Animalia Chordata Reptilia


edited by: Meru Nangia, Omer Zaidi, Yasheka Sharma, Jesse Carmen, Sarah Schwarzschild, Rachel Kornetsky, Josh Czik, Becca Levenson, Brittany Marcus-Blank, Hilary Stepansky, Sarah Vlach, Hanna Zhu, Denny Poliferno, Daisy Joo, Grace Rehnquist, Ethan Richman

Diagnostic Characteristics

There are about 6500 modern day extant species of reptiles. These species are divided into four orders: Sphenodonita (tuatra), Testudines (turtles), Squamata (lizards and snakes) and Crocodilia (alligators and crocodiles). For the most part, reptiles lay eggs, although certain species can give live birth. The fertilization of eggs occurs internally inside the female. Reptiles have several evolutionary adaptations such as scales that contain the protein keratin and waterproof skin that help them survive in terrestrial environments. Reptiles were the dominant terrestrial vertebrates for about 200 million years dating back to the first species dinosaurs.(1)

Acquiring and Digesting Food

Reptiles are a large group of diverse species that contains both carnivores and herbivores. The adaptations for acquirement of food are as numerous as the number of reptile species. One particularly interesting method of acquiring food is seen in snakes. Some snakes have acute chemical sensors and heat detecting organs that help them home in on their prey. Once the prey is located, the snake will use its hollow fangs to inject toxins that paralyze and digest the prey from the inside.Also, some snakes, such as the anaconda in the video above (OZ), have a loosely articulated jaw structure that allows them to swallow prey that is larger than the snake in body diameter. Other reptiles such as certain types of lizards and crocodiles will use camouflage in order to disguise themselves until unsuspecting prey approaches. When the prey is within reach, most reptiles use speed and agility to capture it.(1)

external image moz-screenshot.jpgexternal image moz-screenshot-1.jpgexternal image moz-screenshot-2.jpg
A snake can unhinge its jaws in order to accomodate prey even larger than the bird in this picture. (DP)
A snake can unhinge its jaws in order to accomodate prey even larger than the bird in this picture. (DP)

Sensing Environment

The majority of carnivorous reptiles have a highly developed olfactory sense that helps them in detection prey. Although snakes don’t have ears, they are highly sensitive to vibrations in the ground, which allows them to detect predators and prey in their vicinity. Additionally, reptiles use their eyes to perceive the environment around them.(1) Lizards and snakes also use an acute sense of smell to detect what is around them. They have an extension of their nasal organ in the roof of their mouth, known as the Jacobson's organ. whenever snakes and lizards try to detect nonairbourne odors, they stick out their tongue, touch it against any object around them, and retract it back in their mouth. Any odor on their tongue is adhered to the Jacobson's organ and is processed by the brain. (5) [JAC]

The snake can process the smell detected by their tongue because of the sensitive tissue of the Jacobson's organ that aids in the sense of smell. (13 SV)


For the most part, reptiles have legs (with the exception of snakes). When it comes to chasing prey or running away from predators, the relatively short legs of most reptiles are capable of surprising speed. The reason snakes don’t have legs is because snakes are believed to evolve from lizards in order to suit a burrowing lifestyle (although most modern day snake species live above ground).(1) Most lizards walk on all fours although some use their hind legs when running. Some snakes and other legless reptiles move by attaching their belly scales to rough surfaces and pulling themselves forward. (11) (BMB)
Snakes are able to move due to their ventral scales, the rectangular scales on the underside. These grip the surface and propel the snake forward in 4 basic movements, illustrated below (14 DJ).

external image snake-motion.gif
The four basic movements of the snake, each dependent on the ventral scales (14 DJ).


One major difference that exists between reptiles and amphibians is the reptiles’ ability to conduct all of their gas exchange through the lungs (with the exception of certain turtles that can conduct gas exchange through the moist surfaces of their cloaca).(1) This means when the reptile inhales, oxygen fills the lungs then switches places with the old oxygen so the new oxygen can go through the blood stream. This is called diffusion.(SJB)(10)

Metabolic Waste Removal

Reptiles use a similar waste removal mechanism to that of mammals. The matter that cannot be digested is excreted through the process of defecation. Excretion happens by the two small kidneys.(1) Reptile kidneys are unable to produce liquid urine more concentrated than their body fluid, so many reptiles use the colon, which is part of the digestive system, to help with the reabsorption of water or some can take water stored in the bladder. Wastes are excreted from the kidney as uric acid, which is a nitrogenous waste that helps reptiles to conserve water (6 SES). Excess salts are also excreted by nasal and lingual salt-glands in some reptiles. (3. Sharma)


Reptiles have a complex circulatory system. Blood is utilized to transport oxygen and a variety of other substances into every single cell of the body. Blood is also used to remove waste products from cells. A three chambered heart carries out the task of pumping the blood through the body of the reptile.(1)
Most reptiles posses a three chambered heart, with the exception of alligators and crocodiles. A three chambered heart consists of two atria and one ventricle. Blood from the body enters the right atrium, and is then conducted into the ventricle. The ventricle then pumps the bloods from the ventricle to the lungs, where it becomes oxygenated. The oxygenated blood is then carried into the left atrium. The left atrium them pumps the blood into the ventricle and then into the body. This system is not as efficient as a possible because the deoxygenated blood and the oxygen rich blood mix in the ventricle. This means that organs are not getting as much oxygen as they optimally could. [2 Nangia] (Nangia) (Nangia)

Self Protection

A variety of different reptile species have different adaptations that allow them to protect themselves from predators. Turtles carry a hard shell, which allows them to retreat into its safety whenever predators are nearby. Some reptile species are the top predators in their ecosystem and therefore no self-protection mechanism is necessary. This is observed in some of the larger reptiles such as alligators, crocodiles and komodo dragons. Still other species of reptiles use camouflage in order to disguise themselves from predators and prey.(1)While larger reptiles may not have any mechanisms to protect them from other animals, many of them have tough and scaly skin (made of keratin, a protein) to keep them from drying out and cracking and from physically injuring themselves (6 SES). When scales need to be replaced, some reptiles will shed the first layer of their skin to reveal a new healthy skin layer with intact scales (6 SES). In addition to the use of scales as protection, the reptile's tail can be used as defense mechanism by swinging it from side to side to ward off predators, like the tail of the alligator, pictured below. Other species of reptile use their tails in a very different way defensively. Some lizards will release, or autotomize, their tails which will confuse their predators enough to allow them to escape (9 BL).

external image
external image
Snake venom is used to poison enemies and prey. (15)(RJS)


Most reptiles lay eggs but a few give birth to live young. The male and female usually go through a ritualized courtship before copulation (sex). Once sperm are inserted into the female's cloaca (a chamber where intestinal, reproductive, and urinary systems empty), the female can store the sperm for up to 6 years. Eggs can then be fertilized without further contact with the male (7). (RK) Reptiles reproduce sexually, and fertilization happens internally (6 SES). Reptiles release their eggs, rather than the female keeping the egg within her body, like mammals do (6 SES). Reptile eggs contain food and provide a protective membrane for the baby reptile (6 SES). These factors help the reptile to develop inside the egg until it is ready to hatch (6 SES). One site explains that the evolutionary innovation to produce eggs with a large yolk, the food for the developing young, and a shell allowed for reptiles to dominate the terrestrial landscape for millions of years. Some lizards and snakes have made even further evolutionary innovations, evolving the ability to retain their eggs internally until they have hatched, giving birth to fully developed young, a process called vivipary. Most reptiles, however, lay eggs which have leathery shells which are resistant to drying. After birth, parental care is very rare in reptiles; in most species, the young are independent of their parents from the moment they hatch. (8) (SS) In some species of reptiles, courtship occurs before reproduction, involving both visual and auditory displays to attract the opposite sex. For example, some male lizards expose brightly colored body parts while other types give mating calls. (12) (BMB)

Osmotic Balance

Reptiles are well adapted to terrestrial living. They have scales that contain the protein keratin; these scales are waterproof and therefore help prevent dehydration in dry environments. Keratin scales are similar to the waxy covering of cuticle on plants and the chitin cuticle found on insects (OZ).(1)

Temperature Balance

Since reptiles are ectothermic (absorb external heat instead of generation their own), they can survive on 10% the amount of calories required for a mammal of a similar size. Reptile body temperature is regulated through their behavior as opposed to metabolic processes. They will move into the sun in order to warm up or move into a shady area in order to cool down.(1) A reptile also regulates its temperature physiologically. For instance, for some reptiles that swim in cold waters (such as the marine iguana of the Galapagos Islands) heat is maintained through the constriction of blood vessels. Also, some reptiles may even become endothermic (organisms whose bodies are warmed through metabolic reactions.) An interesting case of an endothermic reptile is in the female python. When the female python is incubating its eggs, it must increase its metabolic activity (through shivering) to produce enough heat for itself and its eggs. (Jesse Carmen)[4]

1) Explain how reptilia are able to sense their environment by using sight, sound, and smell. (HS)
2) How do reptiles use changes in behavior to regulate the temperature of their body? (HZ)
3) State and explain the difference between reptile and amphibian respiration. (VM)
4) What gives snakes the ability to open their jaws so widely that they can inject animals larger than them? (GR)

5) Describe the reproductive methods that reptiles use. (ER)

(1)Campbell, Neil A., and Jane B. Reece. Biology. 6th ed. Boston: Benjamin-Cummings Company, 2002.
[2] "Three-chambered heart." Def. 1. Biology Online. 30 Sept. 2006. Scientific American Partner Network. 30 Nov. 2008 <>.

[3] <>
[4] Campbell, Neil A., and Jane B. Reece. Biology. 6th ed. Boston: Benjamin-Cummings Company, 2002.
[5][6] "Characteristics of Reptiles That Distinguish Them from Amphibians." 7 Dec. 2008. <>
(7) Wissman, Margaret. "Reptile Reproduction: From Egg to Adult." Pet Place. 1999. 7 Dec. 2008 <>.
[8] Hebert, Paul D. "Reptile." The Encyclopedia of Earth. 9 Oct. 2008. Boston University. 7 Dec. 2008 <>.

(9) "reptile." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 07 Dec. 2008 <>.

(11) "reptiles
." Student's Encyclopædia. 2008. Britannica Student Encyclopædia. 7 Dec. 2008 <>.
(12) "
reptiles." Student's Encyclopædia. 2008. Britannica Student Encyclopædia. 7 Dec. 2008 <>.
(13) "Sense organs" 13 Dec. 2008 <>.
(14) Perry, Lacy. "How Snakes Work." How Stuff Works. Discovery. 17 Dec. 2008 <>.
15."Evolution’s Most Effective Killer: Snake Venom ." 18 Dec 2008 <>.