Fossil primates 1 Family Parapithecidae (extinct Fossil primates Oligocene monkeys) Extinct members of the order of mammals to which Infraorder Platyrrhini (New World anthro- humans belong. All current classifications divide the poids) living primates into two major groups (suborders), Superfamily Ateloidea (New World but zoologists differ as to whether the tarsier (Tar- monkeys) sius) should be classified with the lower primates Family Atelidae (howler, spider, (lemurs, lorises, and bushbabies) or the higher pri- saki, titi, and owl monkeys) mates (New and Old World monkeys, greater and Family Cebidae (squirrel, capuchin, lesser apes, and humans). and marmoset monkeys) All primates have a common origin which, how- Infraorder Catarrhini (Old World anthro- ever, is not reflected in the universal possession of poids) a suite of diagnostic features. The order as a whole Parvorder Eocatarrhini (archaic has been characterized in terms of showing a group catarrhines) of progressive evolutionary trends, notably toward Family Propliopithecidae (extinct the predominance of the visual sense, the reduction common ancestors of hominoids of the sense of smell and associated structures, im- and cercopithecoids) proved grasping and manipulative capacities, and en- Family Pliopithecidae (extinct early largement of the higher centers of the brain. Among catarrhines) the extant primates, the lower primates more closely Parvorder Eucatarrhini (advanced catar- resemble forms that evolved relatively early in the rhines) history of the order, while the higher primates rep- Superfamily Hominoidea (apes and resent a group more recently evolved (Fig. 1). A humans) classification of the primates, as accepted here, is as Family Proconsulidae (extinct early follows: apes) Family Hylobatidae (gibbons, lesser Primates apes) Semiorder Plesiadapiformes (archaic extinct Family Hominidae (great apes, primates) humans, and extinct relatives) Superfamily Paromomyoidea (paro- Superfamily Cercopithecoidea (Old momyids, picrodontids) World monkeys) Superfamily Plesiadapoidea (plesia- Family Cercopithecidae (Old World dapids, carpolestids) monkeys) Semiorder Euprimates (modern primates) Suborder Strepsirhini (toothcombed “prosimi- Early primates. The earliest primates are placed in ans” and extinct allies) their own suborder, Plesiadapiformes, because they Infraorder Adapiformes (extinct early have no direct evolutionary links with, and bear strepsirhines) no adaptive resemblances to, any group of living Superfamily Adapoidea (extinct early primates. However, the chewing teeth and the strepsirhines) locomotor anatomy of these fossil forms sufficiently Infraorder Lemuriformes (modern resemble those of later primates to demonstrate strepsirhines) the common origin of the two groups. Best known Superfamily Lemuroidea (typical from the Paleocene Epoch, around 66–54 million lemurs) years ago (Ma), and found in both the Old World Superfamily Indrioidea (indris, and the New World, the plesiadapiforms retained aye-ayes, and subfossil relatives) clawed hands and feet, had rather small brains Superfamily Lorisoidea (lorises, compared to their body size, possessed large special- bushbabies, mouse and dwarf ized front teeth, and were probably arboreal in habit lemurs) (Fig. 2). These animals are also known from fossil Suborder Haplorhini (tarsiers and higher deposits on Ellesmere Island, in Arctic Canada, which primates) was then covered by the subtropical forest stretching Hyporder Tarsiiformes (tarsiers and extinct continuously from western North America across a relatives) landlocked North Atlantic into western Europe. Superfamily Tarsioidea (tarsiers and Eocene primates. There is no known plesiadapi- close relatives) form that is a satisfactory candidate for the ances- Superfamily Omomyoidea (extinct try of the fossil primates of modern aspect typical early haplorhines) of the succeeding epoch, the Eocene (54–34 Ma). Hyporder Anthropoidea (higher primates) Often termed euprimates, they are divided broadly Infraorder Paracatarrhini (archaic anthro- into lemurlike forms, usually grouped into the poids) superfamily Adapoidea, and tarsierlike forms Family Oligopithecidae (archaic (Omomyoidea), although this division may prove to protoanthropoids) be oversimplified. Eocene primates of both the Old 2 Fossil primates STREPSIRHINI TARSIIFORMES Lemuridae Indriidae Daubentoniidae Lorisidae Tarsiidae ANTHROPOIDEA Cebidae Atelidae Cercopithecidae Hylobatidae Hominidae Fig. 1. Representatives of living primate families. and New Worlds already display the trends that mark It is possible that the origins of some specific modern primates as a whole: These arboreal animals groups of extant lower primates may be traced back possessed grasping hands and feet in which sharp to or through certain known primate genera of the claws were replaced by flat nails backing sensitive Eocene. Even if this is not the case, however, it is pads; the snout was reduced, suggesting a deempha- universally accepted that the antecedents of these sis of smell, while the bone-ringed eyes faced more living forms are to be sought somewhere within the forward, producing stereoscopic vision and suggest- Eocene primate radiation, though the details of this ing primary reliance on the sense of sight; and the ancestry may remain unclear. In North America and brain was somewhat enlarged relative to body size Europe, lower primates had nearly disappeared by when compared to those of other mammals of the the close of the Eocene, while virtually all known period. fossil lower primates of later epochs in Africa and 10 cm Fig. 2. Reconstructed skeleton of Plesiadapis tricuspidens, a Eurasian plesiadapiform from about 60 Ma. Known parts are shaded. Fossil primates 3 Asia are closely related to modern primates of these areas. Modern lower primates. The extant lower primates are allocated to the suborder Prosimii if Tarsius is in- cluded, and to the suborder Strepsirhini if this strange primate is excluded, as is provisionally done here. All extant strepsirhines possess dental scrapers (tooth- combs), in which the lower front teeth are elon- 20 cm gated, closely approximated, and forwardly project- ing. These specialized structures are used both in feeding and in social grooming. Additionally,all living strepsirhines retain a moist, naked rhinarium (wet nose, as in a dog) and related structures, reflecting a greater reliance on the sense of smell than is typical of higher primates. All are also united by possessing a toilet claw (used for self-cleaning) on the second digit of the foot. Although all strepsirhines possess grasping hands and feet, their manual dexterity is generally inferior to that of higher primates; their brains are also relatively small. There is no ancient primate fossil record in Mada- gascar, home of the most diverse group of modern lower primates, but extinct species little more than a thousand years old document a much wider adap- tive radiation before the arrival of humans on the Fig. 3. Anjohibe specimen of Paleopropithecus ingens, mounted in probable habitat posture. (Photo courtesy of American Geological Institute) island. Notable among those extinct lemurs are Paleopropithecus, a large-bodied climber-hanger somewhat like the orangutan in its locomotion more recent common ancestry with apes and hu- (Fig. 3); the semiterrestrial and dentally specialized mans, with which they are grouped in the infraorder members of the subfamily Archaeolemurinae, related Catarrhini. to the living indriids but adapted somewhat like ba- The earliest known anthropoids may be repre- boons; and Megaladapis, a very large, vertically sented by a few teeth (of Algeripithecus)from postured, short-limbed, and probably slow-moving Algeria about 45 million years old, but better- climber with adaptive resemblances to the koala preserved forms appear in the Fayum region of Egypt of Australia. Fragmentary remains of lorisoid strep- between 35 and 33 Ma. Although now a desert, at the sirhines are known from the Miocene of East Africa time this was a lush tropical forest through which and Pakistan. meandered the sluggish proto-Nile river. Three main Tarsiers. The tiny Tarsius, which lives today in groups of early higher primates are represented: the Southeast Asia, represents a link between the tooth- oligopithecids, the parapithecids, and the proplio- combed strepsirhines and the anthropoids (mon- pithecids. The former two appear to be only distantly keys, apes, and humans). In many respects (such as related to any of the living monkeys or apes, although lack of toothcomb, dry nasal area, molecular biology, they may be termed monkeys in the broad sense, as and placentation), it is related to the anthropoids, their adaptations are similar to those of modern mon- but dentally it is usually thought primitive, although keys. The propliopithecids (species of Propliopithe- some authors have found similarities to some strep- cus, including Aegyptopithecus) may be close to the sirhines. The extinct Eocene omomyoids are close to common ancestry of later catarrhines (Old World an- tarsiers skeletally; they are often considered broadly thropoids). These arboreal animals were the size of ancestral to the anthropoids for that reason and also small cats, with apelike teeth, small brain, and limbs because some have monkeylike front teeth. A tarsier- similar to those of the acrobatic South American like fossil has been recovered in Egypt from deposits atelines. Representatives of modern lineages begin to of early Oligocene age (35 Ma). Living tarsiers