Primate Evolution: Fossils and Origins

• Lectures cover primate evolution focusing on early primates, anthropoids, and hominoids.

The Fossil Record

• The fossil record is incomplete.
• Fossil teeth and jaws change very little so are useful for identification.
• Fossils provide clues about primate size and diet; frugivores possessed flat, rounded cusps.
• Primate studies involve dating techniques and reconstructing environments.
• A lemur-like primate was discovered in Asia dating back about 34 million years ago.

Emergence of Primates

• Plesiadapiforms are archaic primates mostly identified by their molar teeth.
• Plesiadapiforms had small bodies and brains, large snouts, lateral eyes, and a herbivorous diet.
• Flexible ankle bones suggest that Plesiadapiforms were arboreal
• Purgatorius sp., dating back approximately 65.9 million years ago, may be the first primate.
• Three families included in Plesiadapiformes are Paromomyidae, Carpolestidae, and Plesiadapidae.

First Primates

• Adapoids/Adapids are modern Strepsirhines.
• Adapoids had forward-facing eyes, large brains, reduced snouts and were leaper movers.

Tarsiformes: Omomyides (Modern Haplorhines)

• Defining traits include short faces, large eyes, large brains, a post-orbital bar, and elongated ear bones which are similar to modern tarsiers/catrrhines.

Conditions Leading to Primate Evolution

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

Theories: Emergence of Primates

• The arboreal theory of emergence defines that life in trees led to vision over smell
• The visual predation theory suggests that insect prey required 3D vision, grasping hands, and feet.
• The angiosperm-primate coevolution hypothesis refers to primates co-evolving with angiosperms

Emergence of Anthropoids

• Adapoid origins traits include robust chewing, fusion of the mandible, and canine sexual dimorphism.
• Omomyoid origins show similar cranial traits that were retained for millions of years.
• Tasier origins include haplorrhine traits, a post orbital septum, no tapetum lucidum and placentation.
• Also found in Asian Eocene primates.

Early Anthropoids: Fayum, Egypt

• Anthropoid fossils here are from the late Eocene to early Oligocene epochs.
• All anthropoid fossil crania had orbital closure and ring-like ear bones.
• Dental formula of 2.1.3.3 or 2.1.2.3 present here.
• Parapithecids and Propliopithecids families found here.

Oligocene Parapithecids

• They may be ancestral platyrrhines or only stem anthropoids.
• Parapithecids had Prosimian along with anthropoid features.
• Prosimian features include 3 premolars.
• Bony eye sockets, broad incisors, projecting canines are anthropoid features.
• Low, rounded cusps on molars.

Oligocene Propliopithecids

• Possible ancestors to Old World Monkeys and Hominoids?
• Dentition is similar to modern Catarrhines.
• They has 2 premolars.
• They had broad incisors, projecting canines, low rounded cusps on molars and bony eye sockets.

Early Anthropoid Fossils in Asia

• Eosimiidae are tiny anthropoids from 45-40mya.
• Pondaungia sp. and Amphipithecus sp. are small-medium sized anthropoids from the early to mid Eocene.
• All had dental similarities to anthropoids

Dispersal of New World Monkeys

• Two Hypotheses for the dispersal of new world monkeys include island hopping and floating on large mats of vegetation.
• Oldest Platyrrhine fossils from Peru date to ~36mya (million years ago).

Emergence of Hominoids

• Hominoids emerged in the Miocene epoch (~24m – 5.2mya).
• Mountain building led to drier continental weather.
• Adaptive radiation of monkey and ape species
• One of the Miocene apes is ancestral to hominins.

Early Miocene Proto-Apes

• Proconsul existed ~20 mya, primarily in Africa.
• Proconsul was an arboreal quadruped that consumed fruit and leaves.
• Hominoid features include a lack of tail and specific dentition.
• Possible ancestors to later apes and humans.

Middle Miocene Apes

• Around 17mya there were distinct hominoid genera in Africa, Europe, and Asia.
• Pierolapithecus existed around 13mya and showed brachiation traits with distinct facial and dental features.
• Kenyapithecus existed around 14mya and had Proconsul features.
• In Kenyapithecus the teeth and faces are similar to modern hominoids

Late Miocene Apes

• Apes were present in most habitats between 11mya-5mya in Europe and Asia, and an increasing number in Africa
• Eurasian Apes may be the common ancestor to Hominins.
• The number of African Ape species increased between 13mya-9mya.
• There is a retained unbroken lineage from early Miocene through late Miocene apes to Hominin lines.

Late Miocene Eurasian Apes

• Sivapithecus lived 15-5mya.
• Sivapithecus had thick enameled teeth, a diet of hard, gritty or tough plants, was arboreal and had brachiation capabilities.
• Can be considered a likely ancestor to Orangutans.
• Dryopithecus existed 16-11mya
• Dryopithecus resembles Apes, with a small face, slight brow ridge, lighter jaws and brachiation capabilities

Late Miocene African Apes

• Otavipithecus lived in the late-Middle Miocene (13 to 12 million years ago) in Namibia.
• Chororapithecus lived 10.7 to 10.1 million years ago.
• Nakalipithecus existed 9.9 million to 9.8 million years ago in Kenya
• Samburupithecus lived 9.5 mya from Kenya

Divergence of Hominins

• There is a gap in the African fossil record between 13.5 to 5 mya.
• Primates with hominin characteristics appeared after 5 mya in East Africa.
• Recent African fossil finds include Orrorin tugenensis (~6 mya) and Sahelanthropus tchadensis (~7 mya).

Molecular Clocks and Divergence of Species

• Calculate divergence between species using molecular clocks.
• Neutral mutations accumulate at a set rate.
• Stable mutation rate + stable generation time can be used to calculate divergence.
• The number of different mutations is proportional to the age of the most recent common ancestor.