Transcript 33-1 Chordate Evolution

Biology
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33-1 Chordate Evolution
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33-1 Chordate Evolution
Chordate Origins
Chordate Origins
Much of what scientists know about the origins of
chordates comes from studying the embryos of
living organisms.
Studies suggest that ancient chordates were
closely related to echinoderms.
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33-1 Chordate Evolution
Chordate Origins
Fossils preserved in Canada's Burgess Shale include
a peculiar organism called Pikaia.
Notochord
Tentacle
Head
region
Paired muscle
blocks
Tail fin
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33-1 Chordate Evolution
Chordate Origins
Pikaia had a notochord—a long, supporting rod that
runs through a chordate’s body just below the nerve
cord. It also had paired serial muscles.
Because of these characteristics, scientists now
classify Pikaia as an early chordate.
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33-1 Chordate Evolution
Chordate Origins
Tunicates are the simplest living animals to have key
characteristics of chordates:
• a notochord
• a dorsal hollow nerve cord
• a tail that extends posterior to the anus
• pharyngeal pouches
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33-1 Chordate Evolution
The Chordate Family Tree
What are the roots of the chordate family
tree?
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33-1 Chordate Evolution
The Chordate Family Tree
The Chordate Family Tree
The chordate family tree has its roots in
ancestors that vertebrates share with
tunicates and lancelets.
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Nonvertebrate
chordates
Mammals
Birds
Lizards, snakes
Crocodilians
Turtles, tortoises
Caecilians
Frogs and toads
Salamanders
The Chordate Family Tree
Lungfishes
Coelacanth
Ray-finned fishes
Lamprey
Sharks and
their relatives
Hagfishes
Tunicates and
lancelets
33-1 Chordate Evolution
Endothermy
Jawless fishes
Amniotic egg
Cartilaginous fishes
Four limbs
Lungs
Bony fishes
Amphibians
Reptiles
Jaws and paired
appendages
Birds
Mammals
Vertebrae
Invertebrate ancestor
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33-1 Chordate Evolution
Evolutionary Trends in Vertebrates
Evolutionary Trends in Vertebrates
The hard body structures of many vertebrates
have left behind an excellent fossil record.
Scientists also infer evolutionary trends by
studying characteristics of living chordates.
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33-1 Chordate Evolution
Evolutionary Trends in Vertebrates
What is a main trend in the evolution of
chordates?
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33-1 Chordate Evolution
Evolutionary Trends in Vertebrates
Adaptive Radiations
Over the course of evolution, the
appearance of new adaptations—such as
jaws and paired appendages—has
launched adaptive radiations in chordate
groups.
Adaptive radiation is the rapid
diversification of species as they adapt to
new conditions.
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33-1 Chordate Evolution
Evolutionary Trends in Vertebrates
Convergent Evolution
Adaptive radiations can produce species that are
similar in appearance and behavior, but not closely
related.
This is called convergent evolution.
Convergent evolution has produced flying
vertebrates as different as birds and bats.
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33-1 Chordate Evolution
Chordate Diversity
Chordate Diversity
Living chordates are diverse:
• nonvertebrate chordates, which include
tunicates and lancelets
• vertebrates, which include fishes, amphibians,
reptiles, birds, and mammals
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33-1 Chordate Evolution
Chordate Diversity
Nonvertebrate chordates (4%)
Mammals (8%)
Fishes (49%)
Birds (17%)
Reptiles (13%)
Amphibians (9%)
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33-1 Chordate Evolution
Chordate Diversity
Tunicates and lancelets (2022)
Mammals (4500)
Hagfishes and lampreys (80)
Sharks and their
relatives (900)
Birds (9100)
Ray-finned
fishes (25,000)
Crocodilians
(22)
Lizards, snakes,
tuatara (6800)
Turtles and
tortoises (260)
Coelacanth and lungfishes (8)
Caecilians (165)
Salamanders (415)
Frogs and toads (4300)
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Species that are similar in appearance and
behavior but are not closely related are
sometimes the result of
a. convergent evolution.
b. adaptive diversity.
c. divergent evolution.
d. disruptive selection.
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The fossil Pikaia found in Cambrian rocks is
thought to be an ancestor of chordates because
it shows evidence of a notochord and
a. paired blocks of muscle.
b. vertebrae.
c. bilateral symmetry.
d. fins.
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In some chordates, pharyngeal pouches develop
into
a. paired skeletal muscles.
b. wings.
c. paired appendages.
d. gills.
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The largest group of chordates is the
a. mammals.
b. fishes.
c. birds.
d. reptiles.
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In the current understanding of the evolution of
the chordates, which of the following appeared
most recently?
a. jaws and paired appendages
b. lungs
c. endothermy
d. vertebrae
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