Transcript 24.2 What Are the Major Groups of Vertebrates?

Chapter 24
Animal Diversity II:
Vertebrates
Lecture Outlines by Gregory Ahearn,
University of North Florida
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Chapter 24 At a Glance
 24.1 What Are the Key Features of Chordates?
 24.2 Which Clades Make Up the Chordates?
 24.3 What Are the Major Groups of Vertebrates?
Biology: Life on Earth, 9e
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24.1 What Are the Key Features of Chordates?
 All chordates have four distinctive structures
– A notochord: a stiff flexible rod extending the
length of the body
– A dorsal, hollow nerve cord: lies above the
digestive tract and expands anteriorly to form the
brain
– Pharyngeal gill slits: located in the pharynx that
may form respiratory organs or may appear as
grooves
– A post-anal tail: the chordate tail extends past
the anus
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Biology: Life on Earth, 9e
Dorsal nerve cord, notochord,
pharyngeal gill slits, post-anal tail
Mammalia
(mammals)
Amphibia
(frogs,
salamanders)
Reptilia
(turtles, snakes
crocodiles,
birds)
Dipnoi
(lungfishes)
Actinistia
(coelacanths)
Actinopterygii
(ray-finned fish)
Chondrichthyes
(sharks, rays)
Petromyzontiformes
(lampreys)
Myxini
(hagfishes)
Cephalochordata
(lancelets)
Urochordata
(tunicates)
An Evolutionary Tree of the Chordates
Craniates
Vertebrates
Tetrapods
Hair, milk
Amniotic egg
Limbs
Lobed fins
Lungs
Jaws
Vertebral column
Skull
Fig. 24-1
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24.1 What Are the Key Features of Chordates?
 Humans are members of the phylum Chordata
– In humans, the chordate features are best seen
during embryonic development, but later, we lose
our notochord, gill slits, and tails
– Only the dorsal nerve cord is retained in post
embryonic human development
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Chordate Features in the Human
eye
heart
liver
tail
limb bud
(future leg)
gill slit
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limb bud (future arm)
Fig. 24-2
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24.2 Which Clades Make Up the Chordates?
 The chordates include three clades
– The lancelets
– The tunicates
– The craniates
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24.2 Which Clades Make Up the Chordates?
 Lancelets are marine filter-feeders
– Lancelets are small, fishlike, invertebrate
chordates that retain all the four chordate
features as adults
– Lancelets live half-buried in the sand, with only
the anterior end of their bodies exposed
– Food particles are drawn into the mouth by
pharyngeal cilia and are then transported to the
digestive tract
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Author Animation: The Phylum Chordata
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Invertebrate Chordates
nerve cord notochord
gut
muscle segments
tail
mouth
gill slits
(a) Lancelet
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anus
Fig. 24-3a
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24.2 Which Clades Make Up the Chordates?
 Tunicates include sea squirts and salps
– Tunicates (sea squirts) live in a marine
environment
–The larvae are motile and exhibit all key
chordate features
–Adults are sessile filter-feeders that have lost
their tail and notochord
–Barrel-shaped tunicates, known as salps, live
in the open ocean and move by contracting an
encircling band of muscle that propels the
organism forward
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Author Animation: Lancelets and Tunicates
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Invertebrate Chordates
incurrent siphon excurrent siphon
(water enters)
(water exits)
mouth
atrial
opening
tail
anus
nerve
attachment gill gut
cord
points
slits
notochord
larva
(b) Tunicate
gill slits
heart
gut
gonad
adult
Fig. 24-3b
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24.2 Which Clades Make Up the Chordates?
 Craniates have a skull
– The craniates include all chordates that have a
skull that encloses a brain
– This group includes the hagfish and the
vertebrates—animals in which the embryonic
notochord is replaced during development by a
backbone, or vertebral column, composed of
bone or cartilage (which resembles bone, but is
more flexible)
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24.2 Which Clades Make Up the Chordates?
 Hagfishes are slimy residents of the ocean floor
– They lack jaws
– They are exclusively marine, and live near the
ocean floor
– They feed primarily on worms
– They secrete massive quantities of slime as a
defense against predators
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24.2 Which Clades Make Up the Chordates?
 Hagfishes are slimy residents of the ocean floor
(continued)
– They respire using gills, have a two-chambered
heart, and are ectothermic (they rely on heat
from the outside environment to regulate body
temperature)
– They lack a true backbone, and thus are not a
true vertebrate but have a rudimentary braincase
– They represent the chordate group that is most
closely related to the vertebrates
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Hagfishes
Fig. 24-4
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24.2 Which Clades Make Up the Chordates?
 Several adaptations have allowed vertebrates to
successfully invade most habitats
– The presence of an internal skeleton that can grow and
repair itself allowed for greater size and mobility, enabling
these animals to invade most habitats
– Jaws evolved to allow these animals to exploit a much
wider range of food sources than jawless animals that
preceded them
– The development of paired appendages (fins, legs, wings)
helped to stabilize movement
– The increased size and complexity of the brain and sensory
structures allowed these animals to perceive their
environment in detail and to respond in a variety of ways
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24.2 What Are the Major Groups of Vertebrates?
 Today, vertebrates include the following groups:
– Lampreys
– Cartilaginous fishes
– Ray-finned fishes
– Coelacanths
– Lungfishes
– Amphibians
– Reptiles
– Mammals
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24.2 What Are the Major Groups of Vertebrates?
 Some lampreys parasitize fish
– Like hagfishes, lampreys are jawless
– They have a large rounded sucker that
surrounds the mouth
– Their spinal cord is protected by cartilaginous
segments
– They live in both fresh and salt waters
–Marine forms must return to fresh water to
spawn
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24.2 What Are the Major Groups of Vertebrates?
 Some lampreys parasitize fish (continued)
– Some lamprey species are parasitic
–A lamprey will attach to a host with its
suckerlike mouth
–It has rasping teeth on its tongue, which are
used to excavate a hole in the hosts body wall
through which the lamprey sucks blood and
body fluids
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Lampreys
Fig. 24-5
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24.2 What Are the Major Groups of Vertebrates?
 Cartilaginous fishes are marine predators
– They are of the class Chondrichthyes, and
include sharks, skates, and rays
– Most are marine
– They possess jaws and a cartilaginous skeleton
– Their body is protected by a leathery skin
embedded with tiny scales
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24.2 What Are the Major Groups of Vertebrates?
 Cartilaginous fishes are marine predators
(continued)
– They respire using gills
– They possess a two-chambered heart
– They have internal fertilization, in which the male
deposits sperm directly into a female’s
reproductive tract
– They tend to sink when they stop swimming
because they lack a swim bladder
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24.2 What Are the Major Groups of Vertebrates?
 Cartilaginous fishes are marine predators (continued)
– While some sharks feed by filtering plankton from the
water, most are predators of larger prey such as fishes,
marine mammals, sea turtles, crabs, or squid
– Many have several rows of razor-sharp teeth
– The back rows move forward as the front teeth are
lost
– Most sharks avoid humans, but some can be dangerous;
in 2008, there were 59 documented attacks in the world,
four of them fatal
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24.2 What Are the Major Groups of Vertebrates?
 Cartilaginous fishes are marine predators
(continued)
– Skates and rays are mostly bottom dwellers with
flattened bodies, wing-shaped fins, and thin tails
– Some have a spine near the base of the tail that
is capable of inflicting dangerous wounds
– Others produce an electrical shock that can stun
prey
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Cartilaginous Fishes
Fig. 24-6
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24.2 What Are the Major Groups of Vertebrates?
 Ray-finned fishes are the most diverse
vertebrates
– Bony fish are found in nearly every watery
habitat, both freshwater and marine
– This group includes:
–Ray-finned fishes, such as the angler fish, the
moray eel, and the sea horse
–Lobe-finned fishes, which include the lungfish
and the coelacanth
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24.2 What Are the Major Groups of Vertebrates?
 The ray-finned fishes are the most diverse and
abundant group of vertebrates
– They are distinguished by the structure of their
fins, which are formed by webs of skin supported
by bony spines
– They have a bony skeleton
– Their skin is covered with interlocking scales
– They have a two-chambered heart
– Their gills are for respiration
– Most have a swim bladder that allows them to
float effortlessly at any level in the water
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24.2 What Are the Major Groups of Vertebrates?
 The ray-finned fishes are the most diverse and
abundant group of vertebrates (continued)
– They are an important human food source
–Populations of almost all economically
important ray-finned fish species have
declined drastically due to increased efficiency
in their capture by humans
–Large predatory fish such as the tuna have
been reduced to 10% of their original
population sizes due to overfishing
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The Diversity of Ray-Finned Fishes
Fig. 24-7
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24.2 What Are the Major Groups of Vertebrates?
 Coelacanths and lungfishes have lobed fins
– Both coelacanths and lungfishes have fleshy fins that
contain rod-shaped bones surrounded by a thick layer of
muscle
– This shared trait is indicative of the groups shared
ancestry, although the lineages have been evolving
separately for hundreds of millions of years
– Some of these modified fleshy fins could be used to drag
the fish from a drying puddle to a deeper pool
– This gave rise to the first vertebrates to invade land—
the amphibians
– Some of the lineages of lobefins left descendents that
survive today and are the tetrapods (amphibians,
reptiles, and mammals)
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24.2 What Are the Major Groups of Vertebrates?
 Lungfish are found in freshwater habitats
– They tend to live in stagnant waters low in
oxygen
– They have both gills and lungs
– Lungs allow them to supplement their supply of
oxygen by breathing air directly
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24.2 What Are the Major Groups of Vertebrates?
 Lungfish are found in freshwater habitats
(continued)
– Some species of lungfish can survive even if the
water dries up
–They burrow into the mud
–They seal themselves in a mucus-lined
chamber and breathe through lungs as their
metabolic rate slows
–They resume their underwater way of life
when the rains return and the pool refills
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Lungfishes are Lobe-Finned Fish
Fig. 24-8
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24.2 What Are the Major Groups of Vertebrates?
 Amphibians live a double life
– This group includes frogs, toads, salamanders,
and caecilians
– The double life of amphibians
–Amphibians begin life adapted to an aquatic
environment (e.g., tadpoles have gills)
–They later mature into semi-terrestrial adults
with lungs
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24.2 What Are the Major Groups of Vertebrates?
 Amphibians
– Amphibians have a three-chambered heart
– Most adults respire through lungs and moist skin
– Most have four limbs
– They reproduce sexually using external
fertilization
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24.2 What Are the Major Groups of Vertebrates?
 Most amphibians are confined to moist habitats
– Their skin must be kept moist to avoid
desiccation when out of water
– Their breeding behavior and use of external
fertilization requires water
–The male sperm swim to the female eggs
–The eggs, protected only by a jelly-like
coating, are vulnerable to water loss
–The larvae, such as the tadpoles of some
frogs and toads, develop in water
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24.2 What Are the Major Groups of Vertebrates?
 Amphibians are represented by the frogs, toads,
salamanders, and caecilians
– Frogs and toads undergo a metamorphosis during their
life cycle, starting out as aquatic tadpoles and developing
into terrestrial hopping adults
– Salamanders have lizard-like bodies with four legs and a
long tail
– They begin life as aquatic larvae with gills that are
retained in adulthood by some species, while others
metamorphose into terrestrial adults
– Caecilians are limbless burrowing amphibians that
resemble an earthworm and can be up to 5 feet long;
they have small eyes and limited vision
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Amphibian Means Double Life
Fig. 24-9
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24.2 What Are the Major Groups of Vertebrates?
 Reptiles belong to the class Reptilia and are
adapted for life on land
– These animals evolved from an amphibian
ancestor about 250 million years ago
–Reptiles include lizards, snakes, alligators,
crocodiles, turtles, and birds
–They respire exclusively through lungs
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The Diversity of Reptiles
Fig. 24-10
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24.2 What Are the Major Groups of Vertebrates?
 Reptiles are adapted for life on land (continued)
– There are three notable adaptations that allowed
the reptiles freedom from their aquatic origins
–They have tough scaly skin that protects the
body and resists water loss
–They have internal fertilization, where the
male deposits sperm in the female’s body
–They have evolved a shelled amniotic egg,
which encapsulates the embryo in a liquidfilled membrane, the amnion, which prevents
the embryo from drying out on land
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24.2 What Are the Major Groups of Vertebrates?
 Reptiles are adapted for life on land (continued)
– All reptiles have modified three- or fourchambered hearts, which separate oxygenated
and deoxygenated blood more effectively than
do amphibian hearts
– All reptiles have more efficient lungs than do
amphibians and do not use their skin as a
respiratory organ
– The reptile skeleton provides better support and
more efficient movement on land than do those
of amphibians
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The Amniotic Egg
Fig. 24-11
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24.2 What Are the Major Groups of Vertebrates?
 Reptiles are represented by lizards, snakes,
alligators, crocodiles, turtles, and birds
– Lizards and snakes form a common lineage
whose ancestors had limbs and whose
representatives are mostly predators
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24.2 What Are the Major Groups of Vertebrates?
 Snakes have a number of adaptations that help
them acquire food
– Many snakes have special sense organs that
help track prey by sensing body temperature
– Some snakes immobilize prey with venom that is
delivered through hollow teeth
– Snakes have a distinctive jaw joint that allows
the jaws to distend so that the snake can
swallow prey much larger than its head
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24.2 What Are the Major Groups of Vertebrates?
 Crocodilians include the alligators and crocodiles and
are found in the warmer waters of Earth
– Crocodilians have nostrils located high on their heads so
that they are able to remain submerged for long periods
with only the uppermost portion of the head above the
water surface
– They have strong jaws and conical teeth to crush and kill
the fish, birds, mammals, turtles, and amphibians that
they eat
– Parental care is extensive in crocodilians; they bury their
eggs in mud nests and, later, the parents guard the
hatched young, moving them safely to water in their
mouths
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24.2 What Are the Major Groups of Vertebrates?
 Turtles occupy a variety of habitats, including deserts,
streams, ponds, and the ocean
– All turtles are protected by a boxlike shell that is fused to
the vertebrae, ribs, and collarbone
– Turtles have no teeth, but have a horny beak instead,
which is used to eat a variety of foods, including both
plant and animal matter
– The largest turtle is the leatherback, which lives in the
ocean and can grow to 6 feet in length and feeds largely
on jellyfish
– Turtles can migrate long distances to reach beaches
where they bury their eggs
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24.2 What Are the Major Groups of Vertebrates?
 Birds are a distinctive group of reptiles
– They appear in the fossil record 150 million
years ago
– They are distinguished from other reptiles by
feathers, which are highly specialized reptilian
body scales
 Modern birds retain scales on their legs, which
is evidence of the ancestry they share with the
rest of the reptiles
– The earliest known bird is called Archaeopteryx
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The Diversity of Birds
Fig. 24-12
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Archeopteryx, the Earliest-Known Bird
Fig. 24-13
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24.2 What Are the Major Groups of Vertebrates?
 Birds are a distinctive group of reptiles adapted for
flight
– Feathers provide lift and control as well as insulation
– Hollow bones reduce the weight of the skeleton
– Bird reproductive organs shrink considerably during nonbreeding periods
– Females have a single ovary, further minimizing their
weight to aid flight
– The nervous system provides extraordinary coordination
and balance for flight, combined with acute eyesight
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24.2 What Are the Major Groups of Vertebrates?
 Birds maintain a constant body temperature
– They are warm-blooded (endothermic)
– Birds have a high metabolic rate, which increases the
demand for energy and requires efficient oxygenation of
tissues
– Therefore, birds must eat frequently, and have
adaptations in their circulatory and respiratory systems to
meet the need for efficiency
– Their heart has four chambers, which prevents the
mixing of oxygenated and deoxygenated blood
– Their respiratory system has air sacs that provide a
continuous supply of oxygenated air to the lungs, even
as the bird exhales
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24.2 What Are the Major Groups of Vertebrates?
 Mammals are in the class Mammalia, and
provide milk to their offspring
– Mammals appeared in the fossil record about
250 million years ago
– They did not diversify and dominate terrestrial
habitats until the dinosaurs became extinct (65
million years ago)
– Mammals are named for milk-producing
mammary glands that females use to nourish
their young
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24.2 What Are the Major Groups of Vertebrates?
 Mammals provide milk to their offspring
– Mammals are warm-blooded with high metabolic
rates
– They have a four-chambered heart
– Most have hair that protects and insulates
– Most have legs designed for running rather than
crawling
– They have sweat, scent, and sebaceous (oilproducing) glands, which are not found in other
vertebrates
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24.2 What Are the Major Groups of Vertebrates?
 Mammals provide milk to their offspring (continued)
– The mammalian brain is highly developed
– Mammals have unparalleled curiosity and learning
ability, allowing them to alter their behavior based on
experience
– This increases their chances of survival in a changing
environment
– Mammals have extended parental care after birth
– This allows some mammals to learn extensively
through parental guidance
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24.2 What Are the Major Groups of Vertebrates?
 Mammals are subdivided into three groups
– Monotremes
– Marsupials
– Placental mammals
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24.2 What Are the Major Groups of Vertebrates?
 Monotremes are egg-laying mammals
– This group includes only three species, the platypus and
two species of spiny anteater (echidnas), and are found
only in Australia and New Guinea
– Platypuses forage for food in the water and eat small
vertebrate and invertebrate animals
– Echidnas are terrestrial and eat insects and worms
they dig out of the ground
– Monotremes lay leathery eggs rather than giving birth to
live young
– The newly hatched young are nourished from milk
secreted by the mother
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Monotremes
Fig. 24-14
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24.2 What Are the Major Groups of Vertebrates?
 Marsupial diversity reaches its peak in Australia
– Species include the opossums, koalas,
kangaroos, wallabies, wombats, and the
Tasmania devil
– In marsupials, embryos begin development in
the uterus of the female
–Young are born at a very immature stage and
must crawl to and grasp a nipple to complete
development
–Post-birth development, in most, is completed
in a protective pouch
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Marsupials
Fig. 24-15
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24.2 What Are the Major Groups of Vertebrates?
 Placental mammals inhabit land, air, and sea
– This highly diverse class includes bats, moles,
impalas, whales, seals, monkeys, and cheetahs
– Rodents account form almost 40% of all mammal
species
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24.2 What Are the Major Groups of Vertebrates?
 Placental mammals inhabit land, air, and sea
(continued)
– Most mammal species are placental mammals
–The uterus contains a placenta that functions
in gas, nutrient, and waste exchange between
circulatory systems of mother and embryo
–In placental mammals, young are retained in
the uterus for their entire embryonic
development
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24.2 What Are the Major Groups of Vertebrates?
 About 20% of mammalian species are bats, the only
mammals to have evolved wings and powered flight
– Most bats have adaptations for feeding on a particular
kind of food, such as species that eat fruit or the nectar
from night-blooming flowers
– Most bats are predators and hunt frogs, fish, flying
insects, or blood that they obtain from the skin of
sleeping mammals or birds
– Bats use echolocation to catch flying prey by emitting
short pulses of high-pitched sound
– These sounds bounce off objects in the environment to
produce echoes that can be detected by the bats
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Author Animation: Vertebrates
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The Diversity of Placental Mammals
Fig. 24-16
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