Diversity of Vertebrate Animals

Transcription

1 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 Anus 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. Digestive track Notochord Heart Gill slits Brain Mouth Vertebrate Diversity Page - vd-1

2 Paleozoic Fishes Amphibians 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 mya Cenozoic 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. Mesozoic Reptiles Mammals Birds Precambrian 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. Vertebrate Diversity Page - vd-2

3 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 CO 2. (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. Vertebrate Diversity Page - vd-3

4 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 leglike 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. Vertebrate Diversity Page - vd-4

5 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 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. Vertebrate Diversity Page - vd-5

6 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. Vertebrate Diversity Page - vd-6

7 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." Formatted: Font: Not Bold 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. Vertebrate Diversity Page - vd-7

8 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). Vertebrate Diversity Page - vd-8

9 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? Vertebrate Diversity Page - vd-9

10 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? Vertebrate Diversity Page - vd-10

11 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? Vertebrate Diversity Page - vd-11

12 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: In this magnification of a feather, identify and label the shaft, barbs and barbules 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: 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. Vertebrate Diversity Page - vd-12

13 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. Vertebrate Diversity Page - vd-13

14 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. Table 1. At maturity, breathe through: Class Fish Amphibians Reptiles Birds Mammals Gills Skin Lungs 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? Table 2. Body covering of: Class Fish Amphibians Reptiles Birds Mammals Bony Scales Naked Skin Scales Feathers Hair Table 3. Reproduction through: 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? Class Fish Amphibians Reptiles Birds Mammals Naked eggs Shelled eggs Table 4. Types of appendages: Internal D. Summarize changes in appendages in Table 4. (Place an X in each appropriate box.) Class Fish Amphibians Vertebrate Diversity Reptiles Page - vd-14 Birds Mammals Fins Legs Wings

15 6) What traits do bats possess and not possess that indicate that they are mammals and not birds? Vertebrate Diversity Page - vd-15