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
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
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.
See also
*
South American land mammal age
The South American land mammal ages (SALMA) establish a geologic timescale for prehistoric South American fauna beginning 64.5 Mya (unit), Ma during the Paleocene and continuing through to the Late Pleistocene (0.011 Ma). These periods are referre ...
- list of fossils from this age and site
*
References
Further reading
* Flynn, John J., André R. Wyss, and
Reynaldo Charrier
Reynaldo Charrier (born 1945) is a Chilean geologist who has contributed to the tectonostratigraphy In geology, tectonostratigraphy is stratigraphy that refers either to rock sequences in which large-scale layering is caused by the stacking of thr ...
, "South America's missing mammals", ''Scientific American'' (May 2007) pp 68–75. The article is the source of the present summary.
on-line text.
* Simpson, George Gaylord, ''Splendid Isolation: The Curious History of South American Mammals'' (Yale University Press) 1980. The previous status quo in this field.
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