Reptiles

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What is a reptile ?

  • vertebrate animals that have lungs, scaly skin, have special adaptations that enable them to live their entire life out of water, and a special type of egg
  • Widely distributed over the earth
  • Temperate and tropical areas on Earth contain populations of reptiles that are remarkably diverse in appearance and lifestyle
  • Cold areas lack of reptiles
  • Resembles amphibians
  • Better adapted to life on land
  • Have reptilian skin that is dry and leathery and usually covered with thick, protective scales which helps to prevent the loss of body water in dry environments
  • The tough scaly layer of skin does not grow when the rest of the reptile grows, so it must shed periodically when a reptile increases in size
  • Most important adaptation of reptiles to life on land is the type of egg they produce
  • Amphibian eggs usually needs to develop under water, reptilian eggs are surrounded by a shell and several membranes that together create a protected environment in which the embryo can develop, which are called amniotic eggs
  • The legacy of an egg adapted to life on land was passed on from early reptiles to their descendants-modern reptiles birds, and mammals
  • Reptiles on land have a more efficient respiratory system
  • Most amphibians take in oxygen and give off waste gases primarily through their moist skin, this method of respiration works only as long as the amphibian’s skin remains moist
  • The dry skin of reptiles prevents gases from moving through

Evolution of Reptiles

  • Several fossils show characteristics of both amphibians and reptiles, it is difficult to say exactly when the first true reptiles appeared on earth
  • One factor that separates living reptiles from amphibians is the type of eggs they produce, but there are no fossil eggs around for paleontologists to study
  • Fossils found must remain on the amphibian-reptilian borderline at least for the present time, these animals are called transition fossils
  • Transition fossils document the slow and steady evolutionary change of amphibian like ancestors into reptiles over time
  • Most of the Carboniferous Period, amphibians outnumbered reptiles
  • During the Permian Period (285 million years ago), the climate became cooler and less humid, which turned into a great period for the reptiles
  • One early reptile line developed into a group of mammal-like reptiles that displayed a mix of reptilian and mammalian characteristics. These animals were extremely successful, but they became extinct in just a few million years
  • Toward the end of the Triassic Period (195 million years ago), the mammal-like reptiles were suddenly replaced in the fossil record but another group of reptiles that had remained in the background for millions of years--the dinosaurs
  • The Triassic Period also saw the appearance of crocodiles and alligators, as well as the first birds
  • At the end of the Cretaceous Period (65 million years ago), a worldwide mass extinction had happened. Within a few million years, dinosaurs and most other animal and plant groups had become extinct
  • Biologists think it was caused by the slow process of climate change that resulted in the movements of the continents into the present positions.
  • Other biologists believe that the change in climate that produced the mass extinction occurred more suddenly
  • Some evidence suggests that a huge meteor struck the Earth, causing an explosion that produced enormous clouds of airborne dust. The explosion may have caused worldwide forest fires, and the smoke from the fires may have blocked the sun’s rays, causing the Earth’s temperature to drop
  • The disappearance of the dinosaurs left open many niches for animals, both on land and in the sea

Form and Function in Reptiles


Feeding

  • Some reptiles such as iguanas are herbivores, others are carnivores
  • Certain carnivorous snakes prey on small animals by grabbing them with their jaws and swallowing them whole
  • Other snakes live on a diet of birds’ eggs
  • After swallowing an egg whole, these snakes crack the egg in their throat by piercing the shell with bony projections of their vertebrae, then the snakes swallow the liquid content of the egg and spits out the shells
  • Other snakes such as the huge king cobra, eat other snakes
  • Crocodiles and alligators eat fish and land animals. If they are successful in snaring a land animal, they pull it underwater and drown it, eating what they want by tearing huge chunks off their prey under water
  • Chameleons have sticky tongues as long as their bodies, which flip out to catch insects on the wing
  • Herbivore reptiles do not chew their food, they must swallow large pieces of material. Their long digestive system enables them to digest these large tough, fibrous pieces of food

Respiration

  • The lungs of reptiles are better developed than those of amphibians. They have muscles around their ribs, so many reptiles are able to expand their chest cavity to inhale and collapse the cavity to force air out
  • Several species of crocodiles also have flaps of skin that can separate the mouth from the nasal passages, thus allowing them to breathe through their nostrils while their mouth remains open
  • Most reptiles have two lungs, some species of snakes have only one
  • The single lung functions quite well, and fits perfectly into their long, thin body
  • Snakes have a special tube in the floor of their mouth through which they breathe, so they don’t suffocate in the time it takes them to swallow their prey
  • This tube can extend out of the snake’s mouth while it is dining
  • Internal Transport
  • Reptiles have a well-developed double-loop circulatory system
  • One of the two loops brings blood to and from the lungs, and the other brings blood to and from the rest of the body
  • Reptiles hearts contain two atria and either one or two ventricles
  • Compared to other reptiles, crocodiles and alligators have 4 the most well-developed heart. Their heart consists of two atria and two ventricles.
  • Most reptiles have a single ventricle with partial internal walls that help keep oxygenated and deoxygenated blood separate during the pumping cycle
  • Amphibians have a less-developed circulatory system than reptiles. Amphibians exchange gases through their moist skin, they do not need to have an efficient circulatory system to deliver oxygen to and remove waste gases from their cells.
  • The development of dry skin necessitated the development of a more efficient circulatory stem—a system up to the task of moving blood between the small, localized region where gas exchange occurs and the most distant parts of the body

Excretion

  • Reptiles eliminate liquid wastes in the form of urine, which is produced in their kidneys
  • In many reptiles, especially desert-dwelling snakes, a large amount of water is removed from the urine in the cloaca and returned to the body tissues
  • Reptiles excrete nitrogen-containing wastes in the form of uric acid rather than ammonia
  • Ammonia is extremely toxic and must be excreted in dilute form to avoid self-poisoning
  • Uric acid is less toxic to cells than ammonia is and thus does not have to be diluted to the same extent that ammonia does
  • Diluting ammonia makes it extremely difficult for terrestrial animals that must conserve water
  • Uric acid does not remain dissolved in urine but rather crystallizes out as a solid precipitate
  • When extra water is removed in the cloaca, urine is reduced to a pasty white material that can be excreted without much water loss

Response

  • Reptilian brain shows the same basic pattern as the amphibian brain, although the reptile cerebrum and cerebellum are somewhat larger
  • Most sense organs are well-developed, except snakes cannot hear
  • Most reptiles that are active during the day have complex eyes that contain several types of photoreceptor cells
  • Many reptiles can see colors quite well, some turtles can see colors better than humans can
  • Many snakes have an extremely good sense of smell
  • Snakes have a pair of nostrils that open near the mouth, and have special organs in the rood of the mouth that aid the nose in smelling
  • The snake’s tongue picks up molecules from the air and carries them into the mouth and onto this pair of special organs. This is how snakes gather information about its environment by “tasting” molecules in the air
  • Some reptiles have simple ears, rather than some other reptiles can be completely deaf
  • Snakes are able to pick up vibrations in the ground through bones in their skull
  • Some reptiles are able to gather heat information from their environment
  • Some pit vipers have heat-sensitive pits on both sides of their head. Using these pits, vipers obtain a temperature picture of the world around them, making it a lot easier to seek out other animals
  • The heat-sensitive pits are very useful at night, when low levels of light make it difficult for a reptile to see its prey

Movement

  • Reptiles with legs have larger, stronger limbs whose movements are well-controlled. The legs of many reptiles are well-adapted for walking, burrowing, swimming, or climbing
  • Snakes, which lost their legs in the course of evolution, move by pressing large central scales against the ground.
  • By expanding and contracting the muscles around their ribs in waves, snakes dig these central scales into the ground and push themselves forward
  • This kind of movement is slow and quiet, it makes snakes masters at stalking prey

Reproduction

  • Leathery outer shell of the egg, protects the delicate tissues inside, and the pores in the shell allow oxygen and carbon dioxide to pass through
  • Reptiles lay eggs that hatch into animals that resemble small adults
  • All reptiles reproduce through internal fertilization
  • Lizards and some snakes have two reproductive structures called hemipenes
  • The internal fertilization makes it possible for the female’s reproductive system to cover the embryos with protective membranes and a shell after fertilization has occurred
  • Reptiles treat their eggs differently
  • Some species, such as turtles, come ashore to bury their eggs in the sand. Leaving them on their own with no parental care
  • Other reptiles provide minimal care for their eggs and their young
  • Certain snakes will bask in the sun to warm their bodies and then wrap themselves around their eggs to incubate them, once the eggs are hatched, they are on their own
  • Alligators build nests in which they lay their eggs and guard them until they hatch
  • Some baby crocodiles and alligators stay with their mother for as long as two years after they hatch
  • Some female snakes and lizards hold their eggs inside their body until the eggs hatch
  • Snakes that bear living young are ovoviviparous

Tuataras

  • Only surviving member of the order Rhynchocephalia, resembles reptiles that lived during the dinosaur age
  • Found only on a few small islands off the coast of New Zealand
  • Active at night, hunting the small animals they eat
  • Have a pineal gland that they use to detect changes in the day length

Lizards and Snakes

  • Belong to the order Squamata
  • Most lizards have legs, clawed toes, external ears, and moveable eyelids
  • Range in size from a few centimeters to three meters in length
  • Gila monsters, large, stocky lizards of the American Southwest and Mexico, have glands in their jaws that produce the venom in which they paralyze small prey
  • Gila monsters bite their prey and hold onto it with their teeth while the venom they produce flows into the wound
  • Monitors are the world’s largest living lizards
  • Monitors are quite intelligent and active for reptiles, many eat birds and mammals
  • Largest monitor lizard are the Komodo dragons with the length of as many as three meters and as mass of up to 75 kilograms
  • Komodo dragons can kill and devour animals as large as a water buffalo
  • Snakes and lizards have lost both pairs of legs during evolution into burrowing forms
  • Millions of years ago some lizards began to live below ground level. In burrows and cracks, these relatively harmless lizards were safe from predators
  • Over time lizards with smaller legs or no legs at all were able to burrow most efficiently
  • These lizards survived, evolving into the legless snakes
  • Snakes vary in size, they can be the size of an earth worm or up to 10 meters in length

Crocodilians

  • Members of the order Crocodilia, such as alligators, crocodiles, caimans, and gavials--split off from the ancient reptiles around the time dinosaurs did
  • These animals live only in the tropics and subtropics, where the climate remains warm all year long
  • Alligators and their relatives, the caimans, live only in fresh water and are found in the Western Hemisphere
  • Crocodiles may live in either fresh or salt water and are native to Africa, india, and Southeast Asia

Turtles

  • Members of the order Chelonia, have changed little in the 200 million years since then
  • The word turtle refers to members of this order that live in water; the word tortoise is to those that live on land
  • All turtles and tortoises have some sort of shell covering their bodies
  • Turtle shells consist of two parts: a dorsal part (carapace), and a ventral part (plastron)
  • The animal’s backbone is fused to the inside of the carapace, and its head, legs, and tail stick out through holes where carapace and plastron join
  • Tortoises have a high, domed carapace and stubby elephant-like legs
  • Tortoises pull into their shells to protect their more delicate body parts
  • Turtles are adapted to life in freshwater ponds and lakes or the open sea
  • The legs and feet of many aquatic turtles have developed into flippers
  • Certain aquatic species cannot pull back into their shells completely, but they do have powerful jaws that are capable of giving a nasty bite

How Reptiles Fit into the World

  • Found in many habitats, from the temperate zone to the tropics and from the tops of rain forest trees to the open ocean
  • Important predators in many ecosystems, for example, snakes keep down the large numbers of rats and mice in farms
  • Without snakes, the world would be overrun by mice and rates
  • Small lizards eat insects, large lizards eat other small animals
  • Reptiles limit the populations of other animal species
  • Sea turtles are in danger of extinction
  • Turtle soup and turtle eggs are eaten in many parts of the world
  • Tortoise shell was once commonly used to manufacture jewelry and as an inlay in furniture
  • The development of their nesting sites have been ruined by seaside development, which threatens the ancient spawning sites of these animals
  • Today, most species of sea turtles are protected by law, but this may lead to an increase in their dwindling numbers