Nothrotheriidae

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Nothrotheriidae
Skeletal reconstruction of Nothrotheriops

Skeletal reconstruction of Nothrotheriops

Temporal occurrence
Lower / Middle Miocene to Lower Holocene
15 million years to 9,000 years
Locations
Systematics
Higher mammals (Eutheria)
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Megatherioidea
Nothrotheriidae
Scientific name
Nothrotheriidae
Gaudin , 1994

The Nothrotheriidae are an extinct family of once ground-living sloths that are closely related to the giant Megatheriidae . In contrast to these and most of the other lines of development of the ground sloth, however, they did not develop excessively large forms. They lived from the transition of the Lower to the Middle Miocene to the end of the Pleistocene and the beginning of the Holocene 15 million to about 8,700 years ago. Their main distribution area was the central and northern South America . One form also appeared in North America from the Pleistocene onwards , but remained there limited to the southern and southwestern parts. Overall, the Nothrotheria were not very rich in form, most representatives are known only from a few fossil finds. However, especially the late representatives have been very well examined due to some excellently preserved remains.

Like all sloths, the Nothrotheria were purely herbivorous. Traditional dung balls provide insight into the preferred food plants, which mainly include softer parts of the plant. In addition, it was possible to infer the landscape that the animals inhabited and which, at least in the southern part of North America, comprised predominantly drier habitats . In addition, only rarely fossilized soft tissue enables the reconstruction of the fur cover and suggests climatic adaptations. A peculiarity is found on the west coast of South America, where a semiaquatic living form has so far been unique to the sloth. The other representatives moved on four feet, but could probably stand up on their hind legs. The first finds of Nothrotheria were discovered by Peter Wilhelm Lund in southeastern Brazil in the 1830s , and later evidence from Argentina was added. The name Nothrotherium was coined more than 50 years later. The first record of Nothrotheria from North America dates back to the beginning of the 20th century. The group of sloths received their family status towards the end of the 20th century.

features

General

The representatives of the Nothrotheriidae were distinguished from most other ground-living sloths by a rather smaller body size. The largest forms were Thalassocnus and Nothrotheriops . The former reached a total length of 255 to 330 cm, the latter from 246 to 275 cm. Weight data for Thalassocnus vary from 130 to 300 kg, for Nothrotheriops from 323 to 463 kg. Overall, the forelegs of the Nothrotheria were slightly longer than the hind legs, and the tail was longer than that of other ground sloths.

Skull and dentition features

Skull of Nothrotherium

The skull of the Nothrotherien was long, narrow and almost cylindrical. The largest forms had skull lengths of around 21 cm for Nothrotherium over 26 to 30 cm for Thalassocnus up to 30 to 33 cm for Nothrotheriops . The zygomatic arches protruded between 9 and 11.5 cm, and the rostrum was very narrow overall . When viewed from the side, the skull looked domed, the strength of the arch varied depending on the species, but it was more pronounced in early phylogenetic forms. Typically, the middle jaw bone was greatly reduced and hardly anchored to the upper jaw; it usually only formed a toothless, Y-like bone process. The nasal bone , on the other hand, was extremely long and in some representatives reached a third or more of the length of the skull. It was laterally in contact with the upper jaw. As with most sloths, the zygomatic arch was not closed, however, unlike the closely related large Megatheriidae . The anterior, posterior arch attachment originated above the posterior teeth and consisted of an ascending and a downwardly directed bony process. The rear, forward-oriented arch attachment represented a horizontally directed, finger-shaped bony process. As a rule, there was a large gap between the two arch parts, only in Nothrotheriops this was almost closed and thus reproduced an almost continuous zygomatic arch. The lower jaw was generally characterized by a spatula-shaped, forwardly drawn, narrow symphysis . The lower edge of the lower jaw showed a protuberance that accommodated the high-crowned teeth, but was not as massive as in the Megatheria. As a result, the height of the lower jaw only reached a quarter of its length. At the ascending end of the joint, three processes were formed, the angular, crown and articular processes, all of which appeared to be relatively equally strong and thus gave the lower jaw a rather primeval character. The articular process reached up so that the connection with the skull was well above the occlusal plane.

The dentition consisted of teeth that had no enamel , which is typical of sloths. As a result, the teeth were largely formed from dentin , which was found in harder and softer forms ( orthodentin and vasodentin ). In the upper jaw, in most forms, there were 5 teeth per half of the jaw, in the lower jaw 4 teeth, a total of 18 teeth. The foremost tooth in each case resembled a canine tooth ( caniniform ), the rear teeth were molar- shaped ( molar-shaped ). This set of teeth, which is to be regarded as originally for the sloths, also occurs in the Megalonychidae and the Mylodontidae , but differs from the Megatheria, in which all teeth had a molar-shaped structure. The caniniform tooth was separated from the posterior teeth by a diastema . In the case of the Nothrotheria, it was located in the upper jaw approximately in the middle of the toothless section between the first posterior molar and the contact of the upper jaw with the middle jawbone; In the Mylodonts, which on average had much larger anterior teeth, they were significantly further apart due to the widening of the symphysis of the lower jaw. Only the genetically youngest representatives of the Nothrotheria, such as Nothrotherium and Nothrotheriops as well as Thalassocnus , had reduced the caniniform tooth, they had only 14 teeth in the dentition. The structure of the molar-like teeth was similar to that of the megatheria. They had a rectangular to slightly oval outline and a bilophodontic chewing surface with two transverse, high ridges, which were separated from each other by an incised valley. In principle, the teeth had extremely high ( hypsodontic ) crowns and grew throughout their life. The two rows of teeth ran parallel to each other.

Body skeleton

Femut from Nothrotheriops

The body skeleton can be reconstructed quite extensively from numerous finds. The spine was composed of 7 cervical, 17 to 19 thoracic, 3 lumbar, 5 sacrum and 21 to 25 tail vertebrae. The number of thoracic vertebrae varied considerably within the Nothrotheria, similar to that of all sloths. In Pronothrotherium it was 19, in Nothrotheriops and Thalassocnus 17. Overall, the thorax and the tail consisted of more vertebrae than comparable in the giant Megatheria . Analogous to the other representatives of the sloths, xenarthric joints (secondary joints or xenarthrals) were formed on the transverse processes of the posterior thoracic and lumbar vertebrae , which gave this area greater strength. Differing features in the musculoskeletal system are less clearly developed. The humerus was characterized by its tubular shaft and the wide protruding lower joint end, which is typical of most ground-living sloths. In agreement with the megatheria, but in contrast to the megalonychids and the mylodonts, there was no prominent bone ridge (crista deltoidea or deltopectoral ridge) on the shaft, instead there was a rather extensive area as an attachment point for the shoulder muscles. A largely original feature was the appearance of an entepicondylar foramen , a bone opening at the lower end of the humerus that is absent in megatheria. As with most ground sloths, the femur was wide and extremely flat in shape. Unlike the large megatheria, the Nothrotheria had a third trochanter as a muscle attachment point on the femoral shaft. The position varied greatly in the individual forms; it could be formed close to the lower joint end as in Nothrotheriops , on the central shaft as in Nothrotherium or Mionothropus or in the upper half as in Thalassocnus . In general, the Nothrotheria had a greatly elongated lower part opposite the upper portion of the hind leg, a feature which they share with the Megatheria but which distinguishes them from the Mylodonts. The length of the lower leg usually made up more than 70% of the upper, Thalassocnus had the longest lower legs, sometimes more than 90%. The tibia and fibula were usually not fused, in contrast to the megatheria.

Hand of Nothrotheriops

The hand comprised a total of five rays, and unlike the very early sloths like Hapalops , claws only existed on rays I to IV, and on the fifth only two very small phalanges were formed. In older forms of Nothrotheria such as Mionothropus , rays II to IV, which were usually the strongest, were made up of three phalanxes each; in some later forms the first two phalanges of the third finger fused together, which is also known from some Megatheria . In the representatives with a known hand skeleton, the claw of the second finger was clearly flattened. In part, the first metacarpal bone together with some elements of the wrist formed the metacarpal-carpal complex typical of various sloths . In general, the first finger was the smallest. In contrast to the hand, the foot consisted of only four rays (II to V), the innermost one was completely or partially reduced. Only the second to fourth toes had claws, which differs significantly from the late Megatheria, which only had one claw on the foot (on the third ray). In older sloths all five toes were still present with claws on rays I to IV. The first two toe phalanges of the third toe were fused together in all Nothrotheria. Overall, the foot showed a clear inward rotation, so that it touched down with the outermost toe and heel bone . This foot position, known as pedolateral , is typical of numerous lines of the ground sloth, but does not occur in today's representatives. In contrast to the rather flat foot of the Megatheria, the closest relative of the Nothrotheria, the foot of the latter was clearly arched so that the heel bone only touched the ground with the end.

distribution

Like almost all lines of secondary articulated animals, the Nothrotheria originated in South America , where they also had their main area of ​​distribution. They were once spread over a large part of the northern and central part of the continent and reached to the south as far as northern Patagonia . Both the forerunners of the Nothrotheria and their earliest finds from the transition from the Lower to the Middle Miocene come from there . Later in the further course of the Miocene and especially in the Pleistocene , the Nothrotheria were more likely to be found in regions further north, where the main distribution was in the areas east of the Andes . Significant finds come from the Conglomerado osifero in north-eastern Argentina , from the western Amazon lowlands in western Peru and from several cave sites in eastern and southeastern Brazil . In the course of the Miocene and the Pliocene , however, the Nothrotheria also settled the coastal areas of today's Peru and Chile and thus occurred west of the Andes. They disappeared there again in the Lower Pleistocene . In contrast to the huge megatheria, no remains of the Nothrotheria have been passed down directly from the high altitudes of the Andes.

In the course of 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 formation of the land bridge between North and South America, the Nothrotheria also reached regions far to the north. However, with Nothrotheriops, only one genus from the sloth family was widespread in North America ; it is found mainly in the south of Mexico and from California to Florida . At Merrill in Klamath County in Oregon it reached its northernmost point of discovery at 42 ° north latitude, the southernmost was at Actun Lak in the Belizean province of Cayo . In total, the genus is known from more than 70 sites. It is noticeable that the sites further north are consistently at a lower altitude than the more southern ones. It is therefore assumed that the minimum winter temperatures were a limiting factor in the spread of the Nothrotheria to the north. Studies on plant debris showed some cave sites in the American Southwest, the habitat of the sloth that there in the late Pleistocene of dry juniper - and ash -Wäldern composed, with Opuntia - yucca - and Encelia were interspersed inventories directly. Only in the subsequent period did the current desert-like conditions develop in this region.

Paleobiology

Locomotion

Live reconstruction of Nothrotheriops

The Nothrotheria moved four-footed forward as ground-living sloths. The large and more or less completely traditional forms such as Nothrotheriops reached a shoulder height of up to 94 cm in this position. The inwardly turned hind feet meant that they only touched the ground with the outer edge. The large claws pointed inward and lay flat on the ground. The forefeet was put on in a similar way to today's great anteater , so that an ankle gait was formed here and the claws pointed backwards. The forelegs were slightly longer than the hind legs, which most likely enabled the Nothrotheria to stand up on their rear extremities and to pull them up with the front branches and twigs, using the massive tail as a support. However , the Nothrotheria probably did not carry out a digging activity as intended for some representatives of the Mylodontidae , since the short olecranon at the upper end of the ulna did not allow much leverage of the arms. A very unusual adaptation existed in Thalassocnus , which lived semi-aquatic. In addition to a general bone compression, there was also a stronger overprinting of the skeleton, for example with more flexible hind legs, longer lower limb sections that increased the leverage when paddling and, secondarily, rear feet turned back again, with which a higher water displacement was possible.

Diet and Metabolism

The design of the dentition with the rectangular teeth, which have two transverse raised ridges, clearly resembles that of the megatheria and suggests a specialization in vegetable food. However, the teeth in the Nothrotheria have almost twice as much orthodentin , the hard component of the dentin , on the chewing surface compared to the Megatheria with 34% , and the ridges are also less clearly developed in some later representatives. Since the teeth of the sloth generally have no tooth enamel , they are not suitable for detailed studies of the former diet. Investigations of signs of wear have so far only been carried out on a few molds. In the case of the semi-aquatic Thalassocnus , it was possible to detect a change from initially taking food close to the coast, where the plant food was mixed with a high sand component, to grazing further in the sea. Based on the alignment of the incisions on the teeth, it was also shown that the originally mostly vertical and forward and backward masticatory movements were replaced in later forms by predominantly laterally oriented. The latter is typical for herbivorous herbivores and could speak for a stronger specialization in seagrasses among the later representatives of the sloth genus . Nothrotheriops, on the other hand, has numerous fine and coarser scratch marks and polished surfaces, a wear pattern similar to that of today's three-toed sloths ( Bradypus ), which represent specialized leaf-eaters. Investigations based on the chewing apparatus of Nothrotheriops showed, due to the high articular processes of the lower jaw and the resulting arrangement of the chewing muscles, also rather back and forth chewing movements, which are also typical of the three-toed sloth, but more distinct from the more generalized two-toed sloth ( Choloepus ) differ with their lower articular processes.

Coprolites from the Rampart Cave

Food residues in the form of coprolites are mainly available for the late representatives of the Nothrotheria. They largely belong to the end of the Pleistocene and were mostly found in caves. From South America, dung residues of Nothrotherium from the Gruta de Brejões in the eastern Brazilian state of Bahia are known. In North America, around half a dozen caves with such remains have been identified, all of which are located in the dry southwestern United States and are assigned to Nothrotheriops . The most important is the Rampart Cave in the Grand Canyon of Arizona , in which the 7 to 10 cm diameter balls of excrement are deposited with a thickness of almost 140 cm. More detailed investigations of the coprolites are only available from Nothrotheriops . About 72 species of plants could be detected, which distinguish the sloth form as herbivores specializing in soft vegetable food. Among the plants there were mainly xerophytes , especially common were sea ​​pigeons , palm lilies , phragmites , sphaeralcea or xanthocephalum , as well as rose and mallow plants . In some cases, the organic remains in the coprolites were so well preserved that individual parasites of the sloths, such as roundworms and scale insects , could still be detected . Imino acid investigations on the collagen from Nothrotheriops revealed an assumed body temperature of 34.4 to 35.7 ° C, which is relatively low for an animal weighing more than 400 kg. In the case of similarly sized hornbeams , the body temperature usually fluctuates between 36.3 and 38.4 ° C. It is concluded that the Nothrotheria may have had a slow metabolism , like today's sloths .

Soft tissues and miscellaneous

The preservation of soft tissue in extinct organisms is extremely rare. It is important that in addition to Mylodon and Glossotherium from the group of Mylodonts, fossilized skin and hair remains have also been detected for the Nothrotheria. They were found in an almost complete skeleton of Nothrotheriops from Aden Crater in New Mexico, in which hair in the pelvic area was passed down. In contrast to the mylodonts, no bone platelets could be observed in the skin, so that it was probably not additionally protected by osteoderms . So far, only the long outer hair is known of the hair , which would correspond to the fur of today's two-toed sloths , which only have one layer of hair. The length of the individual hairs in Nothrotheriops is around 45 mm, their color originally corresponded to a brownish yellow. In contrast to the hair of today's sloths and of Mylodon , which have no central medulla, those of Nothrotheriops showed a double pith. However, this partly consisted of individual small chambers that were filled with pigments . Small air bubbles ( vesicles ) appeared on the hair cortex . As in other mammals, the outermost layer also formed a cuticle made of individual cells. Noteworthy were small, oval formations less than 10 μm in diameter, which did not belong to the hair structure itself. They are interpreted as algae cells , which indicates that these also settled in the fur of Nothrotheriops, analogous to today's sloths. Whether there was a similar symbiotic relationship between Nothrotheriops and the algae, as is the case with the tree sloth, has not yet been established. Further investigations showed that the fur of Nothrotheriops was significantly more heat-permeable than that of Mylodon , which is likely to make the former more sensitive to cold. According to calculations that assume a fur about 23 mm thick, the thermoneutrality of Nothrotheriops fluctuated around 20 ° C, which is between the values ​​of the two-toed sloth (24 ° C) and the three-toed sloth (18 ° C). It is also significantly higher than the assumed value of Mylodon with 15 ° C, which had a denser coat, had a significantly larger body mass and lived much further south in temperate to cool climates. Due to the high thermal neutrality, caves may have played an important role as shelter and retreat, as indicated by the numerous fossil finds in South and North America. In addition, a function of this during the birth and rearing of the young would be conceivable.

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 Nothrotheriidae are an extinct family within the suborder of the sloths (Folivora). The sloths, in turn, together with the anteaters (vermilingua) form the order of the tooth arms (pilosa). This stands within the superordinate order of the secondary articulated animals (Xenarthra), one of the four main lines of the higher mammals , the armored secondary articulated animals (Cingulata) with the armadillos (Dasypoda). The common feature of all articular animals is the formation of xenarthric joints (secondary joints or xenarthrals) on the transverse processes of the posterior thoracic and lumbar vertebrae. Another characteristic that distinguishes this group from the other higher mammals is the different design of the dentition, which is greatly reduced in most of the articular animals and consists of homodontic teeth without developed tooth enamel , only the anteaters have no teeth at all. According to molecular genetic studies, the secondary animals separated from their common ancestors with the other higher mammals as early as the late Lower Cretaceous more than 100 million years ago. The splitting of the tooth arms then took place in the Paleocene around 58 million years ago.

Today, with the two -toed sloth ( Choloepus ) and the three-toed sloth ( Bradypus ), there are only two genera of small, tree-dwelling animals, but in their phylogenetic past, the sloths were very rich in shape and mostly comprised ground-living, sometimes huge shapes. From a skeletal anatomical perspective, two major lines of development can be distinguished. One is represented by the Megatherioidea , which include the Megatheriidae , the actual giant sloths, the Nothrotheriidae and the Megalonychidae . The second line is made up by the mylodontoid . It also includes the sometimes extremely large Mylodontidae , the Scelidotheriidae and the Orophodontidae (the latter two are sometimes only listed as a subfamily of the Mylodontidae). In contrast, molecular genetic studies and protein analyzes with the Megalocnoidea reveal a third lineage, which brings together the Caribbean sloths. According to the latter investigations, the three-toed sloths belong to the Megatherioidea, the two-toed sloths are part of the Mylodontoidea.

Initially, the Nothrotheria were run as a subfamily within the Megatheria and also included original forms from the Santa Cruz Formation of the Lower Miocene such as Hapalops , Pelecyodon or Schismotherium (but these sometimes also formed their own subfamily Schismotheriinae). One of the most detailed anatomical and phylogenetic studies to date on the basis of skull features showed that these primitive representatives can only be understood as basic members of the Megatherioidea with an unclear relationship to one another. The Nothrotheria were thereby limited to the more recent forms and were given their own family status. The assumed closer relationship to the Megatheria was underpinned by the common, superordinate taxon of Megatheria . However, there are only a few common characteristics that actually clearly support this relationship, such as the expression of a long, narrow snout and some special skull features. For this reason, other scientists also see a closer relationship between the Nothrotheria and the megalonychids. The genetic and protein-based analyzes carried out so far have not yet been able to clearly clarify this discrepancy.

Overview of the genera of the Nothrotheriidae

Internal systematics of the Nothrotheriidae according to Varela et al. 2019
 Nothrotheriidae  
  Nothrotheriinae  




 " Xyophorus "


   

 Aymaratherium



   

 Pronothrotherium



   


 Nothrotheriops


   

 Nothrotherium



   

 Mionothropus




   

 Lacucullus



  Thalassocninae  

 Thalassocnus



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The Nothrotheriidae are a less diverse group of large ground sloths. They include only around a dozen genera in two subfamilies. The structure presented here is based on McKenna and Bell 1997, but also takes into account more recent findings:

  • Family Nothrotheriidae Gaudin , 1994
  • Subfamily Nothrotheriinae Ameghino , 1920
  • Subfamily Thalassocninae de Muizon, McDonald, Salas & Urbina , 2004

With Huilabradys , Carlos A. Villarroel established another genus to the Nothrotheriidae in 1998 , which comes from the Middle Miocene of La Venta in Colombia. Today, however, like Hapalops, it is viewed as a rather basal megatherioid without an exact family assignment, possibly Xyophorus should also receive this status. Chasicobradys, on the other hand, is considered to be very similar to Neohapalops , which is why there was sometimes a demand for the unification of both genres. A phylogenetic study from 2017 again sees the Thalassocninae as a member of the Megatheriidae, but another analysis from 2019 contradicts this.

Tribal history

Development tendencies

Common characteristics of the Nothrotherien represent the long and narrow skull and the Megatherien similar molarenartigen rear molars having a rectangular cross-section and two transversely positioned strips ( bilophodont group), the respective foremost tooth is different from its large relatives eckzahnähnlich ( caniniform transformed). The general development trend includes the gradual increase in size of the Nothrotheria during their tribal history . Above all, however, the modification of the dentition is important. The Nothrotheria represent one of the few lines of sloths in which a reduction in the number of teeth can be determined (the Mylodonts are another). The caniniform anterior tooth of the early Nothrotheria is no longer developed in the most recent forms of the phylogenetic history. This applies to both Nothrotheriops and Nothrotherium in the Nothrotheriinae and Thalassocnus in the Thalassocninae.

Miocene

Compared to the other large lines of sloths, the Nothrotheria appear relatively late. The earliest evidence dates back to the end of the Lower Miocene , and some of the early basal megatherioidea of ​​the Santa Cruz Formation in Patagonia can be regarded as ancestral forms. Xyophorus is possibly the earliest representative . A 12 cm long lower jaw with complete posterior dentition and the spatula-like extension of the symphysis was discovered in the Cerdar beds near Potosí in Bolivia and dated around 15 million years ago. Further finds of the genus are then documented from the Middle Miocene, such as the remains of the lower jaw from El Petiso in the north of the Argentine province of Chubut , which are also among the southernmost known finds of the family. A partial skull with associated lower jaw from Quebrada Honda , a very fossil-rich site in southern Bolivia, is also provided for Xyophorus . The large lacucullus has also been described from here using a complete lower jaw. Amphibradys also occur in the Middle Miocene . So far, only a fragmented skull from the Collón-Curá formation in western Argentina has come down to us.

Skeletal reconstruction of Pronothrotherium

Finds from the Upper Miocene are much more extensive. The Conglomerado osifero , the lower section of the Ituzaingó Formation , which is opened up by the Río Paraná near the city of Paraná in the Argentine province of Entre Ríos , should be emphasized. The very rich fauna also contains numerous representatives of all important families of the large ground sloth, the Nothrotheria are represented by the remains of the lower jaws of Pronothrotherium and Neohapalops . The family is found here far less often than the Megatherien or Megalonychiden. From the western Amazon region in the lowlands of Peru, a partial skeleton was found on the Río Acre that dates back to about 7 to 8 million years and belongs to the genus Mionothropus . At the same time, thalassocnus appears for the first time on the other side of the Andes in the Pisco formation on the coast of today's Peru . This semi-aquatic form is documented by numerous fossil finds, which over a period of 5 million years show ever stronger adaptations to life in the water, which is so far unique within the sloth.

Plio and Pleistocene

Skeletal reconstruction of the thalassocnus

At first, Thalassocnus appeared on the coasts of Peru and Chile in the Pliocene , but disappeared in the Old Pleistocene at the latest . In the eastern area of ​​South America, Nothrotherium has been identified during the Pleistocene . Most of the finds are from the predominantly tropical areas in today's Brazil, but mainly date to the late phase of the period and the transition to the Holocene . From the genus, which has been little investigated overall, in addition to individual finds such as two partial skulls plus a few individual teeth and postcranial skeletal elements from the catchment area of ​​the Rio Iguape in the southeast of the state of São Paulo , three more or less complete skeletal finds were also recovered. One of them comes from the Lapa de Escrivania cave n ° 5 near Lagoa Santa near Belo Horizonte in what is now the Brazilian state of Minas Gerais and was discovered by Peter Wilhelm Lund in 1844 . Another came to light in the Gruta de Brejões , a cave in the Iraquara Karst region in the eastern Brazilian state of Bahia , and was associated with a coprolite. The third skeleton was found in the nearby Ioiô-Impossível cave . Its entrance is in a sinkhole below the water level, the almost complete skeleton of a young animal found here comprises more than 190 surviving skeletal remains. Further south in today's Pampa region was in the same period Nothropus common. Little is known about the genus. So far, only two reliable remains of the lower jaw could be assigned, one of which is relatively complete from northern Argentina , the other, more fragmented, from the Tarija basin in Bolivia . A third lower jaw, which is generally placed on Nothropus , came to light in the Argentine province of Santa Fe . Since this, in contrast to the other lower jaws of the genus, lacks the anterior caniniform tooth, it could also represent another genus.

In the course of the Old Pleistocene , the Nothrotheria also reached North America , but only one genus, Nothrotheriops, has been recorded there. In comparison with other groups of sloths that passed the land bridge during the Great American Faun Exchange and colonized the northern continent, the Nothrotheria appeared there relatively late. The earliest finds belong to the El Golfo local fauna , an extremely fossil-rich fauna complex at the mouth of the Colorado River in the Mexican state of Sonora . The more than 4,300 identifiable fossil objects are dated to an age of 1.8 to 1.6 million years. The partial skeleton of the Leisy Shell Pit in Florida , which is still a relatively small member of the genus, is somewhat younger at around 1.2 million years . The early finds of Nothrotheriops are relatively sparse, but are spread over a large area of ​​southern North America, from Florida to California. It was not until the Young Pleistocene that the number of finds increased significantly, but was then limited to the southwestern region of today's USA and northern Mexico. The finds from the asphalt pits of Rancho La Brea in California, which are 45,000 to 14,000 years old, are unique in the world from this period . Noteworthy is the extremely frequent occurrence of predators such as smilodon versus herbivores. It is possible that the predators were attracted in droves by animals caught in the pitch and then fell victim to the natural traps themselves. Among the three traditional sloth forms, Nothrotheriops is present with at least 22 individuals, most of which are found as skulls. They belong to a significantly larger representative of the genus than in the early phase of colonization in North America, but with a body weight of around 460 kg it was still the smallest representative of the ground sloth on the continent. Nothrotheriops may have returned to South America during the Pleistocene. A thigh bone around 31 cm long from the Río Salado in the Argentine province of Santa Fe , which belongs to the Young Pleistocene, was assigned to the genus in 2019. This gives Nothrotheriops an extremely extensive distribution area, ranging from latitude 36 degrees north to 31 degrees south. It is acceptable that Nothrotheriops was the starting point for the formation of the closely related Nothrotherium .

die out

Towards the end of the Pleistocene , the Nothrotheria, like many members of other sloth lines, died out in the course of the Quaternary extinction wave . One of the very late representatives of Nothrotherium in South America is the skeleton with coprolites found in the Gruta de Brejões in Bahia. According to the results of the radiocarbon dating, the animal died on the dung ball that was left behind by 12,200 BP. The skeleton find from the Ioiô-Impossível cave is probably much younger , and its age according to radiocarbon measurements is 8700 BP, which means that the genus still occurred in the early Holocene . Nothrotheriops in North America survived at least until the end of the Pleistocene. The most recent data from the Rampart Cave in the Grand Canyon of Arizona , also obtained from coprolites, indicate an age of 10,400 to 10,780 years ago, with remains from the Upper Sloth Cave in Texas they are 10,750 years ago.

Research history

Peter Wilhelm Lund.

Research on the Nothrotheriidae began in the first half of the 19th century and is inextricably linked with the name Peter Wilhelm Lund (1801–1880). The Danish researcher left his homeland for South America in the early 1830s. There he examined limestone caves in Lagoa Santa in the Brazilian state of Minas Gerais , which in 1835 led to the discovery of innumerable bone fragments . These included a femur and coprolites of a smaller, ground-living sloth that came from the Lapa Nova cave and that Lund referred to in a preliminary report as belonging to a tapir-sized representative of Megatherium . In a first larger report, which was completed in 1839, but only appeared two years later, he had placed the femur in the new genus Coelodon and also assigned it a few teeth. In another cave in the region, the Lapa de Escrivania n ° 5 , Lund discovered an almost complete skeleton of Coelodon in 1844 , which Paul Gervais mentioned and which was described in detail by Johannes Theodor Reinhardt (1816–1882) in 1878 under the same generic name . The name Coelodon was widespread at that time, it was not until 1889 that Richard Lydekker (1849–1915) pointed out that the name had already been preoccupied by a representative of the longhorn beetle and then suggested Nothrotherium . The name is made up of the Greek words νωθρος ( nothros ) for "lazy" and θηρίον ( thērion ) for "animal". In 1891, Florentino Ameghino (1854–1911) introduced the genus Hypocoelus for reasons similar to Lydekker , whose name, like Coelodon, is synonymous with Nothrotherium . In the 1880s further representatives from the family of Nothrotherium / Coelodon were introduced. On Hermann Burmeister (1807-1892) goes Nothropus back, a form which he described in 1882 on the basis of a lower jaw from northern Argentina. In 1887, Florentino Ameghino Xyophorus again set up with the help of a lower jaw from Patagonia .

The first nothrotheria in North America came to light in 1905 in Potter Creek Cave in Shasta County in the US state of California . They consisted of a lower jaw fragment and several teeth and were assigned to the genus Nothrotherium by William J. Sinclair (1877-1935) . Only one year later, John Campbell Merriam identified individual teeth from a crevice filling near Terlingua in Texas as remains of Nothrotherium , but these were lost again in the same year. It was not until 1916 that Oliver Perry Hay (1816–1882) was able to present finds from Texas again. Only three years earlier, Chester Stock (1892–1950) had described the first fossil finds of Nothrotherien in the form of an almost complete skull and individual phalanges from the important fossil site Rancho La Brea in California. For a long time, Nothrotherium was considered the typical representative of the sloth line in North America. In 1954 Robert Hoffstetter established the subgenus Nothrotheriops for the North American finds , in 1971 this was raised to genus status by Carlos de Paula Couto (1910-1982).

The independent subfamily Nothrotheriinae was first mentioned in 1920 by Florentino Ameghino, which was done posthumously . Lucas Kraglievich (1886–1932) named it only three years later as Nothrotherinae with Coelodon / Nothrotherium as the type form. He saw the Nothrotheria as part of the Megalonychidae and defined them on the basis of their long and low nasal area, the arched and partly air-filled wing bone , the characteristic structure of the molars and the flat and wide thigh bone. George Gaylord Simpson adopted Kraglievich's view in his classical classification of mammals in 1945, while Malcolm C. McKenna and Susan K. Bell led the Nothrotheria in 1997 at the rank of a tribe within the Megatheriidae. However, Timothy J. Gaudin had provisionally proposed the family assignment Nothrotheriidae in 1994 . In further, subsequent investigations, on the one hand the ear region and on the other the entire skull morphology, the family character of the Nothrotheria could be confirmed.

Individual evidence

  1. ↑ a b c d e Eli Amson, Christine Argot, H. Gregory McDonald and Christian de Muizon: Osteology and Functional Morphology of the Axial Postcranium of the Marine Sloth Thalassocnus (Mammalia, Tardigrada) with Paleobiological Implications. Journal of Mammalian Evolution 22 (4), 2015, pp. 473-518, doi: 10.1007 / s10914-014-9280-7
  2. ^ A b c d Richard Swann Lull: The ground sloth, Nothrotherium. American Journal of Science 5th series, 119, 1930, pp. 344-352
  3. ^ A b c Richard M. Hansen: Shasta ground sloth food haboits, Rampart Cave, Arizona. Paleobiology 4 (3), 1978, pp. 302-319
  4. ↑ Soledad De Esteban-Trivigno, Manuel Mendoza and Miquel De Renzi: Body Mass Estimation in Xenarthra: A Predictive Equation Suitable for All Quadrupedal Terrestrial Placentals? Journal of Morphology 269, 2008, pp. 1276-1293
  5. ^ 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
  6. ↑ a b Carl D. Frailey: Late Miocene and Holocene mammals, exclusive of the notoungulata, of the Rio Acre region, western Amazonia. Contributions in Science, Natural History Museum of Los Angeles County 374, 1986, pp. 1-74
  7. ^ H. Gregory McDonald and Christian de Muizon: The cranial anatomy of Thalassocnus (Xenarthra, Mammalia), a derived nothrothere from the Neogene of the Pisco Formation (Peru). Journal of Vertebrate Paleontology 22 (2), 2002, pp. 349-365
  8. ↑ a b Chester Stock: Recent studies on the skull and dentition of Nothrotherium from Rancho La Brea. University of California Publications in Geology. Bulletin of the Department of Geology 10, 1917, pp. 137-164 ( [1] )
  9. ↑ a b c d e f g h i Gerardo De Iuliis, Timothy J. Gaudin and Matthew J. Vicars: A new genus and species of Nothrotheriid sloth (Xenarthra, Tardigrada, Nothrotheriidae) from the Late Miocene (Huaquerian) of Peru. Palaeontology 54 (1), 2011, pp. 171-205
  10. ↑ 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
  11. ↑ a b Virginia L. Naples: Reconstruction of cranial morphology and analysis of function in the Pleistocene ground sloth Nothrotheriops shastense (Mammalia, Megatheriidae). Contributions in Science, Natural History Museum of Los Angeles County 389, 1987, pp. 1-21
  12. ^ A b François Pujos, Gerardo De Iuliis and Bernardino Mamani Quispe: Hiskatheriumsaintandrei, gen. Et sp. nov .: An Unusual Sloth from the Santacrucian of Quebrada Honda (Bolivia) and an Overview of Middle Miocene, Small Megatherioids. Journal of Vertebrate Paleontology 31 (5), 2011, pp. 1131-1149
  13. ↑ a b c d H. Gregory McDonald and George T. Jefferson: Distribution and habitat of Nothrotheriops (Xenarthra, Nothrotheridae) in the Pleistocene of North America. In: Wang X. and LG Barnes (Eds.): Geology and Vertebrate Paleontology of Western and Southern North America, Contributions in Honor of David P. Whistler. Natural History Museum of Los Angeles County Science Series 41, 2008, pp. 313-331
  14. ^ A b c François Pujos, Gerardo De Iuliis, Bernardino Mamani Quispe and Ruben Andrade Flores: Lakukullus anatisrostratus, called et sp. nov., A New Massive Nothrotheriid Sloth (Xenarthra, Pilosa) from the Middle Miocene of Bolivia. Journal of Vertebrate Paleontology 34 (5), 2014, pp. 1243-1248
  15. ↑ Timothy J. Gaudin: The Morphology of Xenarthrous Vertebrae (Mammalia: Xenarthra). Fieldiana Geology NS 41, 1999, pp. 1-38
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  23. ↑ Chester Stock: Cenozoic gravigrade edentates of western North America, with special reference to the Pleistocene Megalonychidae and Mylodontidae of Rancho la Brea. Carnegie Institution, Publication No. 331, 1925, pp. 1-206
  24. ↑ a b Diego Brandoni: “Xyophorus” sp. en the Mioceno Medio de Chubut: Implicancias sistemáticas, biogeográficas y biocronológicas del registro de un Nothrotheriinae en el Neógeno de la Argentina. Ameghiniana 51 (2), 2014, pp. 94-105
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  44. ^ Leon Augustus Hausman: Further studies of the hair of the fossil ground sloth (Nothrotherium shastense), and of its problematical "ovate bodies". American Journal of Science 5th series, 181, 1936, pp. 223-228
  45. ↑ 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
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