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''Paramylodon'' is an extinct genus of
ground sloth Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. The term is used to refer to all extinct sloths because of the large size of the earliest forms discovered, compared to existing tree sloths. The Cari ...
of the family
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 ...
endemic to North America during the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the '' Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed ...
epochs, living from around ~4.9 Mya–11,000 years ago. It is also known as Harlan's ground sloth. Due to the partly very good fossil preservation, the body armor typical for the mylodonts has mostly been preserved in the form of
osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct ...
. In addition, a sex-specific difference in cranial structure can be demonstrated. According to the finds, the representatives of ''Paramylodon'' lived in open landscapes, sometimes also in mountainous locations, and most likely fed on grass-eating or mixed plant diets. Unique
trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
s also provide information about the locomotion of the animals, which was quadrupedal. In addition, due to the design of the forelimbs, a certain burrowing way of life cannot be disputed. Within the genus only two species are recognized: ''Paramylodon harlani'' and ''Paramylodon garbanii''. The first fossil findings date back to the beginning of the 1830s. They go back to
Richard Harlan Richard Harlan (September 19, 1796 – September 30, 1843) was an American paleontologist, anatomist, and physician. He was the first American to devote significant time and attention to vertebrate paleontology and was one of the most importa ...
, in whose honor the species was named. The genus ''Paramylodon'' was introduced by
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of ''Tyrannosaurus'' during a career ...
in the early 20th century. Altogether, this genus looks back on an eventful history of research. In their first 150 years, the finds that are now attributed to ''Paramylodon'', and later the genus itself, were repeatedly associated with other forms, first with ''
Mylodon ''Mylodon'' is a genus of extinct ground sloth belonging to the family Mylodontidae, known from the region of Patagonia in Chile and Argentina in southern South America. With a total length of 3 to 4 m, it is one of the best-known and largest rep ...
'', but since the 1950s increasingly with ''
Glossotherium ''Glossotherium'' is an extinct genus of mylodontid ground sloths of the subfamily Mylodontinae, which includes large ground-dwelling sloths. It represents one of the best known members of the family, along with '' Mylodon'' and '' Paramylodo ...
''. Especially with the latter genus ''Paramylodon'' shares numerous features that argue for a close relationship. Only since the 1990s have both genera been considered distinct, with ''Glossotherium'' restricted to
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 souther ...
, while ''Paramylodon'' inhabited North America.


Taxonomy

''Paramylodon'' is an extinct genus of sloth from the extinct family Mylodontidae. Mylodontidae is grouped together with modern two-toed sloths of the family Choloepodidae and the extinct
Scelidotheriidae Scelidotheriidae is a family of extinct ground sloths within the order Pilosa, suborder Folivora and superfamily Mylodontoidea, related to the other extinct mylodontoid family, Mylodontidae, as well as to the living two-toed sloth family Ch ...
, in the superfamily Mylodontoidea, with the former family being their closest living relatives. ''Paramylodon'' is closely related to ''Mylodon'' and ''Glossotherium''. In some later phylogenetic work, the results could be reproduced. In contrast, a study presented in 2019 by Luciano Varela and other involved scientists, which includes numerous fossil forms of the entire sloth suborder, sees this more critically. Here, ''Paramylodon'' and ''Glossotherium'' are closely related, ''Mylodon'', on the other hand, forms the basis of the advanced mylodonts and ''Lestodon'' clades with some forms from northern South America. In the same year, a more-detailed phylogenetic analysis of the mylodonts was published by a research group led by Alberto Boscaini. According to the study, ''Paramylodon'', ''Glossotherium'', and ''Mylodon'' form a closer relationship within the Mylodontinae. This view also finds support from the aforementioned biochemical data, also presented in 2019.Samantha Presslee, Graham J. Slater, François Pujos, Analía M. Forasiepi, Roman Fischer, Kelly Molloy, Meaghan Mackie, Jesper V. Olsen, Alejandro Kramarz, Matías Taglioretti, Fernando Scaglia, Maximiliano Lezcano, José Luis Lanata, John Southon, Robert Feranec, Jonathan Bloch, Adam Hajduk, Fabiana M. Martin, Rodolfo Salas Gismondi, Marcelo Reguero, Christian de Muizon, Alex Greenwood, Brian T. Chait, Kirsty Penkman, Matthew Collins und Ross D. E. MacPhee: ''Palaeoproteomics resolves sloth relationships.'' Nature Ecology & Evolution 3, 2019, S. 1121–1130, doi:10.1038/s41559-019-0909-z Detailed morphological analyses published as early as 2009 by
Robert K. McAfee The name Robert is an ancient Germanic given name, from Proto-Germanic "fame" and "bright" (''Hrōþiberhtaz''). Compare Old Dutch ''Robrecht'' and Old High German ''Hrodebert'' (a compound of '' Hruod'' ( non, Hróðr) "fame, glory, honou ...
also suggest that ''Paramylodon'' and ''Glossotherium'' are very closely related and share a common ancestor. Below is a phylogenetic tree of the Mylodontidae, based on the work of Boscaini ''et al''. 2019, showing the position of ''Paramylodon''.


History of research


Discoveries in North and South America

The research history of ''Paramylodon'' is complex and characterized by more than 150 years of confusion and equation with ''
Mylodon ''Mylodon'' is a genus of extinct ground sloth belonging to the family Mylodontidae, known from the region of Patagonia in Chile and Argentina in southern South America. With a total length of 3 to 4 m, it is one of the best-known and largest rep ...
'' and ''
Glossotherium ''Glossotherium'' is an extinct genus of mylodontid ground sloths of the subfamily Mylodontinae, which includes large ground-dwelling sloths. It represents one of the best known members of the family, along with '' Mylodon'' and '' Paramylodo ...
''. However, it begins with the first discoveries of
Richard Harlan Richard Harlan (September 19, 1796 – September 30, 1843) was an American paleontologist, anatomist, and physician. He was the first American to devote significant time and attention to vertebrate paleontology and was one of the most importa ...
(1796-1843) at Big Bone Lick in Boone County in the U.S. state of
Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virgini ...
in 1831, which included a right mandible and a
clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the rig ...
. Harlan recognized that they were remains of an extinct sloth and referred them to ''
Megalonyx ''Megalonyx'' (Greek, "large claw") is an extinct genus of ground sloths of the family Megalonychidae, native to North America during the Pliocene and Pleistocene epochs. It became extinct during the Quaternary extinction event at the end of the ...
'', which was already known from North America at the time, and within the genus to the species ''Megalonyx laqueatus'' that he had established shortly before.Richard Harlan: ''Description of the jaws, teeth, and clavicle of the Megalonyx laqueatus.'' The Monthly American journal of geology and natural science 1, 1831, S. 74–76Richard Harlan: ''Description of the jaws, teeth, and clavicle of the Megalonyx laqueatus.'' Medical and physical researches, 1835, S. 334–336 The finds were originally preserved in New York, but are now lost. Between the years 1831 and 1836,
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...
made his pioneering voyage on HMS ''Beagle'' to
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 souther ...
and brought back from there a large number of fossils. These were then studied by
Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Ow ...
, one of the most important explorers of the Victorian era, and the results published. In a first publication on mammalian remains in general in 1840, he introduced the genus ''Mylodon'' with the species ''Mylodon darwinii''. The genus and species were based on a mandible Darwin found in
Punta Alta Punta Alta is a city in Argentina, about 20 kilometers southeast of Bahía Blanca. It has a population of 57,293. It is the capital ("cabecera") of the Coronel Rosales Partido. It was founded on 2 July 1898. The city is located near the Atlanti ...
in the
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...
Buenos Aires Buenos Aires ( or ; ), officially the Autonomous City of Buenos Aires ( es, link=no, Ciudad Autónoma de Buenos Aires), is the Capital city, capital and primate city of Argentina. The city is located on the western shore of the Río de la Plata ...
province. As a special characteristic, a total of four molar-like teeth per tooth row stood out. At the same time, Owen also noted similarities in tooth structure between Harlan's mandible and that of ''Mylodon darwinii''. Inferring this, he discarded the name coined by Harlan, ''Megalonyx laqueatus'', and created a new species, ''Mylodon harlani''.Richard Owen: ''Fossil Mammalia.'' In Charles Darwin (Hrsg.): ''Zoology of the Voyage of H.M.S Beagle, under the command of Captain Fitzroy, during the years 1832 to 1836. Part I. Fossil Mammals.'' London, 1840, S. 12–111 (S. 63–73) The genus name ''Paramylodon'' is composed of the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
παρα (para meaning "beside" or "near"), ''μύλη'' (''myle'' " molar") and ''ὀδούς'' (''odoús'' "tooth"), thus translates as "molar tooth". Harlan commented two years later on the use of the name because, in his opinion, it did not describe any outstanding characteristic of the animal and could mean any extinct mammal because almost all of them had the posterior molars.Richard Harlan: ''Notice of two new mammals from Brunswick Cana, Georgia; with observations on the fossil quadrupeds of the United States.'' The American journal of science and arts 43, 1842, S. 141–144

In the same year, 1842, Owen presented a comprehensive description of a skeleton of a mylodont that came from the flood plains of the
Río de la Plata The Río de la Plata (, "river of silver"), also called the River Plate or La Plata River in English, is the estuary formed by the confluence of the Uruguay River and the Paraná River at Punta Gorda. It empties into the Atlantic Ocean and f ...
north of
Buenos Aires Buenos Aires ( or ; ), officially the Autonomous City of Buenos Aires ( es, link=no, Ciudad Autónoma de Buenos Aires), is the Capital city, capital and primate city of Argentina. The city is located on the western shore of the Río de la Plata ...
; he established for it the new species ''Mylodon robustus''.Richard Owen: ''Description of the skeleton of an extinct gigantic Sloth, Mylodon robustus, Owen, with observations on the osteology, natural affinities, and probable habitats of the Megatherioid quadrupeds in general.'' London, 1842, S. 1–176 At this point, then, the genus ''Mylodon'' consisted of three species, two of which occurred in South America and one in North America. Furthermore, it should prove problematic that Owen identified ''Mylodon darwinii'' as the type species of the genus, although, as he admitted, this was the second known and described species after ''Mylodon harlani''. Accordingly, ''Mylodon harlani'' would actually be entitled to the status of
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen( ...
. Subsequently, different type species were assigned to ''Mylodon'', for example,
Johannes Theodor Reinhardt Johannes Theodor Reinhardt (3 December 1816, in Copenhagen – 23 October 1882, in Frederiksberg) was a Danish zoologist and herpetologist. The son of Johannes Christopher Hagemann Reinhardt. Biography He participated as botanist in the firs ...
in 1879 considered it to be ''Mylodon robustus'',
Richard Lydekker Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker ...
in 1887, on the other hand, considered it to be ''Mylodon harlani''.Richard Lydekker: ''Catalogue of the fossil Mammalia in the British Museum of Natural History. Part V.'' London, 1887, S. 1–345 (S. 106)Juan Carlos Fernicola, Sergio F. Vizcaíno und Gerardo De Iuliis: ''The fossil mammals collected by Charles Darwin in South America during his travels on board the HMS Beagle.'' Revista de la Asociación Geológica Argentina 64 (1), 2009, S. 147–159


''Paramylodon'' and the ''Mylodon''-''Glossotherium'' problem

Within the genus ''Paramylodon'', only one
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
, ''P. harlani'', is recognized. Another species, ''P. nebrascensis'', was described in 1903 by
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of ''Tyrannosaurus'' during a career ...
on the basis of a partial skeleton from Hay Spring in
Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the so ...
, but was already united with the
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen( ...
in the 1920s. Only ten years later,
Glover Morrill Allen Glover Morrill Allen (February 8, 1879 – February 14, 1942) was an American zoologist. He was born at Walpole, New Hampshire, the son of Reverend Nathaniel Glover Allen and Harriet Ann (Schouler) Allen, and studied at Harvard University. While s ...
created the species ''Mylodon garmani'' with the help of another partial skeleton from the
Niobrara River The Niobrara River (; oma, Ní Ubthátha khe, , literally "water spread-out horizontal-the" or "The Wide-Spreading Water") is a tributary of the Missouri River, approximately long,U.S. Geological Survey. Many early settlers, such as Mari Sando ...
in Nebraska,Glover M. Allen: ''A new Mylodon.'' Memoirs of the Museum of Comparative Zoology 40 (7), 1913, S. 319–346 but this is also considered a
synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are al ...
of ''Paramylodon harlani''. The same applies to several species named by
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy intereste ...
as early as the 1870s and 1890s, such as ''Mylodon sodalis'' and ''Mylodon sulcidens''. The original subdivision into two subspecies, ''P. h. harlani'' for a robust and ''P. h. tenuiceps'' for a graceful form, as suggested by
Chester Stock Chester Stock (28 January 1892 – 7 December 1950) was an American paleontologist who specialized in the Pleistocene mammalian fauna of the La Brea Tar Pits, Rancho La Brea tar pits. He served as a professor of geology at the California Institut ...
in 1917, is no longer advocated today. However, the species "''Glossotherium''" ''chapadmalense'' is problematic. The species was originally identified in 1925 by Lucas Kraglievich from a 39 cm long, nearly undamaged skull with mandible from Middle Pliocene strata east of Miramar in the Argentina Buenos Aires province.Lucas Kraglievich: ''Cuatro nuevos gravigrados de la fauna Araucana "Chapadmalense".'' Anales del Museo Nacional de Historia Natural de Buenos Aires 33, 1925, S. 215–235 It shows similarities to ''Glossotherium robustum'', but also possesses individual divergences that may justify its own generic status; for example, the name "''Eumylodon''" (which Kraglievich already used for ''Eumylodon chapadmalense'' in 1925) has been suggested. The form could thus be the common ancestor of ''Glossotherium'' and ''Paramylodon''. However, whether this also applies to the North American finds from the Pliocene of Florida and Mexico, first listed under the same species name by Jesse S. Robertson in 1976, or these are closer to ''Paramylodon'' is currently unclear due to lack of comparative studies. Partially, the early mylodont remains are also listed as ''P. garbanii'', a species name given in 1986 to some Pliocene mandible and limb remains from Arroyo EI Tanque in the Mexican State of Guanajuato had been coined (under the scientific name ''Glossotherium garbanii'').Gary S. Morgan: ''Vertebrate fauna and geochronology of the Great American Biotic Interchange in North America.'' New Mexico Museum of Natural History & Science Bulletin 44, 2008, S. 93–140Marisol Montellano-Ballesteros und Oscar Carranza-Castaneda: ''Descripcion de un milodontido del Blancano temprano de la mesa central de Mexico.'' Instituto de Geología, Universidad Nacional Autónoma de México, Revista 6, 1986, S. 193–203 The species is not fully recognized, however, and other authors consider it a synonym of ''Glossotheridium/Glossotherium chapadmalense''. In 1903,
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of ''Tyrannosaurus'' during a career ...
(1873-1963) introduced the generic name ''Paramylodon''. He used for this purpose a partial skeleton from Hay Spring in
Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the so ...
that had been discovered in 1897 during an expedition of the American Museum of Natural History. To the genus he assigned ''Paramylodon nebrascensis'' as a species. As defining differences from the North American ''Mylodon harlani'', which Brown considered the type species of ''Mylodon'', he gave the missing anterior caniniform teeth in the upper jaw. Thus, at that time, two distinct representatives of Mylodonts were recognized in the Pleistocene of North America. Later,
Chester Stock Chester Stock (28 January 1892 – 7 December 1950) was an American paleontologist who specialized in the Pleistocene mammalian fauna of the La Brea Tar Pits, Rancho La Brea tar pits. He served as a professor of geology at the California Institut ...
(1892-1950), based on his studies of the Rancho La Brea find material, pointed out that the feature of missing upper front teeth is highly variably developed in ''Mylodon harlani''. Therefore, synonymized he replaced ''P. nebrascensis'' with ''Mylodon harlani'' in 1917. In 1928, however,
Lucas Kraglievich {{Short pages monitor