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General Zoology


Note: Make sure to read the Nomenclature section afterreading this section!
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Zoology is the field of studying organisms. This include, but is not limited to, their taxonomy/classification, origin, evolutionary development, biology and embryology.

| Introduction | Reptile Classification | Orders & Suborders | Some Biology | Related Topics | References |


Reptiles forms one of the major orders of animals, dating back to the time when dinosaurs and other prehistoric creatures ruled the earth. There are more than 65 000 species alive today, with more being discovered every year in remote parts of the world.

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Table 1 - Reptile Classification:

Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata


  • skull articulates with vertebral column
  • dry skin with epidermal scales
  • respiration through lungs
  • internal fertilisation
  • amniotic eggs
  • urine excretion through metanephric kidneys


  • teeth absent and replaced by a horny beak
  • shell consists of dorsal carapace and ventral plastron
  • bodies are short and broad
  • e.g. turtles


  • specific characteristics of the skull and jaws
  • e.g. snakes, lizards, worm lizards and chameleons.


  • e.g. tuataras


  • e.g. crocodiles and alligators

The earliest members of the class Reptilia were the first vertebrates to process amniotic eggs. Amniotic eggs have outer membranes that protects the embryo from external shocks, cushion the embryo, promote gas transfer and store waste products. The eggs also have a hard or leathery shell that protects the embryo, albumen that cushions and provides moisture and nutrients to the embryo and yolk that supply food. It is this feature that has made reptiles so successful, allowing them to colonize areas where there is little water and this exploit a whole new range of habitats.

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Orders & Suborders:

Order Testudines
There are approximately 225 species of turtles worldwide. This order is characterised by a bony shell, limbs articulating internally to the ribs and a keratinized beak rather than teeth. Turtles have long life spans and most reach sexual maturity after 7 or 8 years and can live for more than 14 years. Large tortoises of the Gala'pagos Islands may live for over 100 years. Turtles are oviparous (lay eggs that develop outside the female body). Females lay about 100 eggs in the soil and development takes about 4 weeks to 1 year.

Order Squamata
This order is divided into three suborders:

Suborder Sauria - The Lizards
The lizards consists of about 3 300 species. In contrast with snakes, though there are a few without legs, most lizards have two pairs of legs. Lizards vary in length from only a few centimeters/inches to as large as 3 meters / 10 feet. Many lizards live on substrate surfaces and retreat under logs and rocks when danger lurks. Some lizards are burrowers or tree dwellers. Most lizards are oviparous (lay eggs that develop outside the female body), but some are oviviparous (eggs that develop inside the female body) or viviparous (offspring develop inside female reproductive track and is nourished by female). Eggs are usually deposited under rocks, debris and in burrows.

Geckos are short and stout. They are nocturnal (night living) and some are capable of clicking vocalization. Their eyes are adapted for night vision. They also have adhesive disks on their digits to aid them in clinging on almost anything (including glass).

Iguanas have robust bodies with short necks and distinct heads. This group includes the marine iguanas and the flying dragons (Draco).

Chameleons are also a group of iguanas. They have arboreal lifestyles and use a long, sticky tongue to capture food. Anolis, or the "pet-store chameleon" is also an iguanid, but is not a true chameleon. Anolis and Chameleons are well known for their ability to change colour in response to their environment or behavioural state.

The only venomous lizards are the Gila monster (Heloderma suspectum) and the Mexican Beaded lizard (Heloderma horridum). These lizards are native to the south-western parts of North America. Venom is released into grooves on the surface of teeth and introduced into prey as the lizard chews. Lizard bites are seldom fatal to humans.

Suborder Serpentes - The Snakes
Snakes consists of about 2 300 species of which about 100 are venomous. Snakes are elongate and lack limbs. The skeleton may consists of more than 200 vertebrae and joints between vertebrae make the body very flexible. Snakes possess skull adaptations that facilitate swallowing large prey. These include upper jaws that are movable on the skull and upper and lower jaws that are loosely jointed so that each half of the jaw can move independently. Most snakes are oviparous (lay eggs that develop outside female body), although a few can give birth to live young.

Suborder Amphisbaenia - Worm Lizards
The worm lizards consists of about 135 species. Worm lizards are specialized burrowers that live in the soil. Most are legless and their sculls are wedge or shovel shaped. A single median tooth in the upper jaw distinguishes Amphisbaenians from other vertebrates. They can move easily forward and backwards. Worm lizards are oviparous (lay eggs that develop outside the female body) and feed on worms and small insects.

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Some Biology:

Some reptiles posses a median or parietal eye that develops from outgrowths of the roof of the forebrain. In the tuatara it is an eye with a lens, a nerve and a retina. In other reptiles it is less developed. It is covered by skin and probably cannot form images. They can however distinguish between light and dark periods and are used in orientation to the sun.

Olfactory senses are better developed in reptiles than in amphibians. In addition to the partial secondary palate providing more surface for olfactory epithelium, many reptiles possess blind-ending pouches that open through the secondary palate into the mouth cavity. These pouches, called the Jacobson's organ, are best developed in the squamates. In other words, snakes smell by sticking out their tongue to "catch" the smell with chemical receptors and then by pressing it into the pouches of the Jacobson's organ.

If you think I should add more information to this section or think that something is incorrect, please contact me and let me know.

Last Updated 6 January 2006 by Renier Delport

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Related Topics:


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Miller, Stephen A. & Harley, John B. 1999 Zoology, Fourth Edition, McGraw-Hill.

Bartlett, R.D. & Bartlett, Patricia P. 1995 Chameleons, A Complete Pet Owner's Manual, Barron's Educational Books.
.:Buy from (RSA):.

Mattison, Chris 1994 A Practical Guide to Exotic Pets - How to Keep & Enjoy A Wide Range Of Unusual Pets.

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| Introduction | Reptile Classification | Orders & Suborders | Some Biology | Related Topics | References |
| Email This Page |


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