{"id":123,"date":"2017-09-13T20:19:23","date_gmt":"2017-09-13T20:19:23","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-history-of-our-tribe\/chapter\/11-australopithecus-afarensis\/"},"modified":"2017-10-03T15:57:55","modified_gmt":"2017-10-03T15:57:55","slug":"11-australopithecus-afarensis","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-history-of-our-tribe\/chapter\/11-australopithecus-afarensis\/","title":{"raw":"11. Australopithecus afarensis","rendered":"11. Australopithecus afarensis"},"content":{"raw":"
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Australopithecus afarensis <\/i>(4.2 mya)<\/b><\/h1>\r\n

(\u201csouthern ape\u201d \/ Afar region of Ethiopia)<\/h2>\r\n[caption id=\"attachment_193\" align=\"aligncenter\" width=\"350\"]\"7.9\" Figure 11.1\u00a0<\/em>Forensic facial reconstruction of Australopithecus afarensis. \u201cAustralopithecus afarensis<\/a>\u201d by Cicero Moraes is licensed under CC BY-SA 3.0<\/a>.[\/caption]\r\n\r\n
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SITES<\/b><\/h3>\r\nEthiopia:<\/b> Afar Depression (e.g., Hadar and Dikika)\r\n\r\nTanzania:<\/b> Laetoli\r\n\r\nChad:<\/b> Bahr el Ghazal\r\n

PEOPLE<\/b><\/h3>\r\nDonald Johanson, Mary Leakey, Zeresenay Alemseged\r\n\r\n<\/div>\r\n

INTRODUCTION<\/strong><\/h2>\r\nAustralopithecus afarensis<\/i>, or the \u201csouthern ape from Afar,\u201d is a well-known species due to the famous \u201cLucy\u201d specimen. It has been extensively studied by numerous famous paleoanthropologists. As mentioned, it is categorized as a gracile form of australopith. The species survived for over a million years in the changing East African landscape, covering a broad geographic range. The famous Laetoli footprints are attributed to Au. afarensis<\/i> (see Figures 11.5 and 11.6). They provided support for the then controversial idea of habitual bipedalism, as well as the species\u2019 presence in a more open environment.\r\n

PHYLOGENY<\/b><\/h2>\r\nThe most logical ancestor for Au. afarensis<\/i> is Au. anamensis<\/i>. The two species overlapped in time and geographic space. Some paleoanthropologists have always believed that genus: Homo<\/i> is descended from Au. afarensis<\/i>. Over time, others\u00a0have changed their taxonomic scenarios from\u00a0Au. africanus<\/i> to\u00a0Au. afarensis<\/i> (which would formerly have been a sister lineage to Au. africanus<\/i>) as our ancestor, and made Au. africanus<\/i> a side branch of the robust forms. Part of the argument for classifying Au. afarensis<\/i> outside of our lineage had to do with aspects of their anatomy being more derived than our own, e.g. the lateral flare of their ilia (the plural of ilium). Since the discovery of Au. sediba<\/i> (Chapter 21), some scholars are back to favoring Au. africanus<\/i> in our ancestry.\r\n\r\n[caption id=\"attachment_95\" align=\"aligncenter\" width=\"151\"]\"image\" Figure 11.2\u00a0<\/em>\u201cLaetoli recreation.\u201d \u201cLaetoli recreated<\/a>\u201d by Wapondaponda is licensed under CC BY-SA 3.0<\/a>.[\/caption]\r\n

DISCOVERY AND GEOGRAPHIC RANGE<\/b><\/h2>\r\nThe geographic range of Au. afarensis<\/i> extends over 1,600 km from the site of Hadar in the Afar Depression of Ethiopia to the Laetoli site in Tanzania (see Figure 11.3). The holotype<\/b> comes from Laetoli. There is conjecture as to whether the Ethiopian and Tanzanian material should be attributed to the same species, since the sites are distant from one another and separated in time by 800 kya. In addition, if Au. bahrelghazali<\/i> is included as a geographic variant of the species, their range expands 2,500 km westward into Chad (McHenry 2015). Thus this species was very successful at exploiting a variety of environments.\r\n\r\n[caption id=\"attachment_195\" align=\"aligncenter\" width=\"325\"]\"7.11\" Figure 11.3\u00a0<\/em>Map showing the major fossil sites where specimens of Australopithecus and Paranthropus have been found.\u00a0From Clement and Hillson (2013)<\/a>,\u00a0licensed under CC BY 3.0<\/a>.[\/caption]\r\n\r\nWith the discovery of \u201cLucy<\/b>\u201d (3.2 mya) (see Figure 11.7) in 1974 by Donald Johanson<\/b>\u2019s crew at the site of Hadar<\/b> in the Afar Depression of Ethiopia, paleoanthropology gained momentum and the rush was on in East Africa to find more evidence of human origins. Certainly Louis<\/b> and Mary<\/b> Leakey<\/b> recognized the importance of the Great Rift Valley, but Johanson \u201cupped the ante\u201d with his 3.2 mya find. In addition, since Lucy\u2019s skeleton was almost 40% complete (making it one of the six most complete fossilized hominin skeletons older than 100 kya), much could be said about her anatomy and locomotor capabilities.\r\n\r\nSite AL 333<\/b> at Hadar yielded remains of 13 individuals, referred to as the \u201cFirst Family<\/b>.\u201d Some researchers speculated that they may have died together and thus possibly represent a social group. However, recent examination of the deposition pattern at the site suggests otherwise (see Behrensmeyer 2008).\r\n\r\n[caption id=\"attachment_196\" align=\"aligncenter\" width=\"200\"]\"7.12\" Figure 11.4\u00a0<\/em>Dikika Baby. \u201cSelamAustralopithecus<\/a>\u201d by Jlorenz1 is licensed under CC BY-SA 3.0<\/a>.[\/caption]\r\n\r\nThe more recently discovered \u201cDikika Baby\u201d<\/b> (3.3 mya) (see Figure 11.4), also known as \u201cSelam\u201d (meaning \u201cpeace\u201d in the Afar language) has contributed greatly to our knowledge of development in early hominins. Dikika, meaning \u201cnipple\u201d in the Afar language, is the name of the nipple-shaped hill at the site of her discovery. Discovered by Zeresenay Alemseged in 2000, the three-year-old female has also been dubbed \u201cLucy\u2019s Baby\u201d due to its proximity to Hadar where Lucy was discovered. Selam is now the oldest, most complete fossil hominin. It took five years to extract the fossils from the surrounding sandstone matrix in which they were embedded. Thus we can see that not only is there difficulty in locating fossils, along with their living conditions in the desert environments of East Africa, the fossils may take years to process before all of their secrets can be revealed.\r\n\r\n[caption id=\"attachment_197\" align=\"aligncenter\" width=\"250\"]\"7.13\" Figure 11.5\u00a0<\/em>Laetoli footprint cast. \u201cAustralopithecus afarensis footprint<\/a>\u201d by Tim Evanson is licensed under CC BY-SA 2.0<\/a>.[\/caption]\r\n\r\n
\r\n\r\nEven more recent material from the Woranso Mille site in the Afar region has some scientists questioning whether the the Au. afarensis<\/em> hypodygm (all fossil material attributed to a particular species) might represent at least two species. Australopithecus deyiremeda<\/em> has been suggested for the newer material.\r\n\r\nMary Leakey discovered the first and oldest (4.2 mya) Au. afarensis<\/i> material at Laetoli, Tanzania, and the holotype (type specimen) comes from that site. Her team recovered fossil material from 23 individuals, as well as the famous Laetoli footprints. The trail of footprints extends for almost 25 m. They were made by two individuals walking side by side, with a possible third, smaller individual hopping within tracks already made by one of the adults. The prints were formed when the hominins walked through wet ash that had erupted from a nearby volcano.\r\n

PHYSICAL CHARACTERISTICS<\/b><\/h2>\r\nNote: Distinguishing primitive versus derived characteristics is difficult because we do not have all body parts to compare from one species to the next. In order to determine what changed, I am considering those aspects that are more Homo<\/i>-like as derived characteristics, regardless of whether predecessors possessed them. In other words, it is not perfect science!\r\n\r\nAll body parts are represented in the hypodigm<\/b>, i.e. all fossils assigned to a particular species. While some debate surrounds the gait and locomotor efficiency of the species, it is fairly well accepted that they were habitual bipeds that retained some arboreal characteristics in the form of upward-oriented shoulder joints, an ape-like scapula, a high intermembral index, and curved finger bones. Their innominates and lower limbs were unquestionably those of a biped, and the big toe, while slightly divergent from the other four digits, was not nearly the grasping digit seen in apes. The buttressing of their ilium, in the form of the iliac pillar, shows that weight was being transferred through the bone in the same manner as our own. While there is evidence of the bicondylar or carrying angle of the femur, the femoral head was small and the neck (narrowing below the head) was longer in australopiths and paranthropines (i.e. robust australopiths\u2014see Chapters 16\u201319), relative to Homo<\/i> species. Lovejoy believes that the degree of lateral iliac flare and long femoral neck in australopiths were associated with increased leverage of the deep gluteal muscles so that they were more biomechanically efficient than modern humans (Lovejoy 1988). As we gave birth to larger-brained infants, our pelvic aperture had to expand laterally so that the femoral neck became shorter and the deep gluteal muscles became less biomechanically stable\u00a0relative to australopiths. The bony elements of the Homo<\/i> pelvis and hip had to become more robust to handle the increased force that the gluteal muscles generated on the bones (discussed in Lovejoy 1988 and Cartmill and Smith 2009). Based upon the Laetoli footprints, it appears that the feet of Au<\/i>. afarensis<\/i> were slightly inverted, which would have helped with climbing.\r\n\r\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"261\"]\"image\" Figure 11.6\u00a0<\/em>Replica of Laetoli footprints. \u201cLaetoli footprints replica<\/a>\u201d by Momotarou2012 is licensed under CC BY-SA 3.0<\/a>.[\/caption]\r\n\r\n<\/div>\r\nAu. afarensis<\/i> had a prognathic, ape-like face (see Figure 11.8), a primitive skull morphology, and a small brain averaging 420 cc. They exhibited a slight sagittal crest for attachment of the temporalis muscle and a more pronounced nuchal crest, where their nuchal (posterior neck) muscles inserted on the posterior skull. The two crests were compound\u2014a compound sagittal-nuchal crest\u2014meaning that the sagittal crest converged at the center of the nuchal crest. Their teeth were large and their dental arcade was U-shaped, and thus more ape-like. The lower first premolar suggests a transitional phase, termed semisectorial<\/b>, between the honing, sectorial (single-cusped) premolar of the apes and our more bicuspid premolars. The canines were monomorphic. Like Au. anamensis<\/i>, their molars were expanded.\r\n\r\nWhile their hands were capable of a precision grip, they did not have the same degree of mobility in their thumbs as later species of australopiths and paranthropines. The conical thorax is linked to climbing and a large gut, and possibly the degree of lateral flare of the iliac blades.\r\n\r\n[caption id=\"attachment_199\" align=\"aligncenter\" width=\"250\"]\"7.15\" Figure 11.7\u00a0<\/em>\u201cLucy.\u201d \u201cLucy Mexico<\/a>\u201d by danrha is in the public domain.[\/caption]\r\n\r\nThe Dikika Baby (see Figure 11.4) revealed inner ear adaptations that allowed them to distinguish their head from their torso; this is important for running. Her brain was of similar size to that of a same-aged chimp. This indicates that they had a more prolonged developmental period, since the adult brain was, for the most part, larger than those of chimps. While chimps\u2019 brains are ~380 cc, Au. afarensis<\/i>\u2019 were on average 434 cc, and ranged from 342 to 540 cc. She had both deciduous and developing permanent teeth in her jaws. Finally, her ribs were in anatomical position, which confirmed the conical thorax.\r\n\r\n[caption id=\"attachment_200\" align=\"aligncenter\" width=\"300\"]\"7.16\" Figure 11.8\u00a0<\/em>Australopithecus afarensis reconstruction. \u201cAustralopithecusafarensis reconstruction<\/a>\u201d by Durova is licensed under CC BY-SA 4.0<\/a>[\/caption]\r\n\r\nAu. afarensis<\/i> exhibited pronounced sexual dimorphism, with males and females averaging 4\u00b411\u02dd and 3\u00b45\u02dd tall, respectively. Weights ranged from 64 to 99 lb. While the differences in size and morphology between the sexes might suggest that they were promiscuous and that males competed for females, their canines were monomorphic, suggesting pair-bonding. This is also supported by the change in the first mandibular premolar to being semi-sectorial.\r\n
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Review of Primitive Characteristics<\/h3>\r\n