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Zoology. Classification The branch of biology that names and groups organisms according to their characteristics and evolutionary history. Classify the thousands of new species discovered each year.
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Zoology Classification The branch of biology that names and groups organisms according to their characteristics and evolutionary history. Classify the thousands of new species discovered each year. Biologists use the characteristics of newly discovered to classify it with organisms having similar characteristics. The way we group organisms today continues to change and reflect the evolutionary history of organisms.
Aristotle • Greek Philosopher 384-322 BC • First classified organisms more than 2000yrs ago as either plants or animals. • Animals: land dwellers, water dwellers, or air dwellers. • Plants: three categories based on differences in their stems.
Carolus Linnaeus • Swedish naturalist (1707-1778) • Devised a system of grouping organisms into hierarchical categories. Nested hierarchy. • Used an organism’s morphology (form and structure)
Levels of Classification Kingdom Phylum or Division Class Order Family Genus Species
Under the modern Linnaean system, the classification of an organism places the organism within a nested hierarchy of taxa. The hierarchy ranges from the most general category (domain) to the most specific (species).
Binomial Nomenclature • Scientific Name has two parts. • 1st part is the genus • 2nd part is the species which is the identifier or descriptive word. • Genus name is capitalized and both names are underlined or written in italics. • Latin used by all scientists as a standard. • Linnaeus classified 1000’s of organisms. Versions of his system are still used today.
Scientific Names • May describe the organism, suggest geographic range, or honor a person • Homo sapiens (sapiens = wise) • Chaos chaos (amoeba never appear the same shape) • Canus familiaris (family dog)
Seven-level System was arbitrary • There is significant variation in some species to establish additional levels.
Variations of a species that occur in different geographical areas. Example: Terrapenecarolina triungui is a subspecies of the common eastern box turtle Terrapenecarolina that has 3 rather than 4 toes on its hind foot. Subspecies of rat snake
Phylogeny • Phylogeny is evolutionary history • Much of Linnaeus’ work in classification is relevant even in the context of phylogeny because morphological features are largely influenced by genes and are clues of common ancestry.
18-2 Modern Phylogenetic Taxonomy • Systematics • Cladistics
Systematics • Molecular biology revealed a wealth of information on organisms’ molecular nature (DNA & Amino acid sequence) and changed the nature of taxonomy. • Taxonomists organize the tremendous diversity of living things in the context of evolution.
Systematic Taxonomy • Systematic Taxonomists use several lines of evidence to construct a phylogenetic tree. • Modern taxonomic placement involves: • Morphology • Chromosomal characteristics • Nucleotide and amino acid sequences (chromosomes) • Embryological development • Information from the fossil record.
Phylogenetic tree • Family tree that shows the evolutionary relationships thought to exist among groups of organisms. • Represents a hypothesis and is based on several lines of evidence. • Subject to change as new information arises.
Interpreting a Phylogenetic Tree • Organism at base of tree is common ancestor to all the others in the tree. • Branch points indicate the evolution of some characteristic that splits a group into two groups. • Groups shown at tips of branches include organisms that have evolved most recently.
The Fossil Record • Provides clues to evolutionary relationships • Some organisms such as some ocean invertebrates have fairly complete fossil records. Others are incomplete. • May provide framework for phylogenetic tree which can then be confirmed with other lines of evidence.
Morphology • Homologous features: • Show descent from a common ancestor. • Common basic structure. Example bird wings and bat wings. • The greater the number of homologous features two organisms share, the more closely related they are thought to be.
Analogous features: • Evolved independently. • Differ in structure. Example: fly’s wings and bat’s wings.
Embryological Patterns of Development • Early patterns of embryological development provide evidence of phylogenetic relationships. • Provide means of testing hypothesis about relationships that have been developed from other lines of evidence. • Blastopore formation: In echinoderms and chordates, indentation forms the posterior end of the digestive system, in other animals it forms the anterior end.
Chromosomes and Macromolecules • Taxonomists use comparisons of macromolecules such as DNA, RNA and proteins as a kind of “molecular clock”. • Scientists compare amino acid sequences for homologous protein molecules of different species. • The number of amino acid differences is a clue to how long ago two species diverged from a shared evolutionary ancestor. • Not perfect because it assumes that all changes in amino acid sequencing are random and not affected by natural selection. Additionally amino acids can change at different rates in different organisms.
Chromosomes and Macromolecules - continued • Molecular clock model is used together with other data to estimate degrees of relatedness. • Scientists also compare karyotypes or patterns of chromosomes of two related species. • Regions of chromosomes that have the same pattern of banding are clues to the degree of relatedness.
This cladogram is based on similar amino acid sequences in a specific protein produced by these plants. The initials M,G, and so on indicate different amino acids. The yellow squares indicate differences within the otherwise-identical sequences.
This phylogenetic diagram is based on analyses of the DNA of many kinds of mammals. These analyses do not support a systematic grouping of pangolins with either African aardvarks or South American anteaters. Instead, pangolins seem to be most closely related to carnivores, such as bears and dogs. Biologists sometimes revise their classifications in light of such new evidence.
Cladistics • Relatively new system of phylogenetic classification. • Uses certain features of organisms called shared derived characteristics to establish evolutionary relationships. • Derived character: feature that apparently evolved only within the group under consideration. Example: feathers in birds are inherited from a common ancestor.
Cladograms • Ancestral diagrams made by means of cladistic analysis. • To interpret a cladogram: • Begin at the bottom and move up the axis that shows branch points. • Groups and derived characteristics appeared in the order shown. • Example: all groups branching above “hair” have hair. Those below do not.
This cladogram groups several major kinds of plants according to their shared, derived characters. The most common character (vascular tissue) is shared by all groups. The least common character (flowers) separates flowering plants from all other plants.
Conflict between tradition taxonomy and newer cladistics • Traditional: Snakes, lizards, crocodiles are all reptiles. Birds in class by themselves. • Newer: Dinosaurs are more closely related to birds and crocs than to snakes and lizards. Reptiles did not spring from one common ancestor but are a composite of several branches that have occurred during evolution of vertebrates.
Traditional systematists placed crocodiles in the class Reptilia, but placed birds in the class Aves. In contrast, cladistic taxonomists have grouped crocodiles and birds together in a clade named Archosauria. Notice that clades do not have category names such as “class” or “phylum”.
18-3 Two Modern Systems of Classification • Six Kingdom System • Three Domain System
Six Kingdom System • Kingdom Archaebacteria • Kingdom Eubacteria • Kingdom Protists • Kingdom Fungi • Kingdom Plantae • Kingdom Animalia
Kingdom Archaebacteria • Unicellular • Prokaryotes with distinctive cell membranes • Biochemical and genetic properties that differ from all other kinds of life. • Some autotrophic – produce food by chemosynthesis and methane waste.
Many live in harsh environments – sulfurous hot springs, salty lakes, anaerobic environments, intestines of animals • “archae” = ancient • May be directly descended from and very similar to first organisms on Earth
Kingdom Eubacteria • “eu” = true • Unicellular, prokaryotes • Bacteria that affect your life: tooth decay, turn milk to yogurt, food poisoning, illness • Most use oxygen, but a few cannot live in O2 • Both Eubacteria and archaebacteria make up the greatest number of living things on Earth.
