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Transcript
Chapter 25 – Phylogeny and Systematics
Taxonomy Phylon = tribe
classifying organisms
Geny = genesis
Systematics –
studying biodiversity
in an evolutionary
context (involves the
se of fossil record)
Phylogeny=Evolutionary History of a
Species/Genus (branch order, branch length)
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.
Petrified
Trees
–
190
million
Dinosaur
footprints
Sand forms sandstone. – 150
years
old!years old!
million
Mud forms shale.
When pieces of organisms settle Leaf with intact chlorophyll –
along with the inorganic material, 40 million years old!
they can be preserved as fossils.
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 by
looking at what’s found in each layer.
youngest
oldest
They can help to
correlate the fossil
record from multiple
locations + serve as
guides to the age of
rocks they are found in.
Index fossils are fossils that are found at different locations.
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 of
fossils found.
Absolute dating of fossils is usually done by radiometric
dating.
Fossils contain isotopes of elements accumulated when
they
were 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
14C
N
14
C
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 animal
1/2 life = 5,600 years
Clam is 11,200 years old.
Isotopes – Carbon Dating
14C
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
250
million 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 probable
evolutionary
relationships
Binomial classification—genus and species (Linneaus
System)
(Domain)
Kingdom
Phylum
Class
Order
Family
Genus
Species
Taxonomic
unit/ Taxa
Cladogram
A phylogenetic diagram cladogram
Classification parallels phylogeny.
Monophyletic—includes most recent common ancestor and all its
descendents
Polyphyletic—members come from 2 or more ancestors; does not include
the most recent common ancestor
Paraphyletic— 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.
a
D
a
•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