Lemur evolutionary history
Encyclopedia
The evolutionary history of lemur
s occurred in isolation from other primate
s, on the island of Madagascar
, for at least 40 million years. Lemur
s are prosimian
primates belonging to the suborder Strepsirrhini
, which branched off from other primates less than 63 mya (million years ago). They share some traits with the most basal
primates, and thus are often confused as being ancestral to modern monkeys, apes, and humans. Instead, they merely resemble ancestral primates.
Lemurs are thought to have evolved during the Eocene
or earlier, sharing a closest common ancestor with loris
es, potto
s, and galago
s (lorisiforms
). Fossil
s from Africa and some tests of nuclear DNA
suggest that lemurs made their way to Madagascar between 40 and 52 mya. Other mitochondrial and nuclear DNA sequence comparisons offer an alternative date range of 62 to 65 mya. An ancestral lemur population is thought to have inadvertently rafted
to the island on a floating mat of vegetation, although hypotheses for land bridge
s and island hopping
have also been proposed. The timing and number of hypothesized colonizations has traditionally hinged on the phylogenetic affinities
of the aye-aye
, the most basal member of the lemur clade
.
Having undergone their own independent evolution on Madagascar, lemurs have diversified to fill many niches
normally filled by other types of mammals. They include the smallest primates in the world, and once included some of the largest. Since the arrival of humans approximately 2,000 years ago, lemurs are now restricted to 10% of the island, or approximately 60000 square kilometres (23,166.1 sq mi), and many face extinction
.
primates belonging to the suborder Strepsirrhini. Like other strepsirrhine
primates, such as loris
es, potto
s, and galago
s, they share ancestral traits with early primates. In this regard, lemurs are popularly confused with ancestral primates; however, lemurs did not give rise to monkeys and apes, but evolved independently on Madagascar.
Primates first evolved sometime between the Middle Cretaceous
and the early Paleocene
periods on either the supercontinent
of Laurasia
or in Africa. According to molecular clock
studies, the last common ancestor of all primates dates to around 79.6 mya, although the earliest known fossil
primates are only 54–55 million years old. The closest relatives of primates are the extinct plesiadapiforms
, the modern colugo
s (commonly and inaccurately named "flying lemurs"), and treeshrew
s. Some of the earliest known true primates are represented by the fossil groups Omomyidae, Eosimiidae
, and Adapiformes
.
The relationship between known fossil primate families remains unclear. A conservative estimate for the divergence of haplorrhines
(tarsier
s, monkey
s, ape
s, and human
s) and strepsirrhines is 58 to 63 mya, and a consensus is emerging that places tarsiers close to omomyids, while eosimids gave rise to the simian
s (non-tarsier haplorrhines) and the adapiforms gave rise to modern strepsirrhines, including lemurs. In 2009, a highly publicized and scientifically criticized publication proclaimed that a 47 million-year-old adapiform fossil, Darwinius masillae
, demonstrated both adapiform and simian
traits, making it a transitional form between the prosimian and simian
lineages. Media sources inaccurately dubbed the fossil as a "missing link" between lemurs and humans.
Lemurs were traditionally thought to have evolved during the Eocene
(55 to 37 mya) based on the fossil record, although molecular tests suggest the Paleocene (65 to 56 mya) or later. Until recently, they were thought to have descended directly from the diverse group of adapiforms due to several shared postcrania
l traits, as well as long snout
s and small brain
s. Although adapiforms also had lemur-like auditory bulla
e, a prosimian characteristic, they had smaller brains and longer snouts than lemurs. There are also several other morphological
differences. Most noticeably, adapiforms lack a key derived
trait, the toothcomb
, and possibly the toilet-claw
, found not only in extant (living) strepsirrhines but also in tarsiers. Unlike lemurs, adapiforms exhibited a fused mandibular symphysis (a characteristic of simians) and also possessed four premolar
s, instead of three or two.
Comparative studies of the cytochrome b
gene, which are frequently used to determine phylogenetic relationships among mammals—particularly within families and genera—have been used to show that lemurs share common ancestry with lorisiforms. This conclusion is also corroborated by the shared strepsirhine toothcomb, an unusual trait that is unlikely to have evolved twice. If adapiforms were the ancestors of the living strepsirrhines, then the last common ancestor of modern strepsirrhines would have to predate the early Eocene, a view supported by molecular phylogenetic studies by Anne D. Yoder and Ziheng Yang in 2004, which showed that lemurs split from lorises approximately 62 to 65 mya. These dates were confirmed by more extensive tests by Julie Horvath et al. in 2008. These molecular studies also showed that lemuriforms diversified before the modern lorisiforms. Using a more limited data set and only nuclear gene
s, another study in 2005 by Céline Poux et al. dated the split between lemurs and lorises at 60 mya, lemur diversification at 50 mya, and the lemur colonization of Madagascar somewhere between these two approximate dates. However, the 2003 discovery of fossil lorisiforms at the Fayum Depression in Egypt pushed the date of lorisiform divergence back to the Eocene, matching the divergence dates predicted by Yoder and Horvath.
The fossil record tells a different story. Although it cannot show the earliest possible date for the appearance of a taxonomic group, other concerns have arisen about these vastly earlier divergence dates predicted independently of the fossil record. First, palaeontologists have expressed concerns that if primates have been around for significantly more than 65 million years, then the first one-third of the primate fossil record is missing. Another problem is that some of these molecular dates have overestimated the divergence of other mammalian orders, such as Rodent
ia, suggesting primate divergence might also be overestimated. Currently the oldest known strepsirrhine, Djebelemur, dates from the early Eocene in northern Africa and lacks a fully differentiated toothcomb. Based on fossils and other genetic tests, a more conservative estimate dates the divergence between lemurs and lorises to around 50 to 55 mya.
To complicate the ancestry puzzle, no terrestrial Eocene or Paleocene fossil
s have been found on Madagascar, and the fossil record from both Africa and Asia around this time is not much better. Fossil sites in Madagascar are restricted to only five windows in time, which omit most of the Cenozoic
, from 65 mya to ~26,000 years ago. What little fossil-bearing rock exists from this vast span of time is dominated by marine strata along the west coast. The oldest lemur fossils on Madagascar are actually subfossil
s dating to the Late Pleistocene
.
, Madagascar broke away from eastern Africa, the likely source of the ancestral lemur population, about 160 mya and then from Antarctica between 80 and 130 mya. Initially, the island drifted south from where it split from Africa (around modern Somalia
) until it reached its current position between 80 and 90 mya. Around that time, it split with India, leaving it isolated in the Indian Ocean
and separated from nearby Africa by the Mozambique Channel
, a deep channel with a minimum width of approximately 560 kilometres (348 mi). These separation dates and the estimated age of the primate lineage preclude any possibility that lemurs could have been on the island before Madagascar pulled away from Africa, an evolutionary process known as vicariance
. In support of this, mammal
ian fossils on Madagascar from the Cretaceous (see Mesozoic mammals of Madagascar
) include gondwanatheres
and other mammalian groups that would not have been ancestral to lemurs or the other endemic mammals present on the island today.
With Madagascar already geographically isolated by the Paleocene and lemur diversification dating to the same time, an explanation was needed for how lemurs had made it to the island. In the 19th century, prior to the theory of continental drift
, scientists including Philip Sclater
, Étienne Geoffroy Saint-Hilaire
, and Ernst Haeckel
suggested that Madagascar and India were once part of a southern continent—named Lemuria
by Sclater—that has since disappeared under the Indian Ocean. By the early 20th century, oceanic dispersal emerged as the most popular explanation for how lemurs reached the island. The idea first took shape under the anti-plate tectonics
movement of the early 1900s, when renowned paleontologist William Diller Matthew
proposed the idea in his influential article "Climate and Evolution" in 1915. In the article, Matthew could only account for the presence of lemurs in Madagascar by "rafting". In the 1940s, American paleontologist George Gaylord Simpson
coined the term "sweepstakes dispersal" for such unlikely events.
As plate tectonics theory took hold, oceanic dispersal fell out of favor and was even considered by many researchers to be "miraculous" if it occurred. Despite the low likelihood of its occurrence, oceanic dispersal remains the most accepted explanation for numerous vertebrate colonizations of Madagascar, including that of the lemurs. Although unlikely, over long periods of time terrestrial animal
s can occasionally raft to remote islands on floating mats of tangled vegetation, which get flushed out to sea from major rivers by floodwaters.
Any extended ocean voyage without fresh water or food would prove difficult for a large, warm-blooded
(or "homeothermic") mammal, but today many small, nocturnal species of lemur exhibit heterothermy, which allows them to lower their metabolism
and become dormant while living off fat reserves. Such a trait in a small, nocturnal lemur ancestor would have facilitated the ocean voyage and could have been passed on to its descendants. However, this trait has not been observed in the closely related lorisiforms studied to date, and could have evolved on Madagascar in response to the island's harsh environmental conditions.
Because only five terrestrial orders of mammals
have made it to the island, each likely to have derived from a single colonization, and since these colonizations date to either the early Cenozoic
or the early Miocene
, the conditions for oceanic dispersal to Madagascar seem to have been better during two separate periods in the past. A report published in January 2010 supported this assumption by demonstrating that both Madagascar and Africa were 1650 km (1,025.3 mi) south of their present-day positions around 60 mya, placing them in a different ocean gyre and reversing the strong current that presently flows away from Madagascar. The currents were even shown to be stronger than they are today, shortening the rafting time to approximately 30 days or less, making the crossing much easier for a small mammal. Over time, as the continental plates drifted northward, the currents gradually changed, and by 20 mya the window for oceanic dispersal had closed.
Since the 1970s, the rafting hypothesis has been called into question by claims that lemur family Cheirogaleidae
might be more closely related to the other Afro-Asian strepsirrhines than to the rest of the lemurs. This idea was initially based on similarities in behavior and molar
morphology, although it gained support with the 2001 discovery of 30 million-year-old Bugtilemur
in Pakistan
and the 2003 discovery of 40 million-year-old Karanisia
in Egypt
. Karanisia is the oldest fossil found that bears a toothcomb, whereas Bugtilemur was thought to have a toothcomb, but also had even more similar molar morphology to Cheirogaleus (dwarf lemurs). If these relationships had been correct, the dates of these fossils would have had implications on the colonization of Madagascar, requiring two separate events. The most parsimonious explanation
, given the genetic evidence and the absence of toothcombed primates in European fossil sites, is that stem
strepsirrhines evolved on the Afro-Arabian landmass, dispersing to Madagascar and more recently from Africa to Asia. More recently, the structure and general presence of the toothcomb in Bugtilemur has been questioned, as well as many other dental features, suggesting it is most likely an adapiform.
An alternative form of oceanic dispersal that had been considered was island hopping
, where the lemur ancestors might have made it to Madagascar in small steps by colonizing exposed seamount
s during times of low sea level. However, this is unlikely since the only seamounts found along the Davie Ridge would have been too small in a such a wide channel. Even though the Comoros Islands
between Africa and Madagascar are significantly larger, they are too young, having been formed by volcanic activity only around 8 mya. A land bridge
between Madagascar and Africa has also been proposed, but a land bridge would have facilitated the migration of a much greater sampling of Africa's mammalian fauna than is endemic to the island. Furthermore, deep trenches separate Madagascar from the mainland, and prior to the Oligocene, sea level was significantly higher than today.
A variant of the land bridge hypothesis has been proposed in an attempt to explain both how a land bridge could have formed, and why other mammalian orders failed to cross it. Geological studies have shown that following the collision of India and Asia, the Davie Fracture Zone had been pushed up by tectonic forces, possibly high enough to create a land bridge. Indeed, core sample
s along the Davie Fracture Zone suggest that at least parts of the Mozambique Channel were above sea level between 45 and 26 mya, or possibly as early as 55 mya. Following the Indian-Asian collision, the fault type changed from a strike-slip fault to a normal fault, and seafloor spreading
created compression along the Davie Fracture Zone, causing it to rise. By the early Miocene, the East African Rift
created tension along the fault, causing it to subside beneath the ocean. The divergence dates of many Malagasy mammalian orders formerly fell within this window. Old World monkey
s, dogs, and cats did not diverge or arrive in Africa until later in the Miocene. However, more recent dating of divergence of the Malagasy mammalian clades falls outside of this land bridge window, and a much greater diversity of mammal groups would be expected on Madagascar had the land bridge been present during that stretch of time.
The dating of the lemur colonization is controversial for the same reasons as strepsirrhine evolution. Using both mitochondrial and nuclear DNA sequences, a single colonization has been estimated at 62 to 65 mya based on the split between the aye-aye
and the rest of the lemurs. On the other hand, the sparse fossil record and some estimates based on other nuclear genes support a more recent estimate of 40 to 52 mya. Furthermore, a fossil strepsirrhine primate from Africa, Plesiopithecus, may suggest that the aye-aye and the rest of the lemurs diverged in Africa, which would require at least two colonization events.
Once safely established on Madagascar, with its limited mammalian population, the lemurs were protected from the increasing competition from evolving arboreal
mammalian groups. Monkey
s had evolved by the Oligocene
, and their intelligence, aggression, and deceptiveness may have given them the advantage in exploiting the environment over the diurnal adapiform primates in Africa and Asia, ultimately driving them to extinction
and leaving only the nocturnal lorisiforms.
anatomy—particularly the cranial foramina and the middle ear
—comparable to that of lemurids
, while being similar to cheirogaleids
in dentition
and postcranial anatomy
.
Nothing definitive is known about the island's biogeography
at the time of the colonization, however, the paleoclimate
(ancient weather patterns) may have been affected by the Madagascar's location below the subtropical ridge
at 30° S latitude and disruption of the weather patterns by India as it drifted northward. Both would have created a drying effect on Madagascar, and as a result, the arid spiny bush
that is currently found in the south and southwest of Madagascar would have dominated the island. This would have placed strong selection pressure
for drought tolerance
on the inhabitants of the island between the Cretaceous and the Eocene. As Madagascar edged above the subtropical ridge and India moved closer to Asia, the climate became less dry and the arid spiny bush retreated to the south and southwest.
Lemurs have diversified greatly since first reaching Madagascar. The aye-aye and its extinct relations are thought to have diverged first, shortly after colonization. According to molecular studies, there have since been two major episodes of diversification, from which all other known extant and extinct family lineages emerged. The remaining families diverged in the first diversification episode, during a 10 to 12 million-year window between the Late Eocene (42 mya) and into the Oligocene (30 mya). The dates for this divergence window span the Eocene–Oligocene extinction event, during which time climate cooling took place and changes in ocean currents altered weather patterns. Outside of Madagascar, these dates also coincide with the divergence of the lorisiform primates and five major clades of squirrels, all occupying niches similar to those of lemurs. The dates do not suggest that increased predation
drove family-level divergence since the first carnivores arrived on the island between 24 and 18 mya.
The second major episode of diversification occurred during the Late Miocene, approximately 8 to 12 mya, and included the true lemurs (Eulemur) and the mouse lemur
s (Microcebus). This event coincided with the beginning of the Indian monsoon
s, the last major change in climate to affect Madagascar. The populations of both the true lemurs and mouse lemurs were thought to have diverged due to habitat fragmentation
when humans arrived on the island roughly 2,000 years ago. Only recently has molecular research shown a more distant split in these genera. Most surprising were the mouse lemurs, a group which is now thought to contain cryptic species
, meaning they are indistinguishable from each other based solely on appearance. In contrast, true lemurs are easier to distinguish and exhibit sexual dichromatism. Studies in karyology
, molecular genetics, and biogeographic patterns
have also assisted in understanding their phylogeny and diversification. Although the divergence estimates for these two genera are imprecise, they overlap with a change to a wetter climate in Madagascar, as new weather patterns generated monsoon
s and likely influenced the plant life.
This difference in evolutionary divergence between the two genera may be due to differences in their activity patterns. True lemurs are often diurnal, allowing potential mates to distinguish each other as well as other related species visually. Mouse lemurs, on the other hand, are nocturnal, reducing their ability to use visual signals for mate selection
. Instead, they use olfactory
and auditory
signaling. For these reasons, true lemurs may have evolved sexual dichromatism while mouse lemurs evolved to be cryptic species.
s are considered. Ranging in size from the 30 g (1.1 oz) Madame Berthe's mouse lemur
, the world's smallest primate, to the extinct 160 – Archaeoindris fontoynonti, lemurs evolved diverse forms of locomotion, varying levels of social complexity, and unique adaptations to the local climate. They went on to fill many niches normally occupied by monkeys, squirrel
s, woodpecker
s, and large grazing ungulate
s. In addition to the incredible diversity between lemur families, there has also been great diversification among closely related lemurs. Yet despite separation by geographical barriers
or by niche differentiation in sympatry
, occasionally hybridization can occur. Lemur diversification has also created generalist species
, such as the true lemurs of northern Madagascar, which are very adaptable, mostly nondescript, and found throughout most of the island's forests.
Most of the 99 living lemur taxa are found only on Madagascar. Two species, the common brown lemur
(Eulemur fulvus) and the mongoose lemur
(Eulemur mongoz), can also be found on the Comoro Islands
, although it is assumed that both species were introduced to the islands from northwestern Madagascar by humans within the last few hundred years. Molecular studies on Eulemur fulvus fulvus (from the mainland) and E. f. mayottensis (from the Comoro Islands) and on Comoro and mainland mongoose lemurs have supported this assumption by showing no genetic differences between the two populations. Because all lemurs, including these two brown lemur species, are only native to the island of Madagascar, they are considered to be endemic.
Historically, lemurs ranged across the entire island inhabiting a wide variety of habitats
, including dry deciduous forests
, lowland forests
, spiny thickets
, subhumid forests
, montane forest
, and mangrove
. Today, their collective range is restricted to 10% of the island, or approximately 60000 km² (23,166.1 sq mi). Most of the remaining forests and lemurs are found along the periphery of the island. The center of the island, the Hauts-Plateaux
, was converted by early settlers to rice paddies
and grassland
through slash-and-burn agriculture
, known locally as tavy. As erosion
depleted the soil, the cyclical forest regrowth and burning ended as the forest gradually failed to return. Today, the level of flora
l diversity increases with precipitation, from the dry southern forests to the wetter norther forests to the rainforest
s along the east coast. Increased foliage corresponds to increased fauna
l diversity, including the diversity and complexity of lemur communities.
Having evolved in Madagascar's challenging environment, replete with poor soils, extreme shifts in poor, seasonal plant productivity, and devastating climatic events such as extended droughts and annual cyclones, lemurs have adopted unique combinations of unusual traits to survive, distinguishing them significantly from other primates. In response to limited, seasonal resources, lemurs may exhibit seasonal fat storage, hypometabolism
(including torpor
and hibernation
in some cheirogaleids
), small group sizes, low encephalization
(relative brain size), cathemeral
ity (activity both day and night), and/or strict breeding seasons
. Secondarily, extreme resource limitations and seasonal breeding are thought to have resulted in three other relatively common lemur traits: female dominance
, sexual monomorphism (lack of size differences between the sexes), and male-male competition for mates involving low levels of agonism (conflict), such as sperm competition
.
The arrival of humans on the island 1,500 to 2,000 years ago has taken a significant toll, not only on the size of lemur populations, but also on their diversity. Due to habitat destruction
and hunting, at least 17 species and 8 genera have gone extinct and the populations of all species have decreased. A couple of species once thought to have gone extinct have since been rediscovered. The hairy-eared dwarf lemur
(Allocebus trichotis) was only known from five museum specimens, most collected in the late 19th century and one in 1965. It was rediscovered in 1989 and has since been identified in five national parks, although it is very rare within its range. Likewise, the greater bamboo lemur
(Prolemur simus) was thought to be extinct as recently as the late 1970s, but a population was located near Ranomafana National Park
in the late 1980s. Historically, it had a much wider geographic distribution, shown by subfossil
remains, but today it remains one of the world's 25 most endangered primates. One distinctive morph
(possibly a species or subspecies) of sifaka
, has not been so fortunate, having been extirpated
from all known localities. Unless trends change, extinctions are likely to continue.
Until recently, giant species of lemur existed on Madagascar. Now represented only by recent or subfossil
remains, they were modern forms and are counted as part of the rich lemur diversity that evolved in isolation. Some of their adaptations were unlike those seen in lemurs today. All 17 extinct lemurs were larger than the extant forms, some weighing as much as 200 kg (440.9 lb), and are thought to have been active during the day. Not only were they unlike the living lemurs in both size and appearance, they also filled ecological niche
s that no longer exist or are now left unoccupied. Large parts of Madagascar, which are now devoid of forests and lemurs, once hosted diverse primate communities that included more than 20 species covering the full range of lemur sizes.
Lemur
Lemurs are a clade of strepsirrhine primates endemic to the island of Madagascar. They are named after the lemures of Roman mythology due to the ghostly vocalizations, reflective eyes, and the nocturnal habits of some species...
s occurred in isolation from other primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s, on the island of Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
, for at least 40 million years. Lemur
Lemur
Lemurs are a clade of strepsirrhine primates endemic to the island of Madagascar. They are named after the lemures of Roman mythology due to the ghostly vocalizations, reflective eyes, and the nocturnal habits of some species...
s are prosimian
Prosimian
Prosimians are a grouping of mammals defined as being primates, but not monkeys or apes. They include, among others, lemurs, bushbabies, and tarsiers. They are considered to have characteristics that are more primitive than those of monkeys and apes. Prosimians are the only primates native to...
primates belonging to the suborder Strepsirrhini
Strepsirrhini
The clade Strepsirrhini is one of the two suborders of primates. Madagascar's only non-human primates are strepsirrhines, and others can be found in southeast Asia and Africa...
, which branched off from other primates less than 63 mya (million years ago). They share some traits with the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
primates, and thus are often confused as being ancestral to modern monkeys, apes, and humans. Instead, they merely resemble ancestral primates.
Lemurs are thought to have evolved during the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
or earlier, sharing a closest common ancestor with loris
Loris
Loris is the common name for the strepsirrhine primates of the subfamily Lorisinae in family Lorisidae. Loris is one genus in this subfamily and includes the slender lorises, while Nycticebus is the genus for the slow lorises....
es, potto
Potto
The potto is a strepsirrhine primate from the Lorisidae family. It is the only species in genus Perodicticus...
s, and galago
Galago
Galagos , also known as bushbabies, bush babies or nagapies , are small, nocturnal primates native to continental Africa, and make up the family Galagidae...
s (lorisiforms
Lorisiformes
Lorisiformes are a group of primates found throughout Africa and Asia. Members of this infraorder include the galagos and the lorises. As strepsirrhines, they are related to the lemurs.* Order Primates** Suborder Strepsirrhini: non-tarsier prosimians...
). Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s from Africa and some tests of nuclear DNA
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
suggest that lemurs made their way to Madagascar between 40 and 52 mya. Other mitochondrial and nuclear DNA sequence comparisons offer an alternative date range of 62 to 65 mya. An ancestral lemur population is thought to have inadvertently rafted
Rafting event
Oceanic dispersal is a type of biological dispersal that occurs when organisms transfer from one land mass to another by way of a sea crossing on large clumps of floating vegetation. Such matted clumps of vegetation are often seen floating down major rivers in the tropics and washing out to sea,...
to the island on a floating mat of vegetation, although hypotheses for land bridge
Land bridge
A land bridge, in biogeography, is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonise new lands...
s and island hopping
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
have also been proposed. The timing and number of hypothesized colonizations has traditionally hinged on the phylogenetic affinities
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
of the aye-aye
Aye-aye
The aye-aye is a lemur, a strepsirrhine primate native to Madagascar that combines rodent-like teeth and a special thin middle finger to fill the same ecological niche as a woodpecker...
, the most basal member of the lemur clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
.
Having undergone their own independent evolution on Madagascar, lemurs have diversified to fill many niches
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
normally filled by other types of mammals. They include the smallest primates in the world, and once included some of the largest. Since the arrival of humans approximately 2,000 years ago, lemurs are now restricted to 10% of the island, or approximately 60000 square kilometres (23,166.1 sq mi), and many face extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
.
Evolutionary history
Lemurs are prosimianProsimian
Prosimians are a grouping of mammals defined as being primates, but not monkeys or apes. They include, among others, lemurs, bushbabies, and tarsiers. They are considered to have characteristics that are more primitive than those of monkeys and apes. Prosimians are the only primates native to...
primates belonging to the suborder Strepsirrhini. Like other strepsirrhine
Strepsirrhini
The clade Strepsirrhini is one of the two suborders of primates. Madagascar's only non-human primates are strepsirrhines, and others can be found in southeast Asia and Africa...
primates, such as loris
Loris
Loris is the common name for the strepsirrhine primates of the subfamily Lorisinae in family Lorisidae. Loris is one genus in this subfamily and includes the slender lorises, while Nycticebus is the genus for the slow lorises....
es, potto
Potto
The potto is a strepsirrhine primate from the Lorisidae family. It is the only species in genus Perodicticus...
s, and galago
Galago
Galagos , also known as bushbabies, bush babies or nagapies , are small, nocturnal primates native to continental Africa, and make up the family Galagidae...
s, they share ancestral traits with early primates. In this regard, lemurs are popularly confused with ancestral primates; however, lemurs did not give rise to monkeys and apes, but evolved independently on Madagascar.
Primates first evolved sometime between the Middle Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
and the early Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
periods on either the supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
of Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
or in Africa. According to molecular clock
Molecular clock
The molecular clock is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation...
studies, the last common ancestor of all primates dates to around 79.6 mya, although the earliest known fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
primates are only 54–55 million years old. The closest relatives of primates are the extinct plesiadapiforms
Plesiadapiformes
Plesiadapiformes is an extinct order of mammals. It is either closely related to the primates or a precursor to them. Many are too derived to be ancestral to primates, but the earliest Plesiadapiformes have teeth that are strongly indicative of a common ancestor...
, the modern colugo
Colugo
Colugos are arboreal gliding mammals found in South-east Asia. There are just two extant species, which make up the entire family Cynocephalidae and order Dermoptera. They are the most capable of all gliding mammals, using flaps of extra skin between their legs to glide from higher to lower...
s (commonly and inaccurately named "flying lemurs"), and treeshrew
Treeshrew
The treeshrews are small mammals native to the tropical forests of Southeast Asia. They make up the families Tupaiidae, the treeshrews, and Ptilocercidae, the pen-tailed treeshrews, and the entire order Scandentia. There are 20 species in 5 genera...
s. Some of the earliest known true primates are represented by the fossil groups Omomyidae, Eosimiidae
Eosimiidae
Eosimiidae is the family of extinct primates believed to be the earliest simians....
, and Adapiformes
Adapiformes
Adapiformes are an extinct group of primitive primates.The adapiformes radiated throughout much of the northern continental mass, reaching as far south as northern Africa and tropical Asia. The adapiformes existed from the Eocene to the Miocene epoch...
.
The relationship between known fossil primate families remains unclear. A conservative estimate for the divergence of haplorrhines
Haplorrhini
The haplorhines, the "dry-nosed" primates , are members of the Haplorhini clade: the prosimian tarsiers and the anthropoids...
(tarsier
Tarsier
Tarsiers are haplorrhine primates of the genus Tarsius, a genus in the family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes...
s, monkey
Monkey
A monkey is a primate, either an Old World monkey or a New World monkey. There are about 260 known living species of monkey. Many are arboreal, although there are species that live primarily on the ground, such as baboons. Monkeys are generally considered to be intelligent. Unlike apes, monkeys...
s, ape
Ape
Apes are Old World anthropoid mammals, more specifically a clade of tailless catarrhine primates, belonging to the biological superfamily Hominoidea. The apes are native to Africa and South-east Asia, although in relatively recent times humans have spread all over the world...
s, and human
Human
Humans are the only living species in the Homo genus...
s) and strepsirrhines is 58 to 63 mya, and a consensus is emerging that places tarsiers close to omomyids, while eosimids gave rise to the simian
Simian
The simians are the "higher primates" familiar to most people: the Old World monkeys and apes, including humans, , and the New World monkeys or platyrrhines. Simians tend to be larger than the "lower primates" or prosimians.- Classification and evolution :The simians are split into three groups...
s (non-tarsier haplorrhines) and the adapiforms gave rise to modern strepsirrhines, including lemurs. In 2009, a highly publicized and scientifically criticized publication proclaimed that a 47 million-year-old adapiform fossil, Darwinius masillae
Darwinius
Darwinius is a genus of Adapiformes, a group of basal primates from the Eocene epoch. Its only known species is Darwinius masillae, dated to 47 million years ago based on dating of the fossil site....
, demonstrated both adapiform and simian
Simian
The simians are the "higher primates" familiar to most people: the Old World monkeys and apes, including humans, , and the New World monkeys or platyrrhines. Simians tend to be larger than the "lower primates" or prosimians.- Classification and evolution :The simians are split into three groups...
traits, making it a transitional form between the prosimian and simian
Simian
The simians are the "higher primates" familiar to most people: the Old World monkeys and apes, including humans, , and the New World monkeys or platyrrhines. Simians tend to be larger than the "lower primates" or prosimians.- Classification and evolution :The simians are split into three groups...
lineages. Media sources inaccurately dubbed the fossil as a "missing link" between lemurs and humans.
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
(55 to 37 mya) based on the fossil record, although molecular tests suggest the Paleocene (65 to 56 mya) or later. Until recently, they were thought to have descended directly from the diverse group of adapiforms due to several shared postcrania
Postcrania
Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...
l traits, as well as long snout
Snout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
s and small brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
s. Although adapiforms also had lemur-like auditory bulla
Auditory bulla
The auditory bulla is a hollow bony structure on the ventral, posterior portion of the skull of placental mammals that encloses parts of the middle and inner ear. In most species, it is formed by the tympanic part of the temporal bone.In extant primates, the structure is found in tarsiers,...
e, a prosimian characteristic, they had smaller brains and longer snouts than lemurs. There are also several other morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
differences. Most noticeably, adapiforms lack a key derived
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
trait, the toothcomb
Toothcomb
A toothcomb is an anatomical structure found in strepsirrhine primates, which includes lemurs, lorises and galagos. A toothcomb consists of long, flat forward-angled teeth, and includes the lower incisors and the canine teeth...
, and possibly the toilet-claw
Toilet-claw
A toilet-claw is the specialized claw or nail on the foot of certain primates, used for personal grooming. All prosimians have a toilet claw, but the digit that is specialized in this manner varies. Tarsiers have a toilet claw on toe two and toe three...
, found not only in extant (living) strepsirrhines but also in tarsiers. Unlike lemurs, adapiforms exhibited a fused mandibular symphysis (a characteristic of simians) and also possessed four premolar
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
s, instead of three or two.
Comparative studies of the cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...
gene, which are frequently used to determine phylogenetic relationships among mammals—particularly within families and genera—have been used to show that lemurs share common ancestry with lorisiforms. This conclusion is also corroborated by the shared strepsirhine toothcomb, an unusual trait that is unlikely to have evolved twice. If adapiforms were the ancestors of the living strepsirrhines, then the last common ancestor of modern strepsirrhines would have to predate the early Eocene, a view supported by molecular phylogenetic studies by Anne D. Yoder and Ziheng Yang in 2004, which showed that lemurs split from lorises approximately 62 to 65 mya. These dates were confirmed by more extensive tests by Julie Horvath et al. in 2008. These molecular studies also showed that lemuriforms diversified before the modern lorisiforms. Using a more limited data set and only nuclear gene
Nuclear gene
A Nuclear gene is a gene located in the cell nucleus of a eukaryote. The term is used to distinguish nuclear genes from the genes in the mitochondrion, and in case of plants, also the chloroplast, which host their own genetic system and can produce proteins from scratch...
s, another study in 2005 by Céline Poux et al. dated the split between lemurs and lorises at 60 mya, lemur diversification at 50 mya, and the lemur colonization of Madagascar somewhere between these two approximate dates. However, the 2003 discovery of fossil lorisiforms at the Fayum Depression in Egypt pushed the date of lorisiform divergence back to the Eocene, matching the divergence dates predicted by Yoder and Horvath.
The fossil record tells a different story. Although it cannot show the earliest possible date for the appearance of a taxonomic group, other concerns have arisen about these vastly earlier divergence dates predicted independently of the fossil record. First, palaeontologists have expressed concerns that if primates have been around for significantly more than 65 million years, then the first one-third of the primate fossil record is missing. Another problem is that some of these molecular dates have overestimated the divergence of other mammalian orders, such as Rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
ia, suggesting primate divergence might also be overestimated. Currently the oldest known strepsirrhine, Djebelemur, dates from the early Eocene in northern Africa and lacks a fully differentiated toothcomb. Based on fossils and other genetic tests, a more conservative estimate dates the divergence between lemurs and lorises to around 50 to 55 mya.
To complicate the ancestry puzzle, no terrestrial Eocene or Paleocene fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found on Madagascar, and the fossil record from both Africa and Asia around this time is not much better. Fossil sites in Madagascar are restricted to only five windows in time, which omit most of the Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
, from 65 mya to ~26,000 years ago. What little fossil-bearing rock exists from this vast span of time is dominated by marine strata along the west coast. The oldest lemur fossils on Madagascar are actually subfossil
Subfossil
Subfossil refers to remains whose fossilization process is not complete, either for lack of time or because the conditions in which they were buried were not optimal for fossilization....
s dating to the Late Pleistocene
Late Pleistocene
The Late Pleistocene is a stage of the Pleistocene Epoch. The beginning of the stage is defined by the base of the Eemian interglacial phase before the final glacial episode of the Pleistocene 126,000 ± 5,000 years ago. The end of the stage is defined exactly at 10,000 Carbon-14 years BP...
.
Colonization of Madagascar
Once part of the supercontinent GondwanaGondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
, Madagascar broke away from eastern Africa, the likely source of the ancestral lemur population, about 160 mya and then from Antarctica between 80 and 130 mya. Initially, the island drifted south from where it split from Africa (around modern Somalia
Somalia
Somalia , officially the Somali Republic and formerly known as the Somali Democratic Republic under Socialist rule, is a country located in the Horn of Africa. Since the outbreak of the Somali Civil War in 1991 there has been no central government control over most of the country's territory...
) until it reached its current position between 80 and 90 mya. Around that time, it split with India, leaving it isolated in the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and separated from nearby Africa by the Mozambique Channel
Mozambique Channel
The Mozambique Channel is a portion of the Indian Ocean located between the island nation of Madagascar and southeast Africa, primarily the country of Mozambique. It was a World War II clashpoint during the Battle of Madagascar...
, a deep channel with a minimum width of approximately 560 kilometres (348 mi). These separation dates and the estimated age of the primate lineage preclude any possibility that lemurs could have been on the island before Madagascar pulled away from Africa, an evolutionary process known as vicariance
Vicariance
Vicariance is a process by which the geographical range of an individual taxon, or a whole biota, is split into discontinuous parts by the formation of a physical barrier to gene flow or dispersal. Vicariance of whole biotas occurs following large-scale geophysical events such as the uplift of a...
. In support of this, mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian fossils on Madagascar from the Cretaceous (see Mesozoic mammals of Madagascar
Mesozoic mammals of Madagascar
Several mammals are known from the Mesozoic of Madagascar. The Bathonian Ambondro, known from a piece of jaw with three teeth, is the earliest known mammal with molars showing the modern, tribosphenic pattern that is characteristic of marsupial and placental mammals...
) include gondwanatheres
Gondwanatheria
Gondwanatheria is an extinct group of mammals that lived during the Upper Cretaceous through the Eocene in the Southern Hemisphere, including Antarctica...
and other mammalian groups that would not have been ancestral to lemurs or the other endemic mammals present on the island today.
With Madagascar already geographically isolated by the Paleocene and lemur diversification dating to the same time, an explanation was needed for how lemurs had made it to the island. In the 19th century, prior to the theory of continental drift
Continental drift
Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...
, scientists including Philip Sclater
Philip Sclater
Philip Lutley Sclater was an English lawyer and zoologist. In zoology, he was an expert ornithologist, and identified the main zoogeographic regions of the world...
, Étienne Geoffroy Saint-Hilaire
Étienne Geoffroy Saint-Hilaire
Étienne Geoffroy Saint-Hilaire was a French naturalist who established the principle of "unity of composition". He was a colleague of Jean-Baptiste Lamarck and expanded and defended Lamarck's evolutionary theories...
, and Ernst Haeckel
Ernst Haeckel
The "European War" became known as "The Great War", and it was not until 1920, in the book "The First World War 1914-1918" by Charles à Court Repington, that the term "First World War" was used as the official name for the conflict.-Research:...
suggested that Madagascar and India were once part of a southern continent—named Lemuria
Lemuria (continent)
Lemuria is the name of a hypothetical "lost land" variously located in the Indian and Pacific Oceans. The concept's 19th century origins lie in attempts to account for discontinuities in biogeography; however, the concept of Lemuria has been rendered obsolete by modern theories of plate tectonics...
by Sclater—that has since disappeared under the Indian Ocean. By the early 20th century, oceanic dispersal emerged as the most popular explanation for how lemurs reached the island. The idea first took shape under the anti-plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
movement of the early 1900s, when renowned paleontologist William Diller Matthew
William Diller Matthew
William Diller Matthew FRS was a vertebrate paleontologist who worked primarily on mammal fossils....
proposed the idea in his influential article "Climate and Evolution" in 1915. In the article, Matthew could only account for the presence of lemurs in Madagascar by "rafting". In the 1940s, American paleontologist George Gaylord Simpson
George Gaylord Simpson
George Gaylord Simpson was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern evolutionary synthesis, contributing Tempo and mode in evolution , The meaning of evolution and The major features of...
coined the term "sweepstakes dispersal" for such unlikely events.
As plate tectonics theory took hold, oceanic dispersal fell out of favor and was even considered by many researchers to be "miraculous" if it occurred. Despite the low likelihood of its occurrence, oceanic dispersal remains the most accepted explanation for numerous vertebrate colonizations of Madagascar, including that of the lemurs. Although unlikely, over long periods of time terrestrial animal
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
s can occasionally raft to remote islands on floating mats of tangled vegetation, which get flushed out to sea from major rivers by floodwaters.
Any extended ocean voyage without fresh water or food would prove difficult for a large, warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...
(or "homeothermic") mammal, but today many small, nocturnal species of lemur exhibit heterothermy, which allows them to lower their metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
and become dormant while living off fat reserves. Such a trait in a small, nocturnal lemur ancestor would have facilitated the ocean voyage and could have been passed on to its descendants. However, this trait has not been observed in the closely related lorisiforms studied to date, and could have evolved on Madagascar in response to the island's harsh environmental conditions.
Because only five terrestrial orders of mammals
Mammal classification
Mammalia is a class of animal within the Phylum Chordata. Mammal classification has been through several iterations since Carolus Linnaeus initially defined the class. Many earlier ideas have been completely abandoned by modern taxonomists, among these are the idea that bats are related to birds...
have made it to the island, each likely to have derived from a single colonization, and since these colonizations date to either the early Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
or the early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
, the conditions for oceanic dispersal to Madagascar seem to have been better during two separate periods in the past. A report published in January 2010 supported this assumption by demonstrating that both Madagascar and Africa were 1650 km (1,025.3 mi) south of their present-day positions around 60 mya, placing them in a different ocean gyre and reversing the strong current that presently flows away from Madagascar. The currents were even shown to be stronger than they are today, shortening the rafting time to approximately 30 days or less, making the crossing much easier for a small mammal. Over time, as the continental plates drifted northward, the currents gradually changed, and by 20 mya the window for oceanic dispersal had closed.
Since the 1970s, the rafting hypothesis has been called into question by claims that lemur family Cheirogaleidae
Cheirogaleidae
Cheirogaleidae is the family of strepsirrhine primates that contains the various dwarf and mouse lemurs. Like all other lemurs, cheirogaleids live exclusively on the island of Madagascar.-Characteristics:...
might be more closely related to the other Afro-Asian strepsirrhines than to the rest of the lemurs. This idea was initially based on similarities in behavior and molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
morphology, although it gained support with the 2001 discovery of 30 million-year-old Bugtilemur
Bugtilemur
Bugtilemur is an extinct genus of Strepsirhine primate tentatively placed within family Cheirogaleidae, which includes the dwarf and mouse lemurs of Madagascar. It is represented by only one species, B. mathesoni, which was found in the Chitarwata Formation of Pakistan...
in Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
and the 2003 discovery of 40 million-year-old Karanisia
Karanisia
Karanisia is an extinct genus of lorisid primate and is represented by two species, K. clarki and K. arenula.K. clarki was described in 2003 from isolated teeth and jaw fragments found in Late Middle Eocene sediments of the Birket Qarun Formation in the Egyptian Faiyum...
in Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
. Karanisia is the oldest fossil found that bears a toothcomb, whereas Bugtilemur was thought to have a toothcomb, but also had even more similar molar morphology to Cheirogaleus (dwarf lemurs). If these relationships had been correct, the dates of these fossils would have had implications on the colonization of Madagascar, requiring two separate events. The most parsimonious explanation
Occam's razor
Occam's razor, also known as Ockham's razor, and sometimes expressed in Latin as lex parsimoniae , is a principle that generally recommends from among competing hypotheses selecting the one that makes the fewest new assumptions.-Overview:The principle is often summarized as "simpler explanations...
, given the genetic evidence and the absence of toothcombed primates in European fossil sites, is that stem
Crown group
A crown group is a group consisting of living representatives, their ancestors back to the most recent common ancestor of that group, and all of that ancestor's descendants. The name was given by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms...
strepsirrhines evolved on the Afro-Arabian landmass, dispersing to Madagascar and more recently from Africa to Asia. More recently, the structure and general presence of the toothcomb in Bugtilemur has been questioned, as well as many other dental features, suggesting it is most likely an adapiform.
An alternative form of oceanic dispersal that had been considered was island hopping
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
, where the lemur ancestors might have made it to Madagascar in small steps by colonizing exposed seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
s during times of low sea level. However, this is unlikely since the only seamounts found along the Davie Ridge would have been too small in a such a wide channel. Even though the Comoros Islands
Comoros
The Comoros , officially the Union of the Comoros is an archipelago island nation in the Indian Ocean, located off the eastern coast of Africa, on the northern end of the Mozambique Channel, between northeastern Mozambique and northwestern Madagascar...
between Africa and Madagascar are significantly larger, they are too young, having been formed by volcanic activity only around 8 mya. A land bridge
Land bridge
A land bridge, in biogeography, is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonise new lands...
between Madagascar and Africa has also been proposed, but a land bridge would have facilitated the migration of a much greater sampling of Africa's mammalian fauna than is endemic to the island. Furthermore, deep trenches separate Madagascar from the mainland, and prior to the Oligocene, sea level was significantly higher than today.
A variant of the land bridge hypothesis has been proposed in an attempt to explain both how a land bridge could have formed, and why other mammalian orders failed to cross it. Geological studies have shown that following the collision of India and Asia, the Davie Fracture Zone had been pushed up by tectonic forces, possibly high enough to create a land bridge. Indeed, core sample
Core sample
A core sample is a cylindrical section of a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, with a hollow steel tube called a core drill. The hole made for the core sample is called the "core hole". A...
s along the Davie Fracture Zone suggest that at least parts of the Mozambique Channel were above sea level between 45 and 26 mya, or possibly as early as 55 mya. Following the Indian-Asian collision, the fault type changed from a strike-slip fault to a normal fault, and seafloor spreading
Seafloor spreading
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics....
created compression along the Davie Fracture Zone, causing it to rise. By the early Miocene, the East African Rift
East African Rift
The East African Rift is an active continental rift zone in eastern Africa that appears to be a developing divergent tectonic plate boundary. It is part of the larger Great Rift Valley. The rift is a narrow zone in which the African Plate is in the process of splitting into two new tectonic plates...
created tension along the fault, causing it to subside beneath the ocean. The divergence dates of many Malagasy mammalian orders formerly fell within this window. Old World monkey
Old World monkey
The Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous...
s, dogs, and cats did not diverge or arrive in Africa until later in the Miocene. However, more recent dating of divergence of the Malagasy mammalian clades falls outside of this land bridge window, and a much greater diversity of mammal groups would be expected on Madagascar had the land bridge been present during that stretch of time.
The dating of the lemur colonization is controversial for the same reasons as strepsirrhine evolution. Using both mitochondrial and nuclear DNA sequences, a single colonization has been estimated at 62 to 65 mya based on the split between the aye-aye
Aye-aye
The aye-aye is a lemur, a strepsirrhine primate native to Madagascar that combines rodent-like teeth and a special thin middle finger to fill the same ecological niche as a woodpecker...
and the rest of the lemurs. On the other hand, the sparse fossil record and some estimates based on other nuclear genes support a more recent estimate of 40 to 52 mya. Furthermore, a fossil strepsirrhine primate from Africa, Plesiopithecus, may suggest that the aye-aye and the rest of the lemurs diverged in Africa, which would require at least two colonization events.
Once safely established on Madagascar, with its limited mammalian population, the lemurs were protected from the increasing competition from evolving arboreal
Arboreal locomotion
Arboreal locomotion is the locomotion of animals in trees. In every habitat in which trees are present, animals have evolved to move in them. Some animals may only scale trees occasionally, while others are exclusively arboreal. These habitats pose numerous mechanical challenges to animals...
mammalian groups. Monkey
Monkey
A monkey is a primate, either an Old World monkey or a New World monkey. There are about 260 known living species of monkey. Many are arboreal, although there are species that live primarily on the ground, such as baboons. Monkeys are generally considered to be intelligent. Unlike apes, monkeys...
s had evolved by the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, and their intelligence, aggression, and deceptiveness may have given them the advantage in exploiting the environment over the diurnal adapiform primates in Africa and Asia, ultimately driving them to extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
and leaving only the nocturnal lorisiforms.
Diversification
The ancestral lemur that colonized Madagascar is thought to have been small and nocturnal. More specifically, it is thought to have had adapiform-like cranialSkull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
anatomy—particularly the cranial foramina and the middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
—comparable to that of lemurids
Lemuridae
Lemuridae is a family of prosimian primates native to Madagascar, and one of five families commonly known as lemurs. These animals were thought to be the evolutionary predecessors of monkeys and apes, but this is no longer considered correct...
, while being similar to cheirogaleids
Cheirogaleidae
Cheirogaleidae is the family of strepsirrhine primates that contains the various dwarf and mouse lemurs. Like all other lemurs, cheirogaleids live exclusively on the island of Madagascar.-Characteristics:...
in dentition
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...
and postcranial anatomy
Postcrania
Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...
.
Nothing definitive is known about the island's biogeography
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
at the time of the colonization, however, the paleoclimate
Paleoclimatology
Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...
(ancient weather patterns) may have been affected by the Madagascar's location below the subtropical ridge
Subtropical ridge
The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...
at 30° S latitude and disruption of the weather patterns by India as it drifted northward. Both would have created a drying effect on Madagascar, and as a result, the arid spiny bush
Madagascar spiny thickets
The Madagascar spiny thickets is an ecoregion in Madagascar. The vegetation type is found on poor substrates with low, erratic winter rainfall. An estimated 14,000 to is covered with this habitat, all in the southwest of the country...
that is currently found in the south and southwest of Madagascar would have dominated the island. This would have placed strong selection pressure
Evolutionary pressure
Any cause that reduces reproductive success in a proportion of a population, potentially exerts evolutionary pressure or selection pressure. With sufficient pressure, inherited traits that mitigate its effects - even if they would be deleterious in other circumstances - can become widely spread...
for drought tolerance
Drought tolerance
Drought tolerance refers to the degree to which a plant is adapted to arid or drought conditions. Desiccation tolerance is an extreme degree of drought tolerance...
on the inhabitants of the island between the Cretaceous and the Eocene. As Madagascar edged above the subtropical ridge and India moved closer to Asia, the climate became less dry and the arid spiny bush retreated to the south and southwest.
Lemurs have diversified greatly since first reaching Madagascar. The aye-aye and its extinct relations are thought to have diverged first, shortly after colonization. According to molecular studies, there have since been two major episodes of diversification, from which all other known extant and extinct family lineages emerged. The remaining families diverged in the first diversification episode, during a 10 to 12 million-year window between the Late Eocene (42 mya) and into the Oligocene (30 mya). The dates for this divergence window span the Eocene–Oligocene extinction event, during which time climate cooling took place and changes in ocean currents altered weather patterns. Outside of Madagascar, these dates also coincide with the divergence of the lorisiform primates and five major clades of squirrels, all occupying niches similar to those of lemurs. The dates do not suggest that increased predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
drove family-level divergence since the first carnivores arrived on the island between 24 and 18 mya.
The second major episode of diversification occurred during the Late Miocene, approximately 8 to 12 mya, and included the true lemurs (Eulemur) and the mouse lemur
Mouse lemur
The mouse lemurs are nocturnal lemurs of the genus Microcebus. Like all lemurs, mouse lemurs are native to Madagascar.Mouse lemurs have a combined head, body and tail length of less than , making them the smallest primates ; however, their weight fluctuates in response to daylight duration.Mouse...
s (Microcebus). This event coincided with the beginning of the Indian monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
s, the last major change in climate to affect Madagascar. The populations of both the true lemurs and mouse lemurs were thought to have diverged due to habitat fragmentation
Habitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
when humans arrived on the island roughly 2,000 years ago. Only recently has molecular research shown a more distant split in these genera. Most surprising were the mouse lemurs, a group which is now thought to contain cryptic species
Cryptic species complex
In biology, a cryptic species complex is a group of species which satisfy the biological definition of species—that is, they are reproductively isolated from each other—but whose morphology is very similar ....
, meaning they are indistinguishable from each other based solely on appearance. In contrast, true lemurs are easier to distinguish and exhibit sexual dichromatism. Studies in karyology
Karyotype
A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...
, molecular genetics, and biogeographic patterns
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
have also assisted in understanding their phylogeny and diversification. Although the divergence estimates for these two genera are imprecise, they overlap with a change to a wetter climate in Madagascar, as new weather patterns generated monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
s and likely influenced the plant life.
This difference in evolutionary divergence between the two genera may be due to differences in their activity patterns. True lemurs are often diurnal, allowing potential mates to distinguish each other as well as other related species visually. Mouse lemurs, on the other hand, are nocturnal, reducing their ability to use visual signals for mate selection
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
. Instead, they use olfactory
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
and auditory
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
signaling. For these reasons, true lemurs may have evolved sexual dichromatism while mouse lemurs evolved to be cryptic species.
Distribution and diversity
Since their arrival on Madagascar, lemurs have diversified both in behavior and morphology. Their diversity rivals that of the monkeys and apes found throughout the rest of the world, especially when the recently extinct subfossil lemurSubfossil lemur
Subfossil lemurs are lemurs from Madagascar that are represented by recent remains dating from nearly 26,000 years ago to approximately 560 years ago. They include both living and extinct species, although the term more frequently refers to the extinct giant lemurs...
s are considered. Ranging in size from the 30 g (1.1 oz) Madame Berthe's mouse lemur
Madame Berthe's Mouse Lemur
Madame Berthe's mouse lemur or Berthe's mouse lemur is the smallest of the mouse lemurs and the smallest primate in the world; the average body length is and seasonal weight is around...
, the world's smallest primate, to the extinct 160 – Archaeoindris fontoynonti, lemurs evolved diverse forms of locomotion, varying levels of social complexity, and unique adaptations to the local climate. They went on to fill many niches normally occupied by monkeys, squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
s, woodpecker
Woodpecker
Woodpeckers are near passerine birds of the order Piciformes. They are one subfamily in the family Picidae, which also includes the piculets and wrynecks. They are found worldwide and include about 180 species....
s, and large grazing ungulate
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...
s. In addition to the incredible diversity between lemur families, there has also been great diversification among closely related lemurs. Yet despite separation by geographical barriers
Allopatric speciation
Allopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become isolated due to geographical changes such as mountain building or social changes such as emigration...
or by niche differentiation in sympatry
Sympatry
In biology, two species or populations are considered sympatric when they exist in the same geographic area and thus regularly encounter one another. An initially-interbreeding population that splits into two or more distinct species sharing a common range exemplifies sympatric speciation...
, occasionally hybridization can occur. Lemur diversification has also created generalist species
Generalist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...
, such as the true lemurs of northern Madagascar, which are very adaptable, mostly nondescript, and found throughout most of the island's forests.
Most of the 99 living lemur taxa are found only on Madagascar. Two species, the common brown lemur
Common Brown Lemur
The common brown lemur , or brown lemur, is a species of lemur in the Lemuridae family. It is found in Madagascar and Mayotte.-Range:...
(Eulemur fulvus) and the mongoose lemur
Mongoose Lemur
The mongoose lemur is a lemur ranging from 12 to 18 inches long plus a tail of 16 to 25 inches. The mongoose lemur lives in dry deciduous forests on the island of Madagascar as well as in the humid forests on the islands of the Comoros...
(Eulemur mongoz), can also be found on the Comoro Islands
Comoro Islands
The Comoros Islands form an archipelago of volcanic islands situated off the south-east coast of Africa, to the east of Mozambique and north-west of Madagascar. They are divided between the sovereign state of Comoros and the French overseas department of Mayotte...
, although it is assumed that both species were introduced to the islands from northwestern Madagascar by humans within the last few hundred years. Molecular studies on Eulemur fulvus fulvus (from the mainland) and E. f. mayottensis (from the Comoro Islands) and on Comoro and mainland mongoose lemurs have supported this assumption by showing no genetic differences between the two populations. Because all lemurs, including these two brown lemur species, are only native to the island of Madagascar, they are considered to be endemic.
Historically, lemurs ranged across the entire island inhabiting a wide variety of habitats
Geography of Madagascar
Madagascar is an island in the Indian Ocean off the eastern coast of southern Africa, east of Mozambique. It is the fourth largest island in the world. The highest point is Maromokotro, in the Tsaratanana Massif region in the north of the island, at . The capital Antananarivo is in the Hauts...
, including dry deciduous forests
Madagascar dry deciduous forests
The Madagascar dry deciduous forests represent a tropical dry forest ecoregion generally situated in the western part of Madagascar. The area has high numbers of endemic plant and animal species but has suffered large-scale clearance for agriculture...
, lowland forests
Madagascar lowland forests
The Madagascar lowland forests are a tropical moist broadleaf forest ecoregion, found on the eastern coast of the island of Madagascar.-Setting:...
, spiny thickets
Madagascar spiny thickets
The Madagascar spiny thickets is an ecoregion in Madagascar. The vegetation type is found on poor substrates with low, erratic winter rainfall. An estimated 14,000 to is covered with this habitat, all in the southwest of the country...
, subhumid forests
Madagascar subhumid forests
The Madagascar subhumid forests are a tropical moist broadleaf forest ecoregion which originally covered most of the Central Highlands of the island of Madagascar.-Setting:...
, montane forest
Cloud forest
A cloud forest, also called a fog forest, is a generally tropical or subtropical evergreen montane moist forest characterized by a persistent, frequent or seasonal low-level cloud cover, usually at the canopy level. Cloud forests often exhibit an abundance of mosses covering the ground and...
, and mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
. Today, their collective range is restricted to 10% of the island, or approximately 60000 km² (23,166.1 sq mi). Most of the remaining forests and lemurs are found along the periphery of the island. The center of the island, the Hauts-Plateaux
Central Highlands (Madagascar)
The Central Highlands, Central High Plateau, or Hauts-Plateaux are a mountainous biogeographical region in central Madagascar. They include the contiguous part of the island's interior above 800 m altitude...
, was converted by early settlers to rice paddies
Paddy field
A paddy field is a flooded parcel of arable land used for growing rice and other semiaquatic crops. Paddy fields are a typical feature of rice farming in east, south and southeast Asia. Paddies can be built into steep hillsides as terraces and adjacent to depressed or steeply sloped features such...
and grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
through slash-and-burn agriculture
Slash and burn
Slash-and-burn is an agricultural technique which involves cutting and burning of forests or woodlands to create fields. It is subsistence agriculture that typically uses little technology or other tools. It is typically part of shifting cultivation agriculture, and of transhumance livestock...
, known locally as tavy. As erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
depleted the soil, the cyclical forest regrowth and burning ended as the forest gradually failed to return. Today, the level of flora
Flora
Flora is the plant life occurring in a particular region or time, generally the naturally occurring or indigenous—native plant life. The corresponding term for animals is fauna.-Etymology:...
l diversity increases with precipitation, from the dry southern forests to the wetter norther forests to the rainforest
Rainforest
Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...
s along the east coast. Increased foliage corresponds to increased fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
l diversity, including the diversity and complexity of lemur communities.
Having evolved in Madagascar's challenging environment, replete with poor soils, extreme shifts in poor, seasonal plant productivity, and devastating climatic events such as extended droughts and annual cyclones, lemurs have adopted unique combinations of unusual traits to survive, distinguishing them significantly from other primates. In response to limited, seasonal resources, lemurs may exhibit seasonal fat storage, hypometabolism
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...
(including torpor
Torpor
Torpor, sometimes called temporary hibernation is a state of decreased physiological activity in an animal, usually characterized by a reduced body temperature and rate of metabolism. Animals that go through torpor include birds and some mammals such as mice and bats...
and hibernation
Hibernation
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food supplies are limited, tapping energy reserves, body fat, at a slow rate...
in some cheirogaleids
Cheirogaleidae
Cheirogaleidae is the family of strepsirrhine primates that contains the various dwarf and mouse lemurs. Like all other lemurs, cheirogaleids live exclusively on the island of Madagascar.-Characteristics:...
), small group sizes, low encephalization
Encephalization
Encephalization is defined as the amount of brain mass exceeding that related to an animal's total body mass. Quantifying an animal's encephalization has been argued to be directly related to that animal's level of intelligence. Aristotle wrote in 335 B.C...
(relative brain size), cathemeral
Cathemeral
A cathemeral organism is one that has sporadic and random intervals of activity during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood are performed...
ity (activity both day and night), and/or strict breeding seasons
Seasonal breeder
Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the births at a time optimal for the survival of the young in terms of factors such as temperature, food and water. Related sexual interest and behaviors are expressed...
. Secondarily, extreme resource limitations and seasonal breeding are thought to have resulted in three other relatively common lemur traits: female dominance
Dominance hierarchy
A dominance hierarchy is the organization of individuals in a group that occurs when competition for resources leads to aggression...
, sexual monomorphism (lack of size differences between the sexes), and male-male competition for mates involving low levels of agonism (conflict), such as sperm competition
Sperm competition
Sperm competition is a term used to refer to the competitive process between spermatozoa of two different males to fertilize an egg of a lone female. Competition occurs whenever females engage in promiscuous mating to increase their chances in producing more viable offspring...
.
The arrival of humans on the island 1,500 to 2,000 years ago has taken a significant toll, not only on the size of lemur populations, but also on their diversity. Due to habitat destruction
Habitat destruction
Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...
and hunting, at least 17 species and 8 genera have gone extinct and the populations of all species have decreased. A couple of species once thought to have gone extinct have since been rediscovered. The hairy-eared dwarf lemur
Hairy-eared Dwarf Lemur
The hairy-eared dwarf lemur , or hairy-eared mouse lemur, is a nocturnal lemur endemic to Madagascar. It is the only member of the genus Allocebus. This species is critically endangered and the population is estimated at 100-1000 individuals. They all live a single location in the northeastern part...
(Allocebus trichotis) was only known from five museum specimens, most collected in the late 19th century and one in 1965. It was rediscovered in 1989 and has since been identified in five national parks, although it is very rare within its range. Likewise, the greater bamboo lemur
Greater Bamboo Lemur
The Greater Bamboo Lemur , also known as the Broad-nosed Bamboo Lemur and the Broad-nosed Gentle Lemur, is the largest bamboo lemur, at over five pounds or nearly 2.5 kilograms. It has greyish brown fur and white ear tufts, and has a head-body length of around one and a half feet, or forty to...
(Prolemur simus) was thought to be extinct as recently as the late 1970s, but a population was located near Ranomafana National Park
Ranomafana National Park
Ranomafana National Park is located in the southeastern part of Madagascar in Haute Matsiatra and Vatovavy-Fitovinany. With more than 41,600 hectares of moist forest climate, the park is home to several rare species of flora and fauna such as the lemur...
in the late 1980s. Historically, it had a much wider geographic distribution, shown by subfossil
Subfossil
Subfossil refers to remains whose fossilization process is not complete, either for lack of time or because the conditions in which they were buried were not optimal for fossilization....
remains, but today it remains one of the world's 25 most endangered primates. One distinctive morph
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
(possibly a species or subspecies) of sifaka
Sifaka
Sifakas are a genus of lemur from the family Indriidae within the order Primates. Their name of the family is an onomatopoeia of their characteristic "shi-fak" alarm call. Like all lemurs, they are found only on the island of Madagascar...
, has not been so fortunate, having been extirpated
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
from all known localities. Unless trends change, extinctions are likely to continue.
Until recently, giant species of lemur existed on Madagascar. Now represented only by recent or subfossil
Subfossil
Subfossil refers to remains whose fossilization process is not complete, either for lack of time or because the conditions in which they were buried were not optimal for fossilization....
remains, they were modern forms and are counted as part of the rich lemur diversity that evolved in isolation. Some of their adaptations were unlike those seen in lemurs today. All 17 extinct lemurs were larger than the extant forms, some weighing as much as 200 kg (440.9 lb), and are thought to have been active during the day. Not only were they unlike the living lemurs in both size and appearance, they also filled ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s that no longer exist or are now left unoccupied. Large parts of Madagascar, which are now devoid of forests and lemurs, once hosted diverse primate communities that included more than 20 species covering the full range of lemur sizes.