Quebrada Honda, Bolivia

Town of Quebrada Honda

The town of Quebrada Honda as it appeared in 2007.

The fossil site of Quebrada Honda is located in the far south of Bolivia, about 40 miles (60 km) southwest of the city of Tarija. It sits at an elevation of about 11,500 feet (3,500 m) in the Eastern Cordillera of the Andes, the mountains that form the eastern border the Altiplano. The fossil-preserving rocks at the site were deposited roughly 13-12 million years ago, during the latter half of the middle Miocene.

A wide variety of fossil animals have been discovered at Quebrada Honda, including more than 30 species of mammals and several types of reptiles and birds. Many of the mammal fossil specimens are very well preserved and provide a great deal of information about the anatomy of these species. In addition, the ancient soils (paleosols) at the site preserve a diversity of ichnofossils including traces of roots, small burrows, nesting chambers of bees and wasps, and brood balls of dung beetles. PhD candidate Angeline Catena is studying these fossils and the ancient soils in which they were preserved in order to gain a better understanding of the site’s ancient climate. Our team is also analyzing various isotopes and studying the ecological requirements of the fauna to provide additional insights.

Quebrada Honda Outcrops

Exposures of the fossil-bearing beds of the Honda Group exposed near the town of Quebrada Honda.

Quebrada Honda is a very important paleontological site for several reasons. For one, it documents a time interval that is poorly represented in South America’s fossil record. It is one of only a handful of sites of its age and one of only two where the remains of many species have been identified. The other well-known site of this age, La Venta, is located in the extreme north of the continent (Colombia), and nearly all the mammal species that have been discovered there are different from those at Quebrada Honda. Thus, both of these sites provide unique information about the mammals and other animals that were living in South America in the late middle Miocene.

A primary question our team is trying to answer is why the mammal faunas of these two sites are so distinct. One possible explanation is that some geographic barrier prevented the exchange of animals between the two areas. A large wetland covered much of the South American tropics (Neotropics) at the time, and this could have resulted in dramatically different mammal faunas in the northern and central parts of the continent. Another possible explanation is that the two sites harbored different species because they had very different climates and habitats.

Vicuñas

Vicuñas (wild relatives of llamas and alpacas) feeding in the low brush typical of high elevation habitats in Bolivia.

Yet another reason we are so interested in the ancient environment of Quebrada Honda is because it can provide insights about its paleoelevation: how high it was when its fossils were deposited. The Andes are a relatively young mountain chain, and plant fossils and other data indicate that most of the area’s uplift occurred within the past 20 million years. (It was at sea level when the dinosaurs went extinct 66 million years ago). Determining precisely when and how this uplift occurred – whether it occurred gradually or in “spurts” – is vital for creating accurate computer models of past and future climate. Recent isotopic data from Quebrada Honda suggest that it sat at a higher elevation during the middle Miocene than Denver, Colorado does today (at least 6,500 feet or 2 km), perhaps much higher (nearly 10,000 feet or 3 km). However, our team’s discovery of giant tortoise fossils and fossils of an aquatic turtle there suggest it was likely much lower, less than one-third that high (3, 200 feet or 1,000 m). The many types of analyses our team is undertaking will allow us to test and refine this paleoelevation estimate.

Representative specimens:

The lower jaw of the tiny rodent Acarechimys, preserving both incisors (left) and several cheek teeth.

The lower jaw of the tiny rodent Acarechimys, preserving both incisors (left) and several cheek teeth (still covered by sediment).

Macraucheniid bones

Articulated limb bones of a macraucheniid litoptern, an extinct type of hoofed mammal that had llama-like proportions.

Glyptodont Shell

Partial shell (carapace) of a glyptodont, an extinct tortoise-like relative of modern armadillos.

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