Chapter 25 – Phylogeny and Systematics

Phylon = tribeGeny = genesis

Phylogeny=Evolutionary History of a Species/Genus (branch order, branch length)

Systematics – studying biodiversity in an evolutionary context (involves the se of fossil record)

Taxonomy - classifying organisms

Fossil record—the order of fossils within layers (strata) of sedimentary rock. (helps determine order of events in history, age of rocks, how environments were in history). Hard parts like bones and shells leave fossils - so record is incomplete.

FOSSIL GUESSING GAME

How are fossils formed?

Sedimentary rocks form from layers of sand and silt that settle to the bottom of seas and swamps.

As deposits pile up, they compress older sediments below them into rock.

The bodies of dead organisms settle along with the sediments, but only a tiny fraction are preserved as fossils.

Sedimentary rocks are made from layers of minerals that settle out of water.

Sand forms sandstone.

Mud forms shale.

When pieces of organisms settle along with the inorganic material, they can be preserved as fossils.

Petrified Trees – 190 million years old!

Leaf with intact chlorophyll – 40 million years old!

Dinosaur footprints – 150 million years old!

Summary:Most parts of dead organisms decay quickly, but mineral-rich parts can remain as fossils.

ex. shells, teeth, bones

Fossils that retain organic (soft) material are rare - a cast is made of the soft parts.

Many fossils are imprints left by organisms that have since decayed.

Paleontologists can determine relative ages of fossils bylooking at what’s found in each layer.

oldest

youngest

Index fossils are fossils that are found at different locations.

They can help to correlate the fossil record from multiple locations + serve as guides to the age of rocks they are found in.

                                                                                                         

               

Relative Dating:The geological time scale consists of eras, periods, and epochs. Date a fossil based on where it is found in a rock strata = relative dating.New eras are marked by a distinct change in the types offossils found.

Absolute dating of fossils is usually done by radiometric dating.Fossils contain isotopes of elements accumulated when theywere alive.

Absolute Dating - Isotopes

Two atoms of the same element that differ in the number of neutrons are called isotopes 99% of carbon atoms have 6

neutrons (12C)

1% of carbon atoms have 7 neutrons (13C)

Rarest C isotope, has 8 neutrons (14C) - RADIOACTIVE

Isotopes – Carbon Dating

N

14C

14C

Each isotope has a fixed half-life—the number of year it takes for half of the sample to decay.

14C: 12C = 1/4 of ratio in living animal1/2 life = 5,600 years

Clam is 11,200 years old.

Isotopes – Carbon Dating14C

Word of Caution:

The fossil record is incomplete, but it gives us a good idea of the organisms living during a particular time of the Earth’s history.

As the Earth’s mantle moves, the continents drift.Arrowheads show areas of violent tectonic events.

The continents came together 250million years ago -Pangaea.

Pangaea started to split about 180 million years ago.

Mass extinctions followed by adaptive radiation of survivors.Permian extinctions—90% of marine animals died

--around the time Pangaea formed, many volcanic

eruptions (global warming)Cretaceous extinctions—dinosaurs

--climate cooled, seas receded, volcanic eruptions,

perhaps an asteriod or comet collision (iridium layer)

Phylogeny = evolutionary history

Phylogenetic trees—show probableevolutionaryrelationships

Binomial classification—genus and species (Linneaus System)

(Domain)KingdomPhylumClassOrderFamilyGenusSpecies

Taxonomic unit/ Taxa

Cladogram

A phylogenetic diagram - cladogram

Classification parallels phylogeny.

Monophyletic—includes most recent common ancestor and all its descendentsPolyphyletic—members come from 2 or more ancestors; does not include the most recent common ancestorParaphyletic— includes the most recent ancestor, but not all its descendents

Homology—likeness from shared ancestry; ex. forelimbs of mammals

Analogy—likeness due to convergent evolution; ex. wings of birds and insects

In developing phylogenetic trees, we should use only homologies.

Daa

•A cladogram presents the chronological sequence of branching during the evolutionary history of a set of organisms.

An outgroup is a species that is kind of related to the species being studied, but not as much as the other species studied are related to each other.

Cladistic analysis--classifies organisms

according to the order that branches arose along a phylogenetic tree

Each branch point is defined by homologies that are unique to the species on that branch.

Molecular Biology Comparisons Amino acid sequence DNA and RNA sequences

DNA-DNA hybridization—extent of H-bonding between DNA of 2 different species restriction maps

comparison of restriction fragments DNA/RNA sequencing

Molecular Clocks – UCCP CD

Classification based on protein and DNA similarities