Transcript Evolution of the Animal Body Plan

Evolution of the Animal
Body Plan
Part 2 – Chordates and Vertebrates
E. Q. – How has the chordate body plan evolved
over time to better suit these animals to their
ecological niches?
Chordate Characteristics
• The members of Phylum
Chordata exhibit many
different kinds of body plans,
but they all have certain
characteristics in common.
• All chordates, at some time in
their lives, have:
(1)A dorsal hollow nerve cord
(2)Pharyngeal gill slits
(3)A stiff rod ventral to the nerve
cord called the notochord
(4)A muscular post-anal tail.
• Some chordates show these
characteristics for their entire
lives, while in other
chordates, they develop into
other structures.
• In vertebrates, the dorsal
hollow nerve cord develops
into the brain and spinal cord.
• In most vertebrates, the
notochord degenerates during
the embryonic stage of
development. The only
remnants appear in adults as
the gelatinous disks between
the vertebrae.
• The pharyngeal gill slits
develop into gills in aquatic
vertebrates, jaw support,
hearing elements, or other
functions in higher vertebrates.
• Most vertebrates retain the
muscular post anal tail as
adults.
The Simplest Chordates
• Tunicates are some of the
simplest chordates. They
belong to the subphylum
Urochordata.
• Most tunicates are sessile
marine filter feeders.
Because they squirt water
when disturbed, they are
often called sea squirts.
• Some others are zooplankton.
Some species are colonial.
• Adult sea squirts no not
resemble other chordates,
but as embryos, all chordate
characteristics are present.
• Lancelets belong to the
subphylum Cephalochordata.
They are shaped like the
blade of a spear, and all of
the chordate characteristics
appear in adults.
• Lancelets burrow into the
sand with their mouths
exposed. Water enters the
mouth and exits the gill slits,
while food is filtered out.
• Although they don’t swim
well, they show the side-toside swimming motion of
fishes.
Simple Chordates
Subphylum Vertebrata
• Vertebrates keep the primitive
chordate characteristics, but
they also have additional
characteristics that separate
them from the non-vertebrate
chordates.
• Many of these features are
associated with large body size
and active lifestyle.
• One vertebrate trait is an
enlarged brain enclosed within a
cranium and a concentration of
the sense organs in the head.
• Another characteristic of
vertebrates is the vertebrate
axial skeleton, the main support
of the central trunk of the body.
• The axial skeleton makes large
body size possible as well as fast
movements.
• Vertebrates have two pairs of
appendages (arms and legs).
• The vertebrate skeleton is made
of bone or cartilage, and is
capable of growing with the
animal.
• Vertebrates have a closed
circulatory system with a ventral,
chambered heart.
• Vertebrates have muscles in their
intestinal walls to propel food
through the digestive system.
• Vertebrates reproduce sexually.
Vertebrate Diversity
Agnatha
Chondrichthyes
Reptilia
Amphibia
Osteichthyes
Mammalia
Aves
Agnatha (Jawless Fishes)
• The oldest vertebrate fossils
are jawless creatures
resembling fish and are about
400-500 m.y.a.
• Superclass Agnatha includes
some extinct fishlike animals
called Ostracoderms. They
had circular or slit-like
mouths without jaws and
were probably mudsuckers or
suspension feeders.
• Lampreys and hagfish are the
only agnathans living today.
• Like extinct agnathans, they
lack paired appendages.
• Agnathans also lack scales.
• Lampreys feed on live fish by
attaching with their round
mouth and using their rasping
tongue to penetrate the skin
of their host. They then
ingest the host’s blood.
Lampreys are considered
both predators and parasites.
They can be freshwater or
marine.
• Hagfish look like lampreys,
but they are mainly
scavengers. Some hagfish
eat dead or dying fish, but
most eat marine worms.
Hagfish are entirely marine.
Fertilization is external.
Jawless Fishes
Chondrichthyes
• The origin of jaws was a major
event in vertebrate history.
Vertebrate jaws evolved from
changes in the skeletal supports
for the most anterior gill slits.
• During the Devonian Period (417354 m.y.a.), Chondrichthyes and
Osteichthyes both evolved. At
the end of the Devonian, the first
amphibians also appeared.
• Sharks, skates, and rays make up
Class Chondrichthyes.
• They are called cartilaginous fish
because their skeletons are
made of cartilage, rather than
bone. They have tooth-like
scales embedded in their skins.
• There are about 750 species in
this group. They all have jaws
and paired fins.
• Sharks have streamlined
bodies. Continual swimming
makes water pass though the
mouth and out the gills.
• Sharks have keen eyesight, an
excellent sense of smell, and a
lateral line system to sense
prey.
• In sharks and rays, fertilization
is internal. Males use claspers
to transfer sperm to the female.
• Sharks have the largest
brain/body size ratio of any fish.
Chondrichthyes
Osteichthyes
• A bony skeleton, an operculum,
and a swim bladder are all
characteristic of Class
Osteichthyes.
• There are more members of
Class Osteichthyes than of any
other class of vertebrates.
• They are abundant in the seas
and in almost all freshwater
habitats.
• Members of this class have a
skin covered with flattened bony
scales different from the toothlike scales of sharks or rays.
• Glands in the skin secrete
mucus that makes fish feel
“slimy” but protects from
parasites.
• Bony fish breathe by drawing
water in through the mouth,
over the gills, and out through
the operculum.
• The muscles attached to the
operculum allow the fish to
breathe while staying in one
place.
• Another adaptation is the
swim bladder, an air sac that
controls the buoyancy of the
fish.
• Bony fish are maneuverable
swimmers because their fins
are better for propulsion and
steering than those of sharks.
Osteichthyes
Amphibia
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According to current theories,
aquatic vertebrates moved onto the
land as shallow pools they live in
dried up.
These animals faced several critical
problems: (1) keep from drying out
(2) support the body on land (3)
reproduce on land.
The oldest known amphibian fossils
date from about 370 m.y.a.
Amphibians are thought to have
evolved from lobe-finned fish. The
earliest amphibians had four strong
limbs, which evolved from the fish’s
fins.
The earliest amphibians breathed
air through lungs and had sense
organs adapted to work on land.
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Modern amphibians have several
key characteristics:
Most change from an aquatic larval
state to a terrestrial adult.
Most have a moist thin skin without
scales used for gas exchange.
Feet, if present, are often webbed
and lack claws.
Fertilization is external. Eggs lack
shells. They are laid in water or
moist places.
Amphibian hearts have 3
chambers:2 atria and 1 ventricle.
Modern amphibians include Order
Anura (frogs and toads), Order
Urodela (newts and salamanders),
and Order Apoda (caecilians,
legless amphibians that resemble
snakes).
Amphibia
Reptilia
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Earliest reptile fossils date to the
Carboniferous Period, about 350
m.y.a.
They diversified rapidly and by the
Permian Period had become the
dominant land vertebrates.
The Mesozoic Era (286-245 m.y.a) is
called the “Age of Reptiles”
because nearly all of the large
vertebrates on Earth were reptiles.
During the Mesozoic, dinosaurs
appeared and evolved to fill many
niches in a variety of environments.
Representatives of the 4 modern
orders of reptiles survived the
mass extinction at the end of the
Cretaceous Period: (1)turtles and
tortoises, (2)lizards and snakes, (3)
tuataras, and (4) crocodilians.
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The success of reptiles on land
resulted from their ability to solve
the major problems facing land
animals: preventing desiccation,
locomotion, respiration and
excretion of N wastes, and
reproduction on land.
A thick skin covered by keratincontaining scales prevents water
loss.
Sturdy limbs with clawed feet
support and propel the reptile body.
Efficient lungs perform gas
exchange, while water is conserved
because most reptiles excrete uric
acid.
Internal fertilization and the
amniotic egg keep the embryo from
drying out as it develops in a selfcontained watery environment.
Reptile Characteristics
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Like all terrestrial vertebrates
(amphibians, reptiles, birds, and
mammals) reptiles have a double
loop circulatory system.
The pulmonary loop takes blood
from the heart to the lungs to be
oxygenated, and the systemic loop
takes blood from the heart to the
tissues of the body where O2 is
absorbed and CO2 is released.
In all reptiles except crocodilians,
the heart has 2 atria and 1 partly
divided ventricle. Crocodiles have 2
atria and 2 ventricles.
Reptile lungs are large with many
small sacs called alveoli that make
them much more efficient than
amphibian lungs.
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The reptile brain is about the
same size as an amphibian brain,
but the cerebrum, which controls
behavior, is much larger.
Most reptiles rely on their senses
of sight and hearing to detect
prey and predators.
Reptiles are ectotherms, and
control their internal body
temperature by changing
behavior to control how much
heat they absorb.
Reptiles have three reproductive
patterns: They may be oviparous
(lay eggs), viviparous (embryo is
incubated within the mother), or
ovoviviparous (produce shelled
eggs that incubate within the
mother’s body).
Reptilia
Aves
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All birds have feathers, and no
other living animals have them.
The forelimbs of birds are
modified into wings.
All birds have a lightweight, rigid
skeleton with a keel on the
sternum. Many bones are thinwalled, hollow, and riddled with
air sacs from the respiratory
system.
All birds are endotherms with a
high metabolic rate and a 4chambered heart..
All birds have the most efficient
respiratory system yet evolved,
that eliminates dead space from
the lungs.
No bird has teeth, and all birds
have a beak.
All birds lay amniotic eggs with a
hard calcium-rich shell.
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Because birds lack teeth, they
have a crop for food storage, a
proventriculus where digestion
begins, and a gizzard for grinding
of food.
Birds are thought to have evolved
from raptor dinosaurs because
of three characteristics which
both groups share: an S-shaped
flexible neck, a unique ankle
joint, and hollow bones.
The first birds are thought to
have descended from small fastrunning carnivorous dinosaurs
during the Jurassic Period (208144 m.y.a.)
Current theories are that
feathers evolved before wings
(for insulation), and wings before
flight (for stabilization while
running).
Aves
Mammalia
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There are about 4,400 species of •
mammals, and they live on every
continent and in every ocean.
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Some can fly.
Like birds, all mammals are
endotherms, with metabolic
control of body temperature.
All mammals (even whales and
dolphins) have hair, which can
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serve as an insulator or for
camouflage.
Like birds and crocodilians, all
mammals have a 4-chambered
heart.
All female mammals produce milk
to nourish their young.
All mammals have a single
jawbone with teeth specialized to
perform different functions.
The ancestors of mammals appeared
more than 300 m.y.a.
A major split occurred in the existing
reptiles of the time. One group
produced the dinosaurs, birds, and all
living reptiles. The other group, called
synapsids, led to mammals and their
closest fossil relatives.
Synapsids like Dimetrodon had skulls
that were different from pther reptiles
and showed some specialized teeth.
Mammals
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In the Permian Period, a sub-group
of the synapsids, the therapsids,
appeared and later gave rise to the
earliest mammals.
Many features of mammals first
appeared in the therapsids—
specialized teeth, endothermy,
limbs located beneath the body, and
hair are examples.
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The first mammals and the first
dinosaurs appeared at about the
same time, during the Triassic
Period. Early mammals were small
and resembled shrews. With the
extinction of the dinosaurs 65 m.y.a.
the mammals diversified to fill newly
available niches.
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Mammals are classified into more
than 20 orders. Important orders of
mammals are the monotremes and
the marsupials. All other mammals
are placentals.
Monotremes are the only mammals
that lay eggs. They are represented
by the duck-billed platypus and the
echidna, or spiny anteater.
Marsupials like kangaroos and the
opossum exist today only in
Australia, New Guinea, and the
Americas. Marsupials give live birth
to very underdeveloped young that
migrate to the mother’s pouch
where they complete development.
Placentals include rodents,
insectivores, primates, carnivores,
proboscideans, and cetaceans,
among other groups.
Mammalia
E. Q. – How has the chordate body plan evolved over time
to better suit these animals to their ecological niches?
How have the following systems changed from
Urochordates and Cephalochordates through the
fishes, amphibians, reptiles, mammals, and birds?
 Nervous system
 Digestive system
 Reproductive system
 Circulatory system
 Respiratory system
 Skeletal system