Tana Bao

Today there exist 6,500 of known species of reptiles, which are classified into four different orders under the class Reptilia:
1. Testudines (turtles)
2. Squamata (lizards and snakes)
There are almost 3800 species of lizards in the world, and around 2900 species of snakes. (CM)
3. Crocodilia (alligators and crocodiles)

  • It’s easy to tell the difference between Alligators and Crocodiles because crocodiles have long, narrow, V-shaped noses, while alligators have shorter, U-shaped noses. (LPE)
4. Sphenodontia (tuataras)
  • Sphenodontia date back to the mesoic era and used to be very diverse. Now only two species still exist. This is very sad. New Zealand has protective measures for these individuals. (LPE)
Today, lizards are the most abundant reptiles that exist.

(Matt B - Source 13)

Diagnostic Characteristics
Reptiles are usually described as "cold blooded." The scientifically correct term, however, is Ectothermic: describing an animal, such as a reptile, fish, or amphibian, that must use environmental energy and behavioral adaptations to regulate its body temperature. Also, the vast majority of reptiles lay shelled amniotic eggs on land. Furthermore, reptiles are characterized by keratinized skin (keratin being a protein that prevents water loss and subsequently dehydration).
Aligator's Anatomy (MS 17)
Aligator's Anatomy (MS 17)

Acquiring and Digesting Food
Snakes, for example, have sharp chemical sensors that can sense oncoming prey or predators. Snakes are also sensitive to ground vibrations and have heat-sensitive organs that allow them to know of slight temperature changes, drawing them towards prey. Some snakes, in addition, may inject chemical toxins through sharp teeth to effectively kill their food.

Most reptiles are carnivores and have noticeably strong jaws that are correspondingly efficient for crushing and gripping. They have a muscular tongue that can serve not only as a touch receptor, but as a tool to catch food. Reptiles typically have teeth, and some, like crocodilian teeth, are constantly replaced. In terms of actual digestion, the stomach is often equipped with pebbles to help grind food, and the liver and pancreas have a large arsenal of digestive enzymes. (JP- Source 4)

Sensing the Environment
Some reptiles are enabled with chemical sensors embedded on their bodies and some reptiles are able to feel slight ground vibrations. Also, some reptiles have the ability to sense temperature change.

In reptiles, senses are thought to be interrelated and not separate senses. Reptiles have a specialized chemically sensitive organ called the Jacobson's organ that is able to convert tastes into smells, increasing awareness of surroundings. Snakes and lizards flick their tongue, capturing particles in the air. They then press these particles against the Jacobson's organ, which is in the roof of the mouth. The organ then processes the particles and provides the reptile with environmental information. This organ helps the reptile find prey, find appropriate mates and even detect nearby predators.(SP)

Although hearing is an important factor to sensing the environment to some reptiles, certain reptiles such as the snake have extremely poor hearing. With only a single inner ear, snakes can only detect ground vibrations and airborne vibrations of low frequency. However, most reptiles can hear low pitch noises, which allows for some hearing ability. Also, some reptiles such as snakes have special organs to detect heat. These organs line in the lips of the snakes and are sensitive to infrared radiation. (RK)

Locomotion: the act or ability to travel from one place to another. Reptiles have evolved the ability to move through both the land and water.

Reptile have limbs that jut out from the body and then bend down, so that the bottom half of the leg is perpendicular with the ground. This causes a very strange gait that conserves energy by lengthening each step. Reptilians also don't keep their body very high off of whatever substrate they are on. (PS - Source 3)
Snakes move in four ways, since they obviously don’t have legs.
  1. Contracting into a pile then flinging themselves forward
  2. “slithering” by pushing of any bump or rock using their muscles and scales in a zig-zag motion (what most people think of when they imagine snakes)
  3. Bending their body then pushing forward (like an inchworm)
  4. Slowly creeping using some scales to grip the ground and pushing forward with others.(LPE)

Reptiles have internal lungs, which are the only respiratory surface they have, and therefore ventilate air in and out of their bodies.
Many species of reptiles are able to absorb oxygen and eliminate carbon dioxide through other body parts too. For example, the tissues (mucous membranes) lining the insides of the mouth of aquatic turtles may extract oxygen from the surrounding water. (SP) Also, some file snakes, part of the family Acrochordidae, and sea snakes, in the family Hydrophiidae, and the soft-shelled turtles, Trionyx, can use their skin for respiration when submerged. (SP)

Metabolic Waste Removal

Reptiles excrete uric acid through their feces. Uric acid is not very toxic nor soluble in water. It allows the organism to conserve water, creating concentrated feces, but producing uric acid uses up more energy than synthesizing urea, another type of waste. In reptile eggs, the waste of uric acid can accumulate in the eggs with damaging the embryos because of uric acid's low toxicity and solubility. (AR)

The blood temperature of reptiles is controlled by the environment and behavioral adaptations of the reptile itself.

Consisting of two atria and a single ventricle, the reptile possesses a three chambered heart. Because of its construction, the reptile heart allows for the mixture of oxygen rich and oxygen poor blood. While the lack of a partition in the heart does complicate circulation and decrease efficiency, the three chambered heart is a more than sufficient system for organisms such as reptiles. (ZJ- source 2)

The hearts of multipe reptiles (PS

Self Protection
Testudines (turtles) have evolved hard shells that protect them from predators.

Other ways that reptiles protect themselves include simply running away, threatening sounds such as hisses, camouflage, venom injections, and different forms of mimicry. (MB)
Coral Snake

Scarlet King Snake

The two pictures above depict Batesian mimicry, a form of self defense, between two different species of snakes. Can you guess which is poisonous? The picture on top shows the poisonous Coral Snake, while the one below is the harmless Scarlet King Snake. You can tell which is which only if you look very closely! The King Snake has a red face while the Coral Snake has a black face. (IL - sources 13 and 14)

Other reptiles have developed a way of offense to be their defense. For example, the crocodile has many very sharp teeth that can be used to defend itself against anything that is trying to hurt it. Multiple lizards and snakes use this form of defense as well. Snakes have fangs that do the same thing.

Horned lizard squirting blood from eyes as a form of self-defense
Horned lizard squirting blood from eyes as a form of self-defense

Some reptiles have very interesting forms of self-protection. For example, the horned lizard found in the southwest region of the United States pressures its own sinus cavities until the blood vessels in its eyes burst when it is attacked. This causes the attacker to be sprayed with blood from the eyes of the lizard. (VN).

Osmotic Balance
Most reptiles live near the water but spend a substantial amount of time in dry air. The scales of reptiles have evolved to contain a waterproof protein called keratin, preventing dehydration. It is important to note that reptilian skin is not a respiratory surface and that all gas exchange occurs in the lungs of reptiles.

Reptiles near the sea accumulate large amounts of salt in their body requiring nasal salt glands to remove the excess salt, secreting it in a concentrated salt solution. (AR)

All reproductive activity occurs through the cloaca the single exit/entrance at the base of the tail where waste is also eliminated. Most reptiles have copulatory organs, which are usually retracted or inverted and stored inside the body. In turtles and crocodilians, the male has a single median penis, while squamates, including snakes and lizards, possess a pair of hemipenes. Most reptiles lay amniotic eggs covered with leathery or calcareous shells. An amnion, chorion, and allantois are present during embryonic life. There are no larval stages of development. Viviparity and ovoviviparity have evolved only in squamates, and many species utilize this mode of reproduction. The degree of viviparity varies: some species simply retain the eggs until just before hatching, others provide maternal nourishment to supplement the yolk, and yet others lack any yolk and provide all nutrients via a structure similar to the mammalian placenta. (RW)

Reptiles lay eggs that are protected by many internal membranes and an outer shell. The amniotic egg has allowed reptiles to adapt to land and expand their locations/habitats by not being bound to water. (CP source 12)

The level of parental involvement demonstrated by reptiles largely depends on the order of the reptile. Testudines (turtles), for example, always lay eggs and often in large quantities. Turtles lay so many eggs because the survival rate of the eggs is so low that, without parental involvement, it is the only way to compensate for the eggs’ high morality. Turtles do not guard or care for their young after the eggs have been laid, choosing instead to bury the eggs in dirt or sand near bodies of water. Squamates (snakes and lizards), on the other hand, as a testament to their wide variety, reproduce in a variety of different forms; some lay eggs and other bear live young. Crocodilinsa (crocodiles and alligators) lay their eggs in nests, where the mother cares for the eggs by keeping them warm under the cover of mud and dead plant matter. After the babies have hatched, the mother provides no additional parental care. Sphenodontias (tuataras) lay eggs, and the young hatch after an incubation period that spans thirteen months.(MR; Source 18)

external image amniotegg.gif

Temperature Control
Reptiles do not control their body temperature. So they are forced to live in warmer climates or micro climates. Reptiles, as poikilothermic creatures, will seek out warm areas in the colder times of day. (RJ)

Review Questions
1. Are birds part of the reptile clade or mammal clade (because mammals and reptiles shared a common ancestor) ? (AP)
2. Sports coaches often say that good defense is the best offense. Is it most beneficial for an individual reptile to have sharp teeth and/or poison, a form of mimicry, or the speed to outrun many predators? Assume the reptile's main goal is self-preservation and not altruistic acts. (JS)

1. Campbell, Neil A., and Jane B. Reece. Biology. Sixth Edition. Boston: Benjamin-Cummings Company, 2002. (Tana Bao)
5. (MB)
7. (AR)
8. "Lizards" 30 Oct 2011
"Predators of snakes and snake defense" 30 Oct 2011 (MM)
9. "Reptiles." Free Webpages - The Fast, Easy and Free Way to Create Websites. 2002. Web. 30 Oct. 2011. <>. (SP)
10. "Reptile Senses: Understanding Their World - Page 1." Pet Place - Pet Care - Pet Names - Pet Health. Web. 30 Oct. 2011. <>. (SP) (LPE) (LPE)

11. "10 of the Most Bizarre Animal Defense Mechanisms | WebEcoist." WebEcoist | Strange Nature, Rare Animals & Weird World Wonders. Web. 06 Nov. 2011. <>. (VN)
12. "Biological Diversity 9." Estrella Mountain Community College. Web. 06 Nov. 2011. <>. (CP)
15. (RW)
16. (RK)
Aligator Anatomy. Digital image. Web. <>.
18. "Reptilia." Animal Sciences. Ed. Allan B. Cobb. New York: Macmillan Reference USA, 2011. Gale Science In Context. Web. 27 Nov. 2011.