Research sheds light on ancient climates and reevaluates the timelines of the Andes Mountains’ uplift.
As the planet grapples with significant climate change, examining Earth’s distant past might offer essential clues about the future.
The understanding of the natural environment from millions of years ago is patchy, but a 15-year investigation at a site in Bolivia, conducted by an international team spearheaded by Case Western Reserve University, presents a detailed picture of an ancient ecosystem thriving during a time when the Earth’s temperatures were significantly warmer.
A summary of the team’s extensive findings has been published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
The research site, called the Quebrada Honda Basin (QHB) located in the Andes of southern Bolivia, dates back 13 million years to the Miocene Epoch. During this era, the Earth’s climate warmed up following a cooling period that preceded it, leading to a rise in global temperatures and an increase in mammalian biodiversity.
At that time, global temperatures were 3 to 4 degrees Celsius higher than today’s levels. Insights gained from ancient ecosystems are vital for forecasting future scenarios linked to human-induced climate change.
“Locations like this one in Bolivia are crucial for fine-tuning our climate models,” stated Darin Croft, a professor of anatomy at Case Western Reserve’s School of Medicine and the leader of the QHB team. “Our understanding of climate change relies on models, which in turn are informed by historical data. As we find ourselves in uncharted territory regarding climate, we need to look further back in time for comparable conditions.”
Situated at an elevation of 11,500 feet (3,500 meters), the QHB was lower when its fossils were formed, but the exact altitude has been a topic of contention. Earlier studies based on geochemical evidence suggested that the Miocene QHB was relatively high, nearing 10,000 feet (3,000 meters).
However, the recent publication indicates that it likely had warmer temperatures and a lower elevation, perhaps below 3,000 feet (1,000 meters), suggesting that the Andes uplift occurred more recently in geological history than previously believed.
The team uncovered fossils of various organisms: mammal bones and teeth, other vertebrates, microscopic plant remnants, ancient soils, and traces of insects and invertebrates. The presence of cold-blooded species such as a giant tortoise, a side-necked turtle, and a large snake implies that the elevation at that time was likely under 1,000 meters, based on the known geographical distribution of related modern species.
The QHB was determined to be a dry forest or wooded savanna, populated with palms and bamboos that thrive at lower elevations, distinctly different from any current ecosystem. Caroline Strömberg, biology professor at the University of Washington and the lead author, analyzed fossilized phytoliths—microscopic silica fragments from plant cell walls. By comparing these ancient phytoliths with those in today’s vegetation, she was able to determine the types of plants that once flourished at the site.
Layers of volcanic ash and magnetic signatures in rocks allowed for precise dating of the fossils. The variety of preserved materials enabled Croft’s team to create thorough reconstructions of the flora, fauna, and their habitats. The group identified 13 new species of fossil mammals based on the remains found, which included marsupials, hoofed mammals, rodents, and armadillos. Most of these species are unique to this region of South America and do not have any modern relatives.
“Nature exhibits a wide range of body forms, often far more diverse than what we observe today,” remarked Russell Engelman, a biology graduate student at Case Western Reserve who contributed to the study of mammal fossils.
Other contributors to the research include: Beverly Saylor, professor of earth, environmental, and planetary sciences at Case Western Reserve; Angeline Catena, geology professor at Diablo Valley Community College in Pleasant Hill, California; Daniel Hembree, professor of earth and planetary sciences at the University of Tennessee; and Federico Anaya, geology professor at Universidad Autonóma Tomás FrÃas in PotosÃ, Bolivia.
Between 2007 and 2017, Croft and Anaya overseen six international research teams at the QHB, funded primarily by the National Science Foundation (NSF). Even six years after the end of Croft’s second NSF grant, the research continues to yield valuable findings and publications.
“Field paleontology is a wise investment for the NSF, as the benefits greatly exceed the costs,” said Croft, who is currently pursuing funding to examine another Bolivian Miocene site of a similar age but over an extended time frame.
