A three-dimensional musculoskeletal model of the pelvis and lower limb of Australopithecus afarensis.

OBJECTIVES: Musculoskeletal modeling is a powerful approach for studying the biomechanics and energetics of locomotion. Australopithecus (A.) afarensis is among the best represented fossil hominins and provides critical information about the evolution of musculoskeletal design and locomotion in the hominin lineage. Here, we develop and evaluate a three-dimensional (3-D) musculoskeletal model of the pelvis and lower limb of A. afarensis for predicting muscle-tendon moment arms and moment-generating capacities across lower limb joint positions encompassing a range of locomotor behaviors. MATERIALS AND METHODS: A 3-D musculoskeletal model of an adult A. afarensis pelvis and lower limb was developed based primarily on the A.L. 288-1 partial skeleton. The model includes geometric representations of bones, joints and 35 muscle-tendon units represented using 43 Hill-type muscle models. Two muscle parameter datasets were created from human and chimpanzee sources. 3-D muscle-tendon moment arms and isometric joint moments were predicted over a wide range of joint positions. RESULTS: Predicted muscle-tendon moment arms generally agreed with skeletal metrics, and corresponded with human and chimpanzee models. Human and chimpanzee-based muscle parameterizations were similar, with some differences in maximum isometric force-producing capabilities. The model is amenable to size scaling from A.L. 288-1 to the larger KSD-VP-1/1, which subsumes a wide range of size variation in A. afarensis. DISCUSSION: This model represents an important tool for studying the integrated function of the neuromusculoskeletal systems in A. afarensis. It is similar to current human and chimpanzee models in musculoskeletal detail, and will permit direct, comparative 3-D simulation studies.

Pliocene hominins from East Turkana were associated with mesic environments in a semiarid basin.

During the middle Pliocene (∼3.8-3.2 Ma), both Australopithecus afarensis and Kenyanthropus platyops are known from the Turkana Basin, but between 3.60 and 3.44 Ma, most hominin fossils are found on the west side of Lake Turkana. Here, we describe a new hominin locality (ET03-166/168, Area 129) from the east side of the lake, in the Lokochot Member of the Koobi Fora Formation (3.60-3.44 Ma). To reconstruct the paleoecology of the locality and its surroundings, we combine information from sedimentology, the relative abundance of associated mammalian fauna, phytoliths, and stable isotopes from plant wax biomarkers, pedogenic carbonates, and fossil tooth enamel. The combined evidence provides a detailed view of the local paleoenvironment occupied by these Pliocene hominins, where a biodiverse community of primates, including hominins, and other mammals inhabited humid, grassy woodlands in a fluvial floodplain setting. Between <3.596 and 3.44 Ma, increases in woody vegetation were, at times, associated with increases in arid-adapted grasses. This suggests that Pliocene vegetation included woody species that were resilient to periods of prolonged aridity, resembling vegetation structure in the Turkana Basin today, where arid-adapted woody plants are a significant component of the ecosystem. Pedogenic carbonates indicate more woody vegetation than other vegetation proxies, possibly due to differences in temporospatial scale and ecological biases in preservation that should be accounted for in future studies. These new hominin fossils and associated multiproxy paleoenvironmental indicators from a single locale through time suggest that early hominin species occupied a wide range of habitats, possibly including wetlands within semiarid landscapes. Local-scale paleoecological evidence from East Turkana supports regional evidence that middle Pliocene eastern Africa may have experienced large-scale, climate-driven periods of aridity. This information extends our understanding of hominin environments beyond the limits of simple wooded, grassy, or mosaic environmental descriptions.

Ledi-Geraru strikes again: morphological affinities of the LD 350-1 mandible with early Homo

The origins of the genus Homo have been a focus of much debate in the paleoanthropological literature due to its importance in understanding the evolutionary trajectories that led to the appearance of archaic humans and our species. On the level of taxonomic classification, the controversies surrounding the origins of Homo are the result of lack of clear classification criteria that separate our genus from australopiths, given the general similarities observed between fossils ascribed to late australopiths and early Homo. The challenge in finding clear autapomorphies for Homo has even led to debates about the classification of Homo habilis and Homo rudolfensis as part of our genus. These debates are further complicated by the scarcity of fossils in the timeframe of appearance of our genus, making any fossils dated to between 3.0 and 2.5 Ma of particular relevance in the context of this discussion. The Ledi-Geraru mandible is one such fossils, which has called the attention of researchers due to its combination of primitive traits seen in Australopithecus and derived traits observed in later Homo. Despite being fragmented and poorly preserved, it is one of the key fossil specimens available from the period mentioned above.

Comparative description and taxonomic affinity of 3.7-million-year-old hominin mandibles from Woranso-Mille (Ethiopia).

Fossil discoveries of early Australopithecus species from Woranso-Mille have played a significant role in improving our understanding of mid-Pliocene hominin evolution and diversity. Here, we describe two mandibles with dentitions, recovered from sediments immediately above a tuff radiometrically dated to 3.76 ± 0.02 Ma, and assess their taxonomic affinity. The two mandibles (MSD-VP-5/16 and MSD-VP-5/50) show morphological similarities with both Australopithecus anamensis and Australopithecus afarensis. Some of the unique features that distinguish Au. anamensis from Au. afarensis are present in the mandibles, which also share a few derived features with Au. afarensis. Their retention of more Kanapoi Au. anamensis-like traits, compared to the fewer derived features they share with Au. afarensis, and the presence of Au. anamensis at Woranso-Mille in 3.8-million-year-old deposits, lends support to their assignment to Au. anamensis. However, it is equally arguable that the few derived dentognathic features they share with Au. afarensis could be taxonomically more significant, making it difficult to conclusively assign these specimens to either species. Regardless of which species they are assigned to, the mosaic nature of the dentognathic morphology and geological age of the two mandibles lends further support to the hypothesized ancestor-descendant relationship between Au. anamensis and Au. afarensis. However, there is now limited fossil evidence indicating that these two species may have overlapped in time. Hence, the last appearance of Au. anamensis and first appearance of Au. afarensis are currently unknown. Recovery of Australopithecus fossils from 4.1 to 3.8 Ma is critical to further address the timing of these events.

New Pliocene hominin remains from the Leado Dido'a area of Woranso-Mille, Ethiopia.

Fossiliferous deposits at Woranso-Mille span the period when Australopithecus anamensis gave rise to Australopithecus afarensis (3.8-3.6 Ma) and encompass the core of the A. afarensis range (ca. 3.5-3.2 Ma). Within the latter period, fossils described to date include the intriguing but taxonomically unattributed Burtele foot, dentognathic fossils attributed to Australopithecus deyiremeda, and one specimen securely attributed to A. afarensis (the Nefuraytu mandible). These fossils suggest that at least one additional hominin lineage lived alongside A. afarensis in the Afar Depression. Here we describe a collection of hominin fossils from a new locality in the Leado Dido'a area of Woranso-Mille (LDD-VP-1). The strata in this area are correlated to the same chron as those in the Burtele area (C2An.3n; 3.59-3.33 Ma), and similar in age to the Maka Sands and the Basal through lower Sidi Hakoma Members of the Hadar Formation. We attribute all but one of the LDD hominin specimens to A. afarensis, based on diagnostic morphology of the mandible, maxilla, canines, and premolars. The LDD specimens generally fall within the range of variation previously documented for A. afarensis but increase the frequency of some rare morphological variants. However, one isolated M3 is extremely small, and its taxonomic affinity is currently unknown. The new observations support previous work on temporal trends in A. afarensis and demonstrate that the large range of variation accepted for this species is present even within a limited spatiotemporal range. The value added with this sample lies in its contribution to controlling for spatiotemporal differences among site samples in the A. afarensis hypodigm and its contemporaneity with non-A. afarensis specimens at Woranso-Mille.

Middle Pliocene hominin distribution patterns in Eastern Africa.

Abundance distributions of large mammals are underused in exploring how ecological pressures vary across contemporaneous sites in the fossil record. To investigate variation in relative abundance across contemporaneous Pliocene mammal communities, we examine the time interval between ∼3.6 and 3.22 Ma at four sites in the Afar and Turkana basins: Hadar and the lower Omo Valley in Ethiopia and East Turkana and West Turkana in Kenya. Taphonomic and collection biases are examined using skeletal parts, body size, and taxonomic data from database collections. Taphonomic biases due to geologic conditions and fossil collection affected all sites, but those in the Turkana Basin appeared particularly affected by collecting bias. As a result, hominin relative abundance is calculated separately using a taphonomic control taxon, which shares similar collection biases and size. Comparisons of mammalian taxonomic groups revealed that the Omo region was dominated by suids and cercopithecids. The other sites are dominated by open habitat and mixed habitat associated bovids. Hominins had higher abundance wherein the dominant mammal taxa indicate a mix of woodland and grassland environments (Hadar) and were rarer at sites where the majority of taxa are associated with woodland vegetation (the Omo Valley). West Turkana is characterized by mixed habitats and the highest relative abundance of hominins relative to control taxa, but sampling issues due to the collection and reporting of papionins likely drive this result. East Turkana has few hominins relative to the control taxon and has dominant habitats indicative of floodplain grasslands but has a small sample size compared with the other sites. These analyses suggest that Kenyanthropus platyops and Australopithecus afarensis inhabited similar types of habitats across different rift basins. Most convincingly, this study contributes to a growing body of evidence suggesting that early hominins diverged from their great ape counterparts by abandoning woodland-dominated habitats.

Statistical estimates of hominin origination and extinction dates: A case study examining the Australopithecus anamensis-afarensis lineage.

Reliable estimates of when hominin taxa originated and went extinct are central to addressing many paleoanthropological questions, including those relating to macroevolutionary patterns. The timing of hominin temporal ranges can be used to test chronological predictions generated from phylogenetic hypotheses. For example, hypotheses of phyletic ancestor-descendant relationships, based on morphological data, predict no temporal range overlap between the two taxa. However, a fossil taxon's observed temporal range is almost certainly underestimated due to the incompleteness of both the fossil record itself and its sampling, and this decreases the likelihood of observing temporal overlap. Here, we focus on a well-known and widely accepted early hominin lineage, Australopithecus anamensis-afarensis, and place 95% confidence intervals (CIs) on its origination and extinction dates. We do so to assess whether its temporal range is consistent with it being a phyletic descendant of Ardipithecus ramidus and/or a direct ancestor to the earliest claimed representative of Homo (i.e., Ledi-Geraru). We find that the last appearance of Ar. ramidus falls within the origination CI of Au. anamensis-afarensis, whereas the claimed first appearance of Homo postdates the extinction CI. These results are consistent with Homo evolving from Au. anamensis-afarensis, but temporal overlap between Ar. ramidus and Au. anamensis-afarensis cannot be rejected at this time. Though additional samples are needed, future research should extend our initial analyses to incorporate the uncertainties surrounding the range endpoints of Ar. ramidus and earliest Homo. Overall, our findings demonstrate the need for quantifying the uncertainty surrounding the appearances and disappearances of hominin taxa in order to better understand the timing of evolutionary events in our clade's history.

Three-dimensional geometric morphometric analysis of the first metacarpal distal articular surface in humans, great apes and fossil hominins.

Understanding the manual abilities of fossil hominins has been a focus of palaeoanthropological research for decades. Of interest are the morphological characteristics of the thumb due to its fundamental role in manipulation, particularly that of the trapeziometacarpal joint. Considerably less attention has been given to the thumb metacarpophalangeal (MCP) joint, which plays a role in stabilizing the thumb during forceful grasps and precision pinching. In this study we use a three-dimensional geometric morphometric approach to quantify the shape of the first metacarpal head in extant hominids (Homo, Pan, Gorilla and Pongo) and six fossil hominin species (Homo neanderthalensis Tabun C1 and La Chappelle-aux-Saints, Homo naledi U.W. 101-1282, Australopithecus sediba MH2, Paranthropus robustus/early Homo SK84, Australopithecus africanus StW 418, Australopithecus afarensis A.L. 333w-39), with the aims of identifying shapes that may be correlated with human-like forceful opposition and determining if similar morphologies are present in fossil hominins. Results show that humans differ from extant great apes by having a distally flatter articular surface, larger epicondyle surface area, and a larger radial palmar condyle. We suggest that this suite of features is correlated with a lower range of motion at the MCP joint, which would enhance the thumbs ability to resist the elevated loads associated with the forceful precision grips typical of humans. Great ape genera are each differentiated by distinctive morphological features, each of which is consistently correlated with the predicted biomechanical demands of their particular locomotor and/or manipulatory habits. Neanderthals and U.W. 101-1282 fall within the modern human range of variation, StW 418, SK 84 and U.W. 88-119 fall in between humans and great apes, and A.L. 333w-39 falls within Pan variation. These results agree with those of traditional linear analyses while providing a more comprehensive quantitative basis from which to interpret the hand functional morphology of extinct hominins.

Comparative description and taxonomy of new hominin juvenile mandibles from the Pliocene of Woranso-Mille (Central Afar, Ethiopia).

Mandibular morphology of Australopithecus afarensis is well known based on abundant fossil mandibles of adult individuals from multiple sites in Ethiopia (Hadar, Woranso-Mille, and Middle Awash) and Tanzania (Laetoli). However, there are only a few juvenile mandibles of the species known from these sites. Here, we describe two recently discovered Pliocene hominin juvenile mandibles from Woranso-Mille (KSD-VP-1/29 and MKM-VP-1/626), that have been radioisotopically dated to 3.6 million years ago. We assign these mandibles to Australopithecus afarensis based on their possession of mandibular morphological features considered as distinctive of the species. These specimens not only increase the sample size of juvenile mandibles of A. afarensis from poorly known time period, but also add new information on the degree of variability in juvenile mandibular morphology within the species. Their dentition samples the whole spectrum of size and shape variation in A. afarensis. Our analysis further indicates that symphyseal morphology of the Laetoli mandibles of early A. afarensis falls within the range of variation of mandibles of the species from Hadar, Woranso-Mille, and Middle Awash. Moreover, the fact that the new 3.6 million-year-old juvenile mandibles from Woranso-Mille have a more receeding symphysis than any of the juvenile and most adult mandibles of A. afarensis from the younger Hadar sequence lends support to the observed trend in symphyseal morphological change in the A. anamensis-A. afarensis chronospecies lineage.

Reply to: Charlier et al. 2018. Mudslide and/or animal attack are more plausible causes and circumstances of death for AL 288 ('Lucy'): a forensic anthropology analysis. Medico-Legal Journal 86(3) 139-142, 2018.

The Pliocene hominin fossil 'Lucy' (A.L. 288-1, Australopithecus afarensis) was discovered in the Afar region of Ethiopia in 1974 and dates to 3.18 million years in age. In Kappelman et al.,1 we presented the results of a detailed investigation of the skeleton that for the first time identified and described unusual bone-into-bone compressive fractures at several of the major long bone joints. Using multiple criteria, we concluded that these fractures are more likely to be perimortem than postmortem in nature. We next evaluated a number of possible mechanisms that could have produced these fractures and, on the basis of all of the evidence, hypothesised that a fall from considerable height, likely out of a tree, with its resulting vertical deceleration event, most closely matched the pattern of fractures preserved in the skeleton and was also the probable cause of death. Charlier et al. disagree with our approach and hypothesis, and instead present what they consider to be better evidence supporting two of the other possible mechanisms for breakage that we also investigated, a mudslide/flood, or an animal attack. We here show that the evidence presented by Charlier et al. is incorrectly interpreted, and that these two alternative hypotheses are less likely to be responsible for the fractures.

Brain size growth in Australopithecus.

Postnatal growth is one of the proximate means by which humans attain massive adult brain size. Humans are characterized by the maintenance of prenatal brain growth rates into the first postnatal year, as well as an overall extended period of growth. The evolution of this pattern is difficult to assess due to its relatively brief duration and the underrepresentation of well-preserved fossil individuals who died during this short period. In this study, I use Monte Carlo methods to reconstruct postnatal brain growth rates in Australopithecus afarensis and Australopithecus africanus, based on estimates of neonatal brain size and of likely brain size and age at death of infant specimens (A.L. 333-105, DIK-1-1, and Taung). Neonatal brain size is reconstructed from the empirical scaling relationship among catarrhines which humans follow, and conservative estimates of fossils' chronological ages and brain sizes are drawn from the literature. Simulated distributions of these values are used to calculate average annual rates (ARs) of brain growth and proportional size change from birth (PSC), which are compared to resampled statistics from humans, chimpanzees and gorillas of known age and sex. Simulated ARs and PSCs for A. afarensis are significantly lower than those of chimpanzees and gorillas. Both ARs and PSCs for A. africanus are similar to chimpanzee and gorilla values. These results indicate that although these early hominins were derived in some aspects of brain anatomy, high rates of brain growth did not appear until later in human evolution. Moreover, findings also imply that brain growth rates are not a simple function of adult brain size. This study provides important new information about the evolution of brain growth, despite limitations inherent in fossil samples.

Visualization of a Juvenile Australopithecus afarensis Specimen: Implications for Functional Foot Anatomy.

Since it was named in 1978, analyses of Australopithecus afarensis have culminated in several dominant theories on how humans acquired many of their unique adaptations. Because bipedal locomotion is one of the earliest characteristics of human functional anatomy to appear in the fossil record, its associated anatomy in early hominins has significant implications for human evolution (Stern 2000). The skeleton and overall morphological characteristics of the foot in Australopithecus afarensis provide important clues about the origins of upright bipedal locomotion. Popularly known as "Selam," the 3.3 million-year-old DIK-1-1 fossil was discovered in Dikika, Ethiopia by Dr. Zeresenay Alemseged and his team in 2000. Selam was an australopithecine who died at three years old, making her the youngest early hominin specimen known today (Alemseged et al. 2006). This discovery allows researchers to investigate not only locomotor patterns of A. afarensis within the context of human evolution, but also to examine what child development may have looked like during this pivotal time. The purpose of this project is to create a 3D animation that accurately reconstructs the anatomy and taphonomy of the Dikika foot. By segmenting CT data, 3D modelling, and animating, this investigation aims to contribute to the breadth of fossil reconstruction techniques in the field of biomedical visualization. This method provides a robust means of communication within, and beyond, the paleoanthropological community about new discoveries and how to visualize them.

A Geometric Morphometric Examination of Hominoid Third Metacarpal Shape and Its Implications for Inferring the Precursor to Terrestrial Bipedalism.

The third metacarpal has been a focus of study when examining questions surrounding early hominin locomotion since this bone is adapted to the diverse range of positional behaviors performed by extant hominoids. The shape of this bone is potentially under strong selective pressure related to the biomechanical demands of terrestrial knuckle-walking, arboreal clambering, and brachiation performed by extant hominoids since the hand directly interacts with the substrate during the performance of these movements. The objective of the present study was to explore shape variation of the third metacarpal and examine how different parts of the bone discriminated between hominoid genera that perform these different locomotor behaviors. In addition to examining general interspecies variation, shape analysis was applied to testing the knuckle-walking hypothesis for human evolution. Fourteen 3D landmark coordinates were collected on hominoid third metacarpals, and principal component analysis and Procrustes distances were used to examine metacarpal shape. Comparable measurements were collected on fossilized third metacarpals of Australopithecus afarensis as an early hominin test case for examining the knuckle-walking hypothesis. Analyses that included landmarks collected on both ends of the bone distinguished humans from great apes and presented a strong functional signal related to suspensory locomotion among nonhuman hominoids, whereas the distal articular surface provided the strongest knuckle-walking signal. The shapes of Australopithecus afarensis metacarpals examined in the current study did not provide evidence for a trajectory of shape change in early hominin evolution that started from a metacarpal adapted for terrestrial knuckle-walking. Anat Rec, 302:983-998, 2019. © 2018 Wiley Periodicals, Inc.

A quantification of calcaneal lateral plantar process position with implications for bipedal locomotion in Australopithecus.

The evolution of bipedalism in the hominin lineage has shaped the posterior human calcaneus into a large, robust structure considered to be adaptive for dissipating peak compressive forces and energy during heel-strike. A unique anatomy thought to contribute to the human calcaneus and its function is the lateral plantar process (LPP). While it has long been known that humans possess a plantarly positioned LPP and apes possess a more dorsally positioned homologous structure, the relative position of the LPP and intraspecific variation of this structure have never been quantified. Here, we present a method for quantifying relative LPP position and find that, while variable, humans have a significantly more plantar position of the LPP than that found in the apes. Among extinct hominins, while the position of the LPP in Australopithecus afarensis falls within the human distribution, the LPP is more dorsally positioned in Australopithecus sediba and barely within the modern human range of variation. Results from a resampling procedure suggest that these differences can reflect either individual variation of a foot structure/function largely shared among Australopithecus species, or functionally distinct morphologies that reflect locomotor diversity in Plio-Pleistocene hominins. An implication of the latter possibility is that calcaneal changes adaptive for heel-striking bipedalism may have evolved independently in two different hominin lineages.

A new fossil cercopithecid tibia from Laetoli and its implications for positional behavior and paleoecology.

Detailed analyses and comparisons of postcranial specimens of Plio-Pleistocene cercopithecids provide an opportunity to examine the recent evolutionary history and locomotor diversity in Old World monkeys. Studies examining the positional behavior and substrate preferences of fossil cercopithecids are also important for reconstructing the paleoenvironments of Plio-Pleistocene hominin sites. Here we describe a new fossil cercopithecid tibia (EP 1100/12) from the Australopithecus afarensis-bearing Upper Laetolil Beds (∼3.7 Ma) of Laetoli in northern Tanzania. The fossil tibia is attributed to cf. Rhinocolobus sp., which is the most common colobine at Laetoli. In addition to qualitative comparisons, the tibial shape of EP 1100/12 was compared to that of 190 extant cercopithecids using three-dimensional landmarks. Discriminant function analyses of the shape data were used to assess taxonomic affinity and shape variation relating to positional behavior. EP 1100/12 clustered with extant colobines, particularly the large-bodied genera Nasalis and Rhinopithecus. Comparisons reveal that EP 1100/12 belongs to a large-bodied monkey that engaged in arboreal pronograde quadrupedalism. These findings add further support to previous inferences that woodland and forest environments dominated the paleoenvironment of the Upper Laetolil Beds, which supported the diverse community of cercopithecids at Laetoli. The inferred paleoecology and the presence of large-bodied arboreally-adapted monkeys at Laetoli show that A. afarensis had access to a range of diverse habitats, including woodlands and forests. This supports the possibility that A. afarensis, with its potential range of positional capabilities, was able to utilize arboreal settings for food acquisition and refuge from predators.

Ecomorphological analysis of bovid mandibles from Laetoli Tanzania using 3D geometric morphometrics: Implications for hominin paleoenvironmental reconstruction.

The current study describes a new method of mandibular ecological morphology (ecomorphology). Three-dimensional geometric morphometrics (3D GM) was used to quantify mandibular shape variation between extant bovids with different feeding preferences. Landmark data were subjected to generalized Procrustes analysis (GPA), principal components analysis (PCA), and discriminant function analysis (DFA). The PCA resulted in a continuum from grazers to browsers along PC1 and DFA classified 88% or more of the modern specimens to the correct feeding category. The protocol was reduced to a subset of landmarks on the mandibular corpus in order to make it applicable to incomplete fossils. The reduced landmark set resulted in greater overlap between feeding categories but maintained the same continuum as the complete landmark model. The DFA resubstitution and jackknife analyses resulted in classification success rates of 85% and 80%, respectively. The reduced landmark model was applied to fossil mandibles from the Upper Laetolil Beds (∼4.3-3.5 Ma) and Upper Ndolanya Beds (∼2.7-2.6 Ma) at Laetoli, Tanzania in order to assess antelope diet, and indirectly evaluate paleo-vegetation structure. The majority of the fossils were classified by the DFA as browsers or mixed feeders preferring browse. Our results indicate a continuous presence of wooded habitats and are congruent with recent environmental studies at Laetoli indicating a mosaic woodland-bushland-grassland savanna ecosystem.

Mudslide and/or animal attack are more plausible causes and circumstances of death for AL 288 ('Lucy'): A forensic anthropology analysis.

Following a global morphological and micro-CT scan examination of the original and cast of the skeleton of Australopithecus afarensis AL 288 ('Lucy'), Kappelman et al. have recently proposed a diagnosis of a fall from a significant height (a tree) as a cause of her death. According to topographical data from the discovery site, complete re-examination of a high-quality resin cast of the whole skeleton and forensic experience, we propose that the physical process of a vertical deceleration cannot be the only cause for her observed injuries. Two different factors were involved: rolling and multiple impacts in the context of a mudslide and an animal attack with bite marks, multi-focal fractures and violent movement of the body. It is important to consider a differential diagnosis of the observed fossil lesions because environmental factors should not be excluded in this ancient archaeological context as with any modern forensic anthropological case.

Thoracic vertebral count and thoracolumbar transition in Australopithecus afarensis.

The evolution of the human pattern of axial segmentation has been the focus of considerable discussion in paleoanthropology. Although several complete lumbar vertebral columns are known for early hominins, to date, no complete cervical or thoracic series has been recovered. Several partial skeletons have revealed that the thoracolumbar transition in early hominins differed from that of most extant apes and humans. Australopithecus africanus, Australopithecus sediba, and Homo erectus all had zygapophyseal facets that shift from thoracic-like to lumbar-like at the penultimate rib-bearing level, rather than the ultimate rib-bearing level, as in most humans and extant African apes. What has not been clear is whether Australopithecus had 12 thoracic vertebrae as in most humans, or 13 as in most African apes, and where the position of the thoracolumbar transitional element was. The discovery, preparation, and synchrotron scanning of the Australopithecus afarensis partial skeleton DIK-1-1, from Dikika, Ethiopia, provides the only known complete hominin cervical and thoracic vertebral column before 60,000 years ago. DIK-1-1 is the only known Australopithecus skeleton to preserve all seven cervical vertebrae and provides evidence for 12 thoracic vertebrae with a transition in facet morphology at the 11th thoracic level. The location of this transition, one segment cranial to the ultimate rib-bearing vertebra, also occurs in all other early hominins and is higher than in most humans or extant apes. At 3.3 million years ago, the DIK-1-1 skeleton is the earliest example of this distinctive and unusual pattern of axial segmentation.

Adaptation to suspensory locomotion in Australopithecus sediba.

Australopithecus sediba is represented by well-preserved fossilized remains from the locality of Malapa, South Africa. Recent work has shown that the combination of features in the limb skeleton of A. sediba was distinct from that of earlier species of Australopithecus, perhaps indicating that this species moved differently. The bones of the arm and forearm indicate that A. sediba was adapted to suspensory and climbing behaviors. We used a geometric morphometric approach to examine ulnar shape, potentially identifying adaptations to forelimb suspensory locomotion in A. sediba. Results indicated suspensory capabilities in this species and a stronger forelimb suspensory signal than has been documented in Australopithecus afarensis. Our study confirms the adaptive significance of functional morphological traits for arboreal movements in the locomotor repertoire of A. sediba and provides important insight into the diversity and mosaic nature of locomotor adaptations among early hominins.