Myanmar
Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...
approximately 37 million years ago, during the late middle
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
. The only
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
in the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Afrasia'', it was a small
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 including huma ...
, estimated to weigh around . Despite the significant geographic distance between them, ''Afrasia'' is thought to be closely related to ''
Afrotarsius
''Afrotarsius'' is a primate found in the Paleogene of Africa.
The first species to be named, ''Afrotarsius chatrathi'', was named in 1985 on the basis of a single lower jaw from the Oligocene of Fayum, Egypt, and tentatively referred to the ...
'', an enigmatic
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
found in
Libya
Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to Egypt–Libya bo ...
and
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediter ...
that dates to 38–39 million years ago. If this relationship is correct, it suggests that early
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 Catarrhi ...
s (a related group or
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 term, ...
consisting of
monkey
Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as the simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes, which constitutes an incomple ...
s,
ape
Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its siste ...
s, and
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
s) dispersed from Asia to Africa during the middle Eocene and would add further support to the hypothesis that the first simians evolved in Asia, not Africa. Neither ''Afrasia'' nor ''Afrotarsius'', which together form the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Afrotarsiidae, is considered ancestral to living simians, but they are part of a side branch or
stem group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
known as eosimiiforms. Because they did not give rise to the stem simians that are known from the same deposits in Africa, early Asian simians are thought to have dispersed from Asia to Africa more than once prior to the late middle Eocene. Such dispersals from Asia to Africa also were seen around the same time in other
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
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 na ...
s and
anthracotheres
Anthracotheriidae is a paraphyletic family of extinct, hippopotamus-like artiodactyl ungulates related to hippopotamuses and whales. The oldest genus, ''Elomeryx'', first appeared during the middle Eocene in Asia. They thrived in Africa and Euras ...
.
''Afrasia'' is known from four isolated molar teeth found in the Pondaung Formation of Myanmar. These teeth are similar to those of ''Afrotarsius'' and
Eosimiidae
Eosimiidae is the possible family of extinct primates believed to be the earliest simians.
Taxonomy
When they were discovered the possibility that Eosimians were outside and ancestral to Simians was considered (Culotta 1992), but subsequent ...
, and differ only in details of the chewing surface. For example, the back part of the third lower molar is relatively well-developed. In the Pondaung Formation, ''Afrasia'' was part of a diverse primate community that also includes the eosimiid '' Bahinia'' and members of the families
Amphipithecidae
The Amphipithecidae were simian primates that lived in Late Eocene and Early Oligocene. Fossils have been found in Myanmar, Thailand, and Pakistan. The limited fossil evidence is consistent with, but not exclusive to, arboreal quadrupedalism. In ...
The name ''Afrasia'' derives from the continental names "Africa" and "Asia", and refers to the occurrence of eosimiiform primates on both continents. The species, ''A. djijidae'', was named in memory of a young girl from
Mogaung
Mogaung ( my, မိုးကောင်း ; ( Shan: မိူင်းၵွင်း) is a town in Kachin State, Myanmar. It is situated on the Mandalay-Myitkyina railway line.
History
Mogaung or Möngkawng was the name and capital (roya ...
village in central
Myanmar
Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...
.
Evolutionary history
''Afrasia djijidae'' was first described in 2012 on the basis of isolated teeth from the 37-million-year-old Pondaung Formation, which is close to the village of Nyaungpinle in Myanmar. Prior to the discovery of ''A. djijidae'', early Asian
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 Catarrhi ...
s were typically classified in two
families
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. Ideall ...
,
Eosimiidae
Eosimiidae is the possible family of extinct primates believed to be the earliest simians.
Taxonomy
When they were discovered the possibility that Eosimians were outside and ancestral to Simians was considered (Culotta 1992), but subsequent ...
and
Amphipithecidae
The Amphipithecidae were simian primates that lived in Late Eocene and Early Oligocene. Fossils have been found in Myanmar, Thailand, and Pakistan. The limited fossil evidence is consistent with, but not exclusive to, arboreal quadrupedalism. In ...
. While eosimiids are generally considered the most basal simian
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 term, ...
(a
stem group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
of simians), the
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
placement of amphipithecids is more disputed. Amphipithecids are usually considered to share affinities with either eosimiids or
crown
A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, partic ...
simians (those simians that are part of the smallest clade that contains the living simians); the latter view is favored.
Eosimiids were first described from findings in
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
in 1994 and are still best known there (two genera are now known, ''
Eosimias
''Eosimias'' is a genus of early primates, first discovered and identified in 1999 from fossils collected in the Shanghuang fissure-fillings of Liyang, the southern city of Jiangsu Province, China. It is a part of the family Eosimiidae, and inclu ...
'' and '' Phenacopithecus''), but have also been recorded in
Pakistan
Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...
(''
Phileosimias
''Phileosimias'' ("''Eosimias'' ally") is an extinct genus of primates with two species, ''P. kamli'' and ''P. bahuiorum'', that are believed to be amongst the early simians.
Marivaux ''et al.'' announced in 2005 their discovery of fossils of t ...
'') and Myanmar ('' Bahinia''). All species had a small body size and a mix of primitive (ancestral) and
derived trait
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
s. The largest eosimiid, ''Bahinia'', is from the Pondaung Formation, the same
stratum
In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...
as ''Afrasia'', and the morphology of its
molars
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
bridges the gap between the more primitive molars of ''Eosimias'' and the more derived molars of the later Eocene African simians. ''Afrasia'', on the other hand, is more comparable in size to the eosimiids from China.
The upper molars of ''Afrasia'' are nearly identical in morphology and size to those of ''
Afrotarsius
''Afrotarsius'' is a primate found in the Paleogene of Africa.
The first species to be named, ''Afrotarsius chatrathi'', was named in 1985 on the basis of a single lower jaw from the Oligocene of Fayum, Egypt, and tentatively referred to the ...
'', an animal known from 38- to 39-million-year-old deposits in
Libya
Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to Egypt–Libya bo ...
(species ''Afrotarsius libycus'') and about 30-million-year-old deposits in
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediter ...
(''A. chatrathi''). ''Afrotarsius'' was originally described as a tarsier, but later suggested to be related to primitive simians. Because of their close similarities, ''Afrasia'' and ''Afrotarsius'' are together placed in the family Afrotarsiidae. A phylogenetic analysis placed ''Afrasia'' as 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 t ...
to ''Afrotarsius'', forming the family Afrotarsiidae. Afrotarsiidae was found to be most closely related to Eosimiidae, and unrelated to tarsiers. The
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 term, ...
formed by Afrotarsiidae and Eosimiidae was designated as the infraorder Eosimiiformes by Chaimanee ''et al.'' in 2012. Eosimiiformes are the sister group of crown simians. However, the classification of ''Afrotarsius'' as a stem simian is not accepted by all researchers, and the phylogenetic claims and their implications rest on only the four molars of ''Afrasia'' initially discovered.
Biogeography
Several hypotheses compete to explain the geographic origins of simians. Of the two most popular views, one hypothesis states that simians originated in Asia, while the other favors Africa as their place of origin. Both their ancient origins and the sparse fossil record in Africa and Asia complicate the debate.
Convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
also makes it difficult for researchers to determine the relationships between fossils. Also, the earliest fossils, which do not match up with
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 nucleoti ...
estimates for simian origins, have been found in both Afro-Arabia and Asia. At the time, both landmasses would have been separated by the
Tethys Sea
The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...
.
The oldest undisputed simians from Africa also date to the late middle Eocene. ''Afrotarsius'' was found in the Dur At-Talah escarpment in
Libya
Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to Egypt–Libya bo ...
, which dates to 38–39 million years ago and also contains the parapithecid ''
Biretia
''Biretia'' is an extinct genus of Old World monkey belonging to the extinct family Parapithecidae. Fossils are found from Late Eocene strata in Egypt.
The first discovery of ''Biretia'' was a single tooth dated to approximately 37 mya, which wa ...
'' and the oligopithecid '' Talahpithecus''. Although diverse, these primates were all very small in size, much like eosimiids. Simian classification for older fossils from Africa are more contested. ''
Altiatlasius
''Altiatlasius'' ("High Atlas" from Latin altus, "high" + Atlas, "Atlas") is an extinct genus of mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands wh ...
'', the oldest suspected fossil primate known from the late
Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
of
Morocco
Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to ...
, is too fragmentary to ascertain its true affinities. ''
Algeripithecus
''Algeripithecus'' is an extinct genus of early fossil primate, weighing approximately . Fossils have been found in Algeria dating from 50 to 46 million years ago.
It was once commonly thought to be one of the oldest simian primates (a group th ...
'' was popularly considered an early middle Eocene simian; however, less fragmentary remains uncovered between 2003 and 2009 suggest it was a type of azibiid, a group of
strepsirrhine
Strepsirrhini or Strepsirhini (; ) is a suborder of primates that includes the lemuriform primates, which consist of the lemurs of Madagascar, galagos ("bushbabies") and pottos from Africa, and the lorises from India and southeast Asia. Collec ...
lemur
Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are Strepsirrhini, wet-nosed primates of the Superfamily (biology), superfamily Lemuroidea (), divided into 8 Family (biology), families and consisting of 15 genera and around 100 exist ...
s and lorisoids).
According to the team who discovered ''Afrasia'', headed by Jean-Jacques Jaeger, the similarities in tooth morphology, body size, and age suggest a phylogenetic relationship with ''Afrotarsius'' despite the geographic separation. They suggested that afrotarsiid simians from Asia dispersed across the Tethys Sea to Africa around the middle Eocene, giving rise to ''Afrotarsius''. A reverse migration—as suggested by the hypothesis of the African origin for simians—is not favored due to the close phylogenetic relationship between the older Asian eosimiids and ''Afrasia''. However, to explain the origins of
Proteopithecidae
Proteopithecidae is an extinct family of primates which lived in the Priabonian (late Eocene) and probably early Oligocene periods. Fossils that have been found are in the Jebel Qatrani Formation in Egypt. Currently two genera are recognised, eac ...
,
Parapithecidae
Parapithecidae is an extinct family of primates which lived in the Eocene and Oligocene periods in Egypt. Eocene fossils from Myanmar are sometimes included in the family in addition. They showed certain similarities in dentition to Condylarthra, ...
, and crown simians from the African fossil record, a higher simian clade also needed to disperse from Asia to Africa before the late middle Eocene since neither ''Afrasia'' nor ''Afrotarsius'' could have given rise to this group. Such dispersals from Asia to Africa were not uncommon, since hystricognathous
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 na ...
s,
anthracotheres
Anthracotheriidae is a paraphyletic family of extinct, hippopotamus-like artiodactyl ungulates related to hippopotamuses and whales. The oldest genus, ''Elomeryx'', first appeared during the middle Eocene in Asia. They thrived in Africa and Euras ...
, and possibly other mammalian fauna from Asia arrived around the same time.
Anatomy
''Afrasia'' is known from four isolated teeth: a first upper molar (M1), with a length of 2.13 mm and width of 3.06 mm; a second upper molar (M2), the
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
, of 2.27 mm by 3.35 mm; a second lower molar (m2) of 2.09 mm by 1.41 mm; and a third lower molar (m3) of 2.05 mm by 1.27 mm. Like other eosimiiforms, it was a small primate that weighed around , which is estimated based on the measurements of its m2 and M1, respectively. It is generally similar to other eosimiiforms in general and ''Afrotarsius'' in particular; some distinguishing features are the well-developed small cusps (conules) on the upper molars, the variable development of the lingual cingulum (a shelf on the inner, or lingual, side of the tooth) of the upper molars, and the unreduced
talonid
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
(posterior portion) on the m3. Its teeth are smaller than those of the eosimiids ''Phenacopithecus'', ''Bahinia'', and ''Phileosimias''.
The M2 is similar to that of eosimiids and almost identical to that of ''Afrotarsius libycus''. It shows well-developed small accessory cusps (the paraconule and metaconule) that are connected to equally well-developed crests. The conules are stronger than in ''Eosimias'' and ''Bahinia'', but weaker than in ''Phileosimias''. The stylar shelf, the outer area of the tooth, is broad, particularly at the
metacone
A cusp is a pointed, projecting, or elevated feature. In animals, it is usually used to refer to raised points on the crowns of teeth.
The concept is also used with regard to the leaflets of the four heart valves. The mitral valve, which has two ...
cusp. However, the shelf is better developed near the
paracone
A paracone is a 1960s atmospheric reentry or spaceflight mission abort concept using an inflatable ballistic cone.ectoflexus (an invagination in the outer wall of the tooth) more symmetrical in the former. The parastyle, a small cusp in the outer front corner of the tooth, is located more buccally (towards the outer side of the tooth) than in ''Afrotarsius'' and is larger. The stylar shelf is larger than that of ''Bahinia'' and ''Phileosimias'', but smaller than that of ''Eosimias''. The parastyle is also less developed than in ''Eosimias'', but the
protocone
A cusp is a pointed, projecting, or elevated feature. In animals, it is usually used to refer to raised points on the crowns of teeth.
The concept is also used with regard to the leaflets of the four heart valves. The mitral valve, which has two ...
, the main cusp on the lingual side of the tooth, is more expansive. The lingual cingulum is incomplete; it is stronger in ''Phenacopithecus''.
M1 is similar to M2, but somewhat smaller. The ectoflexus is less apparent, the stylar shelf is narrower, there is no crest behind the metaconule, and the lingual cingulum is continuous. The condition of the parastyle more closely resembles that in ''Afrotarsius''.
In m2, the
trigonid
The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, ...
(the front portion of the tooth) consists of three very distinct cusps: the paraconid at the front, and behind it the paired
protoconid
Many different terms have been proposed for features of the tooth crown in mammals.
The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...
(on the buccal side) and
metaconid
Many different terms have been proposed for features of the tooth crown in mammals.
The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn ...
(on the lingual side). These three cusps are less discrete in ''Afrotarsius''. The paraconid is distinct from the paracristid, the crest that connects it to the protoconid, and is located more lingually than in ''Afrotarsius''. Between this cusp and the metaconid behind it, the central basin of the trigonid is open towards the lingual margin of the tooth. The protoconid has a V shape, with one arm reaching towards the metaconid and the other towards the paraconid. The back portion of the tooth, the talonid, is broader; ''Eosimias'' has a narrower talonid. The main cusps, the buccal
hypoconid
Many different terms have been proposed for features of the tooth crown in mammals.
The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn ...
and lingual
entoconid
Many different terms have been proposed for features of the tooth crown in mammals.
The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...
, are opposite each other on the margins of the tooth (the entoconid is further to the front in ''Phenacopithecus''). A crest, the cristid obliqua, connects the front side of the hypoconid to the protoconid. It is nearly in line with the main axis of the tooth, contrasting with its more diagonal position in ''Eosimias'' and ''Phenacopithecus''. A crest, the postcristid, descends from the hypoconid along the back margin of the tooth and almost reaches the entoconid, which is separated by a notch. It incorporates the third talonid cusp, the hypoconulid, which is indistinct in ''Afrasia''. In ''Afrotarsius'' and eosimiids (except the Pakistani ''Phileosimias''), this crest reaches the entoconid. There is a cingulum, or shelf, on the buccal side of m2.
The last lower molar, m3, is smaller and has a longer talonid, with a well-developed hypoconulid lobe at the back, and generally resembles that of ''Phenacopithecus'', but the trigonid is smaller. The paraconid is distinct. The hypoconulid lobe is longer than in ''Afrotarsius'' and the entoconid is located further to the front. Unlike on m2, there is no notch between the hypoconulid and entoconid, though a shallow valley is present.
Range and ecology
''Afrasia'' has only been found in the Eocene Pondaung Formation of central Myanmar, a rock unit which has been dated to about 37 million years ago using
magnetostratigraphy
Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their '' ...
and
fission track dating
Fission track dating is a radiometric dating technique based on analyses of the damage trails, or tracks, left by fission fragments in certain uranium-bearing minerals and glasses. Fission-track dating is a relatively simple method of radiomet ...
. This places it at the end of the
Bartonian
The Bartonian is, in the ICS's geologic time scale, a stage or age in the middle Eocene Epoch or Series. The Bartonian Age spans the time between . It is preceded by the Lutetian and is followed by the Priabonian Age.
Stratigraphic definitio ...
Late 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'', "daw ...
boundary. Although many tons of sediments in the area have been screened for fossils, ''Afrasia'' is still known only from four teeth, suggesting that it was a rare species.
Since fossils were first discovered there in 1916, a rich fossil fauna has been recovered in the Pondaung Formation. In addition to ''Afrasia'', primates found there include the eosimiid ''Bahinia''; the amphipithecids '' Pondaungia'', ''
Ganlea
''Ganlea'' is a fossil primate from central Myanmar, formerly known as Burma. Its age is about 38 million years, living during the late Eocene epoch. ''Ganlea'' belongs to the group of anthropoids (i. e. humans, apes and monkeys), and is in the ...