1. THE CLASSIFICATION OF LIVING ORGANISMS
Taxonomy or Systematics: The study of classification
© 2016 Paul Billiet ODWS

2. Why classify organisms?
Over a million species so far identified
Estimates of up to 30 million species on Earth
Need to organise this biodiversity
Systematics tells us about the patterns in nature, the way organisms are related, how they evolve
Systematics can be used to identify organisms that are important to us.
© 2016 Paul Billiet ODWS

3. Systematics
Collections of animals and plants in museums from 17th century
Need for systematic classification established
Carl Linneus (1735) The binomial classification
To “put order into God’s creation”.
Jardins des Plantes Paris
© 2016 Paul Billiet ODWS

4. Binomial system Homo sapiens Genus Species Capital case Small case
© 2016 Paul Billiet ODWS

5. Levels of hierarchy Taxon Domain Kingdom Phylum Class
Based on relatedness (phylogeny) but artificial
Order
Family
Genus
Species
Some biological basis
© 2016 Paul Billiet ODWS

6. The unit of taxonomy: The SPECIES
The term species has biological significance
Species form populations of individuals which may interbreed to form fully fertile offspring
Problem: Some species only use asexual reproduction or rarely use sexual reproduction.
© 2016 Paul Billiet ODWS

7. How taxonomy works
The aim is to group organisms according to their evolutionary relationship (phylogeny)
Established by studying the phenotypes of living organisms or fossils
DNA sequencing compares the genotypes
Use characteristic features to group organisms (e.g. all animals with feathers = Birds)
Taxonomists decide which are the most significant or "important" characteristics by the way they occur in different groups of organisms.
© 2016 Paul Billiet ODWS

8. Comparing phenotypes & genotypes
Taxonomists compare a new specimen with given characteristics to other specimens:
morphology
anatomy
behaviour
embryology
protein structure
karyotypes
DNA sequence (DNA fingerprints).
Phenotype
Genotype
© 2016 Paul Billiet ODWS

9. Hierarchy of characters
Taxonomy uses many different characteristics to define a taxon
One character is not enough
The characteristics are grouped in a hierarchy.
© 2016 Paul Billiet ODWS

10. Example
Acanthostega
Having four legs with five toes is common to all land vertebrates and their fish ancestor
This would be used to group the animals we call tetrapods
Having a nerve cord running down the back is a feature common to all the tetrapods but also all the rest of the vertebrates
So it can be used to group all the vertebrates but not the tetrapods alone.
Lamprey
© 2016 Paul Billiet ODWS

11. The pentadactyl limb
Classification led to comparisons of shape and form that gave rise to comparative anatomy
Comparative anatomists noticed that different species have similar structures used for different functions (e.g. the pentadactyle limb of terrestrial vertebrates)
These are called homologous structures.
© 2016 Paul Billiet ODWS

12. The pendadactyle limb
Lizard
Frog
Bat
Human
© 2016 Paul Billiet ODWS

13. Analogous or homologous characters
Even though the front legs of different mammals may look different they still use the same bones in their structure
The simplest explanation for this is that they all originated from a common ancestor, the ancestor of all mammals
This is called homology
As organisms evolved they split up and specialised in different ways of living
Their bodies changed in shape but they still retain some of their ancestors features.
© 2016 Paul Billiet ODWS

14. Homology in mammalian fore limbs
© 2016 Paul Billiet ODWS

15. Analogous structures
Wolf Canis lupus
Some structures may look very similar but have evolved independently
They are the product of natural selection on an organ adapting an organism to a particular niche.
Thylacine Thylacinus cynocephalus
© 2016 Paul Billiet ODWS