The upper limb of Homo naledi Feuerriegel, Elen M.; Green, David J.; Walker, Christopher S. ...
Journal of human evolution,
March 2017, 2017-03-00, 20170301, Letnik:
104
Journal Article
Recenzirano
Odprti dostop
The evolutionary transition from an ape-like to human-like upper extremity occurred in the context of a behavioral shift from an upper limb predominantly involved in locomotion to one adapted for ...manipulation. Selection for overarm throwing and endurance running is thought to have further shaped modern human shoulder girdle morphology and its position about the thorax. Homo naledi (Dinaledi Chamber, Rising Star Cave, Cradle of Humankind, South Africa) combines an australopith-like cranial capacity with dental characteristics akin to early Homo. Although the hand, foot, and lower limb display many derived morphologies, the upper limb retains many primitive traits. Here, we describe the H. naledi upper extremity (excluding the hand) in detail and in a comparative context to evaluate the diversity of clavicular, scapular, humeral, radial, and ulnar morphology among early hominins and later Homo.
Homo naledi had a scapula with a markedly cranially-oriented glenoid, a humerus with extremely low torsion, and an australopith-like clavicle. These traits indicate that the H. naledi scapula was situated superiorly and laterally on the thorax. This shoulder girdle configuration is more similar to that of Australopithecus and distinct from that of modern humans, whose scapulae are positioned low and dorsally about the thorax. Although early Homo erectus maintains many primitive clavicular and humeral features, its derived scapular morphology suggests a loss of climbing adaptations. In contrast, the H. naledi upper limb is markedly primitive, retaining morphology conducive to climbing while lacking many of the derived features related to effective throwing or running purported to characterize other members of early Homo.
A new species of Homo, Homo naledi, was described in 2015 based on the hominin skeletal remains from the Dinaledi Chamber of the Rising Star cave system, South Africa. Subsequent craniodental ...comparative analyses, both phenetic and cladistic, served to support its taxonomic distinctiveness. Here we provide a new quantitative analysis, where up to 78 nonmetric crown and root traits of the permanent dentition were compared among samples of H. naledi (including remains from the recently discovered Lesedi Chamber) and eight other species from Africa: Australopithecus afarensis, Australopithecus africanus, Paranthropus boisei, Paranthropus robustus, Homo habilis, Homo erectus, Middle Pleistocene Homo sp., and Pleistocene and Holocene Homo sapiens. By using the mean measure of divergence distance statistic, phenetic affinities were calculated among samples to evaluate interspecific relatedness. The objective was to compare the results with those previously obtained, to assess further the taxonomic validity of the Rising Star hominin species. In accordance with earlier findings, H. naledi appears most similar dentally to the other African Homo samples. However, the former species is characterized by its retention and full expression of features relating to the main cusps, as well as the root numbers, with a near absence of accessory traits—including many that, based on various cladistic studies, are plesiomorphic in both extinct and extant African hominins. As such, the present findings provide additional support for the taxonomic validity of H. naledi as a distinct species of Homo.
Objectives
In 2008, an immature hominin defined as the holotype of the new species Australopithecus sediba was discovered at the 1.9 million year old Malapa site in South Africa. The specimen (MH1) ...includes substantial post‐cranial skeletal material, and provides a unique opportunity to assess its skeletal maturation.
Methods
Skeletal maturity indicators observed on the proximal and distal humerus, proximal ulna, distal radius, third metacarpal, ilium and ischium, proximal femur and calcaneus were used to assess the maturity of each bone in comparison to references for modern humans and for wild chimpanzees (Pan troglodytes).
Results
In comparison to humans the skeletal maturational ages for Au. sediba correspond to between 12.0 years and 15.0 years with a mean (SD) age of 13.1 (1.1) years. In comparison to the maturational pattern of chimpanzees the Au. sediba indicators suggest a skeletal maturational age of 9–11 years. Based on either of these skeletal maturity estimates and the body length at death of MH1, an adult height of 150–156 cm is predicted.
Discussion
We conclude that the skeletal remains of MH1 are consistent with an ape‐like pattern of maturity when dental age estimates are also taken into consideration. This maturity schedule in australopiths is consistent with ape‐like estimates of age at death for the Nariokotome Homo erectus remains (KMN‐WT 15000), which are of similar postcranial immaturity to MH1. The findings suggest that humans may have distinctive and delayed post‐cranial schedules from australopiths and H. erectus, implicating a recent evolution of somatic and possibly life history strategies in human evolution.
Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back ...of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in
. We show that MH2 possessed a lower back consistent with lumbar lordosis and other adaptations to bipedalism, including an increase in the width of intervertebral articular facets from the upper to lower lumbar column ('pyramidal configuration'). These results contrast with some recent work on lordosis in fossil hominins, where MH2 was argued to demonstrate no appreciable lordosis ('hypolordosis') similar to Neandertals. Our three-dimensional geometric morphometric (3D GM) analyses show that MH2's nearly complete middle lumbar vertebra is human-like in overall shape but its vertebral body is somewhat intermediate in shape between modern humans and great apes. Additionally, it bears long, cranially and ventrally oriented costal (transverse) processes, implying powerful trunk musculature. We interpret this combination of features to indicate that
used its lower back in both bipedal and arboreal positional behaviors, as previously suggested based on multiple lines of evidence from other parts of the skeleton and reconstructed paleobiology of
.
The thigh and leg of Homo naledi Marchi, Damiano; Walker, Christopher S.; Wei, Pianpian ...
Journal of human evolution,
March 2017, 2017-03-00, 20170301, Letnik:
104
Journal Article
Recenzirano
Odprti dostop
This paper describes the 108 femoral, patellar, tibial, and fibular elements of a new species of Homo (Homo naledi) discovered in the Dinaledi chamber of the Rising Star cave system in South Africa. ...Homo naledi possesses a mosaic of primitive, derived, and unique traits functionally indicative of a bipedal hominin adapted for long distance walking and possibly running. Traits shared with australopiths include an anteroposteriorly compressed femoral neck, a mediolaterally compressed tibia, and a relatively circular fibular neck. Traits shared with Homo include a well-marked linea aspera, anteroposteriorly thick patellae, relatively long tibiae, and gracile fibulae with laterally oriented lateral malleoli. Unique features include the presence of two pillars on the superior aspect of the femoral neck and a tubercular distal insertion of the pes anserinus on the tibia. The mosaic morphology of the H. naledi thigh and leg appears most consistent with a species intermediate between Australopithecus spp. and Homo erectus and, accordingly, may offer insight into the nature of the earliest members of genus Homo. These fossils also expand the morphological diversity of the Homo lower limb, perhaps indicative of locomotor diversity in our genus.
Objective
To examine the effect of a premenopausal risk‐reducing salpingo‐oophorectomy (RRSO) in women at increased risk of ovarian cancer on objective and subjective cognition at least 10 years ...after RRSO.
Design
A cross‐sectional study with prospective follow‐up, nested in a nationwide cohort.
Setting
Multicentre in the Netherlands.
Population or Sample
641 women (66% BRCA1/2 pathogenic variant carriers) who underwent either a premenopausal RRSO ≤ age 45 (n = 436) or a postmenopausal RRSO ≥ age 54 (n = 205). All participants were older than 55 years at recruitment.
Methods
Participants completed an online cognitive test battery and a questionnaire on subjective cognition. We used multivariable regression analyses, adjusting for age, education, breast cancer, hormone replacement therapy, cardiovascular risk factors and depression.
Main Outcome Measures
The influence of RRSO on objective and subjective cognition of women with a premenopausal RRSO compared with women with a postmenopausal RRSO.
Results
After adjustment, women with a premenopausal RRSO (mean time since RRSO 18.2 years) performed similarly on objective cognitive tests compared with women with a postmenopausal RRSO (mean time since RRSO 11.9 years). However, they more frequently reported problems with reasoning (odds ratio OR 1.8, 95% confidence interval 95% CI 1.1–3.1) and multitasking (OR 1.9, 95% CI 1.1–3.4) than women with a postmenopausal RRSO. This difference between groups disappeared in an analysis restricted to women of comparable ages (60–70 years).
Conclusions
Reassuringly, approximately 18 years after RRSO, we found no association between premenopausal RRSO and objective cognition.
Newly exposed cave sediments at the Malapa site include a flowstone layer capping the sedimentary unit containing the Australopithecus sediba fossils. Uranium-lead dating of the flowstone, combined ...with paleomagnetic and stratigraphic analysis of the flowstone and underlying sediments, provides a tightly constrained date of 1.977 ± 0.002 million years ago (Ma) for these fossils. This refined dating suggests that Au. sediba from Malapa predates the earliest uncontested evidence for Homo in Africa.
Homo naledi displays a combination of features across the skeleton not found in any other hominin taxon, which has hindered attempts to determine its placement within the hominin clade. Using ...geometric morphometrics, we assess the morphology of the mandibular premolars of the species at the enamel-dentine junction (EDJ). Comparing with specimens of Paranthropus, Australopithecus and Homo (n = 97), we find that the H. naledi premolars from the Dinaledi chamber consistently display a suite of traits (e.g., tall crown, well-developed P
and P
metaconid, strongly developed P
mesial marginal ridge, and a P
> P
size relationship) that distinguish them from known hominin groups. Premolars from a second locality, the Lesedi Chamber, are consistent with this morphology. We also find that two specimens from South Africa, SK 96 (usually attributed to Paranthropus) and Stw 80 (Homo sp.), show similarities to the species, and we discuss a potential evolutionary link between H. naledi and hominins from Sterkfontein and Swartkrans.
Australopithecus sediba has been hypothesized to be a close relative of the genus Homo. Here we show that MH1, the type specimen of A. sediba, was not optimized to produce high molar bite force and ...appears to have been limited in its ability to consume foods that were mechanically challenging to eat. Dental microwear data have previously been interpreted as indicating that A. sediba consumed hard foods, so our findings illustrate that mechanical data are essential if one aims to reconstruct a relatively complete picture of feeding adaptations in extinct hominins. An implication of our study is that the key to understanding the origin of Homo lies in understanding how environmental changes disrupted gracile australopith niches. Resulting selection pressures led to changes in diet and dietary adaption that set the stage for the emergence of our genus.
The Upper Limb of Australopithecus sediba Churchill, Steven E.; Holliday, Trenton W.; Carlson, Kristian J. ...
Science (American Association for the Advancement of Science),
04/2013, Letnik:
340, Številka:
6129
Journal Article
Recenzirano
The evolution of the human upper limb involved a change in function from its use for both locomotion and prehension (as in apes) to a predominantly prehensile and manipulative role. Well-preserved ...forelimb remains of 1.98-million-year-old Australopithecus sediba from Malapa, South Africa, contribute to our understanding of this evolutionary transition. Whereas other aspects of their postcranial anatomy evince mosaic combinations of primitive (australopith-like) and derived (Homo-like) features, the upper limbs (excluding the hand and wrist) of the Malapa hominins are predominantly primitive and suggest the retention of substantial climbing and suspensory ability. The use of the forelimb primarily for prehension and manipulation appears to arise later, likely with the emergence of Homo erectus.
PDF
