After Darwin at AMNH: John Flynn
Friday, November 20
Fossil Hunting Among Volcanoes With Paleontologist John Flynn
This year, scientists at the American Museum of Natural History are celebrating the 200th anniversary of Charles Darwin’s birth and the 1859 publication of On the Origin of Species with a collection of vignettes describing expeditions and ideas with links to Darwin’s seminal work.
It was during a siesta in the woods that Charles Darwin, exploring the Chilean coast more than three years into his voyage on the H.M.S. Beagle, was shaken by one of the strongest earthquakes known to the local inhabitants. On that February day in 1835, Darwin not only witnessed “the most awful spectacle I ever beheld… [with] not one house left habitable,” as he wrote to his sister Caroline, but he also had an epiphany:
The most remarkable effect of this earthquake was the permanent elevation of the land… [which revealed] mussel-shells still adhering to the rocks, ten feet above high-water mark.… At Valparaiso… similar shells are found at the height of 1,300 feet: it is hardly possible to doubt that this great elevation has been effected by successive small uprisings.
Chilecebus, a reconstruction of which is shown above, is one of the fossils that John Flynn and colleagues have uncovered in the Chilean Andes (Illustration by Velizar Simeonovski, courtesy of John J. Flynn)
While sailing across the Atlantic and past Tierra del Fuego, Darwin had been reading Charles Lyell’s Principles of Geology, in which Lyell laid out the case that massive geological change is based on the slow accumulation of minute changes over time. It was through this lens that Darwin observed the volatile, shifting landscapes that partly informed his theory of evolution.
We now know that the active geology of Chile—the earthquakes, volcanoes, and formation of the Andes Mountains themselves—is caused by the squeezing of the Pacific Ocean plate under South America and back into the Earth’s interior. Paleontologist John Flynn and colleagues André Wyss, Reynaldo Charrier, and Darin Croft have traversed this geology over the last 20 years to learn more about both the history of the Andes and the unusual extinct fauna that lived on this former island continent. Mountain uplift drives fossil beds to the surface, weathering exposes fossil teeth and bone, and volcanic debris dates their time frames.
“We were first drawn to Chile because amateur naturalists found whale bones at 6,000 feet in the 1980s,” says Flynn. “Since then, we’ve uncovered a remarkable mammalian menagerie that explains some of the diversity seen today and also helps us understand more of the uplift history of this 5,000-mile-long mountain chain that forms a spine along then entire western edge of South America.”
Flynn and collaborators began surveying on the slopes of the Río Tinguiririca of central Chile in 1988. One of their first discoveries was a mammal fossil the size of a horse—a specimen too anatomically advanced to have lived during the late Mesozoic, the ancient era to which most geologists had dated the Andes Mountains. New discoveries changed the prevailing thought over the last two decades, and the high range of the Andes is now considered to be about a third that of previously accepted age. “The Andes are vastly younger than we had thought,” says Flynn.
Subsequent expeditions to high-elevation Chile exposed evidence of the oldest-known grassland environment and an array of new mammals from a single time interval, including more than 25 species new to science. Unique South American mammals include unusual hopping or burrowing marsupials (some even had massive cat-like canines), armadillo relatives with solid armor “shells,” and massive ground-dwelling sloths.
Another significant find by Flynn and colleagues is one of the oldest, best-preserved, and well-dated skulls of a fossil primate from the New World, 20-million-year-old Chilecebus. Because Chilecebus has a small brain size, the team recently argued that the larger brain size seen in all living anthropoid primates today must have arisen twice—in both the New and Old Worlds. But Chilecebus is also linked to Darwin’s travels: the fossil was discovered further up the Río Cachapoal valley, which he had explored a month after the earthquake. That March, he wrote:
Daily it is forced home on the mind of the geologist, that nothing, not even the wind that blows, is so unstable as the level of the crust of this earth.
The work of Flynn and his colleagues has benefitted from long-term partnerships between major Chilean and U.S. institutions (Museo Nacional de Historia Natural, Universidad de Chile, Consejo Nacional de Monumentos Naturales, American Museum of Natural History, University of California-Santa Barbara, Case Western Reserve University, and The Field Museum), and funding from the U.S. National Science Foundation, FONDECYT Chile, National Geographic, and other supporters.
When the HMS Beagle sailed from England just after Christmas of 1831, Darwin was on board as the ship’s naturalist and geologist. Over the next five years, he made scientific observations and collections in Cape Verde, tropical Brazil, Tierra del Fuego, the pampas of Argentina, Andean Chile, marsupial-dominated Australia, Mauritius, the tip of Africa, and, of course, the Galápagos Islands that so influenced his thinking about evolution.
Darwin’s observations on this voyage must have been central in his thoughts as he walked the sand path around a thicket in Kent, where he spent the next decades crafting On the Origin of Species by Means of Natural Selection, the foundation of evolutionary biology.
The After Darwin at AMNH series explores links between the scientific research work being done at AMNH today and Darwin’s influential work.
