introduction to vertebrates

how fish evolved

The earliest fish had an endoskeleton made of cartilage rather than bone. They also lacked a complete vertebral column. The first fish with a complete vertebral column evolved about 450 million years ago. These fish had jaws. They may have been similar to living sharks. About 400 million years ago, the first fish with a bony endoskeleton evolved. A bony skeleton could support a bigger body. Early bony fish evolved into modern ray-finned fish and lobe-finned fish.

how other vertebrate classes evolved

The earliest amphibians evolved from a lobe-finned fish ancestor. This occurred about 365 million years ago. Amphibians were the first terrestrial vertebrates. They lived on land as adults, but they had to return to the water to reproduce. The earliest reptiles evolved from an amphibian ancestor. This occurred at least 300 million years ago. Reptiles were the first vertebrates that did not need water to reproduce. Thats because they laid waterproof amniotic eggs. These eggs allowed the embryo inside to breathe without drying out. Mammals and birds both evolved from reptile-like ancestors. The first mammals appeared about 200 million years ago. The earliest birds evolved about 150 million years ago.

vertebrate diversity

There are about 50,000 living species of vertebrates. They are placed in nine different classes. Table 13.1 lists these vertebrate classes and some of their traits. Five of the classes are fish. The other four classes are amphibians, reptiles, birds, and mammals. Class Hagfish Distinguishing Traits They have a cranium but no back- bone; they do not have jaws; their endoskeleton is made of cartilage; they are ectothermic. Example hagfish Class Lampreys Distinguishing Traits They have a partial backbone; they do not have jaws; their endoskele- ton is made of cartilage; they are ectothermic. Example lamprey Cartilaginous Fish They have a complete backbone; they have jaws; their endoskeleton is made of cartilage; they are ec- tothermic. shark Ray-Finned Fish They have a backbone and jaws; their endoskeleton is made of bones; they have thin, bony fins; they are ectothermic. perch Lobe-Finned Fish They have a backbone and jaws; their endoskeleton is made of bones; they have thick, fleshy fins; they are ectothermic. coelacanth Amphibians They have a bony endoskeleton with a backbone and jaws; they have gills as larvae and lungs as adults; they have four limbs; they are ectothermic frog Reptiles They have a bony endoskeleton with a backbone and jaws; they breathe only with lungs; they have four limbs; their skin is covered with scales; they have amniotic eggs; they are ectothermic. alligator Class Birds Distinguishing Traits They have a bony endoskeleton with a backbone but no jaws; they breathe only with lungs; they have four limbs, with the two front limbs modified as wings; their skin is cov- ered with feathers; they have amni- otic eggs; they are endothermic. Example bird Mammals They have a bony endoskeleton with a backbone and jaws; they breathe only with lungs; they have four limbs; their skin is covered with hair or fur; they have am- niotic eggs; they have mammary (milk-producing) glands; they are endothermic. bear

vertebrate evolution

The earliest vertebrates were jawless fish. They evolved about 550 million years ago. They were probably similar to modern hagfish (see Table 13.1). The tree diagram in Figure 13.4 summarizes how vertebrates evolved from that time forward.

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other traits of vertebrates

Most vertebrates share several other traits. The majority of vertebrates have: scales, feathers, fur, or hair covering their skin; muscles attached to the endoskeleton to allow movement; a circulatory system with a heart that pumps blood through a closed network of blood vessels; an excretory system that includes a pair of kidneys for filtering wastes out of the blood; a central nervous system with a brain, spinal cord, and nerve fibers throughout the body; an adaptive immune system that learns to recognize specific pathogens and launch tailor-made attacks against them; and an endocrine system with glands that secrete chemical messenger molecules called hormones.

how vertebrates reproduce

Vertebrates reproduce sexually. Most have separate male and female sexes. Vertebrates have one of three reproduc- tive strategies: ovipary, ovovivipary, or vivipary. Ovipary refers to the development of an embryo within an egg outside the mothers body. This occurs in most fish, amphibians, and reptiles. It also occurs in all birds. Ovovivipary refers to the development of an embryo inside an egg within the mothers body. The egg remains inside the mothers body until it hatches, but the mother provides no nourishment to the developing embryo inside the egg. This occurs in some species of fish and reptiles. Vivipary refers to the development and nourishment of an embryo within the mothers body but not inside an egg. Birth may be followed by a period of parental care of the offspring. This reproductive strategy occurs in almost all mammals including humans.

vertebrate endoskeleton

The vertebral column is the core of the vertebrate endoskeleton, or internal skeleton. You can see a human skeleton as an example of the vertebrate endoskeleton in Figure 13.3. In addition to the vertebral column, the vertebrate endoskeleton includes: a cranium, or bony skull, that encloses and protects the brain; two pairs of limbs (in humans, arms and legs); limb girdles that connect the limbs to the rest of the endoskeleton (in humans, shoulders and hips).

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bone and cartilage

The vertebrate endoskeleton is made of bone and cartilage. Cartilage is a tough, flexible tissue that contains a protein called collagen. Bone is a hard tissue consisting of a collagen framework that is filled in with minerals such as calcium. Bone is less flexible than cartilage but stronger. A bony endoskeleton allows an animal to grow larger and heavier than a cartilage endoskeleton would. Bone also provides more protection for soft tissues and internal organs.

vertebral column

The main trait that sets vertebrates apart from invertebrate chordates is their vertebral column, or backbone. It develops from the notochord after the embryonic stage. As you can see in Figure 13.2 the vertebral column runs from head to tail along the dorsal (top) side of the body. The vertebral column is made up of repeating units of bone called vertebrae (vertebra, singular). The vertebral column helps the vertebrate body hold its shape. It also protects the spinal (nerve) cord that runs through it.

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what are vertebrates

Like all chordates, vertebrates are animals with four defining traits, at least during the embryonic stage. The four traits are: a notochord; a dorsal hollow nerve cord; a post-anal tail; and pharyngeal slits. Some invertebrates also have these traits and are classified as chordates. What traits do vertebrates have that set them apart from invertebrate chordates?

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ectothermy and endothermy

Early vertebrates were ectothermic. Ectothermy means controlling body temperature to just a limited extent from the outside by changing behavior. For example, an ectotherm might stay in the shade to keep cool on a hot, sunny day. On a cold day, an ectotherm might bask in the sun to warm up, like the snake in Figure 13.5. Almost all living fish, amphibians, and reptiles are ectothermic. They can raise or lower their body temperature by their behavior but not by very much. In cold weather, an ectotherm cools down. As its body temperature drops, its metabolism slows down and it becomes inactive. Both mammals and birds evolved endothermy. Endothermy means controlling body temperature within a narrow range from the inside through biochemical or physical means. For example, on a cold day, an endotherm may produce more body heat by increasing its rate of metabolism. On a hot day, it may give off more heat by increasing blood flow to the surface of the body. That way, some of the heat can radiate into the air from the bodys surface. Endothermy requires more energy (and food) than ectothermy. However, it allows the animal to stay active regardless of the temperature outside. You can learn more about how vertebrates regulate their temperature by watching this video: .

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instructional diagrams

No diagram descriptions associated with this lesson

questions

Vertebrate classes include

a. birds

b. amphibians

c. reptiles

-->  d. all of the above

Of the nine classes of modern vertebrates, how many are fish?

a. four

-->  b. five

c. six

d. three

What function(s) does the vertebral column of vertebrates serve?

a. It protects the spinal cord

b. It helps the body hold its shape

c. It provides a counterforce to muscles

-->  d. all of the above

Which statement about the vertebral column of vertebrates is false?

a. It runs along the top side of the body

-->  b. It consists of a single rigid rod of bone

c. It protects the spinal cord that runs through it

d. It develops from the notochord after the embryonic stage

Most vertebrates have four

-->  a. limbs

b. limb girdles

c. kidneys

d. two of the above

The vertebrate endoskeleton includes

-->  a. a cranium

b. two limbs

c. a long tail

d. two of the above

Compared with cartilage, bone is

a. more fragile

b. stronger

c. less flexible

-->  d. two of the above

Which reproductive strategy is used by most mammals?

a. ovipary

b. ovovivipary

-->  c. vivipary

d. none of the above

Vertebrates have an endocrine system with glands that secrete

-->  a. messenger molecules

b. digestive enzymes

c. DNA molecules

d. reproductive cells

The first vertebrates were

a. amphibians

b. reptiles

-->  c. fish

d. birds

Which statement about vertebrate reproduction is false?

a. All vertebrates reproduce sexually

b. Most vertebrates have separate male and female sexes

-->  c. All vertebrates have the same reproductive strategy

d. Some vertebrates lay eggs

The earliest vertebrates to evolve were

a. bony fish

-->  b. jawless fish

c. cartilaginous fish

d. amphibians

Amphibians were the first vertebrates that did not need water to reproduce.

a. true

-->  b. false

Vertebrates evolved endothermy before they evolved ectothermy.

a. true

-->  b. false

Amphibians evolved from a lobe-finned fish ancestor.

-->  a. true

b. false

All animals in Phylum Chordata are vertebrates.

a. true

-->  b. false

The function of vertebrate kidneys is filtering wastes out of the blood.

-->  a. true

b. false

The adaptive immune system of vertebrates learns to recognize and attack specific pathogens.

-->  a. true

b. false

The earliest fish had a cartilage endoskeleton.

-->  a. true

b. false

Birds evolved before the first mammals appeared.

a. true

-->  b. false

An animal with a cartilage skeleton can grow larger than an animal with a bony skeleton.

a. true

-->  b. false

There are more than a million living species of vertebrates.

a. true

-->  b. false

Living species of vertebrates are placed in five different classes.

a. true

-->  b. false

Most vertebrates have separate male and female sexes.

-->  a. true

b. false

__development of an embryo in an egg outside the mothers body

a. bone

b. ovovivipary

c. cartilage

d. ectothermy

e. vivipary

f. endothermy

-->  g. ovipary

__use of behavior to control body temperature from the outside

a. bone

b. ovovivipary

c. cartilage

-->  d. ectothermy

e. vivipary

f. endothermy

g. ovipary

__reproductive strategy that occurs in almost all mammals

a. bone

b. ovovivipary

c. cartilage

d. ectothermy

-->  e. vivipary

f. endothermy

g. ovipary

__tough, flexible tissue that contains collagen

a. bone

b. ovovivipary

-->  c. cartilage

d. ectothermy

e. vivipary

f. endothermy

g. ovipary

__use of biology to control body temperature from the inside

a. bone

b. ovovivipary

c. cartilage

d. ectothermy

e. vivipary

-->  f. endothermy

g. ovipary

__hard tissue that contains minerals in a collagen framework

-->  a. bone

b. ovovivipary

c. cartilage

d. ectothermy

e. vivipary

f. endothermy

g. ovipary

__development of an embryo in an egg inside the mothers body

a. bone

-->  b. ovovivipary

c. cartilage

d. ectothermy

e. vivipary

f. endothermy

g. ovipary

diagram questions

No diagram questions associated with this lesson