Late quaternary biotic homogenization of North American mammalian faunas.

Biotic homogenization-increasing similarity of species composition among ecological communities-has been linked to anthropogenic processes operating over the last century. Fossil evidence, however, suggests that humans have had impacts on ecosystems for millennia. We quantify biotic homogenization of North American mammalian assemblages during the late Pleistocene through Holocene (~30,000 ybp to recent), a timespan encompassing increased evidence of humans on the landscape (~20,000-14,000 ybp). From ~10,000 ybp to recent, assemblages became significantly more homogenous (>100% increase in Jaccard similarity), a pattern that cannot be explained by changes in fossil record sampling. Homogenization was most pronounced among mammals larger than 1 kg and occurred in two phases. The first followed the megafaunal extinction at ~10,000 ybp. The second, more rapid phase began during human population growth and early agricultural intensification (~2,000-1,000 ybp). We show that North American ecosystems were homogenizing for millennia, extending human impacts back ~10,000 years.

The upper limb of Paranthropus boisei from Ileret, Kenya.

Paranthropus boisei was first described in 1959 based on fossils from the Olduvai Gorge and now includes many fossils from Ethiopia to Malawi. Knowledge about its postcranial anatomy has remained elusive because, until recently, no postcranial remains could be reliably attributed to this taxon. Here, we report the first associated hand and upper limb skeleton (KNM-ER 47000) of P. boisei from 1.51 to 1.53 Ma sediments at Ileret, Kenya. While the fossils show a combination of primitive and derived traits, the overall anatomy is characterized by primitive traits that resemble those found in Australopithecus, including an oblique scapular spine, relatively long and curved ulna, lack of third metacarpal styloid process, gracile thumb metacarpal, and curved manual phalanges. Very thick cortical bone throughout the upper limb shows that P. boisei had great upper limb strength, supporting hypotheses that this species spent time climbing trees, although probably to a lesser extent than earlier australopiths. Hand anatomy shows that P. boisei, like earlier australopiths, was capable of the manual dexterity needed to create and use stone tools, but lacked the robust thumb of Homo erectus, which arguably reflects adaptations to the intensification of precision grips and tool use. KNM-ER 47000 provides conclusive evidence that early Pleistocene hominins diverged in postcranial and craniodental anatomy, supporting hypotheses of competitive displacement among these contemporaneous hominins.

Landscape scale heterogeneity in the East Turkana ecosystem during the Okote Member (1.56-1.38 Ma).

Placing the biological adaptations of Pleistocene hominins within a well-resolved ecological framework has been a longstanding goal of paleoanthropology. This effort, however, has been challenging due to the discontinuous nature of paleoecological data spanning many important periods in hominin evolution. Sediments from the Upper Burgi (1.98-1.87 Ma), KBS (1.87-1.56 Ma) and Okote (1.56-1.38 Ma) members of the Koobi Fora Formation at East Turkana in northern Kenya document an important time interval in the evolutionary history of the hominin genera Homo and Paranthropus. Although much attention has been paid to Upper Burgi and KBS member deposits, far less is known regarding the East Turkana paleoecosystem during Okote Member times. This study pairs spatially-resolved faunal abundance data with stable isotope geochemistry from mammalian enamel to investigate landscape-scale ecosystem variability during Okote Member times. We find that during this period 1) taxa within the East Turkana large mammal community were distributed heterogeneously across space, 2) the abundance of C3 and C4 vegetation varied between East Turkana subregions, and 3) the Karari subregion, an area with abundant evidence of hominin stone tool manufacture, had significantly more C3 vegetation than regions closer to the central axis of the Turkana Basin (i.e., Ileret and Koobi Fora). These findings indicate that the East Turkana paleoecosystem during the Okote Member was highly variable across space and provided a complex adaptive landscape for Pleistocene hominins.

Paleolandscape variation and early pleistocene hominid activities: members 1 and 7, Olorgesailie formation, Kenya.

Paleolandscape research tests for variation in the spatial distribution of hominid artefacts and establishes the association of hominid activities with paleoenvironmental features over distances of 100s to 1000s of meters. This approach requires (1) precise definition of narrow stratigraphic intervals based on sedimentary criteria that can be documented over a broad area, and (2) excavation of these intervals in order to establish taphonomic and paleoenvironmental contexts. In this report, excavations of three target intervals within the early Pleistocene deposits (992 to 780 ka) of the Olorgesailie basin are described. Assessment of time-averaging and paleolandscape structure shows that each target interval represents a relatively brief period (

Early pleistocene habitat in member 1 Olorgesailie based on paleosol stable isotopes.

Stable carbon and oxygen isotope values from soil carbonates were used to determine the vegetation context of archaeological sites and local climatic conditions represented in a approximately 0.99 Ma paleosol that is exposed laterally in the Olorgesailie basin, southern Kenya rift valley. As part of this landscape-scale project, samples of an upper Member 1 paleosol were analyzed along nearly 4 km of outcrop in three adjacent parts of the basin. Modern East African soil and plant community analogs are used to interpret the isotope ratios. The carbon isotopic composition of the paleosol carbonates indicates that the area supported a local biomass of about 75-100% C(4)plants during the period of soil formation. After averaging the data for each trench, an open C(4)grassland is represented by half of the carbon values, with wooded grassland more abundant across the paleolandscape than it is in the area now. This vegetational reconstruction is supported by the mammalian faunal assemblage, which has a high percentage of grazers. Although the relatively small sample size outside the main excavation area precludes firm characterization of vegetational diversity across the basin in upper Member 1 times, eastern and western localities in the study area may have had more woody C(3)plants than the widely sampled zone in between. Oxygen isotopes indicate that the lowland basin was slightly cooler and moister than today's semi-arid climate, with greater annual rainfall. Archaeological traces have a virtually continuous distribution across the paleolandscape, but vary in density of occurrence. With the strong evidence for C(4)grassland as the primary vegetation context across most of the study area, no habitat preference by the Acheulean toolmakers at Olorgesailie is shown in our initial comparison between carbon isotope values and stone/bone densities.

Isotopic tracking of change in diet and habitat use in african elephants.

The carbon, nitrogen, and strontium isotope compositions of elephants in Amboseli Park, Kenya, were measured to examine changes in diet and habitat use since the 1960s. Carbon isotope ratios, which reflect the photosynthetic pathway of food plants, record a shift in diet from trees and shrubs to grass. Strontium isotope ratios, which reflect the geologic age of bedrock, document the concentration of elephants within the park. The high isotopic variability produced by behavioral and ecological shifts, if it is representative of other East African elephant populations, may complicate the use of isotopes as indicators of the source region of ivory.

Hominid taphonomy: transport of human skeletal parts in an artificial fluviatile environment.

Flume experiments demonstrate that human skeletal parts sort into lag and transportable groups in a current flow of 31 cm/sec. Orientations, rates and types of movement, and stable positions are recorded. Density of a skeletal part is correlated with the average rate of movement, whereas wet weight in air, weight in water, and volume are not. Shape is an important but unquantifiable factor. Complete crania are the fastest moving elements; individual cranial fragments are in the lag group. Omo fluviatile deposits show a preponderance of hominid lag elements, whereas Olduvai and East Rudolf perilacustrine deposits present a mixture of transportable and lag elements.

Archeological traces of early hominid activities, East of lake Rudolf, kenya.

Excavations have demonstrated that stone artifacts occur stratified within beds of Lower Pleistocene (or end Pliocene) age. At one site a low-density scatter of worked stone objects occurs together with small but significant quantities of broken-up bones. Potassium-argon dates indicate an age greater than 2 million years; thus, this may be the oldest known hominid occupation site. More than 20 hominid fossils have been recovered from various sedimentary formations in the area.

Geology and fauna of a new Pliocene locality in north-western Kenya.

Lothagam Hill reveals a succession of fossil bearing sediments that extend knowledge of the East African Pliocene back from the base of the Omo succession, to about 5.5 million years.