Systematics, then, is no less than understanding the history of all life.

-Diana Lipscomb, 1998

CLADISTICS

LIWALUG, MUSLIMA P.MIB1

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

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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

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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

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Cladistic Analysisby Willi Hennig (1966)

is to determine which character states are primitive and which are derived based on common ancestry

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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

A B

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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

Clade

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

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FOUR LIMBS WITH DIGITS

Tetrapoda clade1

Amniota clade2

Reptilia clade3Diapsida 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

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 ancestryBranch length (scaled trees only) -

represents the number of changes that have occurred in the branch

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Sp e c ie s A

Sp e c ie s E

Sp e c ie s D

Sp e c ie s C

Sp e c ie s BRoot

Branch

CladeNode

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Cladistic Methodologymore

primitivemore

derived

Terminal taxa

X

Y

ZLeopard

Turtle

Salamander

Tuna

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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

P P P

P P

P

A

A

A

A

A A

Characters

TAXON

Moss

Fern

Pine

Daisy

VASCULAR TISSUES SEEDS FLOWERS

P

A

A

A A A

A

P P

P

P

P

Mos

s

(a) All of the plant groups shown here except mosseshave vascular

Pine Dai

sy

Fern

Node1

Common plantancestor

Common ancestorwith vascular tissues

Mos

s

Pine Dai

sy

Fern

Node1

Common plantancestor

Common ancestorwith vascular tissues

Node2

(b) Seeds are a shared character for all plant groupsshown here except mosses and ferns.

Mos

s

Pine Dai

sy

Fern

Node1

Common plantancestor

Common ancestorwith vascular tissues

Node2

Node3

Commonseed-producingancestor

(c) Of the plant groups shown here, only the daisyproduces flowers.

Cladogram

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Phyletic Group of TaxaMONOPHYLETIC GROUPContains an ancestor and all of its descendants - defined by > 1 shared, derived traits.

POLYPHYLETIC GROUPDoes not include common ancestor group. Common ancestor is placed elsewhere

PARAPHYLETIC GROUPIncludes common ancestor but not all of its descendants. Define by what it lacks.

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WHY DO CLASSIFICATION SCHEMES CHANGE?New Data

Rise of new technologies give new sources of character information

New taxaAs previously unknown species are

discovered, classifications will also need to be revised to reflect their placement