9.5.7 Class Reptilia (Latin. Repere; to crawl)
Appendages:
Either tetrapods and pentadactyls or some reptiles are limbless. They have four-chambered hearts (right and left auricle, a partly divided ventricle & a sinus venous) except crocodiles which have completely divided right and left ventricles and right & left
All are cold and blooded thus hibernating in winter. Unisexual and fertilization is internal. Mostly oviparous and amniotic eggs. Lays large yolky-shelled eggs. Skull with one occipital condyle. They respire through lungs thus predominantly terrestrial and the first successful terrestrial group.
History of Reptiles:
The reptiles flourished dominantly throughout the Mesozoic period. (i.e., about 225 million to 65 million years ago) in geological time scale, during these periods they were represented by some giant species commonly known as dinosaurs. Today they are extinct (now only fossils record found). Most reptiles became extinct during the tertiary period (about 50 million years ago) due to adverse climatic
conditions.
Reptiles, in present times, are represented by four evolutionary lines i.e., Lizards and snakes, sphenodon (found only in New Zealand), Crocodiles, Tortoises, and turtles. Present-day reptiles have been derived from dinosaurs of the Jurassic period (196- 136 million years before) and Cretaceous period (136-65 million years ago (mya)). Today reptiles flourished in tropical zones.
Origin of Birds:-
No doubt that birds evolved from ancient running reptiles. The important discovery of two Jurassic (144-208 million years ago) birds: Archaeopteryx, is preserved in the British Museum London.
Archaeornis, preserved in the Berlin Museum Germany, provided evidence of a connecting link between birds and reptiles.
Affinities:
cities to a crow The bird's features are, the presence of feathered wings; a skull, and bird-like bones.
The reptilian characteristics are the presence of jaws and teeth. Long lizard-like tail. Forelimbs with claws. Keel absent. Single occipital condyle. Bones are not pneumatic. Except feathers fossils birds showed great similarity with dinosaurs.
9.4.8 Characteristics of Aves forelimbs
The diagnostic characteristics of birds are the presence of feathers and forelimbs Beak is present and teeth are absent. Sternum is with keel.
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They have a Single occipital condyle. Warm-blooded (homeothermic). The streamlined body is divided into a head, neck, trunk, and tail. Bipedal locomotion and hind limbs are also modified for perching. Hind limbs contain scales and claws and the endoskeleton is light and hollow. Four chambered hearts (two auricles and two ventricles) are present. Only the right aorta (aortic arch) is present. Lungs are their respiratory organs, which are supplemented with air sacs and exhibit double respiration.
Syrinx is a voice box in Birds. feces. Kidneys are their excretory organs. The urinary bladder is absent to reduce weight. Nitrogenous waste is uric acid which is removed as crystals Gizzard is a grinding organ in their digestive system. Unisexual and fertilization is internal. Birds lay large yolk ovary is functional. eggs (Oviparous. Left Some birds have secondarily lost the power of flight: are called running birds, such as kiwi, ostrich, emu, etc. Examples of flying birds: parrot, crows, pigeons, sparrows, kites, etc, An Example of an aquatic bird is a penguin.
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Origin of Class Mammalia: (The Hairy Animals):
There is no doubt that mammal forms the highest group in the animal kingdom. They attained the most complete structural, physiological, and developmental adaptations to terrestrial life and some secondarily also form aquatic life. The two most remarkable features of mammals are the mammary glands in females and the presence of hairs. Mammals have been.
lved from cotylosaurian reptiles (evidence from fossil record). Fossil record exhibits that ancestral mammals and reptiles lived together during the Jurassic period and have been called mammal-like reptiles (in size mice like and arboreal, One of these was genus Varanops found as a fossil in Texas in the USA). Mammals became dominant in the Cenozoic period (66.4 million years ago till now).
9.5.9 General Characteristics of Mammals
The diagnostic characteristics of mammals are the presence of mammary glands (by which females nurse their young ones). The body is mostly covered with hair or fur. The CNS is highly developed. Lungs possess numerous alveoli and bronchioles. The diaphragm is present (muscular partition between chest and abdomen). External ears (pinnae) are mostly present.
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