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Phylogeny and Systematics
chapter 25
WARM UP: What evidence would you use to create a cladogram?
STANDARDS:
8. Evolution is the result of genetic changes that occur in constantly
changing environments.
• d. Students know reproductive or geographic isolation affects
speciation.
• e. Students know how to analyze fossil evidence with regard to
biological diversity, episodic speciation, and mass extinction.
• f.* Students know how to use comparative embryology, DNA or
protein sequence comparisons, and other independent sources of data
to create a branching diagram (cladogram) that shows probable
evolutionary relationships.
• g.* Students know how several independent molecular clocks,
calibrated against each other and combined with evidence from the
fossil record, can help to estimate how long ago various groups of
organisms diverged evolutionarily from one another.
Figure 25.1 A gallery of fossils
Figure 25.0 Fossil of a fish: perch
Figure 25.1a Dinosaur National Monument
Figure 25.1b Skulls of Australopithecus and Homo erectus
Figure 25.1c Petrified trees
Figure 25.1d Leaf impression
Figure 25.1e Ammonite
Figure 25.1f Dinosaur tracks
Figure 25.1g Scorpion in amber
Figure 25.1h Mammoth tusks
Figure 25.1x1 Sedimentary deposit
Figure 25.1x2 Barosaurus
Phylogeny
• Greek phylon, tribe & genesis, origin
• The evolutionary history of a species or group of related
species.
Systematics
• The study of biological diversity in an evolutionary
context.
• Reconstruct phylogeny.
• Name and classify species.
Taxonomy
• The branch of biology concerned with naming and
classifying diverse forms of life.
Figure 25.18 Modern systematics is shaking some phylogenetic trees
Fossil record
• The ordered array in which fossils appear within layers,
or strata, of sedimentary rocks that mark the passing of
geologic time.
Geologic time scale
• Consistent sequence of historical periods based on
fossils collected from many sites.
• Tells the order in which groups of species present in a
strata evolved but not absolute age.
• 4 Eras:
1) Precambrian (4,600 mya - 543 mya) life evolves
2) Paleozoic (543 mya - 245 mya) life leaves water
3) Mesozoic (245 mya - 65 mya) reptiles
4) Cenozoic (65 mya - present) age of mammals
Geologic Time Scale
Radiometric dating
• Measurement of certain radioactive isotopes in fossils
or rocks.
• Method most often used to determine the ages of
rocks and fossils on scale of absolute time.
1) organism accumulates isotopes of elements
while alive- stops upon death.
2) isotopes decay at a fixed rate.
3) half-life is the number of years it takes for 50%
of the original sample to decay.
ex. Carbon-14 / 5,730 years / Nitrogen-14
Uranium-238 / 4.5 billion years / Lead
Figure 25.2 Radiometric dating
Plate tectonics
• Geologic processes resulting from plate
movement
• Modern continents are passengers on crustal
plates that are swept across Earth’s surface
by convection currents of the hot mantle
below.
Figure 25.3 Earth’s crustal plates and plate tectonics (geologic processes resulting
from plate movements)
Figure 25.3x1 Crustal plate boundaries
Figure 25.3x2 San Andreas fault
Figure 25.4 The history of continental drift
Pangaea
• Supercontinent “all land”
• Existed 250 million years ago, near the end of the
Paleozoic era
• Species that had been evolving in isolation came
together and competed.
• Formation had tremendous environmental impact that
reshaped biological diversity by causing extinctions and
providing new opportunities for surviving taxonomic
groups.
• Began to break up 180 million years ago- divergent
evolution.
• ex. Australia isolated for 50 million years (marsupials)
Punctuated mass extinctions
• Fossil record reveals an episodic history of:
- Long, relatively quiescent periods
- briefer intervals of species turnover.
• Mass extinctions are followed by extensive diversification
of surviving taxonomic groups.
-ex. Permian Mass Extinction 250 mya
90% of marine animals (& land) perished
-ex. Cretaceous Mass Extinction 65 mya
more than 1/2 of all species- dinosaurs
Yucatan crater
• Impact Hypothesis- Walter & Luis Alvarez, UCBerkeley
• Chicxulub 180 km (10 km)- asteroid/meteorite impact
was enough to darken the Earth for years.
Figure 25.6 Trauma for planet Earth and its Cretaceous life
Continental drift, volcanism, and asteroid impacts may have all
played a role in mass extinctions.
Figure 25.6x Chicxulub crater
Figure 25.5 Diversity of life and periods of mass extinction
Taxonomic System of Classification
• Developed by Linnaeus in the 18th century
• It is a hierarchical system placing species into
broader and broader groups of organisms.
• The groups include (from broad to specific)
- Kingdom
(keep)
- Phylum
(pots)
- Class
(clean)
- Order
(or)
- Family
(family)
- Genus
(gets)
- Species
(sick)
Figure 25.7 Hierarchical classification
Recently, Domains have been added:
• Archeae
• Bacteria
• Eukarya
Linnaeus also developed a system of binomial
nomenclature
• All organisms are given two-part latinized name
• The genus is the first name and is capitalized
• the species is the second name
• The names are italicized
For example: Canis lupis
•
•
•
•
•
•
•
•
Eukarya
Animalia
Chordata
Mammalia
Carnivora
Canidae
Canis
Lupis
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Phylo-genetic trees reflect the hierarchical classification of
taxonomic groups nested within more inclusive groups.
Cladistics = creating a phylogenic tree based on:
a) Anatomical traits that appear as dichotomies, or twoway branching points
b) Each branch point represents the divergence of two
species from a common ancestor
Various branches in a cladogram indicate a clade
(from Greek clados, branch)
• Consists of an ancestral species and all of its
descendents
• New branches or clades are designated by a shared
derived character
• Backbone contains the shared primitive characters
Unnumbered Figure (page 494) Cladograms
Ability to pur
Retractable claws
Figure 25.12 Cladistics and taxonomy
Figure 25.11 Constructing a cladogram
A problem with anatomical traits:
convergent evolution
• different species possess common characteristics
because they have similar ecological roles and natural
selection pressures.
• Some organisms have analogous structures/ adaptations
• i.e. wings of butterfly/wings of a bird are analogous
flight equipment.
Molecular changes
• Many organisms share similar sequences of DNA and
amino acids (polypeptides)
• Mutations- insertions/deletions occur over time
• Databases & computer programs are used to assess
phylogenetic relationships that cannot be measured by
comparative anatomy or other methods.
Molecular clock: using differences in the sequence of
DNA and in protein amino acid sequence to place the
origin of taxonomic groups in time.
• Based on the observation that at least some regions of
genomes evolve at constant rates.
• The number of nucleotide and amino acid substitutions
is proportional to the time that has elapsed since the
lineages branched.
Figure 25.19 When did most major mammalian orders originate?
The end.
Figure 25.13 Aligning segments of DNA
Figure 25.14 Simplified versions of a four-species problem in phylogenetics
Figure 25.15a Parsimony and molecular systematics
Figure 25.15b Parsimony and molecular systematics (Layer 1)
Figure 25.15b Parsimony and molecular systematics (Layer 2)
Figure 25.15b Parsimony and molecular systematics (Layer 3)
Figure 25.16 Parsimony and the analogy-versus-homology pitfall
Figure 25.17 Dating the origin of HIV-1 M with a molecular clock