Paleontological Expeditions

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Southern Bolivia, May 2007

In May of 2007 I teamed up with a group from the University of Rochester and the University of Florida to visit a couple fossil mammal sites in southern Bolivia: the 16-15 million year old locality of Cerdas and the middle Miocene (Laventan) locality of Quebrada Honda. The Rochester group was primarily interested in studying the geology and taking samples of rocks, bones, and teeth for isotopic analyses. I and our Bolivian collaborators were primarily interested in finding and identifying fossils. It made for a great combination since we were able to divide up some of the costs of the trip, and we were able to help each other achieve our respective goals. On May 5th we arrived at the airport in La Paz; at more than 13,000 feet elevation, it is the highest international airport in the world. We were picked up by our drivers in our two rental vehicles, and then headed for Potosí, which is pretty much as the same elevation.

Potosí is the capital of its department, which is more or less equivalent to a state in the U.S. It is also home to the Universidad Autónoma Tomás Frías, the institution of our primary collaborator, Federico Anaya. Potosí has a long history, in large part thanks to the hill pictured to the right, Cerro Rico (“Rich Hill”). This mountain earned its name from the vast quantity of silver that was mined from it in the town’s early history, tens of thousands of tons. It is still being mined today, primary for tin. Potosí is one of the highest cities in the world, situated at an altitude of just over 13,400 ft.	Cerro Rico, near Potosí.
Because Potosí is a major city, it is the best place around to get supplies. We visited the main market to buy food and other supplies, picked up collecting gear and other equipment at the university, and then loaded everything into (and onto) our vehicles. Because the roads are so rough, securing things adequately to the top of a vehicle is critical. As illustrated here, it usually is at least a two-person job.	Loading the truck with gear in Potosí.
From Potosí we traveled southwest toward Uyuni, a much smaller town that sits near the shores of a giant “salar” (salt lake) of the same name. The Salar de Uyuni is the largest salt flat in the world and is a popular tourist attraction, which helps to support the Uyuni economy. We weren’t there for tourism, of course, but rather because it was a convenient place to spend the night on our way to the field. This photo was taken when we arrived in Uyuni, right about sunset.	A view at sunset in Uyuni.
We took a detour on our way to Cerdas to investigate some rock outcrops near the small town of Cerillos. As you might image, we quickly became the center of attention, especially among the children; it isn’t often that two trucks filled mostly with light-skinned visitors stops to spend the night in a small, isolated town. Being the center of attention have an upside; it usually gives us a good opportunity to take some photos of cute local kids.	Local children in Cerillos.
Potosí, Uyuni, Cerillos, and even the capital of Bolivia, La Paz, are located on a high plateau in the middle of the Andes Mountains known as the Altiplano. This plateau averages about 13,000 feet elevation. La Paz mostly lies in a valley, so it is a bit lower than this, but all the other cities are higher than this baseline, making them about two and a half times as high as Denver (a mere 5,280 feet), and a good 3,000 feet higher than the highest city in the U.S. (Leadville, Colorado). The lack of oxygen at this altitude can cause headaches and other symptoms among visitors until they are acclimated, as illustrated by Dave Auerbach, then a graduate student at the U. of Rochester.	Altitude sickness is no fun.
Pictured to the right is the view we had of the badlands of Cerdas when we arrived. The badlands in the distance are the remnants of vast layers of rocks that have mostly been washed away by the action of water. This water cut down into the Altiplano, so in this view, we are mostly above them. We ended up driving down in the valley and camping there so that we would be closer to the exposures. As a matter of principle, it also usually is better to camp at the base of outcrops rather than above them so that you’re walking downhill at the end of the day rather than up.	Outcrops near Cerdas.
Cerdas isn’t the richest locality I’ve worked, but it does produce some nice fossils. This is one such fossil, the bony part of a sloth claw. The size of the claw can be gauged by the hand holding it, though in life it would have been covered with a fingernail-like sheath, making it a good bit longer. We found this specimen in two parts, illustrating why it is always important look around when you find a partial specimen with what looks to be a fresh break. Often the other piece can be found directly upslope or downslope.	Claw from the hand of a medium-sized sloth.
Sometimes specimens require a bit more work than just picking them up off the ground. Here Bruce is excavating a partial skull of a mesotheriid notoungulate. The first step is trenching around the specimen so that it is left sitting on a pedestal. The specimen can then be undercut a bit and covered with protecting padding and then a plaster jacket. Once the plaster has dried, the base can be can away and the specimen can be flipped over so the other side can be jacketed. This allows its safe transport back to the lab for preparation.	Bruce MacFadden excavates a specimen.
We mostly bring our food with us, but Federico likes to hunt occasionally, and this can provide us with some fresh ingredients. The usually quarry is viscacha (Lagidium viscacia), a rabbit-like relative of the guinea pig that lives among the rocks at high altitudes in the Andes. To the right, Roger Chávez is showing off the day’s catch, which was subsequently cooked up for a surprisingly tasty dinner.	Fresh field food.
Not all of the fossils we find are beautiful. Some are isolated teeth or bones that may not look like much, but that can still be identified to the level of family or even more precisely. Others are mere scraps of bone or teeth that can’t be identified to anything other than “mammal.” All of these are important in different ways, however. For instance, specimens that can’t be precisely identified often can be used for isotopic (chemical) analyses. Pictured here are a diversity of more scrappy specimens from both small and large mammals.	Typical scrappy (but useful) specimens.
On the other hand, sometimes we find something really nice. This is a partial lower jaw (mandible) of a small notoungulate just as we found it in the field. It is missing some of the teeth in the front, but has nearly all of the cheek teeth (grinding teeth), which can be very useful for precise identification. We don’t yet know whether this represents a new species or not, and are studying this and other specimens in detail to determine that. A preliminary description and other photos were included in our 2009 overview paper on Cerdas.	Nice lower jaw from a small notoungulate.
After spending time at Cerdas, we headed for another locality, Quebrada Honda. The first town we passed through after leaving Cerdas was Atocha, and we stopped briefly at the cemetery on the outskirts of town to take a few pictures. As you clearly can see from the photo, the cemeteries in this part of the world are nothing like those in most of the U.S. They are colorful, elaborately decorated, and really convey more a feeling of celebration than of grief. They are welcome visual oases against the stark background of the high desert.	The cemetary at Atocha.
Beauty in southern Bolivia doesn’t come only from man-made structures, of course. For example, the valleys near the town of Tupiza have a mixture of large, green and white cacti and small shrubs that grow against a massive backdrop of eroded, bright red sediments. The picture doesn’t quite do it justice, but it makes for very impressive scenery.	Picturesque formations in valley near Tupiza.
Just like at Cerdas (and at many other sites), fossils at Quebrada Honda mostly occur in badlands: series of rounded hills formed by the erosion of rocks by water. Finding fossils in these types of exposures requires carefully examining all of the surfaces for pieces of tooth and bone. Sometimes a fossil is completely exposed and is just sitting on the surface waiting to be picked up. Other times, only a small piece of the fossil is exposed, and the rest must be excavated. Usually fossils that are partly buried are in better condition because they are somewhat protected form the elements, but this isn’t always the case.	Prospecting the badlands at Quebrada Honda
This lower jaw belongs to one of the more common animals at Quebrada Honda, a type of hegetotheriid notoungulate known as Hemihegetotherium trilobus. It is a species that is unique to Quebrada Honda, and it was described and named by Federico and me back in 2006 based on specimens we studied at the museum in La Paz. The part of the name “trilobus” refers to the fact that its last lower tooth has three lobes, a characteristic that distinguishes it from its closest relatives, which only have two.	A nice partial mandible of Hemihegtotherium.