Chapter 28 Section 1-Reptiles Section 2-Birds Section 3-Mammals Section 4-Mammalian Adaptations
Reptiles have skin that is dry and covered with tough, hard, platelike scales. This skin forms a barrier to water loss in land environments. • Reptilian skin is resistant to water loss because it contains large amounts of lipids and the protein keratin. • Keratin is the tough, wear-resistant material that composes your hair, fingernails and the feathers of birds. • The scales do not contain bone (like fish), but some reptiles develop thick bony plates beneath the scales, such as those that form the shell of turtles.
Reptiles lay amniotic eggs that resist water loss and protects the developing embryo. Since the contains its own water, the reptile does not need to travel to water to reproduce. • Reptiles excrete nitrogenous waste as uric acid. Reptile urine contains so little water that its waste is a paste rather than a liquid. • The circulatory system of most reptiles is a three chambered heart – two atrium and a partially divided ventricle. This reduces mixing oxygenated and deoxygenated blood. • Crocodiles, birds and mammals have a fully divided ventricle which helps them meet increased energy demands.
Reptiles are ectotherms. The metabolism of an ectotherm is too slow to produce enough heat to warm the body. • Lizards and snakes raise their body temperature by absorbing heat from their surroundings. • By day, the body temperature often follows the temperature of its surroundings. The body temperature falls at night when the surrounding air is cool. • In the mornings, many reptiles seek sunny places to warm in the sun’s rays. Once warmed, reptiles maintain constant body temperature by moving into and out of the sunshine – both warming and cooling their bodies as needed. • An endotherm’s slow metabolism limits where it can live and what activities it can perform. The upside is – It doesn’t have to eat as much as a similar-sized mammal.
Science believes that reptilian dominance called the Age of Reptiles lasted between 250 million and 65 million years ago. • Two groups of reptiles lived in the ocean while the dinosaurs lived on land. Ichthyosaurus and plesiosaurus lived in the oceans and probably lived on fish. • Pterosaurs were the first vertebrates to fly. Some were as small as a sparrow and others had wingspans of 11 meters. • 65 million years ago, dinosaurs world-wide became suddenly extinct. The most accepted hypothesis is that a large meteorite struck the Earth and raised large dust clouds that significantly reduced the amount of sunlight, perhaps for months. Age of Reptiles
So who survived? • There remain 4 groups of reptiles: • Lizards and snakes- There are about 6000 species. They live on every continent except Antarctica. Snakes lack limbs, movable eyelids and external ears. Snakes are carnivores with a jaw with five joints. This allows them to engulf prey. Lizards have four limbs and external ears. Most are located in tropics and deserts. Most are carnivores, some herbivores, only two poisonous. • Turtles and tortoises - All turtles have a shell composed of bony plates that are fused together. Turtles have no teeth, but have a sharp beak. Most turtles spend some of their time in water. • Crocodiles and alligators - Only 22 species located in tropical and subtropical regions of the world. They are largely aquatic, feeding on animals • Tuataras- Only two species found only on islands of New Zealand.
Birds do not have teeth and have only a vestigial tail. • They lay amniotic eggs with a hard shell. • Their body covering is feathers and their legs and feet are covered with scales. • Bird feathers are flexible and strong structures that can be regrown. The feathers provide most of the surface area of the wing and a bird can alter its flight pattern by spreading or collapsing its wing feathers or its wing. Chapter 28.2 - Birds
Tail feathers can be used for braking and steering during flight. • Two types of feathers • Contour feathers – these cover the body of the bird and give the wings and tail their shape. They also insulate against heat loss. • Down feathers – fine feathers growing underneath or among the contour feathers. They are specialized for insulation. • Bird skeletons are made of thin and hollow bones. Many are reinforced by internal struts, like the wings of an airplane. The breastbone is large and has a keel which allows the large flight muscles to attach. The breastbone is large and has a good surface area for the attachment of the flight muscles. • The skeleton of birds typically weigh less than its feathers. • Birds must overcome gravity to fly. Lift is produced as air pressure over the wing is less than the air pressure under the wing.
Flight is an energy-demanding activity. They are endothermic. Their rapid metabolism provides the energy needed for flight. • They have a four-chambered heart with separate circulatory loops to the lungs and to the body. Oxygen-rich blood is rapidly delivered to tissues where it is needed, without mixing with deoxygenated blood. • Respiration in birds is very efficient because their system of air sacs permits air to flow in only in one direction. • Types of flight: • Flapping flight- movement up and down of wings • Gliding flight – loses altitude as gravity overcomes lift • Soaring flight – once the bird is flying, it maintains lift.
Mammals are distinguished by two characteristics: the presence of hair or fur on the body and the ability to produce milk. • Even naked whales and dolphins grow sensitive bristles on their snouts. • Fur and the ability to regulate body temperature through the metabolism allows mammals to live in colder environments. • Mammals have a four-chambered heart. There is no mixing of deoxygenated and oxygenated blood in the heart. • Female mammals have mammary glands that secrete milk. Newborns suckle this milk until they are able to feed on their own. Mammals
There are egg-laying mammals. They are monotremes. They include the duck-billed platypus and the spiny anteaters which are both found in Australia. They are the only mammals that lay eggs. • Monotremes drink their mothers milk after hatching from the egg. The babies cannot suckle at the mothers nipple, so milk leaks out onto the mother’s fur and the baby laps it up with their tongue. • In all other mammals, the offspring are born after spending some time developing inside the mother.
Marsupials carry their offspring internally for only a short period of time. The young are born at an early developmental stage and finish developing in a pouch on the mother’s abdomen. • The newborn marsupial is born hairless and small (about the size of a thumbnail). It must crawl up the mother’s fur into the pouch so that it can nurse. • Most marsupial mammals are found in New Zealand and Australia. There are about 20 species. • Kangaroo • Opossum • Koala
In placental mammals, the offspring remain inside the mother until development is complete. They are nourished through a placenta, a cord containing arteries and veins, that connects the mother to the baby. • Placental mammals include dogs, cats, cows, horses, and humans. • Placental mammals are found on every continent except Antarctica. • There are more than 4000 species.