Vertebrates - Advanced Douglas Wilkin, Ph.D. Jennifer Blanchette Niamh Gray-Wilson Jean Brainard, Ph.D. Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) AUTHORS Douglas Wilkin, Ph.D. To access a customizable version of this book, as well as other Jennifer Blanchette interactive content, visit www.ck12.org Niamh Gray-Wilson Jean Brainard, Ph.D. EDITOR Douglas Wilkin, Ph.D. CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-source, collaborative, and web-based compilation model, CK-12 pioneers and promotes the creation and distribution of high-quality, adaptive online textbooks that can be mixed, modified and printed (i.e., the FlexBook® textbooks). 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Printed: January 24, 2016 www.ck12.org Chapter 1. Vertebrates - Advanced CHAPTER 1 Vertebrates - Advanced CHAPTER OUTLINE 1.1 Chordates - Advanced 1.2 Chordate Classification - Advanced 1.3 Chordate Evolution - Advanced 1.4 Vertebrates - Advanced 1.5 Vertebrate Structure and Function - Advanced 1.6 Classification of Vertebrates - Advanced 1.7 Vertebrate Evolution - Advanced 1.8 Fish - Advanced 1.9 Fish Structure and Function - Advanced 1.10 Fish Reproduction - Advanced 1.11 Fish Classification - Advanced 1.12 Fish Evolution - Advanced 1.13 Fish Ecology - Advanced 1.14 Amphibians - Advanced 1.15 Amphibian Structure and Function - Advanced 1.16 Amphibian Reproduction - Advanced 1.17 Amphibian Classification - Advanced 1.18 Amphibian Evolution - Advanced 1.19 Amphibian Ecology - Advanced 1.20 Reptiles - Advanced 1.21 Reptile Structure and Function - Advanced 1.22 Reptile Reproduction - Advanced 1.23 Reptile Classification - Advanced 1.24 Crocidilia - Advanced 1.25 Sphenodontia - Advanced 1.26 Squamata - Advanced 1.27 Snakes - Advanced 1.28 Testudines - Advanced 1.29 Reptile Evolution - Advanced 1.30 Reptile Ecology - Advanced 1.31 Birds - Advanced 1.32 Bird Structure and Function - Advanced 1.33 Bird Reproduction - Advanced 1 www.ck12.org 1.34 Bird Classification - Advanced 1.35 Bird Evolution - Advanced 1.36 Bird Ecology - Advanced 1.37 Importance of Birds - Advanced 1.38 Mammals - Advanced 1.39 Endothermy in Mammals - Advanced 1.40 Mammal Structure and Function - Advanced 1.41 Locomotion in Mammals - Advanced 1.42 Placental Mammals - Advanced 1.43 Marsupials - Advanced 1.44 Monotremes - Advanced 1.45 Ancestors of Mammals - Advanced 1.46 Evolution of Mammals - Advanced 1.47 Classification of Mammals - Advanced 1.48 References Introduction You might think something so pretty and colorful would be female. Guess what? This stunning bird obviously is a peacock. Do you know why he is spreading out his big, colorful tail feathers like a fan? He is trying to attract a female for mating. Both the feathers and the behavior evolved because they increase the chances that males of the species will reproduce and pass their genes to the next generation. Many other vertebrates have similar behaviors for attracting mates. Even fish display some remarkably sophisticated mating behaviors. 2 www.ck12.org Chapter 1. Vertebrates - Advanced Fish and birds are both vertebrates. Vertebrates are a diverse and fascinating group of animals. In many ways, they are very different from the invertebrates described in the previous chapter. Elaborate mating behaviors are just one way they differ. These concepts describe many other differences between vertebrates and invertebrates. It also describes in detail the classes of vertebrates, from fish to birds. 3 1.1. Chordates - Advanced www.ck12.org 1.1 Chordates - Advanced • Discuss the major characteristics of chordates, especially those that distinguish chordates from other phyla. What’s a chordate? Most chordates are animals with backbones. These range from small fish to giant whales and from playful dogs to ferocious cats. They are not nearly as diverse as the invertebrates. But chordates do have many amazing species. The white tiger (Panthera tigris) is a chordate. The tiger is also from the class Mammalia, order Carnivora, and family Felidae, meaning it is a meat-eating cat. 4 www.ck12.org Chapter 1. Vertebrates - Advanced Characteristics of Chordates The animal phylum Chordata includes the animals that we are by far the most familiar with: ourselves! We and all other chordate species, including some quite primitive looking organisms, share several important features that indicate our close evolutionary relationships. All of the phyla we have studied so far have consisted entirely of invertebrate animals. The phylum Chordata includes both nonvertebrate and vertebrate groups. Some groups within the chordates are considered to be very “young” compared to other chordates and to many of the phyla that we have discussed in previous chapters. Birds, for example, have only been around for about 146 million years. Compare that to some arthropods, such as horseshoe crabs, that have existed in basically the same form for over 500 million years. In this lesson we will examine the specific features that define chordates. We will then consider the different taxonomic groups within the phylum and how they evolved, keeping an emphasis on the nonvertebrate chordates. Chordata is a large and diverse phylum that includes roughly 60,000 species. The examples of chordate species shown in the Figure 1.1 illustrate their diversity and vast range in size. Chordates can be anywhere from about one cm (the width of your index finger) to over 30 meters. FIGURE 1.1 Different species of chordates, illustrating their diversity and vast range in size. (a) A tunicate, approximately one inch in length. Notice the tiny fish (also a chordate) swimming in front of the tunicate. (b) A white rhinoceros, approximately 6600 pounds (3000 kg). (c) A kangaroo and joey. (d) A great white shark. (e) A double-crested cormorant bird species. (f) A blue whale. Tunicates, for example, are small marine invertebrate members of the phylum that are generally one to a few centimeters long. In contrast, some mammalian species can be quite large, either in length (for example, blue whales can extend up to 30 meters in length) or in weight and girth (such as elephants, which can weigh up to roughly 20,000 lbs). Chordates can be found all over the planet, with species inhabiting marine, freshwater, terrestrial, and aerial environments. They are found from the equator to the poles and everywhere in between. Members of the phylum Chordata share the following characteristics (those traits specific to the phylum Chordata will be in bold): • Three germ layers (triploblasts). • Bilateral symmetry. • Segmented body. • Coelom. • Complete digestive system. • Closed circulatory system. • Centralized nervous system. • Tail (post-anal). • Notochord. • Nerve cord. • Pharyngeal slits. 5 1.1. Chordates - Advanced www.ck12.org As you read this list, you may be thinking, “humans don’t have tails or slits in their pharynx!” But, in fact, we do. Actually, to be more precise, we did. All chordates possess a tail and pharyngeal slits at some point in their lives, and humans are no exception. Early on in human development, the embryo has both a tail and pharyngeal slits, both of which are lost during the course of development. A human embryo with a prominent tail is shown in the Figure 1.2. FIGURE 1.2 A five-week old (gestational age), ectopic human embryo. Notice the prominent tail that extends beyond the anal region. This embryo is ectopic, meaning it did not successfully implant within the uterine cavity. This complication is almost always fatal to the embryo and is often dangerous to the mother. Chordates, like species in several other phyla such as annelids and arthropods, are bilaterally symmetrical triploblasts. You will recall that bilaterally symmetrical animals can be divided into two equal, mirror-image halves when cut down the middle of the anterior-posterior (front-back) axis. Triploblasts are organisms that develop from three basic cell layers, called germ layers, in the embryo, which are called the endoderm, the mesoderm, and the ectoderm. The endoderm forms the gut of the animal, the ectoderm forms the outer surface and the nervous system, and the mesoderm forms the coelom and many of the internal organs including the muscles and circulatory system. Like the annelids and arthropods, most chordates have at least partially segmented bodies. The segments are often highly specialized into distinct body regions and do not resemble the repeating segments of annelids. In addition, chordates are deuterostomes, meaning that they have a coelom (fluid-filled body cavity) that arises from internalized pouches of tissue in the developing embryo and an anus that is formed from the embryonic blastopore. Chordate species have a complete digestive system, and most species also have a closed circulatory system that relies on a ventral (located on the bottom side of the organism’s interior) heart to pump blood throughout the body in enclosed blood vessels.