November 5, 2024
Reconstructing ancient Andean climate provides clues to climate change
An artistic rendering of Hemihegetotherium, an extinct variety of mammal and one of the more common types of fossilized animal remains found by researchers at the QHB site in southern Bolivia.Velizar Simeonovski
As Earth faces unprecedented climate change, a look into the planet’s deep past may provide vital insights into what may lie ahead. But knowledge of the natural world millions of years ago is fragmented.
A 15-year study of a site in Bolivia by a joint U.S.-Bolivia team has provided a comprehensive view of an ancient ecosystem when Earth was much warmer than it is today. The researchers’ findings were published online Nov. 1 by the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
A present-day view of the QHB site in southern Bolivia. New research shows this may have been at a lower elevation during a warm period 13 million years ago, which helps to better understand Earth’s climate history.Darin Croft/Case Western Reserve University
Located in the Andes Mountains of southern Bolivia, the site, known as the Quebrada Honda Basin — or QHB — was deposited 13 million years ago during the Miocene Epoch, when Earth’s climate was rebounding from a prior period of warming. Globally, temperatures were 3-4 degrees Celsius warmer than today, and mammal biodiversity was increasing markedly.
Today, the site is 11,500 feet above sea level. Back in the Miocene, the site was lower, but exactly how much was a matter of debate. Previous studies using geochemical methods estimated that the Miocene QHB was relatively high, close to 10,000 feet. But the team’s new findings, based on careful analysis of plant and animal fossils and other features at the site, favor an alternative theory: That the Miocene QHB was at a much lower elevation, likely less than 3,000 feet.
“Our new data indicates that this area was once covered by mosaic vegetation with a mix of trees, including palms, bamboos and other grasses,” said lead author Caroline Strömberg, a University of Washington professor of biology. “Although this vegetation lacks a good comparison in today’s South America, it was likely most similar to modern neotropical dry forest or wooded savanna growing at low elevation.”
A lower-elevation Miocene QHB site has potentially global consequences.
“When put together with previous work at QHB, our study — including looking at fossil soils, turtles and other ectothermic vertebrates, and mammal ecologies — suggests that the Central Andes still had not undergone substantial uplift by 12 million years ago,” said Strömberg. “This is important because it helps us understand when this major mountain chain formed. The rise of the Andes is thought to have contributed to making tropical South America the most biodiverse area on Earth.”
Understanding ecosystems of the past can help predict what might happen in the future due to human-related climate change.
“Sites like this one in Bolivia are essential for helping us calibrate climate models,” said co-author and project leader Darin Croft, professor of anatomy at Case Western Reserve University. “Our understanding of climate change is based on models, and those models are based on information from the past.”
Fossilized remains of a tortoise at the QHB site in southern Bolivia.Darin Croft/Case Western Reserve University
Between 2007 and 2017, Croft and co-author Frederico Anaya, a professor of geology at Universidad Autonóma Tomás Frías in Bolivia, led six international teams to the QHB to collect fossils. Despite its warmer, forested past, the site today is a high-altitude desert grassland.
During those trips, the team found many different types of fossils: bones and teeth of mammals and other vertebrates, microscopic plant remains, ancient soils, and tracks and traces of insects and other invertebrates. Analyzing these fossils contributed to the researchers’ conclusion that the Miocene QHB was at a lower elevation. For example, fossils from “cold-blooded” animals found at the site — a giant tortoise, a side-necked turtle and a very large snake — suggest the site’s elevation when these animals lived was less than 3,000 feet, based on modern-day distributions of closely related species.
Strömberg studied fossilized phytoliths from QHB. These are microscopic pieces of silica found in the cells and cell walls of plants, and the shapes of phytoliths differ depending on the type of plant they came from. She compared the fossilized phytoliths with those found in contemporary vegetation to identify the assortment of plants at the site during the Miocene.
Fossil jawbone fragment from a chinchillid, a type of rodent and one of the most common types of animal fossils found at the QHB site.Darin Croft/Case Western Reserve University
Layers of volcanic ash and magnetic signatures in rocks at QHB allowed the fossils to be accurately dated. The diversity of preserved material allowed the team to make detailed reconstructions of the plants and animals and their living conditions. The team named 13 new species of fossil mammals based on remains from the site, including marsupials, hoofed mammals, rodents and armadillos. Most of the species have not been found anywhere else in South America and have no modern descendants.
“Nature has a wide variety of body plans, often much greater than the limited variety we see today,” said co-author Russell Engelman, a Case Western Reserve University graduate student who worked on the mammal fossils.
Moving forward, Croft is hoping to study another Bolivian Miocene site of a similar age, but over a longer time period.
“We are getting into uncharted territory in terms of climate, and you have to go deeper in time to get conditions that are similar,” said Croft.
Other co-authors are Beverly Saylor, Case Western Reserve University professor of Earth, environmental and planetary sciences; Angeline Catena, geology professor at Diablo Valley Community College in California; and Daniel Hembree, professor of Earth and planetary sciences at the University of Tennessee. The research was funded by the National Science Foundation.
For more information, contact Strömberg at caestrom@uw.edu.
Adapted from a press release by Case Western Reserve University.
Tag(s): Caroline Strömberg • climate change • College of Arts & Sciences • Department of Biology • paleontology
