Homo erectus and Middle Pleistocene hominins: Brain size, skull form, and species recognition
G. Philip Rightmire
Hominins that differ from Homo erectus, the Neanderthals, and recent humans are known from Middle Pleistocene localities across the Old World. The taxonomic status of these populations has been clouded by controversy. Perhaps the most critical problem has been an incomplete understanding of variation in skull form. Here, both H. erectus and later mid-Pleistocene hominins are the focus of an investigation aimed at clarifying the relationships among brain volume, basicranial dimensions, neurocranial shape, and certain facial characters. Brain size in H. erectus averages about 950 cm3, while in a series of Middle Pleistocene crania from Africa and Europe, volume is about 1230 cm3. If encephalization is the primary mechanism operating in the mid-Pleistocene, then diverse aspects of cranial form cannot all be treated as independent variables. Correlation is utilized to examine the associations among measurements for more than 30 H. erectus crania that are reasonably well preserved. A similar approach is used with the Middle Pleistocene sample. Patterns of covariation are compared in order to assess integration. Next, factor analysis is applied to the H. erectus specimens in an attempt to identify modules, tightly integrated traits that can evolve independently. Studies of the variation within H. erectus are followed by direct comparisons with the Middle Pleistocene population. Discriminant functions facilitate the description of intergroup differences. Traits that vary independently from brain volume include anterior frontal broadening, lateral expansion of the parietal vault, elevation of the lambda–inion chord, and rounding of the sagittal contour of the occipital. This finding helps to resolve the problem of species recognition. Neurocranial proportions as well as characters from the cranial base and face can be incorporated into a differential diagnosis for the mid-Pleistocene sample. Evidence presented here supports arguments for speciation in the Middle Pleistocene.
Representational bias in phytoliths from modern soils of central North
America: Implications for paleovegetation reconstructions
Ethan Hyland, , Selena Y. Smith, Nathan D. Sheldon
Understanding localized patterns and community compositions of
vegetation in an environment is critical to the reconstruction of
climatic and ecological conditions across all spatiotemporal scales.
One of the most accurate and useful ways to characterize vegetation,
and therefore to describe the climatic and ecological conditions of a
location, is through the plant fossil record. Phytoliths (plant silica
microfossils) are often preserved in the absence of other
paleobotanical data and are becoming more widely used for deep-time
vegetation reconstructions. Significant work has been done to
standardize the analytical methodology of phytolith extraction,
statistical analysis, and interpretation, but more detailed
investigations are needed to understand how well a given soil
assemblage represents the actual aboveground plant biomass for a given
We present results from paired soil phytolith assemblages and local
vegetation assemblages across the central United States, including
temperate forest, grassland, and rangeland/scrubland ecosystems.
Phytolith assemblages obtained via extractions from soil A-horizons
were compared to percent cover of species and plant biomass estimates
obtained via in situ field observations and aerial estimates of tree
cover to analyze differences in the relative abundance of forest/woody
vegetation vs. grasses. Soil phytolith assemblages from all sites
average a 29% bias toward the grass morphotypes as compared to actual
aboveground biomass observations, and comparisons to percent cover
yielded broadly comparable bias figures. Percent bias estimates do not
show significant correlations to most environmental factors
(temperature, precipitation, local elevation), however, an extremely
strong correlation (p < 0.001) was observed with soil order type. This
is likely due to the fact that soil order reflects both vegetation
type and chemical factors known to affect overall phytolith
assemblages; therefore, soil order is a proxy that aggregates several
sources of bias. As a result, we suggest further research into the
development of correction factors between phytolith sample assemblages
and their interpreted past counterpart ecosystems based on estimates
derived from modern analyses of each major soil order type. Such
background corrections are essential to the continued use of
phytoliths as a proxy for past vegetation and ecological
reconstructions of temperate ecosystems throughout the Phanerozoic
Just to make sure everyone will read at least “New Evolutionary Law” if they haven’t already..
Most of Leigh van Valen classics are available here
Late Pleistocene climate change and the global expansion of anatomically modern humans
Eriksson et al.
Published online before print September 17, 2012, doi: 10.1073/pnas.1209494109
The extent to which past climate change has dictated the pattern and timing of the out-of-Africa expansion by anatomically modern humans is currently unclear [Stewart JR, Stringer CB (2012) Science 335:1317–1321]. In particular, the incompleteness of the fossil record makes it difficult to quantify the effect of climate. Here, we take a different approach to this problem; rather than relying on the appearance of fossils or archaeological evidence to determine arrival times in different parts of the world, we use patterns of genetic variation in modern human populations to determine the plausibility of past demographic parameters. We develop a spatially explicit model of the expansion of anatomically modern humans and use climate reconstructions over the past 120 ky based on the Hadley Centre global climate model HadCM3 to quantify the possible effects of climate on human demography. The combinations of demographic parameters compatible with the current genetic makeup of worldwide populations indicate a clear effect of climate on past population densities. Our estimates of this effect, based on population genetics, capture the observed relationship between current climate and population density in modern hunter–gatherers worldwide, providing supporting evidence for the realism of our approach. Furthermore, although we did not use any archaeological and anthropological data to inform the model, the arrival times in different continents predicted by our model are also broadly consistent with the fossil and archaeological records. Our framework provides the most accurate spatiotemporal reconstruction of human demographic history available at present and will allow for a greater integration of genetic and archaeological evidence.
The Tibetan Plateau is the youngest and highest plateau on Earth, and its elevation reaches one-third of the height of the troposphere, with profound dynamic and thermal effects on atmospheric circulation and climate. The uplift of the Tibetan Plateau was an important factor of global climate change during the late Cenozoic and strongly influenced the development of the Asian monsoon system. However, there have been heated debates about the history and process of Tibetan Plateau uplift, especially the paleo-altimetry in different geological ages. Here we report a well-preserved skeleton of a 4.6 million-y-old three-toed horse (Hipparion zandaense) from the Zanda Basin, southwestern Tibet. Morphological features indicate that H. zandaense was a cursorial horse that lived in alpine steppe habitats. Because this open landscape would be situated above the timberline on the steep southern margin of the Tibetan Plateau, the elevation of the Zanda Basin at 4.6 Ma was estimated to be ∼4,000 m above sea level using an adjustment to the paleo-temperature in the middle Pliocene, as well as comparison with modern vegetation vertical zones. Thus, we conclude that the southwestern Tibetan Plateau achieved the present-day elevation in the mid-Pliocene.