17.2 Classification Based on Evolutionary Relationships

KEY CONCEPT Modern classification is based on evolutionary relationships.

17.2 Classification Based on Evolutionary Relationships

Cladistics is classification based on common ancestry.

• Phylogeny is the evolutionary history for a group of species.– evidence from living species, fossil record, and

molecular data– shown with branching tree diagrams

17.2 Classification Based on Evolutionary Relationships

• Cladistics is a common method to make evolutionary trees.

– classification based on common ancestry– species placed in order that they descended from

common ancestor

17.2 Classification Based on Evolutionary Relationships

• A cladogram is an evolutionary tree made using cladistics.

– A clade is a group of species that shares a common ancestor.

– Each species in a clade shares some traits with the ancestor.

– Each species in a clade has traits that have changed.

17.2 Classification Based on Evolutionary Relationships

• Derived characters are traits shared in different degrees by clade members.

– basis of arranging species in cladogram

– more closely related species share more derived characters

– represented on cladogram as hash marks 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

17.2 Classification Based on Evolutionary Relationships

FOUR LIMBS WITH DIGITS

• Nodes represent the most recent common ancestor of a clade.

• Clades can be identified by snipping a branch under a node.

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 AND IN THE JAW

FEATHERS AND TOOTHLESS BEAKS.

SKULL OPENINGS BEHIND THE EYE

NODE

DERIVED CHARACTER

CLADE

17.2 Classification Based on Evolutionary Relationships

• Molecular data may confirm classification based on physical similarities.

• Molecular data may lead scientists to propose a new classification.

Molecular evidence reveals species’ relatedness.

• DNA is usually given the last word by scientists.