Category Archives: News

Late Pleistocene climate change and the global expansion of anatomically modern humans

Late Pleistocene climate change and the global expansion of anatomically modern humans
Eriksson et al.
PNAS
Published online before print September 17, 2012, doi: 10.1073/pnas.1209494109

Abstract

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.

Full-text:

http://www.pnas.org/content/early/2012/09/10/1209494109.abstract.html?etoc

Clade Age and Species Richness in Eukaryotic Tree of Life 

No fossil record included in this study (it is discussed briefly) but interesting paper in any case.

- Laura

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Clade Age and Species Richness Are Decoupled Across the Eukaryotic Tree of
Life

Daniel L. Rabosky, Graham J. Slater, Michael E. Alfaro

Abstract  
Explaining the dramatic variation in species richness across the tree of
life remains a key challenge in evolutionary biology. At the largest
phylogenetic scales, the extreme heterogeneity in species richness observed
among different groups of organisms is almost certainly a function of many
complex and interdependent factors. However, the most fundamental
expectation in macroevolutionary studies is simply that species richness in
extant clades should be correlated with clade age: all things being equal,
older clades will have had more time for diversity to accumulate than
younger clades. Here, we test the relationship between stem clade age and
species richness across 1,397 major clades of multicellular eukaryotes that
collectively account for more than 1.2 million described species. We find no
evidence that clade age predicts species richness at this scale. We
demonstrate that this decoupling of age and richness is unlikely to result
from variation in net diversification rates among clades. At the largest
phylogenetic scales, contemporary patterns of species richness are
inconsistent with unbounded diversity increase through time. These results
imply that a fundamentally different interpretative paradigm may be needed
in the study of phylogenetic diversity patterns in many groups of organisms.

http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001381

Carbonemys cofrinii

This is what happens when you don’t subscribe to Journal of Systematic Paleontology and you don’t check in with twitter!

“New pelomedusoid turtles from the late Palaeocene Cerrejon Formation of Colombia and their implications for phylogeny and body size evolution”

Authors: Edwin Cadena, Dan Ksepka, North Carolina State University; Carlos Jaramillo, Smithsonian Tropical Research Institute, Panama; Jonathan Bloch, Florida Museum of Natural History

Published: In the Journal of Systematic Palaeontology

http://www.tandfonline.com/doi/abs/10.1080/14772019.2011.569031
http://news.ncsu.edu/releases/cadena-turtle/

Jackie

Did Neandertals Paint Early Cave Art?

U-Series Dating of Paleolithic Art in 11 Caves in Spain

Paleolithic cave art is an exceptional archive of early human symbolic behavior, but because obtaining reliable dates has been difficult, its chronology is still poorly understood after more than a century of study. We present uranium-series disequilibrium dates of calcite deposits overlying or underlying art found in 11 caves, including the United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage sites of Altamira, El Castillo, and Tito Bustillo, Spain. The results demonstrate that the tradition of decorating caves extends back at least to the Early Aurignacian period, with minimum ages of 40.8 thousand years for a red disk, 37.3 thousand years for a hand stencil, and 35.6 thousand years for a claviform-like symbol. These minimum ages reveal either that cave art was a part of the cultural repertoire of the first anatomically modern humans in Europe or that perhaps Neandertals also engaged in painting caves.

http://news.sciencemag.org/sciencenow/2012/06/did-neandertals-paint-early-cave.html

http://www.sciencemag.org/content/336/6087/1409

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Laura

How to weigh dinosaurs (and mammals) with lasers

Minimum convex hull mass estimations of complete mounted skeletons

Body mass is a critical parameter used to constrain biomechanical and physiological traits of organisms. Volumetric methods are becoming more common as techniques for estimating the body masses of fossil vertebrates. However, they are often accused of excessive subjective input when estimating the thickness of missing soft tissue. Here, we demonstrate an alternative approach where a minimum convex hull is derived mathematically from the point cloud generated by laser-scanning mounted skeletons. This has the advantage of requiring minimal user intervention and is thus more objective and far quicker. We test this method on 14 relatively large-bodied mammalian skeletons and demonstrate that it consistently underestimates body mass by 21 per cent with minimal scatter around the regression line. We therefore suggest that it is a robust method of estimating body mass where a mounted skeletal reconstruction is available and demonstrate its usage to predict the body mass of one of the largest, relatively complete sauropod dinosaurs: Giraffatitan brancai (previously Brachiosaurus) as 23200 kg.

http://rsbl.royalsocietypublishing.org/content/early/2012/06/04/rsbl.2012.0263.abstract

More on the subject:

http://blogs.discovermagazine.com/notrocketscience/2012/06/05/weigh-dinosaur-with-lasers/

And of course the ‘sensational reporting’:

http://www.huffingtonpost.co.uk/2012/06/05/dinosaurs-lighter-than-previously-thought_n_1570073.html

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Laura

Eocene primate from Myanmar and the initial anthropoid colonization of Africa

Late Middle Eocene primate from Myanmar and the initial anthropoid colonization of Africa

Reconstructing the origin and early evolutionary history of anthropoid primates (monkeys, apes, and humans) is a current focus of paleoprimatology. Although earlier hypotheses frequently supported an African origin for anthropoids, recent discoveries of older and phylogenetically more basal fossils in China and Myanmar indicate that the group originated in Asia. Given the Oligocene-Recent history of African anthropoids, the colonization of Africa by early anthropoids hailing from Asia was a decisive event in primate evolution. However, the fossil record has so far failed to constrain the nature and timing of this pivotal event. Here we describe a fossil primate from the late middle Eocene Pondaung Formation of Myanmar, Afrasia djijidae gen. et sp. nov., that is remarkably similar to, yet dentally more primitive than, the roughly contemporaneous North African anthropoid Afrotarsius. Phylogenetic analysis suggests that Afrasia and Afrotarsius are sister taxa within a basal anthropoid clade designated as the infraorder Eosimiiformes. Current knowledge of eosimiiform relationships and their distribution through space and time suggests that members of this clade dispersed from Asia to Africa sometime during the middle Eocene, shortly before their first appearance in the African fossil record. Crown anthropoids and their nearest fossil relatives do not appear to be specially related to Afrotarsius, suggesting one or more additional episodes of dispersal from Asia to Africa. Hystricognathous rodents, anthracotheres, and possibly other Asian mammal groups seem to have colonized Africa at roughly the same time or shortly after anthropoids gained their first toehold there.

http://www.pnas.org/content/early/2012/05/29/1200644109.abstract

http://www.livescience.com/20738-primate-fossil-origins-asia.html

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Laura