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Tarsiers did not reinvent the eye of the nocturnal early primates, as tarsiers do not have a reflecting tapetum and they have retained the diurnal adaptation of a fovea Collins et al. Jon H. Kaas, in Progress in Brain Research Tarsiers represent tarser odd line of evolution in the primate radiation. Their overall small size and strange body confused early investigators, and tarsiers were grouped with lorises, galagos, and lemurs as prosimian primates, that is, below the monkey simian level. That classification has now been changed, and the molecular evidence places them as an early surviving branch of the anthropoid radiation Ross and Kay, What is unusual about the evolution of tarsiers is that early anthropoids were diurnal and specialized for daytime vision, and the tarsier line started off as diurnal, having lost its specializations for nocturnal vision, but then returned to nocturnal life by re-specializing for dim light.
This largely consisted of evolving huge eyes relative to the head. Consistent with their reclassification, the dorsal lateral geniculate lamination pattern of tarsiers is clearly of the anthropoid type, rather than of the strepsirrhine type Wong et al. As an extreme visual predator of insects and other small prey, tarsiers depend on a large V1 for the detailed representation that is needed for tarser function.
As tarsiers are small, and have small brains, this dependence on a large V1 may have cost them in tarser cortical areas.
They have a V2 and MT and likely other visual areas, but little posterior parietal cortex and little prefrontal cortex. Henry R. Hermann Ph. Tarsiersprosimians from Southeast Asia, with four extant species, tarser in tropical rain forests Clutton-Brock and Wilson, Fig. While tarsiers are included in the prosimian group, some researchers view them as a link between prosimians and tarser.
Clutton-Brock uses the western tarsier as an example of the group. They are nocturnal and adept at climbing and grasping tree branches. It has a small, compact body, with slender tarser, padded toes, and sharp claws. It feeds chiefly on insects and usually sleeps on branches, rarely using nests for shelter.
Figure 5. A Tarsier, a nocturnal prosimian that some biologists feel is a link between prosimians and simians. B Gibbon, a lesser ape, showing its long forelimbs that are used in brachiation. C—F Greater apes. C Orangutan. D Gorilla. E Chimpanzee, showing opposable big toe. F Bonobo. John G. The tarsiers of Southeast Asia Table 4. They show a mixture of prosimian and anthropoid features.
However, their similarities to other prosimians are primitive features: an unfused mandibular symphysis, molar teeth with high cusps, grooming claws on their second and third toes, multiple nipples, and a bicornuate uterus. Their similarities to anthropoid primates seem to be derived specializations indicative of a phyletic relationship.
In addition, tarsiers have many distinctive features all their own Fig. TABLE 4. The skull, dentition, and skeleton of a tarsier, showing some of the distinctive features of the genus. Tarsiers differ from other nocturnal primates, and resemble all diurnal primates in having a retinal fovea and lacking the reflective tapetum found in all lemurs and lorises, as well as many other groups of mammals. Their large eyes are protected by a bony socket that is partly closed posteriorly, similar to that of higher primates.
The nose of tarsiers resembles that of higher primates as well, both externally in the lack of an attached upper lip with a median fold, and internally in the greatly reduced turbinates and in the absence of a sphenoid recess.
In tarsiers, as in higher primates, the major blood tarser to the brain comes through the promontory branch of the internal carotid Fig. The tympanic ring lies external to the auditory bulla and extends laterally to form a bony tube, the external auditory meatus. The tarsier dental formula, 2. The postcranial tarser of tarsiers is striking in many of its proportions.
The hands and feet of these tiny animals are relatively enormous, reflecting both their clinging abilities and their predatory habits Fig. They have extremely long legs and many more specific adaptations for leaping, including a fused tibia and fibula and the very long ankle region responsible for their name. A pair of tarsiers Drawing by Stephen Nash. In their reproductive physiology, tarsiers show several similarities to higher primates, as noted above. They have a hemochorial placenta like that of monkeys, apes, and humans, rather than the epitheliochorial type found in lemurs, and they produce relatively large offspring.
Female tarsiers undergo monthly sexual cycles, with swellings reminiscent of some Old World monkeys. Living tarsiers are currently tarser into three genera and 11 species Table 4.
The genus Tarsius, with nine species, is restricted to Sulawesi and nearby small islands. The other two tarsier genera are, at present, monotypic. Carlito syrichta is from the Philippines, and Cephalopachus bancanus is from Borneo, Sumatra, and nearby small islands.
The allopatric tarsier genera differ in numerous morphological features, including body size, chromosomelimb proportions, orbit size, of nipples, and patterns of vocalization and sociality. The distribution of the three genera of tarsiers in southeast Asia. Drawing by Stephen Nash. Tarsiers seem to be common in tarser types of forest, but they are particularly abundant in secondary forests and scrub.
They are totally nocturnal and spend their days sleeping in the grass or on vines in trees. Tarsiers often travel and feed very near the ground. In Sulawesi, other activities, such as calling and resting, take place higher in the canopy. All tarsiers move mainly by rapid leaps of up to 3 m. The Bornean tarsier seems to be most committed to vertical clinging and leaping, but this may reflect differences in data collection Dagosto et al.
Tarsius pumilus, the pygmy tarsieris unusual in having keeled nails for clinging to moss-covered trees. All tarsiers are totally faunivorous: they eat insects, arachnids, and small vertebrates such as snakes tarser lizards. There is evidence from both naturalistic and captive studies of considerable differences in social behavior among and within species Gursky, Philippine tarser Bornean tarsiers have been reported to live in a noyau system, with solitary individuals living in overlapping ranges. Philippine tarsiers always sleep alone.
Sulawesi tarsiers, on the other hand, live in families or perhaps small polygynous groups. These families sleep together, give complex territorial duet calls early every evening, and then forage together all night. Males and females actually chase other tarsiers out of their territories. All tarsiers have a remarkably long, six-month gestation period tarser one of the lowest rates of fetal growth among mammals Roberts, During that time, they seem to develop adult prey-catching patterns.
Females are largely responsible for care of the infant and usually park the infant while foraging Gursky, In contrast to many monogamous species, there is no indication of male infant care in tarsiers. Valverde Celia R. TarsiersTarser World and Old World monkeys have a flask-shaped simple stomach. The rhesus stomach is positioned lower and more horizontally than in humans, due to the shape and size of their liver Hartman et tarser. The stomach structure of colobines Colobus and Presbytis differs from any other primate and resembles that found in ungulates, with a pseudoruminant anterior fermentation area in a large multichambered stomach.
The stomach is large and sacculated, though not truly compartmentalized. The sacculations are tarser by reduced longitudinal muscle bands. The size of the stomach and colon tend to be proportionally larger in folivorous nonhuman primates.
These animals also tend to be larger in stature to accommodate for their sizeable gastrointestinal tract. The colobine stomach may constitute up to a quarter of the adult body weight and up to half for a semi-weaned infant. The Pongidae stomach is indistinguishable from human beings. For most of the past decade, the enlarging fossil record of early anthropoids and increasing s of detailed phylogenetic analyses appeared to have settled earlier debates over the broader question of the phyletic origins of anthropoids, or, more specifically, which group of prosimians gave rise to higher primates Fleagle and Kay, ; Kay et al.
There is widespread agreement among primatologists and mammalogists that, among living primates, anthropoids seem to be more closely related to the living tarsiers than to living lemurs and lorises. When we consider fossil prosimians, however, the possible phyletic relationships between anthropoids and tarsiers and various groups of living and fossil prosimians are less settled. Thus, tarser are three distinct views regarding which extant or fossil clade is the sister group of Anthropoidea Fig. Hypotheses of anthropoid origins.
As noted in Chapter 4tarsiers share with anthropoids many similarities in reproductive anatomy, eye structure, and cranial anatomy, as well as biochemical similarities not found in other living primates.
Moreover, two features that unite tarsiers and anthropoids, postorbital closure and the development of an anterior accessory chamber of the middle ear, are unique among primates and even among mammals, rather than being similar features that appear to have evolved in numerous groups.Tarser
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