Taxonomy Cladograms

Evolutionary Classification Phylogeny = the study of evolutionary relationships Biologists now group organisms into categories that represent evolutionary descent (and not just physical similarities) How would you classify a hyena? Would you group it with cats or dogs? Photo credit flickr: ibeatty

Taxonomy The branch of biology that is concerned with identifying, naming and classifying organisms is called taxonomy.

Biologists have named over 1. 5 billion organisms out of the over 8 Biologists have named over 1.5 billion organisms out of the over 8.7 billion, estimated organisms that live on the planet. The field of taxonomy is constantly changing due to new species being identified.

Derived Characters Characteristics that appear more recently in a group but are not seen in older organisms Derived characters are used to construct a CLADOGRAM (a diagram that shows evolutionary relationships)

Cladistics – This is used to determine relative timing of divergences (separations of organisms and groups) . The hierarchy, or ranking, of groups derives logically from their genealogical position. For example, birds and crocodiles derive from a common reptilian stem ancestor.

When species are closely related they share an ancestor.

Living Fossil A living fossil is a living species (or clade) of organism that appears to be similar to a species otherwise known only from fossils. Normally the similarity is only a apparent physical resemblance between two different species, one extinct, the other living. Examples: Horseshoe crab

2 major goals of constructing phylogenetic relationships: 1. Clarify evolution/decent of a group 2. Help in the classification of the group

Rules of cladistics: 1. The group of organisms to be studied is related by descent from a common ancestor 2. Descent of organism follows a branching pattern (ancestral form splits into 2 sister taxa, ancestor goes extinct). 3. Changes in physical/behavioral characteristics occurs in lineages over time

How to construct a cladogram: 1. Choose taxa (group of one or more populations of an organism or organisms seen by taxonomists to form a unit) 2.Organisms must be "clades" = ancestor + inferred descendants 3. Determine similar and different characteristics (this step is important and often the most difficult. Are similarities derived homologies or the result of convergent evolution?) 4. Determine polarity (characteristics must be defined as either ancestral or derived. 5. Group by shared derived characters (called synapomorphies), homologies that have evolved after a branch diverged.

5. Build cladogram. This is NOT an evolutionary tree showing which organism is descended from whom. Follow these rules: 1) All taxa go on the endpoints of the cladogram, never at nodes. 2) All nodes must have a list of synapomorphies which are common to all taxa above the node (unless character is later modified). 3) All synapomorphies appear on the cladogram only once unless the character state was derived separately by evolutionary parallelism. For example, anteater-like features have appeared in different lines of mammals that were descended from non-anteater mammalian groups.

Draw and label

Cladograms A diagram that shows evolutionary relationships

HOW TO BUILD A CLADOGRAM Watch this animation on how to build a cladogram http://ccl.northwestern.edu/simevolution/obonu/cladograms/Open-This-File.swf

Identifying Unknown Organisms When biologists do field studies, they often encounter new organisms that they would need to identify. FIELD GUIDES often contain pictures for referencing organisms

“divided into two parts” Greek origin A dichotomous key is a tool that allows the user to determine the identity of items in the natural world based on the items characteristics "Dichotomous" means “divided into two parts” Greek origin dichotomous keys always give two distinct choices in each step, often they are opposites Black/white; good/evil; pointed/rounded

Dichotomous Keys A step-by-step guide to help identify an organism What am I?? A step-by-step guide to help identify an organism Follows a series of choices about the organisms features that lead you to the organism’s name Photo Credit: Sam? (Flickr)

Here are creatures we don’t know! How to use a Dichotomous Key? Here are creatures we don’t know! Lets choose one 23

How to use a Dichotomous Key? Choose only one creature at a time. 24

Decide which statement is true How to use a Dichotomous Key? Read steps 1a and 1b Decide which statement is true 1b is true

Then follow the directions after that step. How to use a Dichotomous Key? Then follow the directions after that step. Go to step 5!

At choice 5, you make another dichotomous choice How to use a Dichotomous Key? At choice 5, you make another dichotomous choice 5a is true Go to step 6!

C How to use a Dichotomous Key? Keep going until you come to a step that gives you the creature’s name. 6 a. The creature has one antennae Go to Step 7. C

How to use a Dichotomous Key? Choose a new creature and start at step 1a and 1b again. Continue until you find the creature’s name. C Where do you start Again?

Then, find the names of all the creatures 30

1. a. wings covered by an exoskeleton – go to step 2 b. wings freely observed – Go to step 3 2. a. body has a round shape ……….ladybug, a red beetle with black spots b. body has an elongated shape ……….grasshopper, a green insect that hops 3. a. wings point out from the side of the body ……….dragonfly, an insect that is 10- 15 cm long and lives in marshes b. wings point to the posterior of the body ……….housefly, a flying insect with red eyes and an annoying buzz