Daniel J. Peppe

Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications

• Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies. • Here we quantify leaf-climate correlations from 92 globally distributed, climatically diverse sites, and explore potential confounding factors. Multiple linear regression models for mean annual temperature (MAT) and mean annual precipitation (MAP) are developed and applied to nine well-studied fossil floras. • We find that leaves in cold climates typically have larger, more numerous teeth, and are more highly dissected. Leaf habit (deciduous vs evergreen), local water availability, and phylogenetic history all affect these relationships. Leaves in wet climates are larger and have fewer, smaller teeth. Our multivariate MAT and MAP models offer moderate improvements in precision over univariate approaches (± 4.0 vs 4.8°C for MAT) and strong improvements in accuracy. For example, our provisional MAT estimates for most North American fossil floras are considerably warmer and in better agreement with independent paleoclimate evidence. • Our study demonstrates that the inclusion of additional leaf traits that are functionally linked to climate improves paleoclimate reconstructions. This work also illustrates the need for better understanding of the impact of phylogeny and leaf habit on leaf-climate relationships.

The extinction of the dinosaurs

Non‐avian dinosaurs went extinct 66 million years ago, geologically coincident with the impact of a large bolide (comet or asteroid) during an interval of massive volcanic eruptions and changes in temperature and sea level. There has long been fervent debate about how these events affected dinosaurs. We review a wealth of new data accumulated over the past two decades, provide updated and novel analyses of long‐term dinosaur diversity trends during the latest Cretaceous, and discuss an emerging consensus on the extinctions tempo and causes. Little support exists for a global, long‐term decline across non‐avian dinosaur diversity prior to their extinction at the end of the Cretaceous. However, restructuring of latest Cretaceous dinosaur faunas in North America led to reduced diversity of large‐bodied herbivores, perhaps making communities more susceptible to cascading extinctions. The abruptness of the dinosaur extinction suggests a key role for the bolide impact, although the coarseness of the fossil record makes testing the effects of Deccan volcanism difficult.

The Pleistocene archaeology and environments of the Wasiriya Beds, Rusinga Island, Kenya.

Western Kenya is well known for abundant early Miocene hominoid fossils. However, the Wasiriya Beds of Rusinga Island, Kenya, preserve a Pleistocene sedimentary archive with radiocarbon age estimates of >33-45xa0ka that contains Middle Stone Age artifacts and abundant, well-preserved fossil fauna: a co-occurrence rare in eastern Africa, particularly in the region bounding Lake Victoria. Artifacts and fossils are associated with distal volcanic ash deposits that occur at multiple localities in the Wasiriya Beds, correlated on the basis of geochemical composition as determined by electron probe microanalysis. Sediment lithology and the fossil ungulates suggest a local fluvial system and associated riparian wooded habitat within a predominantly arid grassland setting that differs substantially from the modern environment, where local climate is strongly affected by moisture availability from Lake Victoria. In particular, the presence of oryx (Oryx gazella) and Grevys zebra (Equus grevyi) suggest a pre-Last Glacial Maximum expansion of arid grasslands, an environmental reconstruction further supported by the presence of several extinct specialized grazers (Pelorovis antiquus, Megalotragus sp., and a small alcelaphine) that are unknown from Holocene deposits in eastern Africa. The combination of artifacts, a rich fossil fauna, and volcaniclastic sediments makes the Wasiriya Beds a key site for examining the Lake Victoria basin, a biogeographically important area for understanding the diversification and dispersal of Homo sapiens from Africa, whose pre-Last Glacial Maximum history remains poorly understood.

Leaf economic traits from fossils support a weedy habit for early angiosperms

Many key aspects of early angiosperms are poorly known, including their ecophysiology and associated habitats. Evidence for fast-growing, weedy angiosperms comes from the Early Cretaceous Potomac Group, where angiosperm fossils, some of them putative herbs, are found in riparian depositional settings. However, inferences of growth rate from sedimentology and growth habit are somewhat indirect; also, the geographic extent of a weedy habit in early angiosperms is poorly constrained. Using a power law between petiole width and leaf mass, we estimated the leaf mass per area (LMA) of species from three Albian (110-105 Ma) fossil floras from North America (Winthrop Formation, Patapsco Formation of the Potomac Group, and the Aspen Shale). All LMAs for angiosperm species are low (<125 g/m(2); mean = 76 g/m(2)) but are high for gymnosperm species (>240 g/m(2); mean = 291 g/m(2)). On the basis of extant relationships between LMA and other leaf economic traits such as photosynthetic rate and leaf lifespan, we conclude that these Early Cretaceous landscapes were populated with weedy angiosperms with short-lived leaves (<12 mo). The unrivalled capacity for fast growth observed today in many angiosperms was in place by no later than the Albian and likely played an important role in their subsequent ecological success.

The Impact of the Geologic History and Paleoclimate on the Diversification of East African Cichlids

The cichlid fishes of the East African Great Lakes are the largest extant vertebrate radiation identified to date. These lakes and their surrounding waters support over 2,000 species of cichlid fish, many of which are descended from a single common ancestor within the past 10u2009Ma. The extraordinary East African cichlid diversity is intricately linked to the highly variable geologic and paleoclimatic history of this region. Greater than 10u2009Ma, the western arm of the East African rift system began to separate, thereby creating a series of rift basins that would come to contain several water bodies, including the extremely deep Lakes Tanganyika and Malawi. Uplifting associated with this rifting backponded many rivers and created the extremely large, but shallow Lake Victoria. Since their creation, the size, shape, and existence of these lakes have changed dramatically which has, in turn, significantly influenced the evolutionary history of the lakes cichlids. This paper reviews the geologic history and paleoclimate of the East African Great Lakes and the impact of these forces on the regions endemic cichlid flocks.

Quantification of large uncertainties in fossil leaf paleoaltimetry

[1]xa0Estimates of paleoelevation potentially constrain geodynamic models of continental deformation and inform interpretations of landscape and climate evolution. One widely used, paleobotanical approach reconstructs paleoelevation from the difference in estimated atmospheric enthalpy between a known sea level and a targeted, coeval, elevated fossil floral site. Enthalpy is estimated using Climate-Leaf Analysis Multivariate Program (CLAMP) on 31 leaf size and shape variables that have been calibrated in living forests. Errors related to CLAMP are significantly greater than often reported, and there are many sources of large potential error related to this method that are either difficult to quantify or unquantifiable and are thus not documented. Here, we quantify one significant bias, toward underestimation of leaf area in the CLAMP data set (∼50%), that affects all CLAMP climate estimates, including enthalpy. Crucially, errors in paleoelevation when the leaf size bias is included are in the range of ±2 km or more, at least 2 times the previous estimates, and exceeding the plausible paleoelevations of many fossil sites. Previously published paleoelevations derived from this technique are unlikely to be accurate either in magnitude or in estimated error.

Late Pleistocene artefacts and fauna from Rusinga and Mfangano islands, Lake Victoria, Kenya

Surveys and excavations in 2009–2011 recovered fossil and artefact assemblages from late Pleistocene sediments on Rusinga and Mfangano islands (Lake Victoria, Kenya). Radiometric age estimates suggest that the Rusinga material dates to between 100 and 33 kya, whereas that from Mfangano may date to ≥35 kya. The preservation of a large and diverse suite of vertebrate fossils is unusual for Pleistocene sites in the Lake Victoria region and the composition of the faunal assemblages from both islands strongly suggest an open, arid, grassland setting very different from that found in western Kenya today. Middle Stone Age (MSA) artefacts from Rusinga and possible Later Stone Age (LSA) or MSA/LSA assemblages from Mfangano are distinct from Lupemban MSA sites characteristic of the Lake Victoria region and instead share a number of typological and technological features with late Pleistocene sites from open grassland settings in the East African Rift System. This highlights the complex roles that shifting environments, as well as temporal change, may have played in the development of regional variation among Equatorial African artefact assemblages in the Pleistocene.

Roles of climate and functional traits in controlling toothed vs. untoothed leaf margins

PREMISE OF THE STUDYnLeaf-margin state (toothed vs. untoothed) forms the basis of several popular methods for reconstructing temperature. Some potential confounding factors have not been investigated with large data sets, limiting our understanding of the adaptive significance of leaf teeth and their reliability to reconstruct paleoclimate. Here we test the strength of correlations between leaf-margin state and deciduousness, leaf thickness, wood type (ring-porous vs. diffuse-porous), height within community, and several leaf economic variables.nnnMETHODSnWe assembled a trait database for 3549 species from six continents based on published and original data. The strength of associations between traits was quantified using correlational and principal axes approaches.nnnKEY RESULTSnToothed species, independent of temperature, are more likely to be deciduous and to have thin leaves, a high leaf nitrogen concentration, a low leaf mass per area, and ring-porous wood. Canopy trees display the highest sensitivity between leaf-margin state and temperature; subcanopy plants, especially herbs, are less sensitive.nnnCONCLUSIONSnOur data support hypotheses linking the adaptive significance of teeth to leaf thickness and deciduousness (in addition to temperature). Toothed species associate with the fast-return end of the leaf economic spectrum, providing another functional link to thin leaves and the deciduous habit. Accounting for these confounding factors should improve climate estimates from tooth-based methods.

Magnetostratigraphy of the Ludlow Member of the Fort Union Formation (Lower Paleocene) in the Williston Basin, North Dakota

To determine the geomagnetic polarity stratigraphy and the duration and age of the Ludlow Member of the Fort Union Formation (Lower Paleocene), we constructed a 325 m composite lithostratigraphic section of the Upper Cretaceous Hell Creek Formation and the Lower Paleocene Ludlow and Tongue River Members of the Fort Union Formation in the Little Missouri River valley of North Dakota, USA. We analyzed paleomagnetic samples from nine of the logged sections. The principal magnetic carrier in the Ludlow Member sediments is likely titanomaghemite, as indicated by predominantly irreversible thermomagnetic curves measured from sandstone, siltstone, and carbonaceous shale samples. The analyzed paleomagnetic samples document a series of polarity zones that can be correlated from C29n to C27r on the geomagnetic polarity time scale (GPTS). We infer that the magnetization of the samples is primary because the characteristic directions are consistent with those of the Paleocene of North America, and the reversal stratigraphy from this section corresponds to the GPTS with reasonable sediment accumulation rates. By extrapolating the measured sediment accumulation rate from the Cretaceous-Tertiary (K-T) boundary to the top of C28n and then to the top of the Ludlow Member, we estimate the duration of the member to range from 2.31 to 2.61 m.y. This is the fi rst estimate for the duration and age of the Ludlow Member, and it can be used as an important tool for interpreting rates of biotic recovery after the K-T extinction.

Stratigraphic interpretation of the Kulu Formation (Early Miocene, Rusinga Island, Kenya) and its implications for primate evolution.

Early Miocene fossils from Rusinga Island, Kenya, provide some of the best evidence for catarrhine evolution and diversification, and, together with more than eighty-five other mammalian species, form an important comparative reference for understanding faunal succession in East Africa. While there is consensus over the stratigraphic position of most of Rusingas volcaniclastic deposits, the lacustrine Kulu Formation has been placed in various parts of the geological sequence by different researchers. To resolve this discrepancy, we conducted detailed geological analyses which indicate that the Kulu Formation was formed in the Early Miocene during a period of volcanic inactivity and subsidence following the early, mainly explosive hyper-alkaline phase of the Kisingiri complex and prior to the final eruptions of nephelinitic lavas. The underlying Hiwegi and older formations were locally deformed and deeply eroded before sedimentation began in the Kulu basin, so that the Kulu sediments may be significantly younger than the 17.8 Ma Hiwegi Formation and not much older than the overlying Kiangata Agglomerata-Lunene Lava series, loosely dated to ca. 15 Ma. The overall similarities between Kulu and Hiwegi faunas imply long-term ecological stability in this region. Our stratigraphic interpretation suggests that the Kulu fauna is contemporaneous with faunas from West Turkana, implying that differences between these assemblages-particularly in the primate communities--reflect paleobiogeographic and/or paleocological differences. Finally, the position of the Kulu Formation restricts the time frame during which the substantial faunal turnover seen in the differences between the primate and mammalian communities of Rusinga and Maboko Islands could have occurred.