161-522: 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 recognized: Paramylodon harlani, also known as Harlan's ground sloth known from Early Pleistocene to the Late Pleistocene ( Irvingtonian - Rancholabrean ) and
322-469: A "wastebasket" taxon on the basis of naming priority, into which numerous closely related forms were placed. George Gaylord Simpson expressed in his 1945 general taxonomy of mammals that if Paramylodon could not be clearly separated from Glossotherium , Glossotherium would be preferable due to having priority over Paramylodon . With the subsequent full inclusion of Paramylodon into the genus, accomplished by Robert Hoffstetter in 1952, Glossotherium
483-502: A land bridge which connected Asia and North America during the last glacial maximum . Mosimann and Martin (1975) suggested the first of these nomads descended from hunting families who had acquired the skills to track down and kill large mammals. By this time, humans had developed proficient hunting weapons, including the Clovis points , which were narrow, carved stone projectiles used specifically for big game. A couple of hundred years later,
644-455: A plesiomorphic extra claw. While other species of Eremotherium had four fingers with only two or three claws, E. eomigrans had five fingers, four of them with claws up to nearly a foot long. Recently recognized, ground sloths of Nothrotheriidae are often associated with those of the Megatheriidae , and together the two form the superfamily Megatherioidea. The most prominent members of
805-513: A bipedal stance while stationary, allowing the forelimbs to be used to grasp vegetation as well as to use their claws for defence, though whether they were capable of moving in this posture is uncertain. Some ground sloths have been suggested to be able to climb. Some authors have suggested ground sloths were largely solitary animals, like living sloths, though other authors have argued that at least some ground sloths are likely to have engaged in gregarious behaviour. Whether or not ground sloths had
966-516: A broad pelvis. Like other xenarthrans, the adult teeth of ground sloths lacked enamel , with the tooth surface being composed of relatively soft orthodentine . The number of teeth in the jaws is considerably reduced in comparison to other mammals, with most ground sloths only having 5 and 4 teeth in each half of the upper and lower jaws respectively, with some ground sloths exhibiting further tooth number reduction. These teeth were rootless and were continuously growing (hypselodont), and typically have
1127-404: A femur length of around 42 cm. It is based on the form introduced by R. Lee Collins in 1934 as Prepotherium venezuelanum . The other two species, which are significantly larger with femur lengths of 56 to 59 cm, were recognized in 2006 by a work team led by Alfredo A. Carlini but were originally included in the genus Mirandabradys . Carlini and colleagues had defined this using numerous finds from
1288-475: A formidable defense against predators. The earliest megatheriid in North America was Eremotherium eomigrans which arrived 2.2 million years ago, after crossing the recently formed Panamanian land bridge. With more than five tons in weight, 6 meters in length, and able to reach as high as 17 feet (5.2 m), it was larger than an African bush elephant bull. Unlike relatives, this species retained
1449-458: A fossil-rich limestone fissure in Florida . The bone platelets were round to oval, sometimes irregularly shaped, and 5 to 30 mm long. They exhibited a rough surface with irregular depressions, whereas the underside was smooth and convex in design. In cross-section, they possessed a compact structure consisting of numerous fiber bundles mixed with hard bone lamellae ( osteomae ). In principle,
1610-554: A high diversity, almost reaching that of the contemporary fauna of southern South America in the Pampas region or Mesopotamia. Armadillos, the Pampatheriidae and Glyptodontinae , as well as sloths , have been proven. Mainly in the late 20th and early 21st century, numerous new forms were described, such as Urumacocnus and Pattersonocnus from the family Megalonychidae , Urumaquia and Proeremotherium as representatives of
1771-470: A juvenile Purussaurus . The size of the bite marks, from three to 15 mm in diameter, allows the length of the attacker to be reconstructed to be around 4m. It caught its prey with its front teeth. Attacks on the hind legs are also known by modern crocodiles . Pseudoprepotherium is a member of the Mylodontidae family within the suborder (Folivora). The Mylodontidae, in turn, are often placed together with
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#17328595060661932-491: A new one with Pseudoprepotherium . At first, he saw their systematic position as ambiguous. In 1985, Sue Hirschfeld moved Pseudoprepotherium to the Mylodontidae. Their assessment was based on extensive finds from the important Middle Miocene fossil site of La Venta in Colombia in connection with Collins' thigh find. In hindsight, Hirschfeld's characterization diagnosis turned out to be incorrect since Collins' find from
2093-405: A note that reads "deposited by Theodore Roosevelt ". Mylodontids are the only ground sloths confirmed to have had osteoderms embedded within their skin, though osteoderms were only present in a handful of genera and absent in many others. The largest mylodontid is Lestodon , with an estimated mass of 3,400–4,100 kilograms (7,500–9,000 lb). The ground sloth family Scelidotheriidae
2254-545: A relatively simple morphology. Some ground sloths have canine-like teeth at the front of the jaws separated from the other teeth by a gap (diastema). The skull shapes of ground sloths are highly variable. Those with narrow muzzles are likely to have had prehensile lips, while those with wider muzzles are likely to have had mobile tongues. The hands of ground sloths have ungual phalanges that indicate that they had well developed claws. In many ground sloth families (Megatheriidae, Mylodontidae, Scelidotheriidae and Nothrotheriidae),
2415-428: A skull, to Bolivartherium , to which they attributed further skeletal material; Rincón and McDonald, in turn, kept only the skull at Bolivartherium in 2020 and split off Magdalenabradys based on the postcranial skeletal elements ). As early as 1985, Sue Hirschfeld named the species Pseudoprepotherium confusum . A skull and several limb bones from La Venta formed this basis. Referring to deviations in
2576-489: A slow metabolism like living xenarthrans (including living sloths) is debated. Like living sloths, ground sloths likely only gave birth to a single offspring at a time, with likely several years between the birth of offspring. At least some ground sloths engaged in long-term parental care , with one adult (presumably female) Megalonyx found with two juveniles of different ages, with the oldest juvenile suggested to be 3–4 years old. Juvenile ground sloths may have clung to
2737-515: A synonym of Glossotheridium/Glossotherium chapadmalense . In 1903, Barnum Brown (1873-1963) introduced the generic name Paramylodon . He used for this purpose a partial skeleton from Hay Spring in Nebraska 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
2898-406: A tropical climate with a water-rich environment. Their known remains are limited to limb bones, except for a few skulls and teeth. Based on these remains, they were most likely medium to large-sized mylodontid. The genus was described in 1961 and currently contains three species, which were originally assigned to the genus Prepotherium . Pseudoprepotherium is a medium to a large-sized member of
3059-447: Is 47 to 51 cm long and about 20 cm wide, in outline they actually resemble human footprints, but they are much more laterally indented. Further studies showed that the shape of the prints corresponds very well with the shape of the foot of Paramylodon and that the outline reminiscent of humans is due to the outwardly turned foot of the sloth. The lateral distance between the tracks is about 60 cm, which roughly corresponds to
3220-643: Is a femur found in the first third of the 20th century. The site was then inaccessible for a long time, since it was created during the construction of a reservoir (the Virgen de la Coromoto reservoir) sank. However, a new fossil locality on the lake's eastern shore largely corresponds spatially and temporally to the original site. This was announced in a publication in 2016. The site contained a small collection of vertebrates, such as remains of fish and crocodilians ; such as Purussaurus , as well as armored Peltephilidae and South American ungulates . The Río Yuca Formation
3381-607: Is a phylogenetic tree of the Mylodontidae, based on the work of Boscaini et al. . 2019, showing the position of Paramylodon . Urumacotherium Pseudoprepotherium Paroctodontotherium Octodontotherium Brievabradys Lestodon Bolivartherium Thinobadistes Sphenotherus Lestobradys Pleurolestodon Glossotheridium Simomylodon Kiyumylodon Mylodon Paramylodon Glossotherium The research history of Paramylodon
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#17328595060663542-825: Is an ancestral and very plesiomorphic member of this subfamily and does not belong to the main group of closely related genera, which include Scelidotherium and Catonyx . The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig. 4 of Presslee et al ., 2019). † Neocnus dousman † Parocnus serus † Neocnus comes † Acratocnus ye † Nothrotheriops shastensis † Megatherium americanum † Megalonyx jeffersoni 5 living spp. † Scelidotherium sp. † Scelidodon sp. 2 living spp. † Lestodon armatus † Paramylodon harlani † Mylodon darwinii † Glossotherium robustus Radiocarbon dating places
3703-481: Is broadly developed in Paramylodon and has an unspecialized surface, the associated glenoid fossa on the skull appears shallow, which is typical of herbivores with their rotary chewing movements. However, an additional, nearly vertical articular facet occurs on the inner side, anchored in a depression on the outer wall of the wing bone . This tended to limit overly strong lateral masticatory movements. The arrangement of
3864-470: Is complex and characterized by more than 150 years of confusion with Mylodon and Glossotherium . The history begins with the first discoveries of Richard Harlan (1796-1843) at Big Bone Lick in Boone County in the U.S. state of Kentucky in 1831, which included a right mandible and a clavicle . Harlan recognized that they were remains of an extinct sloth and referred them to Megalonyx , which
4025-501: Is composed largely of limestone and sandstone with discrete interstices of the conglomerate. It originated in a freshwater environment with a formation period possibly in the Middle and Late Miocene . The most extensive fossil material to date belongs to the Urumaco sequence, a complex depositional unit that is predominantly exposed in the approximately 36,000 km² large Falcón Basin in
4186-459: 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 ). The species is not fully recognized, however, and other authors consider it
4347-435: Is grouped together with modern two-toed sloths of the family Choloepodidae and the extinct Scelidotheriidae , in the superfamily Mylodontoidea, with the former family being their closest living relatives. Paramylodon is usually considered closely related to both Mylodon and Glossotherium . In contrast, a study presented in 2019 by Luciano Varela and other involved scientists, which includes numerous fossil forms of
4508-475: Is hardly any variation in size, as studies of the numerous finds from Rancho La Brea dating from 45,000 to 10,000 years Before Present indicate. This is explained with a high flexibility of the genus in relation to the environment and thus a high adaptability. However, the assumption ignores the fact that increasingly cooler conditions should lead to an increase in body size according to the Bergmann's rule . Based on
4669-464: Is highly variably developed in Mylodon harlani . Therefore, synonymized he replaced P. nebrascensis with Mylodon harlani in 1917. In 1928, however, Lucas Kraglievich restricted North American finds to Paramylodon and thus separated the genus from its South American representatives, an opinion that was echoed eight years later by Ángel Cabrera but it found little resonance among most researchers in
4830-658: Is known from remains found across North America, with abundant remains known from the La Brea tar pits in California. Like some other mylodontids, Paramylodon had osteoderms embedded within its skin. Paramylodon lived in open landscapes, sometimes also in mountainous locations, and were grazers or mixed feeders. Preserved footprints are known. The morphology of the forelimbs has led to suggestions that Paramylodon may have engaged in burrowing. Like other ground sloths, Paramylodon became extinct around 14-12,000 years ago as part of
4991-490: Is more closely related to some more modern representatives, such as Thinobadistes , a form widely found in Central and North America. However, the limb bones usually only offer a limited selection of features for determining family relationships. Therefore, investigations on the little skull material see Pseudoprepotherium clearly more basally embedded in the mylodonts and move the form partly closer to Urumacotherium , but also to
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5152-526: 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 . It shows similarities to Glossotherium robustum , but also possesses individual divergences that may justify its own generic status; for example,
5313-742: Is now at the Yale Peabody Museum . The largest samples of Nothrotheriops dung can be found in the collections of the Smithsonian Museum. Another Nothrotheriops was excavated at Shelter Cave , also in Doña Ana County , New Mexico . The mylodontid ground sloths together with their relatives the scelidotheriids form the Mylodontoidea , the second radiation of ground sloths. The discovery of their fossils in caverns associated with human occupation led some early researchers to theorize that
5474-858: Is now the United States and northern Mexico, but also scatter in the western part of the continent as far south as the province of Alberta in Canada . They are found in both lowland and mountainous locations, with the highest finding point reaching about 2900 m elevation in Colorado . One of the most significant sites of the period is the Leisey Shell pit in Hillsborough County in Florida, where several skulls and postcranial skeletal elements have been reported to be about 1.2 million years old. The find material of
5635-415: Is partly deformed laterally, which means that only a few features are recognizable. A bent profile line was characteristic. Because of this, the rostrum and the cranium were at an angle of 130° from each other. At the occipital bone, the articular processes for the cervical spine protruded with little prominence. The alveoli of the five teeth per row of teeth typical of mylodon can be seen on the upper jaw, but
5796-617: Is present with the Diamond Valley Lake Local Fauna in Diamond Valley and Domenigoni Valley in Riverside County also in southern California. Material has been recovered during the construction of Diamond Valley Lake since the mid-1990s and currently includes more than 100,000 specimens from more than 100 taxa , from more than 2600 different localities. In contrast to Rancho La Brea, large herbivores dominate here, while
5957-583: Is widely thought to reflect a greater adaptation to grassy diets. The posterior teeth are round, oval or more complex in cross-section and correspond to molar-like teeth. The foremost tooth is designed like a canine. The rear foot also clearly shows twists so that the sole points inwards. The mylodonts can be detected for the first time in the Oligocene. One of the earliest forms is Paroctodontotherium from Salla-Luribay in Bolivia . The internal organization of
6118-504: The Musculus masseter caused Paramylodon to open its mouth only 22°, which is considerably less than in two-toed sloths , which, however, have comparatively longer caniniform teeth. All in all, the structure of the masticatory apparatus rather suggests a preference for mixed plant diets. Ground sloth Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra . They varied widely in size with
6279-578: The Caribbean than on the American mainland, which correlates with the later colonization of this area by humans. Ground sloths varied widely in size from under 100 kilograms (220 lb) in the Caribbean ground sloths, to 3,700–4,100 kilograms (8,200–9,000 lb) in the largest ground sloth genera Megatherium , Lestodon and Eremotherium . The bodies of ground sloths were generally barrel-shaped, with
6440-543: The Ipururo and Pebas formations. These go back to a phase when the so-called "Proto-Amazon" existed, a landscape characterized by lakes, swamps and rivers connected to the Caribbean. It can now be described as "the Pebas mega wetland " . Some of the finds, however, are assigned to the species Pseudoprepotherium confusum , which is now considered the type form of the genus Magdalenabradys . Other Pseudoprepotherium finds from
6601-469: The Late Pleistocene megafauna extinctions of most large mammals across the Americas. Paramylodon overlapped in time with Paleoindians , the earliest human inhabitants of the Americas, who may have hunted Paramylodon . Its extinction may be the result of climatic change, hunting, or a combination of both factors. Paramylodon is an extinct genus of sloth from the extinct family Mylodontidae . Mylodontidae
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6762-455: The Mylodontidae . A completely reconstructed skeleton from Rancho La Brea shows a total length of 279 cm, of which the tail occupies about 118 cm. At the shoulders it reaches a height of 112 cm, and at the pelvis it measures 122 cm. Paramylodon weighs about 1.39 tons , but earlier mylodontids were quite smaller. Overall, Paramylodon represented a robustly built animal. It
6923-494: The Nevada State Prison near Carson City . The tracks were discovered as early as the second half of the 19th century during sandstone quarrying and initially, in 1882, were interpreted as evidence of giant humans. However, by the following year, Othniel Charles Marsh recognized a connection with extinct ground sloths and sought the originator of the stepping seals among the mylodonts, of which bone remains also exist from
7084-446: The Pliocene (about 5 to 2 million years ago) species were already approximately half the size of the huge Late Pleistocene Megalonyx jeffersonii from the last ice age . Some West Indian island species were as small as a large cat; their dwarf condition typified both tropical adaptation and their restricted island environment. This small size also enabled them a degree of arboreality. Megalonyx , which means "giant claw",
7245-636: The Scelidotheriidae in the superfamily of the Mylodontoidea . In a classic system based on skeletal anatomical features, the Mylodontoidea form a sister group to the Megatherioidea and thus one of the two major lineages of sloths. Molecular genetic analyses and protein studies also differentiate a third large lineage from the Megalocnoidea . According to the results of the latter two analysis methods,
7406-730: The Upper Pleistocene is much more extensive, coming from more than 100 localities, in California alone Paramylodon is known from more than 60 localities. The distribution of the genus is similar to the Lower Pleistocene, but in addition it occurs somewhat further east in the Midwest , such as in Iowa . The northernmost find of the genus is at Sequim in Washington state at 48.1° north latitude; to
7567-521: The atlatl became widely used, which allowed them to throw spears with greater velocity. These inventions would have allowed hunters to put distance between them and their prey, potentially making it less dangerous to approach ground sloths. Certain characteristics and behavioral traits of the ground sloths made them easy targets for human hunting and provided hunter-gatherers with strong incentives to hunt these large mammals. Ground sloths often fed in open fields. Recent studies have attempted to discover
7728-476: The camel Camelops . In contrast, the two other sloths Megalonyx and Nothrotheriops that also occur in Rancho La Brea play are much less abundant, together accounting for 0.5% of the find record. The age of the Diamond Valley Lake Local Fauna corresponds to that of Rancho La Brea according to radiocarbon datings . Like numerous other animal groups, Paramylodon underwent a marked increase in body size in
7889-473: The zygomatic bone and pointing posteriorly, had three processes, one oriented upward, one downward, and the middle one horizontally. The posterior arch section, attached to the temporal bone , had a finger-like shape and joined the middle process of the anterior arch section. On the underside of the skull, the palatine bone protruded much further posteriorly in Paramylodon than in Glossotherium , caused by
8050-680: The Americas during the Late Pleistocene . Paleontologists assign more than 80 genera of ground sloths to multiple families . The megalonychid ground sloths first appeared in the Late Eocene , about 35 million years ago, in Patagonia. Megalonychids first reached North America by island-hopping, prior to the formation of the Isthmus of Panama . Some lineages of megalonychids increased in size as time progressed. The first species of these were small and may have been partly tree-dwelling, whereas
8211-628: The Mylodontidae is complex and currently under discussion. A relatively wide recognition usually only finds the late development lines with the Mylodontinae and Lestodontinae, as several studies have shown since 2004, but they are sometimes also discussed negatively. However, other lineages associated with the Nematheriinae, the Octomylodontinae, or the Urumacotheriinae, depending on
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#17328595060668372-409: The Mylodontoidea with the two-toed sloths ( Choloepus ) also includes one of the two sloth genera that still exist today. The Mylodontidae form one of the most diverse groups within the sloths. Characteristic features can be found in the high-crowned teeth, which, unlike those of the Megatherioidea and Megalocnoidea, have a rather flat ( lobate ) possess chewing surface. This particular tooth structure
8533-543: 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 (1892-1950), based on his studies of the Rancho La Brea find material, pointed out that the feature of missing upper front teeth
8694-469: The Pacific coast of South America during the late Miocene and Pliocene epochs. Ground sloths, which were represented by over 30 living species during the Late Pleistocene , abruptly became extinct on the American mainland as part of the end-Pleistocene extinction event around 12,000 years ago, simultaneously along with the majority of other large animals in the Americas. Their extinction has been posited to be
8855-517: The Río Yuca Formation and the La Venta material is from today's perspective assigned to different genera, but their assessment of the position of Pseudoprepotherium is based on the characteristics of the femur divided until today. A total of three species of Pseudoprepotherium are currently considered to be valid today: P. venezuelanum is the type species and the smallest representative with
9016-589: The Santa Elina rockshelter in Mato Grosso Brazil, a specimen of Glossotherium is associated with hearths and stone tools, dating to 11,833–11,804 years BP. At Fell's Cave in southern Chilean Patagonia, a specimen of Mylodon with fractured and burned bones associated with human activity has been dated to approximately 12,766–12,354 years BP. Humans are believed to have entered the New World via Beringia ,
9177-620: The Scelidotheriidae. The term Pseudoprepotherium was scientifically introduced in 1961 by Robert Hoffstetter. He mentioned them in a publication of a skeletal description of Planops , a member of the Megatheriidae from the Santa Cruz Formation of Patagonia's Early and Middle Miocene. He also referred to the genus Prepotherium , which also occurs there and is closely related. Both had already been described by Florentino Ameghino at
9338-508: The US state of Florida . Of the latter, noteworthy is the partial skeleton from site Haile 15A, a crevice filled with sediments in the limestone in Alachua County , estimated to be 2.1 to 1.8 million years old. These early representatives are commonly referred to as " Glossotherium" chapadmalensis , although the position within the genus Glossotherium is disputed. Only slightly younger are
9499-692: The Urumaco Formation. The rock strata were formed in what was originally a coastal area under the influence of a river delta. From the entire Urumaco sequence, many sites are documented, the exploration of which began as early as the 1950s. They are distributed over a good 60 different stratigraphic levels. The find material consists mainly of fish, especially sharks and rays. In addition, there are also reptiles such as turtles, crocodilians, and isolated snakes, as well as mammals appearing with rodents, South American ungulates, manatees , and minor jointed animals, among others. The secondary articulated animals show
9660-542: The Urumaco sequence in the Falcón Basin of north-western Venezuela, the chronological range of which includes the Middle and Upper Miocene. However, a 2020 revision of the fossil remains by Ascanio D. Rincón and H. Gregory McDonald led to the dissolution of the genus and relegation to the genus Pseudoprepotherium , largely based on the design of the femur. A third species , named Mirandabradys zabasi by Carlini et al , also from
9821-404: The Urumaco sequence, is considered a nomen dubium because its femur does not show the corresponding diagnostic features of Mirandabradys or Pseudoprepotherium (a femur of Mirandabradys zabasi was originally assigned to the giant Lestodon , which did not occur in northern South America; Carlini et al. 2006 simultaneously removed the femur of Mirandabradys zabasi and reassigned the rest,
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#17328595060669982-674: The Venezuelan state of Falcón . It is composed of the lithostratigraphic units of the Socorro , Urumaco and Codore Formations , with remains of Pseudoprepotherium being limited to the two lower and first-mentioned sequences. The Urumaco sequence covers the period from the Middle Miocene to the Early Pliocene . The main components are different layers of sand, clay, and/or silt and limestone in which individual coal seams are embedded, at least in
10143-411: The a proportion of large predators is low. Thus, an undisturbed character of the faunal community can be inferred. Paramylodon is documented with about 280 individual finds, which represents about 8% of the total mammalian fauna. The ground sloth thus forms the fifth most abundant representative of mammals in the Diamond Valley Lake Local Fauna after bison, horses, the mastodon Mammut pacificus , and
10304-479: The animal. This characteristic is also shared by the South American Mylodon . Paramylodon is abundant in numbers primarily because of the finds from Rancho La Brea in California . The material recovered there from several dozen individuals served as the basis of numerous investigations, on which the following descriptive information is largely based on. This genus was a medium-sized representative of
10465-453: The anterior caniniform teeth and the tooth structure, such as of the second molar, or the position of the bony suture between the palatine bone and the maxilla near the posteriormost tooth. In contrast, Mylodon is more distinctly divergent, with its reduced dentition, more simply designed teeth, and the forward bone junction between the palatine and maxilla. The lower jaw reached lengths of 31.5 to 43.6 centimetres (12.4 to 17.2 in). It
10626-496: The author, are more controversial. The latter, in particular, summarizes the late Miocene representatives of northern South America. In principle, many researchers urge a revision for the entire family since many higher taxonomic units have no formal diagnosis. The position of Pseudoprepotherium within the Mylodontidae is, therefore, ambiguous since the genus is largely defined by the limb bones. Based on their characteristics, phylogenetic analyzes indicate that Pseudoprepotherium
10787-559: The body of their mother for some time following birth, as occurs in living tree sloths. The earliest unambiguous fossil evidence of ground sloths comes from the early Oligocene . Ground sloths had dispersed into the Caribbean already by 31 million years ago, as evidenced by a femur found in Puerto Rico. During the Miocene , sloths diversified, with the major families of sloths appearing during this period, with diversity waxing and waning over
10948-629: The bone platelets of mylodonts were simpler in structure than those of other xenarthrans . Sites and specimen ages (not complete): Paramylodon was endemic distributed in North America and possibly also in Central America . The oldest finds clearly assignable to the genus are known from the Lower Pleistocene . Older forms of mylodonts are from the Upper Pliocene of Mexico and from
11109-422: The calcaneus was in contact with the ground at nearly full length. This is consistent with other mylodonts, but differs greatly from the closely related Scelidotheriidae , which had a highly arched foot with only the posterior end of the calcaneus touching the ground. Another distinctive feature is found in the hind limbs. Here the locomotor system is characterized by an extremely short lower section. In Paramylodon
11270-401: The climate changes that others claim wiped out the ground sloths. Additionally, after the continental ground sloths disappeared, insular sloths of the Caribbean survived for approximately 6,000 years longer, which correlates with the fact that these islands were not colonized by humans until about 5500 yr BP. It is difficult to find evidence that supports either claim on whether humans hunted
11431-471: The course of its phylogeny . The weight of members of the Lower Pleistocene is given as about 915 kg, the late representatives from the Upper Pleistocene, however, probably reached up to 1.39 t body weight. Basis for the respective weight estimates are the femurs , whose corresponding lengths are 48.4 and 54.6 cm, respectively. The earliest forms from the Pliocene , whose position within
11592-797: The course of the Miocene. Megalonychid and mylodontid sloths had migrated into North America by the Late Miocene, around 10 million years ago. At the end of the Miocene, ground sloth diversity declined, though their diversity would remain largely stable throughout the Pliocene and Pleistocene periods, up until their extinction. During the Pliocene and Pleistocene, as part of the Great American Interchange , additional lineages of sloths migrated into Central and North America. Prior to their extinction, there were over 30 living species of ground sloths across
11753-407: The dentition then consisted of only 16 teeth. A similar reduction of teeth is not known in Glossotherium . In Mylodon , on the other hand, the anteriormost teeth in the upper dentition were also no longer developed, but the lower caniniform teeth resembled the posterior molars. The caniniform teeth possessed an oval cross-section in Paramylodon and were curved backward. However, they did not reach
11914-468: The deposition suddenly stopped. Steadman et al. argue that it is no coincidence that studies have shown that ground sloths disappeared from an area a few years after the arrival of humans. Trackways preserved in New Mexico (probably dating from 10 to 15.6 thousand years ago) that appear to show a group of humans chasing or harassing three Nothrotheriops or Paramylodon ground sloths may record
12075-505: The description of the first species, the finds that are now attributed to Paramylodon were repeatedly placed in with other genera, first with Mylodon , but since the 1950s increasingly with Glossotherium . Paramylodon shares numerous features that suggest a close relationship with Glossotherium . Only since the 1990s have both genera been considered distinct, with Glossotherium restricted to South America , while Paramylodon inhabited North America. The species Paramylodon harlani
12236-715: The diet of ground sloths through fossils of their dung. Analysis of these coproliths have found that ground sloths often ate the foliage of trees, hard grasses, shrubs, and yucca; these plants were located in areas that would have exposed them, making them susceptible to human predation. Ground sloths were not only easy to spot, but had never interacted with humans before, so would not have known how to react to them. Additionally, these large mammals waddled on their hind legs and front knuckles, keeping their claws turned in. Their movement and massive build (some weighed up to 3,000 kilograms (6,600 lb)) imply they were relatively slow mammals. These reasonable after-the-fact inferences from
12397-524: The disappearance of ground sloths in what is now the United States at around 11,000 years ago. The Shasta ground sloth ( Nothrotheriops shastensis ) visited Rampart Cave (located on the Arizona side of the Lake Mead National Recreation Area ) seasonally, leaving behind a massive stratified subfossilized dung deposit, and seemed to be flourishing from 13,000 until 11,000 BP, when
12558-487: The distance between the two hip sockets on the pelvis of Paramylodon , as does the stride length of about 146 cm, which in turn corresponds to the known hind leg length of 95 cm. Strikingly, thereby almost exclusively hind footprints have survived, which was initially also interpreted with a bipedal locomotion of the animals, analogous to corresponding trace fossils of Megatherium in South America. However, it
12719-414: The earlier Pliocene -Early Pleistocene ( Blancan ) species Paramylodon garbanii, though the placement of the latter in the genus has been questioned by some authors. The first fossil findings date back to the beginning of the 1830s. They go back to Richard Harlan , in whose honor the species was named. The genus Paramylodon was introduced by Barnum Brown in the early 20th century. Over 150 years after
12880-415: The early humans built corrals when they could procure a young ground sloth, to raise the animal to butchering size. However, radiocarbon dates do not support simultaneous occupation of the site by humans and sloths. Subfossil remains like coproliths, fur and skin have been discovered in some quantities. The American Museum of Natural History has exhibited a sample of Mylodon dung from Argentina with
13041-528: The end of the 19th century using finds from the Santa Cruz Formation. In 1934, R. Lee Collins referred a femur from the Río Yuca Formation on the Río Tucupido near Guanare in the Venezuelan state of Portuguesa to Prepotherium and set up with it the new species Prepotherium venezuelanum . In 1961, Hoffstetter classified this femur as part of the Prepotherium genus based on anatomical differences and established
13202-421: The entire sloth suborder, partially challenged this. In this study Paramylodon and Glossotherium were found to be 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
13363-404: The evidence might explain why ground sloths would have been easy prey for hunters, but are not certain. While ground sloths would have been relatively easy to spot and approach, big game hunters' weapons would have been useless from farther than 9.1 metres (30 ft) away. It would have been difficult to take down a ground sloth with a spear-thrower and would have required extensive knowledge of
13524-470: The exception of the middle region (the dome-like bulge in Glossotherium ), was on average higher, measuring about 13.8 cm at the occiput and 13 cm at the snout. The nasal bone was laterally in contact with the upper jaw. This created a nasal interior that was closed at the sides and open only at the front, becoming about as high as it was wide, which was due to the overall narrower skull. The diastema was, typical of sloths, only loosely connected to
13685-424: The extensive fossil record from the late Pleistocene, two morphotypes can be distinguished in Paramylodon, a graceful variant and a robust variant. The morphotypes are not reflected in the general size of the skulls, but mainly concern their expression, for example in the width ratios. Also, differences can be found, for example, in the occipital bone , which is vertical in the robust variant, but oblique backward in
13846-403: The eyes of 12.2 cm, and at the snout of 14 cm. Typical for numerous mylodonts was the continuously widening snout towards the front. The skull, however, was shown to be altogether much narrower than in the comparably sized Glossotherium , the latter showing a dome-like bulge at the frontal line in side view, which did not occur in Paramylodon . However, the skull of Paramylodon , with
14007-400: The family Mylodontidae . The material documented so far consists mainly of limb bones but includes individual skulls and remains of jaws. Body weight of around 550kg is reconstructed for the smaller relatives using a thigh bone around 42cm long. Large molds with femur lengths of 56 to 59cm are estimated to have weighed between 1.52 and 1.86 tons A surviving skull has a length of 43cm, but
14168-416: The far south of Patagonia ( Cueva del Milodón Natural Monument ) to Alaska . Sloths, and xenarthrans as a whole, represent one of the more successful South American groups during the Great American Interchange after the connection of North and South America during the late Pliocene with a number of ground sloth genera migrating northwards. One genus, Thalassocnus , even adapted for marine life along
14329-584: The few known finds from the state. In general, fossil remains of Paramylodon are very rare on the Colorado Plateau in the southwestern United States and additionally in northwestern Mexico, possibly related to the drier climate in this area at the time. Of outstanding global importance, however, are the finds from the tar pits of Rancho La Brea in southern California. From here comes an extensive fossil fauna ranging in age from 45,000 to 14,000 years before present. The first finds were discovered as early as
14490-512: The finds of the fossil-rich El Gulfo local fauna from the estuary of the Colorado River in the Mexican state of Sonora . They are already placed in Paramylodon and date to 1.8 to 1.6 million years ago. Overall, Lower and Middle Pleistocene fossil remains are relatively rare and come from about 20 localities in North America. These are distributed primarily in the southern and central areas of what
14651-465: The following period. Kraglievich, in the same move, also revised Glossotherium as an independent genus to be distinguished from Mylodon . Glossotherium had also originally been placed by Owen in his 1840 paper on Darwin's discoveries on the basis of a skull fragment from Arroyo Sarandí in southwestern present-day Uruguay , but only two years later he united it with Mylodon . Subsequently, after Kraglievich and Cabrera, Glossotherium evolved into
14812-440: The forward widening snout, the tooth rows diverged from each other. The extensive find material from Rancho La Brea allows a comprehensive reconstruction of the body skeleton. The spine was composed of 7 cervical, 16 thoracic 8 to 9 lumbar, sacral, and 21 caudal vertebrae. The humerus was massive, the length was 46 cm, and the head did not stand out particularly clearly. A prominent bony ridge (deltopectoral groin) attached to
14973-519: The fossil record, they were already distinct at the family level. Sloths dispersed into the Greater Antilles during the Oligocene , and the presence of intervening islands between the American continents in the Miocene allowed a dispersal of some species into North America. They were hardy as evidenced by their high species diversity and their presence in a wide variety of environments, extending from
15134-603: 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 . Subsequently, different type species were assigned to Mylodon , for example, Johannes Theodor Reinhardt in 1879 considered it to be Mylodon robustus , Richard Lydekker in 1887, on
15295-511: The genus Paramylodon , however, is widely discussed, had a total weight of about 310 kg with a femur length of 35.5 cm. Taking these early representatives into account, the weight of Paramylodon increased by a factor of 4.5 over the course of a good 2.5 million years. It is particularly striking that especially in the late Pleistocene at the time of the Last Glacial Period with its extremely pronounced climatic fluctuations, there
15456-470: The genus. Paramylodon measured about 3 metres (9.8 ft) in length with a shoulder height of 1.8 meters and weighed as much as 1.5 metric tons. It is known from North America deposits, including in Mexico and the United States and as far south as Guatemala . Paramylodon exhibits the characteristic of having had dermal ossicles , small bones embedded in the skin, presumably adding a degree of protection to
15617-402: The ground sloths to extinction. Removing large amounts of meat from large mammals such as the ground sloth requires no contact with the bones; tool-inflicted damage to bones is a key sign of human interaction with the animal. A number of kill sites are known for ground sloths in the Americas, these include Campo Laborde in the Pampas of Argentina, where an individual of Megatherium americanum
15778-491: The group are the South American genus Thalassocnus , known for being aquatic, and Nothrotheriops from North America. The last ground sloths in North America belonging to Nothrotheriops died so recently that their subfossil dung has remained undisturbed in some caves. One of the skeletons, found in a lava tube (cave) at Aden Crater , adjacent to Kilbourne Hole , New Mexico , still had skin and hair preserved, and
15939-407: The hand an extremely strong construction, alone the claw process measured here about 8.5 cm at the second and 11.1 cm at the third ray and became in each case 3.3 and 3.9 cm high. The outer rays possessed opposite to this again strongly reduced terminal members. The mylodonts are the only known lineage of sloths whose representatives had bony platelets, so-called osteoderms , formed in
16100-463: The heavily built Megatherium (given its name 'great beast' by Georges Cuvier ) and Eremotherium , which are the largest known ground sloths, thought to have had body masses of 3.5-4 tons. The skeletal structure of these ground sloths indicates that the animals were massive. Their thick bones and even thicker joints (especially those on the hind legs) gave their appendages tremendous power that, combined with their size and fearsome claws, provided
16261-410: The height varied from 2.9 to 5.7 cm. The clawless outer fingers possessed phalanges greatly reduced in size. The foot of Paramylodon had a total of four rays (II to V), the innermost ray was completely reduced. Claws existed here only on toes II and III, which were also the most strongly developed. However, the metatarsals here had rather short lengths of 3.6 and 6.5 cm, respectively, at
16422-557: The help of another partial skeleton from the Niobrara River in Nebraska, but this is also considered a synonym of Paramylodon harlani . The same applies to several species named by Edward Drinker Cope 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 gracile form, as suggested by Chester Stock in 1917,
16583-407: The hind foot to the leg, and similar, permanent bipedality of the large ground sloths is unlikely. The stride length of Paramylodon suggests an average speed of 1.8 to 2.2 m/s, which is similar to the determined speed of Megatherium. Studies of the scapulae of both young and adult individuals show a significant change in shape, from a more rounded form in the former to a largely ovoid form in
16744-1082: The hindfoot is inwardly rotated, meaning sole faces inwards and that the body weight was primarily borne on the fifth metatarsus and the calcaneum . Ground sloths are generally regarded as herbivores, with some being browsers , others grazers , and some intermediate between the two as mixed feeders (both browsing and grazing), though a number of authors have argued that some ground sloths may have been omnivores. Sloths that had longer snouts are presumed to have had greater olfactory acuity, but appear to have also had less binocular vision and poorer ability to localize sounds. A number of extinct sloth species are thought to have had hearing abilities optimized for low frequencies, perhaps related to use of infrasound for communication. Some ground sloths are suggested to have dug burrows . Their skeletal anatomy suggests that they were incapable of running, and relied on other strategies to defend against predators, though they were likely significantly more active and agile than living tree sloths. Ground sloths were likely able to adopt
16905-400: The hindlimbs compared to the upper ones. As a result, the tibia was only half the length of the femur. The proportions are broadly similar to Lestodon , while Glossotherium possessed even shorter lower leg sections. The shaft of the tibia narrowed sharply in the middle while the ends of the joints protruded far. Due to its far northern distribution in South America, Pseudoprepotherium
17066-439: The humeral shaft, but was less prominently developed in the upper part than in Glossotherium . The lower end of the joint protruded widely laterally. An entepicondylar foramen , which occasionally occurred in some sloths, was not developed here. The ulna possessed a greatly expanded superior articular process, the olecranon . It grew to about 20 cm in length, the entire bone reaching 40 cm in length. The construction of
17227-469: The lack of enamel in the teeth of sloths makes comparisons difficult. The graminivorous diet was inferred based on the special tooth formation, analyses of the masticatory apparatus of Paramylodon showed that food was predominantly crushed in forward, backward, and lateral chewing movements, which is also indicated by corresponding grinding marks. This is not contradicted by the caniniform front teeth, which - if formed - are rather small. The mandibular joint
17388-415: The large Megatheriidae and Magdalenabradys , Bolivartherium , Eionaletherium and Urumacotherium from the lineage Mylodontidae and their immediate relatives. As a special circumstance of taphonomy, the frequent tradition of limb elements in sloths is to be evaluated, however, from Pseudoprepotherium also documented remains of the skull. Finds possibly related to Pseudoprepotherium come from
17549-425: The largest, belonging to genera Lestodon , Eremotherium and Megatherium , being around the size of elephants . Ground sloths represent a paraphyletic group , as living tree sloths are thought to have evolved from ground sloth ancestors. The early evolution of ground sloths took place during the late Paleogene and Neogene of South America, while the continent was isolated. At their earliest appearance in
17710-611: The late Pliocene and Pleistocene of North America, although work by McDonald lists five species. Jefferson's ground sloth has a special place in modern paleontology , for Thomas Jefferson 's letter on Megalonyx , read before the American Philosophical Society of Philadelphia in August ;1796, marked the beginning of vertebrate paleontology in North America. When Lewis and Clark set out, Jefferson instructed Meriwether Lewis to keep an eye out for ground sloths. He
17871-434: The lateral edges were rather straight and less distinctly curved than in the latter. The width of the symphysis in the anterior region was up to 15 cm. The articular process protruded only slightly above the masticatory plane, and the coronal process was much higher. Its anterior edge ran in a straight line in Paramylodon , deviating from the curved design in Glossotherium . The dentition consisted, as generally usual with
18032-553: The latter. The ontogenetic overprinting are comparable to those of present-day arboreal sloths. The similarity of the shoulder blades of the young representatives of Paramylodon and the young of present-day sloths suggests comparable behaviors. Accordingly, the young of Paramylodon still had various climbing abilities and possibly clung to their mothers during transport. Mylodonts are generally considered to be grazers (graminivores) based on their high-crowned teeth with flat chewing surfaces, similar to those of modern grazers. However,
18193-417: The longer extension of the bone behind the last molar. As in many mylodonts, both flanks of the wing bones were distinctly inflated. In Paramylodon , however, this was not quite as evident as in Glossotherium , so the distended structures were much further apart through the basal phenoid of the sphenoids . Features that link Glossotherium and Paramylodon include, for example, the dentition structure with
18354-404: The lower section of the hind leg often reached only about half the length of the upper. In the case of Paramylodon , the tibia had 45% of the femur length. Its shaft was flattened like that of the femur and likewise exhibited a slight twist. The upper end of the joint was laterally projecting, the width here reaching about three-quarters of the length of the total bone. The fibula was not fused to
18515-405: The lower section reaches less than 50% of the upper. Such a construction plan, exhibited by nearly all mylodonts, suggests a rather slow and cumbersome locomotion. In comparison, the megatherians had significantly longer lower limb sections. Trace fossils that provide evidence of ground sloth locomotion are rarely preserved. For Paramylodon , such definite stepping seals have been demonstrated at
18676-402: The main load when the foot is placed on the outer ray (V). This results in the pedolateral gait characteristic of numerous ground sloths, which required significant restructuring in the shape and bearing of the tarsal bones relative to each other, especially in the talus and calcaneus . In Paramylodon , the outer edge of the foot was little arched up, forming a more or less straight edge, and
18837-409: The more graceful. Thus the joint surfaces for the attachment of the cervical spine are more prominently emphasized in the latter than in the former. Further deviations are found in the formation of the caniniform teeth which, if present, end pointedly in robust individuals, but bluntly in gracile ones. Possibly the two morphotypes are not species or taxonomic variations in the sense of subspecies, as it
18998-590: 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 in the Argentina Buenos Aires province. As a special characteristic, a total of four molar-like teeth per tooth row stood out. At
19159-463: 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
19320-435: The natural traps themselves. Among the sloths, Paramylodon , Megalonyx , and Nothrotheriops are three of the four genera recorded in North America, with Eremotherium being known only from the eastern part of the United States. However, Paramylodon represents by far the most abundant ground sloth at La Brea with over 70 individuals, and 30 skulls alone are notable among the finds. Another very extensive fossil complex
19481-433: The other hand, considered it to be Mylodon harlani . Within the genus Paramylodon , only one species , P. harlani , is recognized. Another species, P. nebrascensis , was described in 1903 by Barnum Brown on the basis of a partial skeleton from Hay Spring in Nebraska , but was already synonymised with the type species in the 1920s. Only ten years later, Glover Morrill Allen created the species Mylodon garmani with
19642-409: The outer rays they became over 11.0 cm long each and were very massive. As in the other two mylodonts, the second ray had only two phalanges, as the first and second phalanx were fused into one unit corresponding to the hand. Deviating from Glossotherium and Lestodon , the third ray of Paramylodon also often consisted of only two limbs. The respective end phalanges with claws showed analogous to
19803-417: The ratio is 3:0. It is noteworthy here that sexual dimorphism is not reflected in the postcranial skeleton and thus, as noted earlier with the skull, no size dimorphism occurs in the form of significant length differences in limb bones. In contrast, Eremotherium , which was also common in North America at the same time but belongs to the Megatheriidae , is known to have a pronounced size difference between
19964-535: The result of hunting by recently arrived humans and/or climate change. A number of kill sites are known where humans butchered ground sloths dating just prior to their extinction. The Caribbean ground sloths , the most recent survivors, lived on Cuba and Hispaniola , possibly until 1550 BCE. However, radiocarbon dating suggests an age of between 2819 and 2660 BCE for the last occurrence of Megalocnus in Cuba . They survived 5,000–6,000 years longer in
20125-524: The same site. In total, numerous tracks of other mammals - such as mammoths , horses , moose , as well as predators - and additionally of birds have been discovered at Carson City in addition to Paramylodon . The stepping seals are distributed over an area of about 8000 m, they are today largely covered by the prison construction, but well documented by casts. A total of ten tracks could be observed from Paramylodon , consisting of 15 to 20 individual alternately impressed tracks. Each individual footprint
20286-515: 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 . The genus name Paramylodon is composed of the Greek παρα (para meaning "beside" or "near"), μύλη ( myle " molar ") and ὀδούς ( odoús "tooth"), thus translates as "molar tooth". Harlan commented two years later on
20447-560: The scene of a hunt. The tracks are interpreted as showing seven instances of a sloth turning and rearing up on its hind legs to confront its pursuers, while the humans approach from multiple directions, possibly in an attempt to distract it. Those who argue in favor of humans being the direct cause of the ground sloths' extinction point out that the few sloths that remain are small sloths that spend most of their time in trees, making it difficult for them to be spotted. Although these sloths were well hidden, they still would have been affected by
20608-411: The second half of the 19th century, but the far more significant material is due to focused scientific investigations in the early 20th century, including a total of over 100 documented sites. A striking feature of the faunal spectrum is the unusual dominance of predators over herbivores. Most likely, the predators were attracted in greater numbers by animals stuck in the asphalt and then fell victim to
20769-431: The second maxillary molar, the lobe-like structure was much more prominent than in Glossotherium . All teeth typically lacked enamel , instead consisting of a harder variant of dentin ( orthodentin ), with an additional outer layer of dental cement. The proportion of orthodentine reached 28% in Paramylodon. The upper row of teeth averaged 14.4 cm in length, of which the posterior molars occupied 12.6 cm. Due to
20930-410: The sexes. In general, a quadrupedal locomotion is assumed for the ground-dwelling sloths. However, due to the body's center of gravity being shifted far to the rear, it was obviously also possible for them to change to a bipedal position, while being able to support themselves with the powerful - in contrast to today's tree sloths - very long tail. The hind foot of Paramylodon is turned inward, so that
21091-480: The size as in Glossotherium or even in Lestodon . A short diastema existed to the posterior row of teeth. The molar-like molars had a flat shape with a somewhat raised margin. They possessed a bilobed shape in outline with strong median constriction, except for the first maxillary molar, which was more rectangular in shape and formed the longest tooth in the maxilla with an average length of 3.7 cm (1.5 in) In
21252-405: The skin, analogous to today's armadillos . Unlike the latter, however, they did not form a solid bony armor in mylodonts, but were rather loosely scattered, as shown by finds of skin remains of Mylodon. Several hundred osteoderms of Paramylodon are known from Rancho La Brea, in addition, among others, also as a dense layer on a slab from Anza-Borrego State Park in California and from Haile 15A,
21413-400: The sloths, of 5 teeth per upper jaw half and 4 teeth per lower jaw half, thus altogether 18 teeth were formed. The front teeth had a canine -like (caniniform) shape, the others were molar-like (molariform). The dentition structure is considered phylogenetically primitive within the sloths. However, in later representatives of Paramylodon the upper caniniform teeth were often reduced, so that
21574-539: The slow-moving giant sloths were likely easy prey for early humans possibly hurling spears. Pseudoprepotherium Pseudoprepotherium is an extinct genus of sloths of the family Mylodontidae . It was widespread across northern South America during the Early to Late Miocene epoch around 21 to 5.3 million years ago. Fossils of the animal have been found in Brazil , Venezuela , and Peru . Pseudoprepotherium lived in
21735-568: The south, the genus is also known from across Mexico. Some finds now indicate that Paramylodon may also have lived in Guatemala and El Salvador . Among others, finds of a juvenile and an adult individual were recovered from Stevenson Bridge in stream deposits of Putah Creek in Yolo County of California, dating to the beginning of the Last Glacial Period . Two nearly complete skeletons have been reported from Shonto and Richville in Arizona , among
21896-466: The southern U.S. about 9 million years ago and is believed to have been the predecessor of Megalonyx . Several species of Megalonyx have been named; in fact it has been stated that "nearly every good specimen has been described as a different species". A broader perspective on the group, accounting for age, sex, individual and geographic differences, indicates that only three species are valid ( M. leptostomus , M. wheatleyi , and M. jeffersonii ) in
22057-767: The species. Additionally, the ground sloths' already thick hide was fortified by osteoderms , making it difficult to penetrate. Since ground sloths thrived in an environment filled with large predators, they evidently would have been able to also defend themselves against human predation, so there is no reason to expect that they would have been "easy pickings". When feeding, they had enough strength to use their long, sharp claws to tear apart tree branches; presumably their strength and formidable claws would be dangerous for hunters that attempted to attack them at close quarters. But fossilized evidence of humans hunting on ground sloth in White Sands National Park suggests that
22218-457: The spherical condyle and the greater trochanter. The great calculus was massive but not very elevated. Its apex was at or slightly below the level of the condyle and thus lower as compared to Magdalenabradys . The lesser trochanter was only weakly developed. The third trochanter appeared as a slight bulge around the middle of the shaft and continued as an edge to the lower end of the joint. The position roughly matched that of Magdalenabradys , but
22379-514: The structure of the femur, Rincón and McDonald reclassified the 2020 form as the type species of the new genus Magdalenabradys . So far , Pseudoprepotherium has only been found in the northern part of South America. The genus defining fossil remains came to Taqe in the Río Yuca Formation on the Río Tucupido about 11km west-southwest of Guanare in the Venezuelan state of Portuguesa . It
22540-404: 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. Detailed morphological analyses published as early as 2009 by Robert K. McAfee also suggest that Paramylodon and Glossotherium are very closely related and share a close common ancestor. Below
22701-545: The third to fifth rays were massive and over 10 cm long, with that of ray IV possessing the most robust construction. At the finger ray I the first two phalanges were additionally intergrown, at the rays II and III existed in each case three phalanges, of which the first two showed however clearly reduced lengths. The respective end members of the three inner rays had extended claw processes, which suggests correspondingly large claws. The length ranged from inner (I) to outer (III) from 7.5 cm to 15.4 cm to 17.4 cm,
22862-519: The tibia, reaching 26.3 cm in length. Hands and feet showed a similar structure as in the other large mylodonts Glossotherium and Lestodon , deviations are present in detail. The hand exhibited a total of five rays (I to V), with only the three inner rays (I to III) having developed claws. The metacarpal of the first ray was fused with the polygonal bone to form a single unit, which is frequently attested in ground-dwelling sloths (so-called metacarpal carpal complex or MCC). The metacarpal bones of
23023-401: The two front teeth are poorly preserved. From the alveoli, it can be seen that the rearmost tooth was the smallest and possibly had two lobes (bilobate). The fourth and third teeth were each elongated. As is usual in the Mylodontidae, the femur stood out due to its flat, board-like shape in front and behind. The shaft was slightly curved at the side. There was only a shallow indentation between
23184-422: The two genera are actually synonymous. In fact, the presence of Paramylodon in North America would rather distinguish it from Glossotherium , which is, in turn, only known from South America. In the following time several skull studies could be presented, which clearly distinguished the two genera and plus Mylodon from each other. Some recent studies have questioned the attribution of the species P. garbanii to
23345-421: The ulna appeared shorter and more robust than in Glossotherium , the shaft was broad and narrowed above anteriorly and posteriorly. Likewise, the radius was short and massive with a length of 29.6 cm. The longest bone was represented by the femur at around 54.6 cm. Very short specimens from Rancho La Brea measured only 51 cm, very long 58 cm. The flat and broad design typical of ground sloths
23506-464: The upper jaw. At the frontal bone , the nasal bone protruded far back, so that the suture between the two skull bones was rather V-shaped. In addition, the frontal bone represented the largest bone of the entire skull. A strong parietal crest existed between the parietal bones , but it appeared much narrower than compared to Glossotherium . The zygomatic arches were secondarily closed again, deviating from most sloths. The anterior arch, originating at
23667-499: 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. 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 north of Buenos Aires ; he established for it the new species Mylodon robustus . At this point, then,
23828-639: The western Amazon basin and date to the Middle to Upper Miocene. They are part of many fossil remains from numerous local sites spread over a large area. Significant find areas are on the Río Sepa and the Río Inuya, which flow into the Río Urubamba in central Peru. From here, the find area extends eastward to western Brazil and northern Bolivia and northward to the Iquitos region of northern Peru. The found material belongs to
23989-606: Was a widespread North American genus that lived past the close of the last (Wisconsin) glaciation , when so many large mammals died out. Remains have been found as far north as Alaska and the Yukon . Ongoing excavations at Tarkio Valley in southwestern Iowa may reveal something of the familial life of Megalonyx . An adult was found in direct association with two juveniles of different ages, suggesting that adults cared for young of different generations. The earliest known North American megalonychid, Pliometanastes protistus , lived in
24150-486: Was already known from North America at the time, and within the genus to the species Megalonyx laqueatus that he had established shortly before. The finds were originally preserved in New York, but are now lost. Between the years 1831 and 1836, Charles Darwin made his pioneering voyage on HMS Beagle to South America and brought back from there a large number of fossils. These were then studied by Richard Owen , one of
24311-634: Was among the few sloth forms that occurred in South and North America, but it also possessed high variability as a result. Numerous researchers during the 20th century favored the view of the synonymy of the two sloth genera. In 1995, however, H. Gregory McDonald again separated the North American Paramylodon from the South American Glossotherium . In doing so, he noted that there have been no studies to date that have demonstrated that
24472-404: Was butchered at the edge of a swamp, dating to approximately 12,600 years Before Present (BP), with another potential Megatherium kill site being Arroyo Seco 2 in the same region, dating to approximately 14,782–11,142 cal yr BP. In northern Ohio, a Megalonyx jeffersoni skeleton dubbed the "Firelands Ground Sloth" has cut marks indicative of butchery, dating to 13,738 to 13,435 years BP. At
24633-434: Was characterized by an elongate skull, a short neck, a short and compact body with a broad pelvis, and strong limbs and tail. The skull of Paramylodon was long and narrow. It reached a typical total length of 42.9 to 49.8 cm (0.429 to 0.498 m). A particularly large skull measured 54.0 cm. In plain view, it possessed a rather rectangular shape with an average width at the occipital bone of 18.8 cm, behind
24794-407: Was demoted in 1995 to the subfamily Scelidotheriinae within Mylodontidae. Based on collagen sequence data showing that its members are more distant from other mylodontids than Choloepodidae , it was elevated back to full family status in 2019. Together with Mylodontidae, the enigmatic Pseudoprepotherium and two-toed sloths , the scelidotheriids form the superfamily Mylodontoidea. Chubutherium
24955-423: Was determined that the individual tread seals of the hind feet overlapped those of the forefeet. Because the anterior foot is much smaller than the posterior and sets on differently, it produces a much smaller impression. In individual cases, footprints have been preserved which show that the forefoot is covered by the hindfoot. For anatomical reasons, such as the bent legs when walking, the position and orientation of
25116-468: Was hoping they would find some living in the Western range. Megalonyx jeffersonii was appropriately named after Thomas Jefferson. The megatheriid ground sloths are relatives of the megalonychids; these two families, along with the family Nothrotheriidae, form the infraorder Megatheria . Megatheriids appeared later in the Oligocene, some 30 million years ago, also in South America. The group includes
25277-406: Was lower than that of Eionaletherium . The lower end of the joint was partially rotated out of the shaft axis. The inner articulated roller became larger than the outer. The lower one was somewhat narrower than the upper end of the joint. A tibia associated with a femur about 56cm long measured 29cm in length. This corresponds to the ratio known in other mylodons of extremely short lower sections of
25438-475: Was massively built and broad. The horizontal bone body continuously increased in height from anterior to posterior, and below the posteriormost tooth its height was up to 10.5 cm. The robust symphysis grew up to 11 cm (4.3 in) and was typical for mylodonts. It extended forward, which is a characteristic of almost all sloths. This spoon-like extension of the symphysis did not project laterally as distinctly in Paramylodon as in Glossotherium , so that
25599-610: Was originally assumed, because they often occur at one and the same locality. Rather, they are more an expression of intraspecific sexual dimorphism . However, it is currently impossible to assign a morphotype to a specific sex. In the 30 known skull finds from Rancho La Brea, the ratio of robust to gracile is 3:1; at the Americas Fall Reservoir in Idaho, with three skulls, the ratio is 2:1; and at Ingleside in Texas , also with three skulls,
25760-476: Was probably more adapted to tropical climate conditions. The find locations in the deposit units of the Urumaco sequence also speak in favor of this. A possibly related Pseudoprepotherium tibia from the Middle Miocene Pebas Formation near Iquitos in the western Amazon Basin, about 23 cm long, shows more than 60 bite marks, the size and arrangement of which suggest that they were probably caused by
25921-461: Was striking, so that the bone appeared almost board-like. The head rose only slightly from the surface and had a more inward position. The shaft was slightly turned inward, and a third trochanter as a muscle attachment point, which appeared in Lestodon , was not visible in Paramylodon . With a length of 24.6 cm, the tibia was significantly shorter than the femur. This is a typical feature of mylodonts, in whose predominantly late representatives
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