Phylogeny and Systematics

Order out of chaos…

Phylogeny

• Phylon = tribe

• Genesis = origin

• The evolutionary history of a species or a group of related species

• Part of the science of Systematics

• Systematics ecompasses phylogeny and taxonomy

The evolutionary history of a species or group of species

Fossils

• Form in sedimentary rocks

• Hard parts such as shell, bone, or teeth

• Hardened by mineralization

• Soft parts replaced by mineralization becoming stone

• Molds or casts of decayed organisms

• Preservation in amber, ice, tar

Relative Dating

• Younger sediments are on top of older ones

• Index fossils are widespread and reliable ones

• Rock layers provide a “relative” age for fossils in the layers

Geological Time Scale

• Four eras: Precambrian, Paleozoic, Mesozoic, and Cenozoic

• Boundaries between eras correspond to mass extinctions

• Eras are subdivided into Periods

• Periods are subdivided into Epochs

Absolute Dating

• Ages given in year quantities

• Ratio of Carbon-12 to Carbon-14

• Carbon-14 decays to Nitrogen-14

• Half-life of C-14 is 5,730 years

• U-238 has a half-life of 4.5 billion years

• L-amino acids convert to D forms over time

• Racemization clock is temperature sensitive

Click here to see a half life simulation

Types of Radioactive Decay

• Alpha decay – Helium nucleus ejected

• Beta decay – Electron or positron ejected

• Gamma decay – Gamma photon emitted

Read more about radioactive decay

Continental Drift

• Major geographic factor in evolution

• Continents move about on the Earth’s surface

• Continents merged as Pangea 250 mya.

• Pangea begins to break up 180 mya.

http://www.ucmp.berkeley.edu/geology/anim1.html

How the dinosaurs died out…

Mass Extinctions• Mass extinctions are followed by

diversification of survivors

• Extinctions are inevitable in a changing world

• Permian extinction: 95% of marine animals became extinct in less than 5 million yrs.

• Cretaceous extinction separates Mesozoic and Cenozoic eras: 65 mya

• Impact hypothesis

SYSTEMATICS

The study of biological diversity in an evolutionary context

Carolus Linnaeus, or Carl Linné, 1707-1778, Swedish botanist.

http://www.english.upenn.edu/~jlynch/Frank/People/linnaeus.html

Taxonomy

• The naming and classification of organisms

• Formalized by Carolus Linnaeus(1707-78)

• Binomial nomenclature: Genus & species

Leopard = Panthera pardus

African Lion = Panthera leo

• Hierarchical classification system

• Taxon = a group at any level (plural,taxa)

Domains

Diversity of Systems

CLADISTICS

A Taxonomic Approach To Classification

Cladistics• Phylogenetic approach to classification

• Based on dichotomous (2-way) branching

• Branches show new species budding from a common ancestor

• Branching symbolizes historical chronology

• Each branch is called a clade

• Clades consist of an ancestral species and all of its descendants: Monophyletic

Examine groups for common ancestors. Branches should bifurcate (split in two).

Taxon one consists of an ancestral species and all of its descendents

Taxon 2 includes some, but not all of A’s descendents

Taxon 3 lacks a common ancestor. Two ancestors for one group (D,E,G,H)

Cladistic Analysis

Clades are defined by their shared-derived characters

The outgoup (Lancelet) and ingroup share characters that were present in the common ancestor. The ingoup is defined by the presence of a vertebral column.

Phylogeny Inferred From

• Morphological data (comparative anatomy)

• Fossil data

• DNA

• Proteins

• Embryology (embryo & fetal development)

Molecular Clocks

• Rely on genomic regions that evolve at a fairly constant rate

• Must be referenced to fossil records to provide accuracy

• Difficult to relate to absolute time