Though South America is often overlooked in many areas, its fossil record commands a great deal of interest from paleontology experts and enthusiasts alike: The continent's dinosaurs include some of the oldest, largest, and weirdest known to science (see Eoraptor, Dreadnoughtus, and Carnotaurus, respectively). Numerous well-preserved pterosaur fossils continue to emerge from the Santana Formation in Brazil. A giant ground sloth skeleton excavated near Buenos Aires in 1788 became one of the first world-famous natural history exhibits. And during the nineteenth century, more of South America’s Ice Age beasts found their way into the Natural History Museum in London, collected by a young Charles Darwin during his voyage aboard the HMS Beagle.
South America’s fossil record also includes 300-million-year old sea scorpions, a snake that dwarfs the modern anaconda, and a diverse cast of giant birds, both airborne and flightless.
While the bulk of these riches come from Argentina and Brazil, Chile’s fossils — especially those announced within the past five years — stand out among this prehistoric treasure trove. The country's contributions to paleontology include an oddball dinosaur of its own, multiple ancient marine graveyards, and vital relics from both native and invasive mammalian herbivores.
Aysén and Magallanes, 150-145 million BCE (“before the common era”; same dating as “BC”)
The herbivorous, ten-foot long Chilesaurus was first discovered by seven-year old Diego Suárez in 2004 and not revealed to the public until April of 2015. Paleontologists placed it near trunk of the Tetanurae ("stiff tales"), a vast family that includes the majority of Jurassic and Cretaceous theropods. Initially, however, certain aspects of the creature’s anatomy made its identity a puzzle for paleontologists.
“Some of the bones look like they belong to an early theropod, others like they belong to a group of weird plant-eating theropods called therizinosauroids and yet others look like they belong to a completely different dinosaur group, the prosauropods", said Paul Barrett of the Natural History Museum in London. "A truly odd mix." Other paleontologists, along with mainstream news courses, likened it to the platypus for its strange combination of features, including its unusually short muzzle and clawless third finger.
Most of South America's standout dinosaurs lived during the Triassic (250-200 million BCE) or the Cretaceous (145-66 million BCE). Though not unknown, dinosaurs from the Jurassic — the period between the two — are rarer and generally receive less attention. Chilesaurus bucked this trend, since it lived towards the end of the Jurassic and was the most abundant animal at its site of excavation, the Toqui Formation in Aysén.
A year earlier, paleontologists announced an equally surprising discovery from Chile: At Torres del Paine National Park in Magallanes, the gradually melting Tyndall Glacier had surrendered a frozen hoard of fossilized ammonites, bivalves, and marine plants, as well with the skeletons of nearly fifty ichthyosaurs. Ranging from unborn juveniles to sixteen-foot long adults, all of these dolphin-like reptiles died around the same time as Chilesaurus and have tentatively been classified as the ophthalmosaurs — a late branch of big-eyed, deep-dwelling ichthyosaurs.
The German and Chilean paleontologists who first exhumed these organisms attribute their demise to a series of underwater mudslides: As the ichthyosaurs congregated in undersea canyons to hunt ammonites, avalanches of sediment would have instantly drowned and buried everything in their path. Volcanism or the gradual splitting of South America from Africa around this time may have triggered these fatal mudflows.
Native American Grazers
Maule, 33-31.5 million BCE
Throughout the Cretaceous, South America and Africa grew further apart, separating for good around 100 million years ago. Modern southern Chile, however, wouldn't divorce itself from western Antarctica completely for another 75 million years.
In place of cattle, deer, or any of the large grass-guzzling mammals familiar to us today, the stocky notoungulates and long-legged litopterns mowed the continent. Protein fragments of these groups' most recent members indicate that they were distant cousins to the perissodactyls, the order of odd-toed herbivores that includes horses, tapirs, and rhinos.
One of the earliest places these herbivores are in evidence is the Tinguiririca River Valley, close to the Argentine border. Excavated since 1988, its fossils date to the early Oligocene Epoch and document a palpable turnover in the local plant-eaters. Most of the continent's earlier mammalian herbivores had low-crowned teeth coated in thin enamel sheaths. The majority of the teeth at Tinguiririca, however, were high-crowned and armed with veritable shields of enamel extending well beyond the gum line. This combination of dental features is ideal for consuming grass — a coarse, low-nutrition plant that needs to be endlessly ground down and consumed in large quantities to sustain an animal. Though no grass fossils are yet known from Tinguiririca, the abundance of grazers' teeth suggest that it harbored one of the Earth’s earliest prairies or savannahs.
The age of the site is also significant: As the Oligocene progressed, the planet largely grew cooler and drier, spurring a worldwide decline in forestry and a general expansion of grassland.
South America's native hoofed mammals are not Tinguiririca’s only known grazers. In 2012, paleontologists described two new rodents from the same area and period, dubbing them Andemys and Eoviscaccia. Though not the oldest known rodents from South America, they are the earliest known to have also developed high-crowned, heavily-enameled teeth. This adaptation is still present in one of Eoviscaccia’s ancestors, the chinchilla — a bushy-tailed, grass-feeding rodent that still inhabits the Chilean Andes.
Atacama, 9-6 million BCE
Receiving less than an inch of rainfall each year, Chile's Atacama Desert is the driest on Earth outside of the poles. In 2010, however, paleontologists discovered a graveyard of large marine animals at the southern end of this wasteland. Known as Cerro Ballena (“whale hill”) and dating to the late Miocene Epoch, most of the site's skeletons belong to an as-yet unnamed relative of modern humpback and blue whales. Though modern whales are highly gregarious animals, the specimens here don’t represent one mass beaching: They were exhumed belly-up across four layers of sediment, representing multiple isolated deaths at sea.
In 2014, paleontologists led by Nicholas Pyenson of the Smithsonian Institution announced a potential culprit: algae. These organisms occasionally discharge toxins that — if inhaled or ingested — can cripple the organs of even the largest marine mammals. In the case of Cerro Ballena, Pyenson and his colleagues argue, an iron runoff from the Andes would have aided the poison's spread. The whales wouldn't have been the only animals felled by the killer algae: Sharks, seals, penguins, and an aquatic sloth called Thalassocnus were also buried at this site.
The Last Giants
Los Lagos and Magallanes, 11.6-8.2 thousand BCE
Roughly four million years ago, the strait separating North and South America finally closed. This event perpetuated an already-ongoing exodus of organisms between the two continents: While sloths, armadillos, and opossums moved north, foreign mammals like horses, deer, and dogs migrated southward. In fact, many of South America's most recognizable "native" mammals today — including jaguars, coatis, and llamas — are descendants of these invaders.
One of the most recent fossil sites preserving these animals in Chile is Pilauco Bajo, located in the city of Osorno in Los Lagos. Since 1986, scientists have exhumed the bones of horses, skunks, and Stegomastodon from this site, all around ten thousand years old.
Stegomastodon was a lowland relative of the elephant, comparable in size to the modern Asian species and equipped with tusks that could grow over ten feet long. Despite the name, it wasn't a close relative of the better-known American mastodon (Mammut americanum), but actually one of the last of the gomphotheres, a more ancient line of trunked and tusked herbivores with a near-global distribution a few million years earlier.
While South America was untouched by the ice sheets of the Pleistocene Epoch (2.6 million-12 thousand BCE), Stegomastodon shared the same fate as its northern counterparts. Though their date of arrival is murky (with estimates ranging from roughly seventeen thousand to as much thirty thousand years ago), the first humans to conquer South America likely played a role in their downfall. Stone tools and the remains of a makeshift work station at Pilauco Bajo hint at this possibility.
Another likely casualty of early human hunting in Chile was a ten-foot long ground sloth called Mylodon. First known from bones Charles Darwin uncovered outside of Buenos Aires in the 1830s, explorers began collecting skin, hair, and dung belonging to this animal in 1895 from a cave in Magallanes.
Since these remnants were not fossilized, a few notable scientists of the early 1900s concluded that Mylodon still roamed Chilean Patagonia. Florentino Ameghino, an eminent Argentine paleontologist of the era, also believed that the sloth accounted for tales of the swamp-dwelling monster told by the native Tehuelche people. To date, no living animals described in Patagonia have borne out this conviction; however, the dung did reveal that Mylodon fed on grass and sedge instead of the deciduous leaves favored by modern tree sloths. Carbon-dating of objects from the cave — now known as Cueva del Milódon— place the animal's age between 10.2 and 13.6 thousand years old.
Horse skin and bones are also known from the cave. Along with the notoungulates, litopterns, and ground sloths, these grazers also vanished in South America after the end of the Pleistocene. They wouldn't return to the continent until the early 1500s, with the arrival of the Spanish and Portuguese.
Other Chilean fossil sites
Both the Quiriquina Formation in Bío Bío and Viñita Formation in Coquimbo date to the end of the Cretaceous; while turtle fossils are known from both localities, early rays are known from the former while the bone of the titanosaur Antarctosaurus hail from the latter.
At over 14,000 feet above sea level, the Chucal Formation in Antofagasta is the highest vertebrate fossil site in the Western Hemisphere. It dates back to the Early Miocene (roughly 18 million BCE) and contains fossilized rodents, notoungulates, and glyptodonts.
Further Miocene marine fossils are known from the Navidad Formation across Valparaíso and O’Higgins, as well the Lacui and Santo Domingo Formations of Los Rios and Los Lagos, respectively.
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cerroballena.si.edu (Smithsonian site focusing on Cerro Ballena)
www.gonfoterio.cl (homepage of Pilauco Bajo)