Megatheriidae

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Megatheriidae
Skeletal reconstruction of Megatherium in the Natural History Museum, London

Skeletal reconstruction of Megatherium in the Natural History Museum, London

Temporal occurrence
Lower Miocene to early Holocene
18 million years to 11,000 years
Locations
Systematics
Higher mammals (Eutheria)
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Megatherioidea
Megatheriidae
Scientific name
Megatheriidae
Gray , 1821

The Megatheriidae are an extinct family of sloths with medium-sized to very large representatives. They first appeared in the Lower Miocene , about 18 million years ago, in the southern part of South America , in Patagonia . These early and comparatively small forms are mostly assigned to the subfamily Planopinae , which differ morphologically from the later members. The genera that were widespread in the Pleistocene and are best known today were Eremotherium and Megatherium , they belong to the younger line of the Megatheriinae , which can be detected for the first time in the Middle Miocene. Representatives of both genres sometimes reached huge dimensions of up to 6 m in length and 4 to 6 t body weight. They therefore represent the largest sloths that have ever lived and the largest endemic land mammals in South America. Megatherium was particularly widespread in the pampas region and in the Andes , Eremotherium inhabited tropical lowlands and was the only form of Megatherium to reach North America . The last representatives of the Megatheriidae died out in the transition from the Upper Pleistocene to the Lower Holocene .

The late Megatheria in particular are among the best-studied sloths of all, but less information is available about the early genera due to the scarce fossil material. Due to their enormous body weight, the megatheria were pure ground dwellers who mostly moved on quadrupeds; later forms could also stand up on their hind legs to look for food in the branches of trees. This mostly consisted of soft plant food that was bitten into with the characteristic teeth. The exploration of the megatheria dates back to the late 18th century and began with a skeleton find in Luján in the pampas region of Argentina. Just 30 years later, in 1821, John Edward Gray established the family name Megatheriidae.

features

General

The Megatheriidae comprise the largest representatives of the sloths. Early forms from the Lower Miocene such as Prepotherium , which belong to the Planopinae group , were still relatively small at around 123 kg, but later, especially those of the subfamily Megatheriinae, were extraordinarily large. The early Megatheriine Pyramiodontherium reached a body weight of 2.5 to 3.6 t, the well-known representatives of the Pleistocene such as Eremotherium and Megatherium weighed around 4 to 6 t. Both were quite variable in the size of the individual species and also include smaller forms that weighed only about 1 to 1.5 tons. As predominantly ground-dwelling mammals, the Megatheria were characterized by their strong limbs and shorter limbs than today's tree sloths. Like all extinct sloths, they also had longer tails than today's species. The tail was long and robust in the early Megatheria, and comparatively shorter in the later, but extremely strong.

Skull and dentition features

Skull of Megatherium

The skull of the small forms such as Prepoplanops reached, if it is fully known, about 25 cm in length, the largest skulls had Eremotherium and Megatherium , which were between 65 and 86 cm long. When viewed from above, the skull was usually long and narrow to tubular. The most striking feature was the bone process formed on the front part of the zygomatic arch , which reached down and served as the attachment point for the masticatory muscles. As a rule, the zygomatic arch in the sloths is not formed closed, only in the largest representatives of the Megatheriidae it showed itself to have grown together again. The lower jaw was usually massive and had a downward, hump-like protuberance on the lower edge of the bone body as a special characteristic. Compared to the size of the lower jaw, this protuberance is deeper than in other sloths, the depth increasing as the megatheria developed. It served to accommodate the alveoli of the ( hypsodontic ) teeth, which were also becoming increasingly crowned .

As with all articular animals, the dentition differed markedly from that of most of the higher mammals . The developed megatheria were in contrast to the today living and the predominant, extinct sloths characterized by completely uniform ( homodontal ) teeth, which had a molar-like appearance and stood in a closed row. Only at the earliest representatives of each front teeth eckzahnförmig (were caniniform ) redesigned, similar to the related Megalonychidae . They were also at a more or less short distance from the rear molars. The molar-like teeth had a bilophodontic structure with two pointed transverse ridges on the chewing surface and had a rectangular to square outline. Like the other secondary articulations, the teeth lacked tooth enamel , the hardest substance in the tooth. They consisted largely of dentin , the hardest variant of which, orthodentine , took up only 16 to 19% of a tooth, which corresponds to about half of that in the Mylodontidae or Nothrotheriidae . This thinning of the orthodentine is explained compared to other sloth lines from the special tooth structure of the Megatheriidae. As a result, the mostly very high cross-bars on the chewing surfaces with a pointed cross-section were subject to a constant self-sharpening process when chewing the food and thus did not dull. Accordingly, the deep notches between the ridges were made of the softer vasodentin .

Body skeleton

Hand of Megatherium with the typical four fingers
Hand of Eremotherium with the typical three fingers

There were also individual modifications in the body skeleton. In addition to the xenarthric joints (secondary joints or xenarthrals) that are typical for all articular animals , which occurred on the transverse processes of the posterior thoracic vertebrae and the lumbar vertebrae and contribute to the more solid anchoring of the spine and prevent lateral dislocation, there are special features to be found in the musculoskeletal system. The humerus was a tubular bone with a protruding lower end. In the megatheria, the third trochanter was missing on the massive and flattened front and back thighbones - a distinctive bony elevation on the shaft as a muscle attachment point - which is otherwise a typical feature of the secondary articular animals. Exceptions are the earliest forms in which this occurred as a slight elevation. The tibia and fibula tended to grow together tightly, in contrast to other groups of sloths with a clear separation of the two bones. Noticeable deviations can still be found in the foot skeleton. The hind foot was rotated more strongly than in other ground sloths, so that the body weight rested on the outermost, fifth ray and the heel bone ( pedolateral ). This is particularly clear with Eremotherium and Megatherium , but the rotation of the foot is more or less present in all developed Megatheria. The rotation to the pedolateral foot is known in all ground sloths with the exception of the Megalonychidae and developed independently with different variants within the individual lines ( convergent evolution ), whereby this rotation mainly took place in the area of ​​the tarsus and strongly reshaped the ankle bone and partly the metatarsal bones. As a result of the rotation, the foot was additionally curved, whereby the curvature was not as extensive and high as in the related Nothrotheriidae . As a result, the heel bone touched the full length of the Megatheria, which differs from the Nothrotheria, in which only the rearmost end of the calcaneum touched the ground. Overall, the rear foot had a highly modified design and had a similar structure in all Megatheria with a known foot skeleton. It consisted only of the three outer rays (III to V), with the last ray also having a clearly flattened shape. Of the three rays, in the late Megatheria, only the central ray (ray III) had three phalanges (of which the first two were fused). The presence of the terminal phalanx on the third foot ray indicates that a claw was formed here. The two outer ones (rays IV and V) only had two toe members, so that there were no claws here. An exception is Pyramiodontherium , in which there was a small, greatly reduced third phalanx on the fourth toe. Possibly this is an indication that early representatives of the Megatherien also had this characteristic. The forefoot is only really well passed on in Eremotherium and Megatherium . In Eremotherium it had five rays (I to V) in early forms and three rays (III to V) in later forms, with claws only being present on rays I to IV or III and IV accordingly. The hand of Megatherium had a shape intermediate between these two variants with four rays (II to V) and claws on rays II to IV. Another specialty is the fusing of the innermost metacarpal bones (partly also the two innermost ones) and some Elements of the wrist, such as the large polygonal bone , form a unit called the metacarpal-carpal complex (MCC).

distribution

The megatheria originated in the Lower Miocene in the southern part of South America and were largely restricted to this continent. Only in the Pliocene and Pleistocene reached eremotherium the only representative in connection with the American Great faunal and North America . The very early forms from the Planopinae group are largely known from Patagonia , but a few teeth from La Venta in today's Colombia also suggest a presence in the north. The younger representatives, the Megatheriinae, then occurred over large parts of South America, but the main focus of the distribution was the regions of the Pampas and Mesopotamia to the north . The spread of the megatheria in the Middle Miocene from south to north could have taken place via an existing corridor in the western Amazon region , as is also assumed for some South American ungulates . However, a route even further to the west is also possible over the area of ​​today's Andes , whose rapid unfolding did not take place until the Upper Miocene in a period between 10.3 and 6.8 million years. The Megatheria found their greatest distribution in the Pleistocene. Eremotherium inhabited the tropical lowland areas in South and North America. Its relative Megatherium, on the other hand, occurred in the temperate regions of the pampas and in higher mountain regions of the Andes, where it has been detected up to an altitude of 4500 m. Also noteworthy is the occurrence of megatheria on the Pacific coast, which in northern Chile and Peru is characterized by an extremely dry desert climate , which in the case of the Atacama has lasted for at least 14 million years. It is assumed here that in the Pleistocene there were oases in the coastal areas in the form of lagoons, swamp areas and grasslands along the coastal zone, which provided a habitat for mammals. This could be confirmed for the region around Sacaco and Ocucaje for the late Middle Pleistocene . The Andes valleys, which were not only used by the Megatheria, but also by the proboscis of South America, are likely to be the routes of spread.

Paleobiology

Early life reconstruction of Megatherium after Heinrich Harder (around 1920)

The megatheria are among the best-studied fossil sloths of all. As a rule, however, the knowledge is limited to the two terminal forms Megatherium and Eremotherium , the older genera are far less extensively investigated. Due to the sometimes enormous weight, all representatives of the Megatheria are to be regarded as terrestrial, i.e. ground-dwelling animals, in contrast to today's tree-living sloths. This also applies to the earliest forms of the Lower Miocene . With their body weight of 100 to 200 kg, these were probably too heavy to climb trees permanently. In addition, early megatheria such as Prepotherium had a massive and short cubit, similar to other early sloths, but differed in the construction and orientation of the olecranon , the upper articular process. As a result, they could not develop as much force and leverage in the forearm above the elbow as is required for climbing or digging. However, other early sloths of this time lived in the trees, moving upright in them like today's anteaters and not hanging down like today's tree sloths, which can be inferred from the structure of the limbs. In the more modern Megatheria the olecranon was very short, and compared to other ground sloths, the humerus had a long and slender structure with a massive lower joint, as has already been demonstrated in the case of Pyramiodontherium from the Upper Miocene. Both speak against the function of the front legs as digging tools. Rather, in addition to intra-species rivalry fights to distribute blows, they were probably also used to eat food by standing up on their back legs and pulling up branches and twigs with their arms. The construction of the rear legs shows a fairly uniform design for all megatheriums. It is particularly noticeable that the thighbone and the shinbone differ less in size than in the Megalonychidae or the Mylodontidae with their long femur and shorter tibia. Longer lower limbs are usually associated with more agile locomotion, as is the case with the nimble horses and deer in contrast to the clumsy rhinos . This is also assumed for the Megatheria with regard to the Mylodonts. Ichnofossils also provide information about the movement of the megatheria . A 59 m long track was discovered in the Río Negro Formation of the Upper Miocene in northern Patagonia . Due to the size of the step seals (average length 66 cm or width 32 cm), Pyramiodontherium can be assumed to be the cause. Another 35 m long track is known from Pehuén-Có in the Argentine province of Buenos Aires . It dates back to the end of the Pleistocene and is related to the Megatherium due to the size of the step seals (average length 88 cm and width 48 cm) . The first-mentioned track indicates a permanent four-footed gait, for the latter, a two-footed locomotion was sometimes considered. However, due to the skeleton structure, it can be assumed that neither Megatherium nor other late Megatheria were permanently biped.

Extremely high-crowned ( hypsodontal ) molars are usually an indicator of a diet that is more specialized in abrasive grass food. The missing enamel of the teeth does not allow detailed examinations of signs of wear. The structure of the transverse strips with a triangular cross-section and a sharp upper edge suggests a diet of soft vegetable food that was only crushed in the mouth and not chewed. In addition to the construction of the chewing apparatus itself, there are also finds of coprolites from Megatherium that contained such plant material. A rather leaf-eating way of life is also assumed for the early Megatheria. It is likely that her very flexible upper lip was used. On the one hand, this is deduced from the toothless front area of ​​the mouth; on the other hand, this could also be reconstructed for Megatherium using the skull.

Systematics

External and internal systematics

Internal systematics of the sloths according to Presslee et al. 2019 (based on protein analysis)
 Folivora  
  Megalocnoidea  

 Acratocnidae (†) 


   

 Parocnidae (†) 



   
  Megatherioidea  


 Nothrotheriidae (†) 


   

 Megatheriidae (†) 



   

 Megalonychidae (†) 


   

 Bradypodidae




  Mylodontoidea  

 Scelidotheriidae (†) 


   

 Choloepodidae


   

 Mylodontidae (†) 






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The megalocnoid is subdivided according to Delsuc et al. 2019

Internal systematics of the sloths according to Varela et al. 2019 (based on skeletal anatomical features)
 Folivora  
  Eufolivora  
  Megatherioidea  


 Megatheriidae (†)


   

 Nothrotheriidae (†)



   

 Megalonychidae



 Mylodontoidea  


 Mylodontidae (†)


   

 Orophodontidae (†)



   

 Scelidotheriidae (†)




   

 Bradypodidae



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The Megatheriidae form a family of medium-sized to very large representatives from the suborder of the sloths (Folivora). The sloths in turn, together with the anteaters (vermilingua), form the order of the tooth arms (pilosa), which is part of the superordinate order of the articulated animals (xenarthra), which also includes the order of the armored articulated animals with today's armadillos (Dasypoda). The secondary joints form one of the four major lines of the higher mammals (Eutheria), their main common feature is the appearance of xenarthric joints (secondary joints or xenarthrals) on the transverse processes of the posterior thoracic vertebrae and the lumbar vertebrae. Within the sloth, the Megatheriidae, together with the Nothrotheriidae and the Megalonychidae, represent a closer family group, which is referred to as the superfamily Megatherioidea . Relying on skeletal anatomical features, the Megatherioidea can be considered one of the two great lines of sloths. The other is indicated by the Mylodontoidea with the Mylodontidae , the Scelidotheriidae and the Orophodontidae as members (the latter two may only have the status as a subfamily of the Mylodontidae). Based on molecular genetic studies and protein analyzes, a third line can be added with the Megalocnoidea , which consists of the sloths of the West Indies . According to the latter investigations, the Megatherioidea with the three-toed sloth ( Bradypus ) include one of the two species of sloth that still exist today. The second genus, the two-toed sloths ( Choloepus ), are assigned to the Mylodontoidea. Most of the time, the Nothrotheria are the closest relatives of the Megatheria within the Megatherioidea. A closer relationship between the Nothrotheria and the Megalonychidae is also discussed. The available genetic and protein-based analyzes have not yet been able to clearly clarify these different views.

Two subfamilies can be distinguished within the megatheries. The phylogenetically older group is represented by the Planopinae from the Lower and Middle Miocene . These still had a canine-shaped front tooth, which was separated from the rear molar-like teeth by a small diastema . The modern Megatheriinae , which are detectable from the Middle Miocene, on the other hand, had completely homodontic molars in a closed row. Originally, the subfamilies of the Nothrotheriinae and the Schismotheriinae were also placed in the Megatheriidae . Based on skull examinations, the Nothrotheriidae, in which Nothrotherium , Nothrotheriops and the semi-aquatic Thalassocnus are placed, but as an independent family that forms the sister group of the Megatheriidae. The representatives of the Schismotheriinae such as Schismotherium , Hapalops or Analcimorphus are only considered to be basic forms of the Megatherioidea, whose relationship to one another and to other members of the superfamily is unclear.

Overview of the genera of the Megatheriidae

Internal systematics of the Megatheriidae according to Varela et al. 2019
 Megatheriidae  
  Megatheriinae  





 Eremotherium


   

 Megatherium



   

 Proeremotherium



   

 Pyramiodontherium



   

 Anisodontherium



   

 Diabolotherium


   

 Megathericulus




  Planopinae  


 Planops


   

 Prepotherium



   

 Prepoplanops




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Today there are two subfamilies with more than a dozen genera:

  • Family Megatheriidae Gray , 1821
  • Subfamily Planopinae Ameghino , 1887 (also Planopsinae Winge , 1923)
  • Subfamily Megatheriinae Gray , 1821

In contrast to this classic view, a phylogenetic study from 2017 considers the Thalassocninae, which were originally assigned to the Nothrotheria and with Thalassocnus, the only known semi-aquatic representative of the sloth, as the third subfamily of the Megatheria. In this they form sister group of the Megatheriinae. Within the Planopinae, the genera Paraplanops , Prepotheriops and Proprepotherium are considered problematic. They were all introduced by Florentino Ameghino at the turn of the 19th to the 20th century, and their type material is mostly heavily fragmented or very poorly preserved. Therefore, the generic names are currently used as nomina dubia . Also problematic is Ocnopus from the group of Megatheriinae, introduced in 1875 by Johannes Theodor Reinhardt , whose holotype shows two teeth that belong to Megatherium . Other postcranial skeletal material that was part of the genus was partially assigned to the Nothrotheriidae or Megalonychidae. According to recent studies, the genus is synonymous with Valgipes from the Scelidotheriidae family , close relatives of the Mylodontidae . The Perezfontanatherium from Uruguay described in 1976 is still regarded as identical to Megatherium or Eremotherium . You may also need Diabolotherium be made to the Megatheriinae. The genus was previously regarded as a member of the Megatherioidea without a more precise assignment.

Tribal history

Development tendencies

In addition to the general increase in body size and the stronger twisting of the foot towards the pedolateral shape, changes in the structure of the teeth can be seen. The phylogenetically older Planopinae still had a set of teeth that resembled their relatives, the Megalonychidae . The foremost tooth in each case was canin-shaped , thus had a canine-like shape, and stood at a certain distance in front of the rear teeth, which became shorter and shorter in the course of development. Furthermore, the rear, molar-like teeth were still oval in shape and narrowed in front and rear, and in addition to the two transverse ridges they had additional cusps on the chewing surface. The Megatheriinae , on the other hand, had a closed row of teeth, the foremost tooth was also shaped like a molar, so that the entire set of teeth had a homodontic structure, while cusps no longer appeared. Early megatheriines were characterized by teeth that were narrowed at the front and back and therefore more rectangular to diamond-shaped, the later ones were characterized by their typically square shape.

Miocene

For the first time, megatheria are recorded in the Lower Miocene . They presumably originated, similar to numerous other groups of collateral animals in southern South America, where they also have their first appearance. The most important finds from this early period come from the Santa Cruz Formation in the southern part of Patagonia and date between 18 and 16 million years ago. Among other things, the genera Planops and Prepotherium , which are among the best-documented representatives of the early megatheria, are found here. A complete skull comes from the former, a partial skeleton without a skull and a lower jaw from the latter. They belong to the subfamily of the Planopinae and, compared to the giant later representatives of the family, were still relatively small forms with a weight of 123 kg for Prepotherium , a member of the Megatheriidae, which has not yet been precisely determined, could have weighed up to 200 kg. Other frequently occurring sloths such as Hapalops , on the other hand, can only be placed in a closer relationship with the Megatheria without belonging directly to them. Outside of this rock unit, Prepoplanops from the Cerro Boleadoras Formation south of Lake Buenos Aires in southern Argentina have been handed down. This was described on the basis of a complete skull with a lower jaw and some leg bones and is chronologically close to the finds of the more southerly Santa Cruz Formation. The Planopinae can still be detected with Planops up to the Middle Miocene, where finds come from the western part of the Argentine province of Neuquén . Teeth of a so far not precisely defined genus with affinities to Planops from the 14 million year old La Venta fossil deposit on the middle reaches of the Río Magdalena in Colombia may also speak for the occurrence of the Planopinae far north of the South American continent.

The Megatheriinae can also be found for the first time in the Middle Miocene. With their later representatives, these belong to the best-studied groups of sloths, but the early forms are mostly fragmented. The earliest known genus is the small Megathericulus , of which numerous remains come from Patagonia, including from 11 to 12 million old deposits of the Río Mayo Formation near Cerro Guenguel and Arroyo Pedregosa , both in western Argentina at the foot of the Andes . It is generally assumed that the Megatheriinae also originated in southern South America, but a toothless lower jaw of Megathericulus from the Río Sepa , a tributary of the Río Urubamba in the Peruvian Amazon , shows that the group was already widespread in the north in the Middle Miocene. The find belongs to a rich fauna community known as the Fitzcarrald local fauna, which is 10 to 17 million years old. The deposits in which the fossils are embedded can be traced back to what used to be a large area of ​​wetland consisting of swamps, lakes and rivers that drained north into the Caribbean , which as Pebas megawetland represents the forerunner of today's Amazon rainforest . Since postcranial skeletal parts of a megatheriine that have not yet been described in detail were discovered in the neighboring area of ​​La Venta , an origin of the more modern representatives further north cannot be ruled out.

From the Upper Miocene, anisodontherium has also been found in southern South America , a medium-sized representative that was first described using a crushed skull with a lower jaw from the Arroyo-Chasicó formation in the Argentine province of Buenos Aires . Further finds, which include remains of the lower jaw and hand bones, are from the Saladillo Formation in northwestern Argentina. Here is one Anisodontherium with its narrow molars still one of the more original Megatheriinen. Another important representative of this period is the pyramiodontherium , which weighs between 2.5 and 3.6 t , which, among other things, has a skull-less partial skeleton from the Toro-Negro formation or a foot skeleton from Andalhuala , both in the north-west, which is so far extraordinarily complete for Miocene Megatheria Argentina, also includes some leg elements from the Conglomerado osífero . The Conglomerado osífero represents the lower section of the Ituzaingó Formation , which is exposed on the banks of the lower reaches of the Río Paraná near the city of Paraná in northeast Argentina. The found there rich faunal also reflects the diversity of Megatheriinen that time resist because of the well-known at least half a dozen genera of Obermiozäns only four occur here: next Pyramiodontherium also Pliomegatherium , Promegatherium and Eomegatherium . Pliomegatherium comprises several mandibular fragments and foot bones. In northern South America, several genera of megatherines have also been recorded since the beginning of the 21st century, which suggests that the taxonomic diversity here was also quite high, but still appears to be limited by the limited number of sites in contrast to the south of the continent. The Upper Miocene Urumaco Formation in northwestern Venezuela proved to be particularly diverse , in which at least 20 different species of collateral articulated animals were detected, including numerous limb bones that are part of the great Urumaquia . From the Codore formation of the Pliocene , also in northwestern Venezuela, there is a complete skull over 41 cm long, which represents Proeremotherium .

As early as the end of the Upper Miocene around 5.8 million years ago, Sibotherium, a member of the Megatheria, appeared in southern North America . This happened even before the Great American Fauna Exchange , which began in the Middle Pliocene around 3.5 million years ago with the closure of the Isthmus of Panama and the creation of a land bridge between the two American continents. The genus has been identified with some teeth, remains of the lower jaw and leg bones in the Curré formation in Costa Rica .

Plio and Pleistocene

Skeletal reconstruction of E. laurillardi based on the finds from Daytona Beach

In the Pliocene, the two largest representatives of the Megatheriidae can be identified for the first time: Megatherium and Eremotherium . The earliest finds of Megatherium come from the highlands of the Altiplano in western Bolivia and are between 5.4 and 2.8 million years old. They include some remains of the lower jaw and skull as well as postcranial elements, including a 39 cm long thigh bone, and thus refer to a small member of the genus who weighed only around 1 to 1.7 t. The geographical origin of Megatherium is discussed, the genus remained restricted to South America and inhabited the temperate southern regions of the pampas and the highlands of the Andes . The oldest evidence of Eremotherium comes from the Upper Pliocene of Florida with several partial skeletons. The found individuals are somewhat more delicate than later representatives of Eremotherium , but have almost reached their size. The origin of Eremotherium is partly sought in the tropical lowland areas of South America, where the genus has its main distribution, but an emergence further north is not excluded. The evidence of Eremotherium in North America also shows that the Megatheria, along with numerous other originally South American animal groups, managed to leave South America in the course of the Great American Fauna Exchange. In the Upper Pleistocene , the largest forms of both the Eremotherium and the Megatherium have been handed down, each weighing between 4 and 6 tons and about 6 m long. Eremotherium disappeared around 11,300 years ago with the end of the last glacial period, Megatherium persisted into the Lower Holocene around 8,000 years ago, possibly only up to around 11,000 years ago, as finds from Campo Laborde in Argentina show.

Research history

John Edward Gray (1800-1875)
The first skeleton of Megatherium , now in the Museo Nacional de Ciencias Naturales in Madrid

The first evidence of a representative of the Megatheria was discovered at the end of the 1780s near the town of Luján in the pampas region of today's Argentina. It was an almost complete skeleton of a huge animal that was brought to Madrid in Spain and was the first skeleton reconstruction of an extinct terrestrial vertebrate to be built there in 1793. The French anatomist Georges Cuvier examined the skeleton and also introduced the scientific name Megatherium americanum , which is still valid today . Its first description appeared in 1796. Further informative finds came to light around 40 years after the skeleton was discovered. The trip of Charles Darwin with the HMS Beagle , on which he found numerous bones of Megatherium in Punta Alta near Bahía Blanca , also in the Pampa region, in 1832 is significant . All fossil material recovered during the voyage was shipped to London, where Richard Owen subjected it to detailed analyzes from 1836 onwards. After a first report in 1840, Owen published several publications on Megatherium between 1851 and 1860 , which significantly shaped the image of the large ground sloth.

Important other finds came to light again at the end of the 19th century. Between 1887 and 1893, Carlos Ameghino visited the early Miocene deposits of the Santa Cruz Formation in southern Patagonia several times . In doing so, he collected countless finds, most of which were presented by his brother Florentino Ameghino . Among other things, the first descriptions of Planops in 1887 and of Prepotherium four years later emerged from these collections , which was the first time that representatives of the ancestral line of the Planopinae were discovered.

As early as 1821, John Edward Gray had introduced a name for the family, which he called Megatheriadae. This was based on Cuvier's Megatherium , the only known representative at the time. The term Megatherium itself is made up of the Greek words μέγας ( mégas “large”) and θηρίον ( thērion “animal”) and was chosen by Cuvier because of the immense size of the original find. Gray briefly described the characteristics of the family as Face short: nose with a short trunk: teeth, grinders, cylindrical: claws compressed: body hairy ("Face short: nose with short proboscis: teeth, molars, cylindrical: claws narrowed: body hairy" ). The name was not corrected to the correct version Megatheriidae until 1843 by Richard Owen. Despite the incorrect spelling, Gray is considered by many scientists to be the first author of the family name.

Individual evidence

  1. ↑ a b c Néstor Toledo, Guillermo Hernán Cassini, Sergio F. Vizcaíno and M. Susana Bargo: Mass estimation of Santacrucian sloths from the Early Miocene Santa Cruz Formation of Patagonia, Argentina. Acta Palaeontologica Polonica 59 (2), 2014, pp. 267-280
  2. ↑ a b c d Gerardo De Iuliis, Guillermo H. Ré and Sergio F. Vizcaíno: The Toro Negro megatheriine (Mammalia, Xenarthra): A new species of Pyramiodontherium and a review of Plesiomegatherium. Journal of Vertebrate Paleontology 24 (1), 2004, pp. 214-227
  3. ^ A b c Ricardo N. Melchor, Mariano Perez, M. Cristina Cardonatto and Aldo M. UmazanoLate: Miocene ground sloth footprints and their paleoenvironment: Megatherichnum oportoirevisited. Palaeogeography, Palaeoclimatology, Palaeoecology 439, 2015, pp. 126-143, doi: 10.1016 / j.palaeo.2015.02.010
  4. ^ Carlos Castor Cartelle: Preguiças terrícolas, essas desconhecidas. Anales Ciência Hoje 27, 2000, pp. 19-25
  5. ^ A b 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
  6. ^ A b c François Pujos: Paleogeographic distribution and anatomical adaptions in Peruvian megatheriine ground sloths (Xenarthra, Megatherioidea). In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 56-63
  7. ↑ 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. ^ Giuseppe Tito: New remains of Eremotherium laurillardi (Lund, 1842) (Megatheriidae, Xenarthra) from the coastal region of Ecuador. Journal of South American Earth Sciences 26, 2008, pp. 424-434
  9. ↑ a b c d e f g h i Alfredo A. Carlini, Diego Brandoni and Carlos N. Dal Molin: A new genus and species of Planopinae (Xenarthra: Tardigrada) from the Miocene of Santa Cruz Province, Argentina. Zootaxa 3694 (6), 2013, pp. 565-578
  10. ^ Virginia L. Naples: Cranial osteology and function in the tree sloths. Bradypus and Choloepus. American Museum Novitates 2739, 1982, pp. 1-21
  11. ↑ H. Gregory McDonald: Xenarthran skeletal anatomy: primitive or derived? Senckenbergiana biologica 83, 2003, pp. 5-17
  12. ↑ a b c d e H. Gregory McDonald and Gerardo de Iuliis: Fossil history of sloths. In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 39-55
  13. ↑ a b c Alfredo A. Carlini, Diego Brandoni and Rodolfo Sánchez: First Megatheriines (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco (Late Miocene) and Codore (Pliocene) Formations, Estado Falcón, Venezuela. Journal of Systematic Palaeontology 4 (3), 2006, pp. 269-278
  14. ↑ Sergio F. Vizcaíno: The teeth of the “toothless”: novelties and key innovations in the evolution of xenarthrans (Mammalia, Xenarthra). Paleobiology 35 (3), 2009; Pp. 343-366
  15. ^ Daniela C. Kalthoff: Microstructure of Dental Hard Tissues in Fossil and Recent Xenarthrans (Mammalia: Folivora and Cingulata). Journal of Morphology 272, 2011, pp. 641-661
  16. ↑ a b Kenneth D. Rose: The beginning of the age of mammals. Johns Hopkins University Press, Baltimore, 2006, pp. 1–431 (pp. 200–204)
  17. ↑ 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
  18. ^ H. Gregory McDonald: Evolution of the Pedolateral Foot in Ground Sloths: Patterns of Change in the Astragalus. Journal of Mammalian Evolution 19, 2012, pp. 209-215
  19. ^ A b 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
  20. ^ A b Diego Brandoni, Alfredo A. Carlini, Francois Pujos and Gustavo J. Scillato-Yané: The pes of Pyramiodontherium bergi (Moreno & Mercerat, 1891) (Mammalia, Xenarthra, Phyllophaga): The most complete pes of a Tertiary Megatheriinae. Geodiversitas 26 (4), 2004, pp. 643-659
  21. ↑ 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 the Linnean Society 127, 1999, pp. 495-515
  22. ↑ Giuseppe Tito and Gerardo De Iuliis: Morphofunctional aspects and paleobiology of the manus in the giant ground sloth Eremotherium Spillmann 1948 (Mammalia, Xenarthra, Megatheriidae). Senckenbergiana biologica 83 (1), 2003, pp. 79-94
  23. Jump up ↑ Gerardo De Iuliis and Cástor Cartelle: The medial carpal and metacarpal elements of Eremotherium and Megather-ium (Xenarthra: Mammalia). Journal of Vertebrate Paleontology 14, 1994, pp. 525-533
  24. ^ A b H. Gregory McDonald: Paleoecology of extinct Xenarthrans and the Great American Biotic Interchange. Bulletin of the Florida Museum of Natural History 45 (4), 2005, pp. 313-333
  25. ^ In A. Croft: The Middle Miocene (Laventan) Quebrada Honda Fauna, Southern Bolivia and a description of its notoungulates. Palaeontology 50 (1), 2007, pp. 277-303
  26. ^ A b Julia V. Tejada-Lara, Rodolfo Salas-Gismondi, François Pujos, Patrice Baby, Mouloud Benammi, Stéphane Brusset, Dario De Franceschi, Nicolas Espurt, Mario Urbina and Pierre-Olivier Antoine: Life in proto-Amazonia: Middle Miocene mammals from the Fitzcarrald Arch (Peruvian Amazonia). Palaeontology 58 (2), 2015, pp. 341-378
  27. ↑ a b c d e François Pujos, Rodolfo Salas-Gismondi, Guillaume Baby, Patrice Baby, Cyrille Goillot, Julia Tejada and Pierre-OlivereAntoine: Implications of the presence of Megathericulus (Xenarthra: Tardigrada: Megatheriidae) in the Laventan of Peruvian Amazonia. Journal of Systematics Palaeontology 11 (7-8), 2013, pp. 973-991
  28. ^ François Pujos and Rodolfo Salas: A systematic reassessment and paleogeographic review of fossil Xenarthra from Peru. Bulletin de l'Institut Français d'Etudes Andines, 33, 2004, pp. 331-378
  29. ^ A b M. Susana Bargo, Néstor Toledo and Sergio F. Vizcaíno: Paleobiology of Santacrucian sloths and anteaters (Cenarthra, Pilosa). In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 216-242
  30. ^ Néstor Toledo, M. Susana Bargo and Sergio F. Vizcaíno: Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia. The Anatomical Record 296, 2013, pp. 305-325
  31. ↑ Adrià Casinos: Bipedalism and quadrupedalism in Megatherium: an attempt at biomechanical reconstruction. Lethaia 29, 1996, pp. 87-96
  32. ^ R. Ernesto Blanco and Ada Czerwonogora: The gait of Megatherium Cuvier 1796 (Mammalia, Xenarthra, Megatheriidae). Senckenbergiana biologica 83 (1), 2003, pp. 61-68
  33. ^ Richard A. Fariña, Sergio F. Vizcaíno and Gerardo De Iuliis: Megafauna. Giant beasts of Pleistocene South America. Indiana University Press, 2013, pp. 1-436 (pp. 254-256) ISBN 978-0-253-00230-3
  34. ^ M. Susana Bargo, Gerardo De Iuliis, and Sergio F. Vizcaíno: Hypsodonty in Pleistocene ground sloths. Acta Palaeontologica Polonica 51 (1), 2006, pp. 53-61
  35. ^ M. Susana Bargo: The ground sloth Megatherium americanum: Skull shape, bite forces, and diet. Acta Palaeontologica Polonica 46 (2), 2001, pp. 173-192
  36. ^ M. Susana M. Bargo, Néstor Toledo and Sergio F. Vizcaíno: Muzzle of South American Pleistocene Ground Sloths (Xenarthra, Tardigrada). Journal of Morphology 267, 2006, pp. 248-263
  37. ↑ a b c Samantha Presslee, Graham J. Slater, François Pujos, Analía M. Forasiepi, Roman Fischer, Kelly Molloy, Meaghan Mackie, Jesper V. Olsen, Alejandro Kramarz, Matías Taglioretti, Fernando Scaglia, Maximiliano Lezcano, José Luis Lanata, John Southon, Robert Feranec, Jonathan Bloch, Adam Hajduk, Fabiana M. Martin, Rodolfo Salas Gismondi, Marcelo Reguero, Christian de Muizon, Alex Greenwood, Brian T. Chait, Kirsty Penkman, Matthew Collins and Ross DE MacPhee: Palaeoproteomics resolves sloth relationships . Nature Ecology & Evolution 3, 2019, pp. 1121-1130, doi: 10.1038 / s41559-019-0909-z
  38. ↑ a b c Frédéric Delsuc, Melanie Kuch, Gillian C. Gibb, Emil Karpinski, Dirk Hackenberger, Paul Szpak, Jorge G. Martínez, Jim I. Mead, H. Gregory McDonald, Ross DE MacPhee, Guillaume Billet, Lionel Hautier and Hendrik N. Poinar: Ancient mitogenomes reveal the evolutionary history and biogeography of sloths. Current Biology 29 (12), 2019, pp. 2031-2042, doi: 10.1016 / j.cub.2019.05.043
  39. ↑ a b c d Luciano Varela, P. Sebastián Tambusso, H. Gregory McDonald and Richard A. Fariña: Phylogeny, Macroevolutionary Trends and Historical Biogeography of Sloths: Insights From a Bayesian Morphological Clock Analysis. Systematic Biology 68 (2), 2019, pp. 204-218
  40. ↑ a b c d Timothy J. Gaudrin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  41. ↑ Christian de Muizon, H. Gregory McDonald, Rodolfo Salas and Mario Urbina: The youngest species of the sloth Thalassocnus and a reassessment of the relationships of the sloths (Mammalia: Xenarthra). Journal of Vertebrate Paleontology 24 (2), 2004, pp. 387-397
  42. ↑ a b c d Malcolm C. McKenna and Susan K. Bell: Classification of mammals above the species level. Columbia University Press, New York, 1997, pp. 1-631 (pp. 96-99)
  43. Jump up ↑ a b Diego Brandoni and Gerardo De Iuliis: A new genus for the Megatheriinae (Xenarthra, Phyllophaga, Megatheriidae) from the Arroyo Chasicó Formation (Upper Miocene) of Buenos Aires Province, Argentina. New Yearbook for Geology and Paleontology Abhandlungen 244 (1), 2007, pp. 53–64
  44. ^ A b Ascanio D. Rincón, Ana L. Valerio, and César Laurito: First fossil record of a Megatheriidae-Megatheriinae in the Early Hemphillian (Late Miocene) from San Gerardo de Limoncito, Curré Formation, Costa Rica. Revista Geológica de América Central 62, 2020, doi: 10.15517 / rgac.v62i0.41278
  45. ^ Eli Amson, Christian de Muizon and Timothy J. Gaudin: A reappraisal of the phylogeny of the Megatheria (Mammalia: Tardigrada), with an emphasis on the relationships of the Thalassocninae, the marine sloths. Zoological Journal of the Linnean Society 179 (1), 2017, pp. 217-236, doi: 10.1111 / zoj.12450
  46. ^ Gerardo De Iuliis, François Pujos and Cástor Cartelle: A new ground sloth (Mammalia: Xenarthra) from the Quaternary of Brazil. Comptes Rendus Palevol 8, 2009, pp. 705-715
  47. ^ A b Diego Brandoni, Jaime E. Powell and Osvaldo E. González: Anisodontherium from the Late Miocene of North-Western Argentina. Acta Palaeontologica Polonica 57 (2), 2012, pp. 241-249
  48. ↑ Gerardo De Iuliis, Diego Brandoni and Gustavo J. Scillato-Yané: New Remains of Megathericulus patagonicusAmeghino, 1904 (Xenarthra, Megatheriidae): Information on Primitive Features of Megatheriine. Journal of Vertebrate Paleontology 28 (1), 2008, pp. 181-196
  49. ↑ H. Gregory McDonald: Xenarthrans: Pilosans. In: Richard F. Kay, Richard H. Madden, Richard L. Cifelli, and John J. Flynn (Eds.): Vertebrate Paleontology in the Neotropics. The Miocene Fauna of La Venta, Colombia. Smithsonian Institution Press, Washington, 1997, pp. 233-245
  50. Jump up ↑ Diego Brandoni and Alfredo A. Carlini: On the presence of Pyramiodontherium (Mammalia, Xenarthra, Megatheriidae) in the Late Miocene of Northeastern Argentina and its biogeographical implications. Revista Italiana di Paleontologia e Stratigrafia 115 (1), 2009, pp. 111-123
  51. ↑ Diego Brandoni: Los Megatheriinae (Xenarthra, Tardigrada) de la Formación Ituzaingó (Mioceno Superior-Plioceno) de la provincia de Entre Ríos. In: FG Aceñolaza (ed.): Temas de la Biodiversidad del Litoral fluvial argentino II, Miscelánea. 14, 2005, pp. 27-36
  52. ^ Diego Brandoni: Los Tardigrada (Mammalia, Xenarthra) del Mioceno Tardío de Entre Ríos, Argentina. In: Diego. Brandoni and JI Noriega (eds.): El Neógeno de la Mesopotamia argentina. Asociación Paleontológica Argentina, Publicación Especial 14, 2013, pp. 135–144
  53. ↑ Diego Brandoni: A review of Pliomegatherium Kraglievich, 1930 (Xenarthra: Phyllophaga: Megatheriidae). Jahrbuch für Geologie und Paläontologie, monthly booklet 4, 2006, pp. 212–224
  54. ↑ Marcelo R. Sánchez-Villagra, Juan D. Carrillo, Alfredo A. Carlini and Carlos Jaramillo: New fossil mammals from the Northern Neotropics (Urumaco, Venezuela, Castilletes, Colombia) and their significance for he latitudinal gradient in diversity and The Great American Biotic interchange. In: Erin Maxwell and Jessica Miller-Camp (Eds.): 74th Annual Meeting of the Society of Vertebrate Paleontology November 5.8, 2014, Berlin, Abstracts and Papers. Berlin, 2014, p. 220
  55. ^ A b Alfredo A. Carlini, Diego Brandoni and Rodolfo Sánchez: Additions to the knowledge of Urumaquia robusta (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco Formation (Late Miocene), Estado Falcón, Venezuela. Paläontologische Zeitschrift 82 (2), 2008, pp. 153–162
  56. ↑ 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
  57. ↑ Dilce de Fátima Rossetti, Peter Mann de Toledo, Heloísa Maria Moraes-Santos and Antônio Emídio de Araújo Santos, Jr .: Reconstructing habitats in central Amazonia using megafauna, sedimentology, radiocarbon, and isotope analyzes. Quaternary Research 61, 2004, pp. 289-300
  58. ^ Gustavo G. Politis, Clara Scabuzzo and Robert H. Tykot: An Approach to Pre-Hispanic Diets in the Pampas during the Early / Middle Holocene. International Journal of Osteoarchaeology 19, 2009, pp. 266-280
  59. ↑ 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
  60. ↑ 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, p. Eaau4546, doi: 10.1126 / sciadv.aau4546
  61. ^ Larry G. Marshall: Fossil localities for Santacrucian (early Miocene) mammals, Santa Cruz Province, southern Patagonia, Argentina. Journal of Paleontology 50, 1976, pp. 1129-1142
  62. ↑ John Edward Gray: On the natural arrangement of vertebrose animals. London Medical Repository 15, 1821, pp. 297-310 (306) (PDF)
  63. ↑ George Gaylord Simpson: The principles of classification and a classification of mammals. Bulletin of the American Museum of Natural History 85, 1945, pp. 1–350 (p. 71)

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