| Plesiopithecus Temporal range: | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Strepsirrhini |
| Family: | † Plesiopithecidae Simons and Rasmussen, 1994 |
| Genus: | † Plesiopithecus Simons, 1992 |
| Species: | †P. teras |
| Binomial name | |
| †Plesiopithecus teras Simons, 1992 | |
Plesiopithecus is an extinct genus of early strepsirrhine primate from the late Eocene.
Originally described from the right mandible (lower jaw), its confusing anatomy resulted in it being classified as an ape—its name translates "near ape". Plesiopithecus teras, the only species so far identified, was discovered in 1992 by Elwyn L. Simons in Egypt at the base of the Jebel Qatrani Formation at Fayum in quarry L-41. Within two years, a more complete, crushed skull was found, demonstrating that it was a strepsirrhine primate. It is thought to be a close relative of lemuriforms (extant strepsirrhines), and a sister group to either lorisoids or all lemuriforms.
Plesiopithecus was a medium-sized strepsirrhine primate, with large orbits, a high muzzle, and a skull exhibiting klinorhynchy (a marked angle between the palate and the basicranium, or the lower region of the braincase). Its large orbits indicate that it was nocturnal, and its teeth suggest that it bored holes in wood in search of soft-bodied insects, just like the aye-aye.
The genus name Plesiopithecus derives from the Greek root plesi- (πλησίος, plēsios), meaning "near", and the Greek word πίθηκος (pithekos), meaning "trickster", which has historically been used to mean "ape". The species name derives from the Greek word τερασ (teras), meaning "wonderful or amazing animal". [1]
Although Plesiopithecus is now clearly recognized as being related to lemuriforms (extant strepsirrhine primates), its phylogenetic relations among the fossil primates are unclear. [2] Phylogenetic analyses using 359 morphological traits place it as a sister group of lemuriforms, [3] along with other Eocene African sister taxa, the djebelemurids, which include Djebelemur and 'Anchomomys' milleri . This Afro-Arabian clade, which includes crown lemuriforms [4] [5] and possibly the disputed azibiids, [4] [6] excludes the Holarctic adapiforms [5] and may be descended from an early Asian branch of adapiforms [7] such as a primitive branch of cercamoniines predating Donrussellia (one of the oldest European adapiforms). [8] A general consensus places Plesiopithecus at the base of the lemuriform clade, possibly closer to the lemuriforms than the djebelemurids. [2] Due to its combination of the lack of a toothcomb (a specialized dental structure found in most lemuriforms) and a front dentition that is enlarged and procumbent, Plesiopithecus has been considered a possible relative of the aye-aye (Daubentonia madagascariensis), suggesting a possible close relationship. This close relationship between Plesiopithecus and the aye-aye within the lemur radiation was recovered by Gunnell et al. (2018), suggesting that lemur evolution involved two dispersal events from Africa to Madagascar. [9] [10]
| General phylogeny of strepsirrhines [11] | ||||||||||||||||||||||||||||||||||||||||||||||||||
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| An Afro-Arabian clade of early strepsirrhines is thought to have given rise modern lemurs, lorises, and galagos. Azibiid taxonomy is still disputed. |
Alternatively, it may have closer ties to the aye-aye (Daubentonia madagascariensis) within the lemuroid (lemur) radiation. [2] The cranial and dental morphology of Plesiopithecus resemble what is predicted of an aye-aye ancestor, with an arched cranial vault suggesting klinorhynchy (a marked angle between the palate and the basicranium, or the lower region of the braincase) similar to that of aye-ayes, significantly enlarged canines and/or incisors, reduced molars and premolars, [12] a high muzzle, and anteriorly placed orbits. However, it lacked ever-growing incisors and the diastema found in the aye-aye. [2] The increased anterior dentition is peculiar because it has only happened in lemuriforms, and has never been observed in any of the numerous adapiforms. [12] Key to this possible close affinity with the aye-aye is the identity (canine vs. incisor) of the procumbent front teeth of both species, neither of which is definitively known. If they are different between the two species, then the similarities would be due to convergence. If they are the same tooth, then it may suggest a close phylogenetic relation and African origins for the aye-aye. [2]
If Plesiopithecus is an African relative of the aye-aye, it would suggest lemuroid primates colonized Madagascar twice. Molecular studies show that the aye-aye diverged early in the evolutionary history of lemurs, followed later by a sudden burst of diversification of the other four lemur families. If Plesiopithecus is an aye-aye relative, lemurs and aye-ayes would have diverged in Africa and the aye-aye ancestor would have colonized Madagascar separately from the other lemurs, which would have diversified immediately upon arrival to the island. If aye-ayes are more closely related to lemurs than Plesiopithecus, then only one colonization event occurred, with the aye-aye branching off first and then the other lemuroid families diverging several million years later following a major extinction event. [12]
Plesiopithecus teras was first described in 1992 by paleoanthropologist Elwyn L. Simons. The holotype, which was found at the base of the Jebel Qatrani Formation at the Egyptian Fayum in quarry L-41 and dated to the latest Eocene, [13] included a right mandible with intact dentition ranging from the third molar up to the first anterior tooth. [1] Simons acknowledged that the taxonomic interpretation was complicated, [14] though he initially decided to classify under superfamily Hominoidea (apes) [1] due to its flat and broad lower molars. Its bizarre and specialized traits made it difficult to classify until the discovery of its skull, reported in 1994, showed it had a postorbital bar, proving that it was a strepsirrhine primate. Plesiopithecus was then placed within a new superfamily, Plesiopithecoidea tentatively under "Infraorder cf. Lorisiformes". [15] The superfamily has also been grouped under the infraorder Lemuriformes. [16]
As of 2010, P. teras was represented by a nearly complete and partially crushed cranium and three partial mandibles. [13] Prior to Simons' discovery of the right jaw, one of its molars had been found a few years earlier and incorrectly attributed to an Eocene lorisoid. [17] Several cranial and facial similarities with living lorisoids indicate that it is closely related to lemuriforms (lemurs and lorisoids), although its lack of a toothcomb precludes it from being ancestral to either branch of the lemuriform clade. [17] Due to the differences in dental anatomy, Plesiopithecus is thought to be a sister group to either lorisoids or all living lemuriforms. [2]
With a skull length of nearly 53 mm (2.1 in), Plesiopithecus was a medium-sized strepsirrhine primate. Its skull is marked by a high muzzle, klinorhynchy, and relatively large orbits. It has very large and procumbent upper canines that are straight and compressed on both sides, and have roots that extend deep into the maxilla (upper jaw). No upper incisors have been found. The unidentified lower front tooth is also enlarged and procumbent. It has three premolars and three molars that decrease in size from front to back. The upper molars are simple and lack a hypocone. The lower molars are relatively broad. [13] [17]
Its large orbits suggest Plesiopithecus was nocturnal. Due to cranial and dental similarities with the aye-aye and signs of wear on the tips of its front teeth, it is thought to have bored holes in wood in search of soft-bodied insects, which likely make up its diet. [2]
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. Collectively they are referred to as strepsirrhines. Also belonging to the suborder are the extinct adapiform primates which thrived during the Eocene in Europe, North America, and Asia, but disappeared from most of the Northern Hemisphere 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.
Lemuriformes is an infraorder of primate that falls under the suborder Strepsirrhini. It includes the lemurs of Madagascar, as well as the galagos and lorisids of Africa and Asia, although a popular alternative taxonomy places the lorisoids in their own infraorder, Lorisiformes.
Adapiformes is a group of early primates. Adapiforms radiated throughout much of the northern continental mass, reaching as far south as northern Africa and tropical Asia. They existed from the Eocene to the Miocene epoch. Some adapiforms resembled living lemurs.
Necrolemur is a small bodied omomyid with body mass estimations ranging from 114 grams to 346 grams. Necrolemur’s teeth feature broad basins and blunt cusps, suggesting their diet consisted of mostly soft fruit, though examination of microwear patterns suggests that populations from lower latitudes also consumed insects and gums. While they do not sport a true tooth comb like modern lemurs, microwear patterns on their lower incisors suggest they engaged in fur grooming behaviors. Like tarsiers, Necrolemur had large, front-facing, close set eyes and were likely nocturnal. Analysis of cranial and postcranial fossils by paleontologists suggest members of the family Omomyidae, including the genus Necrolemur, possessed highly specialized adaptations for leaping.
Notharctinae is an extinct subfamily of primates that were common in North America during the early and middle Eocene. The six genera that make up the group contain species that are among the most primitive of the adapiform group, which is one of the most primitive groups of primates. The evolutionary history of this subfamily has been comparatively well documented and has been used to argue for evolutionary gradualism. Though it is generally accepted that adapiforms gave rise to modern day lemurs and lorises, it is not currently known which branch of Adapiformes these living species are most closely related to. Notharctines became extinct in the middle Eocene, most likely because of a combination of factors including climatic change and competition with other North American primates.
A toothcomb is a dental structure found in some mammals, comprising a group of front teeth arranged in a manner that facilitates grooming, similar to a hair comb. The toothcomb occurs in lemuriform primates, treeshrews, colugos, hyraxes, and some African antelopes. The structures evolved independently in different types of mammals through convergent evolution and varies both in dental composition and structure. In most mammals the comb is formed by a group of teeth with fine spaces between them. The toothcombs in most mammals include incisors only, while in lemuriform primates they include incisors and canine teeth that tilt forward at the front of the lower jaw, followed by a canine-shaped first premolar. The toothcombs of colugos and hyraxes take a different form with the individual incisors being serrated, providing multiple tines per tooth.
Altiatlasius is an extinct genus of mammal, which may have been the oldest known primate, dating to the Late Paleocene from Morocco. The only species, Altiatlasius koulchii, was described in 1990.
Karanisia is an extinct genus of strepsirrhine primate from middle Eocene deposits in Egypt.
Algeripithecus is an extinct genus of early fossil primate, weighing approximately 65 to 85 grams. Fossils have been found in Algeria dating from 50 to 46 million years ago.
Babakotia is an extinct genus of medium-sized lemur, or strepsirrhine primate, from Madagascar that contains a single species, Babakotia radofilai. Together with Palaeopropithecus, Archaeoindris, and Mesopropithecus, it forms the family Palaeopropithecidae, commonly known as the sloth lemurs. The name Babakotia comes from the Malagasy name for the indri, babakoto, to which it and all other sloth lemurs are closely related. Due to its mix of morphological traits that show intermediate stages between the slow-moving smaller sloth lemurs and the suspensory large sloth lemurs, it has helped determine the relationship between both groups and the closely related and extinct monkey lemurs.
Lemurs, primates belonging to the suborder Strepsirrhini which branched off from other primates less than 63 million years ago, evolved on the island of Madagascar, for at least 40 million years. They share some traits with the most basal primates, and thus are often confused as being ancestral to modern monkeys, apes, and humans. Instead, they merely resemble ancestral primates.
Cantius is a genus of adapiform primates from the early Eocene of North America and Europe. It is extremely well represented in the fossil record in North America and has been hypothesized to be the direct ancestor of Notharctus in North America. The evolution of Cantius is characterized by a significant increase in body mass that nearly tripled in size. The earliest species were considered small-sized and weighed in around 1 kg, while the later occurring species were considered medium-sized and likely weighed in around 3 kg. Though significantly smaller, the fossil remains discovered of the various species of Cantius have striking similarities to that of Nothartcus and Smilodectes. It is likely Cantius relied on arboreal quadrupedal locomotion, primarily running and leaping. This locomotor pattern comparable to that of extant lemurs, which has fostered the hypothesis that Cantius and other strepsirrhine adapiforms may have a close phylogenetic affinity to living lemurs.
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. Although it is most fully developed in these primates, similar structures can be found in some other mammals, such as marsupials, treeshrews, and colugos. This "second tongue" lacks taste buds, and in lemuriforms, it is thought to be used to remove hair and other debris from the toothcomb, a specialized dental structure used to comb the fur during oral grooming.
Azibiidae is an extinct family of fossil primate from the late early or early middle Eocene from the Glib Zegdou Formation in the Gour Lazib area of Algeria. They are thought to be related to the living toothcombed primates, the lemurs and lorisoids, although paleoanthropologists such as Marc Godinot have argued that they may be early simians. It includes the genera Azibius and Algeripithecus, the latter of which was originally considered the oldest known simian, not a strepsirrhine.
Azibius is an extinct genus of fossil primate from the late early or early middle Eocene from the Glib Zegdou Formation in the Gour Lazib area of Algeria. They are thought to be related to the living toothcombed primates, the lemurs and lorisoids, although paleoanthropologists such as Marc Godinot have argued that they may be early simians. Originally described as a type of plesiadapiform, its fragmentary remains have been interpreted as a hyopsodontid, an adapid, and a macroscelidid. Less fragmentary remains discovered between 2003 and 2009 demonstrated a close relationship between Azibius and Algeripithecus, a fossil primate once thought to be the oldest known simian. Descriptions of the talus in 2011 have helped to strengthen support for the strepsirrhine status of Azibius and Algeripithecus, which would indicate that the evolutionary history of lemurs and their kin is rooted in Africa.
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 lemuriforms, they are thought to be a related stem group. The one recognized species, Djebelemur martinezi, was very small, approximately 100 g (3.5 oz).
Djebelemuridae is an extinct family of early strepsirrhine primates from Africa. It consists of five genera. The organisms in this family were exceptionally small, and were insectivores. It is predicted that this family existed from early to late Eocene, they lacked a teeth comb and were able to fully rotate their heads. It is also predicted that this family was a pivotal point for primate evolution, and that they were the cause for the adaption of a tooth comb.
Afrasia djijidae is a fossil primate that lived in Myanmar approximately 37 million years ago, during the late middle Eocene. The only species in the genus Afrasia, it was a small primate, estimated to weigh around 100 grams (3.5 oz). Despite the significant geographic distance between them, Afrasia is thought to be closely related to Afrotarsius, an enigmatic fossil found in Libya and Egypt that dates to 38–39 million years ago. If this relationship is correct, it suggests that early simians 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 Afrotarsiidae, is considered ancestral to living simians, but they are part of a side branch or stem group 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 mammalian groups, including hystricognathous rodents and anthracotheres.
Afradapis is a genus of adapiform primate that lived during the Late Eocene. The only known species, Afradapis longicristatus, was discovered in the Birket Qarun Formation in northern Egypt in 2009. While its geographic distribution is confined to Afro-Arabia, Afradapis belongs to the predominately European adapiform family Caenopithecidae. This taxonomic placement is supported by recent phylogenetic analyses that recover a close evolutionary relationship between Afradapis and adapiforms, including Darwinius. While adapiforms have been noted for their strepsirrhine-like morphology, no adapiform fossil possesses the unique anatomical traits to establish an ancestor-descent relationship between caenopithecids and living strepsirrhines. It ate leaves and moved around slowly like lorises.
Propotto is an extinct, monotypic genus of early strepsirrhine primate from the early Miocene of Kenya. It contains one described species, Propotto leakeyi. Although long considered a pteropodid fruit-eating bat after spending a brief sojourn as a prehistoric relative of lorises, recent research shows it to be an extinct relative of the aye-aye.
