CHAPTER 35: VERTEBRATES
WHERE DOES IT ALL FIT IN?
Chapter 35 provides more detail about the diversity of animals highlighted in Chapter 32. It goes into
more detail about modern animals. Students should be encouraged to recall the principles of animal
classification covered in Chapter 32. Segmentation and coelom should be reviewed. The information
in chapter 35 does not stand alone. Students should know that vertebrates are interrelated and
originated from a common ancestor of all animals.
SYNOPSIS
The phylum Chordata includes the animals with which we are most familiar and most closely
related. Their principal features are: a single, hollow, dorsal nerve cord; a flexible, dorsal
notochord; pharyngeal slits; and a postanal tail. All chordates have these four characteristics at
sometime in their development. The most primitive nonvertebrate chordates (subphylum
Urochordata) include tunicates and lancelets. Larval tunicates resemble primitive tadpoles and
clearly possess all chordate characteristics. Adult tunicates are sessile, colonial organisms that
secrete a cellulose tunic around themselves. They seemingly lack many of the expected
characteristics. The lancelets are scaleless, fishlike marine organisms. They are filter feeders and
create water currents via cilia on the anterior end of the gut.
The subphylum Vertebrata is well-represented by marine, freshwater, and terrestrial organisms.
They possess a vertebral column, distinct and well-differentiated head, neural crest cells that
participate in the development of vertebrate structures, internal organs, and an endoskeleton
made up of cartilage and bone. Their circulatory and excretory systems are markedly different
from all other animals. Vertebrates are divided into nine classes; five contain the aquatic fishes
and four are terrestrial tetrapods.
Key characteristics of fishes include a vertebral column, jaws and paired appendages, gills,
single-loop blood circulation and nutritional deficiencies. The class Cephalaspidomorphi is
made up the jawless fishes, the lampreys, parasitic and nonparasitic types, and all breed in fresh
water while the class Myxini contain the hagfishes, jawless fishes with no paired appendages,
scavengers, mostly blind but having a well developed sense of smell. Under the traditional
classification scheme, both were labeled jawless fish and lumped into the superclass Agnatha.
Both retain the notochord as adults and possess cartilaginous skeletons. Larval lampreys
superficially resemble the lancelets, although they are more efficient feeders and create water
currents via a muscular pharynx. Class Chondrichthyes included the sharks, skates, and rays.
These are streamlined hunters, possess cartilaginous skeletons, have no swim bladders and
undergo internal fertilization. They are jawed fishes. The horizontal fins of the sharks and rays
improve their swimming ability, forcing the buoyant animals downward in the water as they
swim forward. Their skin is covered by small denticles from which teeth are derived. Class
Sarcopterygii include the lobe-finned fishes, a group of bony fishes that are ancestral to
amphibians possessing paired lobed fins. Class Actinopterygil consist of the ray-finned fishes,
which are the most diverse group of vertebrates. These fish possess a denser, less buoyant
skeleton and have evolved a gas-filled swim bladder to help position themselves in the water.
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Their scales are composed of thin, bony plates and they possess a well-developed lateral line
sensory system. Bony fish possess several unique characteristics including gills, a gill cover,
and a single-loop circulation.
Terrestrial vertebrates include the classes Amphibia (frogs and salamanders), Reptilia (lizards
and snakes), Aves (birds), and Mammalia (mammals). They evolved from the lobe-finned fishes.
As the first land-dwelling vertebrates, amphibians needed certain characteristics to ensure their
survival. Among these are: legs and strong thoracic skeletons for support and locomotion,
efficient air-breathing structures (lungs) as gills collapse out of water, a redesigned heart and
circulatory system to deliver more oxygen to the walking muscles, water-bound reproduction to
keep their eggs from desiccation and a means to keep their own bodies from drying out. The
three orders of amphibians are Anura consist of frogs and toads, amphibians without tails;
Urodela consist of salamanders and newts that have elongated bodies, long tails and smooth,
moist skin; and, Apoda that includes the caecilians which are a group of tropical, legless,
burrowing amphibians that resemble worms but have jaws with teeth. All are greatly dependent
on maintaining a moist skin for respiration except for the dry-skinned toads.
Reptiles are less dependent upon water having amniotic eggs in which the embryo is encased in a
shell; dry, watertight skin made up of scales; and, pulmonary breathing by expanding and
contracting the rib cage. Their legs are better positioned for mobility and speed, and their heart
and circulatory systems are more efficient. Four major forms of reptiles took turns dominating
the land. In order they are the pelycosaurs, the therapsids, the thecodonts, and the dinosaurs.
Today’s reptile orders include Chelonia (turtles and tortoises), Squamata (snakes and lizards),
Rhynchocephalia (tuataras), and Crocodilia (alligators and crocodiles).
Fishes, amphibians, and reptiles are ectothermic animals; they regulate their body temperature by
taking in heat from the environment. Birds and mammals are endothermic; they maintain their
temperature by the expenditure of internal energy. There are 28 orders of bird, 166 families.
The most ancient birds are the flightless birds such as the ostriches. Next are the waterfowl such
as ducks and geese. Next are the woodpeckers, parrots, swifts, and owls. The songbirds, the
largest order of birds, the Passeriformes evolved next. The more specialized orders such as
shorebirds, birds of prey, flamingos, and penguins appeared later. Birds are clearly evolved
from reptilian ancestors. Two primary characteristics distinguish birds from reptiles: feathers
and flight skeleton. Their feathers are modified reptile scales. Feathers are obviously important
for flight, but also insulate as birds are endotherms. They need to maintain a high body
temperature so that metabolism in their flight muscles can proceed at a faster rate. Bird bones are
thin and hollow to reduce weight. Many are fused to provide rigidity for flight. Birds are the only
vertebrates that have a fused collarbone (wishbone) and a keeled breastbone. Birds have extremely
efficient respiratory and circulatory systems to provide sufficient oxygen to sustain flight.
Mammals evolved from therapsids reptiles over 220 million years ago. They were a minor group as
long as the dinosaurs flourished. With their extinction, mammals rapidly diversified. There are
about 4500 living species of mammals. The key characteristics of mammals are milk producing
glands and hair. Mammal hairs are not derived from reptile scales or bird feathers, though they serve
a similar protective, insulating function. Other characteristics include endothermy, placenta (in some
mammal species), and heterodont dentition (different forms of teeth), digestion of plants, hooves and
horns, flight (different from birds). Monotremes are egg-laying mammals that retain many
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primitive, reptilian characteristics. The duck-billed platypus and two species of spiny anteater are
the only living monotremes. Marsupials are the pouched mammals found almost exclusively in
Australia. A major difference between marsupials and other mammals is their pattern of embryonic
development – completing its development outside of the mother’s body in a pouch. Placental
mammals produce a true placenta that nourishes their embryos through the course of development.
Gestation is totally internal for an extended period of time. Both marsupials and placental mammals
give birth to live young and nourish them with milk. Although not the most numerous vertebrates,
because of their size, mammals are certainly among the most obvious. There are 19 orders of
mammals, 17 are placental mammals.
Primates are an order of mammals and have two distinct features: grasping fingers and toes and
binocular vision. Primates further split into two groups: prosimians (before monkeys) and the
anthropoids (monkeys, apes and humans). The hominoids include the apes such as the gibbon,
orangutan, gorilla, and chimpanzee. Apes have larger brains than monkeys and lack tails. Hominids
include humans and their direct ancestors. Hominids walked upright, their vertebral column is more
curved, human spinal cord exists from the bottom of the skull, the pelvis has become broader, the
big toe is no longer sideways, and the lower limbs are longer than the upper limbs. A hominid
evolutionary tree is made up of six species of Australopithecus (A. anamenis, A. boisei, A.
aethiopicus, A. africanus, A. robustus, and A. afarensis) and, seven Homo species (H. rudolfensis,
H. habilis, H. ergaster, H. erectus, H. neanderthalensis, H. heidelbergensis and H. sapiens).
LEARNING OUTCOMES
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Indicate the four principal characteristics of chordates.
Compare the two non-vertebrate chordates with each other and to the vertebrates.
Indicate the major characteristics possessed by all vertebrates and those features that separate
them.
Understand how the jawless fish differ from all other vertebrates.
Explain the value of the Chondrichthyes skeleton and indicate the structure(s) seen in the bony
fish. Explain how the bony fish evolved to counteract the comparative disadvantage of their
skeleton.
Know the characteristics required to evolve a terrestrial form of life from an aquatic one.
Understand how amphibians differ from the three other classes of terrestrial vertebrates.
Describe how the reptiles are evolutionarily more advanced than amphibians and why they are
better adapted for a truly terrestrial existence.
Differentiate between endothermy and ectothermy, the advantages and disadvantages of each,
and indicate which classes of vertebrates fit into each category.
Understand the special adaptations found in the birds.
Differentiate among monotremes, marsupials, and placental mammals.
Review the differences found prosimians versus anthropoids.
Contrast the differences seen in Australopithecine and Homo species.
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COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 35 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students do not understand the persistence of segmentation in the vertebrates
Students do not fully comprehend the location of the coelom in animals
Students are unsure of the evolutionary relationships between different vertebrate groups
Students think that all vertebrate groups evolved at about the same time
Students believe that deuterostomes evolved from protostomes
Students believe that all animals are mobile
Students believe that most animals are vertebrates
Students are unfamiliar with interrelations of the different organ systems
Students believe that all animals have identical organ system structures
Students believe that animals exclusively reproduce sexually
Students believe that the fins of modern fish evolved into limbs
Students do not equate wings to tetrapod front limbs
Students are unaware of molecular methods of animal classification
Students are resistant to the anthropoid lineage of humans
Students believe that vertebrate evolution is flawed because of the absense of “missing
links”
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Discuss flight and the anatomy of wings in birds and mammals. Discuss endothermy versus
ectothermy relative to insects, birds, and mammals. Discuss the developmental structure of the
cardiovascular system in various classes of vertebrates. Discuss the differences between
monotremes, marsupials, and placental birth/hatching. Discuss the theory of birds and mammals
from reptiles with respect to the development of feathers and fur.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 35.
Application
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Have students describe the value of the coelom in large vertebrates.
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Have students explain the evidence of segmentation in mammals.
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Ask students to explain amphibians are more diverse warmer climates.
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Analysis
Synthesis
Evaluation
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Have students explain why some land living amphibians lack lungs while
not known mammal has no lungs.
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Have students explain the benefits and risks of flight in vertebrates.
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Ask students to explain why terrestrial mammals do not achieve the
tremendous size of aquatic mammals.
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Ask students explain the discovery that reptiles are capable of producing a
placenta.
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Have students hypothesize why sharks are the top ocean predator instead
of a bony fish.
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Ask the students to find a medical application that exploits the knowledge
gained by research on limb formation in amphibians.
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Ask students to evaluate the claim that vertebrate evolution is restricted in
diversity compared to arthropods.
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Ask students to evaluate the consequences of people replacing meat and
poultry with fish as a staple diet.
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Ask students to evaluate the accuracy of using amphibians as an indicator
of environmental disturbances.
VISUAL RESOURCES
Compare the larval stages of tunicates, lancelets, and lampreys. Obtain the jaw of a small shark
and compare the teeth to scales found on shark skin to tactilely illustrate the denticles.
Bring in skulls and skeletons for all vertebrate animals to show similarities in bone types but
differences in structure. Show that differences in structure are related to differences in use as
dictated by their environment and/or habitat.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Virtual Vertebrate.
Introduction
This demonstration permits the class to see a virtual frog dissection to supplement a
discussion on vertebrate morphology and organ systems.
Materials
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Computer with Media Player and Internet access
LCD hooked up to computer
Web browser linked to Virtual Frog Dissection at http://froggy.lbl.gov/cgi-bin/dissect
Procedure & Inquiry
1. Explain to the class that you will be demonstrating the vertebrate characteristics using a
virtual frog
2. Load up the website and click on the White Diamond icon to flip the frog around while
describing various vertebrate characteristics
3. Then “check” the various buttons underneath the frog to add or remove organ systems.
4. Have the students explain the characteristics of the organ systems.
5. Ask the students briefly explain how the environment and lifestyle affect the morphology
of the various organ systems in the different vertebrates.
USEFUL INTERNET RESOURCES
1. Images of vertebrates are available from the University of California at Berkeley
CalPhotos: Animal website. These images are valuable teaching resources for lecture and
laboratory sessions. The site is available at http://calphotos.berkeley.edu/fauna/.
2. The Tree of Life website provides up to date information about animal classification. It
has useful information and images for showing students diversity vertebrates. The
website can be found at http://tolweb.org/Animals/2374.
3. Hox genes play a strong role in the variation seen in the vertebrate body plan. A
Developmental Biology course website at Memorial University of Newfoundland has
excellent information an images about hox gene vertebrate development. The website is
located at www.mun.ca/.../BIOL3530/DB_Ch04/DBNVert2.html.
4. Case studies are an effective tool for stimulating interest in a lesson vertebrate diversity.
The University of Buffalo has a case study called “Threats to Biodiversity: A Case Study
of Hawaiian Birds” which has students investigating the impacts of human activities on
vertebrate diversity. The case study can be found at
http://www.sciencecases.org/hawaii/hawaii.asp.
LABORATORY IDEAS
A. Comparative Vertebrate Anatomy
This activity asks students to investigate the similarities and variation in vertebrate body
plans.
a. Review the generalized characteristics of chordates to the class.
b. Tell students that they will be forming research teams to investigate the similarities and
differences of the vertebrate body plan compared to a purported vertebrate ancestor.
c. Provide students with the following materials to be distributed into research teams who
dissect one animal:
a. Preserved perch
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b. Preserved lizard or salamander
c. Preserved rat
d. Preserved pigeon
e. Dissecting materials
f. Rulers
First have the students design a “model” ancestral vertebrate body plan that can be drawn
as a reference for comparison on the board.
Instruct students to investigate and describe the body and organ system characteristics of
their specimen.
Then tell the students to explain the similarities and differences of their vertebrate to the
hypothetical vertebrate ancestor model.
Have students share their findings and explain the reasons for differences in the body
plans. They should be encouraged to discuss the role of hox genes and embryological
devlepment in determining the adult body form.
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students do a lesson do a program the importance of vertebrate biodiversity for a
civic group.
2. Have students tutor high school students animal diversity.
3. Have students volunteer on environmental restoration projects with a local conservation
group.
4. Have students volunteer at the educational center of a zoo or marine park.
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