• Similar traits often indicates common ancestry• Phylogeny (fahy-loj-uh-nee):

evolutionary histories of a species• Determined by examining:

– Fossils– Living specimens– Molecular data– Development

Despite the physicaldifferences, which

taxon do thesebelong to?

Domain EukaryaKingdom AnimaliaPhylum ChordataFamily Mammalia

Fossil Evidence

• Homologous structures: body parts that have a similar structure, but different function

• Relationships identified among different species• Fossils link past life to modern life

Anatomy shows nonrelationships also

• Comparing DNA, amino acids, chromosomes, proteins– Similarities and differences can be found– Splits in evolution can be estimated

Chromosome order: Human, orangutan, gorilla, pygmy chimp

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

new classification.

Molecular evidence reveals species’ relatedness.

• DNA is usually given the last word by scientists.

• Cladistics is a common method to make evolutionary trees.

– classification based on common ancestry

– species placed in order that they descended from common ancestor

– Shown in tree branching diagrams

• A clade is a group of species that share a common ancestor.• Derived characters are traits shared in different degrees by

clade members.

– Derived Characteristic– 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

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

CLADE

NODE

• List 2 characteristics of a salamander. Where would a 3rd be located?• From the diagram, which organism is most closely related to the

Chimp?

• 1) What does an amphibian & crocodile have in common?Vertebrae, Bony skeleton, Four limbs

• 2) List the traits of a ray-finned fish.Doesn’t have 4 limbs, has bony skeleton, has vertebrae