This document discusses cladistics, a method of classifying organisms based on shared derived characteristics. Cladistics groups organisms into clades, which represent the most recent common ancestor of a group and all its descendants. A cladogram depicts these evolutionary relationships through a branching diagram. Key concepts include synapomorphies (shared derived traits), homology, homoplasy, and parsimony. Cladistics aims to determine ancestral character states and place taxa based on requiring the fewest evolutionary changes. This phylogenetic approach aims to represent natural evolutionary relationships between organisms.

2. Systematics, then, is no less
than understanding the history of
all life.
-Diana Lipscomb, 1998

3. CLADISTICS
LIWALUG, MUSLIMA P.
MIB1

4.  Method that groups
organisms that share
derived characteristics
 The value or form of a
feature is referred to as a
character state
 Relationships are portrayed
in straight line diagrams
Phylogenetic Systematics

5. HOMOLOGY
• traits have common
ancestry
• may/may not share
function
• may/may not look alike
HOMOPLASY
• traits are similar
because of
convergent
evolution
ANALOGY
• traits with common
function
• may/may not share
ancestry
• may/may not look
alike

6. Synapomorphies
• is a trait that is shared by 2 or more taxonomic groups
• is derived through evolution from a common ancestral
form
Plesiomorphic
• ancestral state
• character state that a taxon is inferred to have been
retained from its ancestors
Apomorphic
• derived state
• can be used to diagnose a clade – or even to define a
clade name in phylogenetic nomenclature

7. Cladistic Analysis
by Willi Hennig (1966)
 is to determine which character states are
primitive and which are derived based on
common ancestry

8. Principles
Parsimony – states that any hypothesis that
requires fewer assumptions is a more
defendable hypothesis
Occam’s Razor - one should not make more
assumptions than the minimum needed to
explain anything

9. A B

11. Cladogram
is an evolutionary tree which shows evolutionary
relationships by showing points at which lineages
diverged from common ancestral forms
is constructed such that the number of changes
from one character state to the next is minimized
is interpreted as that which requires the fewest
evolutionary changes in the taxa involved

12. Clade
 a group of two or more taxa that includes
both their common ancestor and all their
descendants

13. FOUR LIMBS WITH DIGITS
Tetrapoda clade1
Amniota clade2
Reptilia clade3
Diapsida clade4
Archosauria clade5
EMBRYO PROTECTED BY AMNIOTIC FLUID
OPENING IN THE SIDE OF THE SKULL
SKULL OPENINGS IN FRONT OF THE EYE &
IN THE JAW
FEATHERS & TOOTHLESS
BEAKS.
SKULL OPENINGS BEHIND THE EYE
DERIVED CHARACTER

14. Node - a branch points based on
homologous, shared derived traits
Root - the common ancestor of all taxa
Branch - defines the relationship between
the taxa in terms of descent and ancestry
Branch length (scaled trees only) - represents
the number of changes that have occurred in
the branch

15. Species A
Species E
Species D
Species C
Species B
Root
Branch
CladeNode

16. Cladistic Methodology
more
primitive
more
derived
Terminal taxa
X
Y
Z
Leopard
Turtle
Salamander
Tuna

17. Outgroup Comparison
If the taxon that is not a member of the group
of organisms being classified has a character
state that is the same as some of the
organisms in the group then the character can
be considered plesiomorphic

18. P P P
P P
P
A
A
A
A
A A

19. Characters
TAXON
Moss
Fern
Pine
Daisy
VASCULAR TISSUES SEEDS FLOWERS
P
A
A
A A A
A
P P
P
P
P

20. Moss
(a) All of the plant groups shown here except mosses
have vascular
Pine
Daisy
Fern
Node
1
Common plant
ancestor
Common ancestor
with vascular tissues

21. Moss
Pine
Daisy
Fern
Node
1
Common plant
ancestor
Common ancestor
with vascular tissues
Node
2
(b) Seeds are a shared character for all plant groups
shown here except mosses and ferns.

22. Moss
Pine
Daisy
Fern
Node
1
Common plant
ancestor
Common ancestor
with vascular tissues
Node
2
Node
3
Common
seed-
producing
ancestor
(c) Of the plant groups shown here, only the daisy
produces flowers.

24. Cladogram

26. Phyletic Group of Taxa
MONOPHYLETIC GROUP
Contains an ancestor and all of its
descendants - defined by > 1 shared,
derived traits.
POLYPHYLETIC GROUP
Does not include common ancestor
group. Common ancestor is placed
elsewhere
PARAPHYLETIC GROUP
Includes common ancestor but not all
of its descendants. Define by what it
lacks.

28. WHY DO CLASSIFICATION SCHEMES CHANGE?
New Data
Rise of new technologies give new sources
of character information
New taxa
As previously unknown species are
discovered, classifications will also need to
be revised to reflect their placement