Taxonomy 6p5p9

Taxonomy

The purpose and importance of Taxonomy • In order to study the great diversity of organisms and ecosystems and to effectively communicate their findings, biologists must organize their knowledge. • Taxonomy is the science of naming, describing and classifying organisms.

• Classification involves arranging organisms into groups based on their similarities, which reflect evolutionary relationship among lineages.

IMPORTANCE • To distinguish between beneficial and harmful varieties. • To record the world’s biodiversity. • To communicate biological knowledge efficiently between the scientists. • To develop strategies for protection and conservation of endangered species.

Classification systems

Artificial classification

Natural classification -Phenetic -Phylogenetic

Artificial Classification • Simple to make and convenient to use. • Involves separating organisms into groups according to their differences. • These difference may be chosen for convenience rather than for any biological significance. • Use easily observable characteristics with no biological significance. • But no information about evolutionary relationships or patterns.

Example:

Earthworms

Snake

Frog

Crayfish

• The animals may be separated into two groups by asking the question: Do they have legs? This produces: (a)Group A- Crayfish and frog (b)Group B-snake and earthworm.

Natural Classification • Consider embryological(developmental), morphological, anatomical, biochemical,cytological and even behaviourial similarities between organisms. • 2 types: phenetic( numerical) and phylogenetic.

Phenetic classfication • Based on the number of shared observable characteristics between organisms. • It is a quantitative approach- the more measurable similarities there are, the more likely two organisms are to belong to the same group. • Phenetics do not differentiatiate between homology and analogy(homoplasy). This is because they believe that if the number of shared characters is very large, the classfication is valid.

Phylogenetic classification • Based on shared characteristics which reflect evolutionary relationships. • This mean that organisms in the same group are believed to have a common ancestor.

• Shared ancestral charaters(plesiomorphic characters) are traits that were present in an ancestral species and remain present in all groups descended from the ancestor. • Shared derived characters(synapomorphic charaters) are traits found in two or more taxa that first appaeared in their most recent common ancestor.

• Ancestral characteristics: The egg-laying trait is both reptiles and birds. • But, only bird have feathers and beaks, not reptiles.—derived traits. • So, the common egg-laying ancestor for birds and reptiles appeared earlier in evolutionary history than the common feathered ancestor for different groups of birds.

• Cladogram: • The base of the cladogram represents the common ancestor. • Each mode or branch point represents a more recent common ancestor.

Homologous Strucutures • The wing of a bird, a whale’s flipper and the front leg of a horse, although superficially dissimilar, can all be seen to have similar bone structure and on further study can be seen to have evolved from a common form of forelimb. Known as the pentadactyl limb. They are homologous characters.

Analogous characters • The wings of a butterfly and a humming bird may be flapping extensions but they are totally different in basic structure.

• Notochords were the first "backbones" serving as structures in chordates • The amniotes are a group of tetrapod vertebrates (four-footed animals with backbones or spinal columns) that have a terrestrially adapted egg.