17.1 The Linnaean System of Classification

KEY CONCEPT Organisms can be classified based on physical similarities.

17.1 The Linnaean System of Classification

Linnaeus developed the scientific naming system still used today.

• Taxonomy is the science of naming and classifying organisms.

• A taxon is a group of organisms in a classification system.

White oak:Quercus alba

17.1 The Linnaean System of Classification

• Binomial nomenclature is a two-part scientific naming system.– uses Latin words. Why? – scientific names always written in italics. Why? – two parts are the genus name and species descriptor.

Why?

17.1 The Linnaean System of Classification

• A genus includes one or more physically similar species.– Species in the same genus are thought to be closely

related.– Genus name is always capitalized.

• A species descriptor is the second part of a scientific name.– always lowercase– always follows genus

name; never written alone

Tyto alba

17.1 The Linnaean System of Classification

• Scientific names help scientists to communicate. How? – Some species have very similar common names.– Some species have many common names.

17.1 The Linnaean System of Classification

Linnaeus’ classification system has seven levels.

• Each level is included in the level above it.

• Levels get increasingly specific from kingdom to species.

Ah yes, it’s time for another mnemonic device!

• How will you remember the order of classification groups? K-P-C-O-F-G-S

• Kingdom• Phylum• Class• Order• Family• Genus• Species

17.1 The Linnaean System of Classification

The Linnaean classification system has limitations.

• Linnaeus taxonomy doesn’t account for molecular evidence. Why?– The technology didn’t exist during Linneaus’ time.– Linnaean system based only on physical similarities.

17.1 The Linnaean System of Classification

• Physical similarities are not always the result of close relationships.

• Genetic similarities more accurately show evolutionary relationships.

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

molecular data– shown with branching tree diagrams using a method

called Cladistics.

17.2 Classification Based on Evolutionary Relationships

• Cladistics is a common method to make evolutionary trees.

– 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.

– more closely related species share more derived characters

– Derived characters are represented on cladograms as hash marks

– Oldest relatives are at the bottom of the cladogram.

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. In this example, the different clades are distinguished by different colors.

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. What would you expect to see when comparing the DNA of two closely related species?

• DNA is usually given the last word by scientists.

17.2 Classification Based on Evolutionary Relationships

If two organisms are in the same phylum, what other taxon do they have in common?

• A. class • B. kingdom • C. family • D. genus

17.2 Classification Based on Evolutionary Relationships

If two organisms are in the same phylum, what other taxon do they have in common?

• A. class • B. kingdom • C. family • D. genus • Correct Answer = B

What is a species? • A. a group of organisms that live in the same habitat • B. a group of organisms that have similar structures • C. a group of organisms that compete for the same food source • D. a group of organisms that can breed and produce offspring that can

reproduce

17.2 Classification Based on Evolutionary Relationships

If two organisms are in the same phylum, what other taxon do they have in common?

• A. class • B. kingdom • C. family • D. genus • Correct Answer = B

What is a species? • A. a group of organisms that live in the same habitat • B. a group of organisms that have similar structures • C. a group of organisms that compete for the same food source • D. a group of organisms that can breed and produce offspring that can

reproduce • Correct Answer = D

Review

• Taxonomy is the science of naming and classifying organisms

• Binomial nomenclature is a two-part scientific naming system

• The classification groups from largest to smallest = kingdom, phylum, class, order, family, genus, species

• Cladistics is classification based on common ancestry• Molecular evidence reveals species’ relatedness• DNA is usually given the last word by scientists