The history of reptiles, from their first appearance during the Carboniferous to the present, is traced on this chart. (Each white area represents a major order plotted according to when it first began to flower and how long it lasted.) In addition to the major groups, many short-lived offshoots developed. For reasons of space only two of them, represented by the marine forms Geosaurus and Tylosaurus, have been included here. Solid bars on the chart indicate lines of descent which have been fairly well established by the fossil record. Broken bars are used where the fossil evidence is sketchy.
A striking aspect of reptile history is how, from the primitive cotylosaurs (here represented by Seymouria), these creatures radiated to occupy an enormous variety of niches on land, in the water, and in the air. One group of cotylosaurian descendants that played a profound role in the development of reptiles was the thecodonts, primitive archosaurs. Not only did they give rise to the Ornithischia and Saurischia (popularly called dinosaurs), but also the Pterosauria (flying reptiles) and the Crocodilia. Thecodonts were even related to the ancestral birds. The mammals evolved from another group, the therapsids, shown at lower left.
Another curious fact of reptilian evolution revealed by this chart is the relative suddenness with which order after order disappeared toward the end of the Cretaceous, described as “the time of the great.”
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Reptiles are sexual animals and are the group that introduced internal fertilization to the vertebrate line. Thus, in a manner of speaking, they laid the foundation for the family unit in higher vertebrates, and from this came human society itself, with all its excitement and troubles. The ancestral amphibians deposited their eggs virtually naked in the water, and fertilized them by simply releasing sperm in the general vicinity. The hazards of such an informal operation to both sperm and egg are obvious. The reptilian egg, however, enters the world already fertilized, and packaged against a certain amount of environmental adversity. One need only compare the dozen or so eggs laid by the average lizard with the thousands laid by toads to see the great economy the new method has brought.
But even an egg with a shell is delicate. It can incubate successfully only within a narrow range of conditions of temperature, humidity and concealment. It is thus not surprising to find that a few reptiles have independently hit upon the recourse that we think of as one of the main attributes of the mammals – that of producing living young.
A fertile sea turtle lays round in a hole it has dug in warm, incubating sand of Australia’s Great barrier Reef. When about 100 eggs are laid, it will cover the hole and depart. During one breeding season a mature female will deposit from two to five clutches.
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Correct feeding is probably the most important aspect of keeping your iguana in good health, and is also the area in which most problems occur. Iguanas are herbivorous, that is, they eat plants; but they will also devour insects and small rodents in the wild.
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Their large size means adult iguanas have few natural predators, but they are the prey of large snakes, such as boas and anacondas. Baby iguanas are more vulnerable, being preyed on by turtles, large fish, and a variety of mammals and birds.
Related Websites Up to two-thirds of an iguana’s length is taken up by the tail, which, interestingly, can be shed as a defensive mechanism if the iguana is attacked. This behavior is rarely seen in captivity, but care should be taken with young iguanas because they may react like this if grabbed by the tail. The tail, incidentally, does grow back, but will never be as attractive as the original.
The green or common iguana is a reptile and therefore is considered cold-blooded. The proper term for this is ectothermic, which means the animal derives its body heat from its surroundings, rather than producing heat internally as mammals do. This makes reptiles very efficient because they do not have to waste energy producing heat. Much of the food eaten by mammals goes into producing the energy.
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Related Websites From the time of Aristotle through Linnaeus and even more recently, the classes of animal life were described as warm-blooded or cold-blooded. Unfortunately for describers of animal life who like to simplify, there is no absolute black and no absolute white in nature. All life is full of shades of gray. Mammals that hibernate do so with body temperatures much lower than their normal operating temperature. This goes for the bear and the woodchuck and doubtless many others.
Among reptiles the temperature regulation is managed by their behavior. A cool snake will bask in the sun or partially bury itself in warm sand. An overheated lizard will seek shade or a burrow. Perhaps additional study will show that when the Indian python incubates her eggs she is actually providing some temperature regulation as well. If thermo-regulation is necessary for reptile health (and this does seem to be the case), and this regulation is behavioral, then the pet keeper is duty bound to provide the environment in which his pet can behave to suit his temperature requirements. Nothing profound about that, but it is up to you to furnish a heat source with basking areas at various distances from it and also a shadow area where your pet can escape if the heat gets to be too much. All this can easily fit into a cage. Mount a light at the top, then several shelves or branches at various distances and then perhaps you will discover that the shadows created under the shelves provide the cool escape areas as well. Just make sure that what you erect is rugged and stable. A light that falls down and traps or burns your pet is your fault. Don’t blame the stupid iguana.
Related Websites The erect posture of dinosaurs is often said to be the key to their success. Why is this? An important reason is that an erect posture is mechanically more satisfactory than a sprawling one. The weight of the body is supported entirely from below. In a sprawler, the weight of the body is supported from the sides. While gravity effectively pulls straight down from the center of the body mass, in a sprawler this force has to be converted into a sideways component along the femur or humerus (upper arm bone), and then a vertical component down the tibia and fibula, and the radius and ulna (forearm bones), which causes great stresses are avoided if the gravitational force of the animal’s mass is transferred down through a straight, erect limb.
This mechanical advantage is important. Firstly, erect animals can run in a more sustained way: not necessarily faster, but with more stamina, because the effort of supporting the body weight is much less than in a sprawler. This would have been an immediate advantage to an archosaur chasing sprawling prey animals or escaping from a sprawling carnivore. Interestingly, the main plant-eating groups of the Middle Triassic, the pig-like rhynchosaurs and dicynodonts, were evolving semi-erect gaits at the same time. Indeed, the ancestors of the mammals, the cynodonts – which were moderate-sized carnivores at that stage – also showed similar advances.
Related Websites The inturned head of the femur (the beginnings of the full right-angled femur head seen in dinosaurs and in a different from in mammals); the straight knee joint; the reduced hinge-like ankle joint (technically termed the advanced mesotarsal, or AM, ankle); the long toes and the digitigrade posture of the foot, in which only the toes touch the ground, not the sole of the foot as in earlier archosaurs – and in humans today.
Most of the dinosaur-like characters are also seen in the flying pterosaurs. Certain paleontologists argue that Lagosuchus, the pterosaurs, and the dinosaurs together form a major clade that arose in the Middle to Late Triassic, some 230 million years ago.
The dinosaur-like synapomorphies of this clade, and their further modification in the dinosaurs proper, are part of a major series of related anatomical changes that took place among the archosaurs during the Triassic, and which may have been the key to the origin of the dinosaurs.
Related Websites All reptiles practice internal fertilization . In all modern forms , except for the tautara , the male has an organ turned outside in , in the base and basal areas of the tail area , and everted through the opening of the cloaca during erection. In the tautara the and this transfer of sperm is accomplished by bringing the genital openings into contact as in birds and avian creatures. Perhaps this is a left over vestigial remnant of dinosaur harbingers. This of course was probably the means and mechanism as the method used by ancestral reptiles - it is most clear in any case and cases , that the penis and penises had separate origins in turtles, crocodiles and mammals , on the one hand , and in most lizards and snakes on the other side.
Thus , male lizards as well as snakes , not just one , but indeed a full pair and pairing of what are essentially hollow structures called or referred to as “hemipenes” , which make up what are in effect “copulatory” organs . Located as amazingly they are , in the tail areas , behind the opening of the cloaca , these hemipenes often give the tail of the male reptiles , a thicker more gradually contoured tail than that of the females . In many species the sex of the reptile can be distinguished by this difference – which is sometimes rather slight in some.
A “groove” serves as the channel for the sperm . This groove extends from the opening of the sperm duct extends from the opening of the sperm duct along the inner wall ( which of course serves as the outer wall during the erection period / periods), of the hemipenis, and the surface may be pleated or set with actual spines which keep it in place in the oviduct of the female during mating. Either one of the hemipenes may be used , but only one and only one. The hemipene nearest to the female is everted and protruded from the cloaca during the erectile period . This is brought into effect by both a combination and combinations of muscular action and muscular actions and distension of the very walls with blood and blood fluids.
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