19.1 Overview of Vertebrates

Lesson Objectives

  • List the characteristics of vertebrates.
  • Explain how vertebrates reproduce.
  • Identify the nine classes of vertebrates.
  • Learn the Creationist view of the origin of vertebrates.

Vocabulary

  • bone
    • hard tissue in most vertebrates that consists of a collagen matrix, or framework, filled in with minerals such a calcium
  • cartilage
    • dense connective tissue that provides a smooth surface for the movement of bones at joints
  • cranium
    • part of a vertebrate endoskeleton that encloses and protects the brain; also called the skull
  • ectothermy
    • regulation of body temperature from the outside through behavioral changes such as basking in the sun
  • endothermy
    • regulation of body temperature from the inside through metabolic or other physical changes
  • immune system
    • body system that consists of skin, mucous, membranes, and other tissues and organs that defends the body from pathogens and cancer
  • kidney
    • main organ of the excretory system that filters blood and forms urine
  • ovipary
    • type of reproduction in which an embryo develops within an egg outside the mother’s body
  • ovovivipary
    • type of reproduction in which an embryo develops inside an egg within the mother’s body but in which the mother provides no nourishment to the developing embryo in the egg
  • vertebrae (singular, vertebra)
    • repeating bony units that make up the vertebral column of vertebrates
  • vivipary
    • type of reproduction in which an embryo develops within, and is nourished by, the mother’s body

Introduction

Vertebrates are a subphylum of the phylum Chordata. Like all chordates, vertebrates have a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. What other characteristics do vertebrates have? What traits set them apart from invertebrate chordates?

Characteristics of Vertebrates

The main distinguishing feature of vertebrates is their vertebral column, or backbone (see Figure below). The backbone runs from the head to the tail along the dorsal (top) side of the body. The vertebral column is the core of the endoskeleton. It allows a vertebrate to hold its shape. It also houses and protects the spinal (nerve) cord that passes through it. The vertebral column is made up of repeating units called vertebrae (singular, vertebra). In many species, there are shock-absorbing discs between the vertebrae to cushion them during movement.

19.1a

Human Vertebral Column and Vertebrae. The human vertebral column consists of 33 vertebrae. Two vertebrae are shown here enlarged.

Vertebrate Endoskeleton

Another distinguishing feature of vertebrates is an endoskeleton made of bone or cartilage. Cartilage is a tough tissue that contains a protein called collagen. Bone is a hard tissue that consists of a collagen matrix, or framework, filled in with minerals such as calcium. Bone is less flexible than cartilage but stronger. An endoskeleton made of bone rather than cartilage allows animals to grow larger and heavier. Bone also provides more protection for soft tissues and internal organs. As shown in Figure below, the vertebrate endoskeleton includes a cranium, or skull, to enclose and protect the brain. It also generally includes two pairs of limbs. Limb girdles (such as the human hips and shoulders) connect the limbs to the rest of the endoskeleton.

19.1b

Vertebrate Endoskeletons. The vertebrate endoskeleton includes a vertebral column, cranium, limbs, and limb girdles. Can you find these parts in each endoskeleton shown here?

Other Vertebrate Traits

There are several additional traits found in virtually all vertebrates.

  • Vertebrates have a system of muscles attached to the endoskeleton to enable movement. Muscles control movement by alternately contracting (shortening) and relaxing (lengthening). Generally, muscles work together in opposing pairs.
  • Vertebrates have a closed circulatory system with a heart. Blood is completely contained within blood vessels that carry the blood throughout the body. The heart is divided into chambers that work together to pump blood. There are between two and four chambers in the vertebrate heart. With more chambers, there is more oxygen in the blood and more vigorous pumping action.
  • Most vertebrates have skin covered with scales, feathers, fur, or hair. These features serve a variety of functions, such as waterproofing and insulating the body.
  • Vertebrates have an excretory system that includes a pair of kidneys. Kidneys are organs that filter wastes from blood so they can be excreted from the body.
  • Vertebrates have an endocrine system of glands that secrete hormones. Hormones are chemical messengers that control many body functions.
  • Vertebrates have an adaptive immune system. The immune system is the organ system that defends the body from pathogens and other causes of disease. Being adaptive means that the immune system can learn to recognize specific pathogens. Then it can produce tailor-made chemicals called antibodies to attack them. This allows the immune system to launch a rapid attack whenever the pathogens invade the body again.
  • Vertebrates have a centralized nervous system. As shown in Figure below, the nervous system consists of a brain in the head region. It also includes a long spinal cord that runs from the brain to the tail end of the backbone. Long nerve fibers extend from the spinal cord to muscles and organs throughout the body.
19.1c

Nervous System (Human). The vertebrate nervous system includes a brain and spinal cord. It also includes a body-wide network of nerves, called peripheral nerves. They connect the spinal cord with the rest of the body.

Crash Course: The Nervous System

Vertebrate Reproduction

Vertebrates reproduce sexually, and almost all of them have separate male and female sexes. Generally, aquatic species have external fertilization, whereas terrestrial species have internal fertilization. Can you think of a reason why aquatic and terrestrial vertebrates differ in this way? Vertebrates have one of the following three reproductive strategies: ovipary, ovovivipary, or vivipary.

  • Ovipary refers to the development of an embryo within an egg outside the mother’s body. This occurs in most amphibians and reptiles and in all birds.
  • Ovovivipary refers to the development of an embryo inside an egg within the mother’s body until it hatches. 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 mother’s body. Birth may be followed by a period of parental care of the offspring. This reproductive strategy occurs in almost all mammals.

Vertebrate Classification

There are about 50,000 vertebrate species, and they are placed in nine different classes. Five of the classes are fish. The other classes are amphibians, reptiles, birds, and mammals. Table below lists some of the distinguishing traits of each class.

Class Distinguishing Traits Example
Hagfish They have a cranium but no backbone; they do not have jaws; their endoskeleton is made of cartilage; they are ectothermic.

hagfish

19.1d

Lampreys They have a partial backbone; they do not have jaws; their endoskeleton is made of cartilage; they are ectothermic.

lamprey

19.1e

Cartilaginous Fish They have a complete backbone; they have jaws; their endoskeleton is made of cartilage; they are ectothermic.

shark

19.1f

Ray-Finned Fish They have a backbone and jaws; their endoskeleton is made of bones; they have thin, bony fins; they are ectothermic.

perch

19.1g

Lobe-Finned Fish

They have a backbone and jaws; their endoskeleton is made of bones; they have thick, fleshy fins; they are ectothermic.

*Note: The coelacanth pictured to the right was believed to be extinct. Read a great article about how to use this fish as a witnessing tool to evolutionists:

http://creation.com/correcting-the-headline-coelacanth-yes-ancient-no

coelacanth

19.1h

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

19.1i

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

19.1j

Birds 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 covered with feathers; they have amniotic eggs; they are endothermic.

bird

19.1k

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 amniotic eggs; they have mammary (milk-producing) glands; they are endothermic.

bear

19.1l

 Creation Moments Minutes: Coelacanth

Lesson Summary

  • Vertebrates are a subphylum of chordates that have a vertebral column and an endoskeleton made of cartilage or bone. Vertebrates also have complex organ systems, including a closed circulatory system with a heart, an excretory system with a pair of kidneys, and an adaptive immune system.
  • Vertebrates reproduce sexually, and almost all have separate male and female sexes. Aquatic species generally have external fertilization, whereas terrestrial species usually have internal fertilization. Vertebrates have one of three reproductive strategies, known as ovipary, ovovivipary, or vivipary.
  • The 50,000 species of living vertebrates are placed in nine classes: hagfish, lampreys, cartilaginous fish, ray-finned fish, lobe-finned fish, amphibians, reptiles, birds, and mammals.

Lesson Review Questions

Recall

1. Describe the vertebrate vertebral column, and list its functions.

2. Contrast cartilage and bone, and state the advantages of a bony endoskeleton relative to a cartilaginous endoskeleton.

3. Identify the components of the vertebrate nervous system.

4. What is an adaptive immune system?

5. Define ovipary, ovovivipary, and vivipary. Which vertebrates use each type of reproductive strategy?

Reading Assignment

book

Read Chapter 9 from Evolution Exposed Biology

The Origin of Vertebrates

http://www.answersingenesis.org/articles/ee/origin-of-vertebrates

Previous: Echinoderms and Invertebrate Chordates

Next: Fish

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