Paleoecology Symposium: Latest methods in reconstructing Cenozoic terrestrial environments and ecological communities

September 10-12, 2015

POSTER ABSTRACTS

Hosted by: Cleveland Museum of Natural History Co-sponsored by: Institute for the Science of Origins at the Case Western Reserve University

Effects of allochthonous pollen influx on paleoclimate reconstructions: Evidence from the late Eocene Florissant flora, Colorado

BAUMGARTNER, K.A.; MEYER, H.W.

Baylor University, Waco, TX

Abstract Both fossil leaves and pollen are frequently used to reconstruct ancient climates; however, the possible influence of variations in regional paleotopography and paleoelevation on these paleoclimate reconstructions must be considered. The late Eocene Florissant flora is a prime example of a fossil flora that has produced different quantitative paleoclimate estimates when the influence of paleoelevation has and has not been considered. Over the years many different paleobotanical paleoclimate proxies have been utilized. Reconstructions using only fossil leaves or fossil leaves and pollen, including the nearest living relative (NLR) and leaf margin analysis, have generated a range of mean annual temperature (MAT) estimates from 10.7 to 18.0 OC. Methods that have utilized only fossil pollen yield a warmer MAT estimate from 15 to 20 OC. Previous studies of modern pollen have demonstrated that pollen can be dispersed across long distances and significant amounts of warm- adapted lower elevation pollen are often transported to higher elevations. Thus fossil pollen assemblages from high elevation sites likely consist of a mixture of autochthonous (cool high elevation) and allochthonous (warm low elevation) pollen. As a means of assessing the influence of the influx of warm, low elevation pollen into the Florissant flora, we utilized the coexistence approach (CA) analysis to reconstruct the paleoclimate of Florissant using previously published paleobotanical fossil identifications at the generic level. Our results indicate that the pollen-based reconstructions of paleoclimate are biased by the influx of warm, low elevation pollen and we submit that the cooler MAT estimates based on the macrofossil assemblage better represent the local paleoclimate of Florissant than the reconstructions based on only the pollen fossil assemblage, which mixes local and distant pollen sources. Florissant is an excellent model for high elevation paleoclimate reconstructions and our results demonstrate that reconstructions of paleoclimate at high elevation sites using pollen-based methods must be treated with a degree of caution.

Paleoenvironmental reconstruction of a semi-arid Late Pleistocene paleocatena from the Lake Victoria Region, Kenya

BEVERLY, Emily J.1*; DRIESE, Steven G.1; PEPPE, Daniel J.1; ARELLANO, Lisabeth1; BLEGEN, Nick2; FAITH, J. Tyler3; TRYON, Christian A.4

1 [email protected], Baylor University, Department of Geology, Waco, TX 76798; 2Department of Anthropology, University of Connecticut, Storrs, CT 06269; 3School of Social Science, University of Queensland, Brisbane, QLD 4072, Australia; 4Department of Anthropology, Harvard University, Peabody Museum, 11 Divinity Ave, Cambridge, MA 02138 *corresponding author; email: [email protected]

Abstract The effect of changing environment on the evolution of Homo sapiens is heavily debated, but few data are available from equatorial Africa prior to the Last Glacial Maximum. The Karungu deposits on the northeast coast of Lake Victoria are ideal for paleoenvironmental reconstructions and are best exposed at the Kisaaka site (94 to >33 ka) where paleosols, fluvial deposits, tufa, and volcaniclastic deposits (tuffs) are exposed over an ~2 km transect. Measured stratigraphic sections reveal Pleistocene fluvial and tufa deposits that directly overlie the paleotopography. Above the fluvial deposits, three well-exposed and laterally continuous paleosols with intercalated tuffs allow for reconstruction of a succession of paleocatenas. The abundance of paleosols allows for reconstructions of modern soil properties and estimates of mean annual precipitation (MAP) using bulk geochemistry. The oldest paleosol is a smectitic paleo-Vertisol with pedogenic slickensides, gilgai topography, and saline and sodic properties that indicate seasonal precipitation and a period of landscape stability of at least 0.5 to 2 ka. Higher in the section, the paleosols are tuffaceous paleo-Inceptisols with Alfisol-like soil characteristics (illuviated clay). MAP proxies indicate little change through time, with an average of 764 ± 182 mm yr-1 for Vertisols (CALMAG) and 813 to 963 ± 108 mm yr-1 for all paleosols (CIA-K). Field observations and MAP proxies suggest Karungu was significantly drier than modern (~1500 mm yr-1) and likely resulted in a significantly smaller Lake Victoria during the Late Pleistocene. This is consistent with the associated faunal assemblage, which is dominated by alcelaphine antelopes and zebras indicative of semi-arid grasslands. The faunal and geologic evidence suggests a seasonally dry, open grassland environment for the Lake Victoria region during the Late Pleistocene that is vastly different from the closed bushland and forest habitats present today. Rainfall reduction and associated grassland expansion may have facilitated human and faunal dispersals across equatorial East Africa.

RECONSTRUCTING THE MIDDLE MIOCENE PALEOENVIRONMENT OF QUEBRADA HONDA, BOLIVIA, USING ICHNOLOGY AND PALEOPEDOLOGY

CATENA, Angeline M.1; CROFT, Darin A.1

1Department of Anatomy, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4930. [email protected]

Abstract Although the Neotropics are home to exceptional levels of mammalian diversity, there are few fossil-producing localities with which to study the history of these diverse and unique faunas. La Venta, Colombia (LV), and Quebrada Honda, Bolivia (QH) are well-sampled, contemporaneous (12-13 Ma; late middle Miocene) Neotropical fossil-producing sites that preserve the remains of many nonvolant (59 and 30 genera, respectively). These two localities have almost no mammalian genera in common, which could reflect different climates and/or habitats. However, unlike LV, the paleoenvironment of QH has not been investigated in detail. In this study, paleopedology and ichnology are used as independent lines of evidence to elucidate the habitat of QH. The paleosols of QH are weakly to moderately developed; features of the paleosols include a silty claystone- to silty sandstone-based lithology, slickensides and calcareous nodules. The paleosols appear to represent Entisols and Inceptisols that formed in proximal and distal floodplains, respectively. The suite of ichnofossils present in QH paleosols include Coprinispharea, Cellicalichnus, Psilonichnus, and Palaeophycus. These ichnofossils are interpreted as dwelling and breeding structures that were primarily produced by solitary arthropods such as beetles, bees, and spiders. Rhizoliths are also abundant in the paleosols and range from small, branched mm-scale rhizohaloes to tapering, dcm-scale rhizocretions. The small, branched rhizohaloes are interpreted as roots from grasses or small plants, while the large, tapering rhizocretions are interpreted as taproots of medium-to-large plants, such as shrubs and trees. Based on these characteristics the paleoenvironment of QH is interpreted as a mixture of seasonal grasslands and savannas located proximal to alluvial systems. The inferred habitat of QH contrasts with that of LV which has been reconstructed as a mixture of river-associated tropical forests and successional stages thereof. Our initial findings indicate that dissimilar habitats could account for some of the differences between the faunas of QH and LV. Ecological niche selectivity in Australopithecus anamensis

DUMOUCHEL, Laurence1; MANTHI, Frederick Kyalo2

1Center for the Advanced Study of Hominid Paleobiology, George Washington University, Washington, D.C.; 2Department of Earth Sciences, National Museums of Kenya

Abstract Kanapoi (Kenya) is the type-site for Australopithecus anamensis, the first indisputably bipedal hominin species and the majority of the fossils attributed to A. anamensis have been found at Kanapoi. In this study, 350 mammal fossils (> 5cm) from the published Kanapoi collections are described and compared to a smaller assemblage (n=30) from the Mursi Formation (Ethiopia). These geographically close assemblages (< 300 km apart) both have estimated ages of over 4 million years. Although there have been faunal fossils found at the Mursi Formation sites, so far, hominin remains have only been recovered at Kanapoi. Can analyzing faunal remains provide insight into possible environmental differences between the Kanapoi and Mursi Formation sites and the criteria used by this human ancestor to select their habitat? Analyses reveal that there were important taphonomic and paleoecological differences between the two assemblages despite the fact that their faunas were found to be similar in composition. The significant difference between the polishing levels of the remains (p = 0.03) suggests that the paleoenvironment of the Mursi Formation was more closely associated with water. In addition, the more evenly distributed weathering levels in the Kanapoi fossils (p<0.001) indicate that the bones in the assemblage accumulated on the surface over an extended period of time prior to burial, which further suggest drier local conditions than at the Mursi Formation. This new evidence provides key information for our understanding of ecological niche selectivity during the time of emergence of the genus Australopithecus.

Funded by The Explorers Club, Exploration Fund and NSF-IGERT to the Center for the Advanced Study of Hominid Paleobiology

Keywords : Australopithecus anamensis, Taphonomy, Pliocene, Paleoecology, Kanapoi, Mursi Creating a modern isotopic framework for understanding paleoecology in C3- dominated paleoecosystems

FERANEC, Robert S.1; GARCIA, Nuria1,2; GONZALEZ, Alvaro1,2 ; VIRGOS, Emilio 3; VALENCIANO, Javier4

1Centro de Investigación Sobre la Evolución y Comportamiento Humanos, Universidad Complutense de Madrid–Instituto de Salud Carlos III, 28029 Madrid, Spain 2Departamento de Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, 28040 Madrid, Spain 4Departamento de Biologıa y Geologıa, Universidad Rey Juan Carlos, Madrid, Spain; 5Consejeria de Agricultura, Castilla-La Mancha, Cuenca, Spain

Abstract Stable isotope analysis has been established as a powerful tool for understanding ecology in both modern and ancient ecosystems. Many studies concentrate on determining ecology in (paleo)ecosystems that contain both C3 and C4 plants due to the large differences in 13C/12C incorporated into plant tissues as the result of their using different photosynthetic pathways, and the subsequent assimilation of these values up the food chain. Studies concentrating on C3-dominated ecosystems are rarer, although C3 plants are typical of most ecosystems today as well as in the past. In fact, ecosystems with an abundance of C4 plants are apparent only after about 7 million years ago worldwide. One important area that has implications for mammalian evolution including humans, has implications on the effects of climate change on mammals, and is dominated by C3 plants, is Europe during the Pleistocene. Although there have been many isotopic studies on Pleistocene European sites, there is a limited isotopic framework for understanding this data within Europe during this time period. Here we present isotopic data from mammals collected in Parque de el Hosquillo (Hosquillo Park, Cuenca, Spain) with the aim of providing a framework for understanding the isotopic values of more ancient mammals in Europe. Samples of scat, hair, bone apatite, bone collagen and tooth enamel were collected from 185 individuals (132 adults) and were sampled for δ13C, δ15N, and δ18O values, depending on the type of sampled tissue. Species sampled within the park include: Capreolus capreolus, Cervus elaphus, Dama dama, Ovis orientalis, and Sus scrofa. Isotopic discrimination factors were determined for each species and for each sampled tissue type. Data show that carbon isotope discrimination factors (∆13C) are similar for all species, and are comparable to previously published values for the different tissues. Once calculated, these discrimination factors were then used to better understand isotopic values obtained from mammals within more ancient Pleistocene-aged sites. The data from Parque de el Hosquillo permit a more accurate understanding of the ancient samples from the Pleistocene of Europe. Histological analyses of Odocoileus virginianus (Mammalia: Cervidae) from Florida during the Pleistocene to Holocene.

GERWITZ, Andrew

Department of Geology, Kent State University

Abstract Histological analyses of mammalian bones can offer insight into organismal responses to changing ecological conditions. Abundant Pleistocene to Holocene fossils of Odocoileus virginianus from Florida offer a unique opportunity to study changes in growth in a mammal species in response to climate and environmental changes over the past 2 million years. To accomplish this, diaphyseal thin sections were created from 54 limb bones (humeri, radii, femora, tibiae) from 4 fossil sites in Florida. Each bone was classified into one of 3 ontogenetic stages (juvenile, sub-adult, adult) based on epiphyseal fusion. Each fossil site is associated with either a glacial or interglacial climate; glacial sites: Inglis 1A - (~1.8 MA), Coleman 2A - (~500,000 Y); interglacial sites; Leisey Shell Pit 1A - (~1.5 MA), Nichol’s Hammock - (~500 Y). In general, cortical tissue in O. virginianus limb bones is fibrolamellar with some lamellar bone in the mid to outer cortex later in life with bone growth marks (BGMs), including annuli and lines of arrested growth (LAGs), present to varying degree. Adults from Nichol’s Hammock preserved more dense, slow-growing lamellar tissue with numerous BGMs in the mid to outer cortex, while adults and sub-adults from Inglis 1A, Leisey 1A and Coleman 2A had more fast- growing plexiform to laminar fibrolamellar tissue with lamellar bone and fewer BGMs. No inter- locality differences were observed for juveniles. In general, these observations suggest a trend of significantly slowed growth in later life for individuals from Nichol’s Hammock compared to mature individuals from chronologically older sites. This trend of decreasing vascularization of bone tissue and increased presence of BGMs in more recent populations may be a result of differences in environmental pressures resulting in changes in resource availability, although geographical, chronological and other paleoecological differences may also be influencing growth. A detailed analysis of bone growth of living deer between southern, central, and northern regions within Florida may help elucidate the cause of observed growth differences in fossil populations from Florida. Paleocommunity Analysis of Four Eurasian Pleistocene Sites

GOGOL, Samantha; CURRAN, Sabrina

Department of Sociology and Anthropology, Ohio University, Athens, OH

Abstract To understand the behavior and evolution of fossil hominins, accurate reconstructions of paleoecological conditions are necessary. There are many methods available to do so, each reconstructing specific aspects of paleoenvironments. Paleocommunity analysis is one such method that uses modern ecological communities to form a comparative database to which paleocommunities can be compared based percentages of species in categories of trophic level and locomotor behavior. This method has been widely applied to the African paleorecord, but has not been used on Eurasian sites. In this poster we present results from a pilot study of modern mammalian communities from Armenia, Azerbaijan, Bulgaria, Georgia, Greece, Moldova, Romania, and Turkey and compare these regions to several Pleistocene sites in France (La Senèze), Georgia (Dmanisi), Greece (Vatera), and Romania (Graunceanu). Cluster analysis (UPGMA) indicated that two fossil sites (Senèze and Vatera) are quite distinct, forming a cluster to the exclusion of all other sites and that Graunceanu and Dmanisi cluster most closely with modern montane ecotones from Georgia. Canonical variates analysis was used to classify each fossil site into the habitat category with which it is most similar (based on modern analogs). All fossil sites were classified as ecotones, except Senèze, which was categorized as a shrubland. These results suggest that similar environments were available across Eurasia at the first appearance of Homo erectus, which has only been recovered from Dmanisi thus far. Seasonal climate reconstruction using synchrotron-based tooth mineralization models in ungulates.

GREEN, Daniel R.1; COLMAN, Albert S.2; GREEN, Gregory M.3; TAFFOREAU, Paul4; SMITH, Tanya M.1

1Department of Human Evolutionary Biology, Harvard University, 2Department of Geophysical Sciences, University of Chicago, 3Center for Astrophysics, Harvard University, 4European Synchrotron Radiation Facility, Grenoble, France.

Abstract Seasonal climate patterns are major determinants ecosystem structure and productivity, and are hypothesized to have influenced early human stone tool industries in Africa. Rainfall patterns are reflected by oxygen isotope ratios in mammalian tooth enamel, which records environmental chemistry throughout the period of incremental crown growth. Ungulate molars are abundant in Cenozoic fossil assemblages, and used for seasonal climate reconstruction through sequential isotope sampling. However, seasonality reconstruction is hampered by incomplete knowledge of tooth mineralization. Here we use synchrotron x-ray imaging and Markov Chain Monte Carlo (MCMC) methods to estimate mineralization trajectories from an ontogenetic series of sheep first molars (n=45). Our results demonstrate that enamel secretion and maturation occur in two waves distinct in timing and geometry. Enamel farther from the enamel-dentin junction (EDJ) begins mineralization later than enamel near the EDJ, but completes maturation simultaneously and at higher densities. These results contrast with a commonly employed mineralization model predicting no pause between secretion and maturation, and similar geometry for both phases. We integrate knowledge of tooth growth and blood oxygen isotope (δ18O‰) turnover to produce high-resolution tooth isomap predictions, and validate these with isotope distributions in the enamel of a sheep molar that was subjected to a controlled water switch. We employ Monte Carlo optimization to reconstruct original seasonal inputs from tooth isotope ratios. These novel methods of may be employed to document seasonal climate patterns using fossil teeth at sites of early stone tool industries in Africa, and further explore the complex relationship between climate, behavior and evolution. The fossil Giraffidae from North China and the diet determination by tooth mesowear methods

HOU, Sukuan1, 2 ; SOLOUNIAS, Nikos3

1Department of Paleobotany and Paleoecology, Cleveland Museum of Natural History, Cleveland, 44106 ([email protected]); 2Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044; 3New York Institute of Technology, College of Osteopathic Medicine, New York, 11568 ([email protected])

Abstract The giraffe and the okapi are the only living species of the Giraffidae. The giraffe lives in the savannas of Africa, which is the largest extant land mammals and has extremely long neck; while the okapi only inhabits forbidding dense forests in Zaire, and has relatively small body size and short neck. Though having differences in body size, neck length, and habitats, the giraffe and the okapi share a similar diet, they are both browsers. During the Late Miocene there were many extinct species of giraffids in Eurasia and Africa. Bohlin (1926) described abundant fossil giraffids from the Late Miocene deposits of North China. At the end of the 20th century more Giraffidae fossils were found from the Linxia Basin in North China. Based on the body size, the skull morphology, the length of the neck, and the limb bones, four genera of Giraffidae were recognized in the Linxia Basin: Palaeotragus, Samotherium, Schansitherium, and Honanotherium. The diet of different genera was determined by the tooth mesowear methods. Mesowear is the wear of enamel bands that can be used to study the diet of ungulates. In ruminants, there are four bands of enamel, which are separated by dentine. The buccal-most band is termed band 1, and the lingual-most band is termed band 4, with bands 2 and 3 in between. The original mesowear investigated band 1 of the second molar from a buccal view, addressing the height of the relief of the paracone and the metacone, and subdividing the morphotypes of the apices, to evaluate large numbers of individuals quickly and easily. Mesowear II combined the relief and the apical morphology into a single variable, which also utilized band 1 of M2 from a buccal view. A new method of tooth mesowear, mesowear III, draws data from enamel band 2 of M2 using an occlusal view. It is a promising method in separating diet of ruminants, and data so far allow a better separation between browsers, grazers, and mixed feeders. We use both mesowear II and mesowear III to study the diet of fossil giraffids from North China. Unlike the living giraffe and okapi, all the fossil giraffids from the North China are mixed feeders, and the data of Schansitherium appear to be more on the grazing side. A simple comparison of the mesowear data was also made between the Linxia specimens and Bohlin’s specimens. The diet of the Linxia giraffids appears to be more browsing than the giraffids that Bohlin described, which may suggest a relatively more humid environment in the Late Miocene of the Linxia Basin than in other localities of North China. Morphological and Functional Analyses of Cercopithecoid Tibiae KOZMA, Elaine, E.1,2

1Department of Anthropology, City University of New York--Graduate Center, 2New York Consortium in Evolutionary Primatology

Abstract Organisms interact directly with their environment through locomotion and substrate use. Relationships between functional locomotor morphology and behavior in extant taxa can directly inform paleoecology. Here I compare tibial morphology using three-dimensional landmarks in 195 extant cercopithecoid specimens from 15 taxa to identify how differences in size and locomotor pattern influence tibial morphology. The aims were (1) to produce a categorization method to classify specimens into locomotor categories based on tibial morphology and (2) to use this model to investigate locomotor patterns in extinct taxa. The specimens were landmarked by Microscribe. The resulting data set underwent general Procrustes analysis and principal component analysis. Principal component scores were regressed onto log centroid size to assess the effects of size. Results indicate that size, as measured by log centroid size, has little effect on proximal and distal tibial morphology in cercopithecoids compared to locomotor pattern. A discriminant analysis (DFA) was used to discriminate between locomotor categories. The resulting DFA performed with 75 % accuracy based on leave-one-out cross validation. Tibiae of three fossil taxa, Theropithecus oswaldi, Paracolobus chemeroni, and cf. Rhinocolobus sp., were classified using the DFA. I discuss these results in with regard to described locomotor and ecological patterns in these taxa.

Chewing efficiency optimality and diet in modern humans

LAIRD, Myra

Department of Anthropology, Center for the Study of Human Origins, New York University, NY, NY

Abstract Food processing is a direct connection between an organism and its ecosystem, and experimental techniques in dietary functional morphology offer new approaches to studying paleoecology. Smaller food particles are digested at a faster rate with greater energy extraction. Thus there are strong selective pressures on the masticatory complex to efficiently process foods. To optimize efficiency, reduction in particle size is maximized, and the amount of energy spent during processing is minimized. Here I present a chewing efficiency optimization model for foods of varying material properties building from previous work relating chewing efficiency to occlusal area and kinematic variance. I hypothesize that temporal and spatial movement of the gape cycle varies with occlusal surface morphology for different foods to optimize chewing efficiency. To test this model, twenty-six human subjects completed chewing trials for six foods ranging in food material properties and fragmentation indices. Chewing efficiency was measured in each subject using electromyography and high-speed motion capture. Dental topographic analysis was used to quantify occlusal surface morphology of each subject from dental casts. Model results show similar efficiency patterns in occlusal areas and gape cycle kinematics. For foods of greater toughness, larger occlusal surfaces are more efficient and gape cycles have increased occlusal contact time. Together these results suggest that humans modulate their gape cycles to optimize particle breakdown over their occlusal surface by lengthening contact time between the teeth and the food item. I discuss these results with reference to occlusal size variation and diet change in the fossil hominin record. LANDSCAPE AND CLIMATE RECONSTRUCTION AT COFFEE RANCH, TX: INSIGHTS INTO ENVIRONMENTS DIRECTLY PRECEDING C4 GRASS EXPANSION

LUKENS, William E.; DRIESE, Steven G.; NORDT, Lee C.

Terrestrial Paleoclimatology Research Group, Department of Geology, Baylor University, Waco, TX 76798

Abstract Paleosols (fossil soils) are the physical records of past terrestrial ecosystems and serve as in situ archives of ancient Critical Zones. Novel pedotransfer functions have given paleosol researchers the tools necessary to reconstruct paleoclimatic, paleobiologic, and paleohydrologic conditions in Deep Time. In this study, we use paleosols to reconstruct suites of landscapes across a 7 km lateral transect to gain insight into the geomorphic and ecologic dynamics at the Late Miocene (6.6 Ma) Coffee Ranch locality in the Texas Panhandle. The Coffee Ranch Local Fauna (Hemphillian Type Section and Late Hemphillian Chronofauna) contains a diverse fossil assemblage, including equids that record the first evidence of C4 grass consumption in the North American geologic record. Although C4 grasses had likely been present in the Great Plains region by 20 Ma, the reason for the initiation of C4 grass herbivory at ~6.6 Ma remains elusive. Paleolandscapes at Coffee Ranch were geomorphically partitioned between mixed-energy fluvial channels, laterally-variable floodplain soils, relatively small floodplain ponds, freshwater springs and localized eolian sand sheets. The presence of paleo-Vertisols with accumulations of pedogenic carbonate, and fluvial channels with slackwater clay drapes and vertebrate trackways, are indicative of seasonal water deficit in a subhumid climate. Eolian sands were mobilized during periodic (~101-102 y) droughts based on comparison to analogous modern systems. Mean annual precipitation and temperature were ~1100 mm/yr and ~13°C based on paleosol bulk geochemistry. Reconstructed base saturation, pH, and cation exchange capacity from paleo- Vertisols are indicative of high soil fertility. The δ13C values of soil organic matter and pedogenic carbonate correspond to < 5% C4 biomass on any landscape position. The lack of any resolvable C4 microbiome at Coffee Ranch suggests that either a few individual equids preferentially consumed C4 grass, or part of the population had migrated from regions elsewhere that contained a greater proportion of C4 vegetation. DIETARY ECOLOGY OF DIVERSE MIOCENE RODENT FAUNAS FROM THE MOJAVE REGION BASED ON IN SITU STABLE ISOTOPE ANALYSIS

SMILEY, Tara M.1; BADGLEY, Catherine2; CERLING, Thure E.3

1Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI; 2Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI; 3Department of Geology and Geophysics and Department of Biology, University of Utah, Salt Lake City, UT

Abstract Terrestrial ecosystems and mammalian communities underwent dramatic changes during the Miocene history of western North America. Tectonic extension generated new topographic complexity in the region, while changes in global and regional climates influenced the distribution of major vegetation types and the diversity and ecology of mammalian faunas. Peak mammal diversity in the tectonically active Basin and Range Province coincided with a major warming interval, the Miocene Climatic Optimum, from 17-14 Ma. The record from the Mojave Region, including the Barstow, Crowder, and Cajon Valley formations, is one of the most continuous and fossil-rich sequences to span this interval of environmental change and high regional diversity. The Crowder and Cajon Valley formations span the entire Miocene Climatic Optimum, providing an important record of ecological response to environmental change. These formations are an archive of diversity for both small and large mammals (106 identified species) with abundant rodent fossils, including species from the Sciuridae, Heteromyidae, Cricetidae, Geomyidae, and Eomyidae. We applied in situ laser ablation mass spectrometry to analyze the carbon isotopic composition of rodent teeth from the Crowder and Cajon Valley formations in order to characterize changes in dietary composition within lineages and in dietary overlap among species through time. Corresponding environmental changes for these formations have been analyzed from the elemental chemistry of paleosols, the carbon isotopic composition of preserved soil organic matter, and phytolith assemblages. These proxies indicate wet (~800 -1 mmyr ), mixed forest-C3 grassland ecosystems with a small (less than 4% of vegetation) and spatially heterogeneous C4 grass component. While the majority of rodent individuals analyzed record a diet composed of C3 food resources, some individuals do exhibit a preference for C4 vegetation. Individuals with isotopically heavier carbon signatures incorporated a greater proportion of C4 vegetation into their diet than was present on the landscape according to other vegetation proxies. This contrast suggests a role for dietary niche differentiation within the diverse rodent faunas of the Crowder and Cajon Valley formations during the Miocene Climate Optimum. The paleoecological implications of middle Pliocene mammalian abundance in the Afar and Turkana Basins: a case study

VILLASEÑOR, Amelia 1; BOBE, René1

1Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington D.C.

Abstract The abundance of is mediated by important ecological factors, such as the type of resources available and the competition for those resources. Thus, analyzing the abundance of a species across geographic space provides insight into the different selective pressures present at those different sites. In the Pliocene hominin fossil record, Australopithecus afarensis has been found to be relatively rare at Laetoli, Tanzania, which is thought to be the result of local ecological pressures. However, there is little information on how hominin abundance varies relative to fauna at other sites in eastern Africa, such as in Ethiopia and Kenya. To address this paucity of knowledge, we analyzed hominin abundance at the sites of Hadar and Omo-Shungura, Ethiopia, where only A. afarensis has been definitively recorded, and East and West Turkana, Kenya, where both A. afarensis and the synchronic hominin Kenyanthropus platyops is found. We also test the hypothesis that Hadar, Ethiopia will have greater numbers of hominins since it has been found in previous research to have ecological qualities that may support greater abundance of hominins. To test this hypothesis, while accounting for differences in collection methods and taphonomy among sites, we examined data from only a subset of the medium-sized mammals from the Hadar, Turkana, and Omo databases (n=361 in Hadar, n=74 in East Turkana, n=220 in West Turkana, n= 194 in the Omo). Using the minimum number of individuals for the tribes Hominini (which includes Australopithecus and Kenyanthropus), Papionini, Aepycerotini, and Antilopini, the relative abundance of hominins within each site was calculated. Chi-square tests indicated significant differences in the proportion of medium sized mammals across sites (p > 0.001), though chi-squared residuals showed that hominins were not driving these differences in distributions. Rather, ecological specialists, such as species within Antilopini and Papionini, were found to influence differences in mammalian distributions between sites where hominins were relatively more abundant in association with greater proportions of medium-sized mammals from more open environments.

Reconstructing the Paleoenvironment of the Santa Cruz Formation, Argentina Using Typothere (: Mammalia) Microwear McGRATH, Andrew J. Case Western Reserve University, Cleveland, Ohio The Santa Cruz Formation in southern Argentina is one of the most important Cenozoic fossil localities in South America. Fossils found at this site are approximately 18-16 Ma old (early Miocene). The Santa Cruz Formation is so fundamental to our understanding of South American paleontology that an entire South American Land Mammal Age (SALMA) is named after it (). Many researchers have attempted to reconstruct the ancient climate and floral community of Santa Cruz in order to better understand the ecosystem as a whole as well as to provide insights about the rest of the continent during this time. This study uses enamel microwear to discover the diets of four common small-bodied ungulates, typotheres, to determine what types of plants were present at Santa Cruz. When compared to a set of 59 modern ungulates of varying diets, two of the typotheres, Protypotherium and Pachyrukhos allied most closely with grazers (grass-eaters). The microwear patterns of the other two typotheres, Hegetotherium and Interatherium more resembled modern browsers (leaf or fruit-eaters). Due to their high-crowned (hypsodont) molars, all four of these species have historically been thought of as grazers. Additionally, Hegetotherium, Protypotherium, and Pachyrukhos exhibited somewhat higher pit counts than average which could be a sign of higher than normal amounts of grit in these animals’ diets. A large amount of grit would suggest a slightly arid climate for Santa Cruz. In more arid environments dust is blown into the air and then settles onto leaves and grasses. The presence of two grazing and two browsing typotheres at Santa Cruz suggests a mixed habitat. Hegetotherium and Interatherium were likely not able to climb trees to reach the leaves nor were they tall enough to reach the branches so it seems that low-level shrubs were important contributors to the plant community. These findings are supported by the other research on the paleoenvironment of Santa Cruz. Other researchers have used various techniques and all have found evidence for Santa Cruz being a mixture of semi-arid and humid forests interspersed with grasslands.