Predator Shaft Joint

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Australopithecus [Au.] sediba Malapa Africa

The fossil remains of an adult female [MH2] and a juvenile male [MH1] were retrieved in Malaga, Africa from a pit, which formed when the roof of a cave collapsed. Subsequent to their demise, their bodies were washed into a pool and cemented with faunal remains. The two Au. sediba fossil skeletons were encased in the poorly sorted, massive, peloidal facies D sandstone, which was bounded by flowstones 1 and 2.The underlying flowstone 1 has a normal polarity correlating with the Hucklebury Ridge event ca 2.05-2.03 Ma. A reversed polarity was recorded for the overlying flowstone 2, which indicates that it was emplaced prior to the beginning of the Olduvai normal subchron ca 1.95Ma. Flowstone 2 most likely dates to the pre-Olduvai excursion ca 1.977 +/-0.002Ma, which was the only geometric event between 2.03 and 1.95 Ma. Facies D and the Au. sediba remains redate 1.977Ma. The oldest relatively complete Homo erectus crania are KNM-ER 37733 [ca!.78Ma] from the Koorbi formation in Kenya and the Dmanisi remains in Georgia. Au sediba is old enough to the ancestor of Homo erectus [R Pickering, 2011].

   A high resolution X-ray scan of the partial MH1 cranium yielded a virtual endocast of his brain case. The endocranial capacity of MH1 was estimated to range between 420 and 440cc, which is lower than the Au. afarensis average and not substantially different from the Flores Island LB1 "hobbit". It is difficult to reconcile the cephalic volume of MH1, with the proposed gradual trend of brain enlargement leading from australopiths  to Homo erectus[J Kristian,2011].

   The high resolution surface morphology reconstruction of the partial MH1 endocast, which may affected by a degree of post-deposition distortion, could not be completely restored. The frontal and left parietal regions might have a greater affinity to modern humans than to chimpanzee endocasts.The temporal poles of MH1 are anteriorly expanded similar to Australopithecus endocasts, but appear more centrally projecting as in modern humans and chimpanzees. Two large horizontal furrows on the left dorsolateral prefrontal surface produce a general configuration that resembles South African australopith endocasts. The sulcal anatomy of MH1, which corresponds to the inferior frontal cortex, seems to have characteristics similar to an ape [ibid].

  The region of the left inferior frontal gyrus anterior to the fronto-orbital sulcus of MH1, in contrast to the typical ape condition, displays a distinct ventrolateral bulge. The MH1 endocast has affinities to the Australopith-like cranial capacity and convolution patterns. It exhibits some evidence of change in the orbital frontal region beyond that seen in australopith endocasts [ibid].

   Analysis of the partial pelvic remains of MH1 and MH2 revealed that several features of the oscoxa of both individuals resemble those of earlier Australopithecus species. They do not appear to have expressed the marked sexual dimorphism of modern humans. The MH1 and MH2 sacrum have a degree of derived morphology, that is either characteristic of Pleistocene and/or modern humans or is intermediate between Australopithecus and Homo. The pelvic inlet diameter of female MH2 approximates that of the Au. afarensis and Au. africanus samples. However the pelvic inlet of MH2 has a greater sagittal dimension than Au. afarensis , AL288-1 and is similar to Au. Africanus ,Sts14, but is less than that of Gona and extant people. [J Kibii,2011].

   The Au sebida iliac blades have Homo-like vertical orientation, with a well defined sigmoid curvature and medial displacement of the ASIS. Moreover the weight transfer region of  the MH1 and MH2 iliac bodies is more robust than that of other australopiths. Some aspects of  pelvic architecture reorganization predated Homo erectus. MH1 has a short ischium in common with Homo. The body size of Au. sediba falls into the low end of the Au. Afarensis and Au. africanus range, which indicates that the above pelvic changes are not related to body size [B Zipfel,2011].

   The well preserved and articulated foot and ankle of MH2 exhibits primitive and derived features. The right tibia has an anteropostiorly expanded metaphysis relative to the anteroposterior dimensions of the articular surface, which is a typical feature of bipedal hominins. The tibal plaford is perpendicular to the shaft, similar to modern and fossil humans. In the sagittal there is a "suggestion" of arching of the foot. The articular facet of the talus varies from apes. The tibia is more robust than that present day people. Morphologically the MH2 talus appears transitional between apes and humans. Canonical variates studies infer that the MH2 calcaneal body has affinities to African apes. The tibal shaft does not have the anterior and lateral bowing, which have been observed in African apes. The ankle and foot of Au seduba have a unique combination of derived and primitive features. The ankle has a number of  human characteristics. The foot's highly mobile subtalar joint and other traits may imply that MH2 was a tree climber. The Au. sediba foot varies from that of Au. afarensis, which has a more derived calconeal corpus and human like medial mallealu. The MH2 foot is anomalous, it does not exhibit the evolutionary direction, that might have been anticipated [ibid].Au. afarensis,Au. sebida,Homo habilis and Homo erectus apear to have had different modes of locomotion.

   Studies of the nearly complete hand of MH2 revealed a combination of Australopithecus and Homo like features. The hand represents a suite of Australopithecus type traits [eg; strong flexor apparatus, which are associated with arboreal locomotion] and characteristics that have affinities to Homo, such as long thumb and short fingers, that are associated with precision gripping. Experimental research indicated that the thumb incurs large loads during tool manufacture, there is no evidence of this on the female MH2 thumb. The robust base of metacarpal 5 compares with that of tree climbing apes. The radial carpel bones of  MH2  have primitive and derived features. The radial carpel and carpometacarpal complex of MH2 appear to have functioned differently from other australopiths and later Homo. The flexo apparatus of MH2 is reduced, when compared to Au. afarensis and was well adapted to cope with arboreal activities. MH2 has a long thumb and short fingers, when compared to other hominins.  MH2 had a number of manual morphological features that are commonly associated with tool production and which are not present to the same extent in Homo habilis OH7 [T Kivell,2011].W Jungers [2011] contends that the Au.sediba hand is essentially australopithecine in all relevant aspects and did not have the capacity for a precision grip.

   MH1 and MH2 have derived and primitive cranial and post cranial morphological features. Some of these characteristics suggest the Au. Sediba might have indulged in arboreal activities to a greater degree than some of their contemporary hominins. Although Au. Sediba has a number of traits, which could infer an ancestral relationship to Homo erectus, other features [eg: the small brain and body size of Au.sediba] tend to suggest that a degree of caution should be exercised and that more definitive data is required before the ancestry of Homo erectus can be established with a reasonable degree of confidence.The remains of at least two other individuals have been discovered at the site.One is an infant

  The largely complete skeletal remains of Stw573 should be extracted from the breccia at Silerberg Grotto,Sterkfontein,about 15km from Malapa by the end of 2011.It has a primative cranium and a more modern hand with a long,strong opposeable thumb and relatively short fingers,when compared to those of modern apes.The hand bones have a short palm and fingers,with the finger bones curved in a similar manner to Au. afarensis,which would have facilitated tree climbing.The feet have ape and human-like features with the most primative parts in the back of the feet similar to other australopithecines and Au. sediba.Stw573 appears to have been fully bipedal and an efficient tree climber.R Clarke [2006] claimed that the Stw573 feet were a good match for the 3.7Ma old foot print trails that were discovered by M Leake et al [1979] at Laetoli.Minimal data has been published by R Clarke et al on Stw573.It might be ancestral to Au. sediba [speculation].Any relationship might be resolved,when additional information becomes available and direct comparisons between the two individuals are made.

  

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