Primate Evolution: Fossils and Emergence

• Primate evolution covers early primates, anthropoids, and hominoids

Early Primate Fossil Records

• Fossil records are incomplete
• Fossil teeth and jaws change very little over time
• Relative primate size and diet can be determined from the fossils
• Frugivores possess flat rounded cusps
• Reconstructing environments and dating techniques aid primate studies
• A lemur-like primate discovered in Asia existed around 34 million years ago

Emergence of Primates

• Plesiadapiforms are archaic primates, mainly identified by molar teeth
• Plesiadapiforms had small bodies and brains, large snouts, lateral eyes, and a herbivorous diet
• Plesiadapiforms possessed robust, agile limbs adapted for arboreal life, and claws for grasping
• Purgatorius sp. may be the first primate, dating back to approximately 65.9 million years ago
• Flexible ankle bones were necessary for arboreal life

Carpolestes

• Three families are classified under Plesiadapiformes: Paromomyidae, Carpolestidae, and Plesiadapidae.

Adapoids

• Adapoids, also known as Adapids, are modern Strepsirhines
• Adapoids possess forward-facing eyes, a large brain, a reduced snout, and adaptations for leaping

Omomyides

• Omomyides are modern Haplorhines belonging to Tarsiformes
• Showcased short faces, large eyes, large brains, a post-orbital bar, and an elongated ear bone, similar to modern tarsiers and catarrhines

Conditions for Evolution

• The breakup of Gondwanaland occurred between 135 and 65 million years ago
• Climate change led to cooler and drier conditions
• During the Cretaceous period, there was a rise in flowering plants, trees, and insects
• A major extinction occurred at the Cretaceous-Palaeozoic transition

Theories of Primate Emergence

• The arboreal theory suggests that life in trees led to the development of vision over smell
• The visual predation theory suggests that insect prey required 3D vision and grasping hands and feet
• The angiosperm-primate coevolution hypothesis explains primate emergence

Adapoid Origins

• Adapoid origins featured adaptations like robust chewing, mandible fusion, and canine sexual dimorphism

Omomyoid Origins

• Omomyoid origins share similar cranial and hindlimb traits; retained for millions of years

Tasier Origins

• Haplorrhine origins featured post-orbital septum, no tapetum lucidum, and placentation
• Asian Eocene primates factored into the Tasier Origins

Early Anthropoids in Fayum, Egypt

• Early anthropoids existed during the Late Eocene and Early Oligocene epochs
• All anthropoid fossil crania show orbital closure and ring-like ear bones
• A dental formula of either 2.1.3.3 OR 2.1.2.3 existed
• These families are Parapithecids and Propliopithecids

Oligocene Parapithecids

• Oligocene Parapithecids may be ancestral platyrrhines or simply stem anthropoids, showed prosimian features, and had 3 premolars
• Anthropoid features included a bony eye socket, broad incisors, projecting canines, and low, rounded cusps on molars

Oligocene Propliopithecids

• Oligocene Propliopithecids are potentially ancestral to Old World Monkeys and Hominoids
• Propliopithecids had dentition similar to modern Catarrhines and 2 premolars
• Anthropoid traits included broad incisors, projecting canines, low, rounded cusps on molars, and a bony eye socket

Asian Anthropoid Fossils

• Eosimias sp. is a tiny anthropoid from approximately 45-40 million years ago
• Jaws and teeth have been discovered
• Two species of amphipithecids existed
• Pondaungia sp. and Amphipithecus sp. were all small-medium-sized anthropoids from the early/middle Eocene epoch
• Dental similarities to anthropoids existed

Dispersal of New World Monkeys

• It is hypothesized that island-hopping
• They could have floated on large mats of vegetation
• The oldest Platyrrhine fossils from Peru are from approximately 36 million years ago

Emergence of Hominoids

• The Miocene epoch (~24m – 5.2mya) saw mountain building lead to dry continental weather
• adaptive radiation of monkey and ape species
• One of the Miocene apes is believed to be ancestral to hominins

Early Miocene Proto-Apes

• Proconsul existed around 20 mya, primarily in Africa
• They were arboreal quadrupeds with a diet of fruit and some leaves
• Hominoid features found in Proconsul included lacking a tail, dentition, and may be ancestral to later apes and humans

Middle Miocene ape characteristics

• Distinct hominoid genera emerge around 17mya in Africa, Europe and Asia
• Pierolapithecus existed around ~13mya, showing brachiation and distinctive face and dentition
• Kenyapithecus existed around ~14mya and shows Proconsul features
• Kenyapithecus also has teeth and facial characteristics close to modern hominoids

Late Miocene Apes

• Apes were present in most habitats from 11mya-5mya, including Europe, Asia, and Africa
• The Eurasian Ape may be the common ancestor to Hominins
• African Ape species numbers grew (ca 13mya- 9mya)
• An unbroken lineage may have been retained from early Miocene through late Miocene apes to Hominin lines

Late Miocene Eurasian Apes

• Sivapithecus existed (15-5mya), possessed thick enameled teeth
• Sivapithecus diet included hard, gritty, or tough plants, arboreal, and shows brachiation capabilities
• Sivapithecus is likely an ancestor to Orangutans
• Dryopithecus existed (16-11mya) and closely resembles African Apes -*Dryopithecus had a small face, slight brow ridge, lighter jaws, likely arboreal, and shows brachiation capabilities

Late Miocene African Apes

• Otavipithecus existed during the late-Middle Miocene (13 to 12 million years ago) in Namibia
• Chororapithecus existed (10.7 million to 10.1 million years ago) in Ethiopia and is a possible Gorilla ancestor
• Nakalipithecus existed (9.9 million to 9.8 million years ago) in Kenya and is a possible gorilla ancestor -Samburupithecus existed (9.5 mya) from Kenya

Divergence of Hominins

• A gap in the African fossil record existed from 13.5 to 5 mya
• Primates with hominin characteristics emerged after 5 mya in East Africa
• Recent African fossil finds: Orrorin tugenensis (~6 mya) and Sahelanthropus tchadensis (~7 mya)

Molecular Clocks

• Molecular clocks calculate divergence between species
• Neutral mutations accumulate at a set rate
• Stable mutation rate + stable generation time are required
• Number of different mutations is proportional to the age of the most recent common ancestor