Monday, April 1, 2013

Fossil Mammals of Panama

In recent years the efforts to know the fossil terrestrial vertebrates of Panama have been revitalized, in part thanks to the expansion of the canal and the efforts of Panama Canal Project-PIRE in collaboration with the Panama Canal Authority. Vegetation grows fast in the tropics, so good fossiliferous deposits are covered and basically lost within years, even months, of being exposed. The new cuts being made for the expansion of the canal offer a unique opportunity to further understand the geology and paleontology of the area.
Interest in the fossil vertebrates of Panama started when Robert H. Stewart, a geologist with the Panama Canal Company, alongside his assistant, started finding and collecting fossil vertebrate remains in the early 1960's. The fossils were being collected from sediments of the Cucaracha Formation exposed along the Gaillard Cut, one of the artificial valleys that was crucial to the making of the canal. Frank C. Whitmore Jr. (who sadly passes away a little more than a year ago) was then a paleontologist with the US Geological Survey (and expert on fossil mammals) and eventually got involved with the collecting and studying of the Panamanian fossil. He and Stewart published the results of their study in 1965 (Whitmore & Stewart, 1965). Prior to these discoveries, very little was known of the fossil vertebrate fauna of the Central American region, and these were actually the first Miocene fossils found between Honduras and Colombia (Whitmore & Stewart, 1965). Up to that point it was not known wether Central America had been separated from North or South America (some even said both) during the Cenozoic, and if so, for how long? So the discovery of Miocene terrestrial mammals in Panama was a big deal!
The Gaillard Cut and Centenario Bridge in the early morning.
One of the main results of Whitmore & Stewart's study was that the Miocene Panamanian fauna was of holarctic* affinities. That meant that at least through the early Miocene, Panama was connected to North America, even though its geographically much closer to northwestern South America**. The fauna studied by them consisted of turtles, crocodylians, horses, rhinos, oreodonts and protoceratids (which I mentioned in a previous post). The mammal assemblage of this fauna is very similar to coeval faunas in North America.
*a term used for the biogeographic region comprising the northern continents.
**we now know that they remained separated by a marine passageway known as the Central American Seaway until about 3 million years ago (Duque-Caro, 1990; Coates et al., 1992).
Another closer look at the Gaillard Cut. Here you can see sediments of the Cucaracha Formation with Centenario Bridge in the Background.
The fauna described by Whitmore & Stewart was eventually called the Gaillard Cut Local Fauna (Ferrusquía-Villafranca, 1978; Rich & Rich, 1983; MacFadden, 2006). However, the fossils that make up this fauna had not been described in detail. It wasn't until until Bruce MacFadden of the Florida Museum of Natural History took on the task of describing them, 40 years after they had been collected (MacFadden, 2006). As a result, the composition of the Gaillard Cut Local Fauna has changed due to new discoveries, and will most likely continue to do so in the upcoming years. So, stay tuned as I'll cover this subject on the next post.

*Access to this and all other paleontological localities along the canal brought to you thanks to the courtesy of the Panama Canal Authority (ACP).


Coates, A. G., J. B. C. Jackson, L. S. Collins, T. M. Cronin, H. J. Dowsett, L. M. Bybell, P. Jung, and J. A. Obando. 1992. Closure of the Isthmus of Panama: the near-shore marine record of Costa Rica and western Panama. GSA Bulletin 104:814-828.

Duque-Caro, H. 1990. Neogene stratigraphy, paleoceanography and paleobiogeography in northwestern South America and the evolution of the Panama Seaway. Plaeogeography, Palaeoclimatology, Palaeoecology 77:203-234.

Ferrusquía-Villafranca, I. 1978. Distribution of Cenozoic vertebrate faunas in middle America and the problems of migrations between North and South America. Instituto de Geología, Universidad Nacional Autónoma de México 101:193-329.

MacFadden, B. J. 2006. North American Miocene land mammals from Panama. Journal of Vertebrate Paleontology 26:720-734.

Rich, P. V., and T. H. Rich. 1983. The Central American dispersal route: biotic history and paleogeography; pp. 12-34 in D. H. Janzen (ed.), Costa Rican Natural History. University of Chicago Press, Chicago, Illinois.

Whitmore, Jr., F. C., and R. H. Stewart. 1965. Miocene mammals and Central American Seaways. Science 148:180-185.

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