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Papers by John Harris
Scientific reports, Feb 24, 2017
Isotopic measurements on junipers growing in southern California during the last glacial, when th... more Isotopic measurements on junipers growing in southern California during the last glacial, when the ambient atmospheric [CO2] (ca) was ~180 ppm, show the leaf-internal [CO2] (ci) was approaching the modern CO2 compensation point for C3 plants. Despite this, stem growth rates were similar to today. Using a coupled light-use efficiency and tree growth model, we show that it is possible to maintain a stable ci/ca ratio because both vapour pressure deficit and temperature were decreased under glacial conditions at La Brea, and these have compensating effects on the ci/ca ratio. Reduced photorespiration at lower temperatures would partly mitigate the effect of low ci on gross primary production, but maintenance of present-day radial growth also requires a ~27% reduction in the ratio of fine root mass to leaf area. Such a shift was possible due to reduced drought stress under glacial conditions at La Brea. The necessity for changes in allocation in response to changes in [CO2] is consisten...
Nature, 1997
Between 8 and 6 million years ago, there was a global increase in the biomass of plants using C 4... more Between 8 and 6 million years ago, there was a global increase in the biomass of plants using C 4 photosynthesis as indicated by changes in the carbon isotope ratios of fossil tooth enamel in Asia, Africa, North America and South America. This abrupt and widespread increase in C 4 biomass may be related to a decrease in atmospheric CO 2 concentrations below a threshold that favoured C 3-photosynthesizing plants. The change occurred earlier at lower latitudes, as the threshold for C 3 photosynthesis is higher at warmer temperatures.
Proceedings of the National Academy of Sciences of the United States of America, Jul 26, 2017
Aridification is often considered a major driver of long-term ecological change and hominin evolu... more Aridification is often considered a major driver of long-term ecological change and hominin evolution in eastern Africa during the Plio-Pleistocene; however, this hypothesis remains inadequately tested owing to difficulties in reconstructing terrestrial paleoclimate. We present a revised aridity index for quantifying water deficit (WD) in terrestrial environments using tooth enamel δ(18)O values, and use this approach to address paleoaridity over the past 4.4 million years in eastern Africa. We find no long-term trend in WD, consistent with other terrestrial climate indicators in the Omo-Turkana Basin, and no relationship between paleoaridity and herbivore paleodiet structure among fossil collections meeting the criteria for WD estimation. Thus, we suggest that changes in the abundance of C4 grass and grazing herbivores in eastern Africa during the Pliocene and Pleistocene may have been decoupled from aridity. As in modern African ecosystems, other factors, such as rainfall seasonal...
Proceedings of the National Academy of Sciences, 2005
The Rancho La Brea tar pit fossil collection includes Juniperus (C 3 ) wood specimens that 14 C d... more The Rancho La Brea tar pit fossil collection includes Juniperus (C 3 ) wood specimens that 14 C date between 7.7 and 55 thousand years (kyr) B.P., providing a constrained record of plant response for southern California during the last glacial period. Atmospheric CO 2 concentration ([CO 2 ]) ranged between 180 and 220 ppm during glacial periods, rose to ≈280 ppm before the industrial period, and is currently approaching 380 ppm in the modern atmosphere. Here we report on δ 13 C of Juniperus wood cellulose, and show that glacial and modern trees were operating at similar leaf-intercellular [CO 2 ]( c i )/atmospheric [CO 2 ]( c a ) values. As a result, glacial trees were operating at c i values much closer to the CO 2 -compensation point for C 3 photosynthesis than modern trees, indicating that glacial trees were undergoing carbon starvation. In addition, we modeled relative humidity by using δ 18 O of cellulose from the same Juniperus specimens and found that glacial humidity was ≈10...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2004
We sampled 143 individuals from Rancho La Brea (RLB) large faunal collections for bone collagen s... more We sampled 143 individuals from Rancho La Brea (RLB) large faunal collections for bone collagen stable carbon (d 13 C) and nitrogen (d 15 N) isotope ratios. These collections were recovered from asphalt seeps in the Los Angeles Basin, California, USA, and date from f 40 to 12 ka. Our findings indicate that despite a slight reduction in collagen nitrogen content, RLB skeletal remains are relatively well preserved and most yield proteins diagnostic of diet. Herbivore d 13 C and d 15 N values covary with rumination and are consistent with changes in late Pleistocene vegetation reconstructed from pollen profiles. We find no evidence for reliance on C 4 grasses at RLB, despite low atmospheric CO 2 concentrations. Carnivore d 15 N values indicate Canis dirus, Smilodon fatalis and Panthera leo atrox competed for similar prey sets and were equally reliant on ruminant and nonruminant prey types. The d 15 N values of Mammut americanum indicate partial reliance on vegetation with lower d 15 N values (such as nitrogen-fixing taxa), distinguishing them from the remainder of the study population. A comparison of RLB and European faunal d 15 N values from the late Pleistocene suggests that coastal southern California experienced greater aridity.
New Phytologist, 2011
• While studies of modern plants indicate negative responses to low [CO 2 ] that occurred during ... more • While studies of modern plants indicate negative responses to low [CO 2 ] that occurred during the last glacial period, studies with glacial plant material that incorporate evolutionary responses are rare. In this study, physiological responses to changing [CO 2 ] were compared between glacial (La Brea tar pits) and modern Juniperus trees from southern California. • Carbon isotopes were measured on annual rings of glacial and modern Juniperus. The intercellular : atmospheric [CO 2 ] ratio (c i ⁄ c a) and intercellular [CO 2 ] (c i) were then calculated on an annual basis and compared through geologic time. • Juniperus showed constant mean c i ⁄ c a between the last glacial period and modern times, spanning 50 000 yr. Interannual variation in physiology was greatly dampened during the last glacial period relative to the present, indicating constraints of low [CO 2 ] that reduced responses to other climatic factors. Furthermore, glacial Juniperus exhibited low c i that rarely occurs in modern trees, further suggesting limiting [CO 2 ] in glacial plants. • This study provides some of the first direct evidence that glacial plants remained near their lower carbon limit until the beginning of the glacial-interglacial transition. Our results also suggest that environmental factors that dominate carbon-uptake physiology vary across geologic time, resulting in major alterations in physiological response patterns through time.
Journal of Zoology, 2008
The diet of African hippopotamids can be documented through stable carbon isotope ratios (13 C/ 1... more The diet of African hippopotamids can be documented through stable carbon isotope ratios (13 C/ 12 C) analyses of enamel and other tissues. The common hippopotamus Hippopotamus amphibius is widely assumed to be a pure grazer; however, the 13 C/ 12 C ratios of modern H. amphibius show a higher fraction of dietary C 3 biomass than estimated from traditional observations. Isotope profiles of modern hair and modern tooth enamel confirm that H. amphibius has a variable diet in both the short-(seasonal) and long-(sub-decadal) time scales. Isotopic analyses of extant mammals from the same parks as the analyzed hippos provide comparative examples for diets of C 3-browsers and C 4-grazers. Oxygen isotope ratios (18 O/ 16 O) show that the hippo is consistently the most 18 O-depleted mammal in any one ecosystem; this directly reflects its semi-aquatic habitat.
Journal of Mammalogy, 2003
We provide stable carbon isotope data from 37 species of African bovids to document dietary prefe... more We provide stable carbon isotope data from 37 species of African bovids to document dietary preferences for C 3 browse (or fruits) or C 4 grass. These data provide a quantitative measure of the fraction of C 4 grass in bovid diets, can be applied on regional to local scales, can be derived from tooth enamel and hair or other tissues, and permit the diets of bovids to be considered in the context of a grazer-browser continuum. We recognize hypergrazers (Ͼ95% C 4 grass), grazers (70-95% C 4 grass), mixed feeders (Ͼ30% C 4 grass and Ͼ30% C 3 browse), browsers (70-95% C 3 browse), and hyperbrowsers or frugivores (Ͼ95% C 3 browse or fruit). Our results suggest that, of the extant East African Bovidae, impala (Aepyceros melampus), Thomson's gazelle (Gazella thomsonii), and oribi (Ourebia ourebi) can be construed as mixed feeders. Dietary estimates based on stable isotope analysis are in broad agreement with other measures of diet such as hypsodonty index, mass relationships, and wear scratches on enamel.
Journal of Human Evolution, 1997
Dietary and environmental reconstruction with stable isotope analyses of herbivore tooth enamel f... more 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 13 C and 18 O. The 18 O 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 18 O of tooth enamel indicates differences in water sources between some of the mammals. The 13 C values of tooth enamel ranged from 8•6-13•0‰ which is compatible with a pure C 3 diet, though the possibility of a small C 4 fraction 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 C 4 grasses. This study does not preclude the presence of C 3 grasses at Fort Ternan; it is possible that C 3 grasses could have had a wider geographic range if atmospheric CO 2 levels were higher than the present values.
Global Ecology and Biogeography, 1999
about 30 to 40°. The oxygen data, which vary Carbon and oxygen isotopic data are reported from pr... more about 30 to 40°. The oxygen data, which vary Carbon and oxygen isotopic data are reported from proportionately with temperature, indicate a 116 Pleistocene Equus teeth from sixty-six localities latitudinal gradient (18 O range of 20 parts/mil) in the New World ranging from 68°N (Alaska, between high-latitude and equatorial Equus Canada) to 35°S (Argentina). Equus species have samples. The basic pattern of latitudinal gradients been predominantly grazers, and as such, carbon of C 3 /C 4 grass distribution and temperature as isotopic values of their tooth enamel provide interpreted from these Pleistocene data is similar to evidence of the Pleistocene distribution of C 3 and the modern-day. The use of stable isotopes of fossil C 4 grasses. The carbon data presented here indicate herbivore teeth represents a new means to interpret a gradient (13 C range of 10 parts/mil) in the relative Pleistocene climates and terrestrial ecology. proportion of C 3 and C 4 grasses between high Key words. C 3 and C 4 grasses, latitudinal gradients, latitude and equatorial Equus samples. The largest isotopes, carbon, oxygen, temperature, New World, amount of change from C 3 to C 4 grasses during the Pleistocene, Equus.
Oecologia, 1999
The diet of extant elephants (Loxodonta in Africa, Elephas in Asia) is dominated by C 3 browse al... more The diet of extant elephants (Loxodonta in Africa, Elephas in Asia) is dominated by C 3 browse although some elephants have a signi®cant C 4 grass component in their diet. This is particularly noteworthy because high-crowned elephantid cheek teeth represent adaptation to an abrasive grazing diet and because isotopic analysis demonstrates that C 4 vegetation was the dominant diet for Elephas in Asia from 5 to 1 Ma and for both Loxodonta and Elephas in Africa between 5±1 Ma. Other proboscideans in Africa and southern Asia, except deinotheres, also had a C 4-dominated diet from about 7 Ma (when the C 4 biomass radiated in tropical and subtropical regions) until their subsequent extinction.
Proceedings of the National Academy of Sciences of the United States of America, Jan 3, 2015
A large stable isotope dataset from East and Central Africa from ca. 30 regional collection sites... more A large stable isotope dataset from East and Central Africa from ca. 30 regional collection sites that range from forest to grassland shows that most extant East and Central African large herbivore taxa have diets dominated by C4 grazing or C3 browsing. Comparison with the fossil record shows that faunal assemblages from ca. 4.1-2.35 Ma in the Turkana Basin had a greater diversity of C3-C4 mixed feeding taxa than is presently found in modern East and Central African environments. In contrast, the period from 2.35 to 1.0 Ma had more C4-grazing taxa, especially nonruminant C4-grazing taxa, than are found in modern environments in East and Central Africa. Many nonbovid C4 grazers became extinct in Africa, notably the suid Notochoerus, the hipparion equid Eurygnathohippus, the giraffid Sivatherium, and the elephantid Elephas. Other important nonruminant C4-grazing taxa switched to browsing, including suids in the lineage Kolpochoerus-Hylochoerus and the elephant Loxodonta. Many modern h...
Quaternary Geochronology, 2014
A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis... more A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis from asphalt-impregnated skeletal remains stored in the George C. Page Museum of La Brea Discoveries (Los Angeles, California) is presented. This simple technique requires that bones be crushed (1e2 mm), sonicated in a 2:1 toluene/methanol solution, and gelatinized at 75 C overnight to break down collagen strands for ultrafiltration. However, here the traditional protocol of ultrafiltration is reversed, and the high molecular weight fraction (>30 kDa) contains mainly the asphalt (too big to pass through the filter), while the lower molecular weight fraction (<30 kDa) contains the collagen. A second ultrafiltration (>3 kDa) is then performed on the <30 kDa fraction to remove lower molecular weight contaminants such as hydrocarbons and humic acids. The middle fraction (3e30 kDa) is freeze dried and produces collagen with excellent atomic C:N ratios between 3.2 and 3.5. The steps involved in the design of the protocol will be discussed in detail, and the first isotopic results and radiocarbon dates from the Project 23 site will be presented. In addition, the largest compilation of carbon and nitrogen isotopic results directly paired with radiocarbon ages on bone collagen from 38 land mammals found at the Rancho La Brea site are presented. Finally, while this protocol was specifically designed to extract collagen from samples at the Rancho La Brea site, it is likely that it can be applied to other localities (e.g. Cuba, Ecuador, Peru, Venezuela, etc.) where bones have been impregnated with petroleum.
Nature, 1972
ABSTRACT HOWELL et al. have reported1 the results of uranium-series dating of bone from the Isimi... more ABSTRACT HOWELL et al. have reported1 the results of uranium-series dating of bone from the Isimila prehistoric site, Tanzania. Preliminary identifications of fragmentary mammalian remains recovered during the first excavations at the site (1957–58) were reported in the interim report on the site2. These specimens, which are now housed in the National Museum Centre for Pre-history and Palaeontology, Nairobi (but will in future be preserved in the National Museum, Dar-es-Salaam), are discussed more fully here.
The Quarterly Review of Biology, 2005
Journal of Zoology, 2009
With 2 plates in the text) A skull, three immature mandibles and a number of isolated teeth belon... more With 2 plates in the text) A skull, three immature mandibles and a number of isolated teeth belonging to Deinotherium bozasi have been collected from Plio-Pleistocene sediments to the east of Lake Rudolf, Kenya. D. bozasi is the youngest representative of the family Deinotheriidae and the skull is the most complete yet found of this taxon. The East Rudolf specimens are contrasted with comparable specimens of Prodeinotherium hobleyi from East and North Africa and of Deinotherium giganteum from Europe. The size and morphology of the cranial vault of the East Rudolf skull confirms allocation to the genus Deinotherium but other dental and cranial evidence confirms taxonomic differentiation from D. giganteum and direct descent from P. hobleyi. Although the postcranial elements of D. bozasi are poorly known it is considered unlikely that this species developed the cursorial adaptations of D. giganteum. The extinction of D. bozasi is attributable to major changes in ecologic conditions towards the end of the early Pleistocene.
Quaternary Geochronology, 2014
A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis... more A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis from asphalt-impregnated skeletal remains stored in the George C. Page Museum of La Brea Discoveries (Los Angeles, California) is presented. This simple technique requires that bones be crushed (1e2 mm), sonicated in a 2:1 toluene/methanol solution, and gelatinized at 75 C overnight to break down collagen strands for ultrafiltration. However, here the traditional protocol of ultrafiltration is reversed, and the high molecular weight fraction (>30 kDa) contains mainly the asphalt (too big to pass through the filter), while the lower molecular weight fraction (<30 kDa) contains the collagen. A second ultrafiltration (>3 kDa) is then performed on the <30 kDa fraction to remove lower molecular weight contaminants such as hydrocarbons and humic acids. The middle fraction (3e30 kDa) is freeze dried and produces
collagen with excellent atomic C:N ratios between 3.2 and 3.5. The steps involved in the design of the protocol will be discussed in detail, and the first isotopic results and radiocarbon dates from the Project 23 site will be presented. In addition, the largest compilation of carbon and nitrogen isotopic results directly paired with radiocarbon ages on bone collagen from 38 land mammals found at the Rancho La Brea site are presented. Finally, while this protocol was specifically designed to extract collagen from samples at the Rancho La Brea site, it is likely that it can be applied to other localities (e.g. Cuba, Ecuador, Peru, Venezuela, etc.) where bones have been impregnated with petroleum.
Scientific reports, Feb 24, 2017
Isotopic measurements on junipers growing in southern California during the last glacial, when th... more Isotopic measurements on junipers growing in southern California during the last glacial, when the ambient atmospheric [CO2] (ca) was ~180 ppm, show the leaf-internal [CO2] (ci) was approaching the modern CO2 compensation point for C3 plants. Despite this, stem growth rates were similar to today. Using a coupled light-use efficiency and tree growth model, we show that it is possible to maintain a stable ci/ca ratio because both vapour pressure deficit and temperature were decreased under glacial conditions at La Brea, and these have compensating effects on the ci/ca ratio. Reduced photorespiration at lower temperatures would partly mitigate the effect of low ci on gross primary production, but maintenance of present-day radial growth also requires a ~27% reduction in the ratio of fine root mass to leaf area. Such a shift was possible due to reduced drought stress under glacial conditions at La Brea. The necessity for changes in allocation in response to changes in [CO2] is consisten...
Nature, 1997
Between 8 and 6 million years ago, there was a global increase in the biomass of plants using C 4... more Between 8 and 6 million years ago, there was a global increase in the biomass of plants using C 4 photosynthesis as indicated by changes in the carbon isotope ratios of fossil tooth enamel in Asia, Africa, North America and South America. This abrupt and widespread increase in C 4 biomass may be related to a decrease in atmospheric CO 2 concentrations below a threshold that favoured C 3-photosynthesizing plants. The change occurred earlier at lower latitudes, as the threshold for C 3 photosynthesis is higher at warmer temperatures.
Proceedings of the National Academy of Sciences of the United States of America, Jul 26, 2017
Aridification is often considered a major driver of long-term ecological change and hominin evolu... more Aridification is often considered a major driver of long-term ecological change and hominin evolution in eastern Africa during the Plio-Pleistocene; however, this hypothesis remains inadequately tested owing to difficulties in reconstructing terrestrial paleoclimate. We present a revised aridity index for quantifying water deficit (WD) in terrestrial environments using tooth enamel δ(18)O values, and use this approach to address paleoaridity over the past 4.4 million years in eastern Africa. We find no long-term trend in WD, consistent with other terrestrial climate indicators in the Omo-Turkana Basin, and no relationship between paleoaridity and herbivore paleodiet structure among fossil collections meeting the criteria for WD estimation. Thus, we suggest that changes in the abundance of C4 grass and grazing herbivores in eastern Africa during the Pliocene and Pleistocene may have been decoupled from aridity. As in modern African ecosystems, other factors, such as rainfall seasonal...
Proceedings of the National Academy of Sciences, 2005
The Rancho La Brea tar pit fossil collection includes Juniperus (C 3 ) wood specimens that 14 C d... more The Rancho La Brea tar pit fossil collection includes Juniperus (C 3 ) wood specimens that 14 C date between 7.7 and 55 thousand years (kyr) B.P., providing a constrained record of plant response for southern California during the last glacial period. Atmospheric CO 2 concentration ([CO 2 ]) ranged between 180 and 220 ppm during glacial periods, rose to ≈280 ppm before the industrial period, and is currently approaching 380 ppm in the modern atmosphere. Here we report on δ 13 C of Juniperus wood cellulose, and show that glacial and modern trees were operating at similar leaf-intercellular [CO 2 ]( c i )/atmospheric [CO 2 ]( c a ) values. As a result, glacial trees were operating at c i values much closer to the CO 2 -compensation point for C 3 photosynthesis than modern trees, indicating that glacial trees were undergoing carbon starvation. In addition, we modeled relative humidity by using δ 18 O of cellulose from the same Juniperus specimens and found that glacial humidity was ≈10...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2004
We sampled 143 individuals from Rancho La Brea (RLB) large faunal collections for bone collagen s... more We sampled 143 individuals from Rancho La Brea (RLB) large faunal collections for bone collagen stable carbon (d 13 C) and nitrogen (d 15 N) isotope ratios. These collections were recovered from asphalt seeps in the Los Angeles Basin, California, USA, and date from f 40 to 12 ka. Our findings indicate that despite a slight reduction in collagen nitrogen content, RLB skeletal remains are relatively well preserved and most yield proteins diagnostic of diet. Herbivore d 13 C and d 15 N values covary with rumination and are consistent with changes in late Pleistocene vegetation reconstructed from pollen profiles. We find no evidence for reliance on C 4 grasses at RLB, despite low atmospheric CO 2 concentrations. Carnivore d 15 N values indicate Canis dirus, Smilodon fatalis and Panthera leo atrox competed for similar prey sets and were equally reliant on ruminant and nonruminant prey types. The d 15 N values of Mammut americanum indicate partial reliance on vegetation with lower d 15 N values (such as nitrogen-fixing taxa), distinguishing them from the remainder of the study population. A comparison of RLB and European faunal d 15 N values from the late Pleistocene suggests that coastal southern California experienced greater aridity.
New Phytologist, 2011
• While studies of modern plants indicate negative responses to low [CO 2 ] that occurred during ... more • While studies of modern plants indicate negative responses to low [CO 2 ] that occurred during the last glacial period, studies with glacial plant material that incorporate evolutionary responses are rare. In this study, physiological responses to changing [CO 2 ] were compared between glacial (La Brea tar pits) and modern Juniperus trees from southern California. • Carbon isotopes were measured on annual rings of glacial and modern Juniperus. The intercellular : atmospheric [CO 2 ] ratio (c i ⁄ c a) and intercellular [CO 2 ] (c i) were then calculated on an annual basis and compared through geologic time. • Juniperus showed constant mean c i ⁄ c a between the last glacial period and modern times, spanning 50 000 yr. Interannual variation in physiology was greatly dampened during the last glacial period relative to the present, indicating constraints of low [CO 2 ] that reduced responses to other climatic factors. Furthermore, glacial Juniperus exhibited low c i that rarely occurs in modern trees, further suggesting limiting [CO 2 ] in glacial plants. • This study provides some of the first direct evidence that glacial plants remained near their lower carbon limit until the beginning of the glacial-interglacial transition. Our results also suggest that environmental factors that dominate carbon-uptake physiology vary across geologic time, resulting in major alterations in physiological response patterns through time.
Journal of Zoology, 2008
The diet of African hippopotamids can be documented through stable carbon isotope ratios (13 C/ 1... more The diet of African hippopotamids can be documented through stable carbon isotope ratios (13 C/ 12 C) analyses of enamel and other tissues. The common hippopotamus Hippopotamus amphibius is widely assumed to be a pure grazer; however, the 13 C/ 12 C ratios of modern H. amphibius show a higher fraction of dietary C 3 biomass than estimated from traditional observations. Isotope profiles of modern hair and modern tooth enamel confirm that H. amphibius has a variable diet in both the short-(seasonal) and long-(sub-decadal) time scales. Isotopic analyses of extant mammals from the same parks as the analyzed hippos provide comparative examples for diets of C 3-browsers and C 4-grazers. Oxygen isotope ratios (18 O/ 16 O) show that the hippo is consistently the most 18 O-depleted mammal in any one ecosystem; this directly reflects its semi-aquatic habitat.
Journal of Mammalogy, 2003
We provide stable carbon isotope data from 37 species of African bovids to document dietary prefe... more We provide stable carbon isotope data from 37 species of African bovids to document dietary preferences for C 3 browse (or fruits) or C 4 grass. These data provide a quantitative measure of the fraction of C 4 grass in bovid diets, can be applied on regional to local scales, can be derived from tooth enamel and hair or other tissues, and permit the diets of bovids to be considered in the context of a grazer-browser continuum. We recognize hypergrazers (Ͼ95% C 4 grass), grazers (70-95% C 4 grass), mixed feeders (Ͼ30% C 4 grass and Ͼ30% C 3 browse), browsers (70-95% C 3 browse), and hyperbrowsers or frugivores (Ͼ95% C 3 browse or fruit). Our results suggest that, of the extant East African Bovidae, impala (Aepyceros melampus), Thomson's gazelle (Gazella thomsonii), and oribi (Ourebia ourebi) can be construed as mixed feeders. Dietary estimates based on stable isotope analysis are in broad agreement with other measures of diet such as hypsodonty index, mass relationships, and wear scratches on enamel.
Journal of Human Evolution, 1997
Dietary and environmental reconstruction with stable isotope analyses of herbivore tooth enamel f... more 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 13 C and 18 O. The 18 O 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 18 O of tooth enamel indicates differences in water sources between some of the mammals. The 13 C values of tooth enamel ranged from 8•6-13•0‰ which is compatible with a pure C 3 diet, though the possibility of a small C 4 fraction 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 C 4 grasses. This study does not preclude the presence of C 3 grasses at Fort Ternan; it is possible that C 3 grasses could have had a wider geographic range if atmospheric CO 2 levels were higher than the present values.
Global Ecology and Biogeography, 1999
about 30 to 40°. The oxygen data, which vary Carbon and oxygen isotopic data are reported from pr... more about 30 to 40°. The oxygen data, which vary Carbon and oxygen isotopic data are reported from proportionately with temperature, indicate a 116 Pleistocene Equus teeth from sixty-six localities latitudinal gradient (18 O range of 20 parts/mil) in the New World ranging from 68°N (Alaska, between high-latitude and equatorial Equus Canada) to 35°S (Argentina). Equus species have samples. The basic pattern of latitudinal gradients been predominantly grazers, and as such, carbon of C 3 /C 4 grass distribution and temperature as isotopic values of their tooth enamel provide interpreted from these Pleistocene data is similar to evidence of the Pleistocene distribution of C 3 and the modern-day. The use of stable isotopes of fossil C 4 grasses. The carbon data presented here indicate herbivore teeth represents a new means to interpret a gradient (13 C range of 10 parts/mil) in the relative Pleistocene climates and terrestrial ecology. proportion of C 3 and C 4 grasses between high Key words. C 3 and C 4 grasses, latitudinal gradients, latitude and equatorial Equus samples. The largest isotopes, carbon, oxygen, temperature, New World, amount of change from C 3 to C 4 grasses during the Pleistocene, Equus.
Oecologia, 1999
The diet of extant elephants (Loxodonta in Africa, Elephas in Asia) is dominated by C 3 browse al... more The diet of extant elephants (Loxodonta in Africa, Elephas in Asia) is dominated by C 3 browse although some elephants have a signi®cant C 4 grass component in their diet. This is particularly noteworthy because high-crowned elephantid cheek teeth represent adaptation to an abrasive grazing diet and because isotopic analysis demonstrates that C 4 vegetation was the dominant diet for Elephas in Asia from 5 to 1 Ma and for both Loxodonta and Elephas in Africa between 5±1 Ma. Other proboscideans in Africa and southern Asia, except deinotheres, also had a C 4-dominated diet from about 7 Ma (when the C 4 biomass radiated in tropical and subtropical regions) until their subsequent extinction.
Proceedings of the National Academy of Sciences of the United States of America, Jan 3, 2015
A large stable isotope dataset from East and Central Africa from ca. 30 regional collection sites... more A large stable isotope dataset from East and Central Africa from ca. 30 regional collection sites that range from forest to grassland shows that most extant East and Central African large herbivore taxa have diets dominated by C4 grazing or C3 browsing. Comparison with the fossil record shows that faunal assemblages from ca. 4.1-2.35 Ma in the Turkana Basin had a greater diversity of C3-C4 mixed feeding taxa than is presently found in modern East and Central African environments. In contrast, the period from 2.35 to 1.0 Ma had more C4-grazing taxa, especially nonruminant C4-grazing taxa, than are found in modern environments in East and Central Africa. Many nonbovid C4 grazers became extinct in Africa, notably the suid Notochoerus, the hipparion equid Eurygnathohippus, the giraffid Sivatherium, and the elephantid Elephas. Other important nonruminant C4-grazing taxa switched to browsing, including suids in the lineage Kolpochoerus-Hylochoerus and the elephant Loxodonta. Many modern h...
Quaternary Geochronology, 2014
A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis... more A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis from asphalt-impregnated skeletal remains stored in the George C. Page Museum of La Brea Discoveries (Los Angeles, California) is presented. This simple technique requires that bones be crushed (1e2 mm), sonicated in a 2:1 toluene/methanol solution, and gelatinized at 75 C overnight to break down collagen strands for ultrafiltration. However, here the traditional protocol of ultrafiltration is reversed, and the high molecular weight fraction (>30 kDa) contains mainly the asphalt (too big to pass through the filter), while the lower molecular weight fraction (<30 kDa) contains the collagen. A second ultrafiltration (>3 kDa) is then performed on the <30 kDa fraction to remove lower molecular weight contaminants such as hydrocarbons and humic acids. The middle fraction (3e30 kDa) is freeze dried and produces collagen with excellent atomic C:N ratios between 3.2 and 3.5. The steps involved in the design of the protocol will be discussed in detail, and the first isotopic results and radiocarbon dates from the Project 23 site will be presented. In addition, the largest compilation of carbon and nitrogen isotopic results directly paired with radiocarbon ages on bone collagen from 38 land mammals found at the Rancho La Brea site are presented. Finally, while this protocol was specifically designed to extract collagen from samples at the Rancho La Brea site, it is likely that it can be applied to other localities (e.g. Cuba, Ecuador, Peru, Venezuela, etc.) where bones have been impregnated with petroleum.
Nature, 1972
ABSTRACT HOWELL et al. have reported1 the results of uranium-series dating of bone from the Isimi... more ABSTRACT HOWELL et al. have reported1 the results of uranium-series dating of bone from the Isimila prehistoric site, Tanzania. Preliminary identifications of fragmentary mammalian remains recovered during the first excavations at the site (1957–58) were reported in the interim report on the site2. These specimens, which are now housed in the National Museum Centre for Pre-history and Palaeontology, Nairobi (but will in future be preserved in the National Museum, Dar-es-Salaam), are discussed more fully here.
The Quarterly Review of Biology, 2005
Journal of Zoology, 2009
With 2 plates in the text) A skull, three immature mandibles and a number of isolated teeth belon... more With 2 plates in the text) A skull, three immature mandibles and a number of isolated teeth belonging to Deinotherium bozasi have been collected from Plio-Pleistocene sediments to the east of Lake Rudolf, Kenya. D. bozasi is the youngest representative of the family Deinotheriidae and the skull is the most complete yet found of this taxon. The East Rudolf specimens are contrasted with comparable specimens of Prodeinotherium hobleyi from East and North Africa and of Deinotherium giganteum from Europe. The size and morphology of the cranial vault of the East Rudolf skull confirms allocation to the genus Deinotherium but other dental and cranial evidence confirms taxonomic differentiation from D. giganteum and direct descent from P. hobleyi. Although the postcranial elements of D. bozasi are poorly known it is considered unlikely that this species developed the cursorial adaptations of D. giganteum. The extinction of D. bozasi is attributable to major changes in ecologic conditions towards the end of the early Pleistocene.
Quaternary Geochronology, 2014
A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis... more A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis from asphalt-impregnated skeletal remains stored in the George C. Page Museum of La Brea Discoveries (Los Angeles, California) is presented. This simple technique requires that bones be crushed (1e2 mm), sonicated in a 2:1 toluene/methanol solution, and gelatinized at 75 C overnight to break down collagen strands for ultrafiltration. However, here the traditional protocol of ultrafiltration is reversed, and the high molecular weight fraction (>30 kDa) contains mainly the asphalt (too big to pass through the filter), while the lower molecular weight fraction (<30 kDa) contains the collagen. A second ultrafiltration (>3 kDa) is then performed on the <30 kDa fraction to remove lower molecular weight contaminants such as hydrocarbons and humic acids. The middle fraction (3e30 kDa) is freeze dried and produces
collagen with excellent atomic C:N ratios between 3.2 and 3.5. The steps involved in the design of the protocol will be discussed in detail, and the first isotopic results and radiocarbon dates from the Project 23 site will be presented. In addition, the largest compilation of carbon and nitrogen isotopic results directly paired with radiocarbon ages on bone collagen from 38 land mammals found at the Rancho La Brea site are presented. Finally, while this protocol was specifically designed to extract collagen from samples at the Rancho La Brea site, it is likely that it can be applied to other localities (e.g. Cuba, Ecuador, Peru, Venezuela, etc.) where bones have been impregnated with petroleum.