Chapter 3
Primates Past to Present

Evolutionary History

The discussion on primate evolution will be framed within a geological timescale. We will focus on the major fossil finds within the various epochs and the overall climatic changes occurring throughout the world.

The geological timescale is divided into an era, then periods, followed by epochs. The current era is called the Cenozoic Era, which includes the Tertiary and Quaternary periods. The epochs for each period are outlined below:

Era - Cenozoic (65 million years ago (mya))
Period – Tertiary (65 mya)
Epochs: Paleocene (65 mya)
Eocene (54 mya)
Oligocene (34 mya)
Miocene (23 mya)
Pliocene (5 mya)

Period – Quaternary
Epochs: Pleistocene (1.8 mya)
Holocene (12, 000 ya)

Prior to the beginning of the Cenozoic Era, climatic changes lead to the extinction of the dinosaurs. Since the dinosaurs were no longer present, primates and other mammals were allowed to occupy new ecological niches. The dispersal and new environmental conditions lead to adaptive radiations and, ultimately, speciation.
Primates were also affected by the continental drift. As the plates holding the continents pushed together and pulled apart, the environment changed:
1. changed the rainfall patterns and temperature
2. created barriers and new habitats
3. led to isolation of some animal populations

Why did general primate characteristics evolve?

1. Arboreal Hypothesis: traits evolved due to an arboreal lifestyle

2. Visual Predation Hypothesis: traits evolved because individuals were better equipped to see and capture prey

Primate Origins

Paleocene Epoch
World Climate: Tropical environment and the beginning of a cooling trend

Plesiadapiforms were primate – like mammals discovered in North America, Europe, and Asia.

Eocene Epoch
World Climate: Cooling continues, greater seasonality

The “stem” primates demonstrate a great amount of diversity and resemble modern day prosimians.
Diurnal and nocturnal
Vertical clingers and leapers, plus some quadrupeds
Frugivores, insectivores, and folivores

World Climate: Cooling continued, drying occurred

Earliest anthropoid fossils found in Egypt. Possible anthropoid ancestral remains have also been found in South America. This is puzzling since Africa, North America, and South America were all separated by bodies of water.

How did ancestral anthropoids get to South America?
A journey across the sea on vegetation? (Fig 3.2)

Miocene Epoch
World Climate: Cool and dry, forest replaced by grasslands, ice caps form in Antarctica.

The Miocene is divided into three stages: Early, Middle, and Late
Early Miocene: ancestral hominoids emerge evidenced by the Y5 molar pattern.

Middle Miocene: Remains from Sivapithecus were found in Euarasia. Sivapithecus is believed to be a direct ancestor to the modern day orangutans.
Late Miocene: Divergence between hominoids and hominids.

(Pliostocene and Pleistocene combined)

World Climate: Periods of glaciation

Increase in the remains of ancestral monkeys (OWM and NWM), but a decrease in the amount of ancestral ape remains.

Evidence of bipedalism, which refers to ancestral humans, found in Eastern and Southern Africa.
Changes in the climate lead to the extinction of primate populations due to glacial and interglacial periods.
Glacial periods caused the forests to shrink, which formed isolated pockets known as refuges.
By the time the interglacial period began, some primate populations differed so much they could not interbreed or remained isolated. Others took advantage of the re- expanding forest. 

Holocene Epoch
World Climate: Warming trend

Primates are located along the equatorial belt at low altitudes. Tropical environments have high species diversity due to rainfall and resource availability, although some thrive in savannahs and cold environments.

Human populations are worldwide and have begun to impact the habitats and lives of nonhuman primates.

Those at greatest risk are the species that are endemic because they are localized to specific regions and have adapted to specific environmental conditions

Intraspecific and Interspecific Variation
Intraspecific variation – within species
Interspecific variation – between species

Identify behaviors that respond to environmental conditions
Identify behaviors under phylogenetic control


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