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.
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