Here is an essay on the ‘General Characters and Classification of Reptiles’ for class 11 and 12. Find paragraphs, long and short essays on the ‘General Characters and Classification of Reptiles’ especially written for school and college students.
Essay # 1. General Characters of Reptiles:
Reptiles are cold-blooded, usually scaly vertebrates, with a right and a left aortic arch, a single occipital condyle and pulmonary respiration. the ovum is large and meroblastic, and the embryo has an amnion and allantois. The name Reptilia refers to the mode of locomotion (L., repere or reptum = to creep or crawl). The study of reptiles is called Herpetology (Gr., herpeton = reptiles)
1. Reptiles are cold-blooded, terrestrial or aquatic air-breathing animals.
2. Body is divisible into head, neck, trunk and tail, and covered with horny scales and scutes.
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3. Limbs tetrapodus (2 pairs), pentadactyle type. Digits with horny claws. However, limbs are absent in some lizards (Ophiosaurus) and snakes.
4. Mouth terminal, jaws provided with simple conical teeth. Teeth are replaced by horny beaks in turtles and tortoises. A typical cloaca is present.
5. Skin is dry cornified and skin glands are absent.
6. Endoskeleton bony, skull with single median occipital condyle. Interclavicle is T-shaped.
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7. Mandible consists of many pieces and articulates with the cranium through the quadrate bone.
8. Vertebrae are gastrocentrous.
9. Ribs single-headed.
10. Respiration by lungs throughout life.
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11. Heart is three-chambered, divided into two auricles and incompletely divided ventricle. In crocodiles heart is four-chambered.
12. Right and left aortic arches are complete and functional.
13. Red blood corpuscles (R.B.Cs) are oval and nucleated.
14. Kidneys without nephrostomes and metanephric. Each kidney is provided with separate ureter. Excretion uricotelic.
15. Cerebrum of brain is well developed than that of amphibians. Twelve pairs of cranial nerves.
16. Sexes separate. Male usually with a pair of copulatory organs (snakes and lizards) and unpaired in Chelonia and Crocodilia.
17. Lateral line sense organs are absent. Jacobson’s organs are present in the roof of the buccal cavity.
18. Fertilisation is internal. Eggs are laid on land which are large and covered with leathery shells.
19. Embryonic membranes (amnion and allantois) are present.
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20. Parental care is absent.
Essay # 2. Classification of Reptiles:
Class Reptilia has about 7,000 living and several extinct species (Bogert). These are grouped into about 16 orders, of which only four are living.
The class Reptilia has been divided into the following five subclasses on the basis of presence or absence of temporal vacuities in the skull:
1. Anapsida
2. Euryapsida
3. Parapsida
4. Diapsida
5. Synapsida.
Subclass 1. Anapsida:
1. Solid roof of the skull.
2. No temporal vacuity or fossa in the skull.
3. Quadrate is connected to the otic bones.
4. Limbs are generally strong.
5. Body is enclosed in the dorsal carapace and ventral plastron.
Order 1. Cotylosauria (Stem Reptiles):
1. Extinct reptiles having complete cranial roof in the temporal region.
2. Exhibit resemblances with Labyrinthodont amphibians.
3. Jaws and teeth are poorly developed.
4. Limbs are feeble and project laterally.
5. Pelvic girdle is flat and plate-like.
6. Range in size from one to ten feet.
7. Become extinct in the Triassic.
Example- Seymouria.
Order 2. Chelonia or Testudinata (Gr., chelone = turtle; L., testudo = turtle):
1. Terrestrial or aquatic.
2. Body is enclosed in a bony shell composed of dorsal carapace and ventral plastron, which may or may not be covered with horny shields. Nasal opening single at the front end of snout.
3. Tetrapoda pentadactyle with clawed walking limbs and/or webbed paddles.
4. Tail is always present.
5. Skull anapsid without a parietal foramen. Quadrate bone is fixed. Sternum absent.
6. Jaws without teeth but with horny beaks.
7. Thoracic vertebrae and ribs usually fused with the carapace. Two sacral vertebrae.
8. Humems with entepicondylar foramen.
9. Pubes and ischia form symphyses.
10. Cloacal opening is longitudinal.
11. Copulatory organ is unpaired and simple.
12. Oviparous.
It includes about 400 species of marine turtles, freshwater terrapins and terrestrial tortoises.
Examples- Chelone, Chrysemis, Testudo, Kachuga, Trionyx, Dermochelys.
Subclass 2. Euryapsida (Extinct):
Skull with a single pair of temporal openings (one on either dorso-lateral side) bounded below by postorbital and squamosal bones.
Subclass 3. Parapsida (Extinct):
1. Skull with one pair of temporal vacuities, one on either side. Each temporal vacuity is bounded by post-frontal and supra-temporal below and parietal above.
2. Includes all extinct forms, from Mesozoic to Cretaceous.
Examples- Ichthyosaurus, Plegiosaurus, Protosaurus, Ophthalmosaurus.
Subclass 4. Diapsida:
Two temporal vacuities on each side of the skull which are separated by a bar of post- orbital and squamosal bones.
Superorder I-Lepidosauria (Scaly Lizards):
1. Two temporal vacuities are present (diapsid skull).
2. Anterior orbital vacuities are absent.
3. Post-temporal fenestrae are usually present.
4. Humerus with two foramina.
Order 1. Rhyncocephalia (L., rhynchos = snout + Gr., kephale = head):
1. Two vacuities are present in the skull.
2. Teeth acrodont.
3. An epipterygoid is present.
4. Quadrate bone is fixed or immovable.
5. Large parietal foremen is present. Nonfunctional median eye is present in the living form. No antorbital foramen.
6. Vertebrae amphicoelus and intercenta present. Limbs pentadactylous adapted for walking.
7. External copulatory organs are entirely absent.
8. Ribs single-headed and have uncinate processes. Abdominal ribs and sternum present.
Example- Sphenodon (lizard-like Tuatara).
Order 2. Squamata (L., squama = scale or squamatus = scaly):
1. Body is covered by horny epidermal scales.
2. Single (supra or upper) temporal vacuity in lizards and no temporal vacuity in snakes.
3. Teeth pleurodont or acrodont.
4. Quadrate is movably articulated with skull.
5. Quadratojugal is absent.
6. Vertebrae are usually procoelous. Sacrum with two vertebrae.
7. Limbs clawed, present or absent in snakes and some lizards.
8. Cloacal opening transverse. Jacobson’s organs paired.
9. Male possesses a pair of eversible copulatory organs (penes).
It includes about 6800 species of lizards and snakes which are divided into two following suborders:
Suborder I. Lacertilia (= Sauria):
1. Terrestrial, arboreal, burrowing and aquatic forms.
2. Carnivorous and some are herbivorous.
3. Single (supra or upper) temporal vacuity is present.
4. Limbs pentadactyle and are usually present. Girdles also present.
5. The rami of mandibles are fused in front. Mouth non-expandable. Premaxillae bear teeth.
6. Sternum, epistemum and urinary bladder present.
7. Eyelids movable. Nictitating membrane present.
8. Ear openings and tympanum present.
9. Both lungs equally developed.
Examples- Hemidactylus, Calotes, Chaemeleon, Draco, Phrynosoma, Varanus, Crotaphytus, Mabuiya, Gecko, Ophisaurus, Rhineura, Iguana, Heloderma, Molloch.
Suborder 2. Ophidia (= Serpentes):
1. Terrestrial or aquatic, arboreal or burrowing.
2. Body slender and narrow.
3. Temporal vacuities are entirely absent.
4. Limbs and girdles absent. Vestigial hindlimbs and pelvic girdle in boa and python.
5. Eyelids immovable. Nictitating membrane absent.
6. Ear openings and tympanum absent.
7. Tongue is bifid and protrusible.
8. The rami of mandibles are united by a ligament and can be separated at the time of swallowing.
9. Sternum, episternum and urinary bladder absent.
10. Maxillae, palatines and pterygoids freely movable.
11. Premaxillae toothless.
12. Zygosphene and zygantra are present in the vertebra.
13. Left lung small.
Examples- Typhlops, Python, Eryx johni, Lycodon, Bungarm Naja naja, Enhydrina, Hydrophis, Viper, Ancistrodon, Natrix, Zaemenis, Dendrophis, Crotalus, Elaps.
Superorder II—Archosauria (Ruling Reptiles):
Archosaurs were the dominant land animals of late Mesozoic and include dinosaurs and pterosaurs. Crocodiles are the only living descendants of the group.
1. Skull diapsid with closed upper temporal vacuity but possesses both the temporal arches. Interparietal, tabular bones or a parietal foramen absent.
2. Anterior orbital vacuities are usually present behind the nostrils.
3. Teeth are thecodont.
4. Vertebrae amphicoelous or procoelous.
5. Humerus with foramina. Hindlegs longer and powerful.
Order. Crocodila (Gr., krokodeilos = crocodile):
1. Freshwater and predatory carnivorous forms.
2. Body is covered with an exoskeleton of thick horny epidermal scales, bony plates and scutes.
3. Tail is long, strong and laterally compressed.
4. Limbs short, powerful, clawed and webbed.
5. Maxillae, palatines and pterygoids are united along the middle to form a secondary palate.
6. Quadrate immovable. Parietal foramen absent.
7. Both supra and infra temporal arches present.
8. Teeth are thecodont lodged in sockets.
9. Vertebrae procoelous. Cervical vertebrae with two-headed ribs.
10. Sternum is present.
11. Thoracic ribs double-headed and possess uncinate processes. Abdominal ribs are present.
12. Prepubis present. Pubis does not share in the formation of acetabulum.
13. Heart is four-chambered and ventricle is completely divided into two by a septum.
14. Lungs are spongy.
15. Cloacal opening longitudinal.
16. Males possess a median unpaired erectile and grooved penis.
Examples- Crocodilus, Alligator, Gavialis.
Subclass 5. Synapsida (Extinct):
1. Skull with a pair of temporal vacuities, one on either side, each bounded by the post-orbital and squamosal above and by the jugal and squamosal below.
2. Teeth usually heterodont.
3. Dentary large except in the most primitive members.
4. Pectoral girdle has a coracoid and precoracoid.
5. Includes all extinct forms from Carboniferous to Permian.
Examples- Dimetrodon, Cynognathus.