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18.12.2015 19:41 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.22 Prosimians
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Prosimians
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Prosimians are the most primitive of the living primates, which also include the monkeys and apes. The name prosimian means pre-monkey. The living prosimians are placed in the suborder Prosimii, which includes four families of lemurs, (the Lemuridae, the Cheirogaleidae, the Indriidae, and the Daubentoniidae), the bush babies, lorises and pottos (family Lorisidae), and the tarsiers (family Tarsiidae). Some authorities also include the tree shrews, though others separate the treeshrews into an order of their own.
Prosimian are primarily tree-dwellers. They have a longer snout than the monkeys and apes, and the prosimian snout usually ends in a moist nose, indicating a well-developed sense of smell. A larger proportion of the brain of prosimians is devoted to the sense of smell than the sense of vision. Prosimians actively scent-mark their territories to warn other animals of their occupancy. The scent-marks are made with a strong-smelling fluid produced by special glands, or with urine or feces.
Prosimian eyes are large and are adapted for night vision, with a tapetal layer in the retina of the eye that reflects and reuses light. Prosimian eyes are not as well positioned for stereoscopic vision as are the eyes of other primates.
Like all primates, prosimians have hands and feet that are capable of grasping tree limbs. The second toe of the hind foot of prosimians has a long claw which they use for grooming. The other toes, on both the hands and the feet, have flattened nails instead of curved claws. Lemurs, which walk along branches on all fours, have longer hind legs than front ones. Tarsiers, which are adapted for leaping between vertical tree trunks and then clinging to them, have short legs whose bones are fused together for strength.
Prosimians have inflexible faces compared to those of monkeys and apes. Most prosimians have 36 teeth, while west simians generally have 32 teeth. The lower front teeth of prosimians lie horizontally and protrude, forming a grooming structure called a dental comb. The dental comb is used to comb fur and scrape nourishing gum from trees, after which it is cleaned with a hard structure located beneath the tongue.
Prosimians spend much less time in infancy than simians do, perhaps only about 15% of their lifespan as opposed to 25-30% for monkeys and apes.
The early primates were distributed throughout most of the world. Today, however, the majority of the living prosimians, the ones collectively called lemurs, live only on the large island of Madagascar, off Africa. After human beings arrived on Madagascar about 1,500 years ago, at least 14 species of lemurs have became extinct.
The smallest living Madagascar prosimian are the mouse lemurs in genus Microcebus, while the largest lemur is the indri (Indri indri). Other prosimians, often described as those that do not live in Madagascar, fall into groups—the lorises, pottos, and galagos or bushbabies of Africa, India, and Southeast Asia, and the tarsiers of Southeast Asia.



Archaeoindris was a 1.5 meter long lemur that lived in Madagascar and weighed 200 kg, more than a silverback gorilla.
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Archaeoindris fontoynontii is an extinct, giant lemur and the largest primate known to have evolved on Madagascar, comparable in size to a male gorilla. It belonged to a family of extinct lemurs known as "sloth lemurs" (Palaeopropithecidae), and because of its extremely large size, it has been compared to the ground sloths that once roamed North and South America. It was most closely related to Palaeopropithecus, the second largest type of sloth lemur. Along with the other sloth lemurs, Archaeoindris was related to the living indri, sifakas, and woolly lemurs, as well as the recently extinct monkey lemurs (Archaeolemuridae). The genus, Archaeoindris, translates to "ancient indri-like lemur", even though it probably became extinct recently, around 350 BCE.

Archaeoindris was first described by Herbert F. Standing in 1909 based on subfossil fragmentary jaws, although Charles Lamberton later discovered a complete skull. Only six bones from the lower skeleton have been found, and excavations in the 1980s offered no leads for new finds. Its remains have been found at only one location: Ampasambazimba, a subfossil site in central Madagascar. Following its initial discovery, some subfossil remains of Megaladapis grandidieri (a type of extinct koala lemur) were mistakenly associated with Archaeoindris, while smaller leg bones from a juvenile and a massive adult leg bone were erroneously assumed to belong to two separate species. These errors were gradually corrected between the 1930s and 1980s. The skeleton of Archaeoindris was massive and robust, and shared many traits with that of Palaeopropithecus. The arms were longer than the legs, but no hand or foot bones have been found for comparison with the other sloth lemurs.
Size estimates based on the limited remains have varied widely, ranging as high as 244.1 kg (538 lb), but the most thorough statistical investigation using regression analyses predicts a mass of 160 kg (350 lb). Misattributions and limited remains have resulted in varying opinions about the way Archaeoindris moved in its environment, ranging from tree-dwelling to ground-dwelling. Its skeleton suggests it was a deliberate climber that visited the ground to travel. The diet of Archaeoindris was mostly leaves, and its habitat—prior to human arrival—was a mix of woodlands, bushlands, and savanna, rich in lemur diversity. Today, the region is dominated by grasslands and lemur diversity is very low in the nearest protected area, Ambohitantely Special Reserve. Although it was a rare lemur, it was still extant when humans first arrived on Madagascar, and it would have been vulnerable to hunting and habitat loss.
The generic name, Archaeoindris, meaning "ancient indri-like lemur", deriving from the Greek word ρχαος (archaios, or "ancient") and indris, a common variation of the generic name Indri. The species name, fontoynontii (sometimes spelled fontoynonti), was selected in honor of Antoine Maurice Fontoynont, the president of the Acadйmie Malgache (Malagasy Academy) at the time. Fontoynont was reported to have been supervising the excavation when it was discovered.
Archaeoindris was a type of sloth lemur (family Palaeopropithecidae), a recently extinct family of giant lemurs (known as subfossil lemurs) native to Madagascar. Its ancestors were likely arboreal (tree-dwelling), and this giant sloth lemur has been compared to the extinct giant ground sloths of North and South America.
Archaeoindris was most closely related to Palaeopropithecus, a genus containing the second largest of the sloth lemurs and specialized for suspensory behavior in its arboreal habitat. Traits of the postcranium (skeleton below the skull) indicate that Babakotia was the next most closely related sloth lemur to Archaeoindris and Palaeopropithecus, followed by Mesopropithecus, the smallest of the sloth lemurs.
All four genera of sloth lemurs are known to be a sister taxon (close relatives) of family Indriidae, which includes the indri (Indri), sifakas (Propithecus), and woolly lemurs (Avahi). This relationship is supported by data from morphological, developmental, and molecular research. Another member of this clade (related group) is the family of monkey lemurs (Archaeolemuridae). Dental features, such as the morphology of their molar teeth and the modified number of teeth in their toothcomb (a specialized grooming structure found in lemuriforms), have long suggested a relationship. However, other anatomical and developmental traits suggested that monkey lemurs might be more closely related to family Lemuridae, which include five genera of lemur, including the ring-tailed lemur (Lemur catta). Molecular analysis has shown strong support for the former, placing the monkey lemurs in a clade with the sloth lemurs and indriids.
The skull of Archaeoindris was wide and short, with a pair of bony protrusions around the nasal openings.
Though similar to Palaeopropithecus, Archaeoindris was significantly larger and more robust. Archaeoindris was one of the largest primates to ever evolve, and was the largest-known strepsirrhine primate, weighing an estimated 160 kg (350 lb). It was roughly the size of an adult male gorilla, which was first noted by Lamberton.
Since its discovery, size estimates have varied from "larger than a human" to "possibly the largest primate ever". In a study by Jungers from 1990, the area of its molar teeth predicted a mass of 230.5 kg (508 lb), while the femoral head diameter predicted a mass of 244.1 kg (538 lb). In 1995, Laurie Godfrey estimated a mass of 197.5 kg (435 lb) using the midshaft circumferences of the humerus and femur. Based on multiple regressions of the cortical area of the femur in 2008, Jungers and colleagues generated the current best estimate of 161.2 kg (355 lb) with a possible range of 150–187.8 kg (331–414 lb). These estimates were considered to be more accurate since the harder cortical bone in the midshaft of the femur supported an animal"s weight, and its thickness better correlated with the animal"s mass than the midshaft diameter (which includes both hard cortex and spongy bone).The only fossil primate that was probably larger than Archaeoindris was Gigantopithecus blacki, a close relative of orangutans.
Archaeoindris is thought to have been a leaf-eater (folivorous), a view supported by wear patterns on its teeth.Its fused mandibular symphyses and the likelihood of accelerated dental development suggest that it began processing fibrous foods in the mouth with thorough chewing. Its diet may also have included some fruits and seeds. Like most of the other giant lemurs, Archaeoindris is thought to have been diurnal because of its relatively small orbits, which are comparable to that of gorillas.
Both Standing and Lamberton assumed Archaeoindris to be a slow-moving tree-dweller like Megaladapis, primarily due to the misattributed bones. Lamberton also speculated that it would have resembled a ground sloth—a view later supported by Jungers in 1980 after several misattributions had been corrected and having considered its gorilla-like size. Jungers went on to propose that it would have spent most of its time on the ground (terrestrial). However, the functional morphology of its hip joint indicates a degree of mobility typically seen in more arboreal animals. Other traits shared with Palaeopropithecus, particularly seen in the femur, suggest that Archaeoindris spent considerable time in the trees for feeding and possibly nesting, although it also would have visited the ground to feed and travel. It is described as a deliberate, scansorial (climbing) browser, and it is unknown whether it was like Palaeopropithecus in performing hang-feeding since hand and foot bones are missing. Given its bulky size, this would be unexpected.
Archaeoindris is only known from one subfossil site, Ampasambazimba, in central Madagascar, and all remains date to the Late Quaternary. The area today is dominated by grasslands, particularly of the grass genus Aristida. Prior to human arrival, the area around Ampasambazimba was not completely forested, but more of an open habitat, consisting of a mix of woodlands, bushlands, and savanna. Animal remains at this subfossil site have yielded about 20 species of lemur living in sympatry (sharing the same geographic area). In comparison, the nearby Ambohitantely Special Reserve today contains only 4 species, roughly 20% of the area"s original lemur diversity.
Despite being the most species-rich family among the giant lemurs, all four genera of sloth lemur, including Archaeoindris, have gone extinct. Radiocarbon dating of the stratigraphic level of some of the Archaeoindris remains were dated to 8000 BP, while two other specimens were dated to 2362–2149 BP (412–199 BCE) and 2711–2338 BP (761–388 BCE).From these dates, it is likely that Archaeoindris was still alive on the high plateau in 350 BCE when the first humans reached the west coast of Madagascar, despite being rare by that time. Consequently, it would have been especially vulnerable to hunting and habitat loss.



Megaladapis
is another large extinct lemur at 1.3 to 1.5 m (4.3 to 4.9 ft) in length.
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Megaladapis, informally known as koala lemur, is an extinct genus belonging to the family Megaladapidae, consisting of three extinct species of lemurs that once inhabited the island of Madagascar. The largest measured between 1.3 to 1.5 m (4 to 5 ft) in length.

Megaladapis was quite different from any living lemur. Its body was squat and built like that of the modern koala. Its long arms, fingers, feet, and toes were specialized for grasping trees, and its legs were splayed for vertical climbing. The hands and feet were curved and the ankles and wrists did not have the usual stability needed to travel on the ground that most other Lemurids have. Its head was unlike any other primates, most strikingly, its eyes were on the sides of its skull, instead of forward on the skull like all other primates. Its long canine teeth and a cow-like jaw formed a tapering snout. Its jaw muscles were powerful for chewing the tough native vegetation. Its body weight reached 50 kilograms (110 lb). The shape of its skull was unique among all known primates, with a nasal region which showed similarities to those of rhinoceros, what was probably a feature combined with an enlarged upper lip for grasping leaves.An endocast of the skull was taken and it was found that the brain capacity was about 250cc. This is about 3 to 4 times the size of a common cat"s.
Megaladapis evolved because the island"s topography was always changing. Along with the other lemurs, Megaladapis specialized within its own niche. The general expectations of tree climbers such as Megaladapis is that with an increase in size, the body"s forelimbs will also increase proportionally.
It is often believed that Malagasy legends of the tretretretre or tratratratra, an extinct animal, refer to Megaladapis, but the details of these tales, notably the "human-like" face of the animal, match the related Palaeopropithecus much better.
When humans arrived, between 1,500 and 2,000 years ago, the archaeological record shows that they cleared large areas of the island using "slash-and-burn" techniques. Unable to adapt to the environmental changes and the presence of humans, Megaladapis became extinct approximately 500 years ago.
Megaladapis has been found around the marsh of Ambolisatra on the southwestern side of Madagascar and was one of multiple Megafauna that went extinct on Madagascar during this time period. They were also slow-moving creatures that were active during the day. This might have made them more susceptible to predators, forest fires, habitat destruction, and possibly introduced pathogens.











 

 

 




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Автор: valentint
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