Primate Evolution: Early Primates to Hominoids

• Lectures discuss Primate Evolution, specifically early primates to anthropoids and hominoids.
• Lecture 16 took place on February 24, 2025
• Lecture 17 took place on February 26, 2025

Fossil Record Insights

• The fossil record is incomplete, providing only a partial view of primate evolution
• Fossil teeth and jaws change very little over time and offer clues to primate size and diet
• Frugivores have flat, rounded cusps on their teeth

Research Techniques in Primate Evolution

• Scientists use primate studies, dating techniques, and environmental reconstruction to understand primate evolution

Emergence of Primates

• Plesiadapiforms are archaic primates recognized by their molar teeth
• Plesiadapiforms had small bodies and brains, large snouts, lateral eyes, and a herbivorous diet
• These primates were robust and agile, adapted for arboreal life with claws and grasping capabilities
• Purgatorius sp. may be the first primate, dating back 65.9 million years
• Key traits of early primates include a flexible ankle bone and molar teeth suited for arboreal life

Plesiadapiformes

• Carpolestes is a genus of plesiadapiforms
• Three families within Plesiadapiformes include Paromomyidae, Carpolestidae, and Plesiadapidae

Adapoids

• Adapoids, also known as Adapids, are considered modern Strepsirhines
• Key features of Adapoids are forward-facing eyes, large brain, reduced snout, and adaptations for leaping

Tarsiformes: Omomyides

• Omomyides are modern Haplorhines
• Omomyides possessed short faces, large eyes, large brains indicated by a post-orbital bar, and elongated ear bones
• These features are similar to modern tarsiers/catrrhines

Conditions Promoting Primate Evolution

• The breakup of Gondwanaland between 135 to 65 million years ago set geological stage
• Climate change leading to cooler and drier conditions influenced evolutionary pathways

Environmental Factors in Primate Evolution

• During the Cretaceous period, the rise of flowering plants, trees and insects drove primate evolution
• A major extinction event at the Cretaceous-Paleozoic transition further shaped primate development

Theories on Primate Emergence

• The arboreal theory posits primates emerged due to life in trees, favoring vision over smell
• The visual predation theory suggests primate traits evolved for insect prey, requiring 3D vision and grasping hands and feet
• The angiosperm-primate coevolution hypothesis links primate evolution to the rise of angiosperms

Origins of Key Anthropoid Traits

• Adapoid origins show adaptations like robust chewing and canine sexual dimorphism
• Omomyoid origins demonstrate similar cranial and hind limb traits retained for millions of years
• Features of Tasier origins include Haplorrhine traits such as post orbital septum, absence of tapetum lucidum, and placentation
• Asian Eocene primates also contributed to the emergence of anthropoids

Early Anthropoid Fossils

• Late Eocene to early Oligocene fossils found in Fayum, Egypt had all anthropoid crania
• Key features in the fossils include orbital closure, ring-like ear bones, and a dental formula of either 2.1.3.3 or 2.1.2.3

Oligocene Parapithecids

• Oligocene Parapithecids may be ancestral to platyrrhines or represent only a stem anthropoid
• They display Prosimian features and have 3 premolars
• Their Anthropoid features include a bony eye socket, broad incisors, projecting canines, and low, rounded cusps on molars

Oligocene Propliopithecids

• Propliopithecids could be ancestral to Old World Monkeys and Hominoids
• Dentition is similar to modern Catarrhines, with 2 premolars
• Anthropoid traits include broad incisors, projecting canines, low, rounded cusps on molars, and a bony eye socket.

Early Anthropoid Fossils in Asia

• Eosimiidae family shows the existence of Eosimias sp., a tiny anthropoid from about 45-40mya, known from jaws and teeth
• Amphipithecidae family includes Pondaungia sp. and Amphipithecus sp.
• These were small to medium-sized anthropoids from the early to middle Eocene
• There are dental similarities to other anthropoids

Monkey Dispersal

• Hypotheses for dispersal is island hopping and and floating on large mats of vegetation
• The oldest Platyrrhine fossils from Peru are dated to approximately 36 million years ago

Emergence of Hominoids in the Miocene Epoch

• The Miocene epoch, around 24 to 5.2 million years ago saw mountain building leading to dry continental weather, promoting adaptive radiation of monkey and ape species

Miocene Apes

• One of the Miocene apes is considered ancestral to hominins

Early Miocene Proto-Apes

• Proconsul lived approximately 20 mya in Africa
• It was an arboreal quadruped with a diet of fruit and some leaves
• It had Hominoid features but lacked a tail
• Its dentition and overall features indicate it may be ancestral to later apes and humans

Middle Miocene Apes

• Around 17mya, distinct hominoid genera lived in Africa, Europe, and Asia
• Pierolapithecus lived around 13mya exhibiting brachiation adaptations and specific face and dentition traits
• Kenyapithecus lived around 14mya exhibiting Proconsul features and teeth and face features similar to modern hominoids

Late Miocene Apes Expansion

• Apes were present in most habitats from 11mya-5mya, like Europe and Asia, and numbers grew in Africa
• Eurasian Ape is possibly the common ancestor to Hominins

African Ape Species

• African ape species numbers grew around 13mya-9mya
• There is an unbroken lineage from early Miocene through late Miocene apes to Hominin lines

Late Miocene Eurasian Apes

• Sivapithecus lived 15-5mya, possessed thick enameled teeth, and ate hard, gritty, or tough plants
• It was arboreal with brachiation capabilities, and may be an ancestor to Orangutans
• Dryopithecus, lived 16-11mya, resembled African Apes, and had a small face, slight brow ridge, and lighter jaws
• It was also likely arboreal with brachiation capabilities

Late Miocene African Apes

• Otavipithecus, from the late-Middle Miocene around 13 to 12 million years ago found in Namibia
• Chororapithecus, from 10.7 million to 10.1 million years ago in Ethiopia, is a possible Gorilla ancestor
• Nakalipithecus, lived 9.9 million to 9.8 million years ago in Kenya, may also be a gorilla ancestor

Samburupithecus

• Samburupithecus, from 9.5 mya in Kenya

Hominin Divergence

• There is a gap in the African fossil record from 13.5 to 5 mya
• Primates with hominin characteristics appeared after 5 mya in East Africa
• These have been Recent African fossil finds

Recent African Fossil Discoveries

• Orrorin tugenensis lived ~6 mya
• Sahelanthropus tchadensis lived ~7 mya

Molecular Clocks

• Molecular Clocks are used to compute divergence between species
• Neutral mutations accumulate at a consistent pace
• A stable mutation rate, combined with a stable generation time, enables the estimation of species divergence
• The quantity of various mutations corresponds to the age of the most recent common ancestor