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130-507: Eremotherium (from Greek for "steppe" or "desert beast": ἔρημος "steppe or desert" and θηρίον "beast") is an extinct genus of giant ground sloth in the family Megatheriidae . Eremotherium lived in southern North America, Central America, and northern South America from the Pliocene , around 5.3 million years ago, to the end of the Late Pleistocene , around 10,000 years ago. Eremotherium

260-502: 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,

390-439: A lateral and medial border . These three bordes separates the shaft into three surfaces: One anterior , one medial and one lateral. Due to the vast musculature of the thigh the shaft can not be palpated . The third trochanter is a bony projection occasionally present on the proximal femur near the superior border of the gluteal tuberosity. When present, it is oblong, rounded, or conical in shape and sometimes continuous with

520-455: 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

650-513: 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

780-404: A collection that included fossils of several other Pleistocene megafauna like mammoths and bison . These were all described in more detail by Joseph Leidy in 1855, but they were not all referred to Eremotherium until the late 20th century. In 1842, Richard Harlan named a new species of the turtle Chelonia, Chelonia couperi , based on a supposed femur , or thigh bone, that had been found in

910-449: A far outward curved shape, which was partly caused by the large cranial cavity with a volume of 1600 cm³. The strong zygomatic arch was closed, unlike today's sloths, but like the latter it had a massive bony outgrowth pointing downwards and backwards from the anterior base of the arch. In addition, a third outgrowth protruded diagonally upwards. The downward pointing bony process was clearly steeper than in other sloths. The eye socket

1040-475: 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

1170-623: A fragmentary left femur, as a new species of the South American Scelidotherium , naming it S. guanajatense. The femur had been found in Pleistocene deposits in Guanajuato , Mexico, but the fossil has since been lost and the species is a synonym of E. laurillardi. Another species that is currently considered valid was described in 1997 by Canadian zoologist Gerardo De Iuliis and French paleontologist Pierre-Antoine St-Andréc based on

1300-417: A juvenile of E. laurillardi and adults reached or exceeded the size of M. americanum . Two years earlier, Lund had already figured teeth found at Lapa Vermella, which he assigned to Megatherium americanum due to their dimensions, which he figured alongside those of M. laurillardi in the 1842 publication. They also have been referred to Eremotherium laurillardi . For many years, E. laurillardi 's holotype

1430-405: 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

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1560-442: A partial skeleton, the holotype , that had been unearthed from the latest Blancan ( Latest Pliocene ) layers of Newberry , Florida , USA, though many other fossils from the area were referred to it. Many of the fossils were isolated and had been recovered from sinkholes, river canals, shorelines, and hot springs, with few of the specimens being associated skeletons. So far, the latter has only been found in North America and reached

1690-590: A single, approximately 39 cm long femur from the Pleistocene strata in Ulloma , Bolivia as Eremotherium sefvei, though it was first described in 1915 as a fossil of Megatherium . E. sefvei 's geologic aging is less definite can only be placed in the general Pleistocene, but it is the smallest representative of Eremotherium and all post-Miocene megatheriids. Two years later in 1999, De Iuliis and Brazilian paleontologist Carlos Cartelle erected another species of Eremotherium now seen as valid, E. eomigrans , based on

1820-494: A size similar to E. laurillardi , but comes from the Pliocene and Early Pleistocene and bares a pentadactyl, or five fingered, hand in contrast to the tridactyl hands of Megatherium and E. laurillardi . The genus name Eremotherium was not erected until 1948 by Franz Spillmann, erecting a new species, E. carolinese , as the type species of the genus based on a 65 cm long skull with associated lower jaw, both fossils come from

1950-489: 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

2080-576: 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 the Pacific coast of South America during the late Miocene and Pliocene epochs. Ground sloths, which were represented by over 30 living species during

2210-413: Is genu varum (bow-leggedness) . In the general population of people without either genu valgum or genu varum , the femoral-tibial angle is about 175 degrees. The femur is the largest and thickest bone in the human body. By some tested measures, it is also the strongest bone in the human body, whereas other strength tests show the temporal bone to be the strongest bone. The femur length on average

2340-425: Is 26.74% of a person's height, a ratio found in both men and women and most ethnic groups with only restricted variation, and is useful in anthropology because it offers a basis for a reasonable estimate of a subject's height from an incomplete skeleton . The femur is categorised as a long bone and comprises a diaphysis (shaft or body ) and two epiphyses (extremities) that articulate with adjacent bones in

2470-405: Is a deep depression bounded posteriorly by the intertrochanteric crest on the medial surface of the greater trochanter. The lesser trochanter is a cone-shaped extension of the lowest part of the femur neck. The two trochanters are joined by the intertrochanteric crest on the back side and by the intertrochanteric line on the front. A slight ridge is sometimes seen commencing about the middle of

2600-403: Is also often absent in mammals or alternatively reduced to a series of creases along the surface of the bone. Structures analogous to the third trochanter are present in mammals, including some primates. Some species of whales , snakes , and other non-walking vertebrates have vestigial femurs. In some snakes the protruding end of a pelvic spur , a vestigial pelvis and femur remnant which

2730-825: 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

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2860-436: Is attached to the lower and front part of the medial wall of the fossa and the anterior cruciate ligament to an impression on the upper and back part of its lateral wall. The articular surface of the lower end of the femur occupies the anterior, inferior, and posterior surfaces of the condyles. Its front part is named the patellar surface and articulates with the patella ; it presents a median groove which extends downward to

2990-482: Is exclusively known from Florida, dating to the late Pliocene. Eremotherium sefvei is only known from a single femur found in Bolivia of an uncertain age, while Eremotherium laurillardi is known from numerous fossils spanning from the late Pliocene to the end of the Pleistocene. The range distribution of Eremotherium laurillardi is the widest of any ground sloth, spanning from 30.5° S to 40.3°N. The northernmost record of

3120-474: Is greater than its antero-posterior (front to back). It consists of two oblong eminences known as the condyles . Anteriorly, the condyles are slightly prominent and are separated by a smooth shallow articular depression called the patellar surface. Posteriorly, they project considerably and a deep notch, the Intercondylar fossa of femur , is present between them. The lateral condyle is the more prominent and

3250-606: Is known. Eremotherium is a genus of the extinct ground sloth family Megatheriidae, which includes large to very large sloths in the group Folivora, which, together with the Megalonychidae and the Nothrotheriidae, form the superfamily Megatherioidea. The Megatherioidea also includes the three-toed sloths of the genus Bradypus , one of the two sloth genera still alive today. Eremotherium 's closest relative in Megatheriidae

3380-458: Is not connected to the rest of the skeleton, plays a role in mating. This role in mating is hypothesized to have possibly occurred in Basilosauridae , an extinct family of whales with well-defined femurs, lower legs and feet. Occasionally, the genes that code for longer extremities cause a modern whale to develop miniature legs ( atavism ). One of the earliest known vertebrates to have a femur

3510-742: 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

3640-430: Is quite rough due to attachment of muscles and the hip joint capsule . Here the two trochanters , greater and lesser trochanter , are found. The greater trochanter is almost box-shaped and is the most lateral prominent of the femur. The highest point of the greater trochanter is located higher than the collum and reaches the midpoint of the hip joint . The greater trochanter can easily be felt. The trochanteric fossa

3770-414: Is slightly arched, so as to be convex in front, and concave behind, where it is strengthened by a prominent longitudinal ridge, the linea aspera which diverges proximally and distal as the medial and lateral ridge. Proximally the lateral ridge of the linea aspera becomes the gluteal tuberosity while the medial ridge continues as the pectineal line . Besides the linea aspera the shaft has two other bordes;

3900-510: Is suggested to have been capable of adopting a bipedal posture to feed on high-growing leaves. Finds of Eremotherium are common and widespread, with fossils being found as far north as South Carolina in the United States and as far south as Rio Grande Do Sul in Brazil, and many complete skeletons have been unearthed. Only two valid species are known, Eremotherium laurillardi and E. eomigrans,

4030-547: Is the Eusthenopteron , a prehistoric lobe-finned fish from the Late Devonian period. A recent study revealed that bone is a much richer source of persistent DNA viruses than earlier perceived. Besides Parvovirus 19 and hepatitis B virus, ten additional ones were discovered, namely several members of the herpes- and polyomavirus families, as well as human papillomavirus 31 and torque teno virus. In invertebrate zoology

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4160-404: Is the broader both in its antero-posterior and transverse diameters. The medial condyle is the longer and, when the femur is held with its body perpendicular, projects to a lower level. When, however, the femur is in its natural oblique position the lower surfaces of the two condyles lie practically in the same horizontal plane. The condyles are not quite parallel with one another; the long axis of

4290-512: Is the namesake of the family Megatherium , which was endemic to South America, slightly larger, and preferred more open habitats than Eremotherium . Pyramiodontherium and Anisodontherium are also part of this subfamily, but are smaller and older, dating to the Late Miocene of Argentina. All of these genera belong to the subfamily Megatheriinae , which includes the largest and most derived sloths. The direct phylogenetic ancestor of Eremotherium

4420-653: Is unknown, but may be linked to Proeremotherium from the Codore Formation in Venezuela, which dates to the Pliocene. The genus has numerous characteristics that are akin to those of Eremotherium , but are more primitive. Little is known about the evolution of the genus Eremotherium . It may have evolved in the Early Pliocene in South America, where only a few sites from this period are known, and dispersed by crossing

4550-641: 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 the far south of Patagonia ( Cueva del Milodón Natural Monument ) to Alaska . Sloths, and xenarthrans as

4680-535: 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 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 ,

4810-446: 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",

4940-482: The Quaternary Extinction Event , which saw the arrival of humans in the Americas and the extinction of many megafauna, large or giant animals of an area, habitat, or geological period, extinct and/or extant that were larger than or a comparable size to humans, such as mammoths , glyptodonts , and other ground sloths. One of the latest finds of Eremotherium is from Ittaituba on Rio Tapajós, a tributary of

5070-559: The Santa Elena in Ecuador with 22 individuals, some scientists discuss whether Eremotherium possibly lived and roamed in small, herd-like groups. Especially in Tanque Loma, the individuals recorded are composed of at least 15 adults and six juveniles. They were all found in close association in a single horizon, and they are interpreted as being contemporary with each other. The possible group

5200-569: The Santa Elena Peninsula in Ecuador, and the species name was after the local village of Carolina. Although it was the type species of the genus for many years, the species has since been synonymized with E. laurillardi and has been replaced by it as the type species. The generic name Eremotherium is derived from the Greek words ἔρημος (Erēmos "Steppe", "desert") and θηρίον (Thērion "animal") after

5330-451: The adductor crest . The neck of the femur is generally minimal or absent in the most primitive forms, reflecting a simple attachment to the acetabulum. The greater trochanter was present in the extinct archosaurs , as well as in modern birds and mammals, being associated with the loss of the primitive sprawling gait. The lesser trochanter is a unique development of mammals, which lack both the internal and fourth trochanters. The adductor crest

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5460-521: 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

5590-503: The carpus , such as the trapezium , to form a unit, the metacarpal-carpal complex (MCC). Thus, Eremotherium clearly deviates from Megatherium and other closely related forms, which possessed four-fingered hands. In Eremotherium , the metacarpal of the third digit was the shortest, measuring 19 cm in length, while those of the fourth and fifth were almost the same length, 28 centimetres (11 in) and 27.5 centimetres (10.8 in) respectively. The phalanx (the third phalanx) of

5720-432: The intercondyloid fossa and two convexities, the lateral of which is broader, more prominent, and extends farther upward than the medial. Each condyle is surmounted by an elevation, the epicondyle . The medial epicondyle is a large convex eminence to which the tibial collateral ligament of the knee-joint is attached. At its upper part is the adductor tubercle and behind it is a rough impression which gives origin to

5850-403: The knees , where they articulate with the proximal ends of the tibiae . The angle of convergence of the femora is a major factor in determining the femoral-tibial angle . Human females have thicker pelvic bones , causing their femora to converge more than in males. In the condition genu valgum (knock knee) the femurs converge so much that the knees touch one another. The opposite extreme

5980-454: The round ligament to the sides of the acetabular notch . The head of the femur is connected to the shaft through the neck or collum . The neck is 4–5 cm. long and the diameter is smallest front to back and compressed at its middle. The collum forms an angle with the shaft in about 130 degrees. This angle is highly variant. In the infant it is about 150 degrees and in old age reduced to 120 degrees on average. An abnormal increase in

6110-427: The spoke measuring about 67 cm, and the ulna 57 centimetres (22 in) in length. Massive was the femur , which had the broad build characteristic of megatherians and was narrowed in front and behind. It had an average length of 74 cm, the largest bone found so far was 89.5 centimetres (35.2 in) long and 45.1 centimetres (17.8 in) wide. The third trochanter, a prominent muscle attachment point on

6240-595: The Amazon, that has an uncalibrated C14 date to 11,340 BP (13,470 – 13,140 calibrated) and includes several skull and lower jaw fragments. In a similar period, the finds at Barcelona in the Brazilian state of Rio Grande do Norte come from strata dating from 11,324 to 11,807 years ago. There is no direct evidence of hunting by humans of Eremotherium . A possible indication of interaction is a tooth of Eremotherium that some authors have suggested had been modified by Paleoindians, which

6370-680: 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

6500-456: The BIR. These documented ailments include osteoarthritis and articular depressions, with spondyloarthropathy and calcium pyrophosphate deposition disease potentially present as well. These diseases are evidenced by the presence of osteophytes, bone overgrowth, bone erosion, and rough subchondral bone in various specimens. E. laurillardi is also the only xenarthran species from which linear defect

6630-561: The Brunswick Canal in Glynn County , Georgia and dated to the Pleistocene. It was not until 1977 that further analysis demonstrated that the "femur" was actually a clavicle from Eremotherium . It is unknown, which publication was published first - according to the regulations of the ICZN, the species name of the first publication would have priority, even if it was attached to another genus - but

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6760-467: 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 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

6890-683: The Isthmus of Panama, i.e. the formation of the land bridge connecting North and South America, in the course of the Great American Biotic Interchange. The oldest fossils come from the Pliocene of the southern United States in North America, suggesting that the species instead evolved there before colonizing South America. The discovery of Proeremotherium also supports this hypothesis, indicating that these or other close ancestors of Eremotherium first migrated to North America and evolved there, then moved back southward to South America after

7020-603: The Late Pleistocene (34,705-33,947 cal yr BP ), of Goiás , Brazil, was a mixed feeder, suggesting a high proportion of shrubs and trees, this is in contrast to the presumed diet from specimens from Northeast Brazil , which had a diet of C4 herbaceous plants. A 2020 discovery in Ecuador found 22 individuals ranging in age from juveniles to adults preserved together in anoxic marsh sediments, suggesting that Eremotherium may have been gregarious. Numerous palaeopathologies have been described from E. laurillardi fossils in

7150-589: 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 ,

7280-517: The United States. The fossils were not described until 1852 however, when American paleontologist named Megatherium mirabile , based on the specimens (specimen numbers USNM 825-832 + 837) but the species has since been synonymized with Eremotherium laurillardi . The first published discovery was only a year after M. mirabile was discovered, when portions of 2 teeth that had been also collected from Skidaway Island were referred to Megatherium later in 1823 by Dr. Samuel L. Mitchell. 20 more fossils from

7410-400: The angle is known as coxa valga and an abnormal reduction is called coxa vara . Both the head and neck of the femur is vastly embedded in the hip musculature and can not be directly palpated . In skinny people with the thigh laterally rotated, the head of the femur can be felt deep as a resistance profound (deep) for the femoral artery . The transition area between the head and neck

7540-510: 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

7670-401: 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

7800-623: 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

7930-468: 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

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8060-715: 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

8190-410: The different length of the teeth. In Eremotherium this caused the lower jaw to be 14.5 centimetres (5.7 in) deep below the symphysis, 15 cm below the second tooth and 12.5 cm below the fourth. The thickness of the curvature of the lower margin of the mandible increased significantly in the course of individual development, but the ratio of the height of the mandibular body to the length of

8320-563: The dimensions of those of Megatherium . As the teeth lack enamel , this hypsodonty may not be an expression of specialisation on grass as food, unlike mammals with enamel in their teeth. The different expression of high-crownedness in the two large ground sloths is probably rather to be sought in adaptation to divergent habitats—more tropical lowlands in Eremotherium and more temperate regions in Megatherium . From an anatomical point of view,

8450-524: 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

8580-415: 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

8710-404: 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

8840-414: The femur as an axis, and are separated by tough connective tissue membranes (or septa ). Each of these compartments has its own blood and nerve supply, and contains a different group of muscles . These compartments are named the anterior , medial and posterior fascial compartments . A femoral fracture that involves the femoral head , femoral neck or the shaft of the femur immediately below

8970-444: The first hyaline cartilage model of the femur is formed by chondrocytes . Endochondral ossification begins by the end of the embryonic period and primary ossification centers are present in all long bones of the limbs, including the femur, by the 12th week of development. The hindlimb development lags behind forelimb development by 1–2 days. As the femur is the only bone in the thigh, it serves as an attachment point for all

9100-498: The formation of the Isthmus of Panama, similar to the glyptodont Glyptotherium . The following phylogenetic analysis of Megatheriinae within Megatheriidae was conducted by Brandoni et al., 2018 that was modified from Varela et al. 2019 based on lower molariform and astragalus morphology: Megathericulus Diabolotherium Anisodontherium Pyramiodontherium Proeremotherium Megatherium Eremotherium The disappearance of Eremotherium coincides with

9230-623: The former was named by prolific Danish paleontologist Peter Lund in 1842 based on a tooth of a juvenile individual that had been collected from Pleistocene deposits in caves in Lagoa Santa , Brazil alongside fossils of thousands of other megafauna. Lund originally named it as a species of its relative Megatherium , though Austrian paleontologist Franz Spillman later created the genus name Eremotherium after noticing its distinctness from other megatheriids. The taxonomic history of Eremotherium largely involves it being confused with Megatherium and

9360-637: The front area of the tail suggest a strong musculature. Among other things, this concerns the coccygeus muscle , which attaches to the ischium and fixes the tail. Less well developed, on the other hand, were the epaxial muscles, which could cause the tail to straighten up. Due to some group finds of several individuals at individual sites, such as in El Bajión in Chiapas in Mexico with four animals or in Tanque Loma on

9490-467: 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),

9620-584: The genus in North America north of Mexico are confined to the Gulf Coast and Southern Atlantic Coast , including Texas , Florida, South Carolina and Georgia . By the end of the Late Pleistocene Eremotherium was probably absent from North America north of Mexico, though it maintained a wide distribution from Mexico to Brazil at the time of its extinction. Most records of the genus in Mexico are from

9750-423: The gluteal ridge. A structure of minor importance in humans, the incidence of the third trochanter varies from 17–72% between ethnic groups and it is frequently reported as more common in females than in males. The lower extremity of the femur (or distal extremity) is the thickest femoral extremity, the upper extremity is the shortest femoral extremity. It is somewhat cuboid in form, but its transverse diameter

9880-451: 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

10010-491: 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

10140-523: The hand with an extremely short metatarsal of the third finger. That of the fourth finger reached 24 centimetres (9.4 in), that of the fifth 21 centimetres (8.3 in) in length. Deviating from the hand, only the middle digit (III) had three phalanges with a terminal phalanx bearing a long claw. The two outer digit had only two phalanges. This structure of the foot is typical for evolved megatherians. Fossils of Eremotherium have been found at over 130 sites. The earliest species, Eremotherium eomigrans

10270-417: The hands were turned inwards, in a position somewhat resembling the forefeet of the similarly clawed Chalicotheriidae , a now extinct group of odd-toed ungulates . It also suggests that locomotion was rather slow. It was also unable to perform digging activities, as has been demonstrated for other large ground sloths, which can also be seen in the construction of the forearm, just as the manipulation of objects

10400-463: 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

10530-1082: 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

10660-444: The hip and knee. The upper or proximal extremity (close to the torso ) contains the head , neck , the two trochanters and adjacent structures. The upper extremity is the thinnest femoral extremity, the lower extremity is the thickest femoral extremity. The head of the femur , which articulates with the acetabulum of the pelvic bone , comprises two-thirds of a sphere . It has a small groove, or fovea , connected through

10790-437: The intertrochanteric crest, and reaching vertically downward for about 5 cm. along the back part of the body: it is called the linea quadrata (or quadrate line). About the junction of the upper one-third and lower two-thirds on the intertrochanteric crest is the quadrate tubercle located. The size of the tubercle varies and it is not always located on the intertrochanteric crest and that also adjacent areas can be part of

10920-641: The island were reported in 1824 by naturalist William Cooper , including mandibular, limb, and dental remains, that now reside at the Lyceum of Natural History in New York, that had also been collected by Joseph C. Habersham. Several other discoveries from Georgia and South Carolina were described as Megatherium throughout the 1840s and 1850s, like in 1846 when Savannah scholar William B. Hodgson described some " Megatherium " fossils from Georgia that had been donated by Habersham, including portions of several skulls, in

11050-405: The jaw had 5 teeth in the upper jaw and 4 in the lower jaw, so in total Eremotherium had 18 teeth. They resembled molars and, except for the front one, were quadrangular in shape, usually a good 5 centimetres (2.0 in) long in large individuals and very high-crowned ( hypsodont ) with a height of 15 centimetres (5.9 in). They had no roots and grew throughout their entire life. The enamel

11180-406: 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 a relatively simple morphology. Some ground sloths have canine-like teeth at

11310-537: The landscape in Santa Elena Peninsula that E. carolinese was unearthed from. The following year, French taxonomist Robert Hoffstetter introduced the genus Schaubia for Samuel Schaub's Megatherium rusconii because he recognized its generic distinctness from Megatherium , though the genus name was preoccupied, so it was renamed Schaubtherium the following year. It was not until 1952 that he recognized similarities to Spillmann's Eremotherium and synonymized

11440-414: The largest land-dwelling mammals of that time in the Americas , along with the proboscideans that migrated from Eurasia . As a ground-dwelling sloth, it had relatively shorter and stronger limbs compared to modern arboreal sloths and also had a longer tail. The skull of Eremotherium was large and massive, but lighter in build compared to Megatherium . A complete skull measured 65 cm in length and

11570-611: 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

11700-405: The lateral is almost directly antero-posterior, but that of the medial runs backward and medialward. Their opposed surfaces are small, rough, and concave, and form the walls of the intercondyloid fossa . This fossa is limited above by a ridge, the intercondyloid line , and below by the central part of the posterior margin of the patellar surface. The posterior cruciate ligament of the knee joint

11830-410: The lesser trochanter may be classified as a hip fracture , especially when associated with osteoporosis . Femur fractures can be managed in a pre-hospital setting with the use of a traction splint . In primitive tetrapods, the main points of muscle attachment along the femur are the internal trochanter and third trochanter , and a ridge along the ventral surface of the femoral shaft referred to as

11960-418: The medial head of the gastrocnemius . The lateral epicondyle which is smaller and less prominent than the medial, gives attachment to the fibular collateral ligament of the knee-joint . The femur develops from the limb buds as a result of interactions between the ectoderm and the underlying mesoderm ; formation occurs roughly around the fourth week of development. By the sixth week of development,

12090-500: The more distantly related Mylodontidae and was probably a specialised grazer. Moreover, the total purchase area is within the range of variation of present-day elephants , some of which also prefer mixed plant diets. Support for this view comes from various isotopic analysis on the teeth of Eremotherium . Thus, the animals probably fed on grass in rather open landscapes, but on foliage in largely closed forests. Carbon isotopes and stereo microwear analysis suggest that an individual from

12220-565: 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 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

12350-433: The muscles that exert their force over the hip and knee joints. Some biarticular muscles – which cross two joints, like the gastrocnemius and plantaris muscles – also originate from the femur. In all, 23 individual muscles either originate from or insert onto the femur. In cross-section, the thigh is divided up into three separate fascial compartments divided by fascia , each containing muscles. These compartments use

12480-499: The name femur appears in arthropodology . The usage is not homologous with that of vertebrate anatomy; the term "femur" simply has been adopted by analogy and refers, where applicable, to the most proximal of (usually) the two longest jointed segments of the legs of the arthropoda . The two basal segments preceding the femur are the coxa and trochanter . This convention is not followed in carcinology but it applies in arachnology and entomology . In myriapodology another segment,

12610-463: The naming of many additional species that are actually synonymous with E. laurillardi. For many years fossils from the genus have been known, with records from as early as 1823 when fossil collectors J. P. Scriven and Joseph C. Habersham collected several teeth, skull, and mandible fragments, including a nearly complete set of mandibles, from Quaternary age deposits in Skidaway Island , Georgia in

12740-462: The only moderately wide snout and the large total chewing surface of the teeth advocate a diet adapted to mixed plant foods. The average surface area of all teeth available for chewing food is 11,340 mm², which roughly corresponds to the values of the closely related Megatherium , but clearly exceeds those of the Lestodon , which is also giant but has a much broader snout. The latter genus belongs to

12870-425: The posterior, lower end there was a strong, clearly notched angular process, the upper edge of which was approximately at the level of the masticatory plane. At the anterior edge of the lower jaw there was a strong mental foramen . The dentition was typical for sloths, but in contrast to today's representatives it consisted of completely homodont teeth, which is a characteristic feature of megatherians. Each branch of

13000-417: The quadrate tubercle, such as the posterior surface of the greater trochanter or the neck of the femur. In a small anatomical study it was shown that the epiphyseal line passes directly through the quadrate tubercle. The body of the femur (or shaft) is large, thick and almost cylindrical in form. It is a little broader above than in the center, broadest and somewhat flattened from before backward below. It

13130-560: 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

13260-457: The shaft, typical of xenarthrans, was absent in Eremotherium as in all other megatherians. The shinbone and fibula were only fused together at the upper end and not also at the lower end as in Megatherium . In this case, the tibia became about 60 cm long. The forelegs ended in hands with three fingers (III to V). The two inner phalanges (I and II) were fused together with some elements of

13390-416: 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 the fossil record, they were already distinct at the family level. Sloths dispersed into

13520-457: The slow-moving giant sloths were likely easy prey for early humans possibly hurling spears. Femur The top of the femur fits into a socket in the pelvis called the hip joint, and the bottom of the femur connects to the shinbone ( tibia ) and kneecap ( patella ) to form the knee. In humans the femur is the largest and thickest bone in the body. The femur is the only bone in the upper leg . The two femurs converge medially toward

13650-466: 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

13780-409: The southern and midlatitudes. Fossils of Eremotherium have been found at a wide range of altitudes, ranging from sea level to over 2,000 metres (6,600 ft). The predominantly quadrupedal locomotion took place on inwardly turned feet, with the entire weight resting on the outer, fifth and possibly fourth phalanges (a pedolateral gait), whereby the talus was subject to massive reshaping. Likewise,

13910-748: The species is in New Jersey, which likely represents a northward extension of its range during a warm interglacial period (probably the Last Interglacial / Sangamonian ), while the southernmost record of the genus is in Rio Grande do Sul in southernmost Brazil. Most records of Eremotherium in Brazil are from the Brazilian Intertropical Region (BIR) in the east of the country, and are particularly frequently found in tank deposits (infillings of small depressions caused by erosion). Other records of

14040-402: The species name E. couperi is rarely used, while E. laurillardi is more widely used and has been adopted by more scientists. Fossils from South America were first described by Danish paleontologist and founder of Brazilian paleontology Peter Wilhelm Lund when he established a new species of Megatherium based on two teeth (specimen number ZMUC 1130 and 1131) from Lapa Vermella, a cave in

14170-767: 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

14300-433: The third and fourth fingers had a long and pointedly curved shape, which suggests correspondingly long claws. The fifth finger had only two phalanges and consequently no claw was formed there. (An exception is the older form E. eomigrans , whose hands, in contrast to other megateria, were still five-fingered, with claws on digits I to IV.) The foot, as in all megatheriids, was also three-fingered (digits III to V). It resembled

14430-410: The tooth row remained largely the same. This differs markedly from Megatherium , in which the height of the mandible increased not only in absolute terms, but also relatively in relation to the length of the dentition. The mandibular body was also very thick, leaving little space for the tongue. The crown process rose up to 27 centimetres (11 in), and the articular process was only slightly lower. At

14560-458: The two. Another dubious genus and species, Xenocnus cearensis , was dubbed in 1980 by Carlos de Paula Couto based on a partial unciform (wrist bone), though he mistook as the astragalus (tarsal bone) of a megalochynid, that had been found in Pleistocene deposits in Itapipoca, Brazil . Paula Couto even created a new subfamily, Xenocninae, for the genus, but reanalysis in 2008 proved that the fossil

14690-479: The valley of the Rio de la Velhas in the Brazilian state of Minas Gerais under the name Megatherium laurillardi , the first named species now assigned to Eremotherium . Lund diagnosed the species based on the size of the teeth, which were only a quarter the size of Megatherium americanum , the greatest representative of Megatherium , and he believed that it was a tapir-sized animal. Today, the teeth are considered to be from

14820-439: The vertebral bodies were compressed in length, so that the tail appeared rather short overall and generally did not exceed the length of the lower limb sections. It had 7 neck vertebrae . The humerus represented a long tube with a bulky lower joint end. The total length was about 79 centimetres (31 in). Distinctive, ridge-like muscle attachments on the middle shaft were typical. The forearm bones had much shorter lengths, with

14950-606: 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

15080-430: Was also missing. However, two transverse, sharp-edged ridges were typically formed on the chewing surface to help grind food. The entire upper row of teeth grew up to 22 centimetres (8.7 in) long, while the lower reached up to 21 centimetres (8.3 in). Almost all of the poscranial skeleton is known. The vertebrae were massively shaped, both at the vertebral bodies and at the lateral transverse processes . However,

15210-404: 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

15340-462: 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

15470-520: 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

15600-407: Was instead from Eremotherium laurillardi . Eremotherium was slightly larger than the closely related Megatherium in size, reaching an overall length of 6 metres (20 ft) and a height of 2 metres (6.6 ft) while on all fours, possibly up to 4 metres (13 ft) when it reared up on its hind legs, and weighing around 3,960–6,550 kilograms (8,730–14,440 lb). In any case, it is one of

15730-428: Was its robust physique with comparatively long limbs and front and hind feet especially for later representatives- three fingers. However, the skull is relatively gracile, the teeth are uniform and high-crowned . Like today's sloths, Eremotherium was purely herbivorous and was probably a mixed feeder that dined on leaves and grasses that adapted its diet to local environments and climates. Like Megatherium, Eremotherium

15860-466: Was minimised due to the limited ability of the fingers to move in relation to each other. However, Eremotherium was able to stand up on its hind legs and pull branches and twigs with its hands, for example to reach the foliage of tall trees for feeding, as well as make defensive strikes with its long claws. The standing up was supported by the strong tail, similar to what is still the case today with armadillos and anteaters . The massive tail vertebrae in

15990-477: Was one of the largest ground sloths, with a body size comparable to elephants, weighing around 4–6.5 tonnes (4.4–7.2 short tons) and measuring about 6 metres (20 ft) long, slightly larger than its close relative Megatherium . Eremotherium was widespread in tropical and subtropical lowlands and lived there in partly open and closed landscapes, while its close relative Megatherium lived in more temperate climes of South America. Characteristic of Eremotherium

16120-501: Was only a single species, E. laurillardi , which had a strong sexual dimorphism . Discoveries of extensive material of Eremotherium at sites such as those at Nova Friburgo in Brazil and Daytona Beach in Florida further prove that the two were synonymous and lacked any major differences between populations. Fossils of Eremotherium from Mexico were first described in 1882 by French scientist Alfred Duges , though they consisted only of

16250-455: Was only loosely connected to the upper jaw, whereas in Megatherium the premaxillary bone had a quadrangular shape, as well as a firm connection to the upper jaw. The occipital bone is semicircular in posterior view and sloped backwards in lateral view. The articular surfaces as the point of attachment of the cervical spine curved far outwards and were relatively larger than in tree sloths and numerous other ground sloths. The parietal bones had

16380-416: Was shallow and small and slightly lower than in Megatherium or modern sloths. The lower jaw was about 55 centimetres (22 in) long, both halves were connected by a strong symphysis , which extended forward in a spatulate shape and ended in a rounded shape. Typical for all representatives of the Megatheriidae was the clearly downward curved course of the lower edge of the bone body, which resulted from

16510-481: Was speculated to actually have come from a dwarf species of Eremotherium while the larger fossils belonged to another distinct species like E. rusconii, a species that was erected by Samuel Schaub in 1935 for giant fossils from Venezuela, though it was initially thought to be a species of Megatherium . However, this view is mostly contradicted and argues that at least in the Late Pleistocene in South and North America there

16640-695: Was thought to have gathered at a waterhole and died there relatively abruptly due to an unknown event. On the other hand, sometimes clustered occurrences of Eremotherium such as the 19 individuals from the sinkhole of Jirau in Brazil are considered to be accumulations over a long period of time. In the case of the likewise giant ground sloth Lestodon from central South America, experts also interpret mass accumulations of remains of different individuals in part as evidence of phased group formation. Living tree sloths live solitary lives. Eremotherium possessed extremely high-crowned teeth , which, however, did not reach

16770-540: Was unearthed from a doline on the site of the São-José farm in the Brazilian state of Sergipe. However, other authors have regarded the idea as poorly evidenced, and the modification was more likely the result of natural processes. Ground sloth Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra . They varied widely in size with the largest, belonging to genera Lestodon , Eremotherium and Megatherium , being around

16900-428: Was up to 33 cm wide at the zygomatic arches ; at its highest, it reached 19 cm in height. The forehead line was clearly straight and not as wavy as in Megatherium . The nasal bone was shortened compared to the skull of Megatherium , giving it an overall truncated cone appearance. Further differences to Megatherium existed at the premaxillary bone : In Eremotherium this had an overall triangular shape and

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