Transcript Tracing Phylogency - Thornapple Kellogg High School

Chapter 25
Tracing Phylogeny
Phylogeny
Phylon
= tribe,
geny = genesis or origin
The evolutionary history of a
species or a group of related
species.
Phylogeny
Found
in fossils and the
fossil record.
Fossils
Any
preserved remnant or
impression of a past
organism.
Types of Fossils
1. Mineralized
2. Organic Matter
3. Trace
4. Amber
Mineralized Fossils
Found
in sedimentary rock.
Minerals replace cell contents.
Ex: bone, teeth, shells
Organic Matter Fossils
Retain
the original organic
matter.
Ex: plant leaves trapped in
shale.
Comment – can sometimes
extract DNA from these fossils.
Trace Fossils
Footprints
and other
impressions. No organic
matter present.
Amber
Fossil
tree resin.
Preserve whole specimen.
Usually small insects etc.
Fossils - Limitations
Rare
event.
Hard to find .
Fragmentary.
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
Estimated
from half-life
products in the fossil.
Ex: Carbon - 14
Potassium - 40
Isomer Ratios
Ratio
of L- and D- amino acid
isomers.
L- used by living things.
D- not used by living things.
Death
form  D- form
Age can be calculated from
the ratio of L-/D- as long as
the temperature of the area is
taken into account.
L-
What do fossils tell us?
That
the geographical
distribution of organisms has
changed over time.
Reason? – The land
formations of the earth have
changed.
Continental Drift
The
movement of the earth's
crustal plates over time.
Drift is correlated with events
of mass extinctions and
adaptive radiations of life.
Result of plate movement
Geographical
Isolation.
New environments formed.
Old environments lost.
As the environments
changed, so did Life.
Example
Australian
fauna and flora are
unique.
Separated early and
remained isolated for 50
million years.
Mass Extinctions
The
sudden loss of many
species in geologic time.
May be caused by asteroid
hits or other disasters.
Examples
Permian
Extinction
Cretaceous Extinction
Permian Extinction
250
million years ago.
90% of species lost.
Cretaceous Extinction
65
million years ago.
Loss of the dinosaurs.
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
Climate
changes.
Areas are open for the surviving
species to exploit.
Rapid period of speciation
(adaptive radiation).
Many new species are formed in
a very short period of time.
Systematics
The
study of biological
diversity.
Uses evidence from the fossil
record and other sources to
reconstruct phylogeny.
Systematics fuses:
1. Phylogeny- tracing of
evolutionary relationships.
2. Taxonomy- the identification
and classification of species.
Taxonomy
Natural
to humans.
Modern system developed by
Linnaeus in the 18th century.
Linnaeus Taxonomy
1. Binomial Nomenclature –
two names for each organism.
Ex - Homo sapiens
2. Hierarchical System –
arranges life into groups.
Ex - Kingdom  Species
Goal of Systematics
To
have Taxonomy reflect the
evolutionary affinities or
phylogeny of the organisms.
Phylogenetic tree
Question?
How
to group taxa so that the
phylogenetic relationships
are correct ?
Ideal Situation
Monophyletic
Grouping - a
single ancestor gave rise to
all species in the taxon.
Other Possibilities
Polyphyletic
- grouping where
members are derived from two
or more ancestral forms.
Paraphyletic - grouping that
does not include all members
from an ancestral form.
Problem
Not
all “likeness” is inherited
from a common ancestor.
Problem is of homology vs
analogy.
Homology and Analogy
– likeness attributed
to shared ancestry.
Homology
Ex:
forelimbs of vertebrates
– likeness due to
evolution solution for the same
problem.
Analogy
Ex:
wings of insects and birds
Convergent Evolution
When
unrelated species have
similar adaptations to a
common environment. A
specific example of Analogy.
Ex: Sharks and dolphins
Only one is a cactus
Question
Can
parallel evolution
actually happen?
Need
Methods
to group organisms
by similarities and
phylogenies.
One possible method is
Molecular Systematics.
Molecular Systematics
Compares
similarities at the
molecular level.
Ex: DNA, Proteins
DNA Comparisons
A
direct measure of common
inheritance.
The more DNA in common,
the more closely related.
African Violets
2
nuclear DNA and 2
chloroplast DNA studies
found only 6 groups that
clustered by mountain.
New collections found many
intermediate forms between
the former “species”.
New Taxonomy
Reorganized
into 6 species
and 10 subspecies.
African violets are in the
process of splitting apart.
Schools of Taxonomy
1. Phenetics: Taxonomic
affinities based on
measurable similarities.
2. Cladistics: Branch points
defined by novel
characteristics.
Cladistics
Problem ?
Today’s Systemics:
Uses
clues from evolution.
Balances Phenetics and
Cladistics.
Result
Taxonomy
will become
Genealogies, reflecting the
organism’s
"Descent with Modification“.
Summary
Recognize
the use and limits
of fossils.
What happens to evolution in
mass extinctions.
What is phylogeny?
Summary
What
is a phyletic tree?
How is molecular
systematics used in
phylogeny?