Diabolotherium

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Diabolotherium
Skull of Diabolotherium

Skull of Diabolotherium

Temporal occurrence
Lujanian ( New Pleistocene ) to Lower Holocene ?
29,000 to 10,000 years
Locations
Systematics
Higher mammals (Eutheria)
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Megatherioidea
Diabolotherium
Scientific name
Diabolotherium
Pujos , De Iuliis , Argot & Werdelin , 2007

Diabolotherium is an extinct representative of the sloth and is part of the Megalonychidae family, which also includes the two-toed sloths that are still alive today. It was relatively small, reaching the size of the forms that once inhabited the Caribbean islands . Diabolotherium has been provenwith several fossil remains consisting of parts of the skull and the body skeleton, which were largely found in the western part of South America . Most of the finds come from the Andes and coastal lowlands on the Pacific, a few remains are also known from Patagonia . All previous fossil remains date to the end of the Upper Pleistocene and are between 29,000 and 10,000 years old, but the genus may not become extinct until the early Holocene . What is remarkable is the mixture of anatomical features that can be found in both the Megalonychidae and the giant Megatheriidae , but also in the tree-dwelling sloths that are still alive today. Based on the structure of the fore limbs, it can be concluded that there is a climbing lifestyle. The extensive lack of trees in the high mountain regions of the Andes and the location of some finds in caves that are difficult to access make one think of climbing in difficult rocky terrain. Diabolotherium thus expands the existing knowledge about the way of life of the sloths, which, in addition to the recent tree-climbing, especially extinct ground-dwelling, underground burrowing and semi-aquatic floating forms.

features

Diabolotherium is a relatively small representative of the sloth with a slim body and elongated limbs. It is known from individual finds and a partial skeleton. A complete skull is available, but has not yet been described. On a fragmented rear skull of a not yet fully adult animal, the profile line of the parietal bones was slightly arched. It is very likely that adult individuals had a crest . The occiput was rectangular in shape when viewed from behind, it was low and relatively wide. The joints for the cervical spine pointed slightly downwards and were not very prominent, a feature that also occurs in several representatives of the Megalonychidae of the Caribbean islands. The posterior section of the zygomatic arch started directly in front of the ear canal on the temporal bone . It was extremely short, stood at an angle of 25 ° to the central axis of the skull and ran slightly downwards. The front part of the arch began on the upper jaw above the second and third teeth. The lower jaw is only known in fragments, the two most complete specimens so far differ in size by 10%. The anterior, spatula-like extension of the symphysis, which is typical of numerous sloths, has only been preserved in its posterior part; the full length is unknown. At the base of the process there was an outer mental foramen , an inner one was 14 mm in front of the first tooth. The body of the lower jaw reached its greatest height below the first tooth and measured 3.4 cm there. It became continuously lower towards the rear, with the result that the protuberance of the lower margin of the lower jaw characteristic of the Megatheriidae and Nothrotheriidae was missing. The articular process protruded so that the mandibular joint was at least 4.5 cm above the posterior angular process (angular process).

The majority of the jaw finds so far are toothless, but the structure of the dentition can be read from the structure and arrangement of the alveoli . The dentition had the typical structure of the sloth with five teeth per half of the jaw in the upper and four in the lower jaw, so a total of 18 teeth were formed. All teeth were closed in a row and had a molar shape. This is reminiscent of the Megatheriidae , but differs from the megalonychids, the front teeth of which are reshaped like canines and separated from the rear teeth by a diastema . The shape of the teeth also showed similarities to the large megatheria. They had a rectangular shape in the upper jaw and a more square shape in the lower jaw, but the foremost of each had a slightly triangular outline. The chewing surface of a few teeth that were found had two typical transverse ridges. The length of the lower row of teeth was 4.4 cm.

The body skeleton is not fully known. The atlas (first cervical vertebra) was narrowed in front and back, the three articular surfaces that connected it to the following axis (second cervical vertebra) were in contact with each other. The total of ten tail vertebrae that have been handed down to date have elongated but narrower transverse processes compared to the megatheria. The limb bones became very long and slender compared to those of the other ground sloths and thus resembled today's tree sloths. The humerus reached up to 24 cm in length. The shaft was encompassed by a bone ridge ( crista deltoidea ), which served as a muscle attachment point and was particularly strong in the middle part. As with all sloths, the lower end of the joint had a massive construction. The ulna was almost the same length as the humerus. The upper articular process, the olecranon , was relatively longer than that of today's tree and most of the extinct ground sloths. The spoke had a length of 18 cm, was short and massive and had a circular shaped head that started directly in front of the ulna. The hand comprised at least four rays (II to V), possibly the inner ray (I) was fused with some parts of the wrist to form a bone complex, the metacarpal-carpal complex (MCC) typical of some large ground sloths . Of the four formed rays, however, only three (II to IV) were functional. It is noteworthy that these had metacarpal bones of almost the same size , whose length was 3.9 to 4.1 cm, which is unusual for extinct sloths. In the Megatheria and the Nothrotheria, the length of the metacarpals increased significantly from the second to the fourth ray. The terminal phalanges had a triangular outline in longitudinal section, showing that they had claws. The length of the last phalanx of the central ray was 6 cm, it was built narrow and slightly bent downwards, which suggests a correspondingly shaped claw. Compared to today's tree sloths, however, it seems to have been comparatively shorter. From the posterior musculoskeletal system, apart from the slender iliac bone , the talus and the heel bone as well as individual parts of the metatarsus, hardly any bone elements have survived.

Fossil finds

Erland Nordenskiöld found the first fossil remains of Diabolotherium .

The majority of the fossil finds from Diabolotherium come from western South America , especially from Peru and Chile . There they were unearthed both in the high elevations of the Andes and in the coastal lowlands adjacent to the west. The Swedish researcher Erland Nordenskiöld discovered the first finds at the beginning of the 20th century. At this time he visited Peruvian and Bolivian sites and collected fossil mammal remains. These included a humerus and a toothless upper jaw fragment of a small sloth from the Casa del Diablo cave , which is located near the city of Tirapata on Lake Titicaca at an altitude of around 3800 m. Nordenskiöld believed that the findings could be assigned to a new species of sloth. He did not write his own description, but published the humerus in 1908. Later, in 1926, the Argentine researcher Lucas Kraglievich created the species Nothropus nordenskioldi based on the bones found . It was only at the beginning of the 21st century that other significant finds in the high Andes could be recovered. A nearly complete, but largely toothless skull and an almost complete hand from the Jatun Uchco cave complex near the city of Ambo in the Peruvian region of Huánuco should be emphasized . The cave complex is around 2150 m above sea level. In the Abri Trigo Jirka , which is in the same region in a rock wall 300 m above the Río Marañón at an altitude of 2700 m, an end phalanx was found , which was still sitting on the claw made of keratin . On the other hand, more fragmented bone remnants have been handed down from Cueva Roselló 26 km southwest of Huancayo . At an altitude of 3875 m, the cave is the highest point of discovery to date. As early as 1975, a French team of scientists led by Rudolf Hoffstetter found numerous fossil remains of a small sloth at the Piedra Escrita site in the Cupisnique desert on the west coast of Peru, 80 km south of Trujillo found that represent a partial skeleton of a single individual. The bones lay on the surface and were partially weathered. Finds from the lower layers of the 4 m wide Baño Nuevo cave are known from Chile , including a left, toothed lower jaw and a phalanx. The cave is located around 80 km northeast of the city of Coyhaique . An isolated tooth from the Pampa del Tamarugal depression is also placed at Diabolotherium . Other fossil finds have been reported from Patagonia and include jaw fragments with attached teeth.

All known finds of Diabolotherium are placed in the late Upper Pleistocene . For the fossil remains from the Cupisnique desert, age data obtained with the help of uranium-thorium dating are available, which are between 25,000 and 15,000 years ago; in contrast, radiocarbon data give an age of 8910 years BP . The lower layers of Baño Nuevo are classified as being around 13,000 to 9,000 years old. The phalanx of Trigo Jirka still provided with a claw gave a radiocarbon value of 29,140 years BP. The most recent finds are known from Patagonia and may already belong to the Lower Holocene .

Paleobiology

Locomotion

What is striking about Diabolotherium are the long and slender limb bones, which are rarely found in other extinct sloths and usually appear shorter and more robust. However, they are similar to those of today's tree sloths. The distinctly spherical head of the humerus is characteristic of all sloths, which enables a very flexible arm movement in connection with the shoulder blade . The slightly weaker deltopectoral ridge (crista deltoidea) on the shaft of the humerus suggests less well-developed chest and shoulder muscles compared to the digging-capable sloths. Above all, the design of the upper articular process of the ulna, the olecranon, is decisive for the main activity of secondary articular animals and other mammals. The olecranon is extremely long in burrowing secondary articulated animals, such as armadillos or some large ground sloths. This enables the animals to muster the strength they need to dig, as the triceps that attach here increases the leverage due to the greater length of the appendix. Purely terrestrial forms have a much shorter extension, but the shortest occurs in today's sloths hanging with their backs down in the branches. Diabolotherium has a longer olecranon than the recent sloths, but it is significantly shorter than that of burrowing representatives. Its length corresponds roughly to that of the extinct Hapalops , to which a partly tree-climbing locomotion is attributed, whereby the climbing method corresponded more to that of today's Tamanduas . The fact that Diabolotherium was able to climb is supported by the upper joint capsule of the ulna, which circumscribes an open circle of about 105 ° and is therefore extraordinarily wide. Together with the lower joint of the humerus, which engages here, it forms the elbow joint ; the wide opening of the joint capsule of the ulna gave the forearm significantly more freedom of movement. In connection with the position of the spoke pushed in front of the ulna and its circular, upper head, it can be assumed that the forearm could be turned in and out very well and was overall very mobile. This resulted in a highly flexible upper-lower arm connection. Several bone ridges on the shaft of the spoke also show strongly developed forearm muscles, which in turn led to a more rotatable hand, which is also confirmed by the sometimes short design of some carpal bones. The three equally long rays of the hand in turn indicate an increased ability to grip, which was severely restricted in the large ground sloths. Ultimately, the slim tank - which is less bulky and laterally projecting than that of the large ground sloth and more like that of today's tree sloths - speaks in favor of Diabolotherium's climbing ability . The genus is one of the few fossil-known forms among the sloths that pursued such a mode of locomotion.

The skeletal anatomically verifiable, climbing locomotion of Diabolotherium was originally associated with an arboricolous way of life, analogous to today's sloths or forms that are known from the Lower Miocene of the Santa Cruz Formation . For the Cupisnique desert, where the first partial skeleton comes from, the existence of oases for the Pleistocene could be proven, which could support the possibility of climbing in trees. However, since a large part of the more recent finds were discovered in the high altitudes of the Andes , some of which were in caves and rock roofs that were difficult to access, it is now assumed that Diabolotherium was much more adapted to climbing in rocky and impassable terrain. The sometimes extensive joint surfaces, which enabled the high flexibility of the arm bones, also limited the stability of the joint connections. This makes it likely that Diabolotherium tended to move slowly.

nutrition

The largely high-crowned teeth with their two transverse, sharp-edged ridges on the chewing surfaces are basically similar to those of Megatheria. It can therefore be assumed that Diabolotherium maintained a similar diet. The food therefore probably consisted of different and partly also solid parts of the plant that were searched for selectively. The freely movable forelegs, the strong grip of the hands and the curved claws may also have had a supporting function in obtaining food, as can be seen in today's tree sloths.

Systematics

Diabolotherium is an extinct genus from the suborder of the sloths (Folivora). The sloths, together with the anteaters (Vermilingua) and the somewhat more distantly related armadillos (Dasypoda), form the superordinate order of the secondary articulated animals (Xenarthra), which belong to the four main lines of the higher mammals . Within the sloth, in a classic view, supported by skeletal anatomical features, two broad lines are distinguished. One of these is that of the Megatherioidea , which is composed of the Megatheriidae , Megalonychidae and Nothrotheriidae . Opposite it are the Mylodontoidea with the families of the Mylodontidae , the Orophodontidae and the Scelidotheriidae (the latter two are sometimes only managed as subfamilies within the Mylodontidae). After molecular genetic and protein-based studies, a third line can be added with the megalocnoidea , which encompasses the Caribbean sloths. According to these analyzes, the two genera that exist today are distributed across the first two lines mentioned, namely the two-toed sloth ( Choloepus ) on the Mylodontoidea and the three-toed sloth ( Bradypus ) on the Megatherioidea.

In the first description of Diabolotherium , it was assigned to the Megalonychidae family , which contains small to medium-sized representatives. The members of the Megalonychidae were never particularly numerous in South America compared to the other large sloth families, instead they were quite common in Central America and also reached North America . In their traditional structure, they originally also included the Caribbean forms and the two-toed sloth. Special features can be found in tooth construction. Thus, the respective foremost tooth is eckzahnartig ( caniniform ) and transformed by a diastema of the rear molarenartigen separated teeth. This set of teeth is considered to be more original within the sloth and differs from the modified teeth of the closely related Megatheriidae, in which all teeth are designed like molars, or the Nothrotheriidae, which have reduced their first tooth. Another peculiarity can be found in the design of the foot, which in the Megalonychidae corresponds to that of the typical sole walkers ( plantigrad ). In the Megatheria and Nothrotheria, however, it is turned outwards ( pedolateral ), so that the representatives of these groups appeared with the outer edges of their feet.

Especially in the skeletal structure, Diabolotherium had similarities with the megalonychids. This includes, among other things, the design of the ear canal and the zygomatic arch , which typically started directly on the side of the ear. Further characteristic similarities can be found in the ankle and heel bones and the formation of the ankle joint between the ankle and fibula . Other features, such as the highly mobile connection between the upper arm and forearm as well as the generally slender limb bones, are to be understood as adaptations to the climbing way of life; the latter in particular differ significantly from the massive design of the large ground sloths. However, phylogenetic studies have shown that the genus has a special position within the Megalonychidae. This is mainly due to the dentition, which consists only of molar-like, square to rectangular shaped teeth without a canine- shaped front tooth and thus deviates from the known Megalonychidae. Here Diabolotherium is reminiscent of the Megatheria. Due to this mixture of characteristics, which refer to both the Megalonychidae and the Megatheriidae, Diabolotherium was therefore classified in investigations in 2011 as a representative of the Megatherioidea with an unknown family group. Such a position has several genera without closer relations to each other, for example Hiskatherium , which belongs to the Miocene and was described using a lower jaw from Quebrada Honda in Bolivia . This has a similar set of teeth as Diabolotherium with only molar-like teeth, but the structure of the teeth and the jawbone in both genera differ considerably. Other genera classified in this way such as Hapalops or Huilabradys , on the other hand, have the original dentition shape of the sloths. The position of these forms in the superordinate group of the Megatherioidea is due to the fact that there are still numerous gaps in knowledge about the development of the large sloth lines. A phylogenetic study from 2019 sees Diabolotherium included in the Megatheriidae. The authors consider the genus megalonychid features to be more primal, as they can appear in numerous sloths. Fossil DNA could be obtained from the terminal phalanx with a claw attached, which was discovered in Trigo Jirka in Peru . According to initial results, this is similar to that known from extinct sloths of the Caribbean islands, making Diabolotherium actually close to the Megalonychidae, but no final results are available yet.

The first scientific description of Diabolotherium took place in 2007 by François Pujos and research colleagues. It was carried out on the finds of the Casa del Diablo and the Cupisnique . The holotype (copy number NRM -PZ M4286) includes a right thigh bone from the Casa del Diablo, which Erland Nordenskiöld discovered at the beginning of the 20th century. It is kept in the Swedish Museum of Natural History in Stockholm. With Diabolotherium nordenskioldi only one species is known. The generic name Diabolotherium is made up of the Latin word diabolo for "devil", which stood for the name of Casa del Diablo, and the Greek word θηρίον ( thērion ) for "animal". The species name nordenskioldi refers to Erland Nordenskiöld as the first discoverer of the finds, it was used by Lucas Kraglievich in 1926 when the species Nothropus nordenskioldi was introduced .

About the origin of Diabolotherium

The Megalonychidae represent an ancient family that appeared as early as the Oligocene more than 30 million years ago. Its origin is believed to be in South America, the oldest evidence here is Deseodognathus from Patagonia . Significant representatives of the Megalonychidae in South America then come from the Lower Miocene of the Santa Cruz Formation in Argentina, including Eucholoeops . The Megalonychidae conquered North America very early and probably regardless of their presence on the Caribbean islands, where they often occur in fossil sites. In the Pleistocene of South America, members of the family are mainly known from Brazil and Argentina, but they have so far been absent in the western part of the continent. Assuming that Diabolotherium is closely related to the Megalonychidae, it might be possible to derive the form of immigrants from the tropical lowlands, but this would require a crossing of the Andes, for which there is no fossil record. It is also problematic that for the educational period in question from the Miocene to the Pliocene, the western coastal area of ​​South America was under marine influence, so that the transmission of purely terrestrial animals here is assessed as rather unlikely. The western Andean region in the transition to the Amazon lowlands is currently seen as another possible educational area, especially in today's Bolivia. There numerous different sloth forms are known from the period in question. One of the most important fossil sites in the region is Salla Luribay .

literature

  • François Pujos, Gerardo De Iuliis, Christine Argot and Lars Werdelin: A peculiar climbing Megalonychidae from the Pleistocene of Peru and its implication for sloth history. Zoological Journal of the Linnean Society 149, 2007, pp. 179-235

Individual evidence

  1. ↑ a b c d e Bruce J. Shockey, Rodolfo Salas-Gismondi, Patrice Baby, Jean-Loup Guyot, María Cristina Baltazar, Luis Huamán, Andrew Clack, Marcelo Stucchi, François Pujos, Jenna María Emerson and John J. Flynn: New Pleistocene cave faunas of the Andes of Central Peru: radiocarbon ages and the survival of low latitude, Pleistocene DNA. Paleontologia Electronica 12, 2009, pp. 1-15
  2. ↑ a b c d e f g h i j k l m François Pujos, Gerardo De Iuliis, Christine Argot and Lars Werdelin: A peculiar climbing Megalonychidae from the Pleistocene of Peru and its implication for sloth history. Zoological Journal of the Linnean Society 149, 2007, pp. 179-235
  3. ↑ a b c d e f g h François Pujos, Gerardo De Iuliis and Bernardino Mamani Quispe: Hiskatherium saintandrei, 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
  4. ^ A b c François Pujos and Rodolfo Salas: A systematic reassessment and paleogeographic review of fossil Xenarthra from Peru. Bulletin de l'Institut Français d'Etudes Andines 33 (2), 2004, pp. 331-377
  5. ↑ a b E. Bostelmann, P. López, R. Salas-Gismondi and F. Mena: First record of Diabolotherium cf. Nordenskioldi, Kraglievich 1926, (Mammalia, Tardigrada, Megalonychidae), from the Late Pleistocene of Chile. Ameghiniana 48 (4) suppl, 2011, p. R146
  6. ^ François Pujos, Timothy J. Gaudin, Gerardo De Iuliis and Cástor Cartelle: Recent Advances on Variability, Morpho-Functional Adaptations, Dental Terminology, and Evolution of Sloths. Journal of Mammal Evolution 19, 2012, pp. 159-169
  7. ↑ Maureen A. O'Leary, Jonathan I. Bloch, John J. Flynn, Timothy J. Gaudin, Andres Giallombardo, Norberto P. Giannini, Suzann L. Goldberg, Brian P. Kraatz, Zhe-Xi Luo, Jin Meng, Xijun Ni, Michael J. Novacek, Fernando A. Perini, Zachary S. Randall, Guillermo W. Rougier, Eric J. Sargis, Mary T. Silcox, Nancy B. Simmons, Michelle Spaulding, Paúl M. Velazco, Marcelo Weksler, John R Wible and Andrea L. Cirranello: The Placental Mammal Ancestor and the Post-K-Pg Radiation of Placentals. Science 339, 2013, pp. 662-667, doi: 10.1126 / science.1229237
  8. ↑ a b 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
  9. ↑ Timothy J. Gaudrin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  10. ↑ 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
  11. ↑ 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
  12. ^ 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
  13. ^ Alfredo A. Carlini and Gustavo J. Scillato-Yané: The oldest Megalonychidae (Xenarthra: Tardigrada); phylogenetic relationships and an emended diagnosis of the family. New Yearbook for Geology and Paleontology Abhandlungen 233 (3), 2004, pp. 423–443
  14. ↑ Gerardo De Iuliis, François Pujos, Néstor Toledo, M. Susana Bargo and Sergio F. Vizcaíno: EucholoeopsAmeghino, 1887 (Xenarthra, Tardigrada, Megalonychidae) from the Santa Cruz Formation, Argentine Patagonia: implications for the systematics of Santacrucian sloths. Geodiversitas 36 (2), 2014, pp. 209–255