Dietary adaptations of Plio-Pleistocene Bovidae: implications for hominid habitat use

Reconstructing past migratory behaviour of reindeer (Rangifer tarandus): Insights from geometric morphometric analysis of proximal phalanx morphology from extant caribou populations

Reindeer mobility patterns vary widely in modern ecosystems, notably between more open or more wooded environments. This renders the reconstruction of past reindeer mobility patterns challenging, while being at the same time key if archaeologists want to better understand the role that reindeer herds played in the subsistence and territorial organisation of Prehistoric hunter-gatherer societies. Studying the morphology associated with different habitats and mobility patterns can be a useful method for understanding past reindeer behaviour. To access paleoecological information, the relationship between locomotor anatomy and substrate type can be explored in modern animals and transposed to the past, as previous studies have proven that an animal´s environment affects bone morphology. In this study, 3D Geometric Morphometrics are used to explore the impact of extant reindeer habitat type and mobility pattern on phalanx morphology. Results obtained reflects on the potential archaeological application of such an approach for paleoecological reconstructions. Size and shape of phalanx vary significantly, yet complex to interpret in light of interplaying factors such as subspecies, sexual dimorphism and the influence of migration costs, snow cover and substrate type. If direct application to the archaeological record remains preliminary, this first study permits to highlight promising avenues for future research.

Paleoecological evidence for environmental specialization in Paranthropus boisei compared to early Homo

Since the discovery of Paranthropus boisei alongside early Homo at Olduvai Gorge and East Turkana, paleoanthropologists have attempted to understand the different evolutionary paths of these two hominin lineages. Conventional wisdom is that their prolonged phase of sympatry in eastern Africa reflects different adaptive strategies, with early Homo characterized as the ecologically flexible generalist and Paranthropus as the less versatile specialist. If correct, this should imply differences in their use of ancient environments, with early Homo occurring in a broader range of environmental contexts than Paranthropus. This prediction has yet to be subject to rigorous quantitative evaluation. In this study, we use the 2.0-1.4 Ma fossil bovid assemblages associated with early Homo and P. boisei at East Turkana (Kenya) to quantify the breadth of their environmental associations. We find that early Homo occurs in faunal assemblages indicative of a broader range of environments than P. boisei. A null model taking sampling into account shows that the broad environmental associations of early Homo are indistinguishable from random, whereas P. boisei is one of just a handful of large mammal taxa from East Turkana that has a narrower range of environmental associations than expected by chance. These results support the characterization of P. boisei as an ecological specialist relative to the more generalist Homo. Moreover, the narrow environmental associations observed of P. boisei, unlike those of almost all other C₄ grass-consumers in the Turkana Basin, suggest that it likely did not feed on a spatially widespread C₄ resource like the leaves, seeds, or rhizomes of grass.

Seasonality and Oldowan behavioral variability in East Africa

The extent, nature, and temporality of early hominin food procurement strategies have been subject to extensive debate. In this article, we examine evidence for the seasonal scheduling of resource procurement and technological investment in the Oldowan, starting with an evaluation of the seasonal signature of underground storage organs, freshwater resources, and terrestrial animal resources in extant primates and modern human hunter-gatherer populations. Subsequently, we use the mortality profiles, taxonomic composition, and taphonomy of the bovid assemblages at Kanjera South (Homa Peninsula, Kenya) and FLK-Zinj (Olduvai Gorge, Tanzania) to illustrate the behavioral flexibility of Oldowan hominins, who were targeting different seasonally vulnerable demographics. In terms of the lithic assemblages, the specific opportunities and constraints afforded by dry season subsistence at FLK-Zinj may have disincentivized lithic investment, resulting in a more expedient toolkit for fast and effective carcass processing. This may have been reinforced by raw material site provisioning during a relatively prolonged seasonal occupation, reducing pressures on the reduction and curation of lithic implements. In contrast, wet season plant abundance would have offered a predictable set of high-quality resources associated with low levels of competition and reduced search times, in the context of perhaps greater seasonal mobility and consequently shorter occupations. These factors appear to have fostered technological investment to reduce resource handling costs at Kanjera South, facilitated by more consistent net returns and enhanced planning of lithic deployment throughout the landscape. We subsequently discuss the seasonality of freshwater resources in Oldowan procurement strategies, focusing on FwJj20 (Koobi Fora, Kenya). Although more analytical studies with representative sample sizes are needed, we argue that interassemblage differences evidence the ability of Oldowan hominins to adapt to seasonal constraints and opportunities in resource exploitation.

Phenotypic Covariation and Morphological Diversification in the Ruminant Skull

Differences among clades in their diversification patterns result from a combination of extrinsic and intrinsic factors. In this study, I examined the role of intrinsic factors in the morphological diversification of ruminants, in general, and in the differences between bovids and cervids, in particular. Using skull morphology, which embodies many of the adaptations that distinguish bovids and cervids, I examined 132 of the 200 extant ruminant species. As a proxy for intrinsic constraints, I quantified different aspects of the phenotypic covariation structure within species and compared them with the among-species divergence patterns, using phylogenetic comparative methods. My results show that for most species, divergence is well aligned with their phenotypic covariance matrix and that those that are better aligned have diverged further away from their ancestor. Bovids have dispersed into a wider range of directions in morphospace than cervids, and their overall disparity is higher. This difference is best explained by the lower eccentricity of bovids' within-species covariance matrices. These results are consistent with the role of intrinsic constraints in determining amount, range, and direction of dispersion and demonstrate that intrinsic constraints can influence macroevolutionary patterns even as the covariance structure evolves.

Paleodietary reconstruction using stable isotopes and abundance analysis of bovids from the Shungura Formation of South Omo, Ethiopia

Preservation of the stable carbon isotopic composition of fossil tooth enamel enables us to estimate the relative proportion of C3 versus C4 vegetation in an animal's diet, which, combined with analysis of faunal abundance, may provide complementary methods of paleoenvironmental reconstruction. To this end, we analyzed stable carbon isotopic composition (δ(13)C values) of tooth enamel from four bovid tribes (Tragelaphini, Aepycerotini, Reduncini, and Alcelaphini) derived from six members of the Shungura Formation (Members B, C, D, F, G, and L; ages from ca. 2.90-1.05 Ma (millions of years ago) in the Lower Omo Valley of southwestern Ethiopia. The bovids show a wide range of δ(13)C values within taxa and stratigraphic members, as well as temporal changes in the feeding strategies of taxa analyzed throughout the middle to late Pliocene and early Pleistocene. Such variation suggests that the use of actualistic approaches for paleoenvironmental reconstruction may not always be warranted. Alcelaphini was the only taxon analyzed that retained a consistent dietary preference throughout the sequence, with entirely C4-dominated diets. Reduncini had a mixed C3/C4 to C4-dominated diet prior to 2.4 Ma, after which this taxon shifted to a largely C4-dominated diet. Aepycerotini generally showed a mixed C3/C4 diet, with a period of increased C4 diet from 2.5 to 2.3 Ma. Tragelaphini showed a range of mixed C3/C4 diets, with a median value that was briefly nearer the C4 end member from 2.9 to 2.4 Ma but was otherwise towards the C3 end member. These isotopic results, combined with relative abundance data for these bovids, imply that the environment of the Lower Omo Valley consisted of a mosaic of closed woodlands, with riverine forests and open grasslands. However, our data also signify that the overall environment gradually became more open, and that C4 grasses became more dominant. Finally, these results help document the range and extent of environments and potential diets that were available to the four hominin species encountered in the Shungura sequence.

Ecological continuity between Lower and Upper Bed II, Olduvai Gorge, Tanzania

The sediments of Bed II at Olduvai Gorge, Tanzania, have received less scientific scrutiny than Bed I strata, likely due to the lower density of fossil hominins in the younger layers. Nevertheless, Bed II provides important contextual information about changes over time in early hominin environments. Mammal fossils from Bed II are separated into older and younger faunas by a regional disconformity under which lies an aeolian tuff, the Lemuta Member, dated to ∼1.74 Ma (millions of years ago). Differences between the faunal communities above and below the Lemuta Member have been previously noted and interpreted as evidence for distinct environmental change. Here, we investigate the palaeoecological conditions that characterised the transition between older and younger Bed II sites via analysis of their mammalian community ecological niche exploitation profiles, comparing these to known modern habitats. We present a comprehensive species list for both Bed II faunas. An initial correspondence analysis points to palaeoecological differences in pre- and post-Lemuta Member assemblages, although neither is representative of a forest habitat. When taphonomic differences in body mass profiles are taken into account, however, ecological differences appear far less important. Based on a resampling procedure to generate modern locality data with body mass profiles similar to the Bed II faunas, discriminant correspondence analyses liken both fossil assemblages to modern woodland habitats, with Lower Bed II having some affinity to floodplain and marshy woodlands, likely related to the presence of the Olduvai palaeolake in this stratigraphic interval. A comparison of the Bed II faunas to each other suggests that their differences could reasonably be sampled from within a single modern habitat. Although additional evidence points to an increase in aridity subsequent to the Lemuta Member, the importance of woodland habitats throughout Bed II is clear.

On Mesopithecus habitat: Insights from late Miocene fossil vertebrate localities of Bulgaria

The aim of this study is to describe the environments where the cercopithecid Mesopithecus was found during latest Miocene in Europe. For this purpose, we investigate the paleoecology of the herbivorous ungulate mesofauna of three very rich late Miocene fossil localities from southwestern Bulgaria: Hadjidimovo, Kalimantsi and Strumyani. While Mesopithecus has been found in the two first localities, no primate remains have yet been identified in Strumyani. Comparison between localities with and without primates using the herbivore mesofauna allows the cross-corroboration of paleoenvironmental conditions where this primate did and did not live. A multi-parameter statistical approach involving 117 equid and 345 bovid fossil dental and postcranial (phalanges, metapodia, astragali) remains from these three localities provides species to generic-level diet and locomotor habit information in order to characterize the environment in which Mesopithecus evolved. The analysis of dental mesowear indicates that the bovids were mainly mixed feeders, while coeval equids were more engaged in grazing. Meanwhile, postcranial remains show that the ungulate species from Hadjidimovo and Kalimantsi evolved in dry environments with a continuum of habitats ranging from slightly wooded areas to relatively open landscapes, whereas the Mesopithecus-free Strumyani locality was in comparison reflecting a rather contrasted mosaic of environments with predominant open and some more closed and wet areas. Environments in which Mesopithecus is known during the late Miocene were not contrasted landscapes combining open grassy areas and dense forested patches, but instead rather restricted to slightly wooded and homogeneous landscapes including a developed grassy herbaceous layer.

Fossil mammals and paleoenvironments in the Omo-Turkana Basin

Although best known for its fossil hominins, the Omo-Turkana Basin of Kenya and Ethiopia is the source of one of the best records of vertebrate evolution from the Late Cenozoic of Africa. Located near the heart of the East African Rift Valley, the basin serves as an important frame of reference for the continent. The fossil record from this region plays a key role in our efforts to understand the environmental and ecological context of human evolution in Africa. The Omo-Turkana faunal data shed light on key questions of human evolution: What kinds of environments did early humans inhabit? How did these environments change over time? What is the relationship between faunal change in East Africa and broader patterns of climatic change?

The shape of contention: adaptation, history, and contingency in ungulate mandibles

Mandibles and teeth of ungulates have been extensively studied to discern the functional significance of their design. Grazing ungulates have deeper mandibles, longer coronoid processes, flatter incisor arcades, and more hypsodont molars in comparison to browsers. If the functional significance of both mandible and teeth shapes is well-established, it remains uncertain to what extent mandible shapes are really adapted to grazing, meaning that they evolved either to serve their current biological function or just as a structural requirement to accommodate higher crowned molars. Here, we address this question by studying the contribution of phylogeny, hypsodonty, and body size to mandibular shape variation. The mandible shape appeared to be significantly influenced by hypsodonty but not by body size. Interestingly, hypsodonty-related changes influenced the tooth row in artiodactyls and perissodactyls significantly but in the opposite directions, which is ultimately related to their different digestive strategies. Yet, we obtained a strong phylogenetic effect in perissodactyls, suggesting that their mandible shape should be strongly inherited. The strength of this effect was not significant within artiodactyls (where hypsodonty explained much more variance in mandible shape). Digestive strategy is deemed to interplay with hypsodonty to produce different paths of adaptation to particular diets in ungulates.

Oldest evidence of tool making hominins in a grassland-dominated ecosystem

Background

Major biological and cultural innovations in late Pliocene hominin evolution are frequently linked to the spread or fluctuating presence of C₄ grass in African ecosystems. Whereas the deep sea record of global climatic change provides indirect evidence for an increase in C₄ vegetation with a shift towards a cooler, drier and more variable global climatic regime beginning approximately 3 million years ago (Ma), evidence for grassland-dominated ecosystems in continental Africa and hominin activities within such ecosystems have been lacking.

Methodology/Principal Findings

We report stable isotopic analyses of pedogenic carbonates and ungulate enamel, as well as faunal data from ∼2.0 Ma archeological occurrences at Kanjera South, Kenya. These document repeated hominin activities within a grassland-dominated ecosystem.

Conclusions/Significance

These data demonstrate what hitherto had been speculated based on indirect evidence: that grassland-dominated ecosystems did in fact exist during the Plio-Pleistocene, and that early Homo was active in open settings. Comparison with other Oldowan occurrences indicates that by 2.0 Ma hominins, almost certainly of the genus Homo, used a broad spectrum of habitats in East Africa, from open grassland to riparian forest. This strongly contrasts with the habitat usage of Australopithecus, and may signal an important shift in hominin landscape usage.

New evidence for hominin carcass processing strategies at 1.5 Ma, Koobi Fora, Kenya

Reconstruction of early Pleistocene hominin carcass acquisition and processing behaviors are necessarily based at least in part on butchered fossil bones. This paper provides zooarchaeological and taphonomic analyses and behavioral interpretations of three approximately 1.5 million-year-old archaeofaunas from areas 1A and 103 in the Okote Member of the Koobi Fora Formation, northern Kenya: FwJj14A, FwJj14B, and GaJi14. These sites are all located in similar paleoenvironmental contexts, near shallow water with swampy, seasonally flooded areas, and some evidence for more wooded or gallery forest settings. Both individual specimen--and assemblage-level analyses of butchery-marked bones indicate that the hominins appear to have practiced similar butchery strategies at all of these sites, with butchery (defleshing, disarticulation, and marrow extraction) of both high- and low-ranked skeletal elements with no apparent preference for prey size, skeletal region, limb class, or limb portion. Only four tooth-marked specimens, including one likely crocodile-tooth-marked bone, are preserved in all three archaeofaunas. A paucity of limb epiphyses suggests that bone-crunching hyenids may have deleted these portions subsequent to hominin butchery. Strangely, there are no stone tools preserved with the 292 cut-marked and 27 percussion-marked faunal specimens (out of a total of 6,039 specimens), suggesting that raw material availability may have conditioned hominin lithic discard patterns at these locales. These assemblages increase our knowledge of the dietary behavior and ecology of Homo erectus, and provide support for variability in early Pleistocene hominin carcass foraging patterns.

A proper study for mankind: Analogies from the Papionin monkeys and their implications for human evolution

This paper's theme is that analogies drawn from the cercopithecine tribe Papionini, especially the African subtribe Papionina (baboons, mangabeys, and mandrills), can be a valuable source of insights about the evolution of the human tribe, Hominini, to complement homologies found in extant humans and/or African apes. Analogies, involving a "likeness of relations" of the form "A is to B, as X is to Y," can be usefully derived from nonhomologous (homoplastic) resemblances in morphology, behavior, ecology, or population structure. Pragmatically, the papionins are a fruitful source of analogies for hominins because they are phylogenetically close enough to share many basic attributes by homology, yet far enough that homoplastic modifications of these features are easily recognized as such. In "The Seedeaters," an analogy between Theropithecus among baboons and Australopithecus africanus among hominines was the source of a widely discussed (and often misrepresented) diet-based scenario of hominin origins that explained previously unassociated hominin apomorphies, interpreted basal hominins as nonhuman rather than prehuman primates, and accommodated a basal hominin adaptive radiation of at least two lines. Current usage recognizes an even more extensive evolutionary radiation among the basal hominins, originating no earlier than about 7 ma, with multiple lineages documented or inferred by 2.5 ma. Although multilineage clades (especially the Paranthropus clade) within this complex are widely recognized, and emerge from sophisticated, parsimony-based analyses, it is suspected that in many cases, developmental or functional homoplasies are overwhelming the phylogenetic signal in the data. The papionin analogy (specifically the splitting of the traditional, morphology-based genera Cercocebus and Papio mandated by molecular evidence) illustrates the power of these factors to produce erroneous cladograms. Moreover, the rapid deployment of basal hominins across varied African habitats was an ideal scenario for producing morphologically undetectable homoplasy. There seems to be no foolproof way to distinguish, a priori, homologous from homoplastic resemblances in morphology, but one pragmatic strategy is to severely censor the datset, retaining only resemblances or differences (often apparently trivial ones) that cannot be reasonably explained on the basis of functional resemblance or difference, respectively. This strategy may eliminate most morpological data, and leave many fossil taxa incertae sedis, but this is preferable to unwarranted phylogenetic confidence. Another source of phylogenetic uncertainty is the possibility of gene-flow by occasional hybridization between hominins belonging to ecologically and adaptively distinct species or even genera. Although the evidence is unsatisfactorily sparse, it suggests that among catarrhines generally, regardless of major chromosomal rearrangements, intersterility is roughly proportional to time since cladogenetic separation. On a papionin analogy, especially the crossability of Papio hamadryas with Macaca mulatta and Theropithecus gelada, crossing between extant hominine genera is unlikely to produce viable and fertile offspring, but any hominine species whose ancestries diverged less than 4 ma previously may well have been able to produce hybrid offspring that could, by backcrossing, introduce alien genes with the potential of spreading if advantageous. Selection against maladaptive traits would maintain adaptive complexes against occasional genetic infiltration, and the latter does not justify reducing the hybridizing forms to a conspecific or congeneric rank. Whether reticulation could explain apparent parallels in hominin dentition and brain size is uncertain, pending genetic investigation of these apparently complex traits. Widespread papionin taxa (such as Papio baboons and species-groups of the genus Macaca), like many such organisms, are distributed as a "patchwork" of nonoverlapping but often parapatric forms (allotaxa). Morphologically diagnosable, yet not reproductively isolated, most allotaxa would be designated species by the phylogenetic species concept, but subspecies by the biological species concept, and use of the term "allotaxa" avoids this inconsistency. A line of contact between allotaxa typically coincides with an ecotone, with neighboring allotaxa occupying similar econiches in slightly different habitats, and often exhibiting subtle, adaptive, morphological differences as well as their defining differences of pelage. "Hybrid zones," with a wide variety of internal genetic structures and dynamics, typically separate parapatric allotaxa. Current models attribute the formation and maintenance of allotaxa to rapid pulses of population expansion and contraction to and from refugia, driven by late Neogene climatic fluctuations. An overall similarity in depth of genetic diversity suggests that papionin taxa such as Papio baboons, rather than extant humans, may present the better analogy for human population structure of the "prereplacement" era. Neandertals and Afro-Arabian "premodern" populations may have been analogous to extant baboon (and macaque) allotaxa: "phylogenetic" species, but "biological" subspecies. "Replacement," in Europe, probably involved a rapidly sweeping hybrid zone, driven by differential population pressure from the "modern" side. Since the genetic outcome of hybridization at allotaxon boundaries is so variable, the problem of whether any Neandertal genes survived the sweep, and subsequent genetic upheavals, is a purely empirical one; if any genes passed "upstream" across the moving zone, they are likely to be those conferring local adaptive advantage, and markers linked to these. In general, extant papionin analogies suggest that the dynamics and interrelationships among hominin populations now known only from fossils are likely to have been more complex than we are likely to be able to discern from the evidence available, and also more complex than can be easily expressed in conventional taxonomic terminology.

Mammalian body size changes and Plio-Pleistocene environmental shifts: implications for understanding hominin evolution in eastern and southern Africa

This study examines geographic and temporal variation in three mammalian taxa co-occurring in eastern and southern Africa. The selected taxa-the spotted hyena (Crocuta crocuta), the plains zebra (Equus burchellii), and the impala (Aepyceros melampus)--are geographically widespread in modern times and are abundant in eastern and southern African Plio-Pleistocene fossil sites. Craniodental measurements of modern conspecifics from known geographic locations are compared using multivariate statistical methods to discern patterns of modern geographic variation within taxa. Modern and fossil samples are statistically compared to assess the nature and extent of inferred shifts in body size, both between modern samples and through time in each region. These results indicate that modern spotted hyenas and plains zebras exhibit mainly size variation between regions, with southern African samples possessing statistically larger craniodental metrics than eastern African samples. Comparison of fossil and modern samples reveals that the fossil assemblages do not show the same pattern of geographic variation. Significant temporal changes are more numerous between fossil and modern eastern African samples, and these changes are not mirrored by similar changes in the southern African samples. The changes experienced by taxa in eastern Africa appear to have been more extreme and wide-ranging than those in southern Africa, a presumed refugium. This result accords well with genetic studies of several large mammal species and paleoenvironmental studies suggesting that eastern African localized environments were more affected by tectonism and volcanism than were those in southern Africa. This study suggests that different evolutionary scenarios may have existed within Africa during the Plio-Pleistocene, but that both regions played unique and complementary roles in the evolution of African hominins and the broader faunal community.

Bovid postcranial ecomorphological survey of the Laetoli paleoenvironment

Here we report on a bovid postcranial ecomorphological survey of the fossil assemblages from the Plio-Pleistocene site of Laetoli, Tanzania. A global sample of extant bovids (n=205), cervids (n=14), and tragulids (n=5) from seven known habitat types constitutes the comparative data set. All long bones, carpals, tarsals, and phalanges were measured. Discriminant function analyses (DFA) were conducted in order to evaluate the ability of each element to accurately predict habitat affiliation. The baseline of chance accuracy for DFAs (i.e., the percentage of correct predictions that can be expected when habitat assignments are randomized) served as the cut-off point between good and bad habitat predictors. A total of 22 elements yielded percentages of correct classification over the baseline of accuracy, and these were extended to the Laetoli fossil assemblages. Summaries of the number of specimens predicted to belong to each habitat type were used to reconstruct the paleoenvironment. The results indicate that, at the time of the deposition of the Laetolil Beds, the area had heavy woodland-bushland cover with some lighter tree and bush cover and grass available. These results lend strong support to recent suggestions that the area was on the more wooded end of the habitat spectrum, contra initial conclusions that it represented a mosaic of more open habitats. The results also indicate that, during the deposition of the Ndolanya Beds, the environment had become more open and the grassland component of the environment had increased significantly. Light woodland-bushland and an abundance of grass cover dominated the landscape, although tracts of land with denser vegetation likely existed. This conclusion agrees with earlier suggestions that the area was a semiarid bushland.

Taphonomic bias, taxonomic bias and historical non-equivalence of faunal structure in early hominin localities

Environmental interpretation of fossil assemblages requires an accurate reconstruction of the community from which the assemblage was derived, which in turn depends on the quality of a comparative model usually based on the study of modern equivalents. The degree of inaccuracy introduced by taphonomic and other types of bias is often difficult to assess and the suitability of comparative models has rarely been addressed in this light. Here we apply a recently developed method to assess the bias present in a range of key hominin bearing localities from the Neogene of East and South Africa. The ecological structure of several of the investigated faunas can be shown to depart substantially from that of a comprehensive range of modern comparative faunas. Bias, where present, affects primarily the small mammals, which tend to be under-represented, and the large primary consumers, which tend to be over-represented. This has potentially significant implications for past and future palaeoecological reconstruction of these localities as numerous methods that are currently in use rely extensively on either the small mammals or the large primary consumers, and in particular the bovids. Understanding the nature of the bias, when present, will go some way towards improving the quality of environmental reconstructions.

Patterns of resource use in early Homo and Paranthropus

Conventional wisdom concerning the extinction of Paranthropus suggests that these species developed highly derived morphologies as a consequence of specializing on a diet consisting of hard and/or low-quality food items. It goes on to suggest that these species were so specialized or stenotopic that they were unable to adapt to changing environments in the period following 1.5 Ma. The same conventional wisdom proposes that early Homo species responded very differently to the same environmental challenges. Instead of narrowing their niche it was the dietary and behavioral flexibility (eurytopy) exhibited by early Homo that enabled that lineage to persist. We investigate whether evidence taken across eleven criteria supports a null hypothesis in which Paranthropus is more stenotopic than early Homo. In six instances (most categories of direct evidence of dietary breadth, species diversity, species duration, susceptibility to dispersal, dispersal direction, and non-dietary adaptations) the evidence is inconsistent with the hypothesis. Only one line of indirect evidence for dietary breadth-occlusal morphology-is unambiguously consistent with the null hypothesis that Paranthropus' ability to process tough, fibrous food items (e.g., leaves) was reduced relative to early Homo. Other criteria (habitat preference, population density, direct and indirect evidence of dietary breadth related to incisor use) are only consistent with the hypothesis under certain conditions. If those conditions are not met, then the evidence is either inconsistent with the hypothesis, or ambiguous. On balance, Paranthropus and early Homo were both likely to have been ecological generalists. These data are inconsistent with the conventional wisdom that stenotopy was a major contributing factor in the extinction of the Paranthropus clade. Researchers will need to explore other avenues of research in order to generate testable hypotheses about the demise of Paranthropus. Ecological models that may explain the evolution of eurytopy in early hominins are discussed.

Late pliocene faunal turnover in the turkana basin, kenya and ethiopia

Analysis of a large sample of well-dated fossil mammals from localities in the Turkana Basin of Kenya and Ethiopia revealed sampling biases that affect patterns of faunal turnover during the late Pliocene. When these biases were accounted for, results indicated that 58 to 77 percent of the mammal species were replaced between 3.0 and 1.8 million years ago (Ma). Overall diversity increased from 3.0 to 2.0 Ma but then declined. No distinct turnover pulse is seen between 2.8 and 2.5 Ma; instead, the most significant period of faunal change began after 2.5 Ma and continued through 1.8 Ma.