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Classifying Organisms
•
Understanding Diversity:
Systematics
Chapter 23
Scientific Names
• Why Scientific Names?
- Elk vs. Deer
Classifications help biologists organize their
knowledge
1. Classification:
assigning organisms into groups based on
similarities or relationships
2. Systematics:
– scientific study of diversity of organisms and
their evolutionary relationships
3. Taxonomy:
– branch of systematics
– naming, describing, classifying organisms
Binomial System of Nomenclature
• Used by biologists to name organisms
• Developed by Carolus Linnaeus, mid-18th century
• Basic unit of classification: species
Binomial System of Nomenclature
• Each species name has two parts:
– genus name
– specific epithet
Turdus migratorius
Procyon lotor
Homo sapiens
Myotis evotis
Taxa
• Hierarchical system of taxonomic
classification
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
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DOMAIN
Eukarya
Classification
Categories: arranged
in a hierarchy from
most inclusive
(domain) – contains
all within a wide
group
KINGDOM
Animalia
PHYLUM
Chordata
to least inclusive
(species) – most
closley related
Archaraea/bacteria
Protista
Fungi
Plant
Porifera
Cnidarians
Echinodermata
CLASS
Mammalia
Reptilia
Aves
Chondrichthyes
ORDER
Carnivora
Chiroptera
Rodentia
Lagomorpha
FAMILY
Felidae
GENUS
Felis
SPECIES
Felis catus
Canidae
Ursidae
Panthera
Three-Domain Classification
Three-Domain Classification
• Archaea
– prokaryotes
– Peptidoglycan (protein w carb) absent in cell
walls
• Bacteria
– prokaryotes
– peptidoglycan present in cell walls
• Eukarya
– all eukaryotes: protists, fungi, plants, animals
Six-Kingdom Classification
Domains and Kingdoms
1.
2.
3.
4.
5.
6.
Archaea
- prokaryotes
Bacteria
- prokaryotes
Protista
- unicellular, aquatic eukaryotes
Fungi
- molds, yeasts, and mushrooms
Plantae
- multicellular eukaryotes that photosynthesize
Animalia
- multicellular eukaryotes
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Systematics: study of evolutionary
relationships (Phylogeny)
Bacteria
Archaea
Protista
Plantae Protista
Animalia
Fungi
Common ancestor
of all eukaryotes
• Used to build classifications based on common
ancestry
How do we determine phylogeny?
• Similarities/differences between species/groups in
question
- Homologous structures
- Structural (fossils), physiological,
developmental, behavioral, molecular – any
information out there re. the species.
Common ancestor of
all living organisms
Fig. 23-2, p. 488
Homologous Characters
Taxon: a group
• Homology
– trait in two or more species
– derived from recent common ancestor
• But: Seemingly homologous characters may be
acquired independently
– Convergent evolution (homoplasy)
– Reversal (trait reverses to ancestral state)
i.e., they are not related!!!!!!!
Cladistics: classification based
on recent ancestry (not
structural similarities)
Homology vs. Homoplasy
• Not always easy to distniguish!!!!
• Shared Ancestral Characters “Conservative
characteristics” (Plesiomorphies)
• Traits observed in ancestral species that remain in all
groups that descended from the ancestor (i.e., shared)
• Major traits used to determine relatedness
e.g., vertebrae in all vertebrates
Shared Derived Characters (synapomorphies)
• Traits found in two or more taxa that are present in
their closest common ancestor, but NOT present in
earlier ancestors (the traits evolved relatively
recently – i.e., something new (relatively) –
• Derived Characters – feathers in birds –very recent
development no other group has it.
• Systematists consider shared derived characters in
choosing taxonomic criteria
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Shared ancestral character
Shared derived character
Derived character
a
Molecular Systematics
b
• Molecular structure clarifies phylogeny
d
c
ecdysis
Jaws
tetrapod
ectothermy
time
• Comparisons of
– nucleotide sequences in DNA and RNA
– amino acid sequences in proteins
• Provide information about how closely organisms
are related
z
Divergence
Molecular Phylogeny
Monophyletic Taxon
• A common
ancestor and all of
its decendants
Polyphyletic Group
Paraphyletic Taxon
• A common
ancestor and
some (not all) of
its descendants
Contains a common ancestor
and some but not all of its
decendents
• Organisms
evolved from
different recent
ancestors
Contains several
evolutionary lines that do
not share the same recent
common ancestor
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Cladistics
Cladistics
• Cladograms
– phylogenetic trees
– use shared derived characters to diagram
evolutionary relationships
• Cladogram indicates
– which taxa shared a common ancestor
– how recently they shared that ancestor
• Node
– branch point
– divergence of groups from common ancestor
• Most recent common ancestor of each monophyletic
group is found at node
• Outgroup analysis
– determines which characters in a given group of
taxa are ancestral and which are derived
TAXA
Jaws
Vertebrae
(backbones)
= Present
Tetrapod
(4 limbs)
Amniotic
egg
Mammary
glands
Opposable
thumb
Upright
posture
Shared derived CHARACTERS
= Absent
Outgroups
Lancelet (outgroup)
Lamprey
Sunfish
• Outgroup
– taxon that represents ancestral condition
– diverged earlier than other taxa investigated
Frog
Lizard
Bear
Chimpanzee
Human
Jaws
Absent
Node
Common jawed
B
vertebrate ancestor
Node
A
Common vertebrate
ancestor
Tetrapod
limbs
Absent
Node
C
Node
B
Node
A
Present
Human
Chimpanzee
Bear
Lizard
Frog
Sunfish
Lamprey
Lancelet
Human
Chimpanzee
Bear
Lizard
Frog
Sunfish
Lancelet
Lamprey
Fig. 23-9a, p. 495
Common tetrapod
ancestor
Common jawed
vertebrate ancestor
Common vertebrate
ancestor
Present
Common chordate
ancestor
Common chordate
ancestor
1
All of the seven vertebrate taxa shown here have jaws, except the lamprey.
Jaws are a shared derived character for these six taxa.
Fig. 23-9b, p. 495
2
Tetrapod limbs are a shared derived character for all vertebrate
taxa shown here except the lamprey and sunfish.
Fig. 23-9c, p. 495
5
Amniotic
egg
Absent
Present
Node
Common amniote
D
ancestor
Node
Common tetrapod
C
ancestor
Node
B
Common jawed
Node
vertebrate ancestor
A
Common
vertebrate ancestor
Opposable
thumb
Absent
Present
Human
Chimpanzee
Bear
Lizard
Frog
Sunfish
Node
G
Node
Common primate
F
ancestor
Node
Common mammal
E
Node
ancestor
D
Common amniote
Node
ancestor
C
Common tetrapod ancestor
Node
B
Common jawed vertebrate
Node
ancestor
A
Common vertebrate
ancestor
Common chordate
ancestor
Common chordate
ancestor
The taxa represented by lizard, bear, chimpanzee, and human
3 are amniotes. They share the derived character amniotic egg.
Lamprey
Lancelet
Human
Chimpanzee
Bear
Lizard
Frog
Sunfish
Lamprey
Lancelet
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Fig. 23-9d, p. 495
Of the vertebrate taxa shown here, only the chimpanzee and human share
the derived character opposable thumb.
Fig. 23-9e, p. 495
Principle of Parsimony
• Uses simplest explanation to interpret data
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