diversity of vertebrate animals -...

Vertebrate Diversity Page - vd-1

Anus

NotochordBrain

Mouth

Gill slitsHeartDigestive

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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.


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

Pa

leo

zo

ic

Fis

he

s

Am

ph

ibia

ns

Re

ptil e

s

Bir

ds

Ma

mm

als

Precambrian

Me

so

zo

ic

mya

65

300

250

150

550

450

400

350


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.


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.


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.


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.


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.

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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).


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?


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.


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.


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.


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.


Table 1. At maturity, breathe through:

Class Gil

ls

Sk

in

Lu

ng

s

Fish

Amphibians

Reptiles

Birds

Mammals

Table 2. Body covering of:

Class Bo

ny

Sca

les

Na

ked

Sk

in

Sca

les

Fea

ther

s

Ha

ir

Fish

Amphibians

Reptiles

Birds

Mammals

Table 3. Reproduction through:

Class

Na

ked

egg

s

Sh

elle

d

egg

s

Inte

rnal

Fish

Amphibians

Reptiles

Birds

Mammals

Table 4. Types of appendages:

Class Fin

s

Leg

s

Win

gs

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.)


6) What traits do bats possess and not possess that indicate that they are mammals and not birds?

diversity of vertebrate animals -...

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