The

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

Tinguiririca fauna, entombed in volcanic mudflows and ash layers at the onset of the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

, about 33-31.5 million years ago, represents a unique snapshot of the history of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

's endemic fauna, which was extinguished when the former island continent was joined to

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

by the rising

Isthmus of Panama The Isthmus of Panama ( es, Istmo de Panamá), also historically known as the Isthmus of Darien (), is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country ...

. The fossil-bearing sedimentary layers of the

Abanico Formation Abanico Formation ( es, Formación Abanico) is a thick sedimentary formation exposed in the Andes of Central Chile. The formation has been deposited in a timespan from the Eocene to the Miocene. Abanico Formation's contact with the overlying Mi ...

were first discovered in the valley of the

Tinguiririca River Tinguiririca River is a river of Chile located in the Libertador General Bernardo O'Higgins Region. It rises in the Andes, at the confluence of the rivers ''Las Damas'' and ''Del Azufre''. From its source, it flows northwest for about 56 km t ...

, high in the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

of central

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. The faunal assemblage lends its name to the

Tinguirirican The Tinguirirican ( es, Tinguiririquense) age is a period of geologic time (36.0–29.0 Ma) within the Late Eocene and Early Oligocene epochs of the Paleogene, used more specifically within the SALMA classification in South America. It follows th ...

stage in the South American land mammal age (SALMA) classification.

Description

The

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

fauna bridges a massive gap in the history of those mammals that were unique to South America. Paleontologists knew the earlier

sloth Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their li ...

and

anteater Anteater is a common name for the four extant mammal species of the suborder Vermilingua (meaning "worm tongue") commonly known for eating ants and termites. The individual species have other names in English and other languages. Together with ...

forebears of 40 mya, but no fossils from this previously poorly sampled transitional age had been seen. Fossils of the Tinguiririca fauna include the

chinchilla Chinchillas are either of two species (''Chinchilla chinchilla'' and ''Chinchilla lanigera'') of crepuscular rodents of the parvorder Caviomorpha. They are slightly larger and more robust than ground squirrels, and are native to the Andes mount ...

-like earliest

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

s discovered in South America,Later, a wave of rats and mice invaded from North America about 3.5 mya. a wide range of the hoofed herbivores called

notoungulate Notoungulata is an extinct order of mammalian ungulates that inhabited South America from the early Paleocene to the Holocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms resemb ...

s, a shrew-like

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...

and ancestors of today's

and

armadillo Armadillos (meaning "little armored ones" in Spanish) are New World placental mammals in the order Cingulata. The Chlamyphoridae and Dasypodidae are the only surviving families in the order, which is part of the superorder Xenarthra, along wi ...

s. Many of the herbivores have teeth adapted to grass-eating; though no plant fossils have been recovered, the high-crowned

hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritt ...

teeth, protected by tough enamel well below the gumline, identifies grazers suited to a gritty diet. "The proportion of hypsodont taxa relative to other dental types generally increases with the amount of open habitat," John Flynn explained in ''Scientific American'' (May 2007) "and the Tinguiririca level of hysodonty surpasses even that observed for mammals living in modern, open habitats such as the

Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...

of North America." Statistical analyses of the number of species categorized by body size (" cenogram" analysis, an aspect of body size scaling) and of their broad

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for ...

s ("macroniche" analysis) bears out the existence of dry grasslands. Previously, no

grassland ecosystem A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natural ...

anywhere had been identified prior to

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

systems fifteen million years later than the Tinguiririca fauna. Grasslands spread as the Earth's

paleoclimate Paleoclimatology (British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...

grew cooler and drier. New fossils were uncovered of the New World monkeys and

caviomorph Caviomorpha is the rodent infraorder or parvorder that unites all New World hystricognaths. It is supported by both fossil and molecular evidence. The Caviomorpha was for a time considered to be a separate order outside the Rodentia, but is now a ...

rodents— the group that includes the

capybara The capybaraAlso called capivara (in Brazil), capiguara (in Bolivia), chigüire, chigüiro, or fercho (in Colombia and Venezuela), carpincho (in Argentina, Paraguay and Uruguay) and ronsoco (in Peru). or greater capybara (''Hydrochoerus hydro ...

— which are known not to have evolved ''in situ''. Some of the new fossils demonstrate by the form of their teeth that they lie closer to African fossil relatives than to the North American ones, which previously had been assumed to have rafted to the island continent. Now it appears that some may have made the crossing of a younger, much narrower

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

. A notable discovery was the miniature skull of a delicate progenitor of New World

marmoset The marmosets (), also known as zaris or sagoin, are 22 New World monkey species of the genera ''Callithrix'', ''Cebuella'', ''Callibella'', and ''Mico''. All four genera are part of the biological family Callitrichidae. The term "marmoset" is ...

s and

tamarin The tamarins are squirrel-sized New World monkeys from the family Callitrichidae in the genus ''Saguinus''. They are the first offshoot in the Callitrichidae tree, and therefore are the sister group of a clade formed by the lion tamarins, Goel ...

s; it has been given the name '' Chilecebus carrascoensis''. The first of the fossils were found in 1988. Since then, in strata representing repeated catastrophic

lahar A lahar (, from jv, ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley. Lahars are extreme ...

events, more than 1500 individual fossils have been recovered from multiple sites in the region, ranging in age from 40 to 10 mya. The mammal species '' Archaeotypotherium tinguiriricaense'' is named after the site.

References

External links

John J. Flynn, André R. Wyss, Darin A. Croft and Reynaldo Charrier, "The Tinguiririca fauna, Chile: biochronology, paleoecology, biogeography and a new earliest Oligocene South American Land Mammal 'Age'"
(abstract: pdf file)

including several from the Tinguiririca fauna {{SALMA . Prehistoric biotas Eocene South America Oligocene South America Cenozoic animals of South America Paleogene Chile Paleontology in Chile Biogeography Prehistoric fauna by locality

Description

See also

References

Further reading

External links