Ch. 15 Classification Systems Taxonomy Why Classify? • 2.5 million known species! • Another 20 million unknown species! • We need a system of biological classification that names and orders organisms in a logical manner. – Universally accepted name. – Groups with real biological meaning 1 Biological Classification • Early biological classification used a lot of detail. – Example: “Oak with deeply divided leaves that have no hairs on their undersides and no teeth around their edges” – Problems with this system • Too difficult to use. • Different scientists used different descriptions for the same organism. • Latin is used in classification. – Understood by scientists everywhere. Carolus Linnaeus (Carl von Linne) • Binomial nomenclature – Each organism has a two part name. – Genus species – Must be italicized – The first letter of the genus must be capital. – Examples: Acer rubrum (red maple), Acer palmatum (leaf that resembles a human hand) 2 Carolus Linnaeus • Organisms that share characteristics are grouped together. • Taxa – the group to which an organism is assigned. • Taxonomy – the science of naming organisms and assigning them to these groups. • Current classification rules governed by the International Codes of Zoological or of Botonical Nomenclature (ICZN or ICBN) Linnaeus’ Classification System – Hierarchy • Species – population of organisms that share similar characteristics and that can breed with one another.** 3 Linnaeus’ Classification System – Hierarchy • Genus – Similar species but cannot breed with one another. – Examples: Felis domesticus (house cat) and Felis concolor (mountain lion) – Examples: Ursus arctos (Grizzly bear) and Ursus americanus (Black bear) • Similar feet, teeth and claws but are distinct species. Linnaeus’ Classification System – Hierarchy • Families – Groups of genera (genus plural) which share many common characteristics. – Examples: Panthera leo (lions) , Panthera tigris (tigers), Felis domesticus (house cat), and Felis concolor (mountain lion) • Belong to the family Felidae (catlike animals) – Examples: Ursus arctos (Grizzly bear), Ursus americanus (Black bear) and Ailuropoda melanoleuca (Giant panda) • Belong to the family Ursidae (Bear like animals) 4 Linnaeus’ Classification System – Hierarchy • Order – Several families of similar organisms. – Example: Felidae (cats) and Canidae (dogs). – Examples: Ursus arctos (Grizzly bear), Ursus americanus (Black bear), Ailuropoda melanoleuca (Giant panda) and Vulpes vulpes (Red fox) • Belong to the order Carnivora (meat eaters) Linnaeus’ Classification System – Hierarchy • Class – Grouping of orders – Examples: Ursus arctos (Grizzly bear), Ursus americanus (Black bear), Ailuropoda melanoleuca (Giant panda), Vulpes vulpes (Red fox) and Sciurus carolinensis (grey squirrel) • Belong to the class Mammalia • A “class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain.” - Wikipedia 5 Linnaeus’ Classification System – Hierarchy • Phylum – several classes can be placed into a phylum – Examples: Ursus arctos (Grizzly bear), Ursus americanus (Black bear), Ailuropoda melanoleuca (Giant panda), Vulpes vulpes (Red fox), Sciurus carolinensis (grey squirrel) and Aspidelaps lubricus (coral snake) – Belong to the phylum chordata (Have a nerve cord) Linnaeus’ Classification System – Hierarchy • Kingdom – All phyla belong to one of the six kingdoms. 6 The Species Dilemma. • There is a debate among scientists on the definition of a species. • Some closely related species interbreed. – Example: Different species of mice may interbreed, some species of monkey interbreed. • Some organisms within a species are slightly different and some may consider them a separate species. – Example: Birds of the same species may have slightly different coloration. The Species Dilemma. • Some organisms reproduce asexually. – Example: bdelloid rotifers are all female and produce embryos without the need for sperm. • What about microorganisms such as bacteria? – Classifying them by what they eat (metabolism) is not easy. • Example: Some E.Coli are harmless while others are deadly. Both eat the same type of food. – They all look alike. – Rarely reproduce sexually. 7 8 Phylocode • Linnaeus lived a century before Darwin’s publication of Origin of the Species. • Push for a new system based on evolutionary relationships not based on common characteristics. • Phylocode – Names organized based on evolutionary relationships – Look for common ancestors and group into “clades” – International Society for Phylogenic Nomenclature 9 The Species Dilemma • The solution may be to define a species using several approaches. 10 11.