CLASSIFICATION

OF LIVING

THINGS

Chapter 18

How many species are there?

About 1.8 million species have

been given scientific names

Nearly 2/3 of which are insects

99% of all known animal

species are smaller than

bumble bees

99% of all species that have

ever existed are now extinct

Taxonomy

Classification – the grouping of objects based on similarities

Taxonomy – the science of describing, naming, and

classifying organisms

Organisms are grouped into taxa (plural) or a taxon.

Each category is a taxon.

Freshmen (Class of 2016)

Sophomore (Class of 2015)

Junior (Class of 2014)

Senior (Class of 2013)

History of Classification

Aristotle (384 – 322 BCE) –

developed the first classification

system

Based on easily observable

characteristics

All organisms were classified as

plants or animals.

Plants – herbs, shrubs, and trees

Animals – things that swim, things

that fly, or things that walk.

Carl Linnaeus (1701 – 1778)

Wrote a book Systema Naturae in

1735 that outlined his classification

and naming system

Classification hierarchy (groups within

groups)

Binomial nomenclature

Organisms are grouped based on

similarities in their form and

structure at different levels

Levels of the Modern Linnaean System

DOMAIN

KINGDOM

PHYLUM

CLASS

ORDER

FAMILY

GENUS

SPECIES

Gets

more

specific

as you

move

down.

And,

organisms

are more

closely

related.

Binomial Nomenclature

Binomial Nomenclature – a two-word naming system using the

genus and species names

No two species can have the same scientific name

Both names are in Latin

Both names are italicized (underlined if handwritten)

The genus name is capitalized and the species name is lowercase

The species name is an identifier or descriptor

EXAMPLE – Apis mellifera

mellifera honey

Try these…

Canis lupis

Canis familiaris

Try these…

Felis domesticus Sus domesticus

How are living things classified?

Traditionally, organisms

were classified based

physical characteristics

(what could be seen).

Mammals – have hair,

produce milk and provide

care for young, and most

have live birth

Problems with the Old Way

Some organisms have similar features but are not closely

related

Example – Birds, bats, and bugs all have wings that are used to

fly but each evolved separately.

Problems with the Old Way

Some organisms look different but are closely related

Birds are dinosaurs (reptiles)

The Missing Link… (or at least one of them)

Archaeopteryx

Modern Classification

Based on phylogeny

Phylogeny – the ancestral/evolutionary relationships

among species

Each species has a family tree that includes many

ancestors and descendents and thousands of

generations.

Phylogenetic tree

How is phylogeny determined?

Phylogenetics uses the

presence or absence of traits

to determine relatedness

Morphology – studying the

physical structure or

anatomy of organisms

Very traditional but useful

for living species and

fossils

Homologous, Analogous, or Vestigial

Homologous structures – traits inherited from a common ancestor

May or may not have the same function or the exact same

appearance

Example: forelimbs of tetrapods

Homologous, Analogous, or Vestigial

Analogous structures – structures with common functions

Example – Birds, bats, and bugs all have wings that are used to fly

but each evolved separately.

Homologous, Analogous, or Vestigial

Vestigial Structures – evolutionary

leftover

Example – the human appendix has

no apparent function while rats and

other rodents have an appendix

that aids in digestion

Example – whales and snakes have

a pelvis and femur

How is phylogeny determined?

Biochemical – comparing DNA,

RNA, and protein sequences.

Genes pass from generation to

generation; therefore, all

descendents will have the similar

DNA

The more similar the DNA or

protein sequence the more

closely related the species

Levels of the Modern Linnaean System

DOMAIN

KINGDOM

PHYLUM

CLASS

ORDER

FAMILY

GENUS

SPECIES

Gets

more

specific

as you

move

down.

And,

organisms

are more

closely

related.

Cladistics

Cladisitics – a method of analysis

that infers phylogenies by careful

comparisons of shared traits.

Used to select the most likely

phylogeny among a given set of

organisms.

Comparing traits

Shared traits are defined as ancestral

Derived traits evolve in one group but

not another

Constructing a Cladogram

Cladogram – a phylogenetic

tree that is drawn in a specific

way to show evolutionary

relationships

Clade – all groups that

originate from a certain point

and have one common ancestor

Outgroup – a group that lacks

some of the shared characters

Clade

New species…

Scientists are discovering new species all the time.

So…we have to know where to classify them and how to

name them.

http://blogs.discovermagazine.com/loom/2010/06/30/what-if-anything-is-big-bird/

Constructing a Cladogram

Characters in Vertebrates

Four legs Backbone Amniotic egg Hair

Lizard yes yes yes No

Tuna no yes no No

Frog yes yes no No

Cat yes yes yes Yes

Interpreting Cladograms

Cladogram Questions

After which animals did mammary glands develop?

What animals do not have jaws?

Which animals share the trait for lungs?

Which animals have derived traits that protect them from the elements (weather)?

Why is the trait for feathers marked on the line for pigeons not the main line?

Which animals are probably predators?