Lestodon

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Lestodon
Skeleton reconstruction of Lestodon (American Museum of Natural History, New York)

Skeleton reconstruction of Lestodon
( American Museum of Natural History , New York)

Temporal occurrence
Pliocene to early Holocene
5.33 million years to 10,000 years
Locations
Systematics
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Mylodontoidea
Mylodontidae
Lestodon
Scientific name
Lestodon
Gervais , 1855

Lestodon is a genus of the now-extinct Mylodontidae family, which included large, ground-living sloths . Along with Megatherium and Eremotherium, it is one of the largest known sloths, but was not closely related to these two. Finds of Lestodon are mainly from the Pampa region and areas to the north in South America and date from the Pliocene around 5 million years ago to the end of the Pleistocene around 10,000 years ago, with fossil remains from the Upper Pleistocene being observed far more frequently. They suggest that the sloth representative lived mainly in open landscapes.

Most likely, Lestodon lived mainly on grasses, which can be proven by the construction of the teeth and the general shape of the skull. Due to its body proportions, it represented a rather slow hiker, who could, however, stand up on its hind legs if necessary. The sloth representative may have been able to dig in the ground, as has been demonstrated by other members of the Mylodonts, but he was less well equipped for intensive digging activities. The structure of the hearing suggests that Lestodon was able to perceive frequencies in infrasound and probably also communicated through them.

The first scientific description of the genus dates back to 1855 and was carried out by Paul Gervais . As early as 1841, however, a Danish zoologist had described finds that are now being placed at Lestodon . His used name Platygnathus is not recognized. Numerous species of the genus have been described in the course of research history. Research suggests, however, that most likely only one species was present in the Pleistocene of South America.

features

General and height

Lestodon was a very large representative of the ground-dwelling sloths and by far the largest known representative of the Mylodontidae . His body length is given as 4.6 m. According to some calculations, individual individuals reached a body weight of 2.7 to 3.6 t, other assumptions assume up to 4.1 t. Along with Megatherium and Eremotherium, it was one of the largest known floor sloths, but was not closely related to either. In terms of body proportions, Lestodon differed from the other two giant ground sloths mentioned because, as a representative of the Mylodonts, it had very short lower limbs. Like all ground-living sloths, it was characterized overall by its forelegs, which were shorter than the hind legs, and by a long tail - unlike today's tree-living species.

Skull and dentition features

Skull of Lestodon : The wide nostril is clearly visible.

Lestodon's skull resembled that of its close relative Glossotherium , but was significantly larger. It was generally characterized by an almost prismatic-rectangular shape when viewed from above. Its length varied from 52 to 65 cm, the total height was a maximum of 19 cm. Most of the rostrum was formed by the upper jaw, which was rectangular and very high when viewed from the side. When viewed from above, it widened considerably in the front area, so that the maximum width at the front end of the upper jaw was up to 25 cm. This created a very wide and high nostril, which is a clear difference to the rather narrow snout of Mylodon . The nasal bone was completely fused laterally with the upper jaw, the bone sutures between the two skull bones showed a convex course, so that the nasal bone was clearly constricted in the middle. As a rule, the back width in contact with the frontal bone significantly exceeded the front. As is typical of all sloths, the median jawbone was very short. It was arched and only loosely connected to the upper jaw. Likewise, the zygomatic arch was characterized by numerous other sloths - with the exception of the large megatheria - as not closed. The front, backward-oriented arch part, which starts from the zygomatic bone , had a massive, plate-like widening at the rear and ended in three processes: an ascending upper, a descending lower and a largely horizontally oriented middle. While the ascending and descending processes were each well developed, the middle one was usually short in length. The arched portion of the temporal bone pointed forward and had a slender, finger-like shape. The two ends of the anterior and posterior arch section were very close together, as with all myodonts. The occiput was wider than it was high and had a strong transverse bulge. In its shape it clearly differed from the much flatter occiput in Glossotherium and the more circular in Mylodon .

The lower jaw was between 37 and 51 cm long. The lower edge of the horizontal bone was largely straight. It had its greatest height at the rearmost molar, where it measured up to 12.5 cm. Its height decreased continuously towards the front, in the area of ​​the symphysis it became more powerful again. The symphysis itself was extremely strong and wide, analogous to the very wide upper jaw, and rose at an angle of 45 ° on the front edge of the lower jaw. The extended anterior area reached half the length of the row of teeth, the total length of the symphysis was about 10 cm. It had a straight or only slightly curved edge at the front. The angular process at the rear end of the lower jaw was prominent and was well below the plane of the tooth. The teeth had the structure typical of sloths. It consisted of 5 teeth per branch in the upper jaw and 4 per branch in the lower jaw, so it consisted of a total of 18 teeth. The foremost tooth in each case was designed in the form of a canine tooth ( caniniform ) and was sometimes quite large. Due to the wide construction of the mouth, these canine-like teeth were up to 17 cm apart in the lower jaw. Between the anterior, canine-shaped tooth and the posterior teeth there was a very extensive diasterma , which reached an average of 6.8 cm in the upper jaw and around 5.5 cm in the lower jaw. The back molars showed a molar structure. Characteristic of late Mylodonts was the flat to slightly recessed chewing surface, which was given a lobate design. The inside of the teeth consisted of a hard variant of the dentin ( orthodentine ) and were enclosed on the outside by a shell made of dental cement . The length of the entire row of teeth in the lower jaw was up to 19 cm, of which the molar-like teeth took up about 11 cm. The length of the individual rear molars varied here between 3 and 4 cm, the rearmost was usually the largest.

Body skeleton

Lestodon thighbones
Foot of Lestodon

The body skeleton has been passed down relatively well. The humerus was up to 51 cm long and had a massive lower joint typical of ground sloths with a diameter of 26 cm. Compared to other large mylodonts, the humerus was built relatively gracefully. In contrast, the length of the cubit was up to 46 cm. According to other closely related forms, it had a rather extensive articular process close to the body, the olecranon , which measured up to 16 cm in length. The characteristically designed thigh bone , which was up to 74 cm in length and up to 34 cm wide at the upper joint end, was extremely flattened and thus appeared flat like a board. It was similar to that of Mylodon , but larger in size. The thigh bone differed from the megatheria in that it was less clearly rectangular and wide when viewed from the front. A third trochanter was formed on the shaft as a muscle attachment point, but it did not appear very raised. The tibia and fibula were partly fused together at the upper end, but this occurred rather variably within the genus. Both were characterized by their rather flat and very short construction; the shin was only about half the length of the thigh bone. This is typical of numerous Mylodonts and distinguishes them from the Megatheria, in which the lower leg sections were relatively longer. The hind foot of Lestodon largely coincided with that of other Mylodons. He had a total of four rays (II to V), whereby only the two inner (II and III) had claws. The first two phalanxes of the second ray were usually fused together, but unlike the Paramylodon and the same as the Glossotherium , the third ray consisted of three phalanges . The respective end links could be very long with 14 to 17 cm. The two outer rays (IV and V) each had only two toe phalanges, so there were no claws here. Instead, the metatarsals had a much more massive structure. As with numerous large ground sloths, the foot was turned inwards and supported with the outermost ray and the heel bone on the ground ( pedolateral ).

Distribution and important fossil finds

Skeletal reconstruction of Lestodon
various finds of Lestodon (skull, lower jaw, rib and upper arm fragments, metapodium, cervical vertebrae)

Lestodon lived from the Pliocene to the end of the Pleistocene around 5 million to around 10,000 years ago, its main distribution area included the present-day pampas in South America . The occurrence overlapped with that of the huge Megatherium (especially Megatherium americanum ). It is possible that there were certain ecological differences in these landscapes, which were partly open at the time, which minimized direct competition between the two sloth representatives, but this has not yet been investigated in detail. What is striking is a frequent concentration of sites with remains of Lestodon in present-day Uruguay east of the Río de la Plata , where Megatherium was generally only rarely detected. To the west of the river in what is now Argentina, however, Lestodon is far less common. To the north, fossil finds of the sloth genus reach as far as the Brazilian state of São Paulo , where there is also some overlap with Eremotherium . The 23rd southern latitude is given as the northern limit of distribution. Furthermore, the shelf areas have recently increased in importance as important fossil stores. Overall, however, fossil finds from Lestodon are much rarer than those from Megatherium or Eremotherium .

One of the earliest records of the genus Lestodon comes from Farolo Monte Hermoso in the Argentine province of Buenos Aires with a 33 cm long skull of a young animal . The find was recovered in the Monte Hermoso Formation and dates to the Lower Pliocene . Significant fossil remains of the Lower and Middle Pleistocene are mainly from the Pampa region of Argentina and from the Tarija Valley in southern Bolivia. A skull-less partial skeleton possibly dating from this time came to light in the river deposits of the "Arroio do Lestodon" near Caçapava do Sul in the Brazilian state of Rio Grande do Sul . Most of the known finds can be assigned to the Upper Pleistocene . The coastal region of Uruguay turned out to be extraordinarily rich in finds. Among other things, the coastal cliffs of Arroyo El Caño in the Uruguayan Department of Colonia , where countless fossil remains that belong to the Middle and Upper Pleistocene are stored in fluvial deposits. About 70% of the recovered material can be attributed to Lestodon , but it mostly comprises individual bones in varying degrees of preservation, and skeletal material that belongs together is hardly known. Due to the common occurrence with the large grass-eating ungulate Toxodon or the camel-like Hemiauchenia as well as numerous representatives of the armored Glyptodontidae , open and dry landscapes can be reconstructed here. A nearly complete skeleton of Lestodon came to light from the nearby bay of Colonia de Sacramento . The Arroyo del Vizcaíno site near Sauce in southeastern Uruguay, from which an extensive fossil fauna originates, is of outstanding importance . In the sandy-gravelly deposits exposed there on only 30 m², more than 1000 bone fragments have so far been recovered, the age of which, according to radiometric dating, is about 32,300 to 31,200 years BP . More than 90% of the identifiable material belongs to Lestodon , the approximately 730 pieces so far come from all areas of the skeleton. They represent at least a dozen adult individuals and two juveniles. Some special surface modifications of the bones, such as possible cut marks, made the editors of the site think of human manipulation, which would make Arroyo del Vizcaíno one of the earliest evidence of the colonization of South America by early hunter-gatherer groups (usually Monte Verde in Chile applies with a Age of around 14,800 years as one of the oldest sites in South America). However, the interpretation is not fully shared. Again in Playa del Barco in the southwest of the Argentine province of Buenos Aires, over 280 bones from Lestodon came to light on around 500 m² . These can be assigned to a total of 13 individuals, including young animals, adults and extremely old animals. The age of the site is around 19,849 years ago. The remains were found in association with other large mammals such as ground sloths, such as Megatherium , Glyptodon or proboscis , here especially Notiomastodon , but also various predators .

The most recent finds of Lestodon came from the late Upper Pleistocene. Mention should be made, among other things, of a thighbone 74 cm long and an almost complete skull from the La Paz local fauna from southern Uruguay, which date back to an age of 17,620 years BP. Remains that were found on the important archaeological site Paso Otero  5 in the Argentine province of Buenos Aires belong to the transition to the Holocene . There were over 80,000 bone remnants on almost 100 m², some of which were badly smashed or burned and so can only be determined to a small extent. Only two fragments of Lestodon could be identified. The presence of humans here is attested by more than 80 stone artifacts made of quartzite , including fish tail points . The age of the finds was determined to be 10,440 to 10,190 years BP with the help of the radiocarbon method, some more recent data also suggest a period of 9400 to 9560 years BP. Like many other ground sloths , Lestodon died out at the end of the last glacial period in the course of the Quaternary extinction wave .

Paleobiology

Locomotion

Thighbones (above) and shins (below) of Lestodon : The great difference in length between the two leg bones is clearly visible

The length ratio of the lower to the upper leg sections (crural index) gives an indication of the agility of an animal. Short lower sections are typical of lumbering animals, such as rhinos , while long lower leg bones, as in horses, are associated with fast animals. Mylodonts generally have very short lower limbs. With Lestodon they reach only about half of the upper ones with a shin length of around 34 to 37 cm compared to a thigh bone length of 68 to 73 cm. In contrast, the lower leg sections of the Megatherium were significantly longer. Its tibia length varies between 42 and 62 cm, the femur length between 57 and 77 cm. Thus, like numerous other representatives of the Mylodonts , Lestodon may have been adapted to a much more ponderous gait than the Megatheria, for example . While running, Lestodon moved forward on inwardly turned feet so that they touched the ground with the outer ray (ray V) and the calcaneus . This is known as the pedolateral gait and is characteristic of all ground-living sloths , with the exception of the Megalonychidae . In the Mylodonts, however, the foot was not as strongly arched as in the related Scelidotheriidae , so that the heel bone touched the entire length and not just the rear end. This made the foot more similar to that of the large Megatheriids.

For some representatives of the Mylodonts, such as Glossotherium , researchers suspect that they were good diggers in the ground. In addition to the generally strong appearance of the front limbs, this is indicated by the extremely extensive olecranon , the upper articular process of the ulna. A significant lengthening of the olecranon increases the leverage of the forearm enormously, as this is where the triceps attach. This means that the arm can be used for high power development rather than for reaching high speeds when moving. In Lestodon , the olecranon takes up around 35% of the total length of the bone, which roughly corresponds to the value of Glossotherium and is in the lower range of today's armadillos , which are sometimes considered good graves. A possible soil trench of Lestodon could also have been supported by the position of the body's center of gravity, which is shifted far back in the area of ​​the abdomen, shortly before the attachment of the hind limbs. As a result, around 68 to 71% of the body weight was carried by the hind legs in a four-footed position, which is the opposite of the number of hoofed animals today, where the main load is distributed on the front legs. This enabled the sloth genus to stand up on its hind legs and so change into a bipedal stance, which freed the front legs for other activities. For example, in today's giant armadillo ( Priodontes maximus ) as an excellent grave, the main burden of the body when digging is carried by the hind legs. The symmetrical and clearly curved claws of Lestodon's forefeet were also able to withstand the tensile and compressive forces that occur when digging, according to stress analyzes. However, it can be assumed that the giant sloth with its clearly graceful humerus bones was less equipped for digging activities than its relative Glossotherium . It was probably also less necessary than with smaller representatives, since adult Lestodon individuals hardly needed to fear predators . however, isotope studies on smilodon finds indicate that lestodon may well have belonged to the prey spectrum of the saber-toothed cat . Some extremely large buried burrows from southeastern Brazil, which are estimated to have a Pliocene to Pleistocene age, are nevertheless partially associated with Lestodon (under the name of Ichnospecies Megaichnus major ). At around 2 m high, 4 m wide and sometimes up to 50 m long, these are significantly larger than comparable structures in Argentina, for which Glossotherium is mostly responsible.

nutrition

The representatives of the Mylodontidae are often seen as sloths specializing in grass food. Among other things, the high ( hypsodontic ) crowns of the molars, which also occur in grass-eating ungulates such as horses , speak for this . However, since sloth teeth lack hard enamel , comparisons between these two groups are only possible to a limited extent. Lestodon has comparatively lower molars than Mylodon or Paramylodon within the Mylodonts . They are also significantly lower than Megatherium and Eremotherium from the Megatheriidae family, which, however, ate rather soft vegetable foods. On the outside, the teeth consist of a layer of very hard orthodentine , which forms a slightly raised bar or edge on the chewing surface of the posterior molars. Within the tooth is located in the softer Vasodentin which forms a small depression on the occlusal surface, so that this whole a tab or tongue-like ( lobate ) has expression. This chewing surface pattern, which is characteristic of numerous Mylodonts, suggests that the food was ground up and therefore consisted of hard to fibrous plant material. The chewing apparatus also shows individual features. The more sideways-oriented and slightly arched joint surfaces of the lower jaw allow lateral, forward and backward chewing movements. However, the incompletely formed zygomatic arch speaks against clearly lateral jaw movements, since it could not withstand the opposing forces of the masseter and pterygoideus muscles . For this reason, a dominance of forward and backward chewing movements seems likely, which also corresponds to corresponding signs of wear on the teeth. Due to the low position of the mandibular joint only slightly above the chewing plane, vertical chewing movements were only possible to a limited extent, and the biting force was rather low due to the arrangement of the masticatory muscles. Because of these anatomical features, Lestodon was probably adapted to food containing grass and could ingest larger amounts at once. In contrast to herbivorous ungulates, however, the mylodonts have an extremely small total occlusal surface of all molar-like molars, which in Lestodon was around 1000 to 1100 mm² (a hippopotamus of comparable size has around three to five times as much chewing surface, today's elephants of comparable size around eight- up to eleven times as much and more). From this it is concluded that Lestodon was unable to chop up the food in the oral cavity and therefore either processed a large part of it in the gastrointestinal tract or, like today's sloths, had a rather low metabolic rate.

Indirectly, the shape of the mouth suggests a herbivorous diet. Like Glossotherium , Lestodon has a very wide mouth with widely spaced margins of the upper jaw, which is clearly different from the narrower snout of Mylodon or Megatherium . According to reconstructions, it was equipped with wide, bulging lips, which, comparable to today's white rhinoceros, are well suited to picking up large amounts of grass in a relatively short time. In addition, due to the design of the hyoid bone and its position pushed far back, the Mylodonts with wide snouts suggest a long and flexible tongue . As a rule, however, this bone is rarely preserved, which is due to its fragility. So far, only one specimen of a young animal has been found from Lestodon . In contrast to Mylodon , Lestodon does not contain any manure residues in the form of coprolites , so that the food consumed cannot be analyzed directly. With the help of isotope studies on fossil remains from Arroyo del Vizcaíno in Uruguay, however, the landscape in which the animals lived could be determined, which allows conclusions to be drawn about their basic diet. They gave indications of cool and dry climatic conditions during the end of the Pleistocene and, accordingly, the predominance of open landscapes. The conditions are similar to those found in northern Patagonia today. The grasses, which are mainly spread as a result, are therefore also in accordance with the anatomically determined information on the diet of Lestodon . Further isotope studies on the remains of several individuals from Playa del Barco indicate that Lestodon has a rather mixed vegetable diet with a stronger preference for grass food. However, since there is also a high individual variability in the results, greater flexibility in food intake cannot be ruled out.

Social behavior

The approximately a dozen individuals of Lestodon found at Playa del Barco include young and adult individuals of various ages. Their close spatial distance to one another and their comparable degree of weathering suggest that the former carcasses were embedded at about the same time. Scientists therefore assume that Lestodon also formed larger groups or family associations, at least temporarily. Under what circumstances this happened is not clear, today's tree sloths are strictly solitary. Presumably, competition with other large herbivores or protection from predators had some influence. A comparable way of life is also assumed in mass finds of Eremotherium .

Sensory performance, soft tissues and pathologies

Today's sloths generally have poor visual performance , and their hearing is also poorly developed and designed for frequencies from 0.3 to 30 kHz with an optimum at 2 to 8 kHz. Individual ossicles of the middle ear have come down to us from Lestodon , namely the anvil , the hammer and the stirrup . All three bones transmit the acoustic signals from the outer ear to the cochlea in the inner ear. The size and weight of the auditory ossicles are not directly dependent on the body size of an individual, but, in connection with the expansion of the eardrum and the viscosity of the middle ear, indicate the ability to perceive a certain frequency range. The Lestodon anvil and hammer together weigh around 500 mg. This corresponds roughly to the values ​​that are known for the same bones of Glossotherium and for which, based on a few well-preserved skulls, an eardrum size of 180 to 208 mm² can be assumed. Today's elephants and dog seals are in a similar size range . An ability to perceive very low frequencies has been proven for both mammals. Because of this, a hearing ability in the frequency range of 0.05 to 16.5 kHz with an optimum of 1.7 to 2.4 kHz is assumed for Lestodon . The lower value is clearly in the infrasound range . Sounds with low frequencies are carried over long distances and are hardly distracted by vegetation, so they can be located even from a great distance. Possibly they were used by Lestodon for communication with conspecifics over long distances in the open landscapes of the pampas, for example for rutting calls, similar to what is the case with today's elephants. On the other hand, predators can also be recognized in good time with hearing designed in this way. Last but not least, they may also be related to the burrowing way of life, as some of today's animals actively living underground, such as pocket rats , can also perceive seismic waves in this way .

As with the other giant ground-living sloths, such as Megatherium and Eremotherium , in contrast to numerous live reconstructions, no dense fur cover is assumed for Lestodon due to its distribution in landscapes under moderate to sometimes subtropical climatic conditions . The main argument against the development of a dense body skin is the enormous body size and the associated necessary thermoregulation . Since a thick coat of fur does not dissipate body heat, its availability would require extremely large amounts of drinking water to balance the energy balance. According to this, Lestodon had a more or less bare skin, similar to other large, modern herbivores such as elephants, rhinos or hippos. The hyoid bone already mentioned is fragmentary and 10.5 cm long. It comes from a young animal, compared to the same bone from Glossotherium , the hyoid bone in Lestodon could have reached 17.5 cm in length. Assuming a proportional development as in today's domestic cattle , a weight of about 10 kg can be assumed for the tongue of the young animal.

Several of the Lestodon remains found at Playa del Barco showed pathological changes such as deformed bones, especially in the vertebrae. Mostly these are due to osteoporosis and osteoarthritis , which can often be proven in large mammals. Occasionally osteophytes appeared, which possibly restricted the animals' movements. Also osteochondritis assigned to each caudal vertebrae, which is possibly due to the support function when getting up on their hind legs.

Systematics

Internal systematics of the Mylodontidae according to Boscaini et al. 2019 (based on skeletal anatomical analyzes)
 Mylodontidae  


 Urumacotherium


   

 Pseudoprepotherium



   


 Paroctodontotherium


   

 Octodontotherium



   

 Brievabradys


   



 Lestodon


   

 Bolivartherium



   

 Thinobadistes


   

 Sphenotherus


   

 Lestobradys





   

 Pleurolestodon


   


 "Glossotherium" chapadmalense


   

 Simomylodon



   



 Kiyumylodon


   

 Mylodon



   

 Paramylodon



   

 Glossotherium









Template: Klade / Maintenance / Style
Internal systematics of the sloths according to Presslee et al. 2019 (based on protein analysis)
 Folivora  

 Megalocnoidea


   

 Megatherioidea


  Mylodontoidea  

 Scelidotheriidae


   

 Choloepodidae


  Mylodontidae  

 Lestodon


   

 Paramylodon


   

 Mylodon


   

 Glossotherium









Template: Klade / Maintenance / Style

Lestodon is a now extinct genus from the also extinct family of the Mylodontidae . The Mylodontidae in turn represent part of the subordination of the sloths (Folivora). Together with the Orophodontidae and the Scelidotheriidae, the Mylodontidae together form the superfamily of the Mylodontoidea (sometimes the Scelidotheriidae and the Orophodontidae are also only managed as a subfamily within the Mylodontidae). The Mylodontoidea form in a structure based on skeletal anatomical characteristics, next to the Megatherioidea, the second large and important sloth line. After molecular genetic and protein-based analyzes, the megalocnoid can be added to these two large groups . According to these studies, the Mylodontoidea with the two-toed sloth ( Choloepus ) also contain one of the two species of sloth still alive today. The Mylodontidae represent one of the most diverse groups within the sloth. In general, they are characterized by their high-crowned teeth with, deviating from the Megatherioidea, flat ( lobater ) chewing surfaces, which are an adaptation to more grassy food. The rear teeth show a round or oval cross-section, the front teeth are shaped like a canine. The rear foot also has a clearly laterally twisted shape. The earliest records of the Mylodonts date back to the Oligocene , including Paroctodontotherium , found in the Salla Beds in the Salla Luribay Basin in Bolivia.

Lestodon is often placed within the Mylodontidae in the subfamily of the Lestodontinae (this was introduced as an independent family by Florentino Ameghino in 1889 , but was shifted to the status of the subfamily within the Mylodontidae by Lucas Kraglievich in 1931; sometimes it is now also known as Lestodontini on a tribal level guided). Close relatives thus form forms such as Thinobadistes , possibly also Glossotherium , while the well-known Mylodon , which gives the family its name, is in its own subfamily, the Mylodontinae . This subdivision is mostly accepted and could also be confirmed in one of the most extensive studies on the tribal history of the sloth by Timothy J. Gaudin from 2004 and supported by subsequent studies. An analysis from the year 2019, carried out by a team led by Luciano Varela , in turn refers Lestodon to a group of Mylodonts from northern South America and Central America such as Bolivartherium and Thinobadistes , but sees a greater relational distance to Glossotherium , which is closely tied to Paramylodon . A study by Alberto Boscaini and fellow researchers, which was presented in the same year and which contained a higher-resolution phylogenetic study of the Mylodonts, provided an almost equivalent result with regard to Lestodon . It also confirms the clear dichotomy of the terminal mylodonts into the Mylodontinae and Lestodontinae, which had already been worked out in the aforementioned study by Gaudin from 2004. The development of the front canine-like teeth can be used as a clear difference between the two groups. The Lestodontinae have large canine- shaped teeth at a clear distance from the rear molar-like teeth, in the Mylodontinae these are small or partially receded and are closer to the molar-shaped teeth. The external position of Lestodon compared to Glossotherium , Mylodon and additionally Paramylodon resulted in the already mentioned biochemical studies of the year 2019. In general, the internal structure of the Mylodontidae is complex and varies depending on the processor. In some cases, numerous other subfamilies were established, such as the Nematheriinae for representatives from the Lower Miocene or the Octomylodontinae for all basal forms, which are not generally recognized. With the establishment of the Urumacotheriinae for late Miocene genera of northern South America, a further line within the Mylodonts was worked out in 2004, which, however, does not exist after the studies in 2019. In principle, a revision is requested for the entire family, since many of the higher taxonomic units have no formal diagnosis.

Over a dozen species within the genus Lestodon have been described in the course of the history of research . Usually only three are considered in the scientific literature:

  • Lestodon armatus Gervais , 1855
  • Lestodon australis Kraglievich , 1934
  • Lestodon trigonidens Gervais , 1873

The independence of L. trigonidens is often the subject of discussion. The species goes back to Paul Gervais , who set it up in 1873 on the basis of an anterior lower jaw fragment with canine-like anterior teeth that are even stronger than L. armatus . Most scientists today see these different forms of the front canine-like teeth as an expression of a sexual dimorphism , which means that L. trigonidens would be identical to L. armatus . Accordingly, the former could be associated with males, the latter with females. The status as a separate species is also problematic for L. australis . This has so far only been proven in Argentina and established by Lucas Kraglievich in 1934 with the help of an almost complete, 56 cm long skull with only missing anterior zygomatic arches. He came from Playa del Barco near Monte Hermoso in the Argentine province of Buenos Aires. Anatomical investigations showed, however, that the skull lies within the range of variation of the characteristics of L. armatus and therefore does not have any deviating or defining characteristics. According to this, only one species of Lestodon lived during the Pleistocene, L. armatus . For the so far oldest known find from the Pliocene there is no clear identification of the species due to the fact that the skull belongs to a not fully grown individual. In 2004, two species of Lestodon were described from the Urumaco Formation of the Upper Miocene in northwestern Venezuela , which were not only significantly smaller and older than the previous finds of the genus, but also lay far outside the known range. Two years later they were assigned to the genus Bolivartherium, which is closely related to Lestodon .

Research history

The first finds, discovered by Henrik Nikolai Krøyer in 1841. Right and left: spoke; Middle: lower jaw

Among the earliest finds that can most likely be assigned to Lestodon are those that the Danish zoologist Henrik Nikolai Krøyer (1799–1870) brought back from his trip to South America in 1840 and 1841. During this trip he found numerous bones of extinct animals on the Río de la Plata on the bank opposite Buenos Aires , northwest of the Uruguayan city of Colonia de Sacramento . He presented this in a brief preliminary report in 1841, but only described one lower jaw in more detail, which he gave the scientific name Platygnathus platensis because of its broad shape . Due to the development of his opinion, a total of five teeth, including a pointed front, he referred him to the proximity of the then known sloths such as Choloepus (two-toed sloth) and also drew comparisons to Megatherium , to which he correctly assigned only four lower jaw teeth. It was not until more than 30 years later that the finds were examined again by the likewise Danish zoologist Johannes Theodor Reinhardt (1816–1882). In the meantime, some of them had been badly damaged, but Reinhardt realized that they were not a uniform material due to their different state of preservation. These included the remains of other extinct animals, such as Glyptodon , a large armored representative of the Glyptodontidae , or Toxodon from the group of South American ungulates . The majority, however, comprised the bones of giant sloths, such as parts of the spine and limbs. On the lower jaw described by Krøyer, Reinhardt noticed the incorrect indication of five teeth and corrected the number to the four actually present. The general characteristics of the finds led Reinhardt to assign them to the Lestodon sloth genus described two decades earlier . The name Platygnathus platensis is no longer used today, the genus name Platygnathus has also been preoccupied since 1832 by a representative of the longhorn beetle .

Paul Gervais

In his assignment, Reinhardt referred to the work of the French natural scientist Paul Gervais (1816–1879). He had presented the first scientific description of Lestodon in 1855. Gervais found material from the Argentine province of Buenos Aires , which had been brought to the Muséum national d'histoire naturelle in Paris, was available to introduce the new genre . Gervais noticed similarities to Mylodon , but emphasized the enormous canine-shaped front teeth in the lower and upper jaw. Because of this he named the species Lestodon armatus . The holotypes include a fragmented upper jaw as well as a lower jaw, which is also only partially preserved (specimen numbers MNHNP -PAM 90 and 91). In both pieces, the anterior caniniform tooth, the first in the upper jaw and the first two molar-like teeth in the lower jaw are preserved, as well as the alveolus of the subsequent tooth above and below. Gervais introduced a second species at the same time as Lestodon myloides , in whose shorter, front teeth he saw echoes of Mylodon . ( L. myloides was referred to Pseudolestodon , a today's synonym for Glossotherium, by Henri Frédéric Paul Gervais (1845-1915) and Florentino Ameghino (1854-1911) in 1880. ) The generic name Lestodon derives from the Greek words λῃστής ( lēstḗs "robber") "Thief") and ὀδούς ( odoús "tooth") and refers to the canine-like design of the foremost tooth, which Gervais said gave the animal a predatory character.

In the essay in the first description, Gervais only mentions Lestodon briefly; he presented a much more detailed description in 1873 in which he also included numerous elements of the body skeleton. As early as 1880, Gervais and Ameghino listed a total of eight species of Lestodon (one of them unnamed) in an overview work on the fauna of South America , which, however, did not contain a differentiated description. They do not mention Krøyer's Platygnathus platensis , since Reinhardt's essay dates back to 1875, but did not appear until the same year as Gervais' and Ameghino's overview. Two years later, members of the German Geological Society recognized L. platensis , citing bone finds from Uruguay that had been donated to the society by Rudolf Virchow , and connected the species with the form that Gervais and Ameghino had not clearly identified. More species were introduced primarily by Lucas Kraglievich (1886–1932) in the early 1930s. But already around 20 years later, Carlos de Paula Couto (1910–1982) doubted the numerous different species of lestodon . In 1979 he also spoke out in favor of recognizing L. armatus as only one valid species.

literature

  • Ada Czerwonogora and Richard A. Fariña: How many Pleistocene species of Lestodon (Mammalia, Xenarthra, Tardigrada)? Journal of Systematic Palaeontology 11 (1-2), 2013, pp. 249-261
  • 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. 212-213) ISBN 978-0-253-00230-3

Individual evidence

  1. ↑ American Museum of Natural History: Lestodon armatus. ( [1] )
  2. ↑ a b c d e f g h Ada Czerwonogora and Richard A. Fariña: How many Pleistocene species of Lestodon (Mammalia, Xenarthra, Tardigrada)? Journal of Systematic Palaeontology 11 (1-2), 2013, pp. 249-261
  3. ↑ a b c Richard A. Fariña, Sergio F. Vizcaíno and María S. Bargo: Body mass estimations in Lujanian (Late Pleistocene-Early Holocene of South America) mammal megafauna. Mastozoología Neotropical 5 (2), 1998, pp. 87-108
  4. ↑ a b c d e M. Susana Bargo, Sergio 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
  5. ^ A b c 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. 212-213) ISBN 978-0-253-00230-3
  6. ^ A b M. Susana Bargo, Néstor Toledo and Sergio F. Vizcaíno: Muzzle of South American Pleistocene Ground Sloths (Xenarthra, Tardigrada). Journal of Morphology 267, 2006, pp. 248-263
  7. ↑ Luciano Brambilla and Damián A. Ibarra: The occipital region of late Pleistocene Mylodontidae of Argentina. Boletín del Instituto de Fisiografía y Geología 88, 2018, pp. 1–9
  8. ↑ a b c M. Susana Bargo and Sergio F. Vizcaíno: Paleobiology of Pleistocene ground sloths (Xenarthra, Tardigrada): biomechanics, morphogeometry and ecomorphology applied to the masticatory apparatus. Ameghiniana 45 (1), 2008, pp. 175-196
  9. ↑ a b c M. Susana Bargo, Gerardo De Iuliis and Sergio F. Vizcaíno: Hypsodonty in Pleistocene ground sloths. Acta Palaeontologica Polonica 51 (1), 2006, pp. 53-61
  10. ↑ a b c d Paul Gervais: Mémoire sur plusieurs espècies de mammifères fossils propres a l'Amerique Méridionale. Mémoires de la Société géologique de France, Série 2, 9, 1873, pp. 1–44 ( [2] )
  11. ^ A b 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
  12. ↑ a b Dilson Vargas-Peixoto, Cícero Schneider Colusso, Átila Augusto Stock Da-Rosa and Leonardo Kerber: A new record of Lestodon armatus Gervais 1855 (Xenarthra, Mylodontidae) from the Quaternary of southern Brazil and remarks on its postcranial anatomy. Historical Biology, 2019, doi: 10.1080 / 08912963.2019.1597075
  13. ↑ a b c Ascanio D. Rincón, H. Gregory Mc Donald, Andrés Solórzano, Mónica Núñez Flores and Damián Ruiz-Ramoni: A new enigmatic Late Miocene mylodontoid sloth from northern South America. Royal Society Open Science 2, 2015, p. 140256, doi: 10.1098 / rsos.140256
  14. ↑ Chester Stock: Structure of the pes in Mylodon harlani. University of California Publications. Bulletin of the Department of Geology 10 (16), 1917, pp. 267-286
  15. ^ A b c 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
  16. ^ Carlos Castor Cartelle: Preguiças terrícolas, essas desconhecidas. Anales Ciência Hoje 27, 2000, pp. 19-25
  17. ↑ a b Renato Pereira Lopez, Heinrich Theodor Frank, Francisco Sekiguchi de Carvalho Buchmann and Felipe Caron: Megaichnus igen. nov .: Giant paleoburrows attributed to extinct Cenozoic mammals from South America. Ichnos 24 (2), 2017, pp. 133–145, doi: 10.1080 / 10420940.2016.1223654
  18. ↑ Alex Sandro Schiller Aires and Renato Pereira Lopes: Representativity of Quaternary mammals from the Southern Brazilian continental shelf. Revista Brasileira de Paleontologia 15 (1), 2012, pp. 57-66
  19. ↑ a b Cecilia M. Deschamps, Gracielia I. Esteban and M. Susana Bargo: El registro más Antigua del género Lestodon Gervais 1855 (Xenarthra, Tardigrada, Mylodontidae) (Montehermosense, Plioceno Temprano). Ameghiniana 38 (2), 2001, pp. 151-156
  20. ↑ Esteban Soibelzon, Ángel Ramón Miño-Boilini, Alfredo Eduardo Zurita and Cecilia Mariana Krmpotic: Los Xenarthra (Mammalia) del Ensenadense (Pleistoceno inferior a medio) de la Región Pampeana (Argentina). Revista Mexicana de Ciencias Geológicas 27 (3), 2010, pp. 449-469
  21. ↑ Andrés Rinderknecht: Vertebrados fósiles de la costa uruguaya. In: R. Menafra, L. Rodríguez-Gallego, F. Scarabino and D. Conde (eds.): Bases para la Conservación y el Manejo de la Costa Uruguaya. Montevideo, 2006, pp. 343-349
  22. ↑ Richard A. Fariña and Reynaldo Castilla: Earliest evidence for human-megafauna interaction in the Americas. In: E. Corona-M and J Arroyo-Cabrales (eds.): Human and faunal relationships reviewed: an archaeozoological approach. Oxford, 2007, pp. 31-34
  23. ↑ Richard A. Fariña, P. Sebastián Tambusso, Luciano Varela, Mariana Di Giacomo, Marcos Musso, Andrés Gascue and Roberto Bracco: Among others, cut-marks are archaeological evidence: reply to 'Archaeological evidences are still missing: a comment on Fariña et al. Arroyo del Vizcaíno Site, Uruguay 'by Suárez et al. Proceedings of the Royal Society B 281, 2014, doi: 10.1098 / rspb.2014.1637
  24. ^ Richard A. Fariña: Bone surface modifications, reasonable certainty and human antiquity in the Americas: the case of the Arroyo del Vizcaíno. American Antiquity 80 (1), 2015, pp. 193-200
  25. ↑ a b c P. Sebastián Tambusso, H. Gregory McDonald and Richard A. Fariña: Description of the stylohyal bone of a giant sloth (Lestodon armatus). Palaeontologia Electronica 18 (1), 2015, p. 19A ( [3] )
  26. ↑ 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
  27. ↑ Richard A. Fariña, P. Sebastián Tambusso, Luciano Varela, Ada Czerwonogora, Mariana Di Giacomo, Marcos Musso, Roberto Bracco and Andrés Gascue: Arroyo del Vizcaíno, Uruguay: a fossil-rich 30-ka-old megafaunal locality with cut- marked bones. Proceedings of the Royal Society B 281, 2014, p. 20132211, doi: 10.1098 / rspb.2013.2211
  28. ↑ Rafael Suárez, Luis A. Borrero, Karen Borrazzo, Martín Ubilla, Sergio Martínez and Daniel Perea: Archaeological evidences are still missing: a comment on Fariña et al. Arroyo del Vizcaíno site, Uruguay. Proceedings of the Royal Society B 281, 2014, doi: 10.1098 / rspb.2014.0449
  29. ↑ a b c d Rodrigo L. Tomassini, Claudia I. Montalvo, Mariana C. Garrone, Laura Domingo, Jorge Ferigolo, Laura E. Cruz, Dánae Sanz ‑ Pérez, Yolanda Fernández ‑ Jalvo and Ignacio A. Cerda: Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine pampas. Scientific Reports 10, 2020, p. 10955, doi: 10.1038 / s41598-020-67863-0
  30. ↑ Andrea Corona, Daniel Perea, Pablo Toriño and César Goso: Taphonomy, sedimentology and chronology of a fossiliferous outcrop from the continental Pleistocene of Uruguay. Revista Mexicana de Ciencias Geológicas 29 (2), 2012, pp. 514-525
  31. ^ 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
  32. ↑ 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
  33. ↑ 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
  34. ↑ 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
  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
  36. ↑ Santiago Pantiño, Jorge Peréz Zerpa and Richard A. Fariña: Finite element and morphological analysis in extant mammal's claws and Quaternary sloth 'ungual phalanges. Historical Biology, 2019, doi: 10.1080 / 08912963.2019.1664504
  37. ↑ Hervé Bocherens, Martin Cotte, Ricardo Bonini, Daniel Scian, Pablo Straccia, Leopoldo Soibelzon and Francisco J. Prevosti: Paleobiology of sabretooth catSmilodon populator in the Pampean Region (Buenos Aires Province, Argentina) around the Last Glacial Maximum: Insights from carbon and nitrogen stable isotopes in bone collages. Palaeogeography, Palaeoclimatology, Palaeoecology 449, 2016, pp. 463–474, doi: 10.1016 / j.palaeo.2016.02.017
  38. ↑ Francisco Segikurch de Carvalho Buchmann, Heinrich Theodor Frank, Victor Moreira Ferreira Sandim and Erick Cruz Antal: Evidência de vida Gregaria em paleotocas attribuítas a Mylodontidae (Preguiças gigantes). Revista Brasileira de Paleontologia 19 (2), 2016, pp. 259-270
  39. ↑ Sergio F. Vizcaíno, M. Susana Bargo and Guillermo H. Cassini: Dental occlusal surface area in relation to body mass, food habits and other biological features in fossil xenarthrans. Ameghiniana 43 (1), 2006, pp. 11-26
  40. ↑ Leandro M. Pérez, Néstor Toledo, Gerardo De Iuliis, M. Susana Bargo and Sergio F. Vizcaíno: Morphology and Function of the Hyoid Apparatus of Fossil Xenarthrans (Mammalia). Journal of Morphology 271, 2010, pp. 1119-1133
  41. ↑ Ada Czerwonogora, Richard A. Fariña and Eduardo Pedro Tonni: Diet and isotopes of Late Pleistocene ground sloths: first results for Lestodon and Glossotherium (Xenarthra, Tardigrada). New Yearbook for Geology and Paleontology, Abhandlunge 262, 2011, pp. 257–266
  42. ↑ Emily L. Lindsey, Erick X. Lopez Reyes, Gordon E. Matzke, Karin A. Rice and H. Gregory McDonald: A monodominant late-Pleistocene megafauna locality from Santa Elena, Ecuador: Insight on the biology and behavior of giant ground sloths . Palaeogeography, Palaeoclimatology, Palaeoecology, 2020, p. 109599, doi: 10.1016 / j.palaeo.2020.109599
  43. ↑ Desmond Gilmore, Denia Fittipaldi Duarte and Carlos Peres da Costa: The physiology of two- and three-toed sloth. In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 130-142
  44. ^ R. Ernesto Blanco and Andrés Rinderknecht: Estimation of Hearing Capabilities of Pleistocene Ground Sloths (Mammalia, Xenarthra) from Middle-Ear Anatomy. Journal of Vertebrate Paleontology 28 (1), 2008, pp. 274-276
  45. ^ R. Ernesto Blanco and Andrés Rinderknecht: Fossil evidence of frequency range of hearing independent of body size in South American Pleistocene ground sloths (Mammalia, Xenarthra). Comptes Rendus Palevol 11, 2012, pp. 549-554
  46. ^ Richard M. Fariña, Sergio F. Vizcaíno and Gerardo de Iuliis: Megafauna. Giant beasts of Pleistocene South America. Indiana University Press, Bloomington and Indianapolis, 2013, pp. 1–436 (pp. 259–260)
  47. ↑ a b Alberto Boscaini, François Pujos and Timothy J. Gaudin: A reappraisal of the phylogeny of Mylodontidae (Mammalia, Xenarthra) and the divergence of mylodontine and lestodontine sloths. Zoologica Scripta 48 (6), 2019, pp. 691-710, doi: 10.1111 / zsc.12376
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  49. ↑ a b c 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
  50. ↑ 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
  51. ^ 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.
  52. ↑ Bruce J. Shockey and Federico Anaya: Grazing in a New Late Oligocene Mylodontid Sloth and a Mylodontid Radiation as a Component of the Eocene-Oligocene Faunal Turnover and the Early Spread of Grasslands / Savannas in South America. Journal of Mammal Evolution 18, 2011, pp. 101-115
  53. ↑ Timothy J. Gaudin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  54. ↑ Ascanio D. Rincón, Andrés Solórzano, H. Gregory McDonald and Mónica Núñez Flores: Baraguatherium takumara, Gen. et Sp. Nov., the Earliest Mylodontoid Sloth (Early Miocene) from Northern South America. Journal of Mammalian Evolution 24 (2), 2017, pp. 179-191
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  57. ^ Francisco Ricardo Negri and Jorge Ferigolo: Urumacotheriinae, nova subfamília de Mylodontidae (Mammalia, Tardigrada) do Mioceno Superior-Plioceno, América do Sul. Revista Brasileira de Paleontologia 7 (2), 2004, pp. 281-288
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Web links

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