Examining coevolution in Argentinean fossils

If you are having trouble deciding between two major fields of study, don't fret... you can always go into paleontology, where you can study multiple fields! For the last four years, my advisor, Caroline Strömberg, and I along with several collaborators from the US and Argentina have been working at a famous fossil site known as Gran Barranca, located in Chubut Province, Argentina. The project is multidisciplinary in approach, involving geology, geochemistry, paleobotany and vertebrate paleontology. Our goal was to test hypotheses about early grassland origins and the potential co-evolution of mammalian herbivores between 43 and 18 million years ago. Gran Barranca is well known for its vertebrate fossil record and it has been studied for over 100 years by renowned paleontologists such as the Ameghino brothers and G.G. Simpson. Gran Barranca is a paleontologist's dream as it preserves a long, nearly continuous fossil record of diverse South American biotas including vertebrate remains, insect trace fossils, soils and exquisitely preserved phytoliths (plant silica) all within deposits of volcanic ash that can be dated with great precision.

Here are two very recent publications describing some of our findings. In one paper, we present a new chronology for Gran Barranca using U/Pb radio isotopic dating techniques, and in the second paper we describe the ancient vegetation of Gran Barranca from phytoliths. One of our major findings is that "grazer" tooth forms seem to have evolved in Patagonia in the absence of grasslands. This idea overturns assumptions that many paleontologists have made for years about South American vegetation during this time period. Instead, it appears that grasslands are much more recent than previously presumed, in fact, we are still on the hunt for them. We are exploring other geographic areas and younger rock outcrops to answer this question. Stay tuned...

Strömberg CAE, Dunn RE, Madden RH, Kohn MJ, Carlini AA. (2013) Decoupling the spread of grasslands from the evolution of grazer-type herbivores in South America. Nature Communications 4:1478. doi:10.1038/ncomms2508 (UW Today article)

Dunn RE, Madden RH, Kohn MJ, Schmitz MD, Strömberg CAE, Carlini4 AA, Ré GH, Crowley J. (2013) A new chronology for middle Eocene–early Miocene South American Land Mammal Ages. GSA Bulletin 125(3-4):539-555.

-- Regan Dunn

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