Editing Australopithecus afarensis (section)

==Palaeobiology==
===Diet and technology===
''A. afarensis'' was likely a [[generalist and specialist species|generalist]] [[omnivore]]. [[Isotope analysis#Carbon-13|Carbon isotope analysis]] on teeth from Hadar and Dikika 3.4–2.9 million years ago suggests a widely ranging diet between different specimens, with forest-dwelling specimens showing a preference for [[C3 carbon fixation|C<sub>3</sub> forest plants]], and bush- or [[grassland]]-dwelling specimens a preference for [[C4 carbon fixation|C<sub>4</sub>]] [[Crassulacean acid metabolism|CAM]] savanna plants. C<sub>4</sub> CAM sources include grass, seeds, roots, underground [[storage organ]]s, [[succulents]] and perhaps creatures which ate those, such as [[termite]]s. Thus, ''A. afarensis'' appears to have been capable of exploiting a variety of food resources in a wide range of habitats. In contrast, the earlier ''A. anamensis'' and ''Ar. ramidus'', as well as modern savanna chimpanzees, target the same types of food as forest-dwelling counterparts despite living in an environment where these plants are much less abundant. Few modern primate species consume C<sub>4</sub> CAM plants.<ref>{{cite journal|first1=J. G.|last1=Wynn|first2=M.|last2=Sponheimer|first3=W. H.|last3=Kimbel|display-authors=et al.|year=2013|title=Diet of ''Australopithecus afarensis'' from the Pliocene Hadar Formation, Ethiopia|journal=Proceedings of the National Academy of Sciences|volume=110|issue=26|pages=10495–10500|doi=10.1073/pnas.1222559110|pmid=23733965|pmc=3696813|bibcode=2013PNAS..11010495W|doi-access=free}}</ref> The dental anatomy of ''A. afarensis'' is ideal for consuming hard, brittle foods, but microwearing patterns on the molars suggest that such foods were infrequently consumed, probably as fallback items in leaner times.<ref>{{cite journal|first=P.|last=Ungar|year=2004|title=Dental topography and diets of ''Australopithecus afarensis'' and early ''Homo''|journal=Journal of Human Evolution|volume=46|issue=5|pages=605–622|doi=10.1016/j.jhevol.2004.03.004|pmid=15120268|bibcode=2004JHumE..46..605U }}</ref>

In 2009 at Dikika, Ethiopia, a rib fragment belonging to a cow-sized [[ungulate|hoofed animal]] and a partial femur of a goat-sized juvenile [[bovid]] was found to exhibit cut marks, and the former some crushing, which were initially interpreted as the oldest evidence of butchering with stone tools. If correct, this would make it the oldest evidence of sharp-edged stone tool use at 3.4 million years old, and would be attributable to ''A. afarensis'' as it is the only species known within the time and place.<ref>{{cite journal|first1=S. P.|last1=McPherron|first2=Z.|last2=Alemseged|first3=C. W.|last3=Marean|display-authors=et al.|year=2010|title=Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia|journal=Nature|volume=466|issue=7308|pages=857–860|doi=10.1038/nature09248|pmid=20703305|bibcode=2010Natur.466..857M|s2cid=4356816}}</ref> However, because the fossils were found in a [[sandstone]] unit (and were modified by abrasive sand and gravel particles during the fossilisation process), the attribution to hominin activity is weak.<ref>{{cite journal|first1=M.|last1=Domínguez-Rodrigo|first2=T. R.|last2=Pickering|first3=H. T.|last3=Bunn|year=2010|title=Configurational approach to identifying the earliest hominin butchers|journal=Proceedings of the National Academy of Sciences|volume=107|issue=49|pages=20929–20934|doi=10.1073/pnas.1013711107|pmid=21078985|pmc=3000273|bibcode=2010PNAS..10720929D|doi-access=free}}</ref>

===Society===
It is highly difficult to speculate with accuracy the group dynamics of early hominins.<ref>{{cite journal|first=J. J.|last=Werner|year=2012|title=Mating Behavior in ''Australopithecus'' and Early ''Homo'': A Review of the Diagnostic Potential of Dental Dimorphism|journal=University of Western Ontario Journal of Anthropology|volume=22|issue=1|pages=11–19|url=https://ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1307&context=totem}}</ref> ''A. afarensis'' is typically reconstructed with high levels of sexual dimorphism, with males much larger than females. Using general trends in modern primates, high sexual dimorphism usually equates to a [[Polygyny in animals|polygynous]] society due to intense male–male competition over females, like in the [[harem (zoology)|harem]] society of gorillas. However, it has also been argued that ''A. afarensis'' had much lower levels of dimorphism, and so had a multi-male kin-based society like chimpanzees. Low dimorphism could also be interpreted as having had a [[Monogamy in animals|monogamous]] society with strong male–male competition. Contrarily, the canine teeth are much smaller in ''A. afarensis'' than in non-human primates, which should indicate lower aggression because canine size is generally positively correlated with male–male aggression.<ref>{{cite journal|first=C. S.|last=Larsen|year=2003|title=Equality for the sexes in human evolution? Early hominid sexual dimorphism and implications for mating systems and social behavior|journal=Proceedings of the National Academy of Sciences|volume=100|issue=16|pages=9103–9104|doi=10.1073/pnas.1633678100|pmc=170877|pmid=12886010|bibcode=2003PNAS..100.9103L|doi-access=free}}</ref><ref>{{Cite journal| last1=Reno| first1=P. L.| last2=Lovejoy| first2=C. O.|author2-link=Owen Lovejoy|year=2015| title=From Lucy to Kadanuumuu: balanced analyses of ''Australopithecus afarensis'' assemblages confirm only moderate skeletal dimorphism| journal=PeerJ| volume=3| pages=e925|doi=10.7717/peerj.925|issn=2167-8359|pmc=4419524|pmid=25945314| doi-access=free}}</ref><ref>{{Cite journal| last=Lovejoy|first=C. O.|author-link=Owen Lovejoy|year=2009| title=Reexamining human origins in light of ''Ardipithecus ramidus''| journal=Science |volume=326|issue=5949|pages=74e1–8|issn=1095-9203|pmid=19810200|bibcode=2009Sci...326...74L|doi=10.1126/science.1175834|s2cid=42790876|url=http://doc.rero.ch/record/211449/files/PAL_E4439.pdf}}</ref>

===Birth===
[[File:A Visual Comparison of the Pelvis and Bony Birth Canal Vs. the Size of Infant Skull in Primate Species.png|thumb|left|upright=1.2|Diagram comparing birthing mechanisms of a chimpanzee (left), ''A. afarensis'' (middle) and a modern human (right)]]
The platypelloid pelvis may have caused a different birthing mechanism from modern humans, with the [[neonate]] entering the inlet facing laterally (the head was transversally orientated) until it exited through the [[pelvic outlet]]. This would be a non-rotational birth, as opposed to a fully rotational birth in humans. However, it has been suggested that the shoulders of the neonate may have been obstructed, and the neonate could have instead entered the inlet transversely and then rotated so that it exited through the outlet oblique to the main axis of the pelvis, which would be a semi-rotational birth. By this argument, there may not have been much space for the neonate to pass through the birth canal, causing a difficult [[childbirth]] for the mother.<ref>{{cite journal|first1=J. M.|last1=DeSilva|first2=N. M.|last2=Laudicina|first3=K. R.|last3=Rosenberg|first4=K. R.|last4=Trevathan|year=2017|title=Neonatal Shoulder Width Suggests a Semirotational, Oblique Birth Mechanism in ''Australopithecus afarensis''|journal=The Anatomical Record|volume=300|issue=5|pages=890–899|doi=10.1002/ar.23573|pmid=28406564|doi-access=free}}</ref>

===Gait===
{{Multiple image|direction=vertical|image1=Laetoli footprints S1 and S2.jpg|image2=Test-pit L8 at Laetoli Site S.jpg|footer=Overview of the S1 trackway (above) and image of the L8 test-pit (below)}}
The Laetoli fossil trackway, generally attributed to ''A. afarensis'', indicates a rather developed grade of bipedal locomotion, more efficient than the bent-hip–bent-knee (BHBK) gait used by non-human great apes (though earlier interpretations of the gait include a BHBK posture or a shuffling movement). Trail A consists of short, broad prints resembling those of a two-and-a-half-year-old child, though it has been suggested this trail was made by the extinct bear ''[[Agriotherium|Agriotherium africanus]]''. G1 is a trail consisting of four cycles likely made by a child. G2 and G3 are thought to have been made by two adults.<ref name=Sellers2005/> In 2015, two more trackways were discovered made by one individual, named S1, extending for a total of {{cvt|32|m}}. In 2015, a single footprint from a different individual, S2, was discovered.<ref name=Masao2016>{{cite journal|first1=F. T.|last1=Masao|first2=E. B.|last2=Ichumbaki|first3=M.|last3=Cherin|display-authors=et al.|year=2016|title=New footprints from Laetoli (Tanzania) provide evidence for marked body size variation in early hominins|journal=eLife|volume=5|page=e19568|doi=10.7554/eLife.19568|pmc=5156529|pmid=27964778 |doi-access=free }}</ref>

The shallowness of the toe prints would indicate a more [[anatomical terms of motion#Flexion and extension|flexed]] limb posture when the foot hit the ground and perhaps a less arched foot, meaning ''A. afarensis'' was less efficient at bipedal locomotion than humans.<ref>{{cite journal|first1=K. G.|last1=Hatala|first2=B.|last2=Demes|first3=B. G.|last3=Richmond|year=2016|title=Laetoli footprints reveal bipedal gait biomechanics different from those of modern humans and chimpanzees|journal=Proceedings of the Royal Society B|volume=283|issue=1836|doi=10.1098/rspb.2016.0235|page=20160235|pmid=27488647|pmc=5013756}}</ref> Some tracks feature a {{cvt|100|mm}} long drag mark probably left by the heel, which may indicate the foot was lifted at a low angle to the ground. For push-off, it appears weight shifted from the heel to the side of the foot and then the toes. Some footprints of S1 either indicate asymmetrical walking where weight was sometimes placed on the anterolateral part (the side of the front half of the foot) before toe-off, or sometimes the upper body was rotated mid-step. The angle of gait (the angle between the direction the foot is pointing in on touchdown and median line drawn through the entire trackway) ranges from 2–11° for both right and left sides. G1 generally shows wide and asymmetrical angles, whereas the others typically show low angles.<ref name=Masao2016/>

The speed of the track makers has been variously estimated depending on the method used, with G1 reported at 0.47, 0.56, 0.64, 0.7 and 1&nbsp;m/s (1.69, 2, 2.3, 2.5 and 3.6&nbsp;km/h; 1.1, 1.3, 1.4, 1.6 and 2.2&nbsp;mph); G2/3 reported at 0.37, 0.84 and 1&nbsp;m/s (1.3, 2.9 and 3.6&nbsp;km/h; 0.8, 1.8 and 2.2&nbsp;mph);<ref name=Sellers2005>{{cite journal|first1=W. I.|last1=Sellers|first2=G. M.|last2=Cain|first3=W.|last3=Wang|first4=R. H.|last4=Crompton|year=2005|title=Stride lengths, speed and energy costs in walking of ''Australopithecus afarensis'': using evolutionary robotics to predict locomotion of early human ancestors|journal=Journal of the Royal Society Interface|volume=2|issue=5|doi=10.1098/rsif.2005.0060|pages=431–441|pmid=16849203|pmc=1618507}}</ref><ref name=Masao2016/> and S1 at {{cvt|0.51 or 0.93|m/s|km/h mph}}.<ref name=Masao2016/> For comparison, modern humans typically walk at {{cvt|1–1.7|m/s|km/h mph}}.<ref name=Sellers2005/>

The average step distance is {{cvt|568|mm|ft|2}}, and stride distance {{cvt|1139|mm|ft|2}}. S1 appears to have had the highest average step and stride length of, respectively, {{cvt|505–660|mm2}} and {{cvt|1044–1284|mm|ft|2}} whereas G1–G3 averaged, respectively, 416, 453 and 433&nbsp;mm (1.4, 1.5 and 1.4&nbsp;ft) for step and 829, 880 and 876&nbsp;mm (2.7, 2.9 and 2.9&nbsp;ft) for stride.<ref name=Masao2016/>

''A. afarensis'' was also capable of bipedal running with absolute speeds of {{convert|1.74|-|4.97|m/s|km/h mph|sp=us}}, slower than modern humans with maximum running speeds up to {{convert|7.9|m/s|km/h mph|sp=us}}, and its running energetics was similar to those of mammals and birds of similar body size. It has been suggested that the bipedal gait evolved specifically to improve running rather than to just enhance walking.<ref>{{Cite journal|last1=Bates |first1=K. T. |last2=McCormack |first2=S. |last3=Donald |first3=E. |last4=Coatham |first4=S. |last5=Brassey |first5=C. A. |last6=Charles |first6=J. |last7=O'Mahoney |first7=T. |last8=van Bijlert |first8=P. A. |last9=Sellers |first9=W. I. |year=2024 |title=Running performance in ''Australopithecus afarensis'' |journal=Current Biology |volume=35 |issue=1 |pages=224–230.e4 |doi=10.1016/j.cub.2024.11.025 |doi-access=free |pmid=39701094 }}</ref>

===Pathology===
Australopithecines, in general, seem to have had a high incidence rate of vertebral pathologies, possibly because their vertebrae were better adapted to withstand suspension loads in climbing than compressive loads while walking upright.<ref name=Haile2015/>{{rp|95–97}} Lucy presents marked thoracic [[kyphosis]] (hunchback) and was diagnosed with [[Scheuermann's disease]], probably caused by overstraining her back, which can lead to a hunched posture in modern humans due to irregular curving of the spine. Because her condition presented quite similarly to that seen in modern human patients, this would indicate a basically human range of locomotor function in walking for ''A. afarensis''. The original straining may have occurred while climbing or swinging in the trees, though, even if correct, this does not indicate that her species was maladapted for arboreal behaviour, much like how humans are not maladapted for bipedal posture despite developing [[arthritis]].<ref>{{cite journal|first1=D. C.|last1=Cook|first2=J. E.|last2=Buikstra|first3=C. J.|last3=DeRousseau|first4=D. C.|last4=Johanson|author4-link=Donald Johanson|title=Vertebral Pathology in the Afar Australopithecines|journal=American Journal of Physical Anthropology|volume=60|issue=1|pages=83–101|doi=10.1002/ajpa.1330600113|year=1983|pmid=6408925}}</ref> KSD-VP-1/1 seemingly exhibits compensatory action by the neck and lumbar vertebrae (gooseneck) consistent with thoracic kyphosis and Scheuermann's disease, but thoracic vertebrae are not preserved in this specimen.<ref name=Haile2015/>{{rp|95–97}}

In 2010, KSD-VP-1/1 presented evidence of a [[valgus deformity]] of the left ankle involving the [[fibula]], with a bony ring developing on the fibula's joint surface extending the bone an additional {{cvt|5–10|mm}}. This was probably caused by a [[fibular fracture]] during childhood which improperly healed in a [[nonunion]].<ref name=Haile2015/>{{rp|162–163}}

In 2016, palaeoanthropologist John Kappelman argued that the fracturing exhibited by Lucy was consistent with a [[proximal humerus fracture]], which is most often caused by falling in humans. He then concluded she died from falling out of a tree, and that ''A. afarensis'' slept in trees or climbed trees to escape predators. However, similar fracturing is exhibited in many other creatures in the area, including the bones of [[antelope]], [[elephant]]s, [[giraffe]]s and [[rhino]]s, and may well simply be [[taphonomic bias]] (fracturing was caused by fossilisation).<ref>{{cite journal|first=A.|last=Gibbons|year=2016|title=Did famed human ancestor 'Lucy' fall to her death?|journal=Science|doi=10.1126/science.aah7237}}</ref> Lucy may also have been killed in an animal attack or a [[mudslide]].<ref>{{cite journal|first1=P.|last1=Charlier|first2=Y.|last2=Coppens|author2-link=Yves Coppens|first3=A.|last3=Augias|display-authors=et al.|year=2018|title=Mudslide and/or animal attack are more plausible causes and circumstances of death for AL 288 ('Lucy'): A forensic anthropology analysis|journal=Medico-Legal Journal|volume=86|issue=3|pages=139–142|doi=10.1177/0025817217749504|pmid=29313437|s2cid=20995655}}</ref>

The 13 AL 333 individuals are thought to have been deposited at about the same time as one another, bear little evidence of carnivore activity, and were buried on a {{cvt|7|m|adj=on}} stretch of a hill. In 1981, anthropologists James Louis Aronson and Taieb suggested they were killed in a [[flash flood]]. British archaeologist [[Paul Pettitt]] considered natural causes unlikely and, in 2013, speculated that these individuals were purposefully hidden in tall grass by other hominins (funerary caching).<ref>{{cite book|first=P.|last=Pettitt|author-link=Paul Pettitt|year=2013|title=The Palaeolithic Origins of Human Burial|publisher=Routledge|pages=44–45|isbn=978-1-136-69910-8}}</ref> This behaviour has been documented in modern primates, and may be done so that the recently deceased do not attract predators to living grounds.<ref>{{cite journal|first1=P.|last1=Pettitt|author-link=Paul Pettitt|first2=J. R.|last2=Anderson|year=2019|title=Primate thanatology and hominoid mortuary archeology|journal=Primates|volume=61|issue=1|page=10|doi=10.1007/s10329-019-00769-2|pmid=31646398|pmc=6971134|doi-access=free}}</ref>