Oldest Evidence of Toolmaking 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.     

Fossil Mice and Rats Show Isotopic Evidence of Niche Partitioning and Change in Dental Ecomorphology Related to Dietary Shift in Late Miocene of Pakistan

Stable carbon isotope analysis in tooth enamel is a well-established approach to infer C₃ and C₄ dietary composition in fossil mammals. The bulk of past work has been conducted on large herbivorous mammals. One important finding is that their dietary habits of fossil large mammals track the late Miocene ecological shift from C₃ forest and woodland to C₄ savannah. However, few studies on carbon isotopes of fossil small mammals exist due to limitations imposed by the size of rodent teeth, and the isotopic ecological and dietary behaviors of small mammals to climate change remain unknown. Here we evaluate the impact of ecological change on small mammals by fine-scale comparisons of carbon isotope ratios (δ¹³C) with dental morphology of murine rodents, spanning 13.8 to ∼2.0 Ma, across the C₃ to C₄ vegetation shift in the Miocene Siwalik sequence of Pakistan. We applied in-situ laser ablation GC-IRMS to lower first molars and measured two grazing indices on upper first molars. Murine rodents yield a distinct, but related, record of past ecological conditions from large herbivorous mammals, reflecting available foods in their much smaller home ranges. In general, larger murine species show more positive δ¹³C values and have higher grazing indices than smaller species inhabiting the same area at any given age. Two clades of murine rodents experienced different rates of morphological change. In the faster-evolving clade, the timing and trend of morphological innovations are closely tied to consumption of C₄ diet during the vegetation shift. This study provides quantitative evidence of linkages among diet, niche partitioning, and dental morphology at a more detailed level than previously possible.     

Dietary and environmental reconstruction with stable isotope analyses of herbivore tooth enamel from the Miocene locality of Fort Ternan, Kenya

Tooth enamel of nine Middle Miocene mammalian herbivores from Fort Ternan, Kenya, was analyzed for δ¹³C and δ¹⁸O. The δ¹⁸O values of the tooth enamel compared with pedogenic and diagenetic carbonate confirm the use of stable isotope analysis of fossil tooth enamel as a paleoenvironmental indicator. Furthermore, the δ¹⁸O of tooth enamel indicates differences in water sources between some of the mammals. The δ¹³C values of tooth enamel ranged from −8·6–−13·0‰ which is compatible with a pure C₃diet, though the possibility of a small C₄fraction in the diet of a few of the specimens sampled is not precluded. The carbon isotopic data do not support environmental reconstructions of a Serengeti-typed wooded grassland with a significant proportion of C₄grasses. This study does not preclude the presence of C₃grasses at Fort Ternan; it is possible that C₃grasses could have had a wider geographic range if atmospheric CO₂levels were higher than the present values.     

The carbon isotope ecology and diet of Australopithecus africanus at Sterkfontein,South Africa

The stable carbon isotope ratio of fossil tooth enamel carbonate is determined by the photosynthetic systems of plants at the base of the animal's foodweb. In subtropical Africa, grasses and many sedges have C(4)photosynthesis and transmit their characteristically enriched 13C/(12)C ratios (more positive delta13C values) along the foodchain to consumers. We report here a carbon isotope study of ten specimens of Australopithecus africanus from Member 4, Sterkfontein (ca. 2.5 to 2.0Ma), compared with other fossil mammals from the same deposit. This is the most extensive isotopic study of an early hominin species that has been achieved so far. The results show that this hominin was intensively engaged with the savanna foodweb and that the dietary variation between individuals was more pronounced than for any other early hominin or non-human primate species on record. Suggestions that more than one species have been incuded in this taxon are not supported by the isotopic evidence. We conclude that Australopithecus africanus was highly opportunistic and adaptable in its feeding habits.     

Chimpanzee fauna isotopes provide new interpretations of fossil ape and hominin ecologies

Carbon and oxygen stable isotopes within modern and fossil tooth enamel record the aspects of an animal''s diet and habitat use. This investigation reports the first isotopic analyses of enamel from a large chimpanzee community and associated fauna, thus providing a means of comparing fossil ape and early hominin palaeoecologies with those of a modern ape. Within Kibale National Park forest, oxygen isotopes differentiate primate niches, allowing for the first isotopic reconstructions of degree of frugivory versus folivory as well as use of arboreal versus terrestrial resources. In a comparison of modern and fossil community isotopic profiles, results indicate that Sivapithecus, a Miocene ape from Pakistan, fed in the forest canopy, as do chimpanzees, but inhabited a forest with less continuous canopy or fed more on leaves. Ardipithecus, an early hominin from Ethiopia, fed both arboreally and terrestrially in a more open habitat than inhabited by chimpanzees.     

Phylogeny of early Australopithecus: new fossil evidence from the Woranso-Mille (central Afar,Ethiopia)

The earliest evidence of Australopithecus goes back to ca 4.2 Ma with the first recorded appearance of Australopithecus ‘anamensis’ at Kanapoi, Kenya. Australopithecus afarensis is well documented between 3.6 and 3.0 Ma mainly from deposits at Laetoli (Tanzania) and Hadar (Ethiopia). The phylogenetic relationship of these two ‘species’ is hypothesized as ancestor–descendant. However, the lack of fossil evidence from the time between 3.6 and 3.9 Ma has been one of its weakest points. Recent fieldwork in the Woranso-Mille study area in the Afar region of Ethiopia has yielded fossil hominids dated between 3.6 and 3.8 Ma. These new fossils play a significant role in testing the proposed relationship between Au. anamensis and Au. afarensis. The Woranso-Mille hominids (3.6–3.8 Ma) show a mosaic of primitive, predominantly Au. anamensis-like, and some derived (Au. afarensis-like) dentognathic features. Furthermore, they show that, as currently known, there are no discrete and functionally significant anatomical differences between Au. anamensis and Au. afarensis. Based on the currently available evidence, it appears that there is no compelling evidence to falsify the hypothesis of ‘chronospecies pair’ or ancestor–descendant relationship between Au. anamensis and Au. afarensis. Most importantly, however, the temporally and morphologically intermediate Woranso-Mille hominids indicate that the species names Au. afarensis and Au. anamensis do not refer to two real species, but rather to earlier and later representatives of a single phyletically evolving lineage. However, if retaining these two names is necessary for communication purposes, the Woranso-Mille hominids are best referred to as Au. anamensis based on new dentognathic evidence.     

Tracking changing environments using stable carbon isotopes in fossil tooth enamel: an example from the South African hominin sites

The environmental contexts of the karstic hominin sites in South Africa have been established largely by means of faunal associations; taken together these data suggest a trend from relatively closed and more mesic to open, drier environments from about 3 to 1.5 Ma. Vrba argued for a major shift within this trend ca. 2.4-2.6 Ma, an influential proposal that posited links between bovid (and hominin) radiation in Africa and the intensification of Northern Hemisphere Glaciation. Yet faunal approaches often rely on habitat and feeding preferences of modern taxa that may differ from those of their extinct predecessors. Here we explore ways of extending ¹³C/¹²C data from fossil mammals beyond denoting “presence” or “absence” of C₄ grasses using the evolution of open environments in South Africa as a case study. To do so we calculated the relative proportions of C₃-, mixed-, and C₄-feeding herbivores for all the hominin sites for which we have sufficient data based on ¹³C/¹²C analyses of fossil tooth enamel. The results confirm a general trend towards more open environments since 3 Ma, but they also emphasize a marked change to open grassy habitats in the latest Pliocene/early Pleistocene. Mean ¹³C/¹²C for large felids also mirrored this trend.     

Isotopic dietary reconstructions of Pliocene herbivores at Laetoli: Implications for early hominin paleoecology

Major morphological and behavioral innovations in early human evolution have traditionally been viewed as responses to conditions associated with increasing aridity and the development of extensive grassland-savanna biomes in Africa during the Plio-Pleistocene. Interpretations of paleoenvironments at the Pliocene locality of Laetoli in northern Tanzania have figured prominently in these discussions, primarily because early hominins recovered from Laetoli are generally inferred to be associated with grassland, savanna or open woodland habitats. As these reconstructions effectively extend the range of habitat preferences inferred for Pliocene hominins, and contrast with interpretations of predominantly woodland and forested ecosystems at other early hominin sites, it is worth reevaluating the paleoecology at Laetoli utilizing a new approach. Isotopic analyses were conducted on the teeth of twenty-one extinct mammalian herbivore species from the Laetolil Beds (∼ 4.3–3.5 Ma) and Upper Ndolanya Beds (∼ 2.7–2.6 Ma) to determine their diet, as well as to investigate aspects of plant physiognomy and climate. Enamel samples were obtained from multiple localities at different stratigraphic levels in order to develop a high-resolution spatio-temporal framework for identifying and characterizing dietary and ecological change and variability within the succession. In general, dietary signals at Laetoli suggest heterogeneous ecosystems with both C₃ and C₄ dietary plants available that could support grassland, woodland, and forested communities. All large-bodied herbivores analyzed yielded dietary signatures indicating mixed grazing/browsing strategies or exclusive reliance on C₃ browse, more consistent with wooded than grassland-savanna biomes. There are no clear isotopic patterns documenting shifting ecology within the Laetolil Beds or between the Laetolil and overlying Upper Ndolanya Beds, although limited data from the U. Ndolanya Beds constrains interpretations. Comparison of the results from Laetoli with isotopic enamel profiles of other African fossil and modern communities reveals significant differences in dietary patterns. Relative to extant taxa in related lineages, carbon isotopic ranges of a number of Laetoli fossil herbivores are anomalous, indicating significantly more generalized intermediate C₃/C₄ feeding behaviors, perhaps indicative of dietary niches and habitat types with no close modern analogs. Enamel oxygen isotope ranges of fossil taxa from Laetoli are consistently more ¹⁸O depleted than modern E. African herbivores, possibly indicating more humid conditions during that interval in the past. These data have important implications for reconstructing dietary trajectories of mammalian herbivore lineages, as well as the evolution of ecosystems in East Africa. Isotopic analyses of similar or related taxa at other hominin fossil sites yield signatures generally consistent with Laetoli, suggesting that mammalian communities in East Africa were sampling ecosystems with similar proportions of browse and grass. Collectively, the isotopic dietary signatures indicate heterogeneous habitats with significant wooded or forested components in the Laetoli area during deposition of the Laetolil and Upper Ndolanya Beds. Early hominin foraging activity in this interval may have included access to forest or woodland biomes within this ecosystem, complicating traditional interpretations linking early human evolutionary innovations with a shift to savanna habitats.     

Ecological change in the lower Omo Valley around 2.8 Ma

Late Pliocene climate changes have long been implicated in environmental changes and mammalian evolution in Africa, but high-resolution examinations of the fossil and climatic records have been hampered by poor sampling. By using fossils from the well-dated Shungura Formation (lower Omo Valley, northern Turkana Basin, southern Ethiopia), we investigate palaeodietary changes in one bovid and in one suid lineage from 3 to 2 Ma using stable isotope analysis of tooth enamel. Results show unexpectedly large increases in C₄ dietary intake around 2.8 Ma in both the bovid and suid, and possibly in a previously reported hippopotamid species. Enamel δ¹³C values after 2.8 Ma in the bovid (Tragelaphus nakuae) are higher than recorded for any living tragelaphin, and are not expected given its conservative dental morphology. A shift towards increased C₄ feeding at 2.8 Ma in the suid (Kolpochoerus limnetes) appears similarly decoupled from a well-documented record of dental evolution indicating gradual and progressive dietary change. The fact that two, perhaps three, disparate Pliocene herbivore lineages exhibit similar, and contemporaneous changes in dietary behaviour suggests a common environmental driver. Local and regional pollen, palaeosol and faunal records indicate increased aridity but no corresponding large and rapid expansion of grasslands in the Turkana Basin at 2.8 Ma. Our results provide new evidence supporting ecological change in the eastern African record around 2.8 Ma, but raise questions about the resolution at which different ecological proxies may be comparable, the correlation of vegetation and faunal change, and the interpretation of low δ¹³C values in the African Pliocene.     

Strengthening of the East Asian summer monsoon revealed by a shift in seasonal patterns in diet and climate after 2-3 Ma in northwest China

To examine climate variability in northwest China in the late Cenozoic and to test hypotheses regarding the development of C₄ ecosystems and the dynamics of the Asian monsoons, the carbon and oxygen isotopic compositions of 32 bulk and 368 serial tooth enamel samples from herbivores in the Linxia Basin (Gansu Province), ranging in age from 25 Ma to the present, were determined. The results corroborate and improve the record previously obtained from the area, showing that all mammals in the Linxia Basin lived in habitats consisting primarily of C₃ vegetation prior to 2-3 Ma and that C₄ grasses did not become a significant component of local ecosystems until the Quaternary. The data also show that shifts in climate to drier and/or warmer conditions after about 14, 9.5, 7, and 2.5 Ma, as indicated by positive δ¹⁸O excursions in the bulk enamel-δ¹⁸O record, were accompanied by increased seasonality; whereas negative δ¹⁸O shifts in the bulk data after about 11, 6, and 1.2 Ma, which indicate shifts to wetter and/or cooler climate, were associated with decreases in seasonality. Intra-tooth δ¹³C and δ¹⁸O profiles reveal significant changes in the seasonal patterns of diet and climate after ~ 2-3 Ma. Prior to ~ 2-3 Ma, there was little or no seasonal variation in herbivores' diets and all herbivores fed on C₃ vegetation year around. After that time, the data show a significant seasonal variation in the diets of horses and bovids, ranging from a pure C₃ to a mixed C₃/C₄ diet (with C₄ plants accounting for up to ~ 60% of the diet). An inverse relationship (or negative correlation) between δ¹³C and δ¹⁸O values within individual teeth — a pattern characteristic of the summer monsoon regime — is observed in younger (< 2-3 Ma) horses and bovids but not in older fossils. These changes in intra-tooth isotopic patterns provide strong evidence for an enhanced monsoon climate since about 2-3 Ma.     

Baboon Feeding Ecology Informs the Dietary Niche of Paranthropus boisei

Hominins are generally considered eclectic omnivores like baboons, but recent isotope studies call into question the generalist status of some hominins. Paranthropus boisei and Australopithecus bahrelghazali derived 75%–80% of their tissues’ δ¹³C from C₄ sources, i.e. mainly low-quality foods like grasses and sedges. Here I consider the energetics of P. boisei and the nutritional value of C₄ foods, taking into account scaling issues between the volume of food consumed and body mass, and P. boisei’s food preference as inferred from dento-cranial morphology. Underlying the models are empirical data for Papio cynocephalus dietary ecology. Paranthropus boisei only needed to spend some 37%–42% of its daily feeding time (conservative estimate) on C₄ sources to meet 80% of its daily requirements of calories, and all its requirements for protein. The energetic requirements of 2–4 times the basal metabolic rate (BMR) common to mammals could therefore have been met within a 6-hour feeding/foraging day. The findings highlight the high nutritional yield of many C₄ foods eaten by baboons (and presumably hominins), explain the evolutionary success of P. boisei, and indicate that P. boisei was probably a generalist like other hominins. The diet proposed is consistent with the species’ derived morphology and unique microwear textures. Finally, the results highlight the importance of baboon/hominin hand in food acquisition and preparation.     

Amelioration of Behavioral Abnormalities in BH4-deficient Mice by Dietary Supplementation of Tyrosine

This study reports an amelioration of abnormal motor behaviors in tetrahydrobiopterin (BH₄)-deficient Spr ^−/− mice by the dietary supplementation of tyrosine. Since BH₄ is an essential cofactor for the conversion of phenylalanine into tyrosine as well as the synthesis of dopamine neurotransmitter within the central nervous system, the levels of tyrosine and dopamine were severely reduced in brains of BH₄-deficient Spr ^−/− mice. We found that Spr ^−/− mice display variable ‘open-field’ behaviors, impaired motor functions on the ‘rotating rod’, and dystonic ‘hind-limb clasping’. In this study, we report that these aberrant motor deficits displayed by Spr ^−/− mice were ameliorated by the therapeutic tyrosine diet for 10 days. This study also suggests that dopamine deficiency in brains of Spr ^−/− mice may not be the biological feature of aberrant motor behaviors associated with BH₄ deficiency. Brain levels of dopamine (DA) and its metabolites in Spr ^−/− mice were not substantially increased by the dietary tyrosine therapy. However, we found that mTORC1 activity severely suppressed in brains of Spr ^−/− mice fed a normal diet was restored 10 days after feeding the mice the tyrosine diet. The present study proposes that brain mTORC1 signaling pathway is one of the potential targets in understanding abnormal motor behaviors associated with BH₄-deficiency.     

The oldest known fur seal

The poorly known fossil record of fur seals and sea lions (Otariidae) does not reflect their current diversity and widespread abundance. This limited fossil record contrasts with the more complete fossil records of other pinnipeds such as walruses (Odobenidae). The oldest known otariids appear 5–6 Ma after the earliest odobenids, and the remarkably derived craniodental morphology of otariids offers few clues to their early evolutionary history and phylogenetic affinities among pinnipeds. We report a new otariid, Eotaria crypta, from the lower middle Miocene ‘Topanga’ Formation (15–17.1 Ma) of southern California, represented by a partial mandible with well-preserved dentition. Eotaria crypta is geochronologically intermediate between ‘enaliarctine’ stem pinnipedimorphs (16.6–27 Ma) and previously described otariid fossils (7.3–12.5 Ma), as well as morphologically intermediate by retaining an M₂ and a reduced M₁ metaconid cusp and lacking P_2–4 metaconid cusps. Eotaria crypta eliminates the otariid ghost lineage and confirms that otariids evolved from an ‘enaliarctine’-like ancestor.     

Carbon isotope fractionation between diet and bioapatite in ungulate mammals and implications for ecological and paleoecological studies

 The isotope enrichment ɛ* of ¹³C between tooth enamel of large ruminant mammals and their diet is 14.1 ± 0.5‰. This value was obtained by analyzing both the dental enamel of a variety of wild and captive mammals and the vegetation that comprised their foodstuffs. This isotope enrichment factor applies to a wide variety of ruminant mammals. Non-ruminant ungulates have a similar isotope enrichment, although our data cannot determine if it is significantly different. We also found a ¹³C isotope enrichment ɛ* of 3.1 ± 0.7‰ for horn relative to diet, and 11.1 ± 0.8‰ for enamel relative to horn for ruminant mammals. Tooth enamel is a faithful recorder of diet. Its isotopic composition can be used to track changes in the isotopic composition of the atmosphere, determine the fraction of C₃ or C₄ biomass in diets of modern or fossil mammals, distinguish between mammals using different subpathways of C₄ photosynthesis,and identify those mammals whose diet is derived from closed-canopy habitats. Received: 1 July 1998 / Accepted: 9 February 1999     

Stable isotopes reveal seasonal competition for resources between late Pleistocene bison (Bison) and horse (Equus) from Rancho La Brea,southern California

Determining how organisms partition or compete for resources within ecosystems can reveal how communities are assembled. The Late Pleistocene deposits at Rancho La Brea are exceptionally diverse in large mammalian carnivores and herbivores, and afford a unique opportunity to study resource use and partitioning among these megafauna. Resource use was examined in bison and horses by serially sampling the stable carbon and oxygen isotope values found within tooth enamel of individual teeth of seven bison and five horses. Oxygen isotope results for both species reveal a pattern of seasonal enamel growth, while carbon isotope values reveal a more subtle seasonal pattern of dietary preferences. Both species ate a diet dominated by C₃ plants, but bison regularly incorporated C₄ plants into their diets, while horses ate C₄ plants only occasionally. Bison had greater total variation in carbon isotope values than did horses implying migration away from Rancho La Brea. Bison appear to incorporate more C₄ plants into their diets during winter, which corresponds to previous studies suggesting that Rancho La Brea, primarily surrounded by C₃ plants, was used by bison only during late spring. The examination of intra-tooth isotopic variation which reveals intra-seasonal resource use among bison and horse at Rancho La Brea highlights the utility of isotopic techniques for understanding the intricacies of ecology within and between ancient mammals.     

Stable isotope canopy effects for sympatric monkeys at Ta? Forest,C?te d'Ivoire

This study tests the hypothesis that vertical habitat preferences of different monkey species inhabiting closed canopy rainforest are reflected in oxygen isotopes. We sampled bone from seven sympatric cercopithecid species in the Taï forest, Côte d''Ivoire, where long-term study has established taxon-specific patterns of habitat use and diet. Modern rib samples (n = 34) were examined for oxygen (δ¹⁸O_ap) and carbon (δ¹³C_ap) from bone apatite (‘bioapatite’), and carbon (δ¹³C_co) and nitrogen (δ¹⁵N_co) from bone collagen. Results are consistent for C₃ feeders in a closed canopy habitat. Low irradiance and evapotranspiration, coupled with high relative humidity and recycled CO₂ in forest understory, contribute to observed isotopic variability. Both δ¹³C_co and δ¹³C_ap results reflect diet; however, δ¹³C values are not correlated with species preference for canopy height. By contrast, δ¹⁸O_ap results are correlated with mean observed height and show significant vertical partitioning between taxa feeding at ground, lower and upper canopy levels. This oxygen isotope canopy effect has important palaeobiological implications for reconstructing vertical partitioning among sympatric primates and other species in tropical forests.     

Auxin distribution is differentially affected by nitrate in roots of two rice cultivars differing in responsiveness to nitrogen

Background and Aims

Although ammonium (NH₄⁺) is the preferred form of nitrogen over nitrate (NO₃⁻) for rice (Oryza sativa), lateral root (LR) growth in roots is enhanced by partial NO₃⁻ nutrition (PNN). The roles of auxin distribution and polar transport in LR formation in response to localized NO₃⁻ availability are not known.

Methods

Time-course studies in a split-root experimental system were used to investigate LR development patterns, auxin distribution, polar auxin transport and expression of auxin transporter genes in LR zones in response to localized PNN in ‘Nanguang’ and ‘Elio’ rice cultivars, which show high and low responsiveness to NO₃⁻, respectively. Patterns of auxin distribution and the effects of polar auxin transport inhibitors were also examined in DR5::GUS transgenic plants.

Key Results

Initiation of LRs was enhanced by PNN after 7 d cultivation in ‘Nanguang’ but not in ‘Elio’. Auxin concentration in the roots of ‘Nanguang’ increased by approx. 24 % after 5 d cultivation with PNN compared with NH₄⁺ as the sole nitrogen source, but no difference was observed in ‘Elio’. More auxin flux into the LR zone in ‘Nanguang’ roots was observed in response to NO₃⁻ compared with NH₄⁺ treatment. A greater number of auxin influx and efflux transporter genes showed increased expression in the LR zone in response to PNN in ‘Nanguang’ than in ‘Elio’.

Conclusions

The results indicate that higher NO₃⁻ responsiveness is associated with greater auxin accumulation in the LR zone and is strongly related to a higher rate of LR initiation in the cultivar ‘Nanguang’.     

Isotopic ecology and dietary profiles of Liberian chimpanzees

An extensive suite of isotopic data (δ¹³C, δ¹⁵N, and δ¹⁸O) from enamel apatite and bone collagen of adult male and female wild chimpanzees establishes baseline values for Pan troglodytes verus in a primary rainforest setting. The Ganta chimpanzee sample derives from a restricted region in northern Liberia. Diet is examined using stable light isotopes at three life stages—infant, young juvenile, and adult—and developmental differences are investigated within and between individual males and females. The isotopic data are very homogeneous with few exceptions. Juvenile females show consistent enrichment in ¹³C relative to infants, while juvenile males do not. These data suggest that age at weaning may be more variable for male offspring who survive to adulthood than for female offspring. Alternatively, or additionally, the weaning diet of males and females may differ, with greater consumption of technologically extracted insects and/or nuts by young females. Metabolic differences, including growth and hormone-mediated responses, may also contribute to the observed variation.The Ganta chimpanzee data offer an independent and objective line of evidence to primatologists interested in the dietary strategies of the great apes and to paleoanthropologists seeking comparative models for reconstructing early hominin subsistence patterns. Despite the high diversity of dietary items consumed by chimpanzees, isotopic signatures of chimpanzees from a primary rainforest setting exhibit narrow ranges of variation similar to chimpanzees in more open habitats.     

Paleoenvironmental reconstruction of the Asbole fauna (Busidima Formation, Afar, Ethiopia) using stable isotopes

The Middle Pleistocene environmental and climatic conditions at Asbole, lower Awash Valley, Ethiopia were reconstructed using stable carbon and oxygen isotopic composition (¹³C, ¹⁸O) of fossil tooth enamel coupled with faunal abundance data. We analyzed the isotopic composition of a total of 80 herbivorous tooth enamel samples from 15 mammalian taxa, which archive the dietary preferences and drinking behavior from the “Asbole faunal zone”. The carbon isotopic data signify a wide range of foraging strategies, across the entire spectrum of pure C4 to C4-dominated diet, mixed C3/C4 diet and C3-dominated diet. The oxygen isotopic enrichment between evaporation sensitive and insensitive taxa (?_ES-EI) is 3.7‰ which provides an estimate of the mean annual water deficit of the Middle Pleistocene at Asbole of 1470 mm, a value characteristic of modern arid landscapes in this part of the Awash Valley. The isotopic data coupled with faunal abundance data indicate an arid C4-dominated open-vegetated region, with an abundance of forest-dwelling primates that identify the presence of gallery forests flanking tributary streams to the paleo-Awash River. Thus, with these combined methodologies, it is possible to explicate a more detailed character of the “mosaic” of environments characteristic of Neogene savanna ecosystems. These findings, clearly indicate the importance of avoiding oversimplification of Pleistocene environmental reconstructions, based on single proxies at isolated localities.     

Lineage-Specific Responses of Tooth Shape in Murine Rodents (Murinae,Rodentia) to Late Miocene Dietary Change in the Siwaliks of Pakistan

Past ecological responses of mammals to climate change are recognized in the fossil record by adaptive significance of morphological variations. To understand the role of dietary behavior on functional adaptations of dental morphology in rodent evolution, we examine evolutionary change of tooth shape in late Miocene Siwalik murine rodents, which experienced a dietary shift toward C₄ diets during late Miocene ecological change indicated by carbon isotopic evidence. Geometric morphometric analysis in the outline of upper first molars captures dichotomous lineages of Siwalik murines, in agreement with phylogenetic hypotheses of previous studies (two distinct clades: the Karnimata and Progonomys clades), and indicates lineage-specific functional responses to mechanical properties of their diets. Tooth shapes of the two clades are similar at their sympatric origin but deviate from each other with decreasing overlap through time. Shape change in the Karnimata clade is associated with greater efficiency of propalinal chewing for tough diets than in the Progonomys clade. Larger body mass in Karnimata may be related to exploitation of lower-quality food items, such as grasses, than in smaller-bodied Progonomys. The functional and ecophysiological aspects of Karnimata exploiting C₄ grasses are concordant with their isotopic dietary preference relative to Progonomys. Lineage-specific selection was differentially greater in Karnimata, and a faster rate of shape change toward derived Karnimata facilitated inclusion of C₄ grasses in the diet. Sympatric speciation in these clades is most plausibly explained by interspecific competition on resource utilization between the two, based on comparisons of our results with the carbon isotope data. Interspecific competition with Karnimata may have suppressed morphological innovation of the Progonomys clade. Pairwise analyses of morphological and carbon isotope data can uncover ecological causes of sympatric speciation and define functional adaptations of teeth to resources.