Reptilia: General Characters and Classification
GENERAL CHARACTERS:
1. Reptiles are cold blooded, terrestrial or aquatic animals.
2. Body is covered with horny scales or scutes.
3. Skin is dry and skin glands are absent.
4. Limbs tetrapodus pentadactyle type.
5. Skull with single median occipital condyle.
6. Mandible consists of many pieces and articulates with the cranium through the quadrate bone.
7. Vertebrae are gastrocentrous.
8. Ribs form a true sternum.
9. Respiration by lungs.
10. Heart is divided into two auricles and incompletely divided ventricle.
11. Right and left aortic arches are complete and functional.
12. Red blood corpuscles (R.B.C.) are nucleated.
13. Kidneys without nephrostomes. Each kidney is provided with separate ureter.
14. Twelve pairs of cranial nerves.
15. Lateral sense organs are absent.
16. Embryonic membranes (amnion and allantois) are present.
17. Fertilization is internal. Eggs are laid on land.
18. Typical cloaca is present.
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CLASSIFICATION:
Class Reptilia has been divided into the following four sub. classes :
2. Parapsida
3. Diapeida
4. Parapsida.
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 carapace and plastron.
Order: 1. Cotylosauria
1. Extinct reptiles having complete cranial roof.
2. Exhibit resemblances with Labyrinthodent 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
1. Terrestrial or aquatic
2. Tetrapoda pentadactyle with walking limbs or paddles.
3. Trunk is enclosed in a bony shell composed of dorsal carapace and ventral plastron, which may or may not be covered with horny shields.
4. Tail is always present. horny sheaths.
5. Jaws without teeth but with
6. Quadrate bone is fixed.
7. Thoracic vertebrae and ribs usually fused with the shell.
8. Two sacral vertebrae.
9. Ribs with capitular portion only.
10. Humerus with entepicondylar foramen.
11. Pubes and ischia form symphyses.
12. Copalatory organ is unpaired.
13. Cloacal opening is longitudinal.
14. Oviparous
Example: Chelone, Chrysemis, Kachuga, Trionya.
Subclass: 2. Parapsida
1. Skull with one pair of temporal vacuitios, 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, Opthalmo saurus.
Subclass: 3. Diapsida
1. Two temporal vacuities on each side of the skull vacuities.
2. Post-orbital and squamosal meet between the temporal
Superorder: I-LEPIDOSAURIA
1. Two temporal vacuities are present.
2. Anterior orbital vacuities are absent.
3. Post-temporal fenestrae are usually present.
4. Humerus with two foramina.
Order: 1. Rhyncocephalia
1. Two vacuities are present.
2. Teeth acrodont.
3. An epipterygoid is present.
4. Quadrate bone is fixed or immovable.
5. Parietal foramen is present.
6. Vertebrae amphicoelus.
7. External copulatory organs are entirely absent.
Example: Sphenodon.
Order: 2. Squamata
1. Body is covered by horny epidermal scales.
2. Single (supra or upper) temporal vacuity in lizards and not temporal vacuity in snakes.
3. Teeth pleurodont.
4. Quadrate is movable.
5 Quadratojugal is absent.
6. Vertebrae are usually procoelous.
7. Limbs present or absent.
8. Cloacal opening transverse.
9. Male possesses a pair of eversible copulatory organs.
Suborder: 1. Lacertilia
1. Terrestrial, arboreal or burrowing forms.
2. Single (supra or upper) temporal vacuity is present.
3. Limbe pentadactyle and are usually present.
4. The rami of mandibles are fused infront.
5. Sternum present.
6. Eyelids movable.
7. Tympanum present.
Examples: Hemidactylus, Calotes, Chaemeleon, Draco, Phrynosoma, Varanus, Crotaphytus, Mabuiya, Gecko, Ophisaurus, Rhineura, Iguana, Heloderma, Molloch.
Suborder: 2. Ophidia
1. Terrestrial or aquatic, arboreal or burrowing.
2. Temporal vacuities are entirely absent.
3. Limbs absent.
4. The rami of mandibles are united by a ligament.
5. Sternum absent.
6. Eyelids immovable.
7. Tympanum absent.
8. Tongue is bifid and protrusible.
9. Zygosphene and zygantra are present in the vertebra.
Examples: Typhlops, Python, Bryz Johni, Lycodon, Bungurus Naja naja, Enhydrina, Hydrophis, Viper, Ancistrodon, Natrix, Zaemenis, Dendrophis, Crotalus, Elaps.
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Superorder: II-ARCHOSAURIA
1. Skull with closed upper temporal vacuity but possesses both the temporal.arches.
2. Anterior orbital vacuities are usually present.
3. Teeth are thecodont.
4. Humerus with foramina.
5. Vertebrae amphicoelous or procoelous
Order: Crocodila
1. Fresh water and predatory forms.
2. Body is covered with an exoskeleton of thick horny epidermal scales.
3. Tail is long and laterally compressed.
4. Maxillae, palatines and pterygoids are united along the middle to form a secondary palate.
5. Teeth are thecodont.
6. Quadrate immovable.
7. Both supra and infra temporal arches present.
8. Vertebrae procoelous.
9. Sternum is present.
10. Cervical vertebrae with two headed ribs.
11. Thoracic ribs possess uncinate process. 12. Abdominal ribs are present.
13. Prepubis present. Pubis does not share in the formation of acetabulum.
14. Heart is four chambered and ventricle is completely divided into two by a septum.
15. Lungs are spongy.
16. Closcal opening longitudinal.
17. Males possess a median unpaired penis.
Examples: Crocodilus, Alligator, Gavialis,
Subclass: 4. Synapsida
1. Skull with a pair of temporal vacuities, one on either side, each bounded by the post-orbital and squamosal above and by the jagal and squamosal below.
2. Includes all extinct forms from Carboniferous to Per-mian.
Examples: Dimetrodon, Cynognathus.
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