Evolution of primates

Primates are believed to have diverged from other mammals during the Late Cretaceous period of the Mesozoic Era. Fossils of Cretaceous primates are virtually non-existent, with estimates based on molecular data instead of morphological information. The oldest record of stem-primates comes from the order Plesiadapiformes in the earliest Paleocene epoch shortly following the Cretaceous-Paleogene (K/PG) extinction event. The plesiadapiform subfamily Purgatoriidae represents the earliest plesiadapiform lineage known to diversify, as fossils of the family are known from sediments across North America within ~140,000 years of the K/PG extinction. Though fossils of purgatoriids are rare and limited to fragmentary elements, they are considered to be stem-primates based on the morphology of their ankles which share several features with both Plesiadapiformes and wider members of Euarchonta. This placement has been supported in subsequent phylogenetic analyses. The morphology of purgatoriids suggests an arboreal lifestyle that has been hypothesized as ancestral to crown primates, while their tooth morphology - which possess a mixture of pointed and rounded cusps - is theorized to have supported an insectivorous or omnivorous diet depending on the species. Other fossils in the group reveal long snouts with large upper incisors and laterally facing orbits lacking postorbital bars, also suggesting early primate traits. Throughout the Paleocene and Eocene epochs, plesiadapiforms underwent a substantial radiation based in North America and Europe, though several species are known from Asia as well. In total, 11 different plesiadapiform families are recognized from the fossil record, encompassing over 25 million years of time and displaying a wide diversity of dietary behaviours. This suggests, in combination with molecular studies, that the divergence of haplorhines and strepsirrhines came in the Paleocene, estimated to be sometime between 64 and 63 million years ago. == Evolution of Strepsirrhines ==

A note on 'prosimians' Strepsirrhines, the group of primates including lemurs, lorises, and galagos, is also part of the older categorization "prosimians". The "prosimian" category is a paraphyletic group which includes all strepsirrhines and tarsiers. Tarsiers are part of the monophyletic clade of Haplorrhinii but share some traits with Strepsirrhines leading to the older mis-categorization creating the group "prosimians". Original photo from Leptadapis article, using older genera classification. The earliest strepsirrhines are known as adapiforms, a diverse group that ranged throughout Eurasia and North America. Adapoids share several traits with modern Strepsirrhines including: long snouts, relatively small eyes, a long nasolacrimal canal indicating a rhinarium or "wet nose", a gap between small incisors to access their vomeronasal organ, canines larger than their incisors, and an inflated bony auditory bulla with a suspended tympanic ring. Adapoids originated in the Eocene and though they survived till the late miocene, the earliest known strepsirhines appear in North African fossil beds also from the Eocene. This indicates that despite the longevity of adapoids, an early branch of this clade gave rise to lemuriform primates, which includes lemurs and their kin. Darwinius masillae Darwineus masilae is a primate fossil from an Eocene lagerstätte in Messel, Germany. Meanwhile the lack of postorbital closure, a potentially sloping tibulo-fibular facet, and implacable grooming claw perpetuate the debate by indicating strepsirrhine phylogeny. These authors point out that many of the traits used to associate Darwinius with Haplorhines are athropoid traits while Darwinius lacks many basal Haplorhine traits. They argue spatulate incisors could be (and often are in primates) a symplesiomorphies for diet specialization rather than an indicator of Haplorhine heritage. Loris and Galago phylogeny is difficult to trace for a number of reasons including: the crypsis of both groups, arboreal lifetyles in densly forested environments, and frequent convergence on similar morphologies. Researchers continue to disagree on the phylogenetic organization of extant lorisiformes, primarily whether the subfamily Perodicticinae (Angwantibos and Pottos / African Lorises) is truly a sister group to Lorisinae (Asian Lorises) or more closely related to extant Galagidae (Galagos) and subject to a surprising convergence with Lorises. With continuing disagreement on what constitutes each clade, it can make classifying fragmentary fossil primates even more difficult. Consisting of only a mandible fragment and a few isolated teeth, Karanisia clarki is the oldest fossil primate known to have a tooth comb. Karanisia's estimated body mass is 273grams. Dental morphology and microwear analysis of the molars indicate a potential for folivory. However, a completely folivorous diet is prohibited by the energy and metabolic requirements of its size, leading researchers to reconstruct Karanisia as an omnivore. Karanisia molars closely resembles those of the living lorisid: Arctocebus (the Golden Potto). Although its position as the oldest tooth-combed primate fossil places it confidently within at least stem Strepsirrhini, many researchers debate if it is a crown strepsirhini, stem lorisoid, stem lemuroid. Semicircular canals are held within the petrous portion of the temporal bone, a very thick and often well preserved portion of the skull. In contrast, animals who move more slowly tend to have more variation in general as their canals are not under pressure to maintain a certain morphology. As a result, there is a noticeable and quantifiable difference in their semicircular canal volumes which can be quantified and used to assign fossil crania or partial crania to a range of speed and by extension infer each locomotion. Recent genetic evidence suggests that lemurs are one monophyletic group distinct from lorisiformes, supporting the idea that there was one colonization event, the ancestor of all modern lemurs arrived on Madagascar once rather than several ancestors of different groups arriving at different times. Recent research suggests that the adaptive radiation in Madagascar might have been comparatively gradual, rather than a sudden burst, with hybridization and genetic introgression resulting in more diversity and aiding speciation.There were three primary groups: Archeolemurs, Megladapines, and Paleopropithecines. All three clades are characterized by large size and slow maturation but each is associated with a set of derived traits convergent with separate mammalian groups. Archeolemurines, between 26kg and 35kg, are also called "monkey lemurs" due to their convergent traits with Cercopithecines. This family includes the Genus Hadropithecus and Archeolemur. They have a lemur-like ear and lack a postorbital closure, consistent with their status as lemurs. However, they also have broad flat incisors with no gap between the two central incisors, a fused mandibular symphysis, and bilophodont molar teeth convergent with cercopitheocoid monkeys. It also has unique adaptations like an absence of canines and the anterior-most premolar becoming caniniform. They have a mixture of dental traits similar to Catarrhines including: shearing premolars (indicative of foliovory), low rounded bilophodont molars (indicative of frugivory), and enamel microstructure conducive to hard seed or insect crushing. Altogether researchers believe Archeolemurs likely had an omnivorous diet. The short, limbs relative to trunk length are indicative of Arboreal Quadrupedalism though smaller limb features are more similar to gorilla's terrestrial quadrupedalism. Megaladapines are referred to as "Koala lemurs" due to their hypothesized posturing and folivorous diet. Containing only the genus Megaladapis, at about 70kg, they were as large as than modern gorillas but have no upper incisors. Extremely short limbs, and teeth with well developed crests indicating a highly folivorous diet. Researchers believe it likely clung to thick tree trunks much like a koala and its lack of upper incisors indicate it may have had a horny pad or plate on its maxilla to help grind food like Artiodactyla. The buttressing extending above the nasal aperture has led some researchers to hypothesize it might have had a highly mobile upper lip or proboscis like a giraffe or elephant. Paleopropithecines, rangign in size between 11kg and 160kg, are called "sloth lemurs" because their extremely sloth like limb proportions and reduced dentition. They have a very high intermemrbal index of 144, indicating extemely long forlimbs compared to hindlimbs, aligning well with modern primates and sloths suspensory behavior. Their similarity to sloths extend to the their very curved phalanges, resembling suspensory apes like orangutans morphologically and sloths curved claws ecologically. They also have stubby incisors (indicating they played little role in diet) and molars well adapted to folivory. Due to their similarities to living indriids, (including: suspensory feeding postures, four toothed tooth comb, and reduced dentition overall) they are generally placed in a monophyletic subfamily within Indriidae. This subfamily includes the genuses: Mesopropithecus, Babakotia, Paleopropithecusand Archaeoindris. Archaeoindris, the largest subfossil lemur currently known at around 160kg. == Evolution of Haplorrhines ==

Haplorhines can be separated from the more primitive strepsirrhines. Haplorhines possess a retinal fovea on the posterior surface of their eyeballs. They have an orbital plate disjoining their orbits and temporal fossa, and relatively smaller olfactory bulbs than strepsirrhines with fewer nasal turbinates. Haplorhines also have a reduced vomeronasal organ, a dry rhinarium, and a vertical nasolacrimal duct connecting the orbit to the nasal cavity. The oldest haplorhines in the fossil record are from the Paleocene-Eocene, a period of time associated with a global warming event. The climate of the early and middle Eocene was warm, and more frequent warming events allowed for the survival and spread of early groups. Haplorhine origins are assumed to date to the Eocene in Africa, but they probably radiated from that region due to climate change. Early primates and haplhorhines must have been found much farther north than they are today. Their geographic range is thought to be about 60°N latitude or to the Arctic Circle. The primate superfamilies Tarsioidea and Adapoidea were the major primate groups of the early and middle Eocene. Early Tarsioidea and Adapoidea are thought to be stem or crown groups of haplorhini because of their comparable fossil dentitions. Tarsioidea is now maintained by the living genus Tarsius. Adapoidea members have no living relatives, but are thought to have been precursors of apes and monkeys. Other early haplorhine groups include Ceboidea and Hominoidea from the Oligocene and Cercopithecoidea from the early Miocene. Living haplorhines are tarsiers or anthropoids. == Evolution of color vision ==

Some of the primates' vertebrate ancestors were tetrachromats, but their nocturnal mammalian ancestors lost two of their four cones during the mesozoic. Most modern primates, however, have evolved to be trichromats. All old world monkeys and apes are trichromats, but new world monkeys are polymorphic trichromats, meaning that males and homozygous females are dichromats while heterozygous females are trichromats (with the exceptions of howler monkeys and night monkeys, who have more and less robust color vision respectively). There are four prevailing theories as to what the evolutionary pressure was for primates to develop trichromatic vision. The Fruit Theory suggests that it was easier for trichromatic primates to find ripe fruit against a green background. While there is data supporting the Fruit Theory, there is some dispute about whether or not trichromacy was more advantageous for determining how ripe fruit was up close or spotting fruit from afar. The Young Leaf hypothesis suggests that primates with more advanced color vision could better spot younger and more nutritious leaves during fruit shortages, while there are also theories that suggest more advanced color vision was better for recognizing changes in skin tone, allowing primates to better determine the blood oxygen saturation of others. Still other theories suppose that primates' color vision evolved alongside their sense of smell, though research has shown no direct correlation between concentration of olfactory receptors and acquisition of color vision. == Evolution of Platyrrhines (New World Monkeys) ==

Following the emergence of Simiiformes in Africa, the pavorder Platyrrhini (New World Monkeys) split from Catarrhini during the Eocene period, sometime around 40 million years ago on the African continent. Their present distribution in South America is theorized to have resulted from rafting across the Atlantic Ocean, with dispersal events facilitated by large mats of vegetation capable of transporting small populations to South America. Transportation of vegetation rafts were aided by a relatively narrower Atlantic, which is hypothesized to have been ~1,000 km narrower than today based on calculated rates of mid-ocean ridge spreading at 2.5 mm per year, and differing paleocurrents which produced westwards movement of currents. Three separate transoceanic dispersal events between Africa and South America are theorized to have occurred within primates due to the presence of several non-platyrrhine primates from fossil deposits in South America. The exact timing of platyrrhine dispersal is debated. Historically, a mid-to-late Oligocene dispersal was viewed as likely based on fossil and molecular data. Bayesian estimates of divergence time have indicated the most recent common ancestor of new world monkeys existed between 27-31 million years ago. Additionally, the platyrrhine genus Branisella boliviana, found in the Salla Luribay basin and dated to the Late Oligocene (26 million years ago), was believed to represent the oldest known stem platyrrhine. However, new evidence suggests an earlier origin, as fossils of the genus Perupithecus ucayaliensis from the Peruvian Amazon date to approximately 36 million years ago. This pushes the date of platyrrhine dispersal to the late Eocene, approximately 37 million years ago and 10 million years older than previously considered. Fossils of platyrrhines are infrequent and difficult to access, mainly due to the dense forest cover of South America and the poor probability of fossilization in rainforest habitats. The best material from stem platyrrhines belongs to the Oligocene genus Branisella, whose anatomy suggests it was a semiterrestrial omnivore that occupied woodland habitats. The record of platyrrhines in the Miocene is more extensive. Platyrrhines from the earliest Miocene (20-15 million years ago) are known primarily from fossils in the southern cone of South America, an area that rests outside their present distribution. The southern platyrrhines show adaptations for frugivory and granivory, particularly seeds and hard fruits that reflect the dry habitats occupied by several taxa, and show anatomical affinities with the platyrrhine subfamily Pitheciidae, though this relationship is debated. Fossils from the middle-to-late Miocene are distributed to northern countries in South America, particularly the La Venta fossil site of Colombia, and show the evolution of several modern platyrrhine subfamilies, including relatives of howler monkeys, cebids, night monkeys, callitrichids, and titi monkeys, amongst others. == Evolution of Old World monkeys ==

The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Kenya Rift Valley, dated to 24 million years ago. Its ancestry is thought to be species related to Aegyptopithecus, Propliopithecus, and Parapithecus from the Faiyum depression, at around 35 million years ago. In 2010, Saadanius was described as a close relative of the last common ancestor of the crown catarrhines, and tentatively dated to 29–28 million years ago, helping to fill an 11-million-year gap in the fossil record. Notable species also include Nsungwepithecus gunnelli and Rukwapithecus fleaglei of the Oligocene. '' skeleton In the early Miocene, about 22 million years ago, the many kinds of arboreally adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Fossils dated to be 20 million years old include fragments attributed to Victoriapithecus, believed to be the earliest Old World monkey. Among the genera thought to be in the ape lineage leading up to 13 million years ago are Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, all from East Africa. The presence of other generalized non-cercopithecids of the middle Miocene age from sites far distant—Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France, Spain and Austria—is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the early and middle Miocene. The youngest of the Miocene hominoids, Oreopithecus, is from coal beds in Italy that have been dated to 9 million years ago. Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) diverged from Great Apes some 18–12 million years ago, and that of orangutans (subfamily Ponginae) diverged from the other Great Apes at about 12 million years; there are no fossils that clearly document the ancestry of gibbons, which may have originated in a so-far-unknown South East Asian hominoid population, but fossil proto-orangutans may be represented by Sivapithecus from India and Griphopithecus from Turkey, dated to around 10 million years ago. Human evolution Human evolution is the evolutionary process that led to the emergence of anatomically modern humans, beginning with the evolutionary history of primates – in particular genus Homo – and leading to the emergence of Homo sapiens as a distinct species of the hominid family, the great apes. This process involved the gradual development of traits such as human bipedalism and language. The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, paleontology, neurobiology, ethology, linguistics, evolutionary psychology, embryology and genetics. Early genetic studies suggested that primates diverged from other mammals about , but newer research questions this suggesting a date possibly in the Paleocene, consistent with the earliest fossils being found, around . Within the superfamily Hominoidea (apes), the family Hominidae diverged from the family Hylobatidae (gibbons) some 15–20 million years ago; African great apes (subfamily Homininae) diverged from orangutans (Ponginae) about ; the tribe Hominini (humans, Australopithecines and other extinct biped genera, and chimpanzee) parted from the tribe Gorillini (gorillas) between and ; and, in turn, the subtribes Hominina (humans and biped ancestors) and Panina (chimpanzees) separated about to . == Evolution of the pelvis ==

In primates, the pelvis consists of four parts—the left and the right hip bones, which meet at the ventral mid-line, the sacrum, which connects the hip bones dorsally, and the coccyx. Each hip bone consists of three components, the ilium, the ischium, and the pubis, and at the time of sexual maturity these bones become fused together, though there is never any movement between them. In humans, the ventral joint of the pubic bones is closed. In bipedal primates, the ilium is shortened, widened, and the blades are located more laterally than in other primates. These morphological changes are due to the stresses involved in bipedal locomotion, where the Rectus femoris muscle activates on the stationary leg, to counterbalance as the other leg moves forward. The shape of the pelvic outlet is remarkably small in bipedal primates compared to that of quadrupedal primates because a smaller pelvis provides better balance for bipedal locomotion. As such, modern humans must have fully rotational births. Though it is hypothesized that Australopithecus afarensis had semi-rotational births, no other primates require assisted birth. == See also ==