Tinguiririca fauna
Encyclopedia
The fossil
Tinguiririca fauna, entombed in volcanic mudflows
and ash layers
at the onset of the Oligocene
, about 33-31.5 million years ago, represents a unique snapshot of the history of South America
's endemic fauna, which was extinguished when the former island continent was joined to North America
by the rising Isthmus of Panama
. The fossil-bearing sedimentary layers of the Abanico Formation were first discovered in the valley of the Tinguiririca River
, high in the Andes
of central Chile
.
The endemic fauna bridges a massive gap in the history of those mammals that were unique to South America. Paleontologists knew the earlier sloth
and anteater
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
-like earliest rodent
s discovered in South America, a wide range of the hoofed herbivores called notoungulates, a shrew-like marsupial
and ancestors of today's sloth
and armadillo
s. Many of the herbivores have teeth adapted to grass-eating; though no plant fossils have been recovered, the high-crowned hypsodont
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
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
s ("macroniche" analysis) bears out the existence of dry grasslands. Previously, no grassland ecosystem
anywhere had been identified prior to Miocene
systems fifteen million years later than the Tinguiririca fauna. Grasslands spread as the Earth's paleoclimate grew cooler and drier.
New fossils were uncovered of the New World monkeys and caviomorph rodents— the group that includes the capybara
— 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
. A notable discovery was the miniature skull of a delicate progenitor of New World marmoset
s and tamarin
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
events, more than 1500 individual fossils have been recovered from multiple sites in the region, ranging in age from 40 to 10 mya.
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
Tinguiririca fauna, entombed in volcanic mudflows
Lahar
A lahar is a 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. The term is a shortened version of "berlahar" which originated in the Javanese language of...
and ash layers
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
at the onset of the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, about 33-31.5 million years ago, represents a unique snapshot of the history of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
's endemic fauna, which was extinguished when the former island continent was joined to North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
by the rising Isthmus of Panama
Isthmus of Panama
The Isthmus of Panama, 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 of Panama and the Panama Canal...
. The fossil-bearing sedimentary layers of the Abanico Formation were first discovered in the valley of the Tinguiririca River
Tinguiririca River
Tinguiririca River is a river of Chile located in the 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 to the vicinity of the city of San Fernando. In this portion of its course, the river receives...
, high in the Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
of central Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
.
The endemic fauna bridges a massive gap in the history of those mammals that were unique to South America. Paleontologists knew the earlier sloth
Sloth
Sloths are the six species of medium-sized mammals belonging to the families Megalonychidae and Bradypodidae , part of the order Pilosa and therefore related to armadillos and anteaters, which sport a similar set of specialized claws.They are arboreal residents of the jungles of Central and South...
and anteater
Anteater
Anteaters, also known as antbear, are the four mammal species of the suborder Vermilingua commonly known for eating ants and termites. Together with the sloths, they compose the order Pilosa...
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
Chinchilla
Chinchillas are crepuscular rodents, slightly larger and more robust than ground squirrels, and are native to the Andes mountains in South America. Along with their relatives, viscachas, they make up the family Chinchillidae....
-like earliest rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s discovered in South America, a wide range of the hoofed herbivores called notoungulates, a shrew-like marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
and ancestors of today's sloth
Sloth
Sloths are the six species of medium-sized mammals belonging to the families Megalonychidae and Bradypodidae , part of the order Pilosa and therefore related to armadillos and anteaters, which sport a similar set of specialized claws.They are arboreal residents of the jungles of Central and South...
and armadillo
Armadillo
Armadillos are New World placental mammals, known for having a leathery armor shell. Dasypodidae is the only surviving family in the order Cingulata, part of the superorder Xenarthra along with the anteaters and sloths. The word armadillo is Spanish for "little armored one"...
s. Many of the herbivores have teeth adapted to grass-eating; though no plant fossils have been recovered, the high-crowned hypsodont
Hypsodont
Hypsodont dentition is characterized by high-crowned teeth and enamel which extends past the gum line. This provides extra material for wear and tear. Some examples of animals with hypsodont dentition are cows, horses and deer; all animals that feed on gritty, fibrous material. The opposite...
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
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
of North America." Statistical analyses of the number of species categorized by body size ("cenogram
Cenogram
A cenogram is a graphical comparison of the average adult weight of mammalian species within a terrestrial area. In studying ancient communities, it is used to draw conclusions about biome, including whether a biome is species rich, its relative humidity and level of forestation. Cenograms were...
" analysis, an aspect of body size scaling) and of their broad ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s ("macroniche" analysis) bears out the existence of dry grasslands. Previously, no grassland ecosystem
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
anywhere had been identified prior to Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
systems fifteen million years later than the Tinguiririca fauna. Grasslands spread as the Earth's paleoclimate grew cooler and drier.
New fossils were uncovered of the New World monkeys and caviomorph rodents— the group that includes the capybara
Capybara
The capybara , also known as capivara in Portuguese, and capibara, chigüire in Venezuela, Colombia, and Ecuador ronsoco in Peru, chigüiro, and carpincho in Spanish, is the largest living rodent in the world. Its closest relatives are agouti, chinchillas, coyphillas, and guinea pigs...
— 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
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
. A notable discovery was the miniature skull of a delicate progenitor of New World marmoset
Marmoset
Marmosets are the 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 also used in reference to the Goeldi's Monkey, Callimico goeldii, which is closely related.Most marmosets...
s and tamarin
Tamarin
The tamarins are squirrel-sized New World monkeys from the family Callitrichidae in the genus Saguinus. They are closely related to the lion tamarins in the genus Leontopithecus.- Range :...
s; it has been given the name Chilecebus carrascoensis
Chilecebus carrascoensis
Chilecebus carrascoensis is an extinct species of New World monkey that lived in what is now Chile during the Early Miocene some 20 million years ago. It had a body mass of about 1.3 pounds .-References:...
.
The first of the fossils were found in 1988. Since then, in strata representing repeated catastrophic lahar
Lahar
A lahar is a 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. The term is a shortened version of "berlahar" which originated in the Javanese language of...
events, more than 1500 individual fossils have been recovered from multiple sites in the region, ranging in age from 40 to 10 mya.
External links
- Mammal lineages of island South America
- 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)
- D. A. Croft, "New species" including several from the Tinguiririca fauna