vertebrates are interesting organisms to study, as there are a lot of things we are ignorant of, yet we do not know how to preserve them.

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Anus
Notochord
Brain
Mouth
Gill slits
HeartDigestive
track
Diversity of Vertebrate Animals
Over the last 400 million years, vertebrate animals have
evolved a diverse array of adaptations for life on earth. Vertebrate
animals are those with which people are most familiar, and are the
animals we most commonly use as food, employ for labor, and adopt
as pets – fish, amphibians, reptiles, birds, and mammals.
The biological classification system
Classification is a dynamic subfield of biology. New knowledge of
anatomy, genetics and evolutionary relationships often lead to a
rethinking of how different groups of organisms are related. Thus, today fish have been subdivided
into several classes, and in the near future the group we call ‘reptiles’ may be similarly subdivided.
In the biological system of classification, all organisms are classified into increasingly more detailed
groups (taxa), beginning with the “Kingdom” and continuing downward to the “Genus” and
“Species” classifications. The scientific name is created by combining the genus and species
classifications.
How are animals different from
plants? Animals (Kingdom Animalia)
are heterotrophic (they eat other
organisms- dead or alive – for sustenance)
and have cells that lack rigid cell walls.
Animals are informally
subdivided into invertebrates and
vertebrates. There are many phyla that
contain animals classified as invertebrates.
Some of the animals classified as
invertebrates include arthropods (insects,
spiders, and crustaceans), molluscs
(squids, octopuses and snails), and many
wormlike phyla.
Chordates. As shown in the above figure, all
vertebrates are found within the Chordata
phylum. All chordates evolved from an ancestor
that had a flexible rod (called a notochord) along
the dorsal side (back) to provide support for the
skeleton and muscles. All chordates share a
common internal body plan. There is a dorsal
nerve cord; a digestive tract that extends from the mouth to anus;
a muscular tail that extends beyond the anus and the heart pumps
blood through the body and to the gills (or lungs). Indeed, all
vertebrates contain a tail and gill slits at some stage of development.

2. Vertebrate Diversity Page - vd-2
In the chordate animals we classify as vertebrates, the
bony vertebrae develop and surround the nerve cord along the dorsal
side (back) of the organism. (Other chordates lack these bony
vertebrae and retain the flexible notochord.) Vertebrates are
subdivided into several classes: fishes (which comprise several
classes), amphibians, reptiles, birds, and mammals.
A study of vertebrates reveals progressive evolutionary adaptations
to life on land and a wider range of ecological niches -- adaptations
that can be found in:
• Improved respiration
• Protective and insulating body coverings
• More efficient reproduction (especially on land)
• Paired, muscular appendages
Vertebrate evolution began around 500 million years ago (mya)
during the early Paleozoic era with the evolution of fish, followed
by amphibians and then reptiles during middle Paleozoic. Reptiles
reached their “peak” (at least in size and ferocity) during the
Mesozoic era. Some lizard-like reptiles of the Mesozoic evolved
into small hair-covered mammals, birthing their young rather than
laying eggs, while awaiting the demise of the dinosaurs before
rising to prominence during the Cenozoic. However, before this
eventual demise, the dinosaurs gave rise to another group, the
birds, which, like the mammals, survive to the present day.
The objectives of this lab exercise are for you to understand the:
• difference between vertebrate and invertebrates animals.
• distinguishing characteristics of the major groups of vertebrate animals.
• evolutionary relationships between the vertebrates.
Cenozoic
Paleozoic
Fishes
Amphibians
Reptiles
Birds
Mammals
Precambrian
Mesozoic
mya
65
300
250
150
550
450
400
350

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I. Characteristics of the Vertebrate Animals
A. Fishes
The first vertebrates to become a widespread, predominant life form on earth were fishes.
Prior to this, only invertebrates, such as mollusks, worms and squid-like animals, would have been
found in the oceans. Like most invertebrates, female fish spawn by releasing small, unprotected
eggs outside the body, where they are fertilized by sperm from males, and then mature. What were
the evolutionary innovations to first evolve among the fish?
• Paired appendages. Fish have paired appendages (fins) adapted for movement in water.
• Protected skin. Many fish have scales (modified bones) covering their skin, although some
have lost this trait (e.g., catfish).
• Pharyngeal gill slits. Water passes through the mouth and then out through the pharyngeal
gill slits and over the gills, which absorb oxygen and release CO2. (Pharyngeal means
“relating to the throat”.)
Fish are classified into several classes. Representatives of the following classes are on display in the
lab.
Jawless fish (Class Agnatha)
These are among the most primitive of
the fish; they are considered primitive
because they lack a movable jaw and
have a cartilaginous skeleton
(Cartilage is a softer more flexible
tissue than bone.) Instead, they have a
well-toothed circular mouth, which
among many species, is used to parasitize other fish.
Cartilaginous Fish (Class Chondrichthyes)
This group includes the sharks and rays, and the name
reflects that they have a skeleton composed of
cartilage, which replaced the bone of ancestral fish.
They were the first to evolve jaws (derived from first
pair of gills) that greatly enhanced their ability to feed
on potential food sources. They also evolved paired
fins – pectoral up front, pelvic behind – that allowed
greater swimming ability.
Bony fish (Class Osteichthyes)
This group includes the vast majority of freshwater and
marine fish. These fish retain a bony skeleton, and an
internal organ called a swim bladder used to maintain
buoyancy.

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B. Amphibians (Class Amphibia)
Some fish evolved adaptations minimally adequate for life on
dry land while retaining a need to reproduce in water. These became
amphibians: “Amphi” means “pertaining to opposite ends”, in this
case water and land. Many amphibians reproduce in water,
emerging from jelly-coated eggs as aquatic larvae, and later
maturing into terrestrial, aquatic, or semi-aquatic adults. What
adaptations allowed movement out of water?
• Legs. Some ancestral fish undoubtedly lived in shallow freshwater marshes and lagoons where
they could find more food and deposit eggs “out of reach” of larger aquatic predators. For a
fish even partially out of water, buoyancy would be diminished and more muscular and leg-
like fins would have been an enormous advantage.
• Cutaneous respiration and lungs. Extended visits to land would have
been problematic for fish that extract oxygen from water moving
through gill slits, and this selected for fish that could absorb more
oxygen directly through their skin. Gulping air into pouches in the
gut was another solution and these pouches eventually evolved into
lungs.
• Improved vascular system. Larger muscles require more oxygen, and
the heart and circulatory system allowed greater oxygen transport
between the respiratory tissue and the body.
There are three orders of amphibians: frogs, salamanders, and caecilians. Caecilians are a rather
obscure group entirely lacking limbs and outwardly resembling worms or snakes,. so wWe will
focus on the more common frogs and salamanders.
Salamanders (Order Caudata)
This group includes salamanders, newts and mudpuppies. The term caudata is derived from the Latin
for tail, making this group (roughly) the “tailed-amphibians”. They typically have slender bodies
with long tails, and arms and legs of equal size.
Frogs (Order Anura)
The anatomy of frogs is distinctive, with leg structure more
suited for hopping (an escape mechanism) than walking.
“Anura” comes from the Greek words meaning no tail,
making these the “tail-less amphibians”. Since their skin
absorbs oxygen most efficiently when damp and tends to
lose water rapidly, remaining near water is necessary for
most frogs (and salamanders). As a defense mechanism
some frogs (e.g., poison arrow frogs) secrete potent toxins
into the mucus layer of their skin.

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C. Reptiles (Class Reptilia)
Reptiles were the first animals to fully escape a dependence
upon the availability of an open body of water. What
adaptations were required for this transition?
• Thick, dry skin with scales, which was less prone to
desiccation (water loss).
• Amniotic eggs were one of the most important
evolutionary innovations. In reptilian eggs, the
embryo develops within an internal watery
compartment, the amnion chamber, provided with a
large nutritional supply (in the yolk sac), and
surrounded by a tough outer shell.
• Internal fertilization. A shelled egg layed on dry
land can no longer be fertilized by sperm swimming
freely in water. Internal fertilization allows sperm to swim to the eggs in the moist interior of
the female’s body, and for fertilization to occur before the hard shell is added around the egg.
• Breathing. Muscles of the rib cage expand and contract to pump larger quantities of air into
larger, more advanced lungs.
Image of egg anatomy used with permission of George F. Hart
http://www.scienceand.com/verebrates.htm
Classification of reptiles is still being resolved, and
zoologists have been revising the various classifications of
reptiles. There are three important groups that we will
consider here:
Turtles and Tortoises (Order Chelonia): among which
the body is surrounded by a protective shell.
Lizards and Snakes (Order Squamata): Snakes evolved
from a legged lizard, and some still possess vestigial leg
bones.
Crocodiles and Alligators (Order Crocodylia): In several ways crocodiles more closely resemble
birds than other reptiles, such as in building nests and caring for their young. Possibly there was a
close relationship among the dinosaur ancestors from which crocodiles and birds descended.

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D. Birds (Class Aves)
Birds are the direct descendents of theropod type dinosaurs, and certain key
traits of birds can be linked to anatomical features of these dinosaurs:
• Feathers are composed of the same material (keratin protein) as the scales
of reptiles. They provide efficient insulation to both hot and cold
environments and form an aerodynamic surface necessary for flight.
• Bones and skeleton adapted for flight. If you have ever carved a turkey,
you have encountered the fused collarbone called the furcula (or the ‘wish
bone’) and a large sternum bone called the ‘keel’ to which the large flight
muscles are attached. The bones are said to be pneumatic (filled with air
spaces) to reduce weight, and these air spaces participate in respiratory
oxygen storage.
• Endothermy or being ‘warm-blooded’. Unlike modern reptiles, birds can
generate enough heat internally to regulate and maintain a constant body temperature, thus
allowing birds to inhabit habitats (think of penguins) unacceptably cold for reptiles. There is
some evidence that this trait evolved among the theropod ancestors of birds.
For terrestrial vertebrates the greatest number of species are
found among the birds. Some familiar birds are
representatives of the major Orders, such as:
Eagles and hawks
Hummingbirds
Owls
Penguins
Pigeons
Parrots
Songbirds (robins, warblers, orioles, etc)
Woodpeckers
etc…
Unlike most reptiles, birds care for their young after hatching and until they are able to fend for
themselves.

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E. Chicken egg structure and development
Structure of the egg
After mating, sperm from a male are stored in the female
and used over a period of time. Thus, a hen does not need to
mate with a roster each time she lays a fertile egg. After
mating, her fertility remains high for about 10 days, and
after that she will continue to lay, but the eggs are not
fertile.
Structures of fertilized egg
• Air cell: located in the large end of the egg.
• Yolk: the principal nutritional source for the embryo.
• Albumen: clear, cushioning protein surrounding the
yolk.
• Chalazae: whitish cord-like proteins that support the
yolk in the center of the albumen.
• Shell membranes: there are two of these surrounding
the albumin.
• Shell: is composed mainly of protein embedded with calcium carbonate. If the hen lays brown
eggs, the brown pigments are added to the shell in the last hours of shell formation. The shell
contains several thousand pores that permit the egg to "breathe."
Seven Day-old embryo
The eggs that you will examine in lab will be
approximately 7-days post-fertilization.
Some of the visible structures are listed below.
• Embryo: about 1 cm in length in which you
can see a large dark colored eye, a beating
heart, and small buds that will develop into its
limbs.
• Amnion membrane: surrounds the amniotic
fluid that cushions and protects the embryo.
• Blood vessels: many of which are growing
into the following membranes:
• Allantois: a membrane where gas exchange
occurs and surrounds the allantoic sac, the
place where nitrogenous wastes accumulate.
• Vitelline membrane: surrounds the yolk and
retrieves nutrition from the yolke for the
embryo.
Formatted: Font: Not Bold

8. Vertebrate Diversity Page - vd-8
F. Mammals (Class Mammalia)
Although mammals appear to have evolved early during the Mesozoic (even before birds),
they did not rise to predominance until the ecological niches become vacant with the demise of the
dinosaurs. Some of the key adaptations among mammals included:
• Hair, like feathers of birds evolved from the scales of a reptilian ancestor and are composed of
similar proteins. Endothermy, and insulation provided by hair, allowed mammals to be active
at night and survive even bitter arctic winters.
• Mammary Glands, which secrete milk, assured a food supply during the precarious early life
of the newborn.
• Internal fetal development. Among placental mammals
(the most common type) the circulatory system of the
fetus and mother become intimately intertwined within a
placenta, where exchange of nutrients and waste
products can occur. This allows long-term internal
development of the fetus.
Classification of Mammals. There are three subclasses of
mammals:
• Placental mammals are most familiar and predominate
in most parts of the world. In these animals the fetus
develops internally in a uterus.
• Marsupials (e.g., kangeroos) are less common and predominate in Australia, although some
(e.g., the opossum) occur in other regions. The fetus of marsupials develop in an external
pouch of the mother.
• Monotremes (e.g., the platypus) have retained the ancestral characteristic of laying eggs.
The major orders of the placental mammals are represented by many familiar animals, such as:
Carnivorous predators (e.g., bears, cats and dogs)
Hoofed mammals (e.g., horses)
Marine mammals (e.g., whales, dolphins, porpoises)
Primates (e.g., monkeys, chimpanzees, humans)
Rodents (e.g., mice, rats, beavers – the largest order)
Etc.
Among the mammals certain other traits reached new
heights, including prolonged care for the offspring and
intelligence (although possibly less among some mammals
than they themselves think).

9. Vertebrate Diversity Page - vd-9
II. Lab activities (Ask your instructor when necessary to answer questions.)
A. Read the section on fish and A. Eexamine the displays pertaining to fish.
1. Complete the diagram
to the right. Identify the
fins and internal organs
labeled in the perch displays.
2. The breathing structures
of a fish are called the
_____________ which are
used to obtain ________ from the water.
3. Wearing latex gloves, handle the fish on display. The protective structures on the perch are
called __________________. Examine one of these under the microscope; why does it have
numerous little ring-like structures?
4. For each of the following fishes on display identify the class in which it is classifiedit belongs to
and a distinguishing characteristic:
Fish type Class Distinguishing trait
a) Dogfish _________________ :
b) Lamprey _________________ :
c) Perch _________________ :
Which of these is considered to be the most like the common ancestorancestral?
________________________.
Explain why:
5. One of the fish on display is bearing eggs, which fill a significant volume of the body cavity.
Why is it necessary for fish to produce so many eggs?

10. Vertebrate Diversity Page - vd-10
B. Read the section on amphibians Eand examine the displays pertaining to
amphibians.
1. For each of the following amphibians, identify the order in which it is classified.
Organism Order
a. bullfrog _________________
b. mud puppy _________________
c. salamander _________________
What are two shared characteristics of the external anatomy of these three organisms?
2. Wearing latex gloves, and handle the amphibians on display. How is the skin important to
the survival of these organisms?
3. Examine the dissected frog. What internal organ first evolved among amphibians to allow
better gas exchange on land and to support the activity of larger muscles?
4. Examine the display of the frog life stages. What events happen during the:
First year of growth:
Second year of growth:
5. What are three evolutionary innovations that first appeared among amphibians?
1.
2.
3.

11. Vertebrate Diversity Page - vd-11
C. Read the section on reptiles and examineExamine the displays pertaining to
reptiles.
1. For each of the following reptiles, identify the order in which it is classified.
Organism Order
a. Turtle _________________
b. Copperhead _________________
c. Alligator _________________
2. Examine the turtle egg shells. Unlike eggs of amphibians, reptile eggs are larger, surrounded
by a protective ____________________ and contain a food supply in the _______________.
How did this help reptiles adapt to life on land?
3. Obviously, reptiles produce enough offspring to sustain the species, yet they produce far fewer
eggs than do fish and amphibians. How is this possible?
4. Examine the skin of the snake, which is covered by _________________.
How did this help reptiles adapt to life on land?
5. What are three evolutionary innovations that first appeared among reptiles?
1.
2.
3.

12. Vertebrate Diversity Page - vd-12
In this magnification of a feather,
identify and label the shaft, barbs
and barbules
D. Read the section on birds and examineExamine the displays pertaining to
birds.
Examine the unfertilized egg and compare its structure to the fertilized egg that you will open and
examine. After opening the fertilized egg, examine it under a dissecting microscope and look for
blood cells flowing through the vessels. What are the functions of the:
Amniotic sac and fluid:
Allantois and allantoic sac:
Vitelline blood vessels:
1. Examine examples of bird feathers under the dissecting scope,
and complete the diagram to the right.
Two functions of feathers are:
1.
2.
2. How do the bones of birds differ in structure from those of other
animals, and why?
3. Examine the bird skeleton on display, and in the diagram to the right
label the ‘furcula’ and ‘keel’. Why are these modified bones only
found in birds?
4. Birds lay even fewer eggs than reptiles. How is offspring rearing
among birds different than for most reptiles?
5. What are three evolutionary innovations that first appeared among birds?
1.

13. Vertebrate Diversity Page - vd-13
2.
3.
E. Read the section on mammals and examine Examine the displays pertaining to
mammals.
1. The body covering of mammals is called _______________.
How does this covering benefit these animals?
Why do we believe that hair evolved from scales of reptiles?
2. Examine the reproductive tract from a pregnant pig that is on display. Although the uterus is
not present, the fetus is surrounded by the membrane called the _______________, and is
connected by the umbilical cord to the __________________.
3. How is reproduction in mammals more efficient than that of fish and amphibians?
4. What do you perceive as some of the evolutionary innovations among mammals that have
contributed to development of advanced societies among humans? Explain.
5. What are three evolutionary innovations that first appeared among mammals?
1.

14. Vertebrate Diversity Page - vd-14
Table 1. At maturity, breathe through:
Class
Gills
Skin
Lungs
Fish
Amphibians
Reptiles
Birds
Mammals
Table 2. Body covering of:
Class
Bony
Scales
Naked
Skin
Scales
Feathers
Hair
Fish
Amphibians
Reptiles
Birds
Mammals
Table 3. Reproduction through:
Class
Naked
eggs
Shelled
eggs
Internal
Fish
Amphibians
Reptiles
Birds
Mammals
Table 4. Types of appendages:
Class
Fins
Legs
Wings
Fish
Amphibians
Reptiles
Birds
Mammals
2.
3.
III. Summarize the evolutionary
trends among vertebrates
A. Summarize changes in respiration in Table 1.
(Place an “X” in each appropriate box.)
1) A _________________ located along the
dorsal side of the body first appeared in the
Chordata phylum.
2) In vertebrates, a series of bones called
__________________ surround the
nerve cord.
B. Summarize changes in body covering
in Table 2. (Place an “X” in each
appropriate box.)
3) What structural characteristic is
shared by reptilian scales, feathers and
hair?
C. Summarize changes in reproduction in Table 3.
(Place an “X” in each appropriate box.)
4) Why do fish and amphibians produce so many
eggs?
5) How did the shelled egg benefit land animals?
D. Summarize changes in appendages in Table 4.
(Place an “X” in each appropriate box.)

15. Vertebrate Diversity Page - vd-15
6) What traits do bats possess and not possess that indicate that they are mammals and not birds?