Chapter 25 ~ Phylogeny & Systematics

Phylogeny: the evolutionary history of a species

Systematics: the study of biological diversity in an evolutionary context

The Fossil Record : the ordered array of fossils, within layers, or strata, of sedimentary rock

Paleontologists

The fossil record

Sedimentary rock : rock formed from sand and mud that once settled on the bottom of seas, lakes, and marshes

Dating :

1- Relative~ geologic time scale; sequence of species; stratification, index fossils

2- Absolute~ radiometric dating; age using half-lives of radioactive isotopes

1- Relative~ geologic time scale; sequence of species; stratification, index fossils

Uniformitarianism- thepresent is key to the past

Original horizontality Sediments deposited in horizontal layers

Superposition Youngest rocks are on top (assuming no tectonic activity)

Cross-cutting relationships Cut layer is older than ‘cutting’ rock

Faunal succession Organisms succeed one another in recognizable reproducible pattern

Unconformity Represents a break (gap) in the rock record

Absolute~ radiometric dating; age using half-lives of radioactive isotopes

Isotope Dating relies on the rate of decay of radioactive isotopes within a rock

Radioactive isotopes have nuclei that spontaneously decay emitting or capturing a variety of subatomic particles

Decaying radioactive isotope- parent isotopes decay to form daughter isotopes

Half-life- is the time it takes for half the atoms of parent isotope to decay

Some radioactive isotopes with daughter products

U-238 => Pb-206; K-40 => Ar-40; C-14 => N-14

The Geological Time Scale

Biogeography : the study of the past and present distribution of species

Pangaea -250 mya √ Permian extinction

Geographic isolation -180 mya √ African/South American reptile fossil similarities √ Australian marsupials

Mass extinction

Permian (250 million years ago): 90% of marine animals; Pangea merge

Cretaceous (65 million years ago): death of dinosaurs, 50% of marine species; low angle comet

Phylogenetics

The tracing of evolutionary relationships (phylogenetic tree)

Linnaeus

Binomial

Genus, specific epithet

Homo sapiens

Taxon (taxa)

Phylogenetic Trees

Cladistic Analysis : taxonomic approach that classifies organisms according to the order in time at which branches arise along a phylogenetic tree (cladogram)

Clade : each evolutionary branch in a cladogram

Types:

1- Monophyletic single ancestor that gives rise to all species in that taxon and to no species in any other taxon; legitimate cladogram

2- Polyphyletic members of a taxa are derived from 2 or more ancestral forms not common to all members; does not meet cladistic criterion

3- Paraphyletic lacks the common ancestor that would unite the species; does not meet cladistic criterion

Constructing a Cladogram

Sorting homology vs. analogy...

Homology : likenesses attributed to common ancestry

Analogy : likenesses attributed to similar ecological roles and natural selection

Convergent evolution : species from different evolutionary branches that resemble one another due to similar ecological roles

A Cladogram