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Anatomy of Animals

Chordates :

Fishes, Amphibians, Reptiles, Birds, Mammals, Primates

    Among the chordates are those animals with which we are most familiar, including human beings. Figure 19a shows all the animal classes with indicators about added features. All members of this phylum are observed to have the following three basic characteristics at some time in their life history.

  1. A dorsal supporting rod called a notochord, which is replaced by the vertebral column in the adult vertebrates.
  2. A dorsal hollow nerve cord, in contrast to invertebrates, which have a ventral solid nerve cord. By hollow, it is meant that the cord contains a canal that is filled with fluid.
  3. Pharangeal pouches or gill clefts (slits), which are seen only during embryological development in most vertebrate groups, although they persist in adult fishes. Water passing into the mouth and the pharynx goes through the gill slits, which are supported by gill bars and used for gas exchange.
The tunicates and lancelets sometimes are called the protochordates (Figure 19b) because they possess all three typical chordate structures in either the larval and/or adult forms, as did the first chordates to evolve. These two groups of animals link the vertebrates to the rest of the invertebrates and show how modestly the chordates most likely began. A tunicate, or sea squirt, appears to be a thick-walled, squat sac with two openings. Inside the central cavity of the animal are numerous gill slits,
Vertebrates Protochordates the only chordate feature retained by the adult. The larva of the tunicate, however, has a tadpole shape and possesses the three chordate characteristics. It has been suggested that such a larva may have become sexually mature without developing the other adult tunicate characteristics, and may have evolved into a fishlike vertebrate similar to the lancelet, which is a chordate that shows the three chordate characteristics as an adult.

Figure 19a Vertebrates
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Figure 19b Protochordates
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    There are three classes of fishes (Figure 21a):

  1. Jawless fishes - They are cylindrical, up to a meter long, with smooth, scaleless skin and no jaws or paired fins. There are two families of jawless fishes, e.g., the hagfishes are scavengers, feeding mainly on dead fishes, while some lampreys are parasitic.
  2. Cartilaginous fishes - They are the sharks, the rays, and the skates, which have skeletons of cartilage instead of bone.
  3. Bony fishes - They are by far the most numerous and varied of the fishes. Most of these fishes, such as the grouper in Figure 21a, are a type of bony fish called ray-finned fishes. They have a swim bladder that aids them in changing their depth in the water. The swim bladder seems to have evolved from a primitive lung, some fishes such as bowfins, gars and bichirs, still use it for breathing. Perhaps it forked in evolution and went two ways - one carried its old breathing function out onto the land, and the other had been modified to form the swim bladder. Species of fish that do not possess a swim bladder sink to the bottom if they stop swimming. "Ray-finned" refers to the fact that the fins are thin and are supported by bony rays. Another type of bony fish, called the lob-finned fishes, evolved into the amphibians. These fishes not only have fleshy appendages that could be adapted to land locomotion, they also have a lung that is used for respiration. The coelacanth and shark in Figure 21a are the "living fossil" among the fishes. They are species that have defied the evolutionary odds to survive virtually unchanged for tens or hundreds of millions of years. Other examples with such distinction are shown in Figure 21b. Figure 21a also includes a fish squirting a shot at the cricket (see a video).
  4. Fishes Living Fossils Frilled Shark Meanwhile in 2015, a frilled shark believed to be around in the Cretaceous Period about 80 million years ago is caught off South West Australia. This 6-foot-long fish has 300 teeth in 25 rows (Figure 21c).

    Figure 21a Fishes
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    Figure 21b Living Fossils [view large image]

    Figure 21c Frilled Shark
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The living amphibians include frogs, toads, newts, and salamanders (see Figure 23). The frog will be used for the study of amphibian anatomy (Figure 24a) below.



The reptiles living today are turtles, alligators, snakes, and lizards (see Figure 24c). Reptiles with limbs, such as lizards, are able to lift their body off the ground, and the body is covered with hard, horny scales that protect the animal from desication and from predators. Both of these features are adaptations to life on land. The anatomy of lizard is illustrated in Figure 24d.



Birds Birds are characterized by the presence of feathers, which are actually modified reptilian scales. There are many orders of birds, including birds that are flightless (ostrich), web footed (penguin), divers (loons), fish eaters (pelicans), waders (flamingos), broad billed (ducks), birds of prey (hawks), vegetarians (fowl), shorebirds (sandpipers), nocturnal (owl), small (hummingbirds), and songbirds, the most familiar of the birds. Some of them are showed in Figure 25a. Nearly every anatomical feature of a bird can be related to its ability to fly. Figure 26a shows the anatomy of a common bird.

Figure 25a Birds
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Mammals The chief characteristics of mammals are hair and mammary glands that produce milk to nourish the young. Human mammary glands are called breasts. Mammals are classified according to their means of reproduction: there are egg-laying mammals called monotremes such as the duck-billed platypus; mammals with pouches for immature embryos are the marsupials such as the kangaroos; while the placental mammals are the majority of living mammals. Figure 27a shows just a few of these animals. Table 03 lists the 18 orders of living placental mammals. They are classified largely according to the mode of locomotion and how they get their food. Figure 28 illustrates a cat's anatomy, which is very similar to the human's. See "Age of Animals" for "mammal characteristics and comparison with other vertebrates".

Figure 27a Mammals
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Order Examples Characteristics
Anteater, armadillo, sloth Primitive terrestrial mammal; few or no teeth; well developed claws
Pholidota Pangolin Medium size; large, plate-like scales; lack teeth, use powerful front claws and long tongues to reach ants or termite
Lagomorpha Rabbit, hare, pika Chisel-like incisors; hind legs longer than front legs; herbivorous
Rodentia Mouse, rat, squirrel, beaver, porcupine Incisor teeth grow continuously
Macroscelidea Elephant Shrew African species of shrew-like creatures with long nose
Primates Lemur, monkey, gibbon, chimpanzee, gorilla Mostly tree dwelling; head freely movable on neck; 5 digits, usually with nails; thumbs and/or large toes usually opposable
Dermoptera Flying Lemur With "wings of skin" to support gliding, under-developed new born
Scandentia Tree Shrew High brain/body mass ratio, live in trees, under-developed new born
Chiroptera Bat Digits support membranous wings
Mole, shrew Primitive; small, sharp-pointed teeth
Carnivora Dog, bear, cat, sea lion Long canine teeth; pointed teeth
Artiodactyla Pig, camel, buffalo, giraffe Medium to large; 2/4 toes, each with hoof; many with antlers/horns
Cetacea Whale, porpoise Medium to very large; paddlelike forelimbs; hind limbs absent
Tubulidentata Aardvark Pig-like animal with powerful claws & long tongue for eating termites
Perissodactyla Horse, zebra, tapir, rhinocerose Large, long-legged, one or 3 toes, each with hoof; grinding teeth
Hyracoidea Hyrax Plant-eating with short ears and has toenails resembling hooves
Proboscidea Elephant Large size with trunk, pillow-like limbs, broad and padded foot
Sirenia Manatee Slow moving aquatic mammals with flippers, flattened tail, no legs

Table 03 The 18 Orders of Placental Mammals



Primates Humans are mammals in the order Primates. The first primates may have resembled today's tree shrews, rat-size animals with a snout, claws, and sharp front teeth. By 50 million years ago, however, primates had evolved characteristics suitable to move freely through the trees. The first primates were prosimians (meaning "premonkeys"). They are represented today by several types of animals, including the lemurs. Monkeys, along with apes and humans, are anthropoids. Monkeys evolved from the prosimians about 38 million years ago, when the weather was warm and vegetation was like that of a tropical rain forest. There are two types of monkeys: the New World (South America) monkeys such as the spider monkeys, which have long grasping tails and flat noses, and the Old World (Africa) monkeys such as the baboons, which are now ground dwellers and lack such tails. Ape (gibbon, gorilla, and chimpanzee) evolved later. The human lineage split from that of the apes occurred about 5 - 10 million years ago in Africa. Figure 29 shows some of the primates. Figure 30 illustrates the chimpanzee anatomy, which is virtually identical to the human's.

Figure 29 Primates
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