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“Vertebrates: Amazing Animals” Humans have many of the same kinds of bones that Dinosaurs had many years ago but human bones are just smaller. Your backbone is very much like the one in a dinosaur skeleton. Animals with a backbone are called vertebrates. They belong to the phylum Chordata. Most chordates are vertebrates. Their backbones are segmented into columns of bones called vertebrae. The skeletons of all vertebrate embryos are made of cartilage. But as we grow, the cartilage is replaced by bone. Only four to five percent of animals are chordates. Some examples of vertebrates include: fish, amphibians, reptiles, mammals, and birds. Vertebrates such as birds and mammals are able to warm their bodies by capturing energy released by the chemical reactions in their cells. Because of this unique feature, they are able to maintain a constant body temperature even if the temperature of the environment changes. For this reason they are called endotherms (--or warm-blooded animals). Reptiles, Fish, and Amphibians are ectotherms or cold-blooded animals These are vertebrates that can not control their body temperature. Instead it rises and falls with the temperature of their environment. As they become warm they become more active and are able to hunt for food or even escape predators. Fish live in nearly every single aquatic habitat imaginable They “are the most numerous” of all vertebrates. Fish are aquatic vertebrates characterized by having fins, scales, and gills. They were the first vertebrates to “evolve”. Fish take in oxygen rich water through gills and remove oxygen poor water through gill slits. ALL fish have a closed circulatory system, a four chambered heart, and a swim bladder that controls buoyancy. Most are egg laying and move by contracting opposite muscles. (cartilaginous fish do not have a swim bladder). Three Adaptive features of some fish: 1) fish are able to float because they have a “swim bladder”. It traps gas inside their body in order to regulate their vertical position and help them float. 2) They have the ability to swim. A streamlined shape and muscular tail enables them to move rapidly through the water; pairs of fins allow them to maneuver easily left or right, up or down, and backward and forward. 3) They have a Lateral line system: consists of a row of sensory structures that run the length of the body and connected by nerves to the brain. This allows them to detect vibrations in the water. There are 3 existing classes of fish today: Jawless Fish, Cartilaginous Fish, and Bony Fish. Jawless Fish were the “first fish”. They have mouths with soft tissue and no “true teeth” Jawless fish are eel-like, and have smooth, slimy skin, and a round “jawless” mouth. These fish have a skull, brain, and eyes but they do not have a lateral line system. Examples include: lampreys, and hagfish. Lampreys are - free living or parasitic; mouths are adapted for sucking blood and body fluids of other fish, do not have a stomach: esophagus, or a straight intestine. Hagfish technically, DO NOT HAVE a backbone like other vertebrates. BUT they are classified in this group because they do have a skull just like the other vertebrates do. They are bottom dwellers in cold marine waters and scavengers of dead and dying fish on ocean bottom. They feed by sawing the fish with its “toothed tongue” from the inside out – Yuck!! They are extremely flexible so they can avoid capture or to clean the slime off after self-defense secretions. When not feeding they remain hidden in burrows on the ocean floor. Cartilaginous Fish have skeletons that consist entirely of cartilage, not bone. They are “ectotherms” that have movable jaws and skeletons with paired fins. Examples include sharks, skates, and rays. Sharks are scavengers that eat injured fish, garbage and other waste from ships as well as animals such as seals, turtles, birds, whales, crabs, and a wide range of fish. The shark’s mouth has 6 to 20 rows of backward-pointing teeth. They can detect blood from an injured animal as far as 500 miles away. They swim with a side-to-side motion of their asymmetric tail fins. Sharks are covered with small triangular teeth-like “denticles”. They feel like sand paper. If you rub your hand in the opposite direction (back to front) it can cut your hand very badly!! Rays and Skates are also examples of cartilaginous fish. Skates are a family of “ectothermic” flat-bodied rays found in warm and temperate seas. They have eyes located on the upper surface of the body while the mouth and gills are located on the lower surface. Their color makes them almost invisible because when another animal looks down on them, they are camouflaged with the darkness of the sea bottom. When looked up from underneath, the animal is camouflaged with the light from the sun. Boney Fish include goldfish, trout, catfish, tuna, and cod. Unlike cartilage fish, bony fish can float because they have a swim bladder which traps oxygen and other gases in the blood stream. This also allows them to remain still or float in water for long periods of time. Amphibians are an interesting group of vertebrates. The word "Amphibian" comes from the Greek word meaning ”double life". Amphibians can live in water and on land (have a “double life”). Scientists think that amphibians evolved from bony fish particularly the “Lobe-finned fish”. Amphibians are “ectotherms”. They have moist, smooth, thin skin with no scales. This is an advantage when absorbing water through their skin and keeping it moist. Their feet are webbed and their toes lack claws. They use gills, lungs, skin, and mouth cavities for breathing. Amphibians have many prominent characteristics that are adaptations to a life spent both on land and in water: 1) They change from an aquatic larval stage to a terrestrial adult form. This transformation is called metamorphosis. 2) Their Larvae (babies) have a two-chambered heart; adults have a three-chambered heart and a well-developed closed circulatory system. 3) Amphibians enter a state of dormancy when conditions are unfavorable. They often bury themselves in mud or leaves, emerging when conditions are better. Such inactivity is called “hibernation” when it occurs in the winter and “estivation” when it occurs in the summer. Their eggs lack shells so they are usually laid in water or in a moist environment and fertilized externally. Their eggs are called “larvae”. Biologists have identified about 2,375 living species of amphibians and have classified them into four groups: “Frogs & Toads”, “Salamanders”, “Mud Eels and sirens”, and “Caecilians”. Frogs and toads do not have tails. There are about 3,500 known species of frogs and 300 kinds of toads. They are found on every continent except Antarctica. Some types spend their entire life in or near water, but others live mainly on land and come to the water only to mate. Some frogs and toads are climbers that dwell in trees or burrowers that live underground. Frogs and Toads are different, because toads have dry, warty skin, while frogs have smooth, wet skin. They are similar because both frogs and toads both return to water to reproduce. In nearly all species eggs are fertilized externally. The fertilized eggs hatch into swimming larval forms called “tadpoles”. Salamanders and other amphibians with legs and tails make up the group of "visible tail” amphibians. Salamanders, have elongated bodies, long tails, and smooth, moist skin. Salamanders are less able to remain on dry land, although some can live in dry areas by remaining inactive during the day. Some aquatic species (mud eels & sirens) are referred to as "rough mouthed” amphibians. Caecilians are highly specialized tropical, burrowing worm-like amphibians that are often legless creatures. The caecilian male deposits sperm directly into the female, and the female bears live young. This is called internal fertilization.