''Glossotherium'' is an extinct genus of large mylodontid ground sloths of the subfamily

Mylodontinae Mylodontinae is an extinct subfamily of ground sloths that lived from the Early Miocene to the Early Holocene epochs. Classification The classification of the Mylodontidae is complex and often under discussion. The most widely accepted subfamil ...

. It represents one of the best-known members of the family, along with ''

Mylodon ''Mylodon'' is an extinct genus of ground sloth belonging to the family Mylodontidae, known from southern South America. With a total length of 3 to 4 m and a body mass of 1-2 tonnes, it is one of the largest mylodontids (though it was considerab ...

'' and ''

Paramylodon ''Paramylodon'' is an extinct genus of ground sloth of the family Mylodontidae endemic to North America during the Pliocene through Pleistocene epochs, living from around ~4.9 Mya–12,000 years ago. Within the genus only two species are recog ...

''. Reconstructed animals were between long and possibly weighed up to 1,002.6–1,500 kg. The majority of finds of ''Glossotherium'' date from the Middle and Upper

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

, around 300,000 to 10,000 years ago, with a few dating older, as far back

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

, east of the

Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

roughly from latitude 20 to 40 degrees south, leaving out the

Amazon Basin The Amazon basin is the part of South America drained by the Amazon River and its tributary, tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries ...

in the north. In western South America, finds are also documented north of the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

. The animals largely inhabited the open landscapes of the

Pampas The Pampas (; from Quechua 'plain'), also known as the Pampas Plain, are fertile South American low grasslands that cover more than and include the Argentine provinces of Buenos Aires, La Pampa, Santa Fe, Entre Ríos, and Córdoba; all o ...

and northern

savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...

regions. Like other mylodonts, ''Glossotherium'' was adapted to a more or less grassy diet, as indicated by the broad snout and the design of the teeth. This view is confirmed by isotopic analysis. The

anatomical Anatomy () is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old scien ...

structure of their locomotor system suggests quadrupedal locomotion, but they were also capable of changing to a bipedal stance. The particularly strong construction of the forelimbs is remarkable, leading to the assumption that ''Glossotherium'' burrowed underground. Large fossil burrows with corresponding scratch marks support this assumption, possibly making it the largest known burrowing mammal ever. The structure of the auditory system shows that ''Glossotherium'' could perceive frequencies in

infrasound Infrasound, sometimes referred to as low frequency sound or incorrectly subsonic (subsonic being a descriptor for "less than the speed of sound"), describes sound waves with a Audio frequency, frequency below the lower limit of human audibility ...

and probably produce them with the help of its voluminous nasal cavity. The research history of the genus is very complex. The first description was made in 1840 by

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomy, comparative anatomist and paleontology, palaeontologist. Owen is generally considered to have been an outstanding naturalist with a remarkabl ...

. However, he discarded the genus name just two years later. Subsequently, this led to persistent confusion and equation with ''Mylodon'' and other forms, which was not resolved until the 1920s. Especially during the 20th century, ''Glossotherium'' was considered identical to the North American ''

''. It was not until the 1990s that it became widely accepted that the two genera are independent.

Description

Extm Glossotherium robustum rbh-hlmwh01913-12

''Glossotherium'' belongs to the

Mylodontidae Mylodontidae is a family of extinct South American and North American ground sloths within the suborder Folivora of order Pilosa, living from around 23 million years ago (Mya) to 11,000 years ago. This family is most closely related to another fa ...

, in which it is further subcategorized into the

, characterized both by the loss of the

entepicondylar foramen The entepicondylar foramen is an opening in the distal (far) end of the humerus (upper arm bone) present in some mammals. It is often present in primitive placentals, such as the enigmatic Madagascan '' Plesiorycteropus''. In most Neotominae and a ...

of the distal

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

and anteriorly broad snouts. Mylodontinae has three famous genera: ''

'', ''

'' and ''Glossotherium''. The latter three have frequently been confused for each other in scientific literature, though it is likely ''Paramylodon'' and ''Glossotherium'' share a more recent common ancestor than with any other mylodontid. ''Paramylodon'' is typically larger than ''Glossotherium'', even though there is overlap in their size ranges, and ''Glossotherium'' is generally wider and more robust with a diagnostic increased amount of lateral flare at the predental spout. ''Glossotherium robustum'' was endemic to

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

and weighed about .

records indicate that it was widely distributed between 20°S and 40°S, with a range spanning across

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

Uruguay Uruguay, officially the Oriental Republic of Uruguay, is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast, while bordering the Río de la Plata to the south and the A ...

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

and

Paraguay Paraguay, officially the Republic of Paraguay, is a landlocked country in South America. It is bordered by Argentina to the Argentina–Paraguay border, south and southwest, Brazil to the Brazil–Paraguay border, east and northeast, and Boli ...

Dentition

Sloths have an ever-growing adult

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...

. They lack deciduous dentition and have a reduction in tooth number. Sloth teeth also lack the enamel and cuspation pattern generally present in other mammals. Their tooth forms are oval, subrectangular, or elongate irregular ovoid with chisel-shaped "caniniform" teeth anteriorly and "molariform" cheek teeth. ''Glossotherium'' has a layer of cementum surrounding all molariform cheek teeth with some traces on caniniform teeth. Cheek teeth in ''Glossotherium'' are larger, have more complex shapes, and retain more of the cementum layer around all sides of each tooth than the Shasta ground sloth, ''

Nothrotheriops shastensis ''Nothrotheriops'' is an extinct genus of ground sloths endemic to North America during the Pleistocene to early Holocene (~2.5 Mya until 10,000 years ago). The genus contains two species, ''N. shastensis'' and ''N. texanus'', the former of whic ...

'', and tree sloths.

Discovery

Fossils 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 ...

of this animal have been found in

. It is closely related to ''

'' of North America, whose specimens have often been confused with it and assigned to ''Glossotherium'', which in turn was initially assigned to ''Mylodon''. The earliest ''Glossotherium'' specimens are known from the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Arctotherium ''Arctotherium'' ("bear beast") is an extinct genus of the Pleistocene Tremarctinae, short-faced bears endemic to Central America, Central and South America. ''Arctotherium'' migrated from North America to South America during the Great American In ...

'' and sabre-toothed cats such as ''

Smilodon ''Smilodon'' is an extinct genus of Felidae, felids. It is one of the best known saber-toothed predators and prehistoric mammals. Although commonly known as the saber-toothed tiger, it was not closely related to the tiger or other modern cats ...

''. It is believed to have died out in the

(1.8 million to 12,000 years ago). The most recent reported date is about 8,700 years BP.

Diet

Details of ''Glossotherium'' diet are unclear since no dung deposits are available for analysis. However, based on dental evidence, ''Glossotherium'' was likely more suited to grazing, though it was also probably less efficient at ingesting grasses since its dental apparatus was more suited to shearing, which would have been too ineffective at processing plant materials down to an ingestible size to obtain adequate nutritive value. More recent tree sloths have a very slow rate of passage of food through the gut and it is likely that ''Glossotherium'' did as well. With a likely low metabolic rate, a large body size, a consequently reduced energy requirement for its weight, and an extraordinarily large gut that likely had a foregut fermentation site, ''Glossotherium'' could probably survive better on foods of lower

nutritional value Nutritional value or nutritive value as part of food quality is the measure of a well-balanced ratio of the essential nutrients carbohydrates, fat, protein, minerals, and vitamins in items of food or diet concerning the nutrient requirements of ...

than other sloths could. Though it is likely ''Glossotherium'' primarily ate grasses, it also probably ate a variety of foliage as well and would be better considered a "browser-grazer" than simply a grazer. Evidence from Santa Elina suggests that the niche breadth of ''G. phoenesis'' decreased from the Last Glacial Maximum onward.

Hearing

''Glossotherium'' had large ear ossicles, similar to those in elephants, which imply the loss of hearing acuity of higher frequencies, further implying an advantage for sensing low frequency sounds, infrasound, or bone-conducting seismic waves. Low frequency sound is useful for long range communication and it is possible that ground sloths used low frequency communication in much the same way that it is utilized by elephants. Sloths may have used low frequency sounds for communication in mating calls or other social interactions, or for long-range sound sensing as in predator-prey interactions or weather forecasting. Another possible explanation for hearing in low frequencies may be due to fossorial habits: low hearing frequencies coupled with a short interaural distance suggest that ''Glossotherium'' probably had very poor sound localization. This indicates evidence of an underground lifestyle since loss of high frequency hearing is common to fossorial mammals. ''Glossotherium'' huge nostrils were likely effective for sound emission, with expanded nares possibly related to emission of low frequency sounds up to 600 Hz.

Distribution

Fossils of ''Glossotherium'' have been found in:''Glossotherium''
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org * Luján and Agua Blanca Formations, Argentina * Charana and

Tarija Formation The Tarija Formation is a Pleistocene-age geologic formation found near Tarija, Bolivia. Background Fossils of numerous large herbivorous mammals have been discovered, including toxodonts like ''Toxodon platensis'', glyptodonts, ground sloth ...

s, Bolivia * Japones Cave, Lagoa Santa and Lage Grande, Brazil *

Santa Elena Peninsula The Santa Elena Peninsula is a peninsula in Santa Elena Province, Ecuador. The Santa Elena Peninsula contains the westernmost point on mainland Ecuador and is bordered by the Gulf of Guayaquil to the south and the Santa Elena Bay to the north. Th ...

, Ecuador * General Bruguer/Riacho Negro, Paraguay *

Talara tar seeps Talara is a city in the Talara Province of the Piura Region, in northwestern Peru. It is a port city on the Pacific Ocean with a population of 91,444 as of 2017. Its climate is hot and dry. Due to its oil reserves, and ability to produce aviatio ...

, Peru *

Sopas Formation The Sopas Formation is a Lujanian geologic formation in Uruguay. Fossil content The following fossils have been reported from the formation: * '' Antifer''Taima-Taima Taima-Taima is a Late Pleistocene archaeological site located about 20 kilometers east of Santa Ana de Coro, in the Falcón State of Venezuela. The human settlement at Taima-Taima started about 14,000 years ago. History of research The site was ...

, Venezuela