| Australopithecus sediba | |
|---|---|
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| Reconstructed skeleton of MH1 at theNatural History Museum, London | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Family: | Hominidae |
| Genus: | †Australopithecus |
| Species: | †A. sediba |
| Binomial name | |
| †Australopithecus sediba | |
Australopithecus sediba is anextinctspecies ofaustralopithecine recovered fromMalapa Cave,Cradle of Humankind, South Africa. It is known from a partial juvenile skeleton, theholotype MH1, and a partial adult female skeleton, theparatype MH2. They date to about 1.98 million years ago in theEarly Pleistocene, and coexisted withParanthropus robustus andHomo ergaster /Homo erectus. Malapa Cave may have been a natural death trap, the base of a long vertical shaft which creatures could accidentally fall into.A. sediba was initially described as being a potentialhuman ancestor, and perhaps the progenitor ofHomo, but this is contested and it could also represent a late-surviving population orsister species ofA. africanus which had earlier inhabited the area.
MH1 has a brain volume of about 350–440 cc, similar to other australopithecines. The face of MH1 is strikingly similar toHomo instead of other australopithecines, with a less pronounced brow ridge, cheek bones, andprognathism (the amount the face juts out), and there is evidence of a slight chin. However, such characteristics could be due to juvenility and lost with maturity. The teeth are quite small for an australopithecine. MH1 is estimated at 130 cm (4 ft 3 in) tall, which would equate to an adult height of 150–156 cm (4 ft 11 in – 5 ft 1 in). MH1 and MH2 were estimated to have been about the same weight at 30–36 kg (66–79 lb). Like other australopithecines,A. sediba is thought to have had a narrow andapelike upper chest, but a broad and humanlike lower chest. Like other australopithecines, the arm anatomy seems to suggest a degree of climbing andarboreal behaviour. Thepelvis indicatesA. sediba was capable of a humanlike stride, but the foot points to a peculiar gait not demonstrated in any other hominin involving hyperpronation of the ankle, and resultantly rotating the leg inwards while pushing off. This suite of adaptations may represent a compromise between habitualbipedalism and arboreality.
A. sediba seems to have eaten onlyC3 forest plants such as some grasses andsedges, fruits, leaves, and bark. This strongly contrasts from other earlyhominins which ate a mix of C3 and abundantC4 savanna plants, but is similar to modern savannachimpanzees. No other hominin bears evidence of eating bark as part of regular diet. Such ageneralist diet may have allowed it to occupy a smaller home range than savanna chimps. The Malapa area may have been cooler and more humid than today, featuring closed forests surrounded by more open grasslands.
The first fossil find was a rightclavicle, MH1 (UW88-1), inMalapa Cave,Cradle of Humankind, South Africa, discovered by 9-year-oldMatthew Berger on 15 August 2008 while exploring the digsite headed by his father, South African palaeoanthropologistLee Rogers Berger. Further excavation yielded a partial skeleton for MH1, additionally including a partial skull and jawbone fragments, as well as aspects of the arms, fingers, shoulders,ribcage,spine,pelvis, legs, and feet. MH1 is interpreted as having been a juvenile male due to the apparently pronounced development of the brow ridge andcanineroots, eversion of theangle of the mandible, and large scarring on the bones.[1] However, anthropologistsWilliam Kimbel andYoel Rak contend that these are unreliable methods of determining sex, and suggest that MH1 is female based on the lack of anterior pillars (columns running down alongside the nasal opening down to around the mouth) and a slightly convex subnasal plate, using methods of sex determination forA. africanus.[2] MH1 was nicknamed "Karabo", which means "answer" inTswana, by 17-year-old Omphemetse Keepile fromSt Mary's School, Johannesburg, in a naming contest. She chose this name because, "The fossil represents a solution towards understanding the origins of humankind."[3]
Another partial skeleton, the adult MH2, was recovered by Lee on 4 September 2008 with isolated upper teeth, a partial jawbone, a nearly complete right arm, the rightscapula, and fragments of the shoulders, right arm, spine, ribs, pelvis,knee joint, and feet. Thepubic bone is broad and square, and the muscle scarring on the body is weak to moderate, which suggest that MH2 is female.[1]
The presence of species which evolved after 2.36 million years ago and became extinct around 1.5 million years ago indicates theA. sediba layer dates to sometime within this interval during theEarly Pleistocene.Uranium–lead dating of aflowstone capping the layer yielded a date of 2.026±0.021 million years ago. Usingarchaeomagnetic dating, the sediments have a normalmagnetic polarity (as opposed to the reverse of the magnetic polarity in modern day) and the only time when this occurred during this interval is between 1.95 and 1.78 million years ago.[4] In 2011, the flowstone was more firmly dated to 1.977±0.002 million years ago again using uranium–lead dating.[5]
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The cave networks around Malapa comprise long, interconnected cave openings within a 500 m × 100 m (1,640 ft × 330 ft) area. The Malapa site may have been at the base of an at most 30-metre-deep (98 ft) cavern system. The cave is at the intersection of a north-northeast and north-northwestchert-filled fracture, and the hominin remains were unearthed in a 3.3 m × 4.4 m × 3.5 m (11 ft × 14 ft × 11 ft) section on the north-northwest fracture. The layer was exposed bylimestone mining in the early 20th century. The cave comprises fivesedimentaryfacies A–E of water-laidsandstone, withA. sediba being recovered from facies D, and more hominin remains from facies E. MH1 and MH2 are separated vertically by at most 40 cm (16 in). Facies D is a 1.5-metre-thick (4.9 ft), lightly coloured layer overlying flowstone. Smallpeloids are common, but are fused into large and irregular groups, which indicate they were deposited in a water-logged setting. Peloids may represent faecal matter or soil microbes. The preservation state of MH1 and MH2 indicate they were deposited quickly, were moved very little, and werecemented soon after deposition in aphreatic environment (in a subterranean stream). There is no evidence of scavenging, indicating the area was inaccessible to carnivores.[4]
This could all indicate that Malapa Cave was a deathtrap, with inconspicuous cave openings at the surface. Animals may have been lured by the scent of water emanating from the shaft, and carnivores to the scent of dead animals, and then fallen to their deaths. A large debris flow caused the remains to be deposited deeper into the cave along a subterranean stream, perhaps due to a heavy rainstorm. The chamber eventually collapsed and filled with mud.[4]
In 2010, Lee and colleagues officiallydescribed the speciesAustralopithecus sediba with MH1 as theholotype and MH2 theparatype. The species name "sediba" means "fountain" or "wellspring" in the localSesotho language.[1] BecauseA. sediba had many traits in common withHomo ergaster/H. erectus, particularly in the pelvis and legs, the describers postulated thatA. sediba was atransitional fossil betweenAustralopithecus andHomo.[1] Dental traits are also suggestive of some close relationship betweenA. sediba and the ancestor ofHomo.[6] However, the specimens were found in astratigraphic unit dating to 1.95–1.78 million years ago, whereas the earliestHomo fossils at the time dated to 2.33 million years ago (H. habilis fromHadar, Ethiopia).[1] Currently, the oldestHomo specimen isLD 350-1 dating to 2.8–2.75 million years ago fromLedi-Geraru, Ethiopia.[7] To reconcile the dating discrepancy, the describers also hypothesised thatA. sediba evolved from a population ofA. africanus (which inhabited the same general region) some time before the Malapa hominins, and thatHomo split fromA. sediba sometime thereafter.[1] This would imply an 800,000 yearghost lineage betweenA. africanus and the Malapa hominins.[2] It was also suggested thatA. sediba, instead ofH. habilis orH. rudolfensis, was the direct ancestor ofH. ergaster/H. erectus (the earliest uncontested member of the genusHomo), primarily because the Malapa hominins were dated to 1.98 million years ago in 2011, which at the time predated the earliest representative ofH. ergaster/H. erectus.[5]A. sediba is now thought to have been contemporaneous withH. ergaster/H. erectus andParanthropus robustus in the Cradle of Humankind.[8]
Alternatively,A. sediba could also represent a late-surviving morph orsister species ofA. africanus unrelated toHomo, which would meanHomo-like traits evolved independently inA. sediba andHomo (homoplasy).[2][9][10][11][12] The fossil record of earlyHomo is poorly known and based largely on fragmentary remains, making convincing anatomical comparisons difficult and sometimes unfeasible.[12]A. africanus,A. afarensis, andA. garhi have also been proposed as the true ancestor ofHomo, and the matter is much debated.[7] Further, the holotype is a juvenile, which Kimbel and Rak cite in arguing that some of theHomo-like facial characteristics may have been lost with maturity.[2] Phylogenetic analyses in 2023 based on craniodental morphology recoveredA. sediba in an unstable, varied position among hominins, so the researchers concluded that adult skeletons of this species are required for appropriate classification.[13]
The present classification ofaustralopithecines is in disarray.Australopithecus may be considered agrade taxon whose members are united by their similar physiology rather than close relations with each other over other hominin genera, and, for the most part, it is largely unclear how any species relates to the others.[14]
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Only thecranial vault of MH1 was preserved, which has a volume of 363 cc. The very back of the brain is estimated to have been 7–10 cc. To estimate thecerebellum, the australopithecines KNM-ER 23000 (Paranthropus boisei) and Sts 19 (A. africanus) with volumes of 40–50 cc, as well asKNM-ER 1813 (H. habilis),KNM-ER 1805 (H. habilis), and KNM-ER 1470 (H. rudolfensis) with volumes of 55–75 cc were used to estimate the volume of the MH1 cerebellum as about 50 cc. Considering all these, MH1 may have had a brain volume of about 420–440 cc. This is typical for australopithecines.[1] Using trends seen in modern primates between adult and neonate brain size, neonate brain size may have been 153–201 cc, similar to what is presumed for other australopithecines.[15] Brain configuration appears to have been mostly australopithecine-like, but theorbitofrontal cortex appears to have been more humanlike.[16]
Overall,A. sediba skull anatomy is most similar toA. africanus. However, MH1 has a smaller cranium, a transversely wider cranial vault, more vertically-inclined walls of theparietal bone, and more widely spacedtemporal lines. Much likeHomo, the brow ridge is less pronounced, the cheekbones are less flared, the face does not jut out as far (lessprognathism), and there is a slight chin.[1] However, such characteristics are also found in someA. africanus skulls fromSterkfontein Member 4, which Kimbel and Rak believed could indicate that theseHomo-like attributes would have been lost in maturity. Also, if prognathism is measured using theanterior nasal spine instead of the very base of the nose, prognathism in MH1 falls within the range of that seen inA. africanus.[2] The teeth are quite small for an australopithecine, and are more within the range of those of earlyHomo. However, unlikeHomo, the molars progressively increase in size towards the back of the mouth—as opposed to the second molar being the largest—and the cusps are more closely spaced together.[1]
The shape of themandibular ramus (the bar which connects the jaw to the skull) is quite different between MH1 and MH2. That of MH1 is taller and wider; the front and back border are nearly vertical and parallel, in contrast to the nonparallel borders of MH2 with a concave front border; and thecoronoid process of MH1 is angled towards the back with a deep and asymmetricalmandibular notch, whereas MH2 has an uncurved coronoid process with a shallow mandibular notch. Compared to patterns seen in moderngreat apes, such marked differences exceed what would be expected if these could be explained as due tosexual dimorphism or the juvenile status of MH1. Skeletally,A. sediba may have been a highly variable species.[17]
MH1 and MH2 were estimated to have been roughly the same size, about 30–36 kg (66–79 lb). This is smaller than many contemporary hominins, but reasonable for an australopithecine.[19] MH1 was about 130 cm (4 ft 3 in) tall, but he was a juvenile at about the same skeletal development of a 12-year-old human child or a 9-year-old chimpanzee.A. sediba, much like earlier and contemporary hominins, appears to have had an ape-like growth rate based on dental development rate, so MH1 may have reached about 85% of its adult size assuming a chimpanzeelike growth trajectory, or 80% assuming a humanlike trajectory. This would equate to roughly 150 or 156 cm (4 ft 11 in or 5 ft 1 in).[18]
MH1 preserves 4neck, 6thoracic, and 2lumbar vertebrae; and MH2 preserves 2 neck, 7 thoracic, 2 lumbar, and 1sacral vertebrae.[20] The lordosis (humanlike curvature) and joints of the neck vertebrae, indicating similar head posture to humans. However, the overall anatomy of the neck vertebrae is apelike, and point to a much stiffer neck.A. sediba lacks a humanlikebrachial plexus (which is identified in someA. afarensis), and the human brachial plexus is responsible for nerves and muscle innervation in the arms and hands enhancing motor control.[21] Like humans,A. sediba appears to have had a flexible lumbar series comprising 5 vertebrae—as opposed to 6 static vertebrae in non-human apes—and exhibiting lumbarlordosis (human curvature of the spine) consistent with habitual upright posture. However,A. sediba seems to have had a highly mobile lower back and exaggerated lumbar lordosis,[20] which may have been involved in counteracting torques directed inwards while walking in the hyperpronating gait proposed forA. sediba.[22] MH1 preserves 2 upper thoracic, 1 mid-thoracic, and 3 lower thoracic ribs; and MH2 4 consecutive upper-to-mid-thoracic, and 3 lower thoracic ribs joined with the vertebrae.[20] This indicates thatA. sediba had an apelike constricted upper chest, but the humanlike anatomy of the pelvis may suggestA. sediba had a broad and humanlike lower chest. The narrow upper chest would have hindered arm swinging while walking, and would have restricted the rib cage and prevented heavy breathing and thereby fast walking or long-distance running. In contrast,A. sediba seems to have had a humanlike narrow waist, repositionedabdominal external oblique muscles, and wideriliocostalis muscles on the back, which all would improve walking efficiency by counteracting sideward flexion of the torso.[23]
The pelvis shares several traits with earlyHomo andH. ergaster, as well as KNM-ER 3228 fromKoobi Fora, Kenya, and OH 28 fromOlduvai Gorge, Tanzania, which are unassigned to a species (though generally are classified asHomo spp.) There was more buttressing along theacetabulum andsacrum improving hip extension, enlargement of theiliofemoral ligament attachment shifting the weight behind thecentre of rotation of the hip, more buttressing along the acetabulum andiliac blade improving alternatingpelvic tilt, and more distance between the acetabulum and theischial tuberosity reducingmoment arm at thehamstrings. This may have allowed a humanlike stride inA. sediba. The hip joint appears to have had a more humanlike pattern of load bearing than theH. habilis specimen OH 62.[1] Thebirth canal ofA. sediba appears to be moregynaecoid (the normal human condition) than those of other australopiths which are more platypelloid, thoughA. sediba is not completely gynaecoid which may be due to smaller neonate brain (and thus head) size. Like humans, the birth canal had increased diameter sagittally (from front to back) and the pubis bone curled upwards.[15]
Like other australopithecines and earlyHomo,A. sediba had somewhat apelike upper body proportions with relatively long arms, a high brachial index (forearm tohumerus ratio) of 84, and large joint surfaces. It is debated if apelike upper limb configuration of australopithecines is indicative of arboreal behaviour or simply is a basal trait inherited from the great ape last common ancestor in the absence of major selective pressures to adopt a more humanlike arm anatomy. The shoulders are in a shrugging position, theshoulder blade has a well developedaxillary border, and the conoid tubercle (important in muscle attachment around the shoulder joint) is well defined.[1] Muscle scarring patterns on the clavicle indicate a humanlike range of motion. The shoulder blade is most similar to that oforangutans in terms of the size of theglenoid cavity (which forms the shoulder joint) and its angle with the spine, though the shape of the shoulder blade is most similar to humans andchimpanzees. The humerus has a low degree of torsion unlike humans and African apes, which (along with the short clavicle) suggests the shoulder blade was placed farther from the midline like inHomo, though it is positioned higher up the back like in other australopithecines.[24] The apelike qualities of the arms are apparently more marked inA. sediba than the more ancientA. afarensis, and ifA. afarensis is ancestral toA. sediba, this could indicate an adaptive shift towards arboreal behaviour.[25]
At the elbow joint, thelateral andmedial epicondyles of the humerus are elongated, much like other australopithecines and non-human African apes. The humerus also sports a developed crest at the elbow joint to support thebrachioradialis muscle which flexes the forearm. Like non-human African apes, there is a strong attachment for thebiceps on theradius and for thetriceps on theulna. However, there is lessmechanical advantage for the biceps andbrachialis.[24] The ulna also supports strong attachment for theflexor carpi ulnaris muscle. Theolecranon fossa is large and deep and there is a prominenttrochlear keel, which are important in maintaining stability in the arms while they are extended. The finger bones are long, robust, and curved, and support strongflexor digitorum superficialis muscles important for flexing the fingers.[1] These are sometimes argued as evidence ofarboreal behaviour in australopithecines. The hand also features a relatively long thumb and short fingers, much likeHomo, which could suggest aprecision grip important in creating and using complexstone tools.[26]
Like other australopithecines, the ankle, knee, and hip joints indicate habitualbipedalism. The leg bones are quite similar to those ofA. afarensis. The ankle is mostly humanlike with perhaps a humanlikeAchilles tendon.[27]
Thetalus bone is stout and more like those of non-human apes, and features a medially twisted neck and a low neck torsion angle. It is debated ifA. sediba had a humanlikefoot arch or if the foot was more apelike.[28] Theheel bone is angled at a 45-degree angle, and is markedly angled from the front to the back, most strongly at the peroneal trochlea. The robust peroneal trochlea indicates strongperoneus muscles which extend through the calf to the ankle. The foot lacks the lateral plantar tubercle (which may be involved in dissipate forces when the heel hits the ground in a normal human gait) seen in humans andA. afarensis.[1][27] The gracile body of the heel bone and the robustmalleolus (the bony prominence on each side of the ankle) are quite apelike, with less efficient force transfer between the heel bone and the talus, and apelike mobility at the midfoot.A. sediba is most similar to the condition seen ingorillas, and the foot may have been functionally equivalent to that ofA. africanus.[27][29]
Analysis ofphytoliths (microscopic plant remains) from thedental plaque of both specimens andcarbon isotope analysis shows a diet of almost exclusivelyC3 forest plants despite a presumably wide availability ofC4 plants in their mixed savanna environment. Such a feeding pattern is also observed in modern savanna chimps and is hypothesised for theEarly PlioceneArdipithecus ramidus, but is quite different from any other early hominin. A total of 38 phytoliths were recovered from two teeth from MH1, of which 15 are consistent withdicots, 9monocots, and the other 14 indeterminate. The monocots were probably sourced from C3 grasses andsedges growing in well-watered and shady areas, and other phytoliths were sourced from fruit, leaves, and wood or bark. Though bark is commonly eaten by other primates for its high protein and sugar content, andbark bread has historically been recorded as a famine food, no other hominin is known to have consumed bark regularly. Dental microwearing analysis similarly suggests the two Malapa hominins ate hard foods, complexity values ranging betweenH. erectus and the robustP. robustus.[30] Nonetheless, the jaw does not appear to have been as well adapted for producing high strains compared to other early hominins, which may indicateA. sediba was not as highly dependent on its ability to process mechanically challenging food.[31][32]
The interpretation ofA. sediba as ageneralist herbivore of C3 forest plants is consistent with it being at least partially arboreal. Such a broad diet may have allowedA. sediba to have occupied much smaller home ranges than modern savanna chimps which predominantly consume only fruit, asA. sediba was able to fall back on bark and other fracture-resistant foods.[30]
While walking,A. sediba may have displayed hyperpronation of the ankle joint causing exaggerated transfer of weight inwards during stance phase. For modern human hyperpronators, the foot is highly inverted during the swing phase, and contact with the ground is first made by the outer border of the foot, causing hightorques rotating the entire leg inwards. Similarly, the attachments for therectus femoris andbiceps femoralis muscles inA. sediba are consistent with midline-directed strains across the legs, hips, and knees. This mode of walking is unideal for modern human anatomy, and hyperpronators are at a higher risk of developingplantar fasciitis,shin splints, andtibialstress fractures. To counteract this,A. sediba may have made use of a mobile midfoot as opposed to a stiff humanlike midfoot, which may have prevented overly stressful loading of the ankle.[22]
The hyperpronating gait and related suite of adaptations have not been identified in other hominins, and it is unclear whyA. sediba would develop this.[22] A mobile midfoot would also be beneficial in extensive climbing behaviour,[1][22][27] so hyperpronation may have been a compromise between habitual bipedalism and arboreality.[22]
Thepelvic inlet for a femaleA. sediba is estimated to have been 80.8 mm × 112.4 mm (3.18 in × 4.43 in) long x broad (sagittal x transverse), and since the neonate head size is estimated to have been 89.2 mm (3.51 in) at longest, the neonate probably entered the pelvic inlet transversely orientated similar to other hominins. The midplane of the pelvic inlet is constricted to a minimum of 96.9 mm (3.81 in), so the neonate may not have needed to be rotated while being birthed. Pelvic inlet dimensions were calculated using a composite reconstruction involving the juvenile maleischium; likewise, the birth canal was possibly actually larger than calculated. The shoulders are estimated to have been 74.3 mm (2.93 in) across, so they would not have obstructed birth more than the head would have. Therefore, the neonate would have occupied, at the point of most constriction, about 92.1% of the birth canal, allowing sufficient room for a completely non-rotational birth as is exhibited in non-human apes and possibly other australopithecines (though a semi-rotational birth is also proposed). Though it is possible to pass without any rotation, the midplane expands anteroposteriorly (from front to back), and there would have been more space for the neonate if it rotated so that the longest length of the head lined up with this expansion.[33]
Modern humans, in comparison, have a much more laborious and complex birth requiring full rotation of the neonate, as the large brain and thus head size, as well as the rigid shoulders, of the human neonate make it much more difficult to fit through the birth canal. Using an estimate of 145.8–180.4 cc forA. sediba neonate brain size, neonate head size would have been 73 mm × 89 mm (2.9 in × 3.5 in), similar to a chimp neonate.[33]
Growth trajectory seems to have been noticeably different in MH1 than other hominins. The nasomaxillary (bone from the nose to the upper lip) complex indicates a great degree of bone resorption, most markedly at thetooth roots of the front teeth. This contrasts withA. africanus andA. afarensis which are depository, reflecting increasing prognathism with age.P. robustus also features resorption of the upper jaw, but resorption in MH1 expands along the front teeth to thecanine fossa near the cheek bones, resulting in a mesognathic (somewhat protrusive) face, as opposed to a flat face inP. robustus. Because resorption occurs so close to the cheek bones, this may explain why MH1 does not present flaring cheekbones characteristic ofA. africanus. Tooth eruption probably did not affect the remodeling of the lower face as MH1 already had all of its permanent teeth. Nonetheless, smaller cheek tooth size may have permitted a mesognathic face.A. sediba apparently had a diet markedly in contrast to typical early hominin diets, possibly one similar to that of the modern-dayolive colobus monkey, which mainly eats young leaves; the two species appear to have similar patterns of facial-bone growth. This may indicate diverging resorption and deposition patterns inA. sediba, reflecting different jaw-loading patterns from other hominins. The margins of theeye sockets of MH1 are curved, whereas they are indented inA. africanus, which may indicate bone deposition inA. sediba in regions where bone resorption occurs inA. africanus.[34]
The right lamina of the sixth thoracic vertebra of MH1 presents a penetratingbone tumour, probably abenignosteoid osteoma. The lesion penetrates 6.7 mm (0.26 in) deep and is 5.9 mm (0.23 in) wide, and was still active at the time of death. It did not penetrate theneural canal so it probably did not cause any neurological complications, and there is no evidence ofscoliosis (abnormal curving of the spine). It may have affected movement of the shoulder blade and the upper right quadrant of the back, perhaps causingacute orchronic pain, muscular disturbances, ormuscle spasms. GivenA. sediba may have required climbing ability, the lesion's position near the insertion for thetrapezius,erector spinae, andrhomboid major muscles may have limited normal movement patterns. MH1 has the earliest diagnosed case ofcancer for a hominin by at least 200,000 years, predating the 1.8- to 1.6-million-year-old SK 7923metatarsal fragment presentingosteosarcoma fromSwartkrans, Cradle of Humankind. Tumours are rare in the hominin fossil record, likely due to low incidence rate in general for primates; early hominins likely had the same incidence rates as modern primates. The juvenile MH1 developing a bone tumour is consistent with the general trend of bone tumours mostly occurring in younger individuals.[35]
MH1 and MH2 exhibit perimortem (around the time of death) bone injuries consistent withblunt force trauma. This agrees with the interpretation of the site as the base of a tall shaft, acting as a natural death trap that animals accidentally fell into. MH1 and MH2 may have fallen about 5–10 m (16–33 ft) onto a sloping pile of gravel, sand, and batguano, which probably cushioned the fall to some degree. For MH1, perimortem fracturing is most prominent on the jawbone and teeth, though it is possible that these injuries derived from being hit with a falling object in addition to the fall itself. MH2 bears evidence ofbracing during injury, with loading to the forearm and hand and impact to the chest, perimortem fracturing identified on the right side of the body. These are the first deaths in the australopith fossil record confidently not ascribed to predation or natural causes.[36]
A total of 209 non-hominin fossils were recovered alongside the hominins in facies D and E in 2010, andtaxa identified from these are: thesabre-toothed catDinofelis barlowi, theleopard, theAfrican wild cat, theblack-footed cat, thebrown hyena, thecape fox, themongoosesAtilax mesotes andMungos, agenet, anAfrican wild dog, ahorse, apig, aklipspringer, aMegalotragus antelope, a largealcelaphine antelope, a relative of theharnessed bushbuck, a relative of thegreater kudu, and ahare.[4][37] Today, the black-footed cat and cape fox areendemic to South African grass-, bush-, andscrublands. Similarly, the brown hyena inhabits dry, open habitats and has never been reported in a closed forest setting.Dinofelis andAtilax, on the other hand, are generally indicators of a closed, wet habitat. This may indicate the area featured a closed habitat as well as grasslands—judging by the home range of the cape fox, both existed within 20 km2 (7.7 sq mi) of the site.[37]
Thecoprolite of a carnivore from facies D containedpollen and phytoliths ofPodocarpus orAfrocarpus trees, as well as wood fragments from unidentifiedconifers and dicots. No phytoliths from grasses were found. In modern day, the Malapa site is a grassland, andPodocarpus andAfrocarpus are found 30 km (19 mi) away in theAfromontane forestbiome in the canyons 1,500–1,900 m (4,900–6,200 ft) above sea level in theMagaliesberg mountain range, wherewildfires are less common. This may indicate that Malapa was a cooler, more humid area than today, allowing for enough fire reduction to allow such forest plants to spread that far beyond naturally sheltered areas. Malapa during the Early Pleistocene may have also been at a somewhat lower elevation than today, with valleys and Magaliesberg being less pronounced.[38]
Australopithecines and earlyHomo likely preferred cooler conditions than laterHomo, as there are no australopithecine sites that were below 1,000 m (3,300 ft) in elevation at the time of deposition. This would mean that, like chimps, they often inhabited areas with an average diurnal temperature of 25 °C (77 °F), dropping to 10 or 5 °C (50 or 41 °F) at night.[39] Malapa Cave is currently 1,442 m (4,731 ft) above sea level.[4]A. sediba lived alongsideP. robustus andH. ergaster/H. erectus. BecauseA. africanus went extinct around this time, it is possible that South Africa was arefugium forAustralopithecus until about 2 million years ago with the beginning of major climatic variability and volatility, and potentially competition withHomo andParanthropus.[8]
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