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Phylogeny and Systematics
• Phylogeny – evolutionary history of a species
or group of related species
• Systematics – study of biological diversity in
an environmental context (tracing phylogeny)
• Taxonomy - science of naming, identifying,
and describing diverse forms of life
• Pangaea – supercontinent of land masses
(present 250 mya)
Sedimentary Rock Are The
Richest Source of Fossils
Dinosaur Bones
Skull
Scorpion in Amber
Petrified Trees
Leaf
Fossilized Seashell
Geologic Time Scale
• Major Events in Evolution
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4.6 bya – formation of the Earth (Precambrian)
3.5 bya – prokaryotic cells
2.2 bya – eukaryotic cells
600 mya – soft-bodied invertebrates
500 mya – colonization of land plants (Paleozoic)
420 mya – jawless fish
375 mya – bony fish, amphibians, insects
325 mya – first seed plants, reptiles
220 mya – cone-bearing plants (Mesozoic)
175 mya – dinosaurs abundant
80 mya – angiosperms
60 mya – mammals, birds, pollinating insects (Cenozoic)
30 mya – primate groups
2.5 mya – apelike ancestors
0.5 mya – humans appear
Geologic
Time
Scale
Radiometric Dating
• The measurement of certain radioactive
isotopes in fossils or rocks.
• Half-life – the number of years it takes for
50% of the original sample to decay; it is
unaffected by temperature, pressure, and
other environmental variables
• Carbon-14 to Nitrogen-14 → 5,730 years
• Potassium-40 to Argon-40 → 1.3 billion years
• Uranium-238 to Lead-206 → 4.5 billion years
– Found in Volcanic Rock
Radiometric Dating
The Fossil Record
• The fossil record is far from being complete, it
is slanted in favor of species that existed for a
long time, were abundant and widespread,
and had shells or hard skeletons.
• A substantial fraction of species that have
lived probably left no fossils, most fossils that
formed have been destroyed, and only a
fraction of the existing
fossils have been
discovered.
Plate Tectonics and Pangaea
Major Mass Extinctions
1.
Permian Period – 250 mya
• 90% of marine animal went extinct
• 8 out of 27 orders of Permian insects did not survive
• The extinction occurred in less than 5 million years
• Reasons
• Occurred about the same time the continents merged to
form Pangaea – Marine and terrestrial habitats
disturbed
• Massive volcanic eruptions in what is now Siberia –
increase in atmospheric carbon dioxide = global
warming
• Global warming = reduced temp. differences between
the poles and equator. Could lead to uneven mixing of
the oceans which decrease amount of dissolved oxygen
Major Mass Extinctions
2. Cretaceous Period – 65 mya
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Extinction of dinosaurs
Killed more than half of the marine species
Exterminated many families of terrestrial plants
and animals
Reasons
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The climate became cooler, and shallow seas
receded from continental lowlands
Large volcanic eruption in what is now India
“Impact Hypothesis” – a large comet (dirt and ice)
or small asteroid (rock and metal) collided with
Earth
Taxonomy
• Taxonomy – Binomial;
based on a 2-part Latin
name; genus and
species.
• Ex. Pseudacris nigrita,
Homo sapiens
• Hierarchical
Classification – way for
us to structure and
view of our world
Grizzly bear
Black bear
Giant panda
Red fox
KINGDOM Animalia
PHYLUM Chordata
CLASS Mammalia
ORDER Carnivora
FAMILY Ursidae
GENUS Ursus
SPECIES Ursus arctos
Abert
squirrel
Coral
snake
Sea star
Phylogenetic Systematics
• Phylogenetic Tree – reflect the hierarchical
classification of taxonomic groups
• Cladogram – a “tree” constructed from a
series of dichotomies, or 2-way branch points
that represent divergence of an animal from a
common ancestor; the “deeper” the branch to
greater the divergence
• The sequence symbolizes historical
chronology
• Clades – each branch in a cladogram;
ancestral species and all of its decendents
Phylogenetic Systematics
Phylogenetic Systematics
Phylogenetic Systematics
How Do We Construct a Cladogram?
• Homology – likeness attributed to shared
ancestry; all forelimbs of mammals are
homologous
• Not all likeness qualifies as homology
• Convergent Evolution – Species from different
evolutionary branches may come to resemble
one another if they have similar ecologocial
roles and natural selection has shaped
analogous adaptation. Similarity due to
convergence is called analogy.
• Example – the wings of a bird, bat, and bee.
Convergent Evolution &
Analogous Structures
Ocotillo of southwestern North America
Alluaudia of Madagascar
How Do We Construct a Cladogram?
• As a general rule – the greater the number of
homologous parts between two species, the more
closely the species are related.
• The more complex two similar structures are, the less
likely it is they evolved independently
– Example – the human skull and chimpanzee skull
match almost perfectly bone for
bone, the only difference is the
way they fuse together. Most
likely, the genes required to
build these skulls were inherited
from a common ancestor.
Identifying Shared Derived
Characteristics
These characteristics allow us to identify the sequence in which
derived characters evolved during vertebrate phylogeny
Identifying Shared Derived
Characteristics
Phylogeny Can Be Inferred
From Molecular Data
• Anatomical characteristics and homology
alone cannot account for all evolutionary
relationships
• Systematists compare genes (DNA) and gene
products (proteins) to determine evolutionary
relationships
Phylogeny Can Be Inferred
From Molecular Data
Appendages
Crab
Conical Shells
Barnacle
Limpet
Crustaceans
Crab
Gastropod
Barnacle
Molted
exoskeleton
Segmentation
TRADITIONAL
CLASSIFICATION
CLADOGRAM
Limpet
Phylogeny Can Be Inferred
From Molecular Data
Modern Systematics is Shaking
Some Phylogenetic Trees
When Did Most Modern
Mammalian Orders Originate?
And now that we have finished…
RE-READ YOUR REMARKS AT
THE BEGINNING OF THE UNIT
ON EVERYTHING YOU
BELIEVE TO BE TRUE ABOUT
EVOLUTION……..
HAS YOUR PERSPECTIVE
CHANGED GIVEN THE
INFORMATION PRESENTED
TO YOU IN THIS UNIT?