Thalassocnus

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Thalassocnus
Skeletal reconstruction of Thalassocnus in the Muséum national d'histoire naturelle in Paris.

Skeletal reconstruction of Thalassocnus in the Muséum national d'histoire naturelle in Paris.

Temporal occurrence
Messinian (Upper Miocene ) to Pliocene or Old Pleistocene
8 to 3 or 1.5 million years
Locations
Systematics
Tooth arms (pilosa)
Sloths (folivora)
Megatherioidea
Nothrotheriidae
Thalassocninae
Thalassocnus
Scientific name of the  subfamily
Thalassocninae
de Muizon & McDonald , Salas & Urbina , 2004
Scientific name of the  genus
Thalassocnus
de Muizon & McDonald, 1995

Thalassocnus is an extinct genus of sloths that lived from the Upper Miocene 8 million years ago to the end of the Pliocene 3 million years ago, possibly even as far as the Old Pleistocene 1.5 million years ago. Fossils of the genus were first found on the Pacific coast of Peru , later also on the coast of Chile . The remains are found near the coast, marine deposits with a rich marine fauna. This, as well as the morphology to those of the skull, the proportions of the legs and the similarity of the caudal vertebrae beavers and otters suggest that thalassocnus aquatic and semi-aquatic lived and probably similar to the marine iguanas of the Galapagos islands emerged in the sea to sea grasses and seaweed to eat. Thalassocnus possibly occupiedthe ecological niche of the North Pacific Desmostylia living at the same timeon the Pacific coast of South America. The adaptations of the representatives of Thalassocnus to aquatic life can be traced over a period of around 4 million years due to the richness of the fossil finds and show a gradual formation of characteristics that are typical of land vertebrates with a secondary recapture of marine habitats. The coastal region was then as now, exposed to extremely strong, desert-like climatic conditions, possibly this is a reason for the extreme adaptation in Thalassocnus . The first finds came to light in the 1980s, andthe genus was first described in 1995.

features

General

Thalassocnus comprised medium-sized representatives of the ground-dwelling sloths . Its habitus was similar to that of Nothrotherium and Nothrotheriops , two closely related forms, but it was larger than the former and smaller than the latter. The largest complete skeleton measures 255 cm in total length from the snout to the tip of the tail, the tail took about 85 cm. With reference to the length of the thigh bone , the smallest known representative of thalassocnus can be assumed to have a total length of 210 cm, the largest reached 330 cm and belonged to the latest forms. Weight estimates are around 203 kg for the earlier forms, but apart from the somewhat larger terminal form, the thalassocnus species had comparable body dimensions. Like all ground-dwelling sloths, thalassocnus had comparatively short limbs compared to the tree-dwelling forms of today, with the front limbs being slightly longer than the rear. Thalassocnus also had a strong, long tail.

Skull and dentition features

Skull of Thalassocnus

The skull of Thalassocnus was between 26 and 30 cm long and was generally elongated and narrow. Behind the eyes it had a maximum width of 6 cm, between the two mastoid processes at the base of the skull of 10 cm. In the side view, the forehead line showed a slightly arched course, it was not as pronounced dome-like as in other members of the Nothrotheriidae . The most noticeable feature of the skull was the stretched front part of the skull. This was mainly caused by the large, robustly built and greatly elongated intermaxillary bone, with later representatives the front area of ​​the upper jaw was also stretched. The widened, spatula-shaped front ends also appeared prominent on the intermaxillary bone. The nasal bone , on the other hand, receded far behind the intermaxillary bone , but also had a long and narrow shape. It had a V-shaped incision at the front end. The frontal bone was also relatively elongated and, in some forms, took up to 40% of the length of the skull. A small crest was formed between the two parietal bones . On the occiput , the very deep-seated joints of the cervical spine emerged, which were almost on the abdomen. The zygomatic arch was like not completely closed in many sloths and pointed at the front sheet approach one additional downward spinous process as a starting point the muscles of mastication on. The front part of the zygomatic arch rose steeply and at the top partially reached the level of the forehead line. As a result, there was a large gap to the rear arch base, which was more clearly horizontal.

The lower jaw measured between 20 and 25 cm in length and had a shape similar to that of other Nothrotheria; it also resembled the related Megatheria with a distinctly downwardly arched bone body. The maximum height of the bone body was below the second molar tooth and was about 4.6 cm, the rear joint ends protruded steeply. Analogous to the elongated intermaxillary bone, the symphysis was extended far forward and became longer and longer in the course of tribal history. It reached lengths of 6 to 11 cm and widened in later forms in the front also spatulate. Like the other developed Nothrotheria, Thalassocnus had four molar-like teeth per upper jaw and three per lower jaw half, so a total of 14 teeth were formed in the dentition. Only the earliest Nothrotheria possessed a further, canine- shaped foremost tooth and was reduced in Thalassocnus as in Nothrotherium . The teeth had a trapezoidal shape (only the front upper jaw tooth) to rectangular shape and were altogether high crowned ( hypsodont ). There were two transverse ridges ( bilophodont ) on the chewing surface . As with all secondary articulated animals , the enamel was missing . The size of the teeth varied from 1 to 1.5 cm. The length of the upper row of teeth was 4.2 to 4.6 cm in early species, in later forms it could also exceed 6 cm.

Skeletal features

The body skeleton is known to a relatively large extent. The spine was composed of 7 cervical, 17 thoracic, 3 lumbar, 6 sacrum and 24 to 25 tail vertebrae. The number of cervical, thoracic and lumbar vertebrae corresponded to that of the other Nothrotheria, but the spinal processes of the vertebrae were conspicuous because of the strongly backward sloping spinous processes . In contrast, the tail spine comprised more vertebrae than in the other known floor sloths. In addition, almost all of the tail's vertebral bodies showed the same length, which resulted in the tail as a whole being elongated and reaching the dimensions of the spinal column. As a result, it also exceeded the length of the tail of other ground-living sloths by a third in relation to the size of the animals. The caudal vertebrae had short but very wide transverse processes that were forked at the rearmost vertebrae with openings in between. Such a trait is not known from other sloths.

The musculoskeletal system is particularly well documented. The upper limb sections, which are comparatively shorter than the lower limbs, were noticeable, which is otherwise not known in ground-dwelling sloths. The humerus reached lengths of up to 30 cm and had a graceful construction, but with the protruding lower joint end typical of sloths. The ulna was significantly longer with up to 35 cm, which also had a significantly large upper joint ( olecranon ). The hands had a five-ray ( pentadactylen ) structure, as in the megatheria the first metacarpal bone fused with some elements of the base of the hand to form a very short metacarpal-carpal complex (MCC). The other metacarpal bones became longer towards the outside, with the fourth and fifth being about the same length. The second, third and fourth fingers each had three phalanges (on the third finger, however, the first two phalanges were fused together), the terminal phalanges had a pointed and clearly curved shape and were therefore provided with strong claws. On the very short first finger there was possibly a kind of hoof, which leads to the uncurved shape of the terminal phalanges, which therefore differ significantly in shape from other sloths with a developed first finger. The last phalanx was missing on the outermost finger, so there was no claw here.

The thigh bone was slender and between 26 and 32 cm long, some incomplete bones suggest lengths of up to 40 cm. In contrast to other nothrotheria, the upper joint head sat on a clearly visible neck. The third trochanter also appeared striking as a muscle attachment point on the shaft, which was connected by a continuous bony groin with the great rolling hillock. The end of the joint pointing away from the center of the body was relatively narrow. The knee joint showed partially ossified menisci , which can also be observed in other large ground sloths. Compared to the thigh, the tibia was up to 32 cm long, longer than that of other nothrothoid sloths. It represented a straight bone and was not fused to the fibula . As with other large ground sloths, the foot had a clear inward rotation, so that the ground was only touched with the outermost ray and the heel bone ( pedolateral ). As a result of the rotation, the foot was additionally curved, whereby the curvature of the foot, analogous to the other Nothrotheria and unlike the related megatheria, was relatively high, so that the calcaneus only touched the rearmost end. It is noteworthy, however, that the pedolateral design of the foot was no longer so clearly pronounced in the latest forms and was more like the plantigrade foot of a sole walker. Most likely, the base was constructed with four rays (rays II to V), the innermost ray is so far unknown and fossilized. Only on rays II to IV were there three toe links and consequently claws, but on the two inner ones the first and second links were fused together. The terminal phalanges had a triangular, only slightly curved shape. The largest claw was on the third toe. The outermost toe had no claws due to the missing end link.

Fossil finds

Thalassocnus fossils are known so far only from the Pacific coast of South America . The majority of the finds in the form of complete and partially preserved skeletons come from the Pisco formation in the south of Peru. This is open over a length of around 350 km along the coast between the cities of Pisco and south to Yauca. It is up to 350 m thick and consists of marine deposits, which include sandstones , siltstone and sandstones containing shed . The finer-grained deposits were created in lagoons , the coarser-grained ones in more sheltered beach locations. The period of formation of the Pisco Formation ranges from the Middle Miocene to the end of the Pliocene . A rich fauna of marine vertebrates such as whales , dolphins , seabirds, crocodiles , bony fish , sharks and rays come from the formation's sediments . In addition, thalassocnus is the only mammal of actually terrestrial origin, remains of other land mammals have not yet been found. The vertebrate finds can be assigned to at least six different horizons, which are distributed over the entire height of the formation. Most of the fossil finds of the sloth genus came to light in the area around Sacaco in the Peruvian region of Arequipa in the southern outcrop areas, where the five upper horizons have been handed down. The remains of the sloth genus come from all five horizons, the first were discovered as early as the 1980s. In 1995 thalassocnus was first described scientifically . The fossils used for this, a skull and some postcranial skeletal parts, came from an area from the transition from the Upper Miocene to the Pliocene and were around 6 million years old. They were assigned to the species T. natans . At the beginning of the 21st century, other species were named, such as T. littoralis based on a skull and T. carolomartini based on a partial skeleton. Both came from stratigraphically higher areas and are therefore younger. With T. antiquus , the oldest species to date was discovered in 2003, which is dated to an age of around 7 to 8 million years, while in the following year, T. yaucensis, with an age of 3 to 1.5 million years, the youngest Representative was set up. Both forms were also based on a partially preserved skeleton.

All the finds mentioned so far come from the south of Peru. Additional fossil remains of the genus have been discovered in the Bahía Inglesa Formation near the city of Caldera in northern Chile . This includes a right lower jaw fragment with the preserved molars from the Estanques de Copec locality , which may have been embedded in the upper sections of the rock unit. The Cerro Ballena reveal point in turn produced an edentulous lower jaw fragment and a complete femur. They came to light in the youngest deposits, in the Cerro-Ballena stratum. Both sites are north of the caldera. An upper arm fragment was documented from the areas south of the city in the La Fosforita quarry . With a find position in the Mina-Fosforita strata from the central areas of the Bahía-Inglesa Formation, it is somewhat older than the fossil remains presented so far. The Bahía Inglesa Formation can also be traced back to marine influence. It consists of sandstones and siltstones and contains numerous, partly complete skeletal remains of sea-bound vertebrates, such as sharks, whales and dog seals . The ages of the various sites are given as the Upper Miocene to the Lower Pliocene. The northern Chilean discovery region is around 1,600 km south of the Sacaco area. As a result, it extends the previously known fossil distribution of Thalassocnus considerably to the south. Finds from the Coquimbo Formation near Coquimbo and the Horcón Formation west of Santiago de Chile have been reported even further south . The former hid a partial skeleton with preserved musculoskeletal system at the Lomas del Sauce site . The latter previously only contained one phalanx. Both rock units can be assigned to the end of the Pliocene and thus give indications that thalassocnus was present much longer on the southern coastal areas of the Pacific and shift the known occurrence of the sloth genus by an additional 550 km to the south.

Paleobiology

Diet

The structure of the teeth of Thalassocnus with the two transverse, sharp ridges and the V-shaped valley between them resembled those of the related Megatheriidae in principle . It indicates that the food was crushed rather than painstakingly ground and chewed. Due to the lack of enamel , the teeth are made up of dentin . The hard orthodent in particular can be found in the area of ​​the last. The deep notch in between, on the other hand, is made of the softer vasodentin . This ensures that the opposing teeth regularly re-sharpen each other when biting, which causes a ridge to fill a notch. Due to the lack of tooth enamel, the sloth's teeth are not suitable for detailed isotope examinations to reconstruct the previous diet. However, well-preserved coprolites of the closely related Nothrotheriops have been found, which refer to diverse plant species as the basis of food and certify that the sloth genus prefers a mixed vegetable diet. The megatheria-like shape of the molars is particularly evident in the stratigraphically older species of thalassocnus ( T. antiquus , T. natans , and T. littoralis ), and the appearance of deep traces of abrasion on the teeth is noticeable. Here it is assumed that the older representatives of their food mostly in shallow water, the depth of which was less than a meter examined and there by sea grasses or seaweed -fed. At least seaweed is one of the common plant finds from the Pisco Formation. With their paddling movements in the shallow water, the sloths whirled up sand from the seabed, which they swallowed with them. A diet of washed up seaweed is also considered, which is then eaten on the sandy beach. The orientation of the grooves indicates that the food was mainly chewed with forward, backward and vertical movements. The two younger species ( T. carolomartini and T. yaucensis ) lack such traces of wear, but they grazed in deeper water similar to today's manatees , which means that they did not take in any grains of sand. Since the joint attachments for the cervical spine were also shifted a little upwards, this was probably done in a possible position with the head down. In addition, the molars do not have a clearly bilophodontic character, they are rather oval in outline with less raised ridges and thus a shallower depression in between. Here they are more like the teeth of specialized grass-eaters, in which the teeth designed in this way are accompanied by lateral chewing movements.

Special adaptations to a plant-based diet can also be found on the skull. The elongated intermaxillary bone and the also long mandibular symphysis possibly served as supports for well-developed lips. The widened ends of the intermaxillary bone and the symphysis in the later forms speak for very strong and flexible lips, especially the upper lip, the good muscle development of which is also indicated by prominent muscle attachment points on the infraorbital foramen . Assuming a development similar to that of herbivorous ungulates , this could indicate very broad lips and therefore a more grass-eating diet. The early representatives of Thalassocnus , on the other hand, had a shorter intermaxillary bone and not so much widened at the end and a similar mandibular symphysis, in these characteristics they were largely similar to Nothrotheriops or Nothrotherium . According to them, the lips were not quite as pronounced and the food probably consisted of softer or mixed plant material. This assumed change in the nutritional basis is also reflected in the bone processes of the zygomatic arches and the articulated arms of the lower jaw, which are longer and more powerful in the later forms than in the earlier ones, so that overall better developed masticatory muscles are assumed in the younger Thalassocnus species can be.

The fact that thalassocnus was most likely to get its food from a more watery environment can be seen from further changes in the skull, particularly at the base of the skull. The wing legs were very prominent in the younger forms . As a result, there was probably a well-developed soft palate , which separates the respiratory tract from the food tract, a function that is particularly important in aquatic organisms. The choanas of the palatine bone , which are shifted far back, also caused something similar. In addition, this enlarged the oral cavity, so that the later representatives could take in more food there compared to the older ones, which in turn is advantageous with low-energy food, which was also taken under water.

Locomotion and special adaptations to the aquatic way of life

Live reconstruction of thalassocnus

Special features of the terrestrial vertebrates , which adapted again to a life in water, are characteristic bone swelling ( pachyostosis ) and bone compression ( osteosclerosis ), which provided the necessary ballast and thus counteracts buoyancy in the water. A marked increase in the compactness of the bone structure can be seen in the limb bones of thalassocnus . The thighbones of the younger species were built up to 22% more densely than the older ones, and in the case of the shin it is still 20%. In T. carolomartini, the medullary cavity of the tibia, which is still clearly present in T. antiquus , almost completely disappeared , only a slight decrease in the density of the compacta , the hard bone substance, can be observed in the bone interior. This increase still exceeds that of the Desmostylia , which also adapted to an aquatic life; but they still have a small medullary cavity. Furthermore, an increasing bone compression can be demonstrated in the ribs, which is also in the range of about 22% and thus approximately reaches the degree of desmostylia. In addition to these changes in the postcranial skeleton, comparable overprints also occur on the skull. Here, for example, the bone density increased in the area of ​​the nasal cavity and the nasal septum . In addition, the frontal sinuses closed in the later species , so that the compactness of the bones increased from 41 to 96%. This led, among other things, to the fact that the frontal bone reached a thickness of 15 mm, which is far more than that of the giant Megatherium . The increasing adaptation to aquatic life and the associated bone changes have been continuously handed down in Thalassocnus from the earliest representatives to the latest and cover a period of about 4 million years. They belong to one of the most complete series of such gradual adjustments. It is noteworthy that the bone density of secondary articulated animals is on average higher than that of other mammals. Possibly this helped the thalassocnus to return to the water and to adapt to this milieu ( exaptation ).

In principle, all land-dwelling vertebrates (with a few exceptions) are able to swim with paddling movements of the limbs. However, aquatic or semi-aquatic terrestrial vertebrates often have special adaptations in the body skeleton. The musculoskeletal system is generally similar to that of the other ground-dwelling sloths, but shows some significant variations. In general, the terrestrial sloths have a very short tibia compared to the thigh bone, which, with a few exceptions, reaches less than 80% of the length of the femur. In the case of thalassocnus , the value is 85 to 94%, depending on the species, so that the shin is significantly longer. An elongated lower section of the hind limbs primarily increases the leverage that provides propulsion when paddling in the water. Likewise, the approach of a thigh neck in Thalassocnus is unique among sloths and thus indicates a significantly expanded range of rotating movement of the hind legs. This is in contrast to the massive, wide and clearly flat femora without the neck of the other ground-dwelling sloths. Here the design of the thigh bone was designed for an occasionally upright bipedal gait, in which sideways rotating movements had to be prevented. The strong ability of the thigh bone of thalassocnus to rotate is also indicated by the presence of a clearly pronounced femoral head fossa (fovea capitis femoris) on the head of the thigh bone, which speaks for well-developed ligaments. The formation of the third trochanter in the form of a bone ridge, which is connected to the great rolling mound, as a muscle attachment point on the shaft supports this assumption. Muscles were anchored to this ridge, which promoted the splaying and splaying of the leg. Another peculiarity is the development from the clearly pedolateral position of the foot in the earliest representatives of Thalassocnus to a secondary plantigrade in the later. However, this was not achieved by regression of the foot itself, but by reorienting the joint connection between the ankle and shin. Such a plantigrade orientation of the foot significantly increased the water displacement when paddling compared to the twisted foot of the earlier species.

In contrast to the hind legs, the front legs of Thalassocnus are only slightly different from those of the other ground sloths. Overall, they appear short and strong, the flexible shoulder-upper arm connection allowed paddling movement in the water, as with the hind legs. The shape of the bones of the forearm was very similar to that of the manatees and seals in the latest representatives , and the phalanges of the fingers also widened in relation to the earlier shapes, which may be related to the displacement of water when paddling. It can be assumed that thalassocnus was also able to walk on the bottom of the sea and could hook itself there with the massive claws of the front feet. The comparatively short humerus also shows adaptations to a digging activity, as is often demonstrated in ground sloths. In an aquatic way of life, this digging activity can also include the picking up or tearing up of food from the seabed, so that the forelegs not only assisted locomotion but also with nutrition.

Some peculiarities can also be found on the spine. The spinous process on the last cervical vertebra appears noticeably short in thalassocnus , in ground-dwelling sloths it is usually very long and sometimes thickened and shows the strong muscles to hold up the head. The rather short spinous process in thalassocnus suggests less strong muscles, which can be interpreted as an adaptation to a life in a watery environment, which makes such muscles unnecessary due to the buoyancy. The thoracic vertebrae have spinous processes pointing clearly backwards (up to 70 °), as has also been proven for the desmostylia and which increases the stability of the spine. However, this position of the spinous processes also entails weaker epiaxial (lateral) back muscles, which are necessary for strong movements of the spine. As a result, a rapid flexion and extension of the spine and thus the use of the trunk during swimming movement in the water was only possible to a limited extent with Thalassocnus . With their forked transverse processes , the caudal vertebrae have similarities with otters who use their tails when swimming with powerful, upward and downward movements. However, such formations also occur in tree-living mammals with well-developed prehensile tails, so that it can be assumed that the forked transverse processes are more an indicator of strong muscles than an indicator of locomotion. In terms of its length relative to the body and the number of vertebrae, the tail of the thalassocnus most closely resembles that of the beaver and platypus . Both use their tails less for forward movement in the water, but rather to balance the balance that keeps balance when diving and looking for food underwater. The same is assumed for thalassocnus .

Overall, thalassocnus appears to be an animal that, due to its anatomical features, was more adapted to life in water. It was paddling forward there with its front and rear legs, although it was not a fast swimmer overall. In addition, it could probably run very well on the sea floor and look for food there. The degree of adaptation to aquatic life increased over the course of the evolutionary history of the sloth species.

Others

Possible competitors for food eventually came manatees in appearance, although they are rarely detected so far in the Pisco Formation, but also coastal waters used as pastures. In contrast, the approximately 7 m long acrophyseter, which is related to the sperm whale , is considered a potential predator . Its remains are fairly well documented in the Pisco Formation, where it appeared with several species. At the moment there is no direct evidence of a predator-prey relationship between the two forms. Under certain circumstances, massive algal blooms can also have led to the death of individual individuals, as indicated by the mass accumulation of skeletons of various vertebrates at the Cerro Ballena site in the coastal area of ​​the Atacama Desert .

Systematics

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




 " Xyophorus "


   

 Aymaratherium



   

 Pronothrotherium



   


 Nothrotheriops


   

 Nothrotherium



   

 Mionothropus




   

 Lacucullus



  Thalassocninae  

 Thalassocnus



Template: Klade / Maintenance / Style

Thalassocnus is a genus from the now extinct family of the Nothrotheriidae . The Nothrotheriidae are represented by rather medium-sized representatives of the subordination of the sloths (Folivora). In contrast to other groups of sloths, their younger relatives had a set of teeth that was reduced by the foremost tooth of each jaw arch. The Nothrotheriidae form together with the sometimes gigantic Megatheriidae and with the Megalonychidae a more closely related group within the sloth, the superfamily of the Megatherioidea . According to the classical view, determined by skeletal anatomical studies, the Megatherioidea can be regarded as one of the two great lines of sloths, the second being the Mylodontoidea . With the inclusion of molecular genetic and protein-based studies, a third line is added with the megalocnoid . According to the latter studies, the Megatherioidea with the three-toed sloths ( Bradypus ) also include one of the two current genera of sloths. Within the Megatherioidea, the Megatheria and the Nothrotheria are in a sister group relationship , but a closer relationship between the Nothrotheria and the Megalonychidae is sometimes also being discussed. In total, the Nothrotheria only comprise around a dozen genera, the earliest evidence of which comes from the Middle Miocene. Two subfamilies can be distinguished within the family. Thalassocnus is commonly assigned to the Thalassocninae as their only member. The other subfamily is represented by the Nothrotheriinae , which also includes the more well-known forms of the Pleistocene such as Nothrotherium from South America and Nothrotheriops from North America. A phylogenetic study from 2017, on the other hand, comes to the conclusion that the Thalassocninae can be classified within the Megatheriidae, which, however, contradicts a further analysis from 2019.

So far, five types of thalassocnus have been described:

Internal systematics of Thalassocnus according to Amson et al. 2016
 Thalassocnus  

 T. antiquus


   

 T. natans


   

 T. littoralis


   

 T. carolomartini


   

 T. yaucensis






Template: Klade / Maintenance / Style
  • T. antiquus Muizon , McDonald , Salas & Urbina , 2003
  • T. Natans Muizon & McDonald , 1995
  • T. littoralis McDonald & Muizon , 2002
  • T. carolomartini McDonald & Muizon , 2002
  • T. yaucensis Muizon, McDonald, Salas & Urbina , 2004

The two older species T. antiquus and T. natans are generally assigned to the Upper Miocene , dating between 8 and 6 million years ago. The three younger representatives, on the other hand, belong to the Pliocene , with the most recent form, T. yaucensis , still occurring in the Lower Pleistocene with an age of 3 to 1.5 million years .

The first description of thalassocnus was made in 1995 by Christian de Muizon and H. Gregory McDonald basis of a partial skeleton consisting of the skull with the lower jaw, vertebrae, ribs and elements of the limbs. This also represents the holotype (copy number MNHN SAS 734), which is kept in the Natural History Museum in Paris . The skeleton was found in Sud-Sacaco (SAS) in southern Peru. The meaning of the generic name Thalassocnus was not explicitly mentioned in the first description, but it is composed of the Greek words θάλασσα ( thálassa "sea") and ὄκνος ( oknos "slowness" "delay"). The latter is often used in its Latinized form ocnus when naming genera related to the Megalonychidae.

Tribal history

The oldest evidence of Thalassocnus dates back to the Upper Miocene 8 to 7 million years ago and comes from the Pisco Formation in Peru. Over the next five to six million years, the sloth representative at the fossil outcrops of the west coast of Peru and Chile is well documented and shows an increasingly stronger, gradual adaptation to a life in water. Within the fossil communities of the Pisco and Bahía Inglesa Formations, thalassocnus is the only originally terrestrial land mammal. At the time the two formations were formed, the Pacific coast of South America was exposed to extremely arid climatic conditions that contributed to the formation of the Atacama around 14 million years ago . It can be assumed that these desert-like dry conditions forced the representatives of Thalassocnus to look for their food in the salty sea water. The formation of the Isthmus of Panama but above about 3 million years ago meant that the waters of the eastern Pacific and auskühlten probably the disappearance of seagrass has contributed, often only thrive in warm conditions. In order to compensate for the now cooler water temperatures, the thalassocnus would have required the formation of a thick layer of fat, which would, however, contradict the adaptation of the late representatives grazing on the seabed and would have resulted in a switch to other food plants. In addition, the sloth genus most likely had a low metabolic rate , analogous to today's sloths and also documented in Nothrotheriops , a close relative of Thalassocnus . However, cooler water temperatures require a high metabolic rate in order to maintain the body temperature. Perhaps these are ultimately the reasons for the disappearance of thalassocnus during the Pliocene .

literature

  • Christian de Muizon and H. Gregory McDonald: An aquatic sloth from the Pliocene of Peru. Nature 375, 1995, pp. 224-227, doi: 10.1038 / 375224a0
  • Christian de Muizon, H. Gregory McDonald, Rodolfo Salas and Mario Urbina: The evolution of the feeding adaptions of the aquatic sloth Thalassocnus. Journal of Vertebrate Paleontology 24 (2), 2004, pp. 398-410, doi: 10.1671 / 2429b
  • Eli Amson, Christine Argot, H. Gregory McDonald and Christian de Muizon: Osteology and Functional Morphology of the Hind Limb of the Marine Sloth Thalassocnus (Mammalia, Tardigrada). Journal of Mammalian Evolution 22 (3), 2015, pp. 355-419, doi: 10.1007 / s10914-014-9274-5
  • Eli Amson, Christine Argot, H. Gregory McDonald and Christian de Muizon: Osteology and Functional Morphology of the Forelimb of the Marine Sloth Thalassocnus (Mammalia, Tardigrada). Journal of Mammalian Evolution 22 (2), 2015, pp. 169-242, doi: 10.1007 / s10914-014-9268-3
  • 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

Individual evidence

  1. ↑ a b c d e f g 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
  2. ↑ a b c d 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
  3. ↑ 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
  4. ↑ a b c d e f g h i j k Christian de Muizon and H. Gregory McDonald: An aquatic sloth from the Pliocene of Peru. Nature 375, 1995, pp. 224-227, doi: 10.1038 / 375224a0
  5. ^ A b c Eli Amson, Christine Argot, H. Gregory McDonald and Christian de Muizon: Osteology and Functional Morphology of the Forelimb of the Marine Sloth Thalassocnus (Mammalia, Tardigrada). Journal of Mammalian Evolution 22 (2), 2015, pp. 169-242, doi: 10.1007 / s10914-014-9268-3
  6. ↑ a b c Eli Amson, Christine Argot, H. Gregory McDonald and Christian de Muizon: Osteology and Functional Morphology of the Hind Limb of the Marine Sloth Thalassocnus (Mammalia, Tardigrada). Journal of Mammalian Evolution 22 (3), 2015, pp. 355-419, doi: 10.1007 / s10914-014-9274-5
  7. ↑ a b c d e Christian de Muizon, H. Gregory McDonald, Rodolfo Salas and Mario Urbina: A new early species of the aquatic sloth Thalassocnus (Mammalia, Xenarthra) from the Late Miocene of Peru. Journal of Vertebrate Paleontology 23 (4), 2003, pp. 886-894
  8. ↑ a b c d e f g Christian de Muizon, H. Gregory McDonald, Rodolfo Salas and Mario Urbina: The youngest species of the sloth Thalassocnus and a reassessment of the relationships of the sloths (Mammalia: Xenarthra). Journal of Vertebrate Paleontology 24 (2), 2004, pp. 387-397
  9. ↑ Rodolfo Salas, François Pujos and Christian de Muizon: Ossified meniscus and cyamo-fabella in some fossil sloths: a morpho-functional interpretation. Geobios 38, 2005, pp. 389-394
  10. ↑ Christian de Muizon and Thomas J. Devries: Geology and paleontology of late Cenozoic marine deposits in the Sacaco area (Peru). Geologische Rundschau 74 (3), 1985, pp. 547-563
  11. ↑ a b Jhoann Canto, Rodolfo Salas-Gismondi, Mario Cozzuol and José Yáñez: The Aquatic Sloth Thalassocnus (Mammalia, Xenarthra) from the Late Miocene of North-Central Chile: Biogeographic and Ecological Implications. Journal of Vertebrate Paleontology 28 (3), 2008, pp. 918-922
  12. ↑ a b c Nicholas D. Pyenson, Carolina S. Gutstein, James F. Parham, Jacobus P. Le Roux, Catalina Carreño Chavarría, Holly Little, Adam Metallo, Vincent Rossi, Ana M. Valenzuela-Toro, Jorge Velez-Juarbe, Cara M. Santelli, David Rubilar Rogers, Mario A. Cozzuol and Mario E. Suárez: Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea. Proceedings of the Royal Society B 281 (1782), 2014, pp. 1-6, doi: 10.1098 / rspb.2013.3316
  13. ^ A b Jacobus P. Le Roux, Luciano Achurra, Álvaro Henríques, Catalina Cerreño, Huber Rivera, Mario E. Suárez, Scott E. Ishman, Nicholas D. Pyenson and Carolina S. Gutstein: Oroclinal bending of the Juan Fernández Ridge suggested by geohistory analysis of the Bahía Inglesa Formation, north-central Chile. Sedimentary Geology 333, 2016, pp. 32-49
  14. ↑ Javiera Peralta-Prato and Andrés Solórzano: How many species of the aquatic sloth Thalassocnus (Xenarthra: Megatheriidae) were in Chile ?: new evidences from the Bahía Inglesa Formation with a reappraisal of their biochronological affinities. Andean Geology 46 (3), 2019, pp. 693-702
  15. ^ Saleta De Los Arcos, Diego Partarrieu, Jorge Carrillo-Briceño and Eli Amson: The southernmost occurrence of the aquatic sloth Thalassocnus (Mammalia, Tardigrada) in two new Pliocene localities in Chile. Ameghiniana 54, 2017, pp. 351-369, doi: 10.5710 / AMGH.29.12.2016.3004
  16. ^ Robert S. Thompson, Thams R. van Devender, Paul S. Martin, Theresa Foppe and Austin Long: Shasta Ground Sloth (Nothrotheriops shastense Hoffstetter) at Shelter Cave, New Mexico: Environment, Diet, and Extinction. Quaternary Research 14, 1980, pp. 360-376
  17. ↑ a b c d Christian de Muizon, H. Gregory McDonald, Rodolfo Salas and Mario Urbina: The evolution of the feeding adaptions of the aquatic sloth Thalassocnus. Journal of Vertebrate Paleontology 24 (2), 2004, pp. 398-410
  18. ↑ Eli Amson, Guillaume Billet and Christian de Muizon: Evolutionary adaptation to aquatic lifestyle in extinct sloths can lead to systemic alteration of bone structure. Proceedings of the Royal Society B 285, 2018, p. 20180270, doi: 10.1098 / rspb.2018.0270
  19. ↑ Eli Amson, Christian de Muizon, Michel Laurin, Christine Argot and Vivian de Buffrénil: Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru. Proceedings of the Royal Society B 281 (1782), 2014, pp. 1-6, doi: 10.1098 / rspb.2014.0192
  20. ^ A b 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 Mammalian Evolution 19, 2012, pp. 159-169
  21. ↑ Olivier Lambert, Giovanni Bianucci and Christian de Muizon: Macroraptorial sperm whales (Cetacea, Odontoceti, Physeteroidea) from the Miocene of Peru. Zoological Journal of the Linnean Society 179, 2017, pp. 404-474, doi: 10.1111 / zoj.12456
  22. ↑ 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
  23. ^ 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.
  24. ↑ 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
  25. ↑ 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
  26. ↑ Timothy J. Gaudin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  27. ^ François Pujos, Gerardo De Iuliis, Bernardino Mamani Quispe and Ruben Andrade Flores: Lakukullus anatisrostratus, gen. 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
  28. ↑ 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 (Huayquerian) of Peru. Palaeontology 54 (1), 2011, pp. 171-205
  29. ^ A b Eli Amson, Christian de Muizon and Timothy J. Gaudin: A reappraisal of the phylogeny of the Megatheria (Mammalia: Tardigrada), with an emphasis on the relationships of the Thalassocninae, the marine sloths. Zoological Journal of the Linnean Society 179 (1), 2017, pp. 217-236, doi: 10.1111 / zoj.12450
  30. ^ Ross DE MacPhee and Manuel A. Iturralde-Vinent: Origin of the Greater Antillean Land Mammal Fauna, 1: New Tertiary Fossils from Cuba and Puerto Rico. American Museum Novitates 3141, 1995, pp. 1-31
  31. ^ François Pujos, Rodolfo Salas-Gismondi, Guillaume Baby, Patrice Baby, Cyrille Goillot, Julia Tejada and Pierre-Olivere Antoine: Implications of the presence of Megathericulus (Xenarthra: Tardigrada: Megatheriidae) in the Laventan of Peruvian Amazonia. Journal of Systematics Palaeontology 11 (7-8), 2013, pp. 973-991

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