Strepsirrhini or Strepsirhini (; ) is a
suborder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
of
primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...
s that includes the
lemuriform primates, which consist of the
lemurs of
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...
,
galagos ("bushbabies") and
pottos from
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, and the
lorises from
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
and
southeast Asia
Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
. Collectively they are referred to as strepsirrhines. Also belonging to the suborder are the extinct
adapiform
Adapiformes is a group of early primates. Adapiforms radiated throughout much of the northern continental mass (now Europe, Asia and North America), reaching as far south as northern Africa and tropical Asia. They existed from the Eocene to the ...
primates which thrived during the
Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...
in Europe, North America, and Asia, but disappeared from most of the
Northern Hemisphere
The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
as the climate cooled. Adapiforms are sometimes referred to as being "lemur-like", although the diversity of both lemurs and adapiforms does not support this comparison.
Strepsirrhines are defined by their "wet" (moist)
rhinarium (the tip of the snout) – hence the colloquial but inaccurate term "wet-nosed" – similar to the rhinaria of canines and felines. They also have a smaller brain than comparably sized
simian
The simians, anthropoids, or higher primates are an infraorder (Simiiformes ) of primates containing all animals traditionally called monkeys and apes. More precisely, they consist of the parvorders New World monkeys (Platyrrhini) and Cat ...
s, large
olfactory lobes
The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OFC) ...
for smell, a
vomeronasal organ
The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary olfactory (smell) sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth (the hard palate) in various tetrapo ...
to detect
pheromones, and a
bicornuate uterus with an
epitheliochorial placenta. Their eyes contain a
reflective layer to improve their
night vision
Night vision is the ability to see in low-light conditions, either naturally with scotopic vision or through a night-vision device. Night vision requires both sufficient spectral range and sufficient intensity range. Humans have poor night v ...
, and their
eye sockets include a
ring of bone around the eye, but they lack a wall of thin bone behind it. Strepsirrhine primates produce their own
vitamin C
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) ...
, whereas
haplorhine
Haplorhini (), the haplorhines ( Greek for "simple-nosed") or the "dry-nosed" primates, is a suborder of primates containing the tarsiers and the simians (Simiiformes or anthropoids), as sister of the Strepsirrhini ("moist-nosed"). The name is ...
primates must obtain it from their diets. Lemuriform primates are characterized by a
toothcomb, a specialized set of teeth in the front, lower part of the mouth mostly used for combing fur during
grooming.
Many of today's living strepsirrhines are
endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...
due to
habitat destruction
Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...
, hunting for
bushmeat, and live capture for the
exotic pet trade. Both living and extinct strepsirrhines are behaviorally diverse, although all are primarily
arboreal (tree-dwelling). Most living lemuriforms are
nocturnal
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed sens ...
, while most adapiforms were
diurnal. Both living and extinct groups primarily fed on
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in partic ...
,
leaves
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...
, and
insects.
Etymology
The
taxonomic name Strepsirrhini derives from the
Greek ''strepsis'' "a turning round" and ''rhis'' "nose, snout, (in pl.) nostrils" (
GEN ''rhinos''), which refers to the appearance of the sinuous (comma-shaped) nostrils on the
rhinarium or wet nose. The name was first used by French
naturalist Étienne Geoffroy Saint-Hilaire
Étienne Geoffroy Saint-Hilaire (15 April 177219 June 1844) 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 ...
in 1812 as a
subordinal rank comparable to Platyrrhini (
New World monkeys) and Catarrhini (
Old World monkeys). In his
description, he mentioned "''Les narines terminales et sinueuses''" ("Nostrils terminal and winding").
When British
zoologist
Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and d ...
Reginald Innes Pocock
Reginald Innes Pocock Fellow of the Royal Society, F.R.S. (4 March 1863 – 9 August 1947) was a British zoologist.
Pocock was born in Clifton, Bristol, the fourth son of Rev. Nicholas Pocock (historian), Nicholas Pocock and Edith Prichard. He ...
revived Strepsirrhini and defined
Haplorhini in 1918, he omitted the second "r" from both ("Strepsi
rhini" and "Haplo
rhini" instead of "Strepsi
rrhini" and "Haplo
rrhini"), although he did not remove the second "r" from Platyrrhini or Catarrhini, both of which were also named by É. Geoffroy in 1812. Following Pocock, many researchers continued to spell Strepsirrhini with a single "r" until
primatologists Paulina Jenkins and Prue Napier pointed out the error in 1987.
Evolutionary history
Strepsirrhines include the extinct adapiforms and the
lemuriform primates, which include lemurs and lorisoids (
lorises,
pottos, and
galagos). Strepsirrhines diverged from the haplorhine primates near the beginning of the primate
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
between 55 and 90 mya. Older divergence dates are based on
genetic analysis estimates, while younger dates are based on the scarce
fossil record. Lemuriform primates may have evolved from either
cercamoniines or
sivaladapids, both of which were adapiforms that may have originated in Asia. They were once thought to have evolved from
adapids, a more specialized and younger branch of adapiform primarily from Europe.
Lemurs
rafted from Africa to Madagascar between 47 and 54 mya, whereas the lorises split from the African galagos around 40 mya and later colonized Asia. The lemuriforms, and particularly the lemurs of Madagascar, are often portrayed inappropriately as "
living fossil
A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living foss ...
s" or as examples of "
basal", or "inferior" primates. These views have historically hindered the understanding of
mammalian evolution and the evolution of strepsirrhine traits, such as their reliance on smell (
olfaction
The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
In humans, ...
), characteristics of their skeletal anatomy, and their brain size, which is relatively small. In the case of lemurs,
natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
has driven this isolated population of primates to diversify significantly and fill a rich variety of
ecological niche
In ecology, a niche is the match of a species to a specific environmental condition.
Three variants of ecological niche are described by
It describes how an organism or population responds to the distribution of resources and competitors (for ...
s, despite their smaller and less complex brains compared to simians.
Unclear origin
The divergence between strepsirrhines, simians, and tarsiers likely followed almost immediately after primates first evolved. Although few fossils of
living
Living or The Living may refer to:
Common meanings
*Life, a condition that distinguishes organisms from inorganic objects and dead organisms
** Living species, one that is not extinct
*Personal life, the course of an individual human's life
* H ...
primate groups – lemuriforms, tarsiers, and simians – are known from the Early to Middle Eocene, evidence from genetics and recent fossil finds both suggest they may have been present during the early
adaptive radiation
In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic in ...
.
The origin of the earliest primates that the simians and tarsiers both evolved from is a mystery. Both their place of origin and the group from which they emerged are uncertain. Although the
fossil record demonstrating their initial
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
across the Northern Hemisphere is very detailed, the fossil record from the tropics (where primates most likely first developed) is very sparse, particularly around the time that primates and other major
clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
s of
eutherian mammals first appeared.
Lacking detailed tropical fossils,
geneticists and primatologists have used genetic analyses to determine the relatedness between primate lineages and the amount of time since they
diverged. Using this
molecular clock
The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleo ...
, divergence dates for the major primate lineages have suggested that primates evolved more than 80–90 mya, nearly 40 million years before the first examples appear in the fossil record.
The early primates include both
nocturnal
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed sens ...
and
diurnal small-bodied species, and all were arboreal, with hands and feet specially adapted for maneuvering on small branches.
Plesiadapiforms
Plesiadapiformes (" Adapid-like" or "near Adapiformes") is a group of Primates, a sister of the Dermoptera. While none of the groups normally directly assigned to this group survived, the group appears actually not to be literally extinct (in ...
from the early
Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pala ...
are sometimes considered "archaic primates", because their teeth resembled those of early primates and because they possessed adaptations to living in trees, such as a divergent big toe (
hallux
Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plan ...
). Although plesiadapiforms were closely related to primates, they may represent a
paraphyletic
In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
group from which primates may or may not have directly evolved, and some
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
may have been more closely related to
colugos, which are thought to be more closely related to primates.
The first true primates (euprimates) do not appear in the fossil record until the early
Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...
(~55 mya), at which point they radiated across the Northern Hemisphere during a brief period of rapid
global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
known as the
Paleocene–Eocene Thermal Maximum
The Paleocene–Eocene thermal maximum (PETM), alternatively (ETM1), and formerly known as the "Initial Eocene" or "", was a time period with a more than 5–8 °C global average temperature rise across the event. This climate event o ...
. These first primates included ''
Cantius'', ''
Donrussellia'', ''
Altanius
''Altanius'' is a genus of extinct primates found in the early Eocene of Mongolia. Though its phylogenetic relationship is questionable, many have placed it as either a primitive omomyid or as a member of the sister group to both adapoids and o ...
'', and ''
Teilhardina
''Teilhardina'' (, ) was an early marmoset-like primate that lived in Europe, North America and Asia during the Early Eocene epoch, about 56-47 million years ago. The paleontologist George Gaylord Simpson is credited with naming it after the Fr ...
'' on the northern continents, as well as the more questionable (and fragmentary) fossil ''
Altiatlasius'' from Paleocene Africa. These earliest
fossil primates are often divided into two groups, adapiforms and
omomyiforms. Both appeared suddenly in the fossil record without
transitional forms to indicate ancestry, and both groups were rich in diversity and were widespread throughout the Eocene.
The last branch to develop were the adapiforms, a diverse and widespread group that thrived during the
Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...
(56 to 34 million years ago
Mya_(unit)">mya.html" ;"title="Mya_(unit).html" ;"title="/nowiki>Mya (unit)">mya">Mya_(unit).html" ;"title="/nowiki>Mya (unit)">mya/nowiki>) in Europe, North America, and Asia. They disappeared from most of the Northern Hemisphere
The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
as the climate cooled: The last of the adapiforms died out at the end of the Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
(~7 mya).
Adapiform evolution
Adapiform primates are extinct strepsirrhines that shared many anatomical similarities with lemurs. They are sometimes referred to as lemur-like primates, although the diversity of both lemurs and adapiforms do not support this analogy.
Like the living strepsirrhines, adapiforms were extremely diverse, with at least 30 genera and 80 species known from the fossil record as of the early 2000s. They diversified across Laurasia
Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...
during the Eocene, some reaching North America via a land bridge.They were among the most common mammals found in the fossil beds from that time. A few rare species have also been found in northern Africa. The most basal of the adapiforms include the genera ''Cantius'' from North America and Europe and ''Donrussellia'' from Europe. The latter bears the most ancestral traits, so it is often considered a sister group
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
or stem group of the other adapiforms.
Adapiforms are often divided into three major groups:
* Adapids were most commonly found in Europe, although the oldest specimens ('' Adapoides'' from middle Eocene China) indicate that they most likely evolved in Asia and immigrated. They died out in Europe during the Grande Coupure, part of a significant extinction event
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...
at the end of the Eocene.
* Notharctids, which most closely resembled some of Madagascar's lemurs, come from Europe and North America. The European branch is often referred to as cercamoniines. The North American branch thrived during the Eocene, but did not survive into the Oligocene
The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...
. Like the adapids, the European branch were also extinct by the end of the Eocene.
* Sivaladapids of southern and eastern Asia are best known from the Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
, and the only adapiforms to survive past the Eocene/Oligocene boundary (~34 mya). Their relationship to the other adapiforms remains unclear. They had vanished before the end of the Miocene (~7 mya).
The relationship between adapiform and lemuriform primates has not been clearly demonstrated, so the position of adapiforms as a paraphyletic stem group is questionable. Both molecular clock data and new fossil finds suggest that the lemuriform divergence from the other primates and the subsequent lemur-lorisoid split both predate the appearance of adapiforms in the early Eocene. New calibration methods may reconcile the discrepancies between the molecular clock and the fossil record, favoring more recent divergence dates. The fossil record suggests that the strepsirrhine adapiforms and the haplorhine omomyiforms had been evolving independently before the early Eocene, although their most basal members share enough dental similarities to suggest that they diverged during the Paleocene (66–55 mya).
Lemuriform evolution
Lemuriform origins are unclear and debated. American paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Philip Gingerich proposed that lemuriform primates evolved from one of several genera of European adapids based on similarities between the front lower teeth of adapids and the toothcomb of extant lemuriforms; however, this view is not strongly supported due to a lack of clear transitional fossils. Instead, lemuriforms may be descended from a very early branch of Asian cercamoniines or sivaladapids that migrated to northern Africa.
Until discoveries of three 40 million-year-old fossil lorisoids ('' Karanisia'', '' Saharagalago'', and '' Wadilemur'') in the El Fayum deposits of Egypt between 1997 and 2005, the oldest known lemuriforms had come from the early Miocene (~20 mya) of Kenya
)
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, image_map =
, map_caption =
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, capital = Nairobi
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and Uganda
}), is a landlocked country in East Africa. The country is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the south-west by Rwanda, and to the south by Tanzania. The ...
. These newer finds demonstrate that lemuriform primates were present during the middle Eocene in Afro-Arabia and that the lemuriform lineage and all other strepsirrhine taxa had diverged before then. ''Djebelemur
''Djebelemur'' is an extinct genus of early strepsirrhine primate from the late early or early middle Eocene period from the Chambi locality in Tunisia. Although they probably lacked a toothcomb, a specialized dental structure found in living l ...
'' from Tunisia
)
, image_map = Tunisia location (orthographic projection).svg
, map_caption = Location of Tunisia in northern Africa
, image_map2 =
, capital = Tunis
, largest_city = capital
, ...
dates to the late early or early middle Eocene (52 to 46 mya) and has been considered a cercamoniine, but also may have been a stem lemuriform. Azibiids from Algeria
)
, image_map = Algeria (centered orthographic projection).svg
, map_caption =
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, capital = Algiers
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date to roughly the same time and may be a sister group of the djebelemurids. Together with ''Plesiopithecus
''Plesiopithecus '' is an extinct genus of early strepsirrhine primate from the late Eocene.
Anatomy
Originally described from the right mandible (lower jaw), its confusing anatomy resulted in it being classified as an ape—its name translate ...
'' from the late Eocene Egypt, the three may qualify as the stem lemuriforms from Africa.
Molecular clock estimates indicate that lemurs and the lorisoids diverged in Africa during the Paleocene, approximately 62 mya. Between 47 and 54 mya, lemurs dispersed to Madagascar by rafting. In isolation, the lemurs diversified and filled the niches often filled by monkeys and apes today. In Africa, the lorises and galagos diverged during the Eocene, approximately 40 mya. Unlike the lemurs in Madagascar, they have had to compete with monkeys and apes, as well as other mammals.
History of classification
The taxonomy of strepsirrhines is controversial and has a complicated history. Confused taxonomic terminology and oversimplified anatomical comparisons have created misconceptions about primate and strepsirrhine phylogeny
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological s ...
, illustrated by the media attention surrounding the single "Ida" fossil in 2009.
Strepsirrhine primates were first grouped under the genus ''Lemur'' by Swedish taxonomist Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, ...
in the 10th edition of ''Systema Naturae'' published in 1758. At the time, only three species were recognized, one of which (the colugo) is no longer recognized as a primate. In 1785, Dutch naturalist Pieter Boddaert
Pieter Boddaert (1730 – 6 May 1795) was a Dutch physician and naturalist.
Early life, family and education
Boddaert was the son of a Middelburg jurist and poet by the same name (1694–1760). The younger Pieter obtained his M.D. at the Unive ...
divided the genus ''Lemur'' into two genera: ''Prosimia'' for the lemurs, colugos, and tarsiers and ''Tardigradus'' for the lorises. Ten years later, É. Geoffroy and Georges Cuvier
Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in na ...
grouped the tarsiers and galagos due to similarities in their hindlimb morphology, a view supported by German zoologist Johann Karl Wilhelm Illiger, who placed them in the family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Macrotarsi while placing the lemurs and tarsiers in the family Prosimia (Prosimii) in 1811. The use of the tarsier-galago classification continued for many years until 1898, when Dutch zoologist Ambrosius Hubrecht
Ambrosius Arnold Willem Hubrecht (2 March 1853, in Rotterdam – 21 March 1915, in Utrecht) was a Dutch zoologist.
Hubrecht studied zoology at Utrecht University with Harting and Donders, for periods joining Selenka in Leiden and later Er ...
demonstrated two different types of placentation
Placentation refers to the formation, type and structure, or arrangement of the placenta. The function of placentation is to transfer nutrients, respiratory gases, and water from maternal tissue to a growing embryo, and in some instances to remo ...
(formation of a placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
) in the two groups.
English comparative anatomist William Henry Flower
Sir William Henry Flower (30 November 18311 July 1899) was an English surgeon, museum curator and comparative anatomist, who became a leading authority on mammals and especially on the primate brain. He supported Thomas Henry Huxley in an ...
created the suborder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
Lemuroidea in 1883 to distinguish these primates from the simians, which were grouped under English biologist
A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual cell, a multicellular organism, or a community of interacting populations. They usually specialize ...
St. George Jackson Mivart's suborder Anthropoidea (=Simiiformes). According to Flower, the suborder Lemuroidea contained the families Lemuridae (lemurs, lorises, and galagos), Chiromyidae (aye-aye
The aye-aye (''Daubentonia madagascariensis'') is a long-fingered lemur, a strepsirrhine primate native to Madagascar with rodent-like teeth that perpetually grow and a special thin middle finger.
It is the world's largest nocturnal primate. ...
), and Tarsiidae (tarsiers). Lemuroidea was later replaced by Illiger's suborder Prosimii. Many years earlier, in 1812, É. Geoffroy first named the suborder Strepsirrhini, in which he included the tarsiers. This taxonomy went unnoticed until 1918, when Pocock compared the structure of the nose and reinstated the use of the suborder Strepsirrhini, while also moving the tarsiers and the simians into a new suborder, Haplorhini. It was not until 1953, when British anatomist William Charles Osman Hill wrote an entire volume on strepsirrhine anatomy, that Pocock's taxonomic suggestion became noticed and more widely used. Since then, primate taxonomy has shifted between Strepsirrhini-Haplorhini and Prosimii-Anthropoidea multiple times.
Most of the academic literature provides a basic framework for primate taxonomy, usually including several potential taxonomic schemes. Although most experts agree upon phylogeny
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological s ...
, many disagree about nearly every level of primate classification.
Controversies
The most commonly recurring debate in primatology during the 1970s, 1980s, and early 2000s concerned the phylogenetic position of tarsiers compared to both simians and the other prosimians. Tarsiers are most often placed in either the suborder Haplorhini with the simians or in the suborder Prosimii with the strepsirrhines. Prosimii is one of the two traditional primate suborders and is based on evolutionary grades (groups united by anatomical traits) rather than phylogenetic clades, while the Strepsirrhini-Haplorrhini taxonomy was based on evolutionary relationships. Yet both systems persist because the Prosimii-Anthropoidea taxonomy is familiar and frequently seen in the research literature and textbooks.
Strepsirrhines are traditionally characterized by several symplesiomorphic
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, and ...
(ancestral) traits not shared with the simians, particularly the rhinarium. Other symplesiomorphies include long snout
A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is ...
s, convoluted maxilloturbinals, relatively large olfactory bulb
The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex ...
s, and smaller brains. The toothcomb is a synapomorphy (shared, derived trait) seen among lemuriforms, although it is frequently and incorrectly used to define the strepsirrhine clade. Strepsirrhine primates are also united in possessing an epitheliochorial placenta. Unlike the tarsiers and simians, strepsirrhines are capable of producing their own and do not need it supplied in their diet. Further genetic evidence for the relationship between tarsiers and simians as a haplorhine clade is the shared possession of three SINE markers.
Because of their historically mixed assemblages which included tarsiers and close relatives of primates, both Prosimii and Strepsirrhini have been considered wastebasket taxa
Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically defined ...
for "lower primates". Regardless, the strepsirrhine and haplorrhine clades are generally accepted and viewed as the preferred taxonomic division. Yet tarsiers still closely resemble both strepsirrhines and simians in different ways, and since the early split between strepsirrhines, tarsiers and simians is ancient and hard to resolve, a third taxonomic arrangement with three suborders is sometimes used: Prosimii, Tarsiiformes, and Anthropoidea. More often, the term "prosimian" is no longer used in official taxonomy, but is still used to illustrate the behavioral ecology of tarsiers relative to the other primates.
In addition to the controversy over tarsiers, the debate over the origins of simians once called the strepsirrhine clade into question. Arguments for an evolutionary link between adapiforms and simians made by paleontologists Gingerich, Elwyn L. Simons
Elwyn LaVerne Simons (July 14, 1930 – March 6, 2016) was an American paleontologist, paleozoologist, and a wildlife conservationist for primates. He was known as the father of modern primate paleontology for his discovery of some of humanki ...
, Tab Rasmussen, and others could have potentially excluded adapiforms from Strepsirrhini. In 1975, Gingerich proposed a new suborder, Simiolemuriformes, to suggest that strepsirrhines are more closely related to simians than tarsiers. However, no clear relationship between the two had been demonstrated by the early 2000s. The idea reemerged briefly in 2009 during the media attention surrounding ''Darwinius masillae
''Darwinius'' is a genus within the infraorder Adapiformes, a group of basal strepsirrhine primates from the middle Eocene epoch. Its only known species, ''Darwinius masillae'', lived approximately 47 million years ago (Lutetian stage) based on ...
'' (dubbed "Ida"), a cercamoniine from Germany that was touted as a " missing link between humans and earlier primates" (simians and adapiforms). However, the cladistic analysis was flawed and the phylogenetic inferences and terminology were vague. Although the authors noted that ''Darwinius'' was not a "fossil lemur", they did emphasize the absence of a toothcomb, which adapiforms did not possess.
Infraordinal classification and clade terminology
Within Strepsirrhini, two common classifications include either two infraorders (Adapiformes and Lemuriformes) or three infraorders (Adapiformes, Lemuriformes, Lorisiformes). A less common taxonomy places the aye-aye (Daubentoniidae) in its own infraorder, Chiromyiformes. In some cases, plesiadapiforms are included within the order Primates, in which case Euprimates is sometimes treated as a suborder, with Strepsirrhini becoming an infraorder, and the Lemuriformes and others become parvorders. Regardless of the infraordinal taxonomy, Strepsirrhini is composed of three ranked superfamilies and 14 families, seven of which are extinct. Three of these extinct families included the recently extinct giant lemurs of Madagascar, many of which died out within the last 1,000 years following human arrival on the island.
When Strepsirrhini is divided into two infraorders, the clade containing all toothcombed primates can be called "lemuriforms". When it is divided into three infraorders, the term "lemuriforms" refers only to Madagascar's lemurs, and the toothcombed primates are referred to as either "crown strepsirrhines" or "extant strepsirrhines". Confusion of this specific terminology with the general term "strepsirrhine", along with oversimplified anatomical comparisons and vague phylogenetic inferences, can lead to misconceptions about primate phylogeny and misunderstandings about primates from the Eocene, as seen with the media coverage of ''Darwinius''. Because the skeletons of adapiforms share strong similarities with those of lemurs and lorises, researchers have often referred to them as "primitive" strepsirrhines, lemur ancestors, or a sister group to the living strepsirrhines. They are included in Strepsirrhini, and are considered basal members of the clade. Although their status as true primates is not questioned, the questionable relationship between adapiforms and other living and fossil primates leads to multiple classifications within Strepsirrhini. Often, adapiforms are placed in their own infraorder due to anatomical differences with lemuriforms and their unclear relationship. When shared traits with lemuriforms (which may or may not be synapomorphic) are emphasized, they are sometimes reduced to families within the infraorder Lemuriformes (or superfamily Lemuroidea).
The first fossil primate described was the adapiform '' Adapis parisiensis'' by French naturalist Georges Cuvier
Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in na ...
in 1821, who compared it to a hyrax
Hyraxes (), also called dassies, are small, thickset, herbivorous mammals in the order Hyracoidea. Hyraxes are well-furred, rotund animals with short tails. Typically, they measure between long and weigh between . They are superficially simila ...
("''le Daman''"), then considered a member of a now obsolete group called pachyderms
Pachydermata (meaning 'thick skin', from the Greek grc, παχύς, pachys, thick, label=none, and grc, δέρμα, derma, skin, label=none) is an obsolete order of mammals described by Gottlieb Storr, Georges Cuvier, and others, at one time re ...
. It was not recognized as a primate until it was reevaluated in the early 1870s. Originally, adapiforms were all included under the family Adapidae, which was divided into two or three subfamilies: Adapinae, Notharctinae, and sometimes Sivaladapinae. All North American adapiforms were lumped under Notharctinae, while the Old World forms were usually assigned to Adapinae. Around the 1990s, two distinct groups of European "adapids" began to emerge, based on differences in the postcranial skeleton and the teeth. One of these two European forms was identified as cercamoniines, which were allied with the notharctids found mostly in North America, while the other group falls into the traditional adapid classification. The three major adapiform divisions are now typically regarded as three families within Adapiformes (Notharctidae, Adapidae and Sivaladapidae), but other divisions ranging from one to five families are used as well.
Anatomy and physiology
Grooming apparatus
All lemuriforms possess a specialized dental structure called a "toothcomb", with the exception of the aye-aye, in which the structure has been modified into two continually growing (hypselodont) incisors (or canine teeth), similar to those of rodent
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...
s. Often, the toothcomb is incorrectly used to characterize all strepsirrhines. Instead, it is unique to lemuriforms and is not seen among adapiforms.
Lemuriforms groom orally, and also possess a grooming claw
A grooming claw (or toilet claw) is the specialized claw or nail on the foot of certain primates, used for personal grooming. All prosimians have a grooming claw, but the digit that is specialized in this manner varies. Tarsiers have a grooming ...
on the second toe of each foot for scratching in areas that are inaccessible to the mouth and tongue. It is unclear whether adapiforms possessed grooming claws. The toothcomb consists of either two or four procumbent
This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnify ...
lower incisors and procumbent lower canine teeth followed by a canine-shaped premolar. It is used to comb the fur during oral grooming. Shed hairs that accumulate between the teeth of the toothcomb are removed by the sublingua
The sublingua ("under-tongue") is a muscular secondary tongue found below the primary tongue in tarsiers and living strepsirrhine primates, which includes lemurs and lorisoids (collectively called " lemuriforms"). Although it is most fully devel ...
or "under-tongue". Lemuriforms also possess a grooming claw
A grooming claw (or toilet claw) is the specialized claw or nail on the foot of certain primates, used for personal grooming. All prosimians have a grooming claw, but the digit that is specialized in this manner varies. Tarsiers have a grooming ...
on the second digit of each foot for scratching. Adapiforms did not possess a toothcomb. Instead, their lower incisors varied in orientation – from somewhat procumbent to somewhat vertical – and the lower canines were projected upwards and were often prominent. Adapiforms may have had a grooming claw, but there is little evidence of this.
Eyes
Like all primates, strepsirrhine orbits (eye sockets) have a postorbital bar, a protective ring of bone created by a connection between the frontal
Front may refer to:
Arts, entertainment, and media Films
* ''The Front'' (1943 film), a 1943 Soviet drama film
* ''The Front'', 1976 film
Music
*The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ea ...
and zygomatic bones. Both living and extinct strepsirrhines lack a thin wall of bone behind the eye, referred to as postorbital closure, which is only seen in haplorhine primates. Although the eyes of strepsirrhines point forward, giving stereoscopic vision, the orbits do not face fully forward. Among living strepsirrhines, most or all species are thought to possess a reflective layer behind the retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
of the eye, called a tapetum lucidum (consisting of riboflavin
Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved i ...
crystals), which improves vision in low light, but they lack a fovea
Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure.
Human anatomy
*Fovea centralis of the retina
* Fovea buccalis or Dimple
* Fovea of the femoral head
* Trochlear fovea of the fr ...
, which improves day vision. This differs from tarsiers, which lack a tapetum lucidum but possess a fovea.
Skull
Strepsirrhine primates have a brain relatively comparable to or slightly larger in size than most mammals. Compared to simians, however, they have a relatively small brain-to-body size ratio. Strepsirrhines are also traditionally noted for their unfused mandibular symphysis
In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral halve ...
(two halves of the lower jaw), however, fusion of the mandibular symphysis was common in adapiforms, notably ''Notharctus''. Also, several extinct giant lemurs exhibited a fused mandibular symphysis.
Ears
Many nocturnal species have large, independently movable ears, although there are significant differences in sizes and shapes of the ear between species. The structure of the middle and inner ear
The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in th ...
of strepsirrhines differs between the lemurs and lorisoids. In lemurs, the tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound.
Structure
On its lateral surface, it abuts the external auditor ...
, which surrounds the middle ear, is expanded. This leaves the ectotympanic ring, which supports the eardrum
In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit sound from the ...
, free within the auditory bulla. This trait is also seen in adapiforms. In lorisoids, however, the tympanic cavity is smaller and the ectotympanic ring becomes attached to the edge of the auditory bulla. The tympanic cavity in lorisoids also has two accessory air spaces, which are not present in lemurs.
Neck arteries
Both lorisoids and cheirogaleid lemurs have replaced the internal carotid artery
The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these ...
with an enlarged ascending pharyngeal artery.
Ankle bones
Strepsirrhines also possess distinctive features in their tarsus (ankle bones) that differentiate them from haplorhines, such as a sloping talo-fibular facet (the face where the talus bone
The talus (; Latin for ankle or ankle bone), talus bone, astragalus (), or ankle bone is one of the group of foot bones known as the tarsus. The tarsus forms the lower part of the ankle joint. It transmits the entire weight of the body from the ...
and fibula
The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity ...
meet) and a difference in the location of the position of the flexor fibularis tendon on the talus. These differences give strepsirrhines the ability to make more complex rotations of the ankle and indicate that their feet are habitually inverted, or turned inward, an adaptation for grasping vertical supports.
Sex characteristics
Sexual dichromatism (different coloration patterns between males and females) can be seen in most brown lemur species, but otherwise lemurs show very little if any difference in body size or weight between sexes. This lack of sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
is not characteristic of all strepsirrhines. Some adapiforms were sexually dimorphic, with males bearing a larger sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exception ...
(a ridge of bone on the top of the skull to which jaw muscles attach) and canine teeth. Lorisoids exhibit some sexual dimorphism, but males are typically no more than 20 percent larger than females.
Rhinarium and olfaction
Strepsirrhines have a long snout that ends in a moist and touch-sensitive rhinarium, similar to that of dogs and many other mammals. The rhinarium is surrounded by vibrissae that are also sensitive to touch. Convoluted maxilloturbinals on the inside of their nose filter, warm, and moisten the incoming air, while olfactory receptors of the main olfactory system lining the ethmoturbinals detect airborne smells. The olfactory bulbs of lemurs are comparable in size to those of other arboreal mammals.
The surface of the rhinarium does not have any olfactory receptors, so it is not used for smell in terms of detecting volatile substances. Instead, it has sensitive touch receptors (Merkel cell
Merkel cells, also known as Merkel-Ranvier cells or tactile epithelial cells, are oval-shaped mechanoreceptors essential for light touch sensation and found in the skin of vertebrates. They are abundant in highly sensitive skin like that of the f ...
s). The rhinarium, upper lip, and gums are tightly connected by a fold of mucous membrane called the philtrum
The philtrum ( la, philtrum from Ancient Greek ''phíltron,'' lit. "love charm"), or medial cleft, is a vertical indentation in the middle area of the upper lip, common to therian mammals, extending in humans from the nasal septum to the tuberc ...
, which runs from the tip of the nose to the mouth. The upper lip is constrained by this connection and has fewer nerves to control movement, which leaves it less mobile than the upper lips of simians. The philtrum creates a gap (diastema
A diastema (plural diastemata, from Greek διάστημα, space) is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition ...
) between the roots of the first two upper incisors.
The strepsirrhine rhinarium can collect relatively non-volatile, fluid-based chemicals (traditionally categorized as pheromones) and transmit them to the vomeronasal organ
The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary olfactory (smell) sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth (the hard palate) in various tetrapo ...
(VNO), which is located below and in front of the nasal cavity
The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal ...
, above the mouth. The VNO is an encased duct-like structure made of cartilage
Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck ...
and is isolated from the air passing through the nasal cavity. The VNO is connected to the mouth through nasopalatine ducts (which communicate via the incisive foramen), which pass through the hard palate at the top, front of the mouth. Fluids traveling from the rhinarium to the mouth and then up the nasopalatine ducts to the VNO are detected, and information is relayed to the accessory olfactory bulb, which is relatively large in strepsirrhines. From the accessory olfactory bulb, information is sent to the amygdala
The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex ver ...
, which handles emotions, and then to the hypothalamus
The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...
, which handles basic body functions and metabolic processes. This neural pathway differs from that used by the main olfactory system.
All lemuriforms have a VNO, as do tarsiers and some New World monkeys. Adapiforms exhibit the gap between the upper incisors, which indicates the presence of a VNO, but there is some disagreement over whether or not they possessed a rhinarium.
Reproductive physiology
Extant strepsirrhines have an epitheliochorial placenta, where the maternal blood does not come in direct contact with the fetal chorion like it does in the hemochorial placenta of haplorhines. The strepsirrhine uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
has two distinct chambers (bicornuate). Despite having similar gestation period
In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once ...
s to comparably sized haplorhines, fetal growth rates are generally slower in strepsirrhines, which results in newborn offspring that are as little as one-third the size of haplorhine newborns. Extant strepsirrhines also have a lower basal metabolic rate
Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). P ...
, which elevates in females during gestation, putting greater demands on the mother.
Most primates have two mammary gland
A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in ...
s, but the number and positions vary between species within strepsirrhines. Lorises have two pairs, while others, like the ring-tailed lemur, have one pair on the chest (pectoral). The aye-aye also has two mammary glands, but they are located near the groin (inguinal). In females, the clitoris
The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), above the op ...
is sometimes enlarged and pendulous, resembling the male penis, which can make sex identification difficult for human observers. The clitoris may also have a bony structure in it, similar to the baculum
The baculum (also penis bone, penile bone, or ''os penis'', ''os genitale'' or ''os priapi'') is a bone found in the penis of many placental mammals. It is absent from the human penis, but present in the penises of some primates, such as the ...
(penis bone) in males. Most male primates have a baculum, but it is typically larger in strepsirrhines and usually forked at the tip.
Behavior
Approximately three-quarters of all extant strepsirrhine species are nocturnal, sleeping in nests made from dead leaves or tree hollows during the day. All of the lorisoids from continental Africa and Asia are nocturnal, a circumstance that minimizes their competition with the simian primates of the region, which are diurnal. The lemurs of Madagascar, living in the absence of simians, are more variable in their activity cycles. The aye-aye, mouse lemurs, woolly lemur
The woolly lemurs, also known as avahis or woolly indris, are nine species of strepsirrhine primates in the genus ''Avahi''. Like all other lemurs, they live only on the island of Madagascar.
With a body size of and a weight of , the woolly ...
s, and sportive lemur
The sportive lemurs are the medium-sized primates that make up the family Lepilemuridae. The family consists of only one extant genus, ''Lepilemur''. They are closely related to the other lemurs and exclusively live on the island of Madagascar. ...
s are nocturnal, while ring-tailed lemurs and most of their kin, sifakas, and indri
The indri (; ''Indri indri''), also called the babakoto, is one of the largest living lemurs, with a head-body length of about and a weight of between . It has a black and white coat and maintains an upright posture when climbing or clinging. ...
are diurnal. Yet some or all of the brown lemurs (''Eulemur'') are cathemeral, which means that they may be active during the day or night, depending on factors such as temperature and predation
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
. Many extant strepsirrhines are well adapted for nocturnal activity due to their relatively large eyes; large, movable ears; sensitive tactile hairs; strong sense of smell; and the tapetum lucidum behind the retina. Among the adapiforms, most are considered diurnal, with the exception of '' Pronycticebus'' and '' Godinotia'' from Middle Eocene Europe, both of which had large orbits that suggest nocturnality.
Reproduction in most strepsirrhine species tends to be seasonal, particularly in lemurs. Key factors that affect seasonal reproduction include the length of the wet season, subsequent food availability, and the maturation time of the species. Like other primates, strepsirrhines are relatively slow breeders compared to other mammals. Their gestation period and interbirth intervals are usually long, and the young develop slowly, just like in haplorhine primates. Unlike simians, some strepsirrhines produce two or three offspring, although some produce only a single offspring. Those that produce multiple offspring tend to build nests for their young. These two traits are thought to be plesiomorphic
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, and ...
(ancestral) for primates. The young are precocial (relatively mature and mobile) at birth, but not as coordinated as ungulate
Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, ...
s (hoofed mammals). Infant care by the mother is relatively prolonged compared to many other mammals, and in some cases, the infants cling to the mother's fur with their hands and feet.
Despite their relatively smaller brains compared to other primates, lemurs have demonstrated levels of technical intelligence in problem solving that are comparable to those seen in simians. However, their social intelligence differs, often emphasizing within-group competition over cooperation, which may be due to adaptations for their unpredictable environment. Although lemurs have not been observed using objects as tools in the wild, they can be trained to use objects as tools in captivity and demonstrate a basic understanding about the functional properties of the objects they are using.
Social systems and communication
The nocturnal strepsirrhines have been traditionally described as "solitary", although this term is no longer favored by the researchers who study them. Many are considered "solitary foragers", but many exhibit complex and diverse social organization, often overlapping home ranges, initiating social contact at night, and sharing sleeping sites during the day. Even the mating systems are variable, as seen in woolly lemurs, which live in monogamous
Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
breeding pair
Breeding pair is a pair of animals which cooperate over time to produce offspring with some form of a bond between the individuals.Gaston, A. J.The evolution of group territorial behavior and cooperative breeding" The American Naturalist 112.988 ...
s. Because of this social diversity among these solitary but social primates, whose level of social interaction is comparable to that of diurnal simians, alternative classifications have been proposed to emphasize their gregarious, dispersed, or solitary nature.
Among extant strepsirrhines, only the diurnal and cathemeral lemurs have evolved to live in multi-male/multi-female groups, comparable to most living simians. This social trait, seen in two extant lemur families ( Indriidae and Lemuridae), is thought to have evolved independently. Group sizes are smaller in social lemurs than in simians, and despite the similarities, the community structures differ. Female dominance, which is rare in simians, is fairly common in lemurs. Strepsirrhines spend a considerable amount of time grooming each other (allogrooming
Social grooming is a behavior in which social animals, including humans, clean or maintain one another's body or appearance. A related term, allogrooming, indicates social grooming between members of the same species. Grooming is a major socia ...
). When lemuriform primates groom, they lick the fur and then comb it with their toothcomb. They also use their grooming claw to scratch places they cannot reach with their mouth.
Like New World monkeys, strepsirrhines rely on scent marking
In ethology, territory is the sociographical area that an animal consistently defends against conspecific competition (or, occasionally, against animals of other species) using agonistic behaviors or (less commonly) real physical aggression. A ...
for much of their communication. This involves smearing secretions from epidermal scent glands on tree branches, along with urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellul ...
and feces
Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a rela ...
. In some cases, strepsirrhines may anoint themselves with urine ( urine washing). Body postures and gestures may be used, although the long snout, non-mobile lips, and reduced facial enervation restrict the use of facial expressions in strepsirrhines. Short-range calls, long-range calls, and alarm calls are also used. Nocturnal species are more constrained by the lack of light, so their communication systems differ from those of diurnal species, often using long-range calls to claim their territory
A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal.
In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
.
Locomotion
Living strepsirrhines are predominantly arboreal, with only the ring-tailed lemur spending considerable time on the ground. Most species move around quadrupedally (on four legs) in the trees, including five genera of smaller, nocturnal lemurs. Galagos, indriids, sportive lemurs, and bamboo lemurs leap from vertical surfaces, and the indriids are highly specialized for vertical clinging and leaping. Lorises are slow-moving, deliberate climbers.
Analyses of extinct adapiforms postcranial skeletons suggest a variety of locomotor behavior. The European adapids ''Adapis'', '' Palaeolemur'', and '' Leptadapis'' shared adaptations for slow climbing like the lorises, although they may have been quadrupedal runners like small New World monkeys. Both '' Notharctus'' and '' Smilodectes'' from North America and '' Europolemur'' from Europe exhibit limb proportions and joint surfaces comparable to vertical clinging and leaping lemurs, but were not as specialized as indriids for vertical clinging, suggesting that they ran along branches and did not leap as much. Notharctids ''Cantius'' and ''Pronycticebus'' appear to have been agile arboreal quadrupeds, with adaptations comparable to the brown lemurs.
Diet
Primates primarily feed on fruits (including seeds), leaves (including flowers), and animal prey (arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s, small vertebrates, and eggs). Diets vary markedly between strepsirrhine species. Like other leaf-eating ( folivorous) primates, some strepsirrhines can digest cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wa ...
and hemicellulose. Some strepsirrhines, such as the galagos, slender lorises, and angwantibo
Angwantibos are two species of strepsirrhine primates classified in the genus ''Arctocebus'' of the family Lorisidae. They are also known as golden pottos because of their yellow or golden coloration.
Angwantibos live in tropical Africa and the ...
s, are primarily insectivorous
A robber fly eating a hoverfly
An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects.
The first vertebrate insectivores were ...
. Other species, such as fork-marked lemurs and needle-clawed bushbabies, specialize on tree gum, while indriids, sportive lemurs, and bamboo lemurs are folivores. Many strepsirrhines are frugivore
A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance and ...
s (fruit eaters), and others, like the ring-tailed lemur and mouse lemurs, are omnivore
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...
s, eating a mix of fruit, leaves, and animal matter.
Among the adapiforms, frugivory seems to have been the most common diet, particularly for medium-sized to large species, such as ''Cantius'', '' Pelycodus'' and ''Cercamonius
''Cercamonius'' is a genus of adapiform primate that lived in Europe during the late Eocene. It was first described by Stehlin in 1912. The genus is named after the Occitan poet Cercamon, one of the earliest troubadours
A troubadour (, ; ...
''. Folivory was also common among the medium and large-sized adapiforms, including ''Smilodectes'', ''Notharctus'', ''Adapis'' and ''Leptadapis''. Sharp cusps on the teeth of some of the smaller adapiforms, such as '' Anchomomys'' and ''Donrussellia'', indicate that they were either partly or primarily insectivorous.
Distribution and habitat
The now extinct adapiform primates were primarily found across North America, Asia, and Europe, with a few species in Africa. They flourished during the Eocene when those regions were more tropical in nature, and they disappeared when the climate became cooler and drier. Today, the lemuriforms are confined in the tropics, ranging between 28° S to 26° N latitude. Lorises are found both in equatorial Africa and Southeast Asia
Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
, while the galagos are limited to the forests and woodlands of sub-Saharan Africa
Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
. Lemurs are endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
to Madagascar, although much of their diversity and habitat has been lost due to recent human activity.
As with nearly all primates, strepsirrhines typically reside in tropical rainforest
Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equator ...
s. These habitats allow strepsirrhines and other primates to evolve diverse communities of sympatric species. In the eastern rainforests of Madagascar, as many as 11 or 12 species share the same forests, and prior to human arrival, some forests had nearly double that diversity. Several species of lemur are found in drier, seasonal forests, including the spiny forest on the southern tip of the island, although the lemur communities in these regions are not as rich.
Conservation
Like all other non-human primates, strepsirrhines face an elevated risk of extinction due to human activity, particularly deforestation
Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated ...
in tropical regions. Much of their habitat has been converted for human use, such as agriculture and pasture. The threats facing strepsirrhine primates fall into three main categories: habitat destruction
Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...
, hunting (for bushmeat or traditional medicine
Traditional medicine (also known as indigenous medicine or folk medicine) comprises medical aspects of traditional knowledge that developed over generations within the folk beliefs of various societies, including indigenous peoples, before the ...
), and live capture for export or local exotic pet trade. Although hunting is often prohibited, the laws protecting them are rarely enforced. In Madagascar, local taboos known as '' fady'' sometimes help protect lemur species, although some are still hunted for traditional medicine.
In 2012, the International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
(IUCN) announced that lemurs were the "most endangered mammals", due largely to elevated illegal logging
Illegal logging is the harvest, transportation, purchase or sale of timber in violation of laws. The harvesting procedure itself may be illegal, including using corrupt means to gain access to forests; extraction without permission, or from a ...
and hunting following a political crisis in 2009. In Southeast Asia, slow lorises are threatened by the exotic pet trade and traditional medicine, in addition to habitat destruction. Both lemurs and slow lorises are protected from commercial international trade under CITES Appendix I.
Explanatory notes
References
Citations
Literature cited
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External links
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{{Authority control
Primate taxonomy
Mammal suborders
Extant Eocene first appearances
Taxa named by Étienne Geoffroy Saint-Hilaire
Taxa described in 1812