Biology 201 Dr. Edwin DeMont St. Francis Xavier University Animal Classification, Phylogeny and Organization In the News: The case of the vanishing taxonomists

Classification St. Francis Xavier University About 1.4 million species have been identified and named; three-fourths of these species are animals. This requires a very organized approach to classify the very large number of species.

Classification St. Francis Xavier University Systematics is the arrangement of organisms based on evolutionary relationships indicated by shared characters. Recent studies on RNA provide three domains. (Molecular approaches to animal systematics.) Three schools of systematics: 1. Evolutionary systematics 2. Numerical taxonomy 3. Phylogenetic systematics (cladists)

Classification St. Francis Xavier University Evolutionary systematics is a traditional approach which looks for similar characters and homologies to group organisms into taxa. 1. Evolutionary systematics Phylogenetic tree of vertebrate phylogeny The forelimbs of vertebrates evolved from an ancestral pattern.

Classification St. Francis Xavier University 2. Numerical taxonomy Numerical taxonomy is based on a quantitative analysis of characters to determine taxa and does not attempt to distinguish between shared states due to common ancestry and shared states due to convergence.

Classification St. Francis Xavier University 3. Phylogenetic systematics (cladistics) Phylogenetic systematics analyzes both shared ancestral characters and shared derived characters to evolutionary relationships and as data to construct cladograms. A hypothetical cladogram

Patterns of Organization St. Francis Xavier University Basic body plans of animals can be analyzed to illustrate evolutionary trends. Two general methods: 1. Body symmetry 2. Cellular organization Feather duster worms

Patterns of Organization St. Francis Xavier University Body symmetry Three different types of symmetry: 1. Asymmetrical 2. Radial symmetry 3. Bilateral symmetry Feather duster worms

Patterns of Organization St. Francis Xavier University Body symmetry 1. Asymmetrical Asymmetrical animals lack complex sensory and locomotory functions. A red encrusting sponge

Patterns of Organization St. Francis Xavier University Body symmetry 2. Radial symmetry Body parts are arranged such that a plane passing through the oral-aboral axis divides the animal into mirror images. Tube coral polyp

Patterns of Organization St. Francis Xavier University Body symmetry 3. Bilateral symmetry Most organisms are bilaterally symmetrical. Bilateral symmetry is correlated with cephalization, an active life style, and movement in one direction.

Patterns of Organization St. Francis Xavier University Cellular organization Three different types: 1. Single celled organisms 2. Diploblastic organisms 3. Triploblastic organisms Feather duster worms

Patterns of Organization St. Francis Xavier University Cellular organization 1. Single celled organisms (Protozoa) These cells have very little interdependence and do not form tissues, exhibit cytoplasmic level of organization. Not ‘simple’ – needs to perform all functions of multicellular organisms. Naegleria fowleri, causes amebic meningoencephalitis in humans

Patterns of Organization St. Francis Xavier University Cellular organization 2. Diploblastic organisms Have two tissue layers formed from the ectoderm and endoderm. Between these two layers is a noncellular mesoglea. A hydrozoan medusa

Patterns of Organization St. Francis Xavier University Cellular organization 3. Triploblastic organisms Third layer between ectoderm and endoderm – the mesoderm which gives rise to supportive, contractile, etc. Most have organ-system level of organization and are bilaterally symmetrical and relatively active. Chinese liver fluke

Online Tools St. Francis Xavier University Tree of Life Web project PubMed and