Eremotherium(from Greek for "steppe" or "desert beast": ἔρημος "steppe or desert" and θηρίον "beast" ) is an extinct genus of giantground slothin the familyMegatheriidae.Eremotheriumlived in southern North America, Central America, and northern South America from thePliocene,around 5.3 million years ago, to the end of theLate Pleistocene,around 10,000 years ago.Eremotheriumwas 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 relativeMegatherium.
Eremotherium Temporal range:Early Pliocene-Early Holocene(Blancan-Rancholabrean(NALMA) &Montehermosan-Lujanian(SALMA)
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E. laurillardiat theHMNS | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Pilosa |
Clade: | †Megatheria |
Family: | †Megatheriidae |
Subfamily: | †Megatheriinae |
Genus: | †Eremotherium Spillmann, 1948 |
Type species | |
†Megatheriumlaurillardi Lund,1842
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Other species | |
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Range ofEremotherium |
Eremotheriumwas widespread in tropical and subtropical lowlands and lived there in partly open and closed landscapes, while its close relativeMegatheriumlived in more temperate climes of South America. Characteristic ofEremotheriumwas 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 andhigh-crowned.Like today's sloths,Eremotheriumwas purely herbivorous and was probably a mixed feeder that dined on leaves and grasses that adapted its diet to local environments and climates. LikeMegatherium, Eremotheriumis suggested to have been capable of adopting a bipedal posture to feed on high-growing leaves.
Finds ofEremotheriumare 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 laurillardiandE. eomigrans,the former was named by prolific Danish paleontologistPeter Lundin 1842 based on a tooth of a juvenile individual that had been collected from Pleistocene deposits in caves inLagoa Santa,Brazil alongside fossils of thousands of other megafauna. Lund originally named it as a species of its relativeMegatherium,though Austrian paleontologist Franz Spillman later created the genus nameEremotheriumafter noticing its distinctness from other megatheriids.
History and naming
editThe taxonomic history ofEremotheriumlargely involves it being confused withMegatheriumand the naming of many additional species that are actually synonymous withE. 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 inSkidaway Island,Georgiain the United States.[1][2][3]The fossils were not described until 1852 however, when American paleontologist namedMegatherium mirabile,based on the specimens (specimen numbersUSNM825-832 + 837) but the species has since been synonymized withEremotherium laurillardi.[1]The first published discovery was only a year afterM. mirabilewas discovered, when portions of 2 teeth that had been also collected from Skidaway Island were referred toMegatheriumlater in 1823 by Dr. Samuel L. Mitchell.[4]20 more fossils from the island were reported in 1824 by naturalistWilliam Cooper,including mandibular, limb, and dental remains, that now reside at theLyceum of Natural Historyin New York, that had also been collected by Joseph C. Habersham.[4][5]
Several other discoveries from Georgia andSouth Carolinawere described asMegatheriumthroughout the 1840s and 1850s, like in 1846 whenSavannahscholarWilliam B. Hodgsondescribed some "Megatherium"fossils from Georgia that had been donated by Habersham, including portions of several skulls, in a collection that included fossils of several other Pleistocene megafauna likemammothsandbison.[2][4]These were all described in more detail byJoseph Leidyin 1855, but they were not all referred toEremotheriumuntil the late 20th century.[2]In 1842,Richard Harlannamed a new species of the turtleChelonia, Chelonia couperi,based on a supposedfemur,or thigh bone, that had been found in the Brunswick Canal inGlynn County,Georgia and dated to the Pleistocene.[6]It was not until 1977 that further analysis demonstrated that the "femur" was actually a clavicle fromEremotherium.[7]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 the species nameE. couperiis rarely used, whileE. laurillardiis more widely used and has been adopted by more scientists.[1]
Fossils from South America were first described by Danish paleontologist and founder of Brazilian paleontologyPeter Wilhelm Lundwhen he established a new species ofMegatheriumbased on two teeth (specimen numberZMUC1130 and 1131) from Lapa Vermella, a cave in the valley of the Rio de la Velhas in the Brazilian state of Minas Gerais under the nameMegatherium laurillardi,the first named species now assigned toEremotherium.[8]Lund diagnosed the species based on the size of the teeth, which were only a quarter the size ofMegatherium americanum,the greatest representative ofMegatherium,and he believed that it was a tapir-sized animal.[8]Today, the teeth are considered to be from a juvenile ofE. laurillardiand adults reached or exceeded the size ofM. americanum.[9]Two years earlier, Lund had already figured teeth found at Lapa Vermella, which he assigned toMegatherium americanumdue to their dimensions, which he figured alongside those ofM. laurillardiin the 1842 publication.[10][8]They also have been referred toEremotherium laurillardi.For many years,E. laurillardi's holotype was speculated to actually have come from a dwarf species ofEremotheriumwhile the larger fossils belonged to another distinct species likeE. 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 ofMegatherium.[11][12]However, this view is mostly contradicted and argues that at least in the Late Pleistocene in South and North America there was only a single species,E. laurillardi,which had a strongsexual dimorphism.[12]Discoveries of extensive material ofEremotheriumat sites such as those atNova Friburgoin Brazil andDaytona Beachin Florida further prove that the two were synonymous and lacked any major differences between populations.[12]
Fossils ofEremotheriumfrom Mexico were first described in 1882 by French scientistAlfred Duges,though they consisted only of a fragmentary left femur, as a new species of the South AmericanScelidotherium,naming itS. guanajatense.[13]The femur had been found in Pleistocene deposits inGuanajuato,Mexico, but the fossil has since been lost and the species is a synonym ofE. laurillardi.[14]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 a single, approximately 39 cm long femur from the Pleistocene strata inUlloma,BoliviaasEremotherium sefvei,though it was first described in 1915 as a fossil ofMegatherium.[15][16]E. sefvei's geologic aging is less definite can only be placed in the general Pleistocene, but it is the smallest representative ofEremotheriumand all post-Miocene megatheriids.[17][10]
Two years later in 1999, De Iuliis and Brazilian paleontologist Carlos Cartelle erected another species ofEremotheriumnow seen as valid,E. eomigrans,based on a partial skeleton, theholotype,that had been unearthed from the latestBlancan(Latest Pliocene) layers ofNewberry,Florida,USA, though many other fossils from the area were referred to it.[18]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.[18]So far, the latter has only been found in North America and reached a size similar toE. laurillardi,but comes from the Pliocene and Early Pleistocene and bares a pentadactyl, or five fingered, hand in contrast to the tridactyl hands ofMegatheriumandE. laurillardi.[18]
The genus nameEremotheriumwas 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 theSanta Elena Peninsulain Ecuador, and the species name was after the local village of Carolina.[19]Although it was the type species of the genus for many years, the species has since been synonymized withE. laurillardiand has been replaced by it as the type species. The generic nameEremotheriumis derived from the Greek words ἔρημος (Erēmos "Steppe", "desert" ) and θηρίον (Thērion "animal" ) after the landscape in Santa Elena Peninsula thatE. carolinesewas unearthed from.[19]The following year, French taxonomistRobert Hoffstetterintroduced the genusSchaubiafor Samuel Schaub'sMegatherium rusconiibecause he recognized its generic distinctness fromMegatherium,[20]though the genus name was preoccupied, so it was renamedSchaubtheriumthe following year.[21]It was not until 1952 that he recognized similarities to Spillmann'sEremotheriumand synonymized the two.[22]Another dubious genus and species,Xenocnus cearensis,was dubbed in 1980 by Carlos de Paula Couto based on a partialunciform(wrist bone), though he mistook as theastragalus(tarsal bone) of a megalochynid, that had been found in Pleistocene deposits inItapipoca, Brazil.[23][24]Paula Couto even created a new subfamily, Xenocninae, for the genus,[23]but reanalysis in 2008 proved that the fossil was instead fromEremotherium laurillardi.[24]
Description
editSize
editEremotheriumwas slightly larger than the closely relatedMegatheriumin 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,[25]and weighing around 3,960–6,550 kilograms (8,730–14,440 lb).[26][27][28]In any case, it is one of the largest land-dwelling mammals of that time inthe Americas,along with theproboscideansthat migrated fromEurasia.[29][30]As a ground-dwelling sloth, it had relatively shorter and stronger limbs compared to modern arboreal sloths and also had a longer tail.[31]
Skull
editThe skull ofEremotheriumwas large and massive, but lighter in build compared toMegatherium.A complete skull measured 65 cm in length and was up to 33 cm wide at thezygomatic arches;at its highest, it reached 19 cm in height. The forehead line was clearly straight and not as wavy as inMegatherium.Thenasal bonewas shortened compared to the skull ofMegatherium,giving it an overall truncated cone appearance. Further differences toMegatheriumexisted at thepremaxillary bone:InEremotheriumthis had an overall triangular shape and was only loosely connected to the upper jaw, whereas inMegatheriumthe premaxillary bone had a quadrangular shape, as well as a firm connection to the upper jaw.[1]Theoccipital boneis 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. Theparietal boneshad a far outward curved shape, which was partly caused by the largecranial cavitywith 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. Theeye socketwas shallow and small and slightly lower than inMegatheriumor modern sloths.[32][33][34][35]
The lower jaw was about 55 centimetres (22 in) long, both halves were connected by a strongsymphysis,which extended forward in a spatulate shape and ended in a rounded shape. Typical for all representatives of theMegatheriidaewas the clearly downward curved course of the lower edge of the bone body, which resulted from the different length of the teeth. InEremotheriumthis 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 the tooth row remained largely the same. This differs markedly fromMegatherium,in which the height of the mandible increased not only in absolute terms, but also relatively in relation to the length of the dentition.[36]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 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 strongmental foramen.The dentition was typical for sloths, but in contrast to today's representatives it consisted of completelyhomodontteeth, which is a characteristic feature of megatherians. Each branch of the jaw had 5 teeth in the upper jaw and 4 in the lower jaw, so in totalEremotheriumhad 18 teeth. They resembledmolarsand, 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. Theenamelwas 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).[32][37][38][35]
Postcrania
editAlmost all of the poscranial skeleton is known. The vertebrae were massively shaped, both at the vertebral bodies and at the lateraltransverse processes.However, 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.[39]It had 7neck vertebrae.Thehumerusrepresented 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 thespokemeasuring about 67 cm, and theulna57 centimetres (22 in) in length.[40][34]Massive was thefemur,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 the shaft, typical of xenarthrans, was absent inEremotheriumas in all other megatherians. Theshinboneandfibulawere only fused together at the upper end and not also at the lower end as inMegatherium.In this case, the tibia became about 60 cm long.[39][34][41]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 thecarpus,such as thetrapezium,to form a unit, the metacarpal-carpal complex (MCC).[42]Thus,Eremotheriumclearly deviates fromMegatheriumand other closely related forms, which possessed four-fingered hands. InEremotherium,themetacarpalof 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. Thephalanx(the third phalanx) of 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 formE. eomigrans,whose hands, in contrast to other megateria, were still five-fingered, with claws on digits I to IV.)[34][43]The foot, as in all megatheriids, was also three-fingered (digits III to V). It resembled the hand with an extremely shortmetatarsalof 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.[39]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.[44][45]
Fossil distribution
editFossils ofEremotheriumhave been found at over 130 sites.[46]The earliest species,Eremotherium eomigransis exclusively known from Florida, dating to the late Pliocene.Eremotherium sefveiis only known from a single femur found in Bolivia of an uncertain age, whileEremotherium laurillardiis known from numerous fossils spanning from the late Pliocene to the end of the Pleistocene.[35]The range distribution ofEremotherium laurillardiis the widest of any ground sloth, spanning from 30.5° S to 40.3°N. The northernmost record of the species is in New Jersey, which likely represents a northward extension of its range during a warminterglacialperiod (probably theLast Interglacial/Sangamonian), while the southernmost record of the genus is inRio Grande do Sulin southernmost Brazil. Most records ofEremotheriumin Brazil are from the Brazilian Intertropical Region (BIR) in the east of the country,[47]and are particularly frequently found in tank deposits (infillings of small depressions caused by erosion).[48]Other records of the genus in North America north of Mexico are confined to theGulf Coastand SouthernAtlantic Coast,includingTexas,Florida,South CarolinaandGeorgia.[49]By the end of the Late PleistoceneEremotheriumwas probably absent from North America north of Mexico, though it maintained a wide distribution from Mexico to Brazil at the time of its extinction.[47]Most records of the genus in Mexico are from the southern and midlatitudes.[50]Fossils ofEremotheriumhave been found at a wide range of altitudes, ranging from sea level to over 2,000 metres (6,600 ft).[50]
Palaeobiology
editLocomotion
editThe 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 thetaluswas subject to massive reshaping.[51][52]Likewise, the hands were turned inwards, in a position somewhat resembling the forefeet of the similarly clawedChalicotheriidae,a now extinct group ofodd-toed ungulates.[43]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 was minimised due to the limited ability of the fingers to move in relation to each other. However,Eremotheriumwas 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,[39][53]as well as make defensive strikes with its long claws.[43]The standing up was supported by the strong tail, similar to what is still the case today witharmadillosandanteaters.The massive tail vertebrae in the front area of the tail suggest a strong musculature. Among other things, this concerns thecoccygeus muscle,which attaches to theischiumand fixes the tail. Less well developed, on the other hand, were the epaxial muscles, which could cause the tail to straighten up.[39]
Social behaviour
editDue to some group finds of several individuals at individual sites, such as inEl BajióninChiapasinMexicowith four animals or inTanque Lomaon theSanta ElenainEcuadorwith 22 individuals, some scientists discuss whetherEremotheriumpossibly lived and roamed in small, herd-like groups.[46][54]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 was thought to have gathered at a waterhole and died there relatively abruptly due to an unknown event.[54]On the other hand, sometimes clustered occurrences ofEremotheriumsuch as the 19 individuals from thesinkholeofJirauinBrazilare considered to be accumulations over a long period of time.[55]In the case of the likewise giant ground slothLestodonfrom central South America, experts also interpret mass accumulations of remains of different individuals in part as evidence of phased group formation.[56]Living tree sloths live solitary lives.[57]
Diet
editEremotheriumpossessed extremelyhigh-crowned teeth,which, however, did not reach the dimensions of those ofMegatherium.As the teeth lackenamel,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 inEremotheriumand more temperate regions inMegatherium.[38]From ananatomicalpoint of view, 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 relatedMegatherium,but clearly exceeds those of theLestodon,which is also giant but has a much broader snout. The latter genus belongs to the more distantly relatedMylodontidaeand was probably a specialised grazer. Moreover, the total purchase area is within the range of variation of present-dayelephants,some of which also prefer mixed plant diets.[58][59]Support for this view comes from variousisotopic analysison the teeth ofEremotherium.Thus, the animals probably fed on grass in rather open landscapes, but on foliage in largely closed forests.[60][27]Carbon isotopes and stereo microwear analysis suggest that an individual from the Late Pleistocene (34,705-33,947cal yrBP), ofGoiás,Brazil, was a mixed feeder, suggesting a high proportion of shrubs and trees, this is in contrast to the presumed diet from specimens fromNortheast Brazil,which had a diet ofC4herbaceousplants.[61]A 2020 discovery in Ecuador found 22 individuals ranging in age from juveniles to adults preserved together in anoxic marsh sediments, suggesting thatEremotheriummay have been gregarious.[62]
Palaeopathologies
editNumerouspalaeopathologieshave been described fromE. laurillardifossils in the BIR. These documented ailments includeosteoarthritisand articular depressions, withspondyloarthropathyandcalcium pyrophosphate deposition diseasepotentially present as well. Thesediseasesare evidenced by the presence of osteophytes, bone overgrowth, bone erosion, and rough subchondral bone in various specimens.[63]E. laurillardiis also the only xenarthran species from which linear defect is known.[64]
Classification
editEremotheriumis 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.[65][66]The Megatherioidea also includes the three-toed sloths of the genusBradypus,one of the two sloth genera still alive today.[67][68]Eremotherium's closest relative in Megatheriidae is the namesake of the familyMegatherium,which was endemic to South America, slightly larger, and preferred more open habitats thanEremotherium.PyramiodontheriumandAnisodontheriumare also part of this subfamily, but are smaller and older, dating to the Late Miocene of Argentina. All of these genera belong to the subfamilyMegatheriinae,which includes the largest and most derived sloths. The direct phylogenetic ancestor ofEremotheriumis unknown, but may be linked toProeremotheriumfrom theCodore Formationin Venezuela, which dates to the Pliocene. The genus has numerous characteristics that are akin to those ofEremotherium,but are more primitive.[17]Little is known about the evolution of the genusEremotherium.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 the Isthmus of Panama, i.e. the formation of the land bridge connecting North and South America, in the course of theGreat 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.[69]The discovery ofProeremotheriumalso supports this hypothesis, indicating that these or other close ancestors ofEremotheriumfirst migrated to North America and evolved there, then moved back southward to South America after the formation of the Isthmus of Panama, similar to the glyptodontGlyptotherium.[17]
The following phylogenetic analysis of Megatheriinae within Megatheriidae was conducted by Brandoniet al.,2018[70]that was modified from Varelaet al.2019 based on lower molariform and astragalus morphology:[71]
Relationship with humans and extinction
editThe disappearance ofEremotheriumcoincides with theQuaternary 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 asmammoths,glyptodonts,and other ground sloths. One of the latest finds ofEremotheriumis from Ittaituba on Rio Tapajós, a tributary of 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.[72]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.[citation needed]There is no direct evidence of hunting by humans ofEremotherium.A possible indication of interaction is a tooth ofEremotheriumthat some authors have suggested had been modified by Paleoindians, which was unearthed from a doline on the site of the São-José farm in the Brazilian state of Sergipe.[73]However, other authors have regarded the idea as poorly evidenced, and the modification was more likely the result of natural processes.[74]
References
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