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Evolutionary Patterns
Chapter 23
PHYLOGENY
Phylogeny: history of descent with
branching/modification and the
accumulation of change over time
Node: represents the common
ancestor from which the descendent
species divergent; can be rotated
without changing evolutionary
relationships
23.1 A phylogenetic tree is a reasoned hypothesis of the
evolutionary relationships of organisms.
PHYLOGENY OF VERTEBRATES
The order of branches indicates the sequence of events in time
SISTER GROUPS
Sister groups: 2 groups that share a common ancestor not shared by any other group
MONOPHYLETIC, PARAPHYLETIC, AND
POLYPHYLETIC GROUPS
Only monophyletic groups
reflect evolutionary relationships
Only they include all descendents
of a common ancestor
CLASSIFICATION
Taxonomic classification:
Domain (most general)
Kingdom
Phylum
Class
Order
Family
Genus
Species (most specific; called
binomial nomenclature)
3 Domains (Superkingdoms) of life: Eukarya, Bacteria, Archae
HOMOLOGOUS AND ANALOGOUS
FEATURES
Shared derived characters:
•Anatomical
•Physiological
•Molecular features
that are in common
Homologies: similarities based on
shared common ancestor
Analogies: similarities based on
independent adaptations
23.2 A phylogenetic tree is built on the basis of shared
derived characters.
HOMOLOGOUS VS ANALOGOUS
Homologies: similarities based on shared common ancestor
Analogies: similarities based on independent adaptations
QUICK CHECK
 Fish and dolphins have many traits in common,
including a stream-lined body and fins. Are these
traits homologous or analogous?
ANSWER
 The traits are analogous, the result of convergent evolution.
 Both animals are adapted for swimming in water and
converged independently of their traits.
 However, they are only distantly related, as one is a fish and
the other is a mammal.
SYNAPOMORPHIES
Synapomorphies: are shared
derived
characters
Useful in constructing phylogenetic
tree
because the homology is shared by
some,
but not all, of the members of the
group.
Cladistics: phylogenetic
reconstruction
based on synapomorphies
CONSTRUCTION OF A TREE
DETERMINING THE BEST FIT
USING MOLECULAR DATA TO BUILD
PHYLOGENETIC TREES
PRACTICAL USES OF PHYLOGENETIC
TREES
PALEONTOLOGY
23.3 The fossil record provides a direct glimpse of evolutionary
history
 Paleontology: The branch of biology that reconstructs
evolutionary history by collecting and evaluating fossils
 Fossils: preserved remains or impressions left by organisms
from the past
1. Allow us to calibrate phylogenies in terms of time
2. Provides a record of extinct species
3. Places evolutionary events in context with Earth’s history
FOSSILS
Fossils only preserve the mineral-rich hard parts of an organism
FORMATION OF THE FOSSIL RECORD
TRACE/MOLECULAR FOSSILS
1. Tracks and trails
2. Molecular fossils: DNA, proteins, lipids
BURGESS SHALE
Preserved the deep seafloor of 505 mya
MESSEL SHALE
GEOLOGIC TIMESCALE
Relative dating:
The order in which fossils appear
in strata (layers) of sedimentary
rock indicates relative age of
fossil
•Lower fossils: older
•Higher fossils: more recent
•Compare to index fossil…shells
of marine organisms
RADIOACTIVE DECAY
Absolute dating:
Uses radioactive isotopes to give the age of fossil,
with <10% error, in wood and bones
•Compare half-life of isotope in living organism to
ratio of same isotopes in fossil
•Half-life: number of years for half (50%) of the
original sample to decay
GEOLOGICAL TIME SCALE
 Grouped into 3 eons, 3 eras, then periods, then epochs
 The 1 st two eons (the oldest) lasted about 4 billion years and
is referred to as the Precambrian eon…….the age of ancient
life
 Origin of Earth: 4.6 bya
 First prokaryotic cell: 3.5 bya (fossils)
 Origin of eukaryotes: about 2 bya
PHANEROZOIC EON
 Phanerozoic eon: last 500 million years
 Most of the time that multicellular eukaryotes have existed
 Divided into 3 eras
 Paleozoic era: age of ancient eukaryotic life
 Cambrian period: 544-505 mya; Cambrian explosion= sudden increase
in diversity of many animal phyla
 Permian period: 286-245 mya; Permian extinction= mass extinction of
many marine and terrestrial organisms
 Mesozoic era: age of reptiles
 Jurassic period: dinosaurs abundant/diverse; NOTE: dinosaurs existed
for 200 million years!
 Cretaceous period: 144-65 mya; Cretaceous extinction= many groups of
organisms became extinct, including dinosaurs
PHANEROZOIC EON (CONTINUED)
 Cenozoic era: age of mammals (newest era)
 Paleocene epoch: 65-54 mya; mammals flourished
 Pliocene epoch: 5-1.8 mya; ape-like ancestors of humans appear;
Australopithicus africanus
 Pleistocene epoch: 1.8 million -10,000 years ago; Ice ages; humanlike hominids appear; Homo erectus. Homo Neanderthal
 Holocene epoch: 10,000 years to present age; age of Homo sapiens
BIOGEOGRAPHY
 Biogeography: Geographical distribution of species
 Continental drift: drifting of continents
 Results from movement of plates of crust/upper mantle that float on
Earth’s molten core
 Called “plate tectonics”
 Where 2 plates meet, many important geological phenomena occur;
i.e. earthquakes, volcanoes
PANGAEA
• Formation of Pangea……”all land”
• Occurred at end of Paleozoic era (250 mya)
• Supercontinent
• Had tremendous environmental impact…..possibly Permian extinction?
BREAKUP OF PANGEA
• Occurred during Mesozoic era
(180 mya)
• Pangea broke into northern
(Laurasia) and southern
(Gondwana) land masses
• About 65 mya S. America split
from Africa; India moved north;
Australia split from Antarctica;
Laurasia split into N. America and
Eurasia
• The final split occurred in the
Cenozoic era between North
America and Eurasia, which led to
present distribution of continents
DINOSAUR AND BIRD PHYLOGENY
Archeopteryx is a fossil organism that demonstrates the bird-dinosaur transition.
FISH TO TETRAPOD VERTEBRATES
Tiktaalik is a fossil organism
that demonstrates the
fish-tetrapod transition.
MASS EXTINCTIONS
 The history of life is characterized
by rare mass extinctions.
 There have been 5 major mass
extinctions over the past 500 my,
including:
Permian Extinction:
250 mya
Eliminated >90% marine life
Cretaceous Extinction:
65 mya
Dinosaurs became extinct
Impact Hypothesis: an asteroid or
comet struck Earth while extinction
was already in progess
PHYLOGENY AND FOSSILS TOGETHER
23.4 Phylogeny and fossils provide independent and
corroborating evidence of evolution.
EVIDENCE OF EVOLUTION
 Biogeography
 Geographic distribution of species
 First suggested common descent to Darwin
 Different geographic regions, different mammalian “brand
 Fossil Record
 Shows that prokaryotes are ancestors of ALL life
 Fish…amphibians….reptiles….birds…..mammals
 Have found transitional fossils linking past and present
 Comparative Anatomy
 Homologous structures….likeness due to common ancestry
 The higher the amount of homology, the more closely related the species
 i.e. forelimbs of mammals
 i.e. humans and chimps share 98% of same genome
EVIDENCE OF EVOLUTION (CONTINUED)
 Vestigial Structures: remnants of features that served
important functions in organism’s ancestors
 i.e. skeletons of some snakes show vestiges of pelvis/leg bones of
walking ancestors
 Comparative Embryology
 May see anatomical homologies nor visible in adult organisms
 i.e. ALL vertebrate embryos have a post-anal tail
 Molecular Data
 Shows similarity of DNA and proteins between closely related species
 i.e. all organisms use same genetic code