Tracing Phylogeny

Phylogeny u Phylon = tribe, geny = genesis or origin u The evolutionary history of a species or a group of related species.

Phylogeny u Found in fossils and the fossil record.

Fossils u Any preserved remnant or impression of a past organism.

Types of Fossils 1. Mineralized 2. Organic Matter 3. Trace 4. Amber

Mineralized Fossils u Found in sedimentary rock. u Minerals replace cell contents. u Ex: bone, teeth, shells

Organic Matter Fossils u Retain the original organic matter. u Ex: plant leaves trapped in shale. u Comment – can sometimes extract DNA from these fossils.

Trace Fossils u Footprints and other impressions. No organic matter present.

Amber u Fossil tree resin. u Preserve whole specimen. u Usually small insects etc.

Fossils - Limitations u Rare event. u Hard to find. u Fragmentary. u Dating.

Fossil Dating Methods 1. Relative - by a fossil's position in the strata relative to index fossils. 2. Absolute - approximate age on a scale of absolute time.

Absolute - Methods 1. Radioactive 2. Isomer Ratios

Radioactive u Estimated from half-life products in the fossil. u Ex: Carbon - 14 Potassium - 40

What do fossils tell us? u That the geographical distribution of organisms has changed over time. u Reason? – The land formations of the earth have changed.

Continental Drift u The movement of the earth's crustal plates over time. u Drift is correlated with events of mass extinctions and adaptive radiations of life.

Pangaea u 250 million years ago. u One super continent. u Many life forms brought into contact with each other.

Mesozoic era u Pangaea began to break up. u 180 million years ago.

Result u Geographical Isolation. u New environments formed. u Old environments lost. u As the environments changed, so did Life.

Example u Australian fauna and flora are unique. u Separated early and remained isolated for 50 million years.

Mass Extinctions u The sudden loss of many species in geologic time. u May be caused by asteroid hits or other disasters.

Examples u Permian Extinction u Cretaceous Extinction

Permian Extinction u 250 million years ago. u 90% of species lost.

Cretaceous Extinction u 65 million years ago. u Loss of the dinosaurs. u Good evidence that this event was caused by an asteroid that hit in the Yucatan, causing a “nuclear winter”.

The crater

Result of Mass Extinctions u Areas are open for the surviving species to exploit. u Rapid period of speciation (adaptive radiation). u Many new species are formed in a very short period of time.

Convergent Evolution u When unrelated species have similar adaptations to a common environment. u Ex: Sharks and dolphins

Only one is a cactus

Need u Methods to group organisms by similarities and phylogenies.

DNA Comparisons u A direct measure of common inheritance. u The more DNA in common, the more closely related.

DNA Comparison Methods 1. DNA-DNA Hybridization 2. Restriction Mapping 3. DNA Sequencing All three methods have been used, but DNA Sequencing is becoming the most common.

Protein Comparisons u Examines the Amino Acid sequence of homologous proteins. u Ex: Cytochrome C Study

Schools of Taxonomy 1. Phenetics 2. Cladistics

Phenetics u Makes no phylogenetic assumptions. u Taxonomic affinities based on measurable similarities. u Ex: Numerical Taxonomy

Cladistics u Branch points defined by novel characteristics. u Branch pattern may not reflect evolutionary history.

Cladistics