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. Common Name: White oak: Scientific Name: Quercus alba Compare the scientific name of this white oak with the owl on the next slide.

17.1 The Linnaean System of Classification Binomial nomenclature is a two-part scientific naming system. –uses Latin words - because it’s a “dead” language (no longer used or changing) and universal (all scientists can communicate using Latin. –scientific names always written in italics –two parts are the genus name and species descriptor

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 Scientific Name: Tyto alba Common Name: Barn Owl NOTE: The white oak and the barn owl belong to different genera. The species parts of their scientific name are both alba, meaning white.

17.1 The Linnaean System of Classification Scientific names help scientists to communicate. –Some species have very similar common names. –Some species have many common names. Contrast: Describe the difference between a genus and a species.

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. Linnaean taxonomy classifies living things into a hierarchy of groups called taxa. The classification of the gray wolf is illustrated here.

17.1 The Linnaean System of Classification The Linnaean classification system has limitations. Linnaeus taxonomy doesn’t account for molecular evidence. –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. Figure: This red panda (Ailurus fulgens) is more closely related to raccoons than to giant pandas. Infer: Why is the common name red panda misleading in terms of classification based on relatedness?

17.1 The Linnaean System of Classification 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

17.1 The Linnaean System of Classification Cladistics is a common method to make evolutionary trees. –classification based on common ancestry –species placed in order that they descended from common ancestor Figure: The glyptodon (Glyptotherium arizonae) illustrated here (right), was the size of a small car and lived more than 10,000 years ago. It is the common ancestor to about 20 modern armadillo species, including the nine-banded armadillo (Dasypus novemcinctus) (left).

17.1 The Linnaean System of Classification A cladogram presents hypothesized evolutionary relationships among a group of species based on common ancestry and derived characters. –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. Contrast: What is the difference between a clade and a taxon?

17.1 The Linnaean System of Classification 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 clade 1 Amniota clade 2 Reptilia clade 3 Diapsida clade 4 Archosauria clade 5 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

17.1 The Linnaean System of Classification 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 clade 1 Amniota clade 2 Reptilia clade 3 Diapsida clade 4 Archosauria clade 5 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

17.1 The Linnaean System of Classification 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. WHY?? Figure: Based on structural similarities, scientists previously classified segmented worms and arthropods as sister taxa. The discovery of a hormone found only in roundworms and arthropods has led scientists to propose a new phylogeny for these taxa.