Figure 1: Comparing Reptiles and Amphibians

Review padlets (pass: bio)

Biology 2-1 review question padlet

Biology 1-1 review question padlet

  • Reptiles were the first animals adapted to life entirely on land.
  • Reptiles evolved from amphibians ~ 320 million years ago and displaced amphibians in many environments.
  • Reptiles are ectotherms (“cold-blooded”)

Major Evolutionary Advancement – Amniotic Egg

  • Developed from internal fertilization and provides the embryo with atmospheric oxygen, food, and water.
  • Egg covered in a mineralized shell – reptiles have leathery eggs
  • Removes nitrogenous wastes and protects the embryo from drying out.
  • This marks the start of the amniotes (animals with amniotic eggs)
  • Amniotes include : Class Reptilia, Class Aves, and Class Mammalia.

The amniotic egg is different because they have four extra membranes:

a.Amnion– thin membrane enclosing the fluid in which the embryo floats/prevents drying out.

b.Allantois– stores wastes produced by the embryo.

c.Yolk Sac– Surrounds the yolk (nutrients for embryo)

d.Chorion– Outermost membrane of the egg – protects embryo and allows gas exchange

Figure 2: Diagram of a reptilian Amniotic Egg

General Anatomy

  • Have claws to protect and help them obtain food
  • 90 degree leg position Provides greater body support compared to amphibians.

Integument: Tough, dry scaly skin that offers protection against desiccation (drying out) and physical injury.

  • Skin can also have chromatophores for colouration.
  • All reptiles shed their skin, however snakes shed the entirety of their skin in one session. This replaces old worn out skin and removes parasites.
Figure 3: Komodo Dragon (taken by me!)


  • Ectothermy – “Cold blooded”
  • Reptiles are ectotherms, meaning they rely on environmental (or outside) heat sources
  • Since they do not produce much internal sources of heat/regulation, ectotherms are able to use much less energy and have lower metabolic.
  • The term “cold-blooded” is technically not correct since blood temperature changes with environmental temp.
Figure 4: Graph of ambient temperature vs. body temperature. Notice how the ectotherms temperature is rises with the ambient temperature, where as endotherms (who produce their own heat) maintain a relatively steady temperature.
  • But, What about fish and amphibians?
  • Fish and amphibians are all ectothermic as well!
  • Question: Reptiles and all previous vertebrate classes are ectothermic – can you make a prediction as what major evolutionary advancement will occur in terms of thermoregulation?

Physiology – Senses

Jacobson’s Organ

Figure 5: Jacobson’s organ
  • The olfactory areas in the nose are not well developed in reptiles.
  • Using their tongues, many reptiles, amphibians, and mammals can can detect chemicals (smell/taste) in the air via the Jacobson’s organ.

Heat-sensitive organs (or pits)

  • In some snakes
  • Detect the heat from prey, and nerves transmit this info to the same area in the brain that receives optic nerve impulses (sees a “heat image” of prey – just like an infrared camera!)

Physiology – Digestive System

  • Digestive tract is similar to amphibians, however is longer, with a larger J shaped s
    Figure 6: Comparing vertebrate digestive systems (first five classes)

    tomach (similar to higher vertebrates such as mammals)

  • It includes the mouth and its salivary glands, the esophagus, the stomach, and the intestine and ends in a cloaca.
  • One pair of salivary glands evolved to become venom glands in many reptiles. (yes, snake venom is modified saliva!)


Fun fact: Evolution of Snake Venom

  • In snakes, venom has evolved to kill or subdue prey and due to its effectiveness, snakes diversified relatively rapidly.
  • Interestingly, the venom system has also subsequently atrophied, or has been completely lost in many species after its evolution.
  • For example, many American Rat Snakes lost their venom following the evolution of constriction as a means of prey capture. (however they still possess remnants of the system)
  • BC has its own venomous rattlesnake – The Northern Pacific Rattlesnake (Crotalus oreganus oreganus)

Figure 7: Northern Pacific Rattlesnake range

Physiology – Reproduction

  • Oviparous with internal fertilization (lays amniotic eggs)
  • Most male reptiles have two sex organs called hemipenes. They are housed internally in males just at the base of the tail, and are everted when needed.
Figure 8: Everted hemipenes (Order Squamata)
  • In many snakes, the hemipenes possesses spines or hooks, in order to anchor the male within the female.
  • Unlike many other reptiles, alligators/crocodiles use a penis that is always erect and “pops” out of their bodies to mate

    Figure 9: A graph plotting proportion of female turtles born vs. incubation temperature
  • In some reptiles, nest temperature determines sex of the hatchlings. This is called temperature-dependent sex determination.For example, In turtles, low temperatures during incubation produce males and high temperatures produce females.
Parthenogenesis – reproduction
  • Parthenogenesis = reproduction from an ovum without fertilization
  • The only vertebrates that show true parthenogenesis are the squamates, with about 50 lizard species and one snake being obligate parthenotes.
  • These are unisexual species, all individuals being females that reproduce asexually without the intervention of any male.
  • Ex. Tropical Night Lizards

Physiology – Circulatory system

  • Figure 10: Comparing vertebrate hearts

    Most reptiles have a three-chambered heart and double loop blood circulation (similar to amphibians)

  • However, reptiles have an incomplete septum, or wall dividing the ventricle into two.
  • More efficient than amphibians, but still not the most complex!
Figure 11: Typical reptilian circulation (Order Crocodilia not included)
Figure 11-b: Comparing Vertebrate respiratory systems

Crocodiles – a big difference!

Order Crocodilia (Alligators and crocodiles­) have developed four chambered hearts and are closely related to birds – What heart structure would you expect in Class Aves?

Physiology – Respiration

  • Reptiles are more active than amphibians, so they need more oxygen.
  • Reptiles cannot skin breathe; their dry scaly skin is “watertight” to avoid water loss.
  • The lungs of reptiles contain a larger surface area
Figure 12: Comparing amphibian and reptile lungs

Groups of Reptiles

Order Testudines (“Turtles, tortoises, terrapins”)

In North America:


  • Are usually water-dwelling and have streamlined, disk-shaped shells and webbed feet or flippers to rapidly move in water.
  • They swim, but they also climb out onto banks, logs, or rocks to bask in the sun.
Figure 13: Turtle!


  • Are land-dwelling and tend to have dome-shaped shell to retract their head & limbs.
  • They have thick sturdy legs and feet for moving on land and eats low-growing shrubs, grasses, and even cactus.
  • Tortoises that live in hot, dry habitats use their strong forelimbs to dig burrows.
Figure 14: Tortoise!


  • Spend their time both on land and in water, and live along rivers, ponds, and lakes. Terrapins are often found in brackish, swampy areas.
Figure 15: Terrapin!

Order Squamata (“Lizards and Snakes”)

  • Snakes and lizards have a kinetic skull, which means it is modified to have movable joints, specialized for eating large prey.
  • In snakes, the two halves of the lower jaw (mandibles) are joined only by muscles and skin, allowing them to spread widely apart.
  • Since a snake must keep breathing during the slow process of swallowing, its tracheal opening (glottis) is thrust forward between the two mandibles.
  • Swallowing may take several hours but saliva begins digestion during swallowing.
Figure 16: The kinetic jaw of a snake
  • Snakes have no external ears or tympanic membrane, but are quite sensitive to vibrations carried in the ground – their jaw carries the vibrations into the ear to the cochlear bone

Order Crocodilia (“Crocodiles and alligators”

  • Crocodilians are large, aquatic reptiles; of the living reptiles, they are the most closely related to dinosaurs.
  • Live in tropical and subtropical regions around world and can usually be distinguished based on head morphology:

Crocodiles – Long triangle-shaped heads; when mouth is closed you can see the upper and lower teeth showing; teeth vary in size.

Alligators – Wide flat heads with round noses; When mouth is closed only the upper teeth are showing; Teeth vary in size.

Figure 17: Crocodile and alligator morphology
  • All are aggressive carnivores

Order Sphenodontia (“Tuataras”)

  • Tuataras are nocturnal, lizard-like reptiles that live in burrows often shared with petrels. They usually hide in burrows during the day and feed on insects, worms, and other small animals at night
  • Only 2 living species; both inhabit only a few small islands of New Zealand.
  • They were once widespread throughout the two main islands of New Zealand. Humans introduced non-native animals, including rats, cats, dogs, and goats, which prey upon tuataras and their eggs.

    Figure 18: Tuatara