2. In this tutorial, you will learn:
The traditional classification scheme of
Linnaeus.
Two theories of taxonomy:
Traditional evolutionary taxonomy
Cladistics
How to read a cladogram
Credits:
Figures and images by N. Wheat unless otherwise noted.
Image of Linnaeus from Wikipedia
Funded by Title V-STEM grant P031S090007.
3. Introduction
The practice of categorizing organisms
according to similar features goes back to
Aristotle.
The goal of Taxonomy today is to produce a
formal system for naming and classifying
species to illustrate their evolutionary
relationships.
4. Classification
In classification, the taxonomist asks
whether the species being classified contains
the defining feature of a certain taxonomic
grouping.
Focus is on features.
5. Systematization
In systematization, the taxonomist asks
whether the characteristics of a species
support the hypothesis that it descends from
the most recent common ancestor of the
taxonomic group.
Focus is on evolutionary origin of those
features.
6. Linnaeus and Classification
In the 18th century, Carolus Linnaeus
designed the hierarchical classification
system still in use today.
Kingdom
Phylum
Class
Order
Family
Genus
Species
7. Taxa
Taxa (singular = taxon) are the major groups
of organisms.
Each rank can be subdivided into additional
levels of taxa.
Superclass, suborder, etc.
8. Binomial Nomenclature
Binomial nomenclature is the system
Linnaeus developed for naming species.
The two-part scientific name includes the genus
and species
Names are latinized and italicized, only the
genus is capatilized.
Sitta carolinensis
9. Phylogeny
The goal of systematics is to determine the
phylogeny – the evolutionary history – of a
species or group of related species.
10. Phylogeny (2)
Phylogenies are inferred by identifying
organismal features, characters, that vary
among species.
These characters can be:
Morphological
Chromosomal
Molecular
Behavioral or ecological
12. Homoplasy
Homoplasies are shared characters that are
not a result of common ancestry, but of
independent evolution of similar characters
(they are not homologous).
Can result from convergent evolution.
13. Convergent Evolution
Convergent evolution occurs when natural
selection, working under similar
environmental pressures, produces similar
(analogous) adaptations in organisms from
different evolutionary lineages.
14. Phylogeny
When trying to determine evolutionary
relationships (inferring a phylogeny), we only
want to consider homologous characters.
Homoplasies can create errors.
15. Shared Primitive and Shared
Derived Characteristics
Focusing on homologous structures, we need
to determine when that character arose.
Newer characters tell us more!
Primitive (older) vs. derived (newer) characters
16. Shared Primitive Characteristics
A shared primitive character is a
homologous structure that is older than the
branching of a particular clade from other
members of that clade.
It is shared by more than just the taxon we are
trying to define.
Example – mammals all have a backbone, but
so do other vertebrates.
17. Shared Derived Characteristics
A shared derived character is a new
evolutionary feature, unique to a particular
group.
Example - all mammals have hair, and no other
animals have hair.
These are the features that are most useful
for determining evolutionary relationships!
18. Ancestral Character States
The ancestral character state is the form of
the character that was present in the common
ancestor of the group.
Variations of the character that arose later are
called derived character states.
19. Polarity
Polarity (which version of the trait is
ancestral) is determined by using outgroup
comparison.
An outgroup is closely related, but not part of
the group being examined (the ingroup).
20. Polarity (2)
An ancestral character is one that is found in
both the study group and the outgroup.
Derived character groups are those found in
the study groups but not the outgroups.
21. Clades
Clades are groups that share derived
characters and form a subset within a larger
group.
A clade is a unit of common evolutionary
descent.
22. Synapomorphy
A synapomorphy is a derived character that
is shared by all the members of the clade.
Using synapomorphies to define clades will
result in a nested hierarchy of clades.
23. Symplesiomorphy
Ancestral character states for a taxon are
called plesiomorphic.
Symplesiomorphies are shared ancestral
characters.
Symplesiomorphies do not provide useful
information for forming a nested series of
clades.
30. Cladistics (2)
Since all groupings must
be monophyletic in
cladistics, the
paraphyletic arrangement
of ape families doesn’t
work.
Humans, chimpanzees,
gorillas, and orangutans
are now all included
together in one
monophyletic family -
Hominidae.
31. Sister Groups
A sister group is a pair of taxa that are most
closely related to each other.
Humans are most closely related to
chimpanzees, so humans & chimpanzees
form a sister group.
Gorillas form a sister group to the clade
containing humans and chimpanzees.
32. Cladistics vs. Evolutionary
Taxonomy
The important difference between these two
theories of taxonomy is that traditional
evolutionary taxonomy sometimes accepts
paraphyletic clades, while cladistics does not.
Both accept monophyletic clades.
Both reject polyphyletic clades.
33. Question 1
Who developed the classification
system including the binomial scientific
name in use today?
Darwin
Mendel
Linnaeus
Aristotle
39. Question 3
Which example of binomial
nomenclature is formatted correctly?
Homo sapiens
homo sapiens
Homo Sapiens
Homo Sapiens
It doesn’t matter, they are all
correct
42. Question 4
Which of these terms is associated with
characters that share common
ancestry.
Homology
Convergent evolution
Homoplasy
Analogy
All of the above
45. Question 5
When defining a clade, what type of
characters should we use?
Homoplasies
Shared primitive characters =
symplesiomorphies
Shared derived characters =
synapomorphies
All of the above
48. Question 6
The branching diagram that illustrates
the nesting hierarchy of clades is called
a
Family tree
Cladogram
Phylogenetic diagram
Taxonomic web
51. Question 7
A monophyletic clade is one that
contains
An ancestor and all of its
descendants.
An ancestor and some of its
descendants.
Several species that lack a
common ancestor.
One species.
54. Question 8
A polyphyletic clade is one that
contains
An ancestor and all of its
descendants.
An ancestor and some of its
descendants.
Several species that lack a
common ancestor.
One species.
57. Question 9
A paraphyletic clade is one that
contains
An ancestor and all of its
descendants.
An ancestor and some of its
descendants.
Several species that lack a
common ancestor.
One species.
63. Question 11
Which of the following statements about the
difference between cladistics and traditional
evolutionary taxonomy is false?
Both accept monophyletic clades
Both accept paraphyletic clades
Cladistics rejects paraphyletic clades, while
evolutionary taxonomy sometimes accepts
them.
Both reject polyphyletic clades.
