hominin species

''Australopithecus anamensis'' is the intermediate species between ''Ardipithecus ramidus'' and ''Australopithecus afarensis'', and has several shared traits with humans and other apes. Fossil studies of the wrist morphology of ''A. anamensis'' have suggested knuckle-walking, which is a derived trait shared with other African apes. The ''A. anamensis'' hand portrays robust phalanges and metacarpals, and long middle phalanges. These characteristics show that the ''A. anamensis'' likely engaged in arboreal living, but were largely bipedal, although not in an identical way to ''

''. All ''Australopithecus'' species were bipedal and small-brained, and had large teeth. ''A. anamensis'' is often confused with ''Australopithecus afarensis'' due to their similar bone structure and their habitation of woodland areas. These similarities include thick tooth enamel, which is a shared derived trait of all ''Australopithecus'' species, and shared with most

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

hominoids. Tooth size variability in ''A. anamensis'' suggests that significant body size variation existed. In relation to their diet, ''A. anamensis'' species has similarities with their predecessor '' Ardipithecus ramidus''. ''A. anamensis'' sometimes had much larger canines than later ''Australopithecus'' species. ''A. anamensis'' and ''A. afarensis'' have similarities in their humeri and the

e. They both have human-like features and matching sizes. The bodies of ''A. anamensis'' were found to be somewhat larger than those of ''A. afarensis''. Based on additional ''A. afarensis'' collections from the Hadar, Ethiopia, site, the ''A. anamensis'' radius is similar to that of ''A. afarensis'' in the

lunate Lunate is a crescent or moon-shaped microlith. In the specialized terminology of lithic reduction, a lunate flake is a small, crescent-shaped lithic flake, flake removed from a stone tool during the process of pressure flaking. In the Natufian cu ...

and

scaphoid The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and forearm on the thumb side of the wrist (also called the lateral or radial side). It forms the radial border of the carpal tunnel. The scaphoid bone ...

surfaces. Additional findings suggest that ''A. anamensis'' had long arms compared to modern humans.

Physical characteristics

Based on fossil evidence, ''A. anamensis'' expresses high degrees of

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

. Although considered to be the more primitive of the australopiths, ''A. anamensis'' had parts of the knee, tibia, and elbow that were different from apes, which indicates bipedalism as the species' form of locomotion. Specifically, the tibia bone of ''A. anamensis'' has a more expansive upper end with bone. In addition to the modified body parts that indicate bipedalism, ''A. anamensis'' fossils show evidence of tree climbing. Archeology finds indicate that ''A. anamensis'' had long forearms, as well as modified features of the wrist bone. Both the forearms and finger bones of ''A. anamensis'' indicate a potential of using the upper limbs as support when operating in trees or on the ground. Forearm bones belonging to ''A. anamensis'' have been found to be 265 to 277 mm in length. The curved proximal hand phalanx of ''A. anamensis'' in the fossil record that contains strong ridges is indicative of its potential ability to climb. Fossil evidence reveals that ''A. anamensis'' had a somewhat wide jaw joint that was flat from front to back, which resembles a curvature similar to those seen in great apes. Furthermore, the ear canals of ''A. anamensis'' fossils are narrow in diameter. The ear canal most resembles that of chimpanzees and is contrasting to the wide ear canals of both later ''Australopithecus'' and ''Homo.'' The first lower premolar of ''A. anamensis'' is characterized by a singular large cusp. Additionally, ''A. anamensis'' has a narrow first milk molar that contains a large dominant cusp with minimum surface area, which may have been used for crushing.

References

External links

Human Timeline (Interactive)
– Smithsonian,

National Museum of Natural History The National Museum of Natural History (NMNH) is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. With 4.4 ...

(August 2016). {{Taxonbar, from=Q310520 anamensis Pliocene primates Fossil taxa described in 1995 Prehistoric Ethiopia Prehistoric Kenya Pliocene mammals of Africa