Reptiles: Classification Study Guide


The four classes of reptilia are:

  1. Crocodilia (crocodiles and alligators),
  2. Sphenodontia (tuataras),
  3. Squamata (lizards and snakes), and
  4. Testudines.
  • Crocodilia has 25 species, Sphenodontia has two species, Squamata has roughly 9,200 species, and Testudines has about 325 species.

1. Crocodilia

  • Crocodilia emerged as a separate lineage during the middle Triassic, with alligators, crocodiles, gharials, and caimans as living species.

  • Crocodilians may be found in Africa, South America, Southern Florida, Asia, and Australia’s tropics and subtropics.

  • They live in freshwater, saltwater, and brackish ecosystems, including rivers and lakes, and spend most of their life in water.

  • Crocodiles are derived from terrestrial reptiles. Therefore they can still walk and sprint.

class crocodiliaSource

  • They frequently move swimming on their bellies, pushed by alternate leg motions. On the other hand, some animals can raise their bodies off the ground by bringing their legs beneath them and rotating their feet to face front. This style of mobility consumes a lot of energy and appears to be employed largely to remove obstructions on the ground.

  • Some crocodiles can even gallop, propelling themselves forward with their hind legs and moving their rear and forelegs in pairs. Galloping crocodiles have been observed at speeds of over 17 kph.

  • They are, however, short-distance runners that aren’t interested in a protracted chase.

2. Sphenodontia

class SphenodontiaSource

  • Sphenodontia developed during the early Mesozoic epoch, with considerable radiation, but only two live species remain, Sphenodon punctatus and Sphenodon guntheri, both located on offshore islands in New Zealand.

  • The term “tuatara” is derived from a Maori word that describes the crest on its back.

  • Tuataras have biconcave vertebrae and a rudimentary diapsid skull.

  • They may reach 80 centimeters in length and weigh around a kilogram.

  • Despite their apparent resemblance to an iguanid lizard, the skull and jaws have significant distinguishing traits that set them apart from the Squamata.

  • Tuataras have a third (parietal) eye in the center of their forehead with a lens, retina, and cornea. Only extremely young animals have visible eyes, quickly covered by skin. Parietal eyes can detect light, although color differentiation is restricted.

  • Other lizards have light-sensing systems that are similar to this one.

  • Tuataras have two rows of teeth in their upper jaw that bracket a single row of teeth in the lower jaw. These teeth are essentially projections from the jawbones, and when they wear down, they are not replaced.

3. Squamata

  • Extant species include lizards and snakes, and the Squamata (“scaly or possessing scales”) evolved in the late Permian.

  • Except for Antarctica, both are present on every continent.

  • Unlike snakes, most lizards have four limbs, although they have been deleted or drastically reduced in at least 60 lineages.

  • Snakes do not have eyelids or external ears, seen in lizards.

  • There are around 6,000 different kinds of lizards, ranging in size from tiny chameleons and geckos that are just a few centimeters long to the 3-meter long Komodo dragon.

  • Chameleons and other lizards may alter their skin color by dispersing pigment inside their chromatophores. Chameleons alter their color for concealment as well as social signaling.

  • Lizards’ retinal cells contain a variety of colored oil droplets, allowing them to see a wide spectrum of colors.

class squamataSource

  • Unlike snakes, lizards may change the shape of their lens to focus their eyes, and Chameleons’ eyes may move independently.

  • Both lizards and snakes use their tongues to sample the environment, and Jacobson’s organ, a pit in the roof of the mouth, is used to analyze the sample gathered.

  • Most lizards eat meat. However, some big species, such as iguanas, eat plants.

  • The skulls of most snakes are extremely flexible, including eight rotating joints.

  • They also vary from other squamates in that their mandibles (lower jaws) lack anterior bony or ligamentous attachment.

  • The majority of snakes are non venomous, and they swallow their prey whole or constrict it before swallowing it. Snakes with venom use it to kill or immobilize their prey, as well as to aid digestion.

  • Snakes do not have eyelids, but a transparent scale protects their eyes. Their retinas include both rods and cones, and unlike many mammals, they lack red light receptor pigments.

4. Testudines

  • The clade Testudines includes turtles, terrapins, and tortoises.

  • Turtles’ shells are more than simply an epidermal covering; they are also part of their skeletal structure.

  • The carapace is the dorsal shell, which contains the backbone and ribs, whereas the plastron is the ventral shell.

  • Pleurodira and Cryptodira, the two extant families of turtles, have substantial structural variations that are most clearly distinguished by how they retract their necks.

  • Crocodiles, lizards, and snakes were preyed upon by the Testudines, who appeared some 200 million years ago.

  • Turtles and tortoises are found in around 325 different species.

  • Turtles, like other reptiles, are ectotherms.

  • Although many species dwell in or near water, all turtles are oviparous, meaning they lay their eggs on land.


Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (Testudines) are the four living orders that make up the class of reptilia.


1. What classification level is a reptile?

The classification level of reptiles is ‘class.’ It’s also termed “class Reptilia.”

2. How many orders of reptiles are there?

  • Crocodilia (crocodiles and alligators),
  • Sphenodontia (tuataras),
  • Squamata (lizards and snakes), and
  • Testudines

3. What are the 5 characteristics of reptiles?

  • Reptiles are four-legged vertebrate animals.
  • The majority of them lay eggs. (oviparous)
  • Reptiles have scales (or scutes) covering their skin.
  • Reptiles have cold-blooded metabolisms.
  • They need their lungs to breathe.

4. What are the main features of reptiles?

The 7 main characteristics of reptiles include:

  • Dry skin with scales but no feathers (as in birds) or hair (as in mammals)
  • internal fertilisation
  • a three- or four-chambered heart
  • cold-bloodedness
  • the presence of lungs
  • direct development, without larval forms as in amphibians
  • an amniote egg

5. Why are reptiles classified together?

Reptiles were formerly classed based on their physical characteristics (morphology): they are ectothermic, have leathery or hard-shelled eggs, scale-covered skin, and are amniotes. Reptiles, like other vertebrates, have a bone skeleton to support their body.

6. What best describes a reptile?

Cold-blooded animals are reptiles, and they have scales on their dry skin. And Reptiles are distinguished from other animals by their dry, rough skin. Reptiles include snakes, turtles, and crocodiles, to name a few.

8. What are 3 facts about reptiles?

  • Most reptiles are cold-blooded animals.
  • Crocodiles are known for sweating through their mouths.
  • Not all reptiles lay shelled eggs, although the majority do.

9. How do you describe a reptile?

Reptiles are air-breathing animals with scales, bony plates, or a mix of both on their skin. Crocodiles, snakes, lizards, turtles, and tortoises are among them. Reptiles are cold-blooded due to their sluggish metabolism and heat-seeking habit.

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  1. Reptile Classification. Accessed on 6 Dec 2021.
  2. Reptilia. Accessed on 6 Dec 2021.
  3. Reptile. Accessed on 6 Dec 2021.
  4. Reptile Classification. Accessed on 6 Dec 2021.

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