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THE CHORDATES
(30-1)
What is chordate?
A chordate (Phylum Chordata) is an animal that has four
things at some point during its life cycle:
1) A dorsal, hollow nerve chord
2) A notochord
3) Pharyngeal pouches
4) A tail that extends beyond the anus
*** the animal may not keep these for their entire life
Hollow Nerve Chord
Runs along the dorsal part of the body, has branches at
regular intervals that connect to internal organs,
muscles, and sense organs.
Notochord
Notochord- a long supporting rod that runs through the
body just below the nerve chord.
Most chordates have a notochord only when they are
embryos.
Pharyngeal Pouches
Pharyngeal pouches- paired structures in the throat region:
Fishes and Amphibians- develop into gills for gas
exchange.
Other Chordates- only present when they are
embryos
Tail
At some point in their lives, most chordates have a tail that
extends beyond the anus.
hollow nerve chord
notochord
mouth
tail
anus
pharyngeal pouches
Most Chordates are Vertebrates
• 96% of all chordates are placed in the
subphylum Vertebrata.
• Vertebrates have a strong support column or
backbone that originates from the notochord.
• The backbone is made up of individual
segments called vertebrae that enclose and
protect the spinal chord.
• In vertebrates, the dorsal hollow chord is
called a spinal cord.
• The anterior end of the spinal cord develops
into the brain in vertebrates.
Compare and Contrast: Endoskeleton (Vertebrates)
vs. Exoskeleton (Arthropods)
Made of
living cells
internal
Grows as
the animal
grows
Gives
muscles a
place to
attach
supports
protects
Made of
non-living
material
external
sheds
periodically
Vertebrate Phylogeny
•
Look at Figure 30-2 on page 768
1) What does this diagram demonstrate?
Evolution of major features
2) Where would you place the derived character
“vertebrae” on the main branch?
between the nonvertebrate chordates and jawless fish
3) What does this say about the relationship between
reptiles and birds?
they are most closely related to each other
4) What derived character would you put on the branch to
birds only?
feathers
5) What derived characters do all animals have in common
on this cladogram?
Hollow dorsal chord, notochord, pharyngeal pouches, tail
There are two groups of Non-Vertebrate Chordates:
(the other 4%)
•
•
•
•
Tunicates
Filter feeders
Larva and Adult are
quite different in
form
Larva has all four
chordate
characteristics
Adult is sessile
•
•
•
•
•
•
•
Lancelets
No fins or legs
Live in sand
Cephalization
Pharynx- for feeding
and gas exchange
Gills are part of
pharynx
CCS- no true heart
Paired muscles
Common Ancestor Evidence:
Fossils from Cambrian Period, Embryological Development
CHORDATE EVOLUTION
(33-1)
Chordate Orgins
How do scientists study the origins of chordates?
• Studying the embryos of living organisms
• Indications that the most ancient chordates are most
closely related to echinoderms.
• Pikaia- an early chordate discovered by scientists in
the Burgess Shale (Canadian Place with many
Cambrian fossils).
• Scientists also study a nonvertebrate chordate alive
today: the tunicate.
• Today, biologists study the genes that control the four
traits of a chordate:
Can you name all four?
Chordate Family Tree
•
Look at Figure 33-2 on page 850
1) What does this diagram demonstrate?
Evolution of major features
2) What do the colored branches represent?
The traditional groupings of these animals
3) Which group is considered the “out group”- meaning the
one that is outside of the first adaptation?
Tunicates and lancelets
4) What animals have amniotic eggs?
reptiles, birds, and mammals
5) What derived characters separates lampreys from
sharks?
jaws and paired appendages
6) What is believed to be the common ancestor of all these
chordates? invertebrates
Evolutionary Trends in Vertebrates
Adaptive Radiation- the rapid diversification of species as
they adapt to new conditions. (notable derived characters)
Over the course of evolution, the appearance of new
adaptations like jaws and paired appendages has
launched adaptive radiations in chordate groups.
Convergent Evolution- adaptive radiations that produce
species that are similar in appearance and behavior even
though they are not closely related.
How does this happen?
Animals in similar ecological conditions evolved similar adaptations.
Example- convergent evolution produced flying vertebrates as
different as birds and bats.
Chordate Diversity
• 96% are vertebrates that make up 50,000 species
throughout the world.
• The six living groups are: nonvertebrate chordates,
fishes, amphibians, reptiles, birds, and mammals.
Chordate Diversity
Nonvertebrate
Chordates
Jawless Fishes
Sharks and Relatives
Fishes
Amphibians
Reptiles
CONTROLLING BODY TEMPERATURE
(33-2)
Body Temperature and Homeostasis
Why is it important for animals to body temperature to
maintain a certain range? (think of chapter 2)
metabolic processes/chemical reactions only take
place within a certain “operating range.”
The control of body temperature is important for
maintaining homeostasis in vertebrates, particularly in
habitats where the temperature varies with time of day
and season.
All methods of controlling body temperature incorporate
three important features:
1) A source of heat
2) A way to conserve heat
3) A method of eliminating excess heat
Generating and Controlling Body Heat:
Animals are classified in two main groups:
1) Ectotherms
2) Endotherms
Ectotherms
Ectotherm- body temperature is mainly determined by the
environment.
• Most reptiles, fishes, and amphibians are ectothermsthey pick up heat from their environment and lose heat
to their environment.
• Most bask in the sun for heat, and burrow unground to
cool down.
• Ectotherms have low metabolisms when resting, thus
generating little heat.
• When active, the heat that is generated is lost to the
environment due to the lack of insulation.
Endotherms
Endotherm- body temperature is controlled from within.
Birds and mammals are endotherms- they can generate and
retain heat inside their bodies.
Endotherms have high metabolisms even when resting, thus
generating a significant amount of heat.
• Birds retain heat primarily through their feathers serving
as insulation.
• Mammals have body fat and
hair for insulation.
• Mammals also get rid of
excess heat through
sweating and panting.
Endothermy
Ectothermy
Pro- move around easily
during cool nights because
they generate and retain
their own heat
Pro- Need much less food to
keep metabolic rate where
it needs to be.
Con- Requires a lot of fuel
to keep up that metabolic
rate.
In environments where
temperature is steady,
ectothermy is more effcient.
Con- But in enviroments
where there are swings in
temperature, it takes a long
time to warm up or cool
down.
Evolution of Temperature Control
There is little doubt that the first land vertebrates were
ectotherms.
But there is doubt as to when endothermy developed.
Theory #1- Some dinosaurs were endotherms
Theory #2- Endothermy evolved long after the dinosaurs
Theory #3- Endothermy evolved more than once:
Line 1- Reptiles to Birds
Line 2- Reptiles to Mammals
FORM AND FUNCTION IN CHORDATES
(33-3)
Nonvertebrate chordates represent very simple body
systems, but that does not mean they are inferior.
Lancelets and Tunicates are simple, but have survived to
present day to perform the essential functions of life.
Vertebrates exhibit a wide range of organs and organ
systems that are specialized to perform many functions and
maintain homeostasis.
Feeding
Feeding and digestion help maintain homeostasis by
providing the body with a continuous supply of nutrients.
Depending on the needs of the animal, and the environment
they live in, there are many different adaptations for feeding.
Example of Adaptations for Feeding:
• Teeth adapted to strain food from water (filter feeders)
or to eat meat (carnivores)
• The digestive systems of vertebrates have organs that
are well adapted for different feeding habits:
- Carnivores: short digestive tracts with enzymes
- Herbivores: long digestive tracts with bacteria
Respiration
As a general rule, aquatic chordates use gills for
respiration. Land vertebrates use lungs.
However, there are many exceptions to this rule: several
fishes have both lungs and gills.
Additional Respiratory Structures that aid in respiration:
• Nostrils, mouth, throat
• Trachea
• Air sac
• Operculum
How do gills work?
Water passes over gill filaments, oxygen molecules diffuse
into blood through capillaries. At the same time carbon
dioxide diffuses from the blood to the water. Water and
carbon dioxide are pumped out of fish through the
operculum (gill slits).
How do lungs work?
Oxygen rich air is inhaled into the trachea then to lungs,
oxygen diffuses into blood through capillaries, carbon
dioxide diffuses out, oxygen-poor air is exhaled.
From amphibians to reptiles to birds to mammals- the
surface area of lungs increases (birds are slightly different
in form).
• Amphibians- a little sac with ridges for more surface
area.
• Reptiles- lungs divided into chambers for more surface
area.
• Mammals- lungs branch extensively, filled with aveolibubble-like structures that provide surface area in lungs.
Air must travel two-ways (in and out in same passages)
•
Birds- one-way system of tubes and air sacs that allow
birds to fly at high altitudes where there is less oxygen.
Circulation
Circulatory systems maintain homeostasis by transporting
needed materials throughout the body.
Single Loop vs. Double Loop Circulation
Single Loop is for animals that use gills for respiration:
Blood travels from heart- to gills- to the rest of the
body- back to the heart in one circuit.
Question:
Why do you think the blood goes to
the gills first, then the rest of the
body?
Answer:
Because oxygen is picked up from
the water and then it is carried to
the rest of the body.
Double Loop is for animals that use lungs for respiration:
Loop #1: Carries blood between heart and lungs
-Oxygen-poor blood goes to the lungs
- Oxygen-rich blood goes back to heart
Loop #2: Carries blood between the heart and the body.
- Oxygen-rich blood goes to body
- Oxygen- poor blood goes back to heart
Question:
How does blood become
“oxygen-poor?”
Answer:
Oxygen diffuses from the blood
vessels out to body tissues and
organs to be used for cellular
processes.
Heart Chambers
During the course of chordate evolution, the heart
developed chambers and partitions that help separate
oxygen-rich blood from oxygen-poor blood.
Fishes and Larval Amphibians: 2-chambered heart
Atrium: receives blood from the body
Ventricle: pumps blood to the gills and then the rest
of the body.
Adult Amphibians: 3-chambered heart
Left Atrium : receives oxygen-rich blood from lungs
Right Atrium: Receives oxygen-poor blood from the body
*Both Atria: Empty into the ventricle
Ventricle: There is a “flow” that dictates that oxygen-rich
goes to the body and oxygen-poor goes to the
lungs, but there is some mixing.
Reptiles: 3-chambered heart
*Same as Adult Amphibians except:
Ventricle: There are partial partitions to
allow for less mixing of oxygen-poor and
oxygen-rich blood
Crocodilians, Birds, Mammals: 4-chambered
heart
Left and Right Atria- same as 3-chambered
Left and Right Ventricles- completely
partitioned so there is no mixing of oxygenpoor and oxygen-rich blood.
On the pictures below, first write the type of heart demonstrated on
the line, then, outline the oxygen-poor blood in blue and the oxygenrich blood in red. (see pg. 860 for help)
___________
____________
___________ ___________
Excretion
Excretory Systems help maintain homeostasis by
eliminating nitrogenous wastes from the body.
Nitrogenous wastes are produced from the breakdown
of proteins and are first in the form of ammonia- toxic
until converted or released from body.
Nonvertebrate chordates use gills and gill slits to rid
themselves of nitrogenous wastes.
Most vertebrates use kidneys- system of tubes that
filter blood and remove wastes.
Response
• Compared to invertebrates, most chordates have
elaborate systems that allow them to respond to
stimuli in their environment.
• Nonvertebrate chordates have a relatively simple
nervous system with a mass of nerve cells that form
a brain.
• Vertebrates have a more complex brain with distinct
regions that specialize in function.
• Vertebrate brain regions:
1) olfactory bulb
4) cerebellum
2) cerebrum
5) medulla oblongata
3) optic lobe
Structure
Function
Olfactory bulb
Sense of smell
Cerebrum
“thinking” region of brain, receives, interprets, and determines
the response of sensory information, learning, memory,
conscious thought.
Optic lobe
Vision
Cerebellum
Coordinates movement, controls balance
Medulla Oblongata
Functioning of many internal organs
Movement
• Nonvertebrate chordates: no bones, but they do have
muscles.
• Vertebrates: the skeletal and muscular systems support
a vertebrate’s body and make it possible to control
movement.
• Skeletons can be bone or in the case of sharks and their
relatives: cartilage.
• Most vertebrates have ligaments that connect the bones
and allow for flexibility without breaking.
• Most vertebrates have girdles that support fins or limbs.
• Fishes and Snakes: main muscles in blocks on either
side of the backbone and contract in waves.
• Amphibians and Reptiles: Limbs stick out sideways
• Mammals:walk on 2 or 4 legs to support body weight
Reproduction
• Almost all chordates reproduce sexually.
• In general, evolution shows a trend from external to
internal fertilization.
• After fertilization the development of chordates can be:
1) oviparous- eggs develop outside the mother’s body;
nutrition for embryo from yolk.
ex: fish, amphibians, birds
2) ovoviviparous- eggs develop inside of mother,
embryo gets nutrition from yolk in the egg.
ex: sharks
3) viviparous- development inside of mother’s body,
embryo gets nutrition directly from mother.
ex: mammals
• Some vertebrates care very little for their young (many young)
• Some vertebrates show a lot of care for their young (few young)