Transcript 0495810843_246868

Chapter 6
Macroevolution and the Early
Primates
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
What Is Macroevolution?

When and Where Did the First
Primates Appear, and What Were
They Like?

When Did the First Monkeys and Apes
Appear, and What Were They Like?
Macroevolution and the
Process of Speciation

macroevolution = evolution above the
species level (i.e. the creation of new
species)

speciation = the process of forming new
species.
Macroevolution and the
Process of Speciation

Since species are populations who are capable of
interbreeding and producing viable and fertile
offspring

To create new species, populations must separate
through reproductive isolating mechanisms –
biological and behavioral factors that separate
breeding populations and prevent gene flow
Reproductive Isolating
Mechanisms: For Class
Discussion

What types of biological (morphology,
genetics) and behavioral factors could lead to
reproductive isolation?
Macroevolution and the
Process of Speciation
Cladogenesis = speciation occurs when descendants of an
ancestral population become reproductively isolated
Anagenesis = speciation through the gradual accumulation of
advantageous traits
The Shape of Macroevolution
(A) cladogenesis; (B) convergent evolution; (C) parallel evolution
Cladogenesis
(Divergent Evolution)
Convergent Evolution
Ancestral populations are very distantly related
Convergent Evolution
Ancestral populations are very distantly related
Parallel Evolution
Ancestral populations are more closely related
The Timing of Evolution
Gradual evolution – suggested by Charles
Darwin, physical traits change slowly and
consistently over time
Punctuated equilibria – suggested by
Stephen Gould, evolution occurs via long
periods of stability or stasis punctuated by
periods of rapid change.
The Timing of Evolution
Gradualism
Punctuated
Equilibrium
The Timing of Evolution and
Genetics
Change in the timing of growth and
development -- heterochrony, can be
responsible for changes in the shape or size
of a body part.
There are also homeobox genes that are
responsible for large-scale effects on the
growth and development of the organism.
They may be linked to patterns of evolutionary
timing predicted by the punctuated equilibria
model.
Visual Counterpoint: For
Class Discussion
The differences between chimpanzees and humans are
sometimes linked to a type of heterochrony known as
neotony (the retention of juvenile traits). Which juvenile
chimp traits do you think we have retained?
Constructing Evolutionary
Relationships

Evolutionary relationships can be
traced through:
(1)
homologous traits = originate from
a common ancestor
analogous traits = reflect similar
environmental pressures not
ancestry
(2)
Constructing Evolutionary
Relationships
Constructing Evolutionary
Relationships
The legs of prosimians and humans do not have a close
evolutionary relationship; they are a result of the convergent
evolution of homologous traits.
Constructing Evolutionary
Relationships

In addition to homologous and
analogous traits, evolutionary
relationships can be traced through:
(1) Derived traits = traits found in a group of
organisms that did not exist in ancestral
populations.
(2) Ancestral traits = traits possessed by an
organism or group of organisms due to
shared ancestry.
Macroevolution of the Early
Primates
Continental Drift and
Geological Time
Because primate evolution extends so far back in time,
paleoanthropologists reconstruct primate evolution in conjunction
with information about the geological history of the earth.
Continental Drift and
Geological Time
Continental drift =
According to the theory of
plate tectonics, the
movement of continents
embedded in underlying
plates on the earth’s surface
in relation to one another
over the history of life on
earth. Such changes can
also affect the climate and
environment.
Early Mammals
Mammals appear as early as 190 million years ago.
Around 70 mya, the earth began to experience sever
climatic changes and many of the larger reptiles and
dinosaurs went extinct, opening new environmental
niches for mammals.
Mammal-like animals were preadapted to advantages of
these changes and underwent an adaptive radiation -a rapid increase in the number of related species
following a change in their environment.
Early Mammals: Adaptive
Traits
• Mammals are homeotherms - animals that
maintain a relatively constant body temperature
despite environmental fluctuations.
• By contrast, reptiles are isotherms -animals
whose body temperatures rise or fall according to
the temperature of the surrounding environment.
Early Mammals: Adaptive
Traits
• Mammals are k-selected – reproduction involves
the production of relatively few offspring with high
parental investment in each.
• Other animals are more r-selected - reproduction
involves the production of large numbers of offspring
with relatively low parental investment in each.
The Proto-Primates (65 mya)

The first primate-like mammals, or proto-primates,
were roughly similar to squirrels and tree shrews in
size and appearance.

The existing, very fragmentary fossil evidence
(mostly from North Africa) suggests that they were
adapted to an arboreal way of life in warm, moist
climates.
The Rise of the Primates

The rise of primates appears to be an
adaptive radiation linked to the spread
of flowering plants (angiosperm
radiation) and pollinating insects.
The Rise of the Primates
(1) arboreal hypothesis – a hypothesis for
primate evolution that proposes that life in
the trees was responsible for enhanced
visual acuity and manual dexterity in
primates.
(2) visual predation - a hypothesis for
primate evolution that proposes that hunting
behavior in tree-dwelling primates was
responsible for their enhanced visual acuity
and manual dexterity.
Timeline of Primate
Evolution
True Primates - Early
Prosimians

Their bones have been found in 55 million year old
geological deposits in North America-Europe-Asia
(Laurasia) and Africa.

The rainforest environments were warm and wet.

They were somewhat squirrel-like in size and appearance,
but apparently they had grasping hands and feet that were
increasingly more efficient in manipulating objects and
climbing trees.
True Primates - Early
Prosimians

Early prosimians had postorbital bars and relatively long
snouts.
Early Strepsirhines

Fossils of lemur and loris ancestors are found in
North America, Europe, Asia, and possibly Africa.

Main Features: small eye sockets, elongated
snouts, cheek teeth adapted for folivorous or
frugivorous diets, and relatively large body mass
(greater than 1 kg).
Early Haplorhines

Fossils of haplorhines
(ancestors of tarsiers and
anthropoids) are found in North
America, Europe, Asia, and
possibly Africa.

Main Features: large eye
sockets, shortened snouts,
cheek teeth adapted for
insectivorous or frugivorous
diets, and relatively small body
mass (less than 500 g)
Oligocene Anthropoids
By the Oligocene period, prosimians are out-competed
by anthropoids (except in Madagascar).
Deposits in Fayum (Egypt) and other parts of North
Africa, show the development of anthropoids some
with the dental formula similar to Platyrrhines (2-1-33) and others with the Catarrhine dental formula (21-2-3)
Aegyptopithecus
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the size of a large domestic cat (13-20 pounds)
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fruit and seed eating forest tree-dweller
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had fewer teeth, less long snout, larger brains, and
increasingly more forward-looking eyes than the
prosimians
The Origin of New World
Monkeys
• The earliest platyrrhine fossils are found in South
America and are only about 25 million years old.
• Both platyrrhines and catarhines originated from
prosimian ancestors – although anthropologists still
debate if it was the same ancestor.
• A possible African origin for platyrrhines is suggested
by the “rafting” and “island hopping” hypotheses but
the geological evidence for these is inconclusive.
Miocene Apes
Evolutionary relationships are based
on a molecular clock - a hypothesis
that dates of divergences among
related species can be calculated
through an examination of the genetic
mutations that have accrued since the
divergence.
Proconsul
• existed from 27 to 17 million years ago in Africa
• ranged in size from 22-84 lbs (10-40 kg)
• its monkey-like features included: thin tooth enamel,
a light build with a narrow chest and short forelimbs,
and an arboreal quadrupedal lifestyle
• its ape-like features are its lack of a tail, ape-like
elbows, and a slightly larger brain relative to body
size
Proconsul
Dryopithecus
• existed from 12 to 9 million years ago in
Eastern Africa and Eurasia
• had a Y-5 cusp arrangement on its molar
teeth – typical of hominoids
Dryopithecus
Sivapithecus
• existed from 12.5 to 8.5 million years ago in
India and Pakistan
• possible ancestor of the orangutan and
gigantopithecus – already had separated from
the common ancestor of chimpanzees and
gorillas
Sivapithecus
Gigantopithecus
• existed from 1.0 million to 300,000 years
ago in China, India and Vietnam
• it stood about 10 feet (3 meters) tall and
weighed as much as 1200 pounds (545 kg)
• Gigantopithecus was probably a quadruped
and an herbivore, existing on a diet primarily
of bamboo, possibly supplemented with
seasonal fruits
Gigantopithecus