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
Orcinus orca
 Binomial nomenclature is a two-part scientific naming system
– uses Latin words
– scientific names always written in italics
– two parts are the genus name and species descriptor
• 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
Callinectes sapidus
• Scientific names help scientists to communicate
– Some species have very similar common names
– Some species have many common names
Dolphin, porpoise, dolphinfish, mahi mahi
http://www.foxnews.com/science/2013/07/23/hey-flipper-dolphins-use-names-to-reunite/
Linnaeus’ classification system has seven levels
 Each level is
included in the
level above it
• Levels get
increasingly
specific from
kingdom to species
The Linnaean classification system has limitations
Organisms can be classified based on physical similarities
 Linnaeus taxonomy doesn’t account for molecular evidence.
 The technology didn’t exist during 1700’s when Linnaeus lived
 Linnaean system based only on physical similarities.
 Physical similarities are not always the result of close
relationships
 Genetic similarities more accurately show close relationships
Modern classification is based on genetic similarity
Molecular evidence reveals species’ relatedness
 Molecular data may confirm classification based on physical
similarities
 Molecular data may lead scientists to propose a new
classification
• DNA is usually given the last word by scientists
Mitochondrial DNA and ribosomal RNA
provide two types of molecular clocks
• Different molecules have different mutation rates.
– Mitochondria DNA higher mutation rate
– (10x faster than chromosomal DNA
– passed down un-shuffled from mother to offspring
– better for studying closely related species
– Ribosomal RNA
– lower mutation rate than most DNA
– many conservative regions
– better for studying distantly related species
Domain
 Domain (also superregnum, superkingdom,
empire or regio)
 highest taxonomic rank of organisms
in the three-domain system
 designed by Carl Woese,
an American microbiologist and biophysicist
 Tree of life Introduced in 1990 has 3 domains:
Archaea (a term which Woese created)
Bacteria
Eukarya
The three domains in the tree of life
are Bacteria, Archaea, and Eukarya
 Domains are above the kingdom level
 based on rRNA studies of prokaryotes
 domain model more clearly shows prokaryotic diversity
Domain Eukarya includes all eukaryotes
Kingdom Plantae
Green algae:
Chlorophyta
and
Charophyta
Classification is always a work in progress
 The current tree of life has three domains
 The tree of life shows our most current understanding.
 New discoveries can lead to changes in classification.
 Until 1866: only two kingdoms,
Animalia and Plantae
Animalia
Plantae
Classification is always a work in progress
 The tree of life shows our most current understanding.
 New discoveries can lead to changes in classification.
 Until 1866: only two kingdoms,
Animalia and Plantae
– 1866: all single-celled organisms
moved to kingdom Protista
Plantae
Animalia
Protista
Classification is always a work in progress
 The tree of life shows our most current understanding.
 New discoveries can lead to changes in classification.
 Until 1866: only two kingdoms,
Animalia and Plantae
– 1866: all single-celled organisms
moved to kingdom Protista
Plantae
Animalia
Protista
– 1938: prokaryotes moved to
kingdom Monera
Monera
Classification is always a work in progress
 The tree of life shows our most current understanding.
 New discoveries can lead to changes in classification.
 Until 1866: only two kingdoms,
Animalia and Plantae
– 1866: all single-celled organisms
moved to kingdom Protista
Plantae
Animalia
Protista
– 1938: prokaryotes moved to
kingdom Monera
– 1959: fungi moved to own
kingdom
Monera
Fungi
Classification is always a work in progress
 The tree of life shows our most current understanding.
 New discoveries can lead to changes in classification.
 Until 1866: only two kingdoms,
Animalia and Plantae
Plantae
Animalia
– 1866: all single-celled organisms
moved to kingdom Protista
Protista
– 1938: prokaryotes moved to
kingdom Monera
– 1959: fungi moved to own
kingdom
Fungi
– 1977: kingdom Monera
split into kingdoms Bacteria and Archaea
Archea
Bacteria
kingdom Protista has been adjusted
 The taxonomy of protists is still changing
 Newer classifications attempt to use ultrastructure,
biochemistry, and genetics
 (unranked): Archaeplastida
 Division:
Rhodophyta (red algae)
Kingdom: Chromalveolata
Phylum: Heterokontophyta
The heterokonts or stramenopiles are a major line of
Protists. Currently containing more than 100,000
species. Most are algae, ranging from the giant
kelp to the tiny diatoms.
Originally the heterokont algae were treated as two divisions,
first within the kingdom Plantae and later the Protista
Division Chrysophyta
Class Chrysophyceae (golden algae)
Class Bacillariophyceae (diatoms)
Division Phaeophyta (brown algae)
Marine Phyla –
27 members of Kingdom Animalia
 http://www.mesa.edu.au/phyla/
 http://comenius.susqu.edu/biol/202/taxa.htm
 See all new supergroups