Hominin turnover at Laetoli is associated with vegetation change: Multiproxy evidence from the large herbivore community.

Vegetation change in eastern Africa during the Pliocene would have had an important impact on hominin adaptation and ecology, and it may have been a key driver of hominin macroevolution, including the extinction of Australopithecus and the emergence of Paranthropus and Homo. The Pliocene paleoanthropological site of Laetoli in Tanzania provides an opportunity to investigate the relationship between vegetation change and hominin turnover because it encompasses the time period when grass cover was spreading across eastern Africa and because hominin species turnover occurred locally at Laetoli, with Paranthropus aethiopicus in the Upper Ndolanya Beds (UNB) replacing Australopithecus afarensis in the Upper Laetolil Beds (ULB). However, it remains unresolved how the vegetation of the UNB and the ULB differed from each other. To examine differences between the two stratigraphic units, multiple proxies-hypsodonty, mesowear, and stable carbon isotopes of tooth enamel (δ13Cenamel)-are used to infer the diets of large herbivores and compare the dietary guild structure of the large herbivore communities. All three proxies indicate an increase in the abrasiveness and C4-content in the diets of the large herbivores in the UNB relative to those in the ULB. After inferring the diets of species based on all three proxies, the large herbivore community of the UNB had a greater proportion of grazers and a smaller proportion of mixed feeders than in the ULB but maintained a similar proportion of browsers and frugivores. The ULB community has few modern-day analogs, whereas the UNB community is most closely analogous to those in modern African grasslands. Thus, hominin turnover at Laetoli is associated with an increase in grass cover within a woodland-grassland mosaic and is part of a broader transformation of the herbivore community structure.

Hominin locomotion and evolution in the Late Miocene to Late Pliocene.

In this review, we present on the evolution of the locomotor adaptation of hominins in the Late Miocene to Late Pliocene, with emphasis on some of the prominent advances and debates that have occurred over the past fifty years. We start with the challenging issue of defining hominin locomotor grades that are currently used liberally and offer our own working definitions of facultative, habitual, and obligate bipedalism. We then discuss the nature of the Pan-Homo last common ancestor and characterize the locomotor adaptation of Sahelanthropus, Orrorin, and Ardipithecus-often referred to as facultative bipeds-and examine the debates on the extent of bipedality and arboreality in these taxa. Moreover, the question of Middle Pliocene hominin locomotor diversity is addressed based on information derived from the 'Little Foot' specimen from Sterkfontein, footprints from Laetoli, and the Burtele Foot in Ethiopia. Our review suggests that the most convincing evidence for locomotor diversity comes from Burtele, whereas the evidence from Sterkfontein and Laetoli is unconvincing and equivocal, respectively. Finally, we address the decades old issue of the significance of arboreality in the otherwise habitual biped, Australopithecus, with emphasis on Australopithecus afarensis and its implications for the paleobiology of these creatures. We conclude that many of the apelike features encountered, mostly in the upper part of the Australopithecus skeleton, were retained for their significance in climbing. Approaches that have investigated character plasticity and those exploring internal bone structure have shown that the shoulder and limbs in Au. afarensis and Australopithecus africanus were involved in arboreal activities that are thought to be key for feeding, nesting, and predator avoidance. We conclude that many of the so-called retained ape-like features persisted due to stabilizing selection, that early hominins engaged in a considerable amount of arboreality even after Australopithecus had become a habitual biped, and arboreality only ceased to be an important component of hominin locomotor behavior after the emergence of Homo erectus.

The Australopithecus assemblage from Sterkfontein Member 4 (South Africa) and the concept of variation in palaeontology.

Interpreting morphological variation within the early hominin fossil record is particularly challenging. Apart from the fact that there is no absolute threshold for defining species boundaries in palaeontology, the degree of variation related to sexual dimorphism, temporal depth, geographic variation or ontogeny is difficult to appreciate in a fossil taxon mainly represented by fragmentary specimens, and such variation could easily be conflated with taxonomic diversity. One of the most emblematic examples in paleoanthropology is the Australopithecus assemblage from the Sterkfontein Caves in South Africa. Whereas some studies support the presence of multiple Australopithecus species at Sterkfontein, others explore alternative hypotheses to explain the morphological variation within the hominin assemblage. In this review, I briefly summarize the ongoing debates surrounding the interpretation of morphological variation at Sterkfontein Member 4 before exploring two promising avenues that would deserve specific attention in the future, that is, temporal depth and nonhuman primate diversity.

New paleoecological inferences based on the Early Pleistocene amphibian and reptile assemblage from Dmanisi (Georgia, Lesser Caucasus).

Dmanisi (Georgia) is one of the oldest Early Paleolithic sites discovered out of Africa. In addition, it is the best site to understand the first Homo deme out of Africa and the first hominin occupation of Central to Western Eurasia. It has produced more than 40 hominin remains, including several very informative skulls, found in direct association with faunal remains and numerous lithic artifacts. To date, fossil amphibians and reptiles are one of the few proxies that have been used to propose quantitative climate reconstructions for the time where the hominins were living at Dmanisi. The aim of the present study is to review and amplify the previous paleoclimatic interpretation given by Blain et al. (2014), with an enhanced methodology using geographic information system and based on uncertain distribution area-occupied distribution area discrimination technique. This procedure permits to approach to a more precise common species distribution area and then using the WorldClim v. 2.1 climate database to propose for the first time monthly reconstructions for temperature and rainfall, in addition to annual parameters. The same technique is used to infer dominant ecoregions through the study area and potential tree coverage. Dmanisi climate is newly reconstructed as warm and semi-arid, similar to the present-day Mediterranean climate. New estimates however suggest warmer temperatures than previously reconstructed, together with a slightly higher but much more irregular amount of rainfall. The aridity indexes suggest a six months dry period, from May to October. Associated regional paleoenvironment is mainly characterized by Mediterranean forests, woodlands, and scrub, and the potential tree coverage is around 25%, that is, much less forested than today. New estimates agree with the 'Iberian' hominin ecological model, and with other proxies (large mammals, small mammals and archaeobotanical remains) that indicate a period of increased aridity contemporaneous with human occupations of the site.

Technological innovations at the onset of the Mid-Pleistocene Climate Transition in high-latitude East Asia.

The interplay between Pleistocene climatic variability and hominin adaptations to diverse terrestrial ecosystems is a key topic in human evolutionary studies. Early and Middle Pleistocene environmental change and its relation to hominin behavioural responses has been a subject of great interest in Africa and Europe, though little information is available for other key regions of the Old World, particularly from Eastern Asia. Here we examine key Early Pleistocene sites of the Nihewan Basin, in high-latitude northern China, dating between ∼1.4 and 1.0 million years ago (Ma). We compare stone-tool assemblages from three Early Pleistocene sites in the Nihewan Basin, including detailed assessment of stone-tool refitting sequences at the ∼1.1-Ma-old site of Cenjiawan. Increased toolmaking skills and technological innovations are evident in the Nihewan Basin at the onset of the Mid-Pleistocene Climate Transition (MPT). Examination of the lithic technology of the Nihewan sites, together with an assessment of other key Palaeolithic sites of China, indicates that toolkits show increasing diversity at the outset of the MPT and in its aftermath. The overall evidence indicates the adaptive flexibility of early hominins to ecosystem changes since the MPT, though regional abandonments are also apparent in high latitudes, likely owing to cold and oscillating environmental conditions. The view presented here sharply contrasts with traditional arguments that stone-tool technologies of China are homogeneous and continuous over the course of the Early Pleistocene.

Coping with arid environments: A critical threshold for human expansion in Europe at the Marine Isotope Stage 12/11 transition? The case of the Iberian Peninsula.

Archaeological remains have highlighted the fact that the interglacial Marine Isotope Stage (MIS) 11 was a threshold from the perspective of hominin evolution in Europe. After the MIS 12 glaciation, considered one of the major climate-driven crises experienced by hominins, the archaeological records show an increasing number of occupations, evidence of new subsistence behaviors, and significant technical innovations. Here, we used statistical and geographic techniques to analyze the amphibian- and reptile-based paleoclimate and habitat reconstructions generated from a large data set of the Iberian Peninsula to (1) investigate if temperature, precipitation, and/or forest cover may have impacted the hominin occupation of the territory during the Early and Middle Pleistocene, (2) propose an 'Iberian' ecological model before and after the MIS 12/11 transition, and (3) evaluate, based on this model, the potential hominin occupation at a European scale. The results indicate the existence of climatic constraints on human settlement related to rainfall and environmental humidity. The Early Pleistocene and the first half of the Middle Pleistocene are dominated by the occupation of relatively humid wooded areas, whereas during the second part of the Middle Pleistocene, a broadening of the earlier ecological niche is clearly observed toward the occupation of more open arid areas. Based on the estimated occupational niche for hominins, a maximum potential distribution for early hominins is proposed in Europe before and after 426 ka. Results also indicate that parts of the Iberian Peninsula may not have been suitable for early hominin occupation. Our ecological model is consistent with the pattern of hominin occupation observed in northern and central Europe, where the earliest evidence reflects only pioneering populations merely extending their ranges in response to the expansion of their preferred habitats, as compared with a more sustained occupation by 400 ka.

New fossils of Australopithecus anamensis from Kanapoi, West Turkana, Kenya (2012-2015).

Kanapoi, Kenya, has yielded the earliest evidence of the genus Australopithecus, Australopithecus anamensis. Renewed fieldwork from 2012 through 2015 yielded 18 new fossils attributable to this species. The new specimens include the second maxillary fragment known from a Kanapoi hominin and the first from a relatively young adult. The new maxilla has the distinctive rounded nasal aperture margin characteristic of A. anamensis. A second partial proximal tibia from the site is the first postcranial element from a small A. anamensis individual. A new partial mandible and complete mandibular dentition display distinctive Kanapoi hominin morphology, but the mandible displays a larger trigonid on its fourth premolar than any known so far. Two new complete sets of mandibular incisors are also notably large, especially the lateral ones, a distinctive feature of A. anamensis compared with Australopithecus afarensis. The new fossils also highlight the distinctive morphology of Kanapoi A. anamensis compared to later hominins.

The inner ear of the Paranthropus specimen DNH 22 from Drimolen, South Africa.

OBJECTIVES: Morphological variation within the southern African hypodigm of Paranthropus has been the focus of major interest since the earliest discoveries in the "Cradle of Humankind." Given the relevance of the bony labyrinth for investigating fossil primate paleobiodiversity, this article aims to provide additional evidence for assessing the degree of regional variation within Paranthropus through the comparative analysis of the inner ear of DNH 22. MATERIALS AND METHODS: As comparative material, 18 southern African hominin specimens from Sterkfontein, Swartkrans, and Makapansgat (plus published data from Kromdraai B), attributed to Australopithecus, early Homo or Paranthropus, as well as 10 extant human and 10 extant common chimpanzee specimens are investigated. A landmark-based geometric morphometric method is applied for quantitatively assessing labyrinthine morphology. Additionally, cochlear parameters and oval window area are measured. RESULTS: In terms of semicircular canal and cochlear shape, DNH 22 most resembles the Paranthropus specimen SKW 18 from Swartkrans. Both specimens differ from the other Paranthropus specimens investigated in this study by an anteroposteriorly large posterior semicircular canal and a cochlea with loose turns in the apical portion. Conversely, the oval window area in DNH 22 closely fits the range observed in Paranthropus from Swartkrans and Kromdraai B. DISCUSSION: The inner ear of the DNH 22 specimen represents a unique opportunity to provide further insight into the early hominin labyrinthine variation pattern. In particular, the description of DNH 22 raises critical questions on the diversity of the vestibular system and evolutionary pattern of the auditory apparatus in Paranthropus.

Chimpanzee vertebrate consumption: Savanna and forest chimpanzees compared.

There is broad consensus among paleoanthropologists that meat-eating played a key role in the evolution of Homo, but the details of where, when, and why are hotly debated. It has been argued that increased faunivory was causally connected with hominin adaptation to open, savanna habitats. If savanna-dwelling chimpanzees eat meat more frequently than do forest chimpanzees, it would support the notion that open, dry, seasonal habitats promote hunting or scavenging by hominoids. Here we present observational and fecal analysis data on vertebrate consumption from several localities within the dry, open Ugalla region of Tanzania. Combining these with published fecal analyses, we summarize chimpanzee vertebrate consumption rates, showing quantitatively that savanna chimpanzee populations do not differ significantly from forest populations. Compared with forest populations, savanna chimpanzees consume smaller vertebrates that are less likely to be shared, and they do so more seasonally. Analyses of chimpanzee hunting that focus exclusively on capture of forest monkeys are thus difficult to apply to chimpanzee faunivory in open-country habitats and may be misleading when used to model early hominin behavior. These findings bear on discussions of why chimpanzees hunt and suggest that increases in hominin faunivory were related to differences between hominins and chimpanzees and/or differences between modern and Pliocene savanna woodland environments.

Evolution of group-wise cooperation: Is direct reciprocity insufficient?

Group-wise cooperation, or cooperation among three or more individuals, is an integral part of human societies. It is likely that group-wise cooperation also played a crucial role in the survival of early hominins, who were confronted with novel environmental challenges, long before the emergence of Homo sapiens. However, previous theoretical and empirical studies, focusing mainly on modern humans, have tended to suggest that evolution of cooperation in sizable groups cannot be explained by simple direct reciprocity and requires some additional mechanisms (reputation, punishment, etc.), which are cognitively too demanding for early hominins. As a partial resolution of the paradox, our recent analysis of a stochastic evolutionary model, which considers the effect of random drift, has revealed that evolution of group-wise cooperation is more likely to occur in larger groups when an individual's share of the benefit produced by one cooperator does not decrease with increasing group size (i.e., goods are non-rivalrous). In this paper, we further extend our previous analysis to explore possible consequences of introducing rare mistakes in behavior or imperfect information about behavior of others on the model outcome. Analyses of the extended models show that evolution of group-wise cooperation can be facilitated by large group size even when individuals intending to cooperate sometimes fail to do so or when all the information about the past behavior of group members is not available. We argue, therefore, that evolution of cooperation in sizable groups does not necessarily require other mechanisms than direct reciprocity if the goods to be produced via group-wise cooperation are non-rivalrous.

Major transitions in human evolution.

Evolutionary problems are often considered in terms of 'origins', and research in human evolution seen as a search for human origins. However, evolution, including human evolution, is a process of transitions from one state to another, and so questions are best put in terms of understanding the nature of those transitions. This paper discusses how the contributions to the themed issue 'Major transitions in human evolution' throw light on the pattern of change in hominin evolution. Four questions are addressed: (1) Is there a major divide between early (australopithecine) and later (Homo) evolution? (2) Does the pattern of change fit a model of short transformations, or gradual evolution? (3) Why is the role of Africa so prominent? (4) How are different aspects of adaptation-genes, phenotypes and behaviour-integrated across the transitions? The importance of developing technologies and approaches and the enduring role of fieldwork are emphasized.This article is part of the themed issue 'Major transitions in human evolution'.

Using the morphology of the hominoid distal fibula to interpret arboreality in Australopithecus afarensis.

The fibula has rarely been considered in anthropological studies. However differences in morphology - and inferred function - of the fibula between human and non-human apes have been noted in the past and related to differences in locomotor behavior. Recent studies have pointed out the correlation between diaphyseal rigidity of the fibula and tibia and locomotor behavior in living hominids, and its possible application for inferring early hominin locomotor behavior. The problem with the application of the method proposed in these studies is the extreme rarity of associated early hominin fibula and tibia. Additionally, previous studies investigating morphological traits of fibulotalar articular facets to infer the degree of arboreality in fossil australopiths were often qualitative. In the present study, articular measurements of the distal fibula of living great apes and humans (Pongo, Gorilla, Pan and Homo) are quantified and compared to Australopithecus afarensis distal fibulae. Quantitative analysis is carried out for articular areas and breadths of the fibulotalar articular facets, for the angles formed by the fibulotalar articular facets and the longitudinal axis of the fibula, and for the angle between the proximal fibulotalar articular facet and the subcutaneous triangular area. Results show that the fibula of A. afarensis bears some traits consistent with modern terrestrial bipedalism, like a more laterally facing lateral malleolus, in association with more ape-like traits, like the smaller distal fibulotalar articular facet area and the more inferiorly oriented fibulotalar articular facets, consistent with A. afarensis being a terrestrial hominin adapted for some form of arboreality.

Preparation and use of varied natural tools for extractive foraging by bonobos (Pan Paniscus).

OBJECTIVES: The tool-assisted extractive foraging capabilities of captive (zoo) and semi-captive (sanctuary) bonobo (Pan paniscus) groups were compared to each other and to those known in wild chimpanzee (Pan troglodytes) cultures. MATERIALS AND METHODS: The bonobos were provided with natural raw materials and challenged with tasks not previously encountered, in experimental settings simulating natural contexts where resources requiring special retrieval efforts were hidden. They were shown that food was buried underground or inserted into long bone cavities, and left to tackle the tasks without further intervention. RESULTS: The bonobos used modified branches and unmodified antlers or stones to dig under rocks and in the ground or to break bones to retrieve the food. Antlers, short sticks, long sticks, and rocks were effectively used as mattocks, daggers, levers, and shovels, respectively. One bonobo successively struck a long bone with an angular hammer stone, completely bisecting it longitudinally. Another bonobo modified long branches into spears and used them as attack weapons and barriers. Bonobos in the sanctuary, unlike those in the zoo, used tool sets to perform sequential actions. DISCUSSION: The competent and diverse tool-assisted extractive foraging by the bonobos corroborates and complements the extensive information on similar tool use by chimpanzees, suggesting that such competence is a shared trait. Better performance by the sanctuary bonobos than the zoo group was probably due to differences in their cultural exposure and housing conditions. The bonobos' foraging techniques resembled some of those attributed to Oldowan hominins, implying that they can serve as referential models.

Middle Pliocene hominin mandibular fourth premolars from Woranso-Mille (Central Afar, Ethiopia).

The Woranso-Mille study area has thus far yielded more than 120 early hominin fossil specimens dated to between 3.4 and 3.8 million years ago. Previous studies indicate that dentognathic fossil remains from the study area show a mosaic of features shared by both Australopithecus anamensis and Australopithecus afarensis. Here, we describe 12 isolated mandibular fourth premolars recovered from the Woranso-Mille study area and compare them with those of other early hominins using both traditional comparative methods and geometric morphometric methods. The results indicate that the Woranso-Mille sample is most similar to Au. afarensis among hominins. However, some specimens show distinctive features of crown shape, namely an extremely bulging distolingual corner associated with a relatively large talonid and a mesiodistally elongated crown. This unique morphology is accompanied by a root form that is different from those identified previously. The existence of distinctive P4 morphology is intriguing given the presence of more than one hominin species at Woranso-Mille, although support for taxonomic heterogeneity in this sample is equivocal. Further, the taxonomic significance of these features is unclear, as they fail to distinguish Pan from Gorilla and known hominin species from one another.

Revisiting scoliosis in the KNM-WT 15000 Homo erectus skeleton.

Owing to its completeness, the 1.5 million year old Nariokotome boy skeleton KNM-WT 15000 is central for understanding the skeletal biology of Homo erectus. Nevertheless, since the reported asymmetries and distortions of Nariokotome boy's axial skeleton suggest adolescent idiopathic scoliosis, possibly associated with congenital skeletal dysplasia, it is questionable whether it still can be used as a reference for H. erectus. Recently, however, the presence of skeletal dysplasia has been refuted. Here, we present a morphological and morphometric reanalysis of the assertion of idiopathic scoliosis. We demonstrate that unarticulated vertebral columns of non-scoliotic and scoliotic individuals can be distinguished based on the lateral deviation of the spinous process, lateral and sagittal wedging, vertebral body torsion, pedicle thickness asymmetry, and asymmetry of superior and inferior articular facet areas. A principal component analysis of the overall asymmetry of all seven vertebral shape variables groups KNM-WT 15000 within non-scoliotic modern humans. There is, however, an anomaly of vertebrae T1-T2 that is compatible with a short left convex curve at the uppermost thoracic region, possibly due to injury or local growth dysbalance. Asymmetries of the facet joints L3-L5 suggest a local right convex curve in the lower lumbar region that probably resulted from juvenile traumatic disc herniation. This pattern is incompatible with adolescent idiopathic scoliosis or other types of scoliosis, including congenital, neuromuscular or syndromic scoliosis. It is, however, consistent with a recent reanalysis of the rib cage that did not reveal any asymmetry. Except for these possibly trauma-related anomalies, the Nariokotome boy fossil therefore seems to belong to a normal H. erectus youth without evidence for adolescent idiopathic scoliosis or other severe pathologies of the axial skeleton.

Subocclusal dental morphology of sahelanthropus tchadensis and the evolution of teeth in hominins.

The evolution of the teeth in hominins is characterized by, among other characters, major changes in root morphology. However, little is known of the evolution from a plesiomorphic, ape-like root morphology to the crown hominin morphology. Here we present a study of the root morphology of the Miocene Chadian hominin Sahelanthropus tchadensis and its comparison to other hominins. The morphology of the whole lower dentition (I1 -M3 ) was investigated and described. The comparison with the species Ardipithecus kaddaba and Ardipithecus ramidus indicates a global homogeneity of root morphology in early hominins. This morphology, characterized notably by a reduction of the size and number of the roots of premolars, is a composite between an ape-like morphology and the later hominin morphology. Trends for root evolution in hominins are proposed, including the transition from a basal hominoid to extant Homo sapiens. This study also illustrates the low association between the evolution of tooth root morphology and the evolution of crowns in hominins.