Megatherium

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Megatherium
Skeletal reconstruction of Megatherium americanum in the Muséum national d'histoire naturelle in Paris

Skeletal reconstruction of Megatherium americanum in the Muséum national d'histoire naturelle in Paris

Temporal occurrence
Pliocene to Upper Pleistocene / Lower Holocene
5.33 million years to 11,000 years
Locations
Systematics
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Megatherioidea
Megatheriidae
Megatherium
Scientific name
Megatherium
Cuvier , 1796

Megatherium is a genus of the extinct family of Megatheriidae , a group of sometimes huge sloths . Especially the elephant big M. americanum is one of the best known and most studied forms and provides next eremotherium represents the largest known representatives of the large ground sloths. The genus occurred from the early Pliocene before about 5 million years ago to the transition from the Upper Pleistocene to the Lower Holocene ago about 8,000, possibly only until about 11,000 years ago. There are two lines of development within the genus. One is the lowland form M. americanum , whichinhabitedthe central to partly southernareas of South America , which were subject to temperate climatic influences , primarily the pamphlet region in today's Argentina, the other occurred mainly in the high mountains of the Andes and included several species. Both lines of development can be distinguished on the basis of features on the skeleton .

As a far-reaching herbivore, Megatherium mainly fed on a soft vegetable diet . It was able to stand up on its hind legs to eat, with its strong tail serving as a support on the ground. The massive arms were used to pull up branches and twigs. Sometimes, however, a much more meat-based diet is also being discussed. Also at the center of a scientific debate is the question of whether Megatherium not only straightened itself up for food, but was also permanently able to move on two legs ( bipede ), whereby it would then be the largest known mammal with such a movement. Both the view of a predatory way of life and a permanent two-legged gait are highly controversial.

The discovery of fossil remains from Megatherium goes back to the late 18th century. A skeleton from Luján in today's Argentina led to the first scientific description of the genus by Georges Cuvier in 1796 . Further important finds were made in 1832 by Charles Darwin on his historic trip with the HMS Beagle around South America in the pampas. Megatherium played an important role in the development and establishment of paleontology as a branch of science in the course of the 19th century. The early research history of the genus is not only characterized by numerous new findings, but also by individual, decisive errors.

features

General

Megatherium includes medium-sized to very large representatives of the ground sloths. The smallest species, M. altiplanicum , weighed an estimated between 1.0 and 1.7  t , M. americanum as the largest species with a total length of 6 m and a shoulder height of 2 m probably had a body weight of 3.8 to 6.0 t (based on various determination methods). Megatherium thus had similar dimensions to the related Eremotherium, which lived around the same time . The variability in size within the genus can be seen, among other things, in the characteristic thigh bone . This pointed at M. altiplanicum a length of 39 cm, M. urbinai , M. sundti and M. tarijense represent with 46 to 53 cm long femora medium types, while at the upper end of the size spectrum of the femurs of M. americanum between 57 and Was 78 cm long. This makes Megatherium one of the largest known sloths alongside Eremotherium . In general, Megatherium was not built quite as robustly as its relative Eremotherium and had comparatively shorter limbs, but a longer skull. As with all ground sloths, the arms and legs were significantly shorter in relation to body length than with today's tree sloths. Furthermore, Megatherium had a strong, long tail analogous to other ground-dwelling sloths.

Skull and dentition features

Skull of Megatherium

The skull of the large species was 72 to 87 cm long, on the zygomatic arches it reached a width of 36 to 46 cm, on the occiput from 27 to 31 cm. Overall, it was elongated tubular and narrow in plan. In the side view, the forehead line showed a strikingly sinusoidal curved to slightly dome-like profile. The paired middle jaw bone had a Y- or X- to rectangular shape, whereby the two bones were firmly fused together, as well as a firm fusion with the upper jaw existed. However, in some smaller species, the connection was not very tight, so that the median jawbone is sometimes found separate from the skull or is sometimes unknown. The upper jaw was very high to hold the extremely high-crowned teeth. One characteristic was the zygomatic arches, which were particularly massive and, in contrast to today's tree sloths and numerous fossil forms, were fully developed so that the two arches of the zygomatic and temporal bone touched. There was also a strong, downwardly directed bone outgrowth at the anterior zygomatic arch attachment, which served as a muscle attachment point. The parietal bone had a strong parietal crest that divided in front and led over the temporal bone as a sharp line. The occiput was rectangular in shape when viewed from the side. Especially in the smaller species from the Andean region , the joint attachments for the cervical spine were greatly extended backwards and were therefore very prominent.

The lower jaw showed a massive structure and measured between 62 and 74 cm in length in large species. The symphysis was also strong, relatively flat and, as with most sloths, completely fused. It ended at the level of the first or second molar. To the front it was clearly elongated and so formed a narrow bony outgrowth, the length of which exceeded that of the entire row of teeth in some cases. The downward arching edge of the lower jaw, which is typical of megatheria, was very noticeable. Here the bone body reached a height of up to 25 cm in some cases , which is the highest value for all Megatheria, but with Megatherium the bulge is also the most noticeable compared to the size of the lower jaw. The alveoli of the mandibular teeth were located in the bulge . Furthermore, the articular branches protruded very far upwards. Similar to all megatheria, the dentition consisted of five teeth per upper jaw and four per lower half, so a total of 18 teeth were formed. The teeth were designed homodontically and molar-like , square in shape and had two transverse ridges (bilophodont) on the chewing surface . Typically, the teeth had no enamel and stood closed in a row. The length of the lower row of teeth varied and was between 18.6 and 25.9 cm for the large Americanum muscle, between 15.2 and 20.4 cm for medium-sized forms such as the tarijense muscle, and between 13.0 and 17 cm for the medinae muscle , 2 cm and in the small M. altiplanicum at 14.4 cm.

Body skeleton

The body skeleton is largely fully known due to numerous finds. The spine comprised 7 cervical, 16 thoracic, 3 lumbar, 3 sacrum and 17 to 18 tail vertebrae. In contrast to Eremotherium , in Megatherium the three articular surfaces that connect the cervical vertebrae Atlas and Axis were not fused to one another. Megatherium's limbs were generally shorter on average than Eremotherium's . The humerus consisted of a tubular bone of up to 80 cm in length, the lower joint of which was bulky and up to 37 cm wide. In general, the humerus of the Megatheria was longer, more graceful and flatter than that of other ground sloths. The Elle possessed with 69 cm length of a long and slender construction with laterally narrowed link ends. The upper end of the joint, the olecranon , could be elongated and narrow in most of the smaller species, while in the largest it was wide and bulky. The femur was as in all Megatherien a wide and massive bone is, the front and rear but strong narrowed exhibited, so that the width of the bone exceeding the depth is increased fourfold. The longest known bone was 78 cm long and a good 42 cm wide, the smallest only 39 cm long and 20 cm wide. Sometimes the shaft was clearly rotated. As in all megatheria , the third trochanter as a muscle attachment point on the shaft, which is characteristic of secondary articular animals , was missing. The articular surfaces were clearly protruding, so that the overall view of the bone did not appear as rectangular as in Eremotherium . The tibia and fibula were fused together at both ends and not only on one, as in the related Eremotherium . The length of the shin was around 54 cm.

Left forefoot of Megatherium with the typical four rays
Right hind foot of Megatherium with the typical three rays

The hand was basically constructed with four rays (rays II to V) and thus deviated from its close relative Eremotherium with a three- rayed hand (in the case of late representatives). As with Eremotherium , the metacarpal bones of the two outer rays were most developed in Megatherium and reached lengths of 25 and 23 cm, respectively. They clearly exceeded the two inner rays. The metacarpal bone of the first ray and individual carpal bones such as the large polygonal bone were fused together to form the so-called metacarpal-carpal complex (MCC) (with Eremotherium also the second metacarpus). In total, only the second, third and fourth fingers each had three phalanges , on the third, however, the two rearmost phalanges were fused into one unit. The respective terminal phalanges had claws and mostly had a triangular shape in cross section. Due to the massive formation of the last phalanx on the third ray, the largest claw was originally formed here. There were only two phalanges on the fifth finger, the distal phalanx was missing. Analogous to that of the other Megatheria, the foot had three rays (rays III to V), with the metatarsal bone being significantly shorter on the third ray. This was also the only toe beam that encompassed three phalanges - but like the hand, the first two limbs were fused together - and thus had a claw. The two other, outer rays had only two toe joints that were greatly reduced in length and therefore had no claws.

Distribution and important fossil finds

Skeletal reconstruction of M. americanum in the Natural History Museum, London

Megatherium was widespread from the Pliocene to the early Holocene , especially in the central and partly southern areas of South America , only in the high mountain regions of the Andes did it advance further north. Finds are mainly known from Argentina , Uruguay , Chile , Bolivia , Peru and Ecuador . In contrast, the more northerly and more tropical lowland regions were inhabited by the closely related genus Eremotherium , which, unlike Megatherium, also reached North America . One of the few common occurrences of the two giant ground sloths so far was found in the middle to upper Pleistocene Santa Vitória Formation on the banks of the Arroio Chuí and other rivers in the Brazilian state of Rio Grande do Sul . Megatherium has been handed down here with a partial skull and individual elements of the body skeleton. The majority of the finds come from the pampas region in Argentina and, in the opinion of many researchers, they are all related to the very large species M. americanum , which in this opinion was the only representative in the lowlands east of the Andes. Important points include Punta Alta near Bahía Blanca in the province of Buenos Aires , where Charles Darwin collected finds during his trip with the HMS Beagle in 1832, or Luján , one of the most fossil-rich sites in Argentina in the same province where the skeleton came from. the Georges Cuvier for the first description of Megatherium served. The almost complete lower jaw of M. americanum from La Chumbiada on the Río Salado in the north of the province of Buenos Aires, which is around 12,000 years old and was found in association with the big cat Smilodon and the horse Hippidion , is representative of the numerous other finds in the pampas has been. Overall, M. americanum is not only the largest representative of Megatherium , but also the most frequently documented and best investigated. However, there are also isolated finds of smaller forms such as M. filholi from the pampa areas, so that the genus Megatherium probably had a more complex history of distribution in the region. Of particular note are the Rocas Negras site near Mar del Sur in the south and Carmen de Areco as well as various other sites in the north of the province of Buenos Aires.

Otherwise mostly smaller species of Megatherium from the Andes have been described. As a rule, however, there is only very little finds of them and they evidently occurred less frequently than their larger relative in the lowlands of the Pampas. As a result, these species are usually less well researched, which means that, for example, hardly any statements can be made about intra-species variability. M. medinae is known from Chile , a medium-sized and graceful form, which was described using a remnant of a set of teeth and individual hind leg bones from the Pampa del Tamarugal . Other finds, such as a lower jaw, vertebrae and ribs, come from the vicinity of Santiago de Chile . The smallest and oldest species is M. altiplanicum , which has been identified through some skull remains and postcranial skeletal elements from the sub-Pliocene Umala formation near Ayo Ayo in the La Paz department in western Bolivia. In geographical proximity also in the northern part of the Altiplano , the medium-sized species M. sundti is documented from the Ulloma Formation of the early Middle Pleistocene near Ulloma on the Río Desaguadero . Their finds include two skulls, including one with a lower jaw, which were used to describe the species in 1893, including a partial skeleton of a not fully grown individual. From the Tarija formation near Tarija in southern Bolivia, on the other hand, the approximately similarly large M. tarijense comes in the form of a complete skeleton, which was recovered in the 1920s. A partial skeleton from Yuntac in Peru can also be assigned to the same species. Located at 4500 m above sea level, this is one of the highest finds of Megatherium . A thigh bone is still passed down from the Cuzco Valley. An incomplete skeleton from the Santa Rosa Cave near Celendin in the Peruvian province of Cajamarca was used to describe M. celendinense , the largest representative of the Andean species to date, which was almost as large as M. americanum itself. M. urbinai , on the other hand, was significantly smaller and very graceful . A partial skeleton from Sacaco in the coastal area of ​​southwestern Peru and another from the Tres Vantanas Cave 70 km southeast of Lima at an altitude of around 4000 m were recovered. A third skeleton - a young animal, also located in the Aeolian sediments near Uyujalla in the coastal area - was also reported, but was lost before it was recovered. A partial skeleton of M. elenense was found in La Brea near Talara in the northwestern coastal country of Peru , as well as at Cerro de Pasco in the Pasco region at an altitude of 4300 m. This smaller representative of Megatherium was first introduced by Robert Hoffstetter in 1952 on the basis of some finds from the Santa Elena peninsula in Ecuador , but under the generic name Eremotherium . The type material of Eremotherium , which was described by Franz Spillmann in 1948 , also comes from the same peninsula .

Paleobiology

Locomotion

Life picture of Megatherium in the Pampa region (with fur and Glyptodon left)

In contrast to today's sloths and comparable to numerous other extinct giant sloths, Megatherium was a pure ground dweller who mainly moved on four feet. A special characteristic are the feet turned inwards, so that Megatherium largely carried its weight on the two outermost rays (IV and V) of the hind feet (pedolateral). The sole of the foot pointed inwards and lifted off the ground at a 35 ° angle. The pedolateral gait is a peculiarity that developed several times within the sloth and above all required massive modifications to the ankle bone . The hand also showed a similar twist. When it was placed on the ground, it was also on the outer beam, whereby the position has similarities to the clawed Chalicotheriidae , but which are to be put to the odd-toed ungulates . The rotation, especially of the forefeet, severely restricted the manipulation of objects, but they could be used to pull up branches. In addition, the position of the hands and feet suggests an overall slow movement.

However, it is possible that Megatherium was nevertheless significantly more agile than today's tree-dwelling sloths. This is inferred from studies of the inner ear, wherein the size of the semicircular canals is directly related to the dexterity of an animal. According to the results, Megatherium should have up to three times more agility than today's sloths. In general, the clearly curved claws could also be used well for digging and, thanks to their symmetrical shape, withstood the tensile and compressive forces that arise, as stress analyzes have shown, but the structure of the entire forearm speaks largely against a soil-digging lifestyle. In Megatherium, for example, the upper articular process of the ulna ( olecranon ) is clearly too short and thus could not generate the lever movements necessary to break up the soil substrate. For other very large ground sloths from the Mylodontidae group, such as Glossotherium , a way of life that sometimes burrows in the ground can be well documented.

An intense debate was held about whether Megatherium could also move in an upright position. Raising up on the hind legs to forage for food in higher treetops can be considered likely due to the configuration of the pelvis and hind legs, as well as the fact that the center of gravity of the body was very far back, around 70% of the Weight were carried by the hind legs, making it easier to stand up. The idea of bipedal locomotion came up at the beginning of the 20th century and attempts were also made to prove this with the help of Ichnofossils . Such trace fossils of Megatherium are found, among others, from Monte Hermosa and from Pehuén-Có , both sites are in the Argentine province of Buenos Aires . The traces of Pehuén-Có near Bahía Blanca play a central role here . This site, discovered in 1986, is one of the most important of Ichnofossils in the world. The traces are spread over an area of ​​1.5 km² and are imprinted in an originally soft substrate. They include many mammals, such as the camelid Megalamaichnum ( Hemiauchenia ), the South American ungulate Eumacrauchenichnus ( Macrauchenia ) or the large armadillo relatives Glyptodontichnus ( Glyptodon ), and birds, such Aramayoichnus from the group of rheas . Their age has been dated to 12,000 years.

Among the trace fossils there are also imprints of a giant sloth, which are assigned to the Ichnospecies Neomegatherichnum . The size of the individual step seals is on average 88 cm in length and 48 cm in width, it corresponds roughly to the dimensions of the rear foot of the M. americanum . The depth is about 26 cm. A total of around 80 tracks, each with at least five individual tracks, have come down to us from Megatherium , which makes the sloth species one of the most frequently identified animals at the site. The claws of the middle toe can still be seen as a separate imprint on some of the kick seals. This is usually at an angle of 50 to 90 ° to the longitudinal axis of the foot and is up to 15 cm long. One of the longest tracks runs over about 35 m in length and consists of a total of 35 individual tracks. The distance to each other is about 1.5 to 1.8 m, which is assumed to be the stride length. Since the size of the impressions is relatively uniform, it was concluded that Megatherium mostly moved on its hind legs. Only about in the middle of the series of tracks are individual, smaller, only 33 cm long, 27 cm wide and 14 cm deep prints to be seen, where the animal evidently moved into a four-footed position for a short time. The assumed speed is 1.2 to 1.4 m / s, which corresponds to a little more than 4 km / h, the maximum speed was set at 1.7 m / s. Biomechanical investigations also showed that the special shape of the thigh bone - here especially the long, narrow cross-section - was able to withstand stresses occurring laterally, which are more effective when walking on two legs than when walking on four legs.

However, this interpretation is mostly rejected because, from a functional morphological point of view, a complete bipede of Megatherium is rather improbable. An alternative explanation for the traces of Pehuén-Có would be that the larger hind feet cover the traces of the smaller front feet, as was also observed in trace fossils of Paramylodon from Nevada. The discussion about the bipedia of Megatherium is mostly limited to the large M. americanum widespread in the pampa region . For the species from the Andean region, on the other hand, a more or less permanent quadruped locomotion is assumed to adapt to the terrain of the high mountains. This can be demonstrated, among other things, by the upwardly shifted and more prominent protruding joint surfaces of the occiput, the relatively flat thighbones and the sometimes more twisted hind feet in some species as well as the design of the hand. The two outer metacarpal bones, i.e. those that touch the ground when Megatherium walks on four feet, are almost equally long and have superficial roughening, which indicates frequent contact with the ground.

nutrition

Megatherium is generally considered to be a herbivore. The high-crowned teeth would indicate specialization in hard grass food, as is the case with numerous hoofed animals today with such teeth. Due to the lack of tooth enamel , detailed studies on wear marks cannot be carried out. The construction of the chewing apparatus contradicts a stronger specialization in grasses. For example, the very high articular processes of the lower jaw, the row of teeth clearly shifted to the rear, but also the downward protruding bone on the anterior zygomatic arch, to which the masseter muscle attaches, advocate strong vertical chewing movements. The bilophodontic teeth with their two transverse, sharp ridges also suggest that the food was cut up rather than laboriously chewed. Compared to other sloths and in relation to its body size, Megatherium had a large total occlusal surface of all molars, which comprised around 10,500 to 11,100 mm². This corresponds to about ten times the area of ​​the almost equally large Lestodon from the group of the Mylodontidae and is in the range of today's elephants . The effective enlargement of the chewing surface was mainly the result of the formation of the transverse ridges on the molars. However, the cutting action of the teeth compared to the grinding one meant that the cell walls were not always broken open when chewing and so fewer nutrients were directly available. However, due to the large total chewing area, Megatherium was able to process more food at the same time in the oral cavity.

It is doubtful whether a long, flexible tongue was used when eating, as is often assumed. The structure of the hyoid bone is highly modified in Megatherium ; the geniohyoideus muscle attached there must have been very short due to the short distance to the symphysis of the lower jaw, which is long drawn back, which speaks against a very mobile tongue. However, reconstructions of the overall narrow snout show that most likely a movable upper lip was formed, similar to today's black rhinoceros . This movable lip functioned as a grasping organ when ingesting food and is indicated by several roughened surfaces as muscle attachment points near the eye window and the infraorbital foramen, as well as in the area of ​​the upper jaw and the middle jawbone.

The structure of the teeth and the masticatory muscles of Megatherium speak in favor of a diet of rather soft vegetable food. This is also confirmed by the finds of coprolites from Megatherium , which, in addition to the remains of seaweed, also contained those from Fabiana , Acantholippia , Junellia and Chuquiraga . However, isotope studies on remains of teeth from the western Argentine province of Mendoza , which date to the late Pleistocene period, revealed a rather mixed vegetable diet consisting of leaves and grasses. Here it is assumed that the animals may have adapted their feeding behavior to the ecological conditions of the region. This was subject to major changes at the end of the last glacial period and was characterized by a stronger montane influence. Similar results were obtained from a study of fossil remains from the Argentine pampa region, in which comparative material from modern mammals was also used. The corresponding data for the carbon isotopes ( δ13C ) speak of a purely vegetable diet, the very high values ​​for the nitrogen isotopes are attributed to the dry climate. Investigations of traces of abrasion on the teeth of individuals from northern Argentina have so far not provided a clear picture of the nutritional behavior of Megatherium in relation to a stronger preference for hard or soft vegetable food. The high number of grinding marks noted, which is actually typical for animals that have adapted to a rather tougher plant-based diet, is also attributed to the dry climate and the resulting increased dust development in the pampa region, which led to faster wear of the teeth.

Contrary to the analyzes mentioned above, especially in the transition from the 20th to the 21st century, the view was also expressed that Megatherium ate meat and lived as a kleptoparasite that competed with large predators for its prey or used freshly dead carcasses as scavengers. This was explained by the fact that the foreleg was not suitable for digging due to the nature of the olecranon, but for high and powerful speeds. According to this, an animal with a movement of the arm, the weight of which is estimated at around 115 kg, could release around 2700 years (comparable to the energy generated when a 10 kg object hit from a height of 20 m). The force thus achieved was sufficient to open large carcasses. In addition, Megatherium had long, sharp claws on the three middle fingers (II to IV), which were also narrowed at the sides, and so could have promoted the tearing off of meat. According to this, it would be possible that the claws were not only used in intra-species rival fights, but also to capture meat. As an indication of a partly carnal diet, a rib of a large sloth or proboscis is also valid, on which there are gnawing marks, which show typical marks of the bilophodont teeth of Megatherium . As a rule, the sloths are largely herbivorous, but even today's herbivores occasionally feed on meat.

Soft tissue morphology and pathologies

Historical reconstruction of the life of Megatherium after Heinrich Harder (around 1920) with fur

In numerous live reconstructions, Megatherium is shown with a thick fur. This idea is favored by the fact that, on the one hand, today's tree sloths also have fur, on the other hand there are fossilized remains of fur from extinct sloths such as Mylodon or Nothrotheriops . The enormous size of the animals with a body weight of up to 6 t and their distribution in more temperate regions of South America make this rather unlikely, at least for the largest representatives such as M. americanum . The necessary thermoregulation of such a large body to better dissipate heat and avoid significant overheating speaks in favor of more or less bare skin, as is the case with other large mammals such as elephants , rhinos or hippos . A dense coat of fur would require an enormous amount of drinking water to balance the heat balance, but this would have been difficult to obtain in the semi-arid pamphlet region of South America.

The question of whether Megatherium had osteoderms in the skin similar to the large representatives of the Mylodontidae remains unanswered . The bone platelets are randomly distributed in the Mylodonts, similar to those of the bony armor of the armadillos and Glyptodontidae , but have a simpler structure. Occasionally, such formations are also described for Megatherium (and for the related Eremotherium ), for the former from the Campo Laborde site in the pampas region of Argentina. Since at most of the sites where Megatherium remains are also associated with various Mylodonts and glyptodonts are also relatively common, there is currently no clear anatomical evidence for this.

Disease-related bone changes are often found in Megatherium as in numerous other Megatheria. They mostly affect the spine. They often appear on the tail and pelvis. Among other things, the type skeleton of M. celendinense is characterized by numerous pathological changes that not only affect both of the above-mentioned skeletal sections , but also the skull and ribs. If M. urbinai is found , there is still bone swelling due to osteoarthritis , which may be due to a fracture.

Systematics

Internal systematics of the Megatheriinae according to De Iuliis et al. 2009 and Pujos et al. 2013
 Megatheriinae  


 Megathericulus


   

 Anisodontherium



   


 Megatheriops


   

 Pyramiodontherium



   

 Eremotherium


  Megatherium  
  M. ( Megatherium ) 

 M. americanum


   

 M. altiplanicum



  M. ( Pseudomegatherium ) 

 M. sundti


   

 M. urbinai


   

 M. celendinense


   

 M. medinae


   

 M. tarijense










Template: Klade / Maintenance / Style

Megatherium is a genus of the extinct family of Megatheriidae . These include medium-sized to very large representatives from the suborder of the sloths (Folivora). Within the sloth, the Megatheriidae, together with the Megalonychidae and Nothrotheriidae, form a more closely related group, the superfamily Megatherioidea . In a classical view, supported by studies of skeletal anatomy, the Megatherioidea form one of the two great lines of sloths, the other is found in the Mylodontoidea . Molecular genetic analyzes and investigations into protein structure establish a third line with the megalocnoidea . According to the results of the latter studies, the three-toed sloths ( Bradypus ) also belong to the Megatherioidea, one of the two species of sloth that still exist today. One of the closest relatives of Megatherium within the Megatheriidae is the similarly large Eremotherium , which is the sister taxon , but in contrast to Megatherium, it inhabited the tropical lowland areas of South America and also penetrated to North America. The older representatives Pyramiodontherium and Megatheriops also belong in a closer relationship . All of these forms form the subfamily of the Megatheriinae , which represent the developed large ground sloths within the Megatheriidae.

The genus is divided into two sub-genera with a total of nine known species today:

  • Subgenus Megatherium Cuvier , 1796

With the exception of M. americanum , the best-known and best-studied species, all other representatives are so far only known of little finds. The subgenus Pseudomegatherium includes the species that are largely found in the Andes or in the narrow coastal strip to the Pacific. It differs from Megatherium , and especially from the previously known main representative, M. americanum , by reducing body size by 20 to 60% - however, M. celendinense is also known to be a species that is almost the size of M. americanum reached. Other differences are the slightly different design of the joint surfaces on the occiput for the cervical spine (higher up and protruding more prominently), shorter snouts, a slightly different design of the hand with two outer metacarpal bones of equal length, flatter thigh bones and certain features on the ankle bone . Some of these properties, such as the shape and position of the occipital condyles as well as the shape of the femur or the hand, are associated with special adaptations to the geographic conditions of the Andes, such as stronger to permanent quadruped movement.

In addition to the species recognized today, other species were named or described, such as M. lundii , M. gaudryi , M. cuvieri or M. parodii , but they are mostly synonymous with M. americanum . There is disagreement with M. gallardoi , a very large representative of Megatherium , who was described in 1921 by Carlos Ameghino and Lucas Kraglievich using a 83 cm long, but toothless skull from Buenos Aires dating to the Middle Pleistocene . Here, some authors consider the species to be valid and emphasize, among other things, the middle jaw bone, which has hardly grown together with the upper jaw, and the lower height of the lower jaw body resulting from a lower hypsodontia of the molars as special characteristics. Other scientists attribute these characteristics in turn to the intraspecific variability of M. americanum , which, according to this view, would be the only representative of its genus in the pampa region. The species M. antiquum , which originates from the Lower Pliocene and was established in 1885 by Florentino Ameghino with the help of isolated teeth, is problematic . The teeth are similar to those of M. americanum , but only one third of the size. The independence of the species is questioned, as the only few pieces of found material show hardly any diagnostic features.

Tribal history

Origins

There are several theories about the origin of the genus Megatherium . On the one hand, an origin is generally assumed in the southern part of South America. From there the genus spread further west and later reached its highest diversity in the Pleistocene in the Andean region . This assumption is congruent with the frequent and, with around half a dozen genera, quite diverse records of Pliocene and Upper Miocene Megatheria in central and southern South America. So come alone in the Upper Miocene conglomerado osífero in the lower section of the Ituzaingó Formation , which at the shore banks of the lower reaches of the Paraná River near the Argentine city of Paraná is open, with Eomegatherium , Pliomegatherium , Pyramiodontherium and Promegatherium four genera. A far more northerly formation cannot be ruled out, however, information from this period in northern South America is often missing. The representatives of the late Megatheria from the transition from the Miocene to the Pliocene, such as Urumaquia and Proeremotherium , found there since the beginning of the 21st century , do not necessarily suggest that the taxonomic diversity here was less than in the more southern regions. The third possibility is that Megatherium originated in the Andes region, which in turn would be consistent with the highest biodiversity proven here. In addition, M. altiplanicum is the oldest record of the genus in this region, dating back to the beginning of the Pliocene, with radiometric data indicating an age between 5.4 and 2.8 million years.

In the Pleistocene, around half a dozen species have survived from the Andean region; their chronological classification is sometimes only imprecise due to the few finds. The most important and common species, M. americanum , comes from the pampas region . This was widespread there and occurred at least since the early Middle Pleistocene . Their occurrence is in the local stratigraphy by the faunal of americanum Megatherium biozone displayed, which coincides with the beginning of the Middle Pleistocene in front of around 780,000 years ago and the previous Tolypeutes pampaeus biozone replaced, named after a now-extinct banded armadillo .

Extinction and human influence

The majority of the finds come from the Upper Pleistocene . The most recent finds dating back to the end of the Pleistocene and early Holocene can also be attributed to it . They belong to the time of the arrival of the first human inhabitants of South America, which can be detected for the first time around 14,800 before today, and at the same time to the phase of the Quaternary extinction wave , to which numerous large mammals fell victim worldwide. To what extent the early colonists of America were directly involved in the extinction of the giant sloth species is a matter of dispute in research. There are so far only few indications of interactions between humans and Megatherium . The findings of Arroyo Seco , a multiphase field site in the province of Buenos Aires in Argentina, are significant in this context . In the lower horizons, which radiocarbon dates indicate between 10,500 and 12,240 years ago, in addition to the remains of human hunter-gatherer groups , remnants of Megatherium were found, which suggests the hunt for or use of the remains of the giant ground sloth. The archaeological site of Paso Otero 5 in the same province contained a good 80,000, for the most part heavily broken, bone fragments on almost 100 m². Their fragmented state allows an exact determination only to a limited extent, however a total of 29 specimens were assigned to Megatherium . The remains of the fauna were associated with over 80 stone artifacts made of quartzite , including individual fish tail points . The age of the site was determined using the radiocarbon method to be 10,440 to 9,400 years BP . A heel bone of Megatherium , which was surrounded by numerous burned bones, proved to be a special feature ; they are interpreted as fuel.

In the transition period from the Upper Pleistocene to the Lower Holocene is Campo Laborde classified, also located in the Argentine province of Buenos Aires. In addition to more than 100 pieces of quartzite as human relics, more than 99,000 bone finds have been made so far, including 108 remnants of Megatherium , which belong to a partial skeleton without a skull of a single individual. The bones as a whole are partly badly bruised. Individual ribs of Megatherium have cutting marks and have been modified to tools in some cases. Overall, the finding shows that the skeleton was clearly dissected by humans. Radiocarbon measurements on individual bones of the sloth originally indicated an age of 7750 to 8700 years ago. They suggested that Megatherium would have survived into the Lower Holocene, with which the sloth genus, in contrast to numerous other large ground sloths, would have survived both the first human arrival in South America and the rapid climatic changes at the end of the last glacial period by several thousand years. More recent dates from 2019, however, show significantly higher age values ​​at 10,250 to 12,730 years ago.

In addition to the few traces of the manipulation of Megatherium's bones by humans, there is a first cervical vertebra showing individual cut marks from stone artefacts. It was discovered in the pampas region and reached the Museo di Storia Naturale in Florence in the mid-19th century . However, there are no references to the exact stratigraphic position of the find and thus to the context of the find, which means that the bone remains are problematic.

Research history

Cuvier and the Megatherium

Skeleton reconstruction of Megatherium after Bru de Rámon, 1793
The first skeleton of Megatherium today in the Museo Nacional de Ciencias Naturales in Madrid

The earliest known find of Megatherium is an almost complete skeleton, which, according to various sources, was discovered between 1787 and 1789 by Manuel Torres, a Dominican , in Luján on the banks of the Río Luján in what is now the Argentine province of Buenos Aires . Nicolás del Campo , then Viceroy of Río de la Plata , shipped the skeleton packed in seven boxes to Spain to the Real Gabinete de Historia Natural de Madrid , where it arrived on September 29, 1789. There Juan Bautista Bru de Ramón (1740–1799) received it. He worked there as a taxidermist and made skeletal reconstructions of dead animals for the natural history cabinet, such as elephants. He started work immediately and finished the reconstruction four years later with the position of the skeleton in a pose that is rather unnatural from today's perspective. However, from a natural history perspective, Brus' skeleton reconstruction of Megatherium was the first of an extinct vertebrate in the world. In addition to listing the skeleton, Bru also prepared a monograph with a description of the skeleton, which also contained 22 illustrations, one of the reconstruction and the rest of individual bones drawn by Manuel Navarro . However, the description was not published publicly, but some copies of the drawings were handed over to a French representative in 1793.

Baron Georges Léopold Chrétien Frédéric Dagobert Cuvier

The copies came into the hands of the French anatomist Georges Cuvier (1769–1832), who was then working at the Muséum national d'histoire naturelle in Paris and was supposed to prepare a report on the find. This appeared in 1796 in the magazine Magasin encyclopédique , in which he gave the giant animal the scientific name Megatherium americanum . The report is therefore the first description of the genus and species. The genus name is derived from the Greek words μέγας ( mégas "large") and θηρίον ( thērion "animal") and refers to the size of the sloth. In his description, Cuvier used the comparative anatomy method, which was new for his time , using the drawings as a basis; Cuvier himself had never personally inspected the Spanish skeleton. In his report he incorrectly referred to the origin of the skeleton as "Paraguay", but Cuvier's article is significant in that it is his first work on extinct animals. Cuvier also noted that similar animals like Megatherium no longer existed today and were thus extinct, which was a revolutionary view at the time.

Cuvier's report was brought to Spain by José Garriga , who wanted to translate it there. He found out that Bru had already written an article and published it together with Cuvier in the same year under his editorship and at his own expense. This book paved the way for another publication by Georges Cuvier, which appeared in 1804 under the title Sur le Megatherium and in which he further worked out the relationship with the sloths. For Cuvier, primarily the features of the skull, such as the structure of the zygomatic arches, and the shoulder region, such as the developed collarbone , spoke for a relationship to today's tree-dwelling sloths, and secondarily the structure of the teeth and the design of the limbs. With the limbs, Cuvier noticed that they were more similar to today's anteaters and armadillos and were significantly shorter than the modern sloths. Later, in 1812, he added his second essay and Brus illustrations to his work Recherches sur les ossemens fossiles , which is one of the foundational works for the development of paleontology as a scientific discipline.

Darwin and Owen

Caricature of Richard Owen riding a Megatherium skeleton

Since the recovery of the first skeleton from Megatherium near Luján, this was the only find of this giant ground sloth for more than four decades. At the beginning of the 1830s , another partial skeleton came to light near Villanueva on the Río Salado , which flows through the pampa plains south of Buenos Aires , which protruded from the river at low water after a particularly long dry phase. The fossil remains were recovered and sent to England by the high-ranking British diplomat Woodbine Parish , where, after thorough preparation, William Clift presented them to the Royal College of Surgeons and published them in 1835. Since Parish assumed that more skeletons could be found in the Pampa region, he asked the then governor of Argentina, Juan Manuel de Rosas , for help in the search, which subsequently led to the discovery of two more skeletons. The voyage of Charles Darwin (1809–1882), which he made with the HMS Beagle between 1831 and 1837, is of great importance for the exploration of Megatherium . At the end of August 1832 he discovered numerous new finds of the genus in rocky outcrops on the coast near Punta Alta near Bahía Blanca in what is now Argentina. Since the on-board library of the Beagle also contained a translated text with a picture of Cuvier's description, Darwin was familiar with Megatherium , but in his journals he described numerous different fossils as belonging to Megatherium . Darwin visited the region again in October 1833 and also reached Luján, from where the first Megatherium skeleton came.

The finds that had been made during the trip were sent to England to the Royal College of Surgeons in London, where from 1836 the important anatomist Richard Owen (1804-1892) began to deal with them. In 1840 Owen published his first treatise on the giant sloth, which he referred to as M. cuvieri (a name introduced by Anselme Gaëtan Desmarest in 1822 as an alternative name for M. americanum , but considered a nomen illegitimum ). Between 1851 and 1860 Owen published a series of monographs on Megatherium , each titled On the Megatherium (Megatherium americanum, Cuvier and Blumenbach) , each devoted to different parts of the skeleton. His final work was published in 1861 and was called Memoir on the Megatherium or giant Ground-sloth of America (Megatherium americanum, Cuvier) . This is how Owen realized that Megatherium lived terrestrially due to its size and placed its weight on the outer rays of the hands and feet (pedolateral) . He also reconstructed that the animal was able to stand up on its hind legs, propping itself up with its tail in order to search for food with its front legs. Due to the precise representations and drawings, these treatises are still considered standard works on ground sloths today. The resulting image of Megatherium had a lasting impact on the public. Because of the enthusiasm that Owen showed for the sloth, he was caricatured several times.

Larrañaga and the armored giant sloth

Another episode that had a lasting impact on the image of Megatherium, at least in the course of the 19th century, was the discovery of a back and tail armor as well as a thigh bone, which, according to today's perspective, belong to a representative of the Glyptodontidae , heavily armored relatives of the armadillos ; the group was not yet known at the time. Dàmaso Antonio Larrañaga (1771-1848), one of the leading naturalists in the Spanish colonies at the time, made a scientific description of it in his Diario de Historia Natural in 1814 and added the name Dasypus ( Megatherium Cuv) to it. The specification of Megatherium as a sub-genus for today's long-nosed armadillos led to the idea of ​​armored giant sloths arising in the subsequent period. Cuvier personally gave Larrañaga's taxonomic name in 1824 an opportunity to include it in the second edition of his work Recherches sur les ossemens fossiles . The idea of ​​armored giant sloths was widespread, as in 1835, when describing the second megatherium skeleton find, Clift assigned the armor parts associated with the remains to the sloth. Even Darwin noted several finds of shell fragments from Megatherium on his Beagle voyage , in some cases he assigned certain remains to the sloth species only on the basis of the presence of bone platelets.

Objections to the armor of Megatherium were raised as early as the 1830s, including in 1833 by Joseph Eduard d'Alton based on armor and bone finds from Uruguay and Brazil, which, after intensive anatomical comparisons, he associated with giant armadillos. The description of Hoplophorus by Peter Wilhelm Lund in 1838 and of Glyptodon by Owen the following year, as representatives of the Glyptodontidae, both showed strong similarities to Larrañaga's Dasypus ( Megatherium Cuv), but ultimately proved that the previously known tank finds were completely different, but also belonged to huge animals. In an extensive description of Glyptodon in 1841, Owen revised the armor remains associated with Megatherium and corrected their actual affiliation. In 1865, the English paleontologist Thomas Henry Huxley (1825–1895) once again pointed out the clear evidence of the different origins of the two groups of fossils in a paper on the skeletal anatomy of Glyptodon . It should be noted that there were actually large ground sloths with bone platelets in their skin, but these never formed a solid shell. In addition, sloths all belong to a different lineage ( Mylodontidae ), which is somewhat distantly related to the Megatheriidae. The existence of similar loosely scattered osteoderms in the skin of Megatherium is also controversial.

The turn of the 20th century

At the end of the 19th and the beginning of the 20th centuries, the Italian brothers Florentino (1854–1911) and Carlos Ameghino (1865–1936) were particularly important for paleontological research in South America. They mostly described several species of Megatherium independently of each other , of which only M. tarijense from 1880 is valid until today. The description of the species followed long after the discovery and first publication of the finds by Paul Gervais in 1855 , but it showed that there were also representatives of the giant sloth that were significantly smaller than M. americanum . This also provided the first evidence of the subgenus Pseudomegatherium . A good dozen years later, two other species followed with M. sundti and M. medinae by Rudolph Amandus Philippi . In the first half of the 20th century, Lucas Kraglievich (1886–1932) and Robert Hoffstetter (1908–1999) had a lasting impact on research.

literature

  • Paul S. Martin and Richard G. Klein (Eds.): Quaternary Extinctions. A Prehistoric Revolution. The University of Arizona Press, Tucson AZ 1984, ISBN 0-8165-1100-4 .
  • Richard A. Fariña, Sergio F. Vizcaíno and Gerardo De Iuliis: Megafauna. Giant beasts of Pleistocene South America. Indiana University Press, 2013, ISBN 978-0-253-00230-3 , pp. 254-256.

Individual evidence

  1. ↑ a b c d e f Pierre-Antoine Saint-André and Gerardo De Iuliis: The smallest and most ancient representative of the genus Megatherium Cuvier, 1796 (Xenarthra, Tardigrada, Megatheriidae), from the Pliocene of the Bolivian Altiplano. Geodiversitas 23 (4), 2001, pp. 625-645.
  2. ^ Carlos Castor Cartelle: Preguiças terrícolas, essas desconhecidas. Anales Ciência Hoje 27, 2000, pp. 19-25.
  3. ↑ a b c d e f g h Gerardo De Iuliis, François Pujos and Giuseppe Tito: Systematic and Taxonomic Revision of the Pleistocene Ground Sloth Megatherium (Pseudomegatherium) Tarijense (Xenarthra: Megatheriidae). Journal of Vertebrate Paleontology 29 (4), 2009, pp. 1244-1251.
  4. ↑ a b c d e f g h i François Pujos and Rodolfo Salas: A new species of the genus Megatherium (Mammalia: Xenarthra: Megatheriidae) from the Pleistocene of Sacaco and Tres Ventanas. Palaeontology 47 (3), 2004, pp. 579-604.
  5. ↑ a b Fariña, Vizcaíno and De Iuliis: Megafauna . 2013, pp. 213-216.
  6. ↑ a b c d e Sergio F. Vizcaíno, M. Susanna Bargo and Richard A. Fariña: Form, function, and paleobiology in xenarthrans. In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 86-99.
  7. ↑ a b c M. Susana Bargo, Segio F. Vizcaíno, Fernando M. Archuby and R. Ernesto Blanco: Limb bone proportions, strength and digging in some Lujanian (Late Pleistocene-Early Holocene) mylodontid ground sloths (Mammalia, Xenarthra). Journal of Vertebrate Paleontology 20 (3), 2000, pp. 601-610.
  8. ↑ a b c d Diego Brandoni, Esteban Soibelzon and Alejo Scarano: On Megatherium gallardoi (Mammalia, Xenarthra, Megatheriidae) and the Megatheriinae from the Ensenadan (lower to middle Pleistocene) of the Pampean region, Argentina. Geodiversitas 30 (4), 2008, pp. 793-804.
  9. ^ A b c Carlos Ameghino and Lucas Kraglievich: Descripción del "Megatherium gallardoi" C. amegh descubierto en el Pampeano inferior de la ciudad de Buenos Aires. Anales del Museo Nacional de Historia Natural de Buenos Aires 31, 1921, pp. 134–156.
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  12. ↑ a b c d e f g h François Pujos: Megatherium celendinense sp. nov. from the Pleistocene of the Peruvian Andes and the relationships of megatheriines. Palaeontology 49 (2), 2006, pp. 285-306.
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  14. ↑ a b Gerardo De Iuliis and Cástor Cartelle: A new giant megatheriine ground sloth (Mammalia: Xenarthra: Megatheriidae) from the late Blancan to early Irvingtonian of Florida. Zoological Journal of the Linnean Society 127, 1999, pp. 495-515.
  15. ↑ Gerardo De Iuliis: Toward the morphofunctional understanding of the humerus of Megatheriinae: The identity and homology of some diaphyseal humeral features (Mammalia, Xenarthra, Megatheriidae). Senckenbergiana biologica 83, 2003, pp. 69-78.
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  23. ↑ Agustín Scanferla, Ricardo Bonini, Lucas Pomi, Enrique Fucks and Alejandro Molinari: New Late Pleistocene megafaunal assemblage with well-supported chronology from the Pampas of southern South America. Quaternary International 305, 2013, pp. 97-103.
  24. ↑ a b Federico L. Agnolin, Nicolás R. Chimento, Diego Brandoni, Daniel Boh, Denise H. Campo, Mariano Magnussen and Francisco De Cianni: New Pleistocene remains of Megatherium filholi Moreno, 1888 (Mammalia, Xenarthra) from the Pampean Region: Implications for the diversity of Megatheriinae of the Quaternary of South America. New Yearbook for Geology and Paleontology Abhandlungen 289/3, 2018, pp. 339–348.
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  35. ↑ Santiago Pantiño and Richard A. Fariña: Ungual phalanges analysis in Pleistocene ground sloths (Xenarthra, Folivora). Historical Biology 29 (8), 2017, pp. 1065-1075, doi: 10.1080 / 08912963.2017.1286653 .
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  66. ^ Gustavo Martínez, María Gutiérrez and José Luis Prado: New Archaeological Evidences from the Late-Pleistocene / Early-Holocene Paso Otero 5 Site (Pampean Region, Argentina). Current Research in the Pleistocene 21, 2004, pp. 16-18.
  67. ↑ Gustavo Martínez: Arqueología del curso medio del Río Quequén Grande: Estado actual y aportes a la arqueología de la región Pampeana. Relaciones de la Sociedad Argentina de Antropología 31, 2006, pp. 249-275.
  68. ↑ Gustavo Martínez, María A. Gutiérrez and Eduardo P. Tonni: Paleoenvironments and faunal extinctions: Analysis of the archaeological assemblages at the Paso Otero locality (Argentina) during the Late Pleistocene – Early Holocene. Quaternary International 299, 2013, pp. 53-63.
  69. ↑ Marína A. Gutiérrez and Gustavo A. Martínez: Trends in the faunal human exploitation during the Late Pleistocene and Early Holocene in the Pampean region (Argentina). Quaternary International 191, 2008, pp. 53-68.
  70. ↑ Anthony D. Barnosky and Emily L. Lindsey: Timing of Quaternary megafaunal extinction in South America in relation to human arrival and climate change. Quaternary International 217, 2010, pp. 10-29.
  71. ↑ Gustavo G. Politis, Pablo G. Messineo, Thomas W. Stafford Jr. and Emily L. Lindsey: Campo Laborde: A Late Pleistocene giant ground sloth kill and butchering site in the Pampas. Science Advances 5, 2019; S. eaau4546, doi: 10.1126 / sciadv.aau4546 .
  72. ↑ Karina V. Chichkoyan, Bienvenido Martínez-Navarro, Anne-Marie Moigne, Elisabetta Cioppi, Margarita Belinchón and José L. Lanata: Description and interpretation of a Megatherium americanum atlas with evidence of human intervention. Rivista Italiana di Paleontologia e Stratigrafia 123 (1), 2017, pp. 51-64.
  73. ↑ Georges Cuvier: Notice sur le squelette d'une très grande espèce quadrupède inconnue jusqu'à présent, trouvé au Paraguay, et déposé au Cabinet d'Histoire naturelle de Madrid. Magasin encyclopédique 1, 1796, pp. 303-310 ( [1] ).
  74. ↑ a b Christine Argot: Changing Views in Paleontology: The Story of a Giant (Megatherium, Xenarthra). In: Eric J. Sargis and Marian Dagosto (Eds.): Mammalian Evolutionary Morphology. Vertebrate Paleobiology and Paleoanthropology Series 2008, pp. 37-50.
  75. ↑ Don Joseph Garriga: Descripción del esqueleto de un quadrúpedo muy corpulento y raro, que se conserva en el Real Gabinete de Historia Natural de Madrid. Madrid, 1796 ( [2] ).
  76. ^ Georges Cuvier: Recherches sur les ossemens fossiles de quadrupèdes. Paris, 1812, chapter 8 and associated plates 2 and 3 ( [3] ).
  77. ^ A b William Clift: Some account of the remains of the Megatherium sent to England from Buenos Ayres by Woodbine Parish. Transactions of the Geological Society 2 (3), 1835, pp. 437-450 ( [4] ).
  78. ↑ a b Paul D. Brinkman: Charles Darwin's Beagle Voyage, Fossil Vertebrate Succession, and `` The Gradual Birth & Death of Species ''. Journal of the History of Biology 43, 2010, pp. 363-399.
  79. ^ Richard Owen: Fossil Mammalia. In: Charles Darwin (Ed.): Zoology of the Voyage of HMS Beagle, under the command of Captain Fitzroy, during the years 1832 to 1836. Part 1 of 4, London, 1840, pp. 13–111 (pp. 100– 106) ( [5] ).
  80. ^ Richard Owen: On the Megatherium (Megatherium americanum Blumebach). Philosophical Transactions of the Royal Society of London: Part I. Preliminary Observations on the Exogenous Processes of Vertebrae. 141, 1851, pp. 719-764 ( [6] ), Part II. Vertebrae of the Trunk. 145, 1855, pp. 359-388 ( [7] ), Part III. The skull. 146, 1856, pp. 571-589 ( [8] ), Part IV. The bones of the anterior extremities. 148, 1858, pp. 261-278 ( [9] ), Part V. The bones of the posterior extremities. 149, 1859, pp. 809-829 ( [10] ).
  81. ^ Richard Owen: Memoir on the Megatherium, or giant ground-sloth of America (Megatherium americanum, Cuvier). London, 1861, pp. 1-84 ( [11] ).
  82. ↑ a b Fariña, Vizcaíno and De Iuliis: Megafauna . 2013, pp. 31–71.
  83. ↑ Georges Cuvier: Recherches sur les ossemens fossiles, où l'on rétablit les caractères de plusieurs animaux dont les révolutions du globe ont détruit les espèces. Tome Cinquième. Paris, 1823, pp. 1-405 (pp. 174-192 [12] ).
  84. ↑ Juan-Carlos Fernicola, Serdio F. Vizcaíno and Richard a. Fariña: The evolution of armored xenarthrans and the phylogeny of the glyptodonts. In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 79-85.
  85. ↑ Joseph Eduard d'Alton: About the fossil armor fragments brought with him by the late Mr. Sellow from the Banda oriental and the associated bone remains. Treatises of the Royal Academy of Sciences in Berlin, 1833, pp. 369–424 ( [13] ).
  86. ↑ Peter Wilhelm Lund: Blik paa Brazil Dyreverden för Sidste Jordomvaeltning. Andean Afhandling: Patteedyrene. Det Kongelige Danske Videnskabernes Selskbas Naturvidenskabelige og Matematiske Afhandlinger 8, 1839, pp. 61–144 (p. 83) ( [14] ).
  87. ↑ Richard Owen: Note on the Glyptodon. In: Woodbine Parish (ed.): Buenos Ayres, and the provinces of the Rio de La Plata: their present state, trade and dept; with some account from original documents of the progress of geographical discovery in those parts of South America during the last sixty years. London, 1839, pp. 178b-178e ( [15] ).
  88. ^ A b Richard Owen: Description of a tooth and part of the skeleton of the Glyptodon clavipes, a large quadrupede of the Edentate order, to which belongs the tesselated bony armor described and figured by Mr. Clift in the former Volume of the Transactions of the Geological Society; with a consideration of the question whether the Megatherium possessed an analogous dermal armor. Transactions of the Geological Society 2 (6), 1841, pp. 81-106 ( [16] ).
  89. ^ Thomas Henry Huxley: On the Osteology of the Genus Glyptodon. Philosophical Transactions of the Royal Society of London 155, 1865, pp. 31-70 ( [17] ).
  90. ^ Robert V. Hill: Comparative Anatomy and Histology of Xenarthran Osteoderms. Journal of Morphology 267, 2005, pp. 1441-1460.

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This article was added to the list of excellent articles in this version on December 23, 2017 .