Ancient latitudinal gradients of C3 /C4 grasses interpreted from stable isotopes of New World Pleistocene horse (Equus ) teeth (original) (raw)
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Quaternary Science Reviews, 2004
Carbon and nitrogen stable isotope ratios of bone and tooth dentine collagen from 142 horses were analysed to consider the potential of isotopic analysis of faunal remains as a palaeoenvironmental and palaeoclimatic proxy. A general trend through time towards lighter d 13 C values was observed, but with an obvious depletion at the Late Glacial/Holocene transition. Horse d 13 C values appear to track plant d 13 C. Although phenomenon such as the canopy effect may influence faunal d 13 C values, we believe that the influence on plants of increasing atmospheric CO 2 is the primary factor in the change in faunal d 13 C values at the Late Glacial/ Holocene transition. A post-glacial depletion in horse d 15 N values is observed in areas proximal to glacial retreat although no data is available in these areas during the Last Glacial Maximum. Horse d 15 N values are presumed to reflect plant d 15 N values. Depleted plant nitrogen may be attributed to a number of factors e.g. water availability, temperature, cycling of nitrogen in the soil, soil nutrient availability (especially phosphorus in the post-glacial period), and the type of mycorrhizal associations formed with plant. These effects may be interrelated, and be linked such that a positive feedback can give a non-linear response to a single parameter. r
Quaternary Science Reviews
The late Pleistocene was a climatically dynamic period, with abrupt shifts between cool-wet and warmdry conditions. Increased effective precipitation supported large pluvial lakes and long-lived spring ecosystems in valleys and basins throughout the western and southwestern U.S., but the source and seasonality of the increased precipitation are debated. Increases in the proportions of C 4 /(C 4 þ C 3) grasses in the diets of large grazers have been ascribed both to increases in summer precipitation and lower atmospheric CO 2 levels. Here we present stable carbon and oxygen isotope data from tooth enamel of late Pleistocene herbivores recovered from paleowetland deposits at Tule Spring Fossil Beds National Monument in the Las Vegas Valley of southern Nevada, as well as modern herbivores from the surrounding area. We use these data to investigate whether winter or summer precipitation was responsible for driving the relatively wet hydroclimate conditions that prevailed in the region during the late Pleistocene. We also evaluate whether late Pleistocene grass C 4 /(C 4 þ C 3) was higher than today, and potential drivers of any changes. Tooth enamel d 18 O values for Pleistocene Equus, Bison, and Mammuthus are generally low (average 22.0 ± 0.7‰, 2 s.e., VSMOW) compared to modern equids (27.8 ± 1.5‰), and imply lower water d 18 O values (À16.1 ± 0.8‰) than modern precipitation (À10.5‰) or in waters present in active springs and wells in the Las Vegas Valley (À12.9‰), an area dominated by winter precipitation. In contrast, tooth enamel of Camelops (a browser) generally yielded higher d 18 O values (23.9 ± 1.1‰), possibly suggesting drought tolerance. Mean d 13 C values for the Pleistocene grazers (À6.6 ± 0.7‰, 2 s.e., VPDB) are considerably higher than for modern equids (À9.6 ± 0.4‰) and indicate more consumption of C 4 grass (17 ± 5%) than today (4 ± 4%). However, calculated C 4 grass consumption in the late Pleistocene is strikingly lower than the proportion of C 4 grass taxa currently present in the valley (55e60%). d 13 C values in Camelops tooth enamel (À7.7 ± 1.0‰) are interpreted as reflecting moderate consumption (14 ± 8%) of Atriplex (saltbush), a C 4 shrub that flourishes in regions with hot, dry summers. Lower water d 18 O values, lower abundance of C 4 grasses, and the inferred presence of Atriplex are all consistent with general circulation models for the late Pleistocene that show enhanced delivery of winter precipitation, sourced from the north Pacific, into the interior western U.S. but do not support alternative models that infer enhanced delivery of summer precipitation, sourced from the tropics. In addition, we hypothesize that dietary competition among the diverse and abundant Pleistocene fauna may have driven the grazers analyzed here to feed preferentially on C 4 grasses. Dietary partitioning, especially when combined with decreased p CO2 levels during the late Pleistocene, can explain the relatively high d 13 C values observed in late Pleistocene grazers in the Las Vegas Valley and elsewhere in the southwestern U.S. without requiring additional summer precipitation. Pleistocene hydroclimate parameters
Quaternary Science Review, 2019
The first analyses of carbon and oxygen stable isotopes (d 13 C, d 18 O) on horses of late Pleistocene beds, between 50 and 30 kyr B.P., at mid-latitudes of South America (northern Uruguay), are reported here. Isotopic analyses on Equus neogeus and Hippidion principale were made on tooth enamel, considering the Suess Effect. Isotopic values have been used as indicators of diets and environmental conditions, alongside with Hypsodonty Index, to pinpoint specific feeding strategies as grazer or browser. E. neogeus was a mixed-grazer that fed mostly on C 3 grass in open wooded areas and grasslands with a variable proportion of C 4 grass in the diet. H. principale was a mixed feeder with preference for open canopy wooded floor C 3 grass and plants. These results could explain the co-occurrence of both taxa that evolved a combination of feeding and habitat preferences that resulted in niche differentiation. The isotopic data supports the diversity of habitats previously proposed by other authors and corroborate the environmental context associated to the mammal assemblage in late Pleistocene at these latitudes of South America. Juveniles show d 13 C depletion and d 18 O enrichment related to adults. This shift could be explained by maternal effect, owing to gestation and lactation (depleted d 13 C and enriched d 18 O). The later because breast milk is significantly enriched in d 18 O in comparison to drinking water and also is not fractionated in the same way as plant-derived carbon.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
Stable isotopes in horse teeth from the North American Great Plains show that equids began to incorporate C 4 plants in their diets about 6.5 million years ago as C 4 grasslands expanded. However, the ecological response of many other ungulates to this expansion is poorly documented. We use stable carbon isotopes in mammalian tooth enamel to test whether other ungulates adapted by incorporating C 4 vegetation in their diets. The openness of habitats before the expansion of C 4 grasslands is uncertain, with plant phytolith studies suggesting a patchy environment with open-habitat grasses and forest, and pollen and macrofloral studies suggesting more forested habitats. To address this problem we use a model that predicts carbon isotope values for tooth enamel for a variety of environments, based on values in modern plants. Carbon and oxygen isotopes were analyzed in medium to large herbivores from three late Miocene and three Pliocene local faunas comprising a total of 13 and 7 genera, respectively, and 59 and 42 individuals. Results indicate that before the expansion of C 4 grasslands, taxa with high-crowned teeth were consuming predominantly C 3 vegetation. In contrast, by the late Pliocene most taxa studied were consuming a component of C 4 vegetation and only the peccary Platygonus sp. had a pure C 3 diet. C 4 consumption increased in the late Pliocene (~3.0 Ma) Big Springs local fauna probably in response to increased C 4 biomass. Most landscapes in the late Miocene of Nebraska were open, such as woodland-savanna or C 3 grassland, although low carbon values from the Pratt Slide local fauna suggest a denser, presumably forested area. This general pattern suggests an expansion of open-habitats no later than 12 Ma (early Clarendonian). Through the Miocene-Pliocene transition there was an overall shift to lower δ 18 O enamel values, which parallels the long-term decrease in global mean annual temperature inferred from the marine record. Our results indicate that major changes in the diets of medium and large herbivores broadly corresponded with increased C 4 biomass and cooling climate from the latest Miocene to the late Pliocene.
Earth and Planetary Science Letters, 1997
6 j3C values in paleosols and fossil teeth have been used to document the expansion of C, plants in South Asia, Africa, and North America during the late Miocene. However, the exact timing and rate of expansion of C, vegetation is unclear outside the Old World because of a lack of high-resolution records. We present a high-resolution record from northwest Argentina in which the S13C values of soil carbonate rise above a threshold of-8%0, suggesting the presence of C, plants, starting at 7.3-6.7 Ma. Sr3C values of fossil teeth from well dated sections in South and North America display a concomitant increase of C, plants in the diets of large herbivores. These results show that the late Miocene expansion of C, plants was global, but occurred at different rates in each region. While it is has been suggested that declining pC0, levels during the late Neogene caused C, plant expansion, climate change, such as an increase in summer-dominated rainfall regimes globally, is an alternative explanation. The 6 "0 soil carbonate records from South Asia, East Africa and now also northwest Argentina all show an increase of at least 3-4%~ in the late Neogene, either the result of climate change or of greater evaporation in average grassland soils.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2004
Stable oxygen isotopes from fossils, both vertebrate and invertebrate, or inorganic sedimentary minerals frequently have been used to make interpretations about ancient global climates. Oxygen isotope values measured from terrestrial vertebrates or sedimentary carbonates provide information about paleotemperature and amounts of precipitation at a particular site. In general, these inferences are made on the centennial to millennial scale. Serial, i.e. ontogenetic, sampling of Equus and Bison tooth enamel provides climatic data on the scale of months to a few years. We present models showing how annual environmental patterns of d 18 O would be replicated in the tooth enamel of Equus and Bison. Changes in d 18 O due to shifts in temperature (in terrestrial environments d 18 O increases with increased temperature) and amount and timing of precipitation (increased precipitation may result in a decrease in d 18 O; a phenomenon called the ''Amount Effect'') are archived in both Equus and Bison teeth. The input signal is better resolved in Bison due to its more rapid enamel growth. Modeled patterns are compared with actual data from modern sites in the Sonoran and Chihuahuan deserts of the southwestern United States. The isotopic patterns from modern teeth agree with that predicted from known variations in meteoric water. Known floral and faunal assemblages as well as computer models suggest summer rain for the Chihuahuan Desert of Late Glacial time (15,000-10,000 years ago), but little summer rain for the Sonoran Desert at that same time. Serial data from fossil teeth show a clear pattern interpreted to represent the Amount Effect that includes increased summer rains in the Chihuahuan Desert and only minor summer rains in the Sonoran Desert.
Hypsodonty, horses, and the spread of C 4 grasses during the middle Miocene in southern California
Evolutionary Ecology Research, 2017
Background: C4 grasses were not abundant in North America during the middle Miocene (c. 15 Ma). They did not become abundant until around 7 Ma. One can analyse stable carbon (δC) and oxygen (δO) isotope values in the enamel of fossil horse teeth to determine the extent to which horses were eating C4 grasses even during the period before those grasses became abundant. Questions: In southern California, what proportion of a middle Miocene horse’s diet was made up of C4 grasses? Was the amount enough to influence the size and shape of horse teeth? Organisms: Eighty-five specimens of five fossil horse species – Acritohippus stylodontus, Archaeohippus mourningi, Merychippus californicus, Scaphohippus intermontanus, and Scaphohippus sumani – from the middle Miocene (c. 16 Ma) of southern California (i.e. Barstow Formation, Cajon Valley Formation, and Temblor Formation). Methods: To determine if C4 grasses were present in middle Miocene horse diets, we analysed stable carbon (δC) and oxyge...
Background: Stable isotope ratios (13C/12C and 18O/16O) in fossil teeth and bone provide key archives for understanding the ecology of extinct horses during the Plio-Pleistocene in South America; however, what happened in areas of sympatry between Equus (Amerhippus) and Hippidion is less understood. Results: Here, we use stable carbon and oxygen isotopes preserved in 67 fossil tooth and bone samples for seven species of horses from 25 different localities to document the magnitude of the dietary shifts of horses and ancient floral change during the Plio-Pleistocene. Dietary reconstructions inferred from stable isotopes of both genera of horses present in South America document dietary separation and environmental changes in ancient ecosystems, including C3/C4 transitions. Stable isotope data demonstrate changes in C4 grass consumption, interspecies dietary partitioning and variation in isotopic niche breadth of mixed feeders with latitudinal gradient. Conclusions: The data for Hippidion indicate a preference varying from C3 plants to mixed C3-C4 plants in their diet. Equus (Amerhippus) shows three different patterns of dietary partitioning Equus (A.) neogeus from the province of Buenos Aires indicate a preference for C3 plants in the diet. Equus (A.) andium from Ecuador and Equus (A.) insulatus from Bolivia show a preference for to a diet of mixed C3-C4 plants, while Equus (A.) santaeelenae from La Carolina (sea level of Ecuador) and Brazil are mostly C4 feeders. These results confirm that ancient feeding ecology cannot always be inferred from dental morphology. While the carbon isotope composition of horses skeletal material decreased as latitude increased, we found evidence of boundary between a mixed C3/C4 diet signal and a pure C4 signal around 32° S and a change from a mixed diet signal to an exclusively C3 signal around 35°S. We found that the horses living at high altitudes and at low to middle latitude still have a C4 component in their diet, except the specimens from 4000 m, which have a pure C3 diet. The change in altitudinal vegetation gradients during the Pleistocene is one of several possibilities to explain the C4 dietary component in horses living at high altitudes. Other alternative explanations imply that the horses fed partially at lower altitudes.
Geology, 2006
Carbon isotope ratios (δ13C values) of herbivores reflect the δ13C values of dietary plants, and the δ13C values of grazers (animals that consume >90% grass) reflect the local abundance of C3 versus C4 grasses. Because grassland C3/C4 ratios correlate with climate, the δ13C of fossil grazers may serve as a proxy for reconstructing paleoclimates and paleovegetation patterns. However, the accuracy of environmental reconstructions based on herbivore δ13C values is often uncertain, because the relationship between the δ13C of many animals and the abundance of C4 and C3 grasses has not been precisely quantified. We analyzed the δ13C of tooth enamel carbonate from modern bison (Bison bison bison) from nine localities in the United States. The C4 grass biomass at these sites ranged from <1% to ˜95% of the total grass biomass. The mean δ13C of enamel for each population correlated well with the local abundance of C4 grasses and with variations in mean annual temperatures. The variability of enamel δ13C values did not differ among habitats and was not correlated with the abundance of C4 grasses. These results demonstrate that analyses of the δ13C values of fossil bison can be used as a quantitative proxy for reconstructing grassland C3/C4 ratios and paleotemperatures, and they will serve as a baseline for interpreting the δ13C of fossil bison and other large herbivores in North America.
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.