Category Environtal Studies

          It is likely that birds evolved from reptiles. Like reptiles but unlike most mammals, they lay eggs that hatch outside the mother. All adult birds have feathers, rather than fur or scales, and most can fly. However, birds are similar to mammals in being warsm blooded.

          When one thinks of the differences between mammals and birds, the first thing that comes to mind is that mammals give birth to their young whereas birds lay eggs. Now let us look at other differences between mammals and birds. The birds have feathers whereas mammals have only fur or hair. This feature is one of the main features of birds that differentiate them from mammals. Birds use feathers for controlling body temperature, flying, and attracting the opposite sex.

          As birds need to fly, they have porous or hollow bones. In contrast, mammals have denser bones. Birds have wings although mammals have paws, hands, and hooves. There is also a difference in the feeding of the young. Mammals feed their young milk produced by the mammary glands. On the other hand, young birds are fed by the parents regurgitating partially digested food.

          Birds and mammals have a larynx. The mammals produce sounds using the larynx. In birds, this organ does not produce sounds. Instead of using the larynx for sound, birds have a syrinx which serves as a voice box. The lungs of birds do not expand or contract as that of the lungs of mammals. In mammals, the oxygen and carbon dioxide is exchanged in the alveoli which are microscopic sacs in the lungs. In birds, the exchange happens in air capillaries which are walls of microscopic tubules. While there is only a single respiratory cycle in mammals, there are two cycles in birds.

          Now comparing the blood, birds have a nucleus in the RBS whereas it is not generally seen in mammals. If there is a nucleus in the RBS in mammals, then it is a sign of sickness. The RBS of birds are oval in shape whereas most of the mammals’ RBSs have a round shape.

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          The chameleon is able to change colour to match its surroundings by releasing or tightening special cells on its skin. As well as this remarkable ability, chameleons are amazing in other ways. They are able to grip very strongly with their toes and tails to balance on precarious branches. Their extraordinary tongues, which are able to shoot out as far as the chameleon’s body length, are sticky and able to scoop back prey like a piece of elastic. Finally, the chameleon’s eyes are bulging and can move in any direction, protected by an eyelid that is fused all-round the eye, leaving only a tiny hole in the middle. Even stranger, the chameleon can move each of its eyes in a different direction at the same time!

          Chameleons are famous for their quick color-changing abilities. It’s a common misconception that they do this to camouflage themselves against a background. In fact, chameleons mostly change color to regulate their temperatures or to signal their intentions to other chameleons. Since chameleons can’t generate their own body heat, changing the color of their skin is a way to maintain a favorable body temperature. A cold chameleon may become dark to absorb more heat, whereas a hotter chameleon may turn pale to reflect the sun’s heat.

          Chameleons will also use bold color changes to communicate. Males become bright to signal their dominance and turn dark in aggressive encounters. Females can let males know if they’re willing to mate by changing the color of their skin. Owners of chameleons can learn to read their pet’s mood based on the color of its skin.

          So how do they pull off these colorful changes? The outermost layer of the chameleon’s skin is transparent. Beneath this are several more layers of skin that contain specialized cells called chromatophores. The chromatophores at each level are filled with sacs of different kinds of pigment. The deepest layer contains melanophores, which are filled with brown melanin (the same pigment that gives human skin its many shades). Atop that layer are cells called iridophores, which have a blue pigment that reflects blue and white light. Layered on top of those cells are the xanthophores and erythrophores, which contain yellow and red pigments, respectively.

          Normally, the pigments are locked away inside tiny sacs within the cells. But when a chameleon experiences changes in body temperature or mood, its nervous system tells specific chromatophores to expand or contract. This changes the color of the cell. By varying the activity of the different chromatophores in all the layers of the skin, the chameleon can produce a whole variety of colors and patterns.

          For instance, an excited chameleon might turn red by fully expanding all his erythrophores, blocking out the other colors beneath them. A calm chameleon, on the other hand, might turn green by contracting his erythrophores and allowing some of the blue-reflected light from his iridophores to mix with his layer of somewhat contracted yellow xanthophores.

          With these layers of cells, some chameleons are capable of producing a dazzling array of reds, pinks, yellows, blues, greens, and browns. These bold statements won’t help them blend into the background, but they will allow them to get their message across to other chameleons loud and clear.

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          Both crocodiles and alligators spend most of their lives in swamps and rivers in warm climates, although they breathe air through nostrils on the top of their snouts, closing these off when they dive. Caymans and gavials are relatives of crocodiles and alligators. The simple way of telling them apart is that crocodiles show the fourth tooth in their lower jaw when their mouths are closed, while alligators do not. It is probably not wise to go near enough to a live crocodilian to find out, however, as they have been known to attack humans!

          Coming face to face with a crocodile or an alligator, you’d see a mouth full of serrated teeth that would likely scare the bejeezus out of you. The two reptile groups are close relatives, so their physical similarities are expected. Upon closer inspection, not recommended out in the wild, you’d spot glaring differences:

          Snout shape: Alligators have wider, U-shaped snouts, while crocodile front ends are more pointed and V-shaped. Toothy grin: When their snouts are shut, crocodiles look like they’re flashing a toothy grin, as the fourth tooth on each side of the lower jaw sticks up over the upper lip. For alligators, the upper jaw is wider than the lower one, so when they close their mouths, all their teeth are hidden.

          Home base: Crocodiles tend to live in saltwater habitats, while alligators hang out in freshwater marshes and lakes. They belong to the subgroup Eusuchia, which includes about 22 species divided into three families: the fish-eating gavials or gharials, which belong to the Gavialidae; today’s crocodiles or the Crocodylidae; and the Alligatoridae, or alligators. Eusuchians appeared on the scene during the late Cretaceous some 100 million or so years ago.

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          Reptiles are cold blooded, so must gain warmth from their surroundings. This means that they can be found anywhere except in the very coldest regions of the Earth. Those that live in cooler areas usually spend the winter hibernating. Most reptiles lay eggs with hard or leathery shells. Their young hatch into miniature versions of their parents, but as reptiles can continue to grow after they are mature, some reach an enormous size.

          The term “reptile” is derived from a Latin word meaning “creeping animals.” These animals include snakes, lizards, crocodiles, caimans, alligators, turtles, geckos, and chameleons, with lizards and snakes species making up the majority of all reptiles. Reptiles are cold-blooded animals which mean they are unable to regulate their own body temperature. The first reptiles evolved approximately 320 million years ago from the advanced four-limbed vertebrates known as reptiliomorph. These early reptiles became adapted to life on dry land. Reptiles have diverse ways of defending themselves from danger including biting, hissing, camouflaging, and avoidance. This article focuses on some of the most outstanding characteristics of reptiles.

          Most reptiles reproduce sexually while others are capable of reproducing asexually. The reproduction activities take place through the cloaca located at the base of the tail. Copulatory organs can be seen in most reptiles which are often stored inside their bodies. Male turtles and crocodiles have a penis while lizards and snakes have a pair of hemipenes. Other species like the tuatara do not have copulatory organs hence mating is through the pressing together of the cloaca. After successful copulation, the female reptile lays eggs which are covered with a shell. The eggshell protects and keeps the embryo from drying out and allows for the exchange of gasses. The egg contains chorion which aids in gaseous exchange, the albumen which is a reservoir for protein and water, and the amniotic fluid which protects embryo and aids in osmoregulation. Some reptiles incubate the eggs by laying on them while others bury them in the sand until they hatch.

          Most reptiles are cold-blooded vertebrates. They do not have the psychological means of regulating their body temperatures and have to depend on the external environment. Other species exhibit a mix of ectothermy, poikilothermy, and brandymetabolism. Reptiles often bask in the sun or hibernate during cold seasons to raise their body temperatures. When the sun is too hot, they will retreat to shady areas or inside the water to cool or lower their body temperatures. Because reptiles have unstable body temperature, their metabolism requires enzymes that are capable of maintaining efficiency over a range of temperatures. It is assumed that reptiles cannot produce enough energy required for long-distance chase like the warm-blooded animals. However, it remains unclear as to whether their cold-bloodedness is as a result of their ecology or not.

          Reptiles have either four legs, or some like snakes, are descendants of four-limbed ancestors. In most snakes, all traces of legs including bones for the legs have disappeared. However, they still remain successful predators even without the legs. Snakes have three ways of moving on land; straight crawling, lateral undulating, and sidewinding. Although lizards have four limbs, most lizards have an alternating gait which limits their endurance. The tail of some lizards is prehensile and can assist them in climbing. Some reptiles like crocodiles have claws on their feet. These claws assist in movement and hunting.

          Reptiles exhibit similar characteristics of other vertebrates like mammals, birds, and some amphibians. They have backbones that house the spinal cords that run the length of their bodies. Reptiles also have chains of bony elements from the tail to the head. The bony endoskeleton consists of cranium or skull, appendages, and limb girdles. The endoskeleton protects the inner tissue and also aids in body movement. Skeletons differ from one species to another, with crocodiles having some of the largest body structures in this class.

There are four orders of reptile, by far the largest of which is the order of lizards and snakes. There are nearly 6000 different species of these. The other orders are much smaller. There are about 200 species of turtles, tortoises and terrapins, and only just over 20 species of crocodiles and alligators. Rarest of all is the tuatara, which forms an order all by itself.

Reptiles are tetrapod animals belonging to the class Reptilia, which includes turtles, snakes, crocodilians, tuatara, lizards, and amphisbaenians. Reptiles likely originated more than 312 million years ago, when the first species evolved from the advanced reptiliomorph tetrapods. Today, animals belonging to class reptilian range in size from tiny geckos to huge saltwater crocodiles that measure more than 19 feet in length. There are approximately 10,700 extant reptile species.

The Reptile Database is a database that lists all living reptiles and their classifications. It also contains images for most reptiles on the list. There are more than 10,700 extant species of reptiles recorded in the Reptile Database, making reptiles one of the most diverse types of vertebrates in the world. Compared to other species, only birds and fish have more types of species than reptiles. Additionally, there are approximately 5,000 and 7,000 species of mammals and amphibians, respectively.

Reptiles form part of the domain Eukaryote, which consists of organisms that have a nucleus within membranes. They are also included in the kingdom Animalia, which are organisms that ingest food and are multicellular. Reptiles are further classified as Chordate because of the presence of a spinal cord running the length of their back. As Chordate with backbones, they belong to subphylum Vertebrata and class Reptilian. There are four major groups of reptiles: Crocodilian, Squamata, Sphenodonita, and Testudines.

Crocodilia

The order Crocodilian is a subclass of Archosauria and contains some of the largest reptiles including crocodiles, caimans, alligators, and gavials. Reptiles in this order are mainly carnivores and typically inhabit tropical and subtropical rivers, swamps, and streams. They have strong jaws which facilitate a powerful bite, advanced brains, and greater intelligence than other reptiles.

Squamata

The Squamata order contains terrestrial reptiles such as snakes and lizards. There are approximately 3,750 species of lizards and 3,000 species of snakes. These animals have the ability to crawl or creep using their abdomen. They possess skin covered with horny scales that are periodically shed. Although snakes do not have legs, they evolved from four-legged ancestors.

Sphenodontia

Sphenodotia is the least specialized group of reptiles, with brains similar to those of amphibians. The best-known sphenodontite is the tuatara, which is a species that has a wedge-like skull with primitive eyes and socketless teeth. The lizard-like creature lives primarily in New Zealand.

Testudines

There are approximately 250 species belonging to the order Testudines, which are primarily turtles and tortoises. The species are four-legged and have a hard shell covering most parts of the body. They are mainly aquatic and are the oldest living reptiles in the world.

          Amphibians have a wide range of ways of protecting themselves. Some brightly coloured amphibians produce poisons in glands on their skins. The bright colours warn birds and animals not to attempt to eat them. Others use camouflage, blending with their surroundings, to prevent enemies from spotting them. Some frogs and toads puff themselves up or stand on tiptoes to look larger than they really are!

          Frogs, salamanders, snakes, and other herps are often small and live on the ground or in the water. Because of these characteristics, they are vulnerable to being preyed on by all kinds of carnivorous animals. In order to avoid being eaten, herps use a variety of strategies and protective mechanisms. As a first line of defense, most herps try to avoid being seen by their predators. Many are nocturnal and use the cover of darkness to avoid notice. During the day, most herps tend to remain hidden beneath dead leaves, rocks, and logs, or in underground burrows.

          Herps also avoid confrontation through camouflage. Using a variety of grays, greens, and browns, these animals can blend remarkably well into the background of their natural environment. It is amazing how difficult it is to see a smooth green snake that is moving through the grass!

          Countershading is an interesting form of camouflage for herps that live in the water. Many turtles, frogs, and salamanders have light colors on their bellies and dark colors on their backs. This color pattern makes them less visible to aquatic predators that see them against a light sky. Birds and other predators hunting from above also have a hard time spotting them against the dark water. Even some of the larger predators, such as snapping turtles and alligators, have countershading, perhaps to be less visible when stalking their prey.

          A lot of species use spots, stripes, and blotches to break up the outline of their bodies when viewed against leaves or soil. The distinctive “x” on the back of the spring peeper is an example of a mark that allows this frog to virtually disappear when on the ground or perched on a blade of grass. Unlike animals that use camouflage, the colors of these animals do not necessarily blend with the background. In fact, many times the markings are quite bright and even gaudy. The eyes of the predator, however, are tricked into thinking the shape they are seeing is not an animal.

          Some herps do not avoid or hide from predators, but instead frighten them off by displaying warning signs. For example, toads and newts have glands in their skin that produce toxins. In order for this toxicity to protect an animal from being eaten, the predators must be reminded that they are about to eat something that will make them sick. A common method of alerting a predator is by being very brightly colored. This explains why the young newts, or efts, that we see walking around the forest are bright orange and yellow. Their color is a vivid advertisement of their toxicity. Other common examples of this aposematic, or warning, coloration are the brightly banded, venomous coralsnakes and the very decorative, poison dart frogs of Central America.

          Interestingly, a herp truly may be poisonous or it may be just bluffing. Some harmless herps have adapted their appearance to mimic that of a more poisonous relative. In this way, they take advantage of markings that bring back unpleasant memories for predators. Such mimicry may protect the brightly colored, red-backed salamander from would-be predators, even though it is not toxic like the similarly colored eastern newt. Some snakes also mimic their poisonous relatives as a means of defense. The nonpoisonous scarlet king snake looks remarkably like the venomous coral snake, both of which are found in the same region.

          Finally, many herps scare off potential predators with threatening postures orbehaviors. Snapping turtles, when encountered on land, can be very aggressive, snapping their jaws and lunging. Probably the most notorious warning among herps is the very d a nearby rattlesnake is enough to make most animals halt in their tracks and mistinctive and chilling sound of a rattlesnake’s tail. The mere suggestion of ake a hasty retreat. Some snakes will rise up as if poised to strike an attacker. This act also has the advantage of making them appear larger and perhaps more threatening.

          The hog-nosed snake, a common resident of the coastal plain, uses a complicated set of behaviors when it is attacked. It first elevates its head and spreads out the skin of its neck in an effort to look bigger and more threatening. If this doesn’t scare off a predator, the hog-nosed snake begins to writhe upside down. It then regurgitates a foul smelling liquid and finally becomes rigid. It holds this position for several minutes, until the predator becomes disinterested and moves off.