The Tree of Life Chapter 26

Linnaeus and Taxonomy  More than 1.5 million species of animals are named Estimated that these account for Estimated that these account for Less than 20% of all extant animalsLess than 20% of all extant animals Less than 1% of extinct animalsLess than 1% of extinct animals  Taxonomy Formal system for naming and classifying species Formal system for naming and classifying species  Systematics Broader science of classifying organisms based on similarity, biogeography, etc. Broader science of classifying organisms based on similarity, biogeography, etc. Systematic zoologists have three goals Systematic zoologists have three goals To discover all species of animalsTo discover all species of animals To reconstruct their evolutionary relationshipsTo reconstruct their evolutionary relationships To classify animals according to their evolutionary relationshipsTo classify animals according to their evolutionary relationships

Classification  PhyloCode New evolutionary classification system New evolutionary classification system Only names groups with a common ancestor and all descendants Only names groups with a common ancestor and all descendants Changes the way taxa are definedChanges the way taxa are defined Most names would be unchangedMost names would be unchanged No longer have ranks (i.e. family, class No longer have ranks (i.e. family, class

Classification Taxonomic Hierarchy Carolus Linnaeus Father of taxonomy Recognized that different species could be grouped into broader categories based on shared characteristics Taxon Any grouping of animals that shares a particular set of characteristics

Classification Linnaeus recognized five taxonomic categories Later scientists added three other categories Domain (Broadest) Kingdom Phylum Class Order Family Genus Species (Most specific)

Classification Nomenclature Binomial system Problems Common names vary Crayfish, crawdad, crawfish Many common names refer to higher taxonomic categories Pillbugs

Classification Binomial nomenclature – two part naming system Binomial nomenclature – two part naming system Each species has a two word name.Each species has a two word name. The first word is the Genus and is always capitalizedThe first word is the Genus and is always capitalized The second word is the species and is never capitalizedThe second word is the species and is never capitalized The two words are always either underlined or written in italicThe two words are always either underlined or written in italic Genus species or Genus species (G. species)Genus species or Genus species (G. species) All words are LatinAll words are Latin

 Introduction of evolutionary theory into animal taxonomy Changed taxonomist’s role from one of classification to systematization Changed taxonomist’s role from one of classification to systematization  Classification Denotes the construction of classes Denotes the construction of classes Grouping or organisms that possess a common feature called an essenceGrouping or organisms that possess a common feature called an essence Used to define the class Used to define the class Linnaeus and Taxonomy

 Systematization Places groups of species into units of common evolutionary descent Places groups of species into units of common evolutionary descent Character variationCharacter variation Used to diagnose systems of common descent Used to diagnose systems of common descent No requirement that an essential character be maintained throughout the system for its recognition as a taxon No requirement that an essential character be maintained throughout the system for its recognition as a taxon Linnaeus and Taxonomy

 In classification Taxonomist asks whether a species being classified contains the defining feature of a particular taxonomic class Taxonomist asks whether a species being classified contains the defining feature of a particular taxonomic class  In systematization Taxonomist asks whether the characteristics of a species confirm or reject the hypothesis that it descends from the most recent common ancestor of a particular taxon Taxonomist asks whether the characteristics of a species confirm or reject the hypothesis that it descends from the most recent common ancestor of a particular taxon Creates phylogeny Creates phylogeny Linnaeus and Taxonomy

Classification  Reading trees Sister taxaA-B, D-E Sister taxaA-B, D-E Basal taxon – early divergence Basal taxon – early divergence Polytomy Polytomy

Classification Animal systematics Monophyletic group A single ancestral species and all of its descendants Characters – anything that has a genetic basis and can be measured Polyphyletic group Individuals that cannot be traced back to a single species Paraphyletic group Some but not all members of the lineage

Classification  Evolutionary systematics Resemblance Homologies – common ancestor Analogies – evolutionary pressure (homoplasies)  Numerical taxonomy Using math to calculate similarity

Classification Phylogenetic systematics (Cladistics) Cladogram – depicts a sequence in the origin of derived characteristics Differentiate between analogies and homologies

Classification  Symplesiomorphies – A character shared by a number of groups, but inherited from ancestors older than the last common ancestor  Plesiomorphies – an ancestral or primitive character  Outgroup – a group that is not included within the other group  Derived Characters (apomorphies) – characters arriving since common ancestry  Synapomorphies – apomorphies shared by all members

Classification

Classification Domains Archaea Prokaryotic microbes that live in extreme environments Eubacteria True bacteria Eukarya All eukaryotic organisms

Classification  The 6 Kingdoms Archeabacteria Eubacteria Protista Fungi Plant Animal

Classification Archebacteria and Eubacteria Prokaryotic and unicellular Most are heterotrophs Bacteria and cyanobacteria make up this kingdom

Classification  Protista Unicellular or colonies of cells, eukaryotes Autotrophs and heterotrophs Algae and amoebas are included in this kingdom

Classification  Fungi Mostly multicellular, eukaryotes All are heterotrophs Cell walls Molds, mildews, mushrooms, and yeasts

Classification  Plant All are multicellular and eukaryotic All are autotrophs Cell walls Mosses, ferns, cone and flower bearing plants

Classification  Animal (Anamalia) All are multicellular and eukaryotic All are heterotrophs Motile Mollusk, Annelid, Arthropods, Echinoderms, Fish, Amphibians, Reptiles, and Mammals

Classification  Patterns of organization Symmetry Describes how parts of an animal are arranged around a point or axis

Classification  Asymmetry The absence of a central point or axis around which body parts are equally distributed Ex. – Corals, sponges

Classification  Radial symmetry The arrangement of body parts such that any plane passing through the central oral- aboral axis divides the animal into mirror images Ex. – Sea Anemone

Classification Bilateral symmetry Arrangement of body parts such that a single plane, passing between the upper and lower surfaces and through the longitudinal axis of an animal, divides the animal into right and left mirror images Cephalization The formation of an anterior end Usually results in a head

Classification Unicellular level of organization Single celled organisms Provide all necessary life functions Colonies Cellular aggregates Some interdependence or division of labor

Classification Diploblastic organization Simplest tissue level of organization Two layers of cells Ectoderm Outside layer analogous to epidermis Endoderm Inside layer analogous to gastrodermis

Classification Triploblastic organization Three layers of embryonic tissues Mesoderm New layer Supportive, contractile, and blood Organ-system level organization

Classification Types of body cavities Acoelomate Without body cavity Pseudocoelomate False body cavity Not entirely lined with mesoderm Coelomate Body cavity surrounded by mesoderm

Classification  Higher Animal Taxonomy Protosomes – early cleavage pattern and determination Mouth develops from blastopore Platyhelminthes Nematoda Mollusca Annelida Arthropoda Deuterostomes – anus develops from blastopore Echinodermata Hemichordata Chordata