Prehistoric Guinea Pigs from Egypt

A study recently published by the Proceedings of the National Academy of Sciences describes how modern day representatives of the Phiomorpha and Caviomorpha groups diverged approximately 37 million years ago.

The phylogeny detailed in the article was derived through combination of biogeographical, genetic and fossil evidence, and serves to demonstrate that the Caviomorpha, a group that includes modern-day guinea pigs, separated from the Phiomorpha during the early Eocene epoch between 34 and 40 million years ago.

Prior to divergence, both groups were bound by the rodent infraorder Hystricognathi and were restricted to Afro-Arabia. In sync with the rise of modern mammals during the Eocene, members of the Cavimorpha parted ways with the Phiomorpha and emmigrated to South America, possibly by rafting or other chance dispersal event. The Phiomorpha remained behind in Afro-Arabia where they radiated into a variety of genera, including the extant genus Thryonomys – commonly known as cane rats.

Key to the study’s finding was morphological examination of fossil assemblages excavated from the Fayum Depression of northeast Egypt. The mandibular and maxillary fossils recovered from the site revealed a mixture of both primitive and derived features. This fossil data was amalgamated with independently calculated genetic estimates to narrow the timing for the early Eocene divergence.


Sallam, H., Seiffert, E., Steiper, M., & Simons, E. (2009). Fossil and molecular evidence constrain scenarios for the early evolutionary and biogeographic history of hystricognathous rodents Proceedings of the National Academy of Sciences, 106 (39), 16722-16727 DOI: 10.1073/pnas.0908702106

Human Evolution Hampered by History

In a earlier post (available HERE), the ability to track ancient Neanderthal geographical distributions and migration patterns through DNA sequencing was discussed in light of recent research by Fabre, Condemi & Degioanni; now, a new study published at PLoS Genetics examines the genome of modern humans in an attempt to gauge rates of selection and correlate geographic patterns over more recent time periods.

In the paper The Role of Geography in Human Adaptation, Graham Coop (et al.) moves beyond expressed phenotypes and investigates the traces of human adaptation found in the genomes of extant and geographically diverse populations. By analyzing nonsynonymous SNPs, the study found that signals expressed in the genome can be used to predict the patterns found within specific loci. Essentially, the patterns they identified demonstrated that closely related populations possessed fewer genetic differences than would be expected having been subject to differing ecological pressures over the past 100,000 years. These apparently resilient genetic patterns - they suggest - are indicative of a selection pressure that “has been strongly constrained by the historical relationships and gene flow between populations.”

(Image from Article)

From the Introduction:
“…Humans have spread out of Africa to colonize almost all of the world's land mass, and in the process have experienced a vast range of new climates, diets and ecosystems. Humans have also encountered new pathogens as they moved around the globe and moved into close proximity with domesticated animals, and as human population densities increased.
These changes in human ecology suggest that there has been ample scope for the action of natural selection in recent human evolution. Moreover, most species, including humans, probably face various additional selection pressures on a persistent basis: e.g., due to sexual competition, viability selection and resistance to evolving pathogens. Hence, it seems reasonable that our genomes would show evidence for recent selection…”

Evidence for natural selection is exactly what they find, however they also conclude that the power of selection on humans can be very weak and therefore easily influenced by historic patterns of migration and genetic drift.

The paper is well worth a look…

Coop, G., Pickrell, J., Novembre, J., Kudaravalli, S., Li, J., Absher, D., Myers, R., Cavalli-Sforza, L., Feldman, M., & Pritchard, J. (2009). The Role of Geography in Human Adaptation PLoS Genetics, 5 (6) DOI: 10.1371/journal.pgen.1000500

Cretaceous Multituberculata from Australia

Thomas H. Rich (et. al.), Curator of Vertebrate Paleontology at the Museum of Victoria in Melbourne, Australia, recently published a description of dentary fragments from a member of the Multituberculata in the Journal Acta Palaeolontologica Polonica.

Several mammalian families have previously been identified from the Aptian formation (where the current fossil was found), most of these are believed to represent species endemic to Australia; however one family – the Ornithorhynchidae – have also been found in Argentina. Ornithorhynchidae, a group of monotremes, have been used to provide evidence for mammalian dispersal between South America and Australia during the Mesozoic.

According to the authors, these prehistoric platypuses provide biogeographical clues because “[g]iven the relative geographic positions of Australia and South America during the Mesozoic, it is reasonable to expect that were it then possible to do so, at least one of these terrestrial mammals would have traversed the Antarctic landmasses, in one direction or the other…”


Abstract:
A dentary fragment containing a tiny left plagiaulacoid fourth lower premolar from the Early Cretaceous (Aptian) of Victoria provides the first evidence of the Multituberculata from Australia. This unique specimen represents a new genus and species, Corriebaatar marywaltersae, and is placed in a new family, Corriebaataridae. The Australian fossil, together with meagre records of multituberculates from South America, Africa, and Madagascar, reinforces the view that Multituberculata had a cosmopolitan distribution during the Mesozoic, with dispersal into eastern Gondwana probably occurring prior to enforcement of climatic barriers (indicated by marked differentiation in regional floras) in the Early Cretaceous.

Holotype of multituberculate mammal Corriebaatar marywaltersae gen. et sp. nov. from Flat Rocks, Wonthaggi Formation (Aptian), Australia (NMV P216655), a left dentary fragment with p4 and anterior root of m1 in labial (A), lingual (B), and occlusal (C) views. Artwork by P. Trusler.

THOMAS H. RICH,et al. (2009). An Australian multituberculate and its palaeobiogeographic implications Acta Palaeolontologica Polonica

The article is available as a PDF HERE.

Beck, R., Godthelp, H., Weisbecker, V., Archer, M., & Hand, S. (2008). Australia's Oldest Marsupial Fossils and their Biogeographical Implications PLoS ONE, 3 (3) DOI: 10.1371/journal.pone.0001858

The Rise of “Homo egocentricis”

Although it was literally a dark and stormy night, such weather conditions were but a novelty to the speaker – a scientist whom had spent the majority of his life scanning barren rocks and desiccated landscapes for fragments of fossil bone beneath the unrelenting and scorching sun of an East African desert. Yet, I can’t help but think that some level of instinctual fear naggingly tickled at his stomach as he approached the waiting crowd…

There was little doubt that villains - the arch enemies of reason and deniers of fact– concealed themselves among the many upstanding community members and university staff in attendance. This was, after all, Tallahassee, Florida. A city of the Southeastern Unite States, geographically located near the eastern extent of the so called “Bible belt.”

How would they react to being told that biological evolution is fact? Moreover, how would they respond to learning that Homo sapiens, despite an egocentric view of the world, have shared a common ancestry with other primates, and in fact, a common lineage with all life on Earth?

Actually, they responded remarkably well, much to the credit of Dr. Don Johanson.

By all accounts, the talk on Human Origins was a success. Dr. Johanson spoke with the confidence and familiarity that has made him a highly sought, world renowned lecturer and scientist.



He began the talk by discussing the development of his personal interest in anthropology as a child and quickly moved through a summary of the major fossil discoveries made during his lifetime - a true story of adventure and discovery. The lecture was given at an IMAX theater and included some fantastic images of hominid fossils and African landscapes; the presentation can be viewed in its entirety by going to the FSU Origins webpage HERE and clicking on the red-highlighted “Webcast” text to the right of Dr. Johanson’s photograph.

As a further suggestion, I’d recommend a quick look at a recent article by Kaye E. Reed of the Institute of Human Origins (which Don Johanson runs in Arizona) discussing the paleoecology of the Hadar hominin site in Ethiopia. The article discusses speciation and environmental transitions associated with Australopithecus afarensis.

Reed, K. (2008). Paleoecological patterns at the Hadar hominin site, Afar Regional State, Ethiopia Journal of Human Evolution, 54 (6), 743-768 DOI: 10.1016/j.jhevol.2007.08.013

Isotopes Used in Tracking Migration and Dispersal of Birds

During last week’s post discussing vertebrates as indicators of climate fluctuation (linked here) isotopes were described as a significant tool in reconstructing the evolutionary and ecological histories of organisms. Today, Megan J. Sellick, et al, published an article in PLoS One discussing the value of using hydrogen and strontium isotopes, taken from the feathers of tree swallows, to track migratory dispersion.

Tree Swallow (Tachycineta bicolor)

The research (linked here) revealed that stable hydrogen isotopes were indicative of the latitude of molting sites and strontium was linked to the longitude of geological features found in proximity to the area where feathers were grown. Taken together, modeling revealed that, “these isotopes have the potential to provide predictable and complementary markers for estimating long-distance animal movements.”






GRAPHIC: Geographic variation of (a) dD and (b) 87Sr/86Sr values in Tree Swallow feathers. Contour maps were produced by ordinary kriging and are based on mean values in primary flight feathers at 18 breeding sites (denoted by black circles).

Megan J. Sellick, T. Kurt Kyser, Michael B. Wunder, Don Chipley, D. Ryan Norris (2009). Geographic Variation of Strontium and Hydrogen Isotopes in Avian Tissue: Implications for Tracking Migration and Dispersal PLoS ONE, 4 (3) DOI: 10.1371/journal.pone.0004735