Chapter 5
Macroevolution: Processes of Vertebrate
and Mammalian Evolution
Classification
• Classification is used to order organisms into
categories to show evolutionary relationships.
• Example - human classification
– Kingdom: Animalia
– Subkingdom: Metazoan
– Phyla: Chordata
– Subphyla: Vertebrata
– Class: Mammalia
Classification:
Definitions
• Metazoa
– Multicellular animals.
• Chordata
– The phylum of the animal kingdom that
includes vertebrates.
• Vertebrates
– Animals with segmented bony spinal
columns; includes fishes, amphibians,
reptiles, birds, and mammals.
Principles of
Classification
• The field that specializes in establishing
the rules of classification is called
taxonomy.
Principles of
Classification
• Homologies
– Similarities based on descent from a common
ancestor.
• Analogies
– Similarities based on common function, with
no assumed common evolutionary descent.
• Homoplasy
– The separate evolutionary development of
similar characteristics in different groups of
organisms.
Homologies
Two Approaches to
Classification
• Evolutionary systematics
• Cladistics
Ancestral and Derived
Characters
• Ancestral characters
• Derived characters
Evolutionary Trees
• Development of
Passenger Vehicles
– The first divergence
is between cars and
trucks (I).
– A later divergence
occurs between luxury
cars and sports cars
(II).
Evolutionary Trees
• Development of
Passenger Vehicles
– SUVs diverge from trucks,
but like sports cars, they
have a decorative racing
stripe.
– This is a homoplasy and
does not make SUVs
sports cars.
– Classifications based on a
characteristic that can
appear independently in
different groups can lead
to an incorrect conclusion.
Evolutionary Relationships of
Birds and Dinosaurs
• (a) Traditional view, showing no close
relationship. (b) Revised view, showing
common ancestry of birds and dinosaurs.
Cladogram
• Shows relationships of birds, dinosaurs, and other
terrestrial vertebrates. There’s no time scale, and both
living and fossil forms are shown along the same
dimension. Ancestor- descendant relationships aren’t
indicated.
Approaches to
Classification
Goal
Similarities
Evolutionary
Systematics
Cladistics
Construction of a
phylogenetic tree
Construction of a
cladogram
•Compare specific traits
•Construct classifications to show
evolutionary relationships
•Focus on homologies
Approaches to
Classification
Evolutionary
Systematics
Differences
Might use any homologous
character
Attempts to make ancestordescendant links
Attempts to place fossils in
a chronological framework
Cladistics
Use only defined derived
characters
No conclusions regarding
ancestor-descendant
relationships
All members of an evolutionary
group are interpreted in one
dimension
Definition of Species
• Biological
species concept
– Depiction of
species as groups
of individuals
capable of
interbreeding, but
reproductively
isolated from other
such groups.
Definition of Species
• Recognition species concept
– The key aspect is the ability of individuals to
identify members of their own species for
purposes of mating.
• Ecological species concept
– The concept that a species is a group of
organisms exploiting a single niche.
• Phylogenetic species concept
– Splitting many populations into separate
species based on an identifiable parental
pattern of ancestry.
Allopatric Speciation
• Living in different areas.
• Important in the divergence of closely
related species from each other which
leads to reproductive isolation.
Speciation
• Process by
which a new
species evolves
from a prior
species.
• Speciation is the
most basic
process in
macroevolution.
Speciation Model
Recognition of
Fossil Species
• The minimum biological category we would like
to define in fossil primate samples is the
species.
– Variations
• Intraspecific vs. Interspecific
Recognition of
Fossil Species
– Splitters vs. Lumpers
Recognition of Fossil
Genera
• A genus is a group of
species composed of
members more closely
related to each other
than to species from
any other genus.
Geological Time Scale
Continental drift
• The positions of the
continents during the
Mesozoic (c. 125
m.y.a.).
• Pangea is breaking
up into a northern
landmass (Laurasia)
and a southern
landmass
(Gondwanaland).
Continental Drift
• (a) Positions of the continents during the Mesozoic.
Pangea is breaking up into a northern landmass
(Laurasia) and a southern landmass (Gondwanaland).
(b) Positions of the continents at the beginning of the
Cenozoic.
Ecological Niches
• The positions of species within their
physical and biological environments,
together making up the ecosystem.
• A species’ ecological niche is defined by
such components as diet, terrain,
vegetation, type of predators,
relationships with other species, and
activity patterns, and each niche is unique
to a given species.
Mammalian Evolution
• The Cenozoic era is known as the Age of
Mammals.
• After dinosaurs became extinct, mammals
underwent adaptive radiation, resulting in rapid
expansion and diversification.
• The neocortex, which controls higher brain
functions, comprised the majority of brain
volume, resulting in greater ability to learn.
Reptilian and Mammalian
teeth
• Mammals are
heterodont, they have
different kinds of
teeth; incisors,
canines, premolars,
and molars.
Major Events in Early
Vertebrate Evolution
Endothermic
• Able to maintain internal body
temperature by producing energy through
metabolic processes within cells;
characteristic of mammals, birds, and
perhaps some dinosaurs.
Major Mammalian
Groups
• Monotremes
• Marsupials
• Placental
Adaptive Radiation
Convergent Evolution
Gradualism versus
Punctuated Equilibrium