Difference Between Mammals and Reptiles

Main Difference – Mammals vs Reptiles

Mammals and reptiles represent two classes of animals that belong to the phylum Chordata. Mammals are warm-blooded animals whereas reptiles are cold-blooded animals. Mammals have hair or fur surrounding the body while reptiles have scales. Mammals give birth to live young and reptiles lay eggs. The main difference between mammals and reptiles is that mammals have mammary glands to feed their babies with milk whereas reptiles do not have mammary glands. Turtles, tortoises, lizards, snakes, crocodiles, alligators, and tuatara are reptiles while marsupials, monotremes, and placentals are the three types of mammals.

Key Areas Covered

1. Mammals
      – Definition, Facts, Characteristics
2. Reptiles
     – Definition, Facts, Characteristics
3. What are the Similarities Between Mammals and Reptiles
     – Outline of Common Features
4. What is the Difference Between Mammals and Reptiles
     – Comparison of Key Differences

Key Terms: Chordates, Eggs, Hair, Mammals, Mammary Glands, Reproduction, Reptiles, Scales

Difference Between Mammals and Reptiles - Comparison Summary

Mammals – Definition, Facts, Characteristics

Mammals are warm-blooded animals that nourish their young with milk secreted by mammary glands. Approximately, 5,500 species of mammals are found in each and every habitat on the earth such as tropical rainforests, deep sea, and deserts. Generally, mammals grow into a large body size. The size of mammals varies from one-ounce (shrews) to 200 tons (Whale). Since mammals are warm-blooded animals, they maintain their body temperature independent from the external environment. This is achieved by the by the heat produced by their endothermic metabolism of the body. One of the main features of a mammal is the presence of fur or hair growing in some parts of the body. The hair can be in different forms such as thick fur, horns, long whiskers, and defensive quills. The main function of hair is the insulation of the body against cold.

Difference Between Mammals and Reptiles

Figure 1: Squirrel

Mammals exhibit internal fertilization, and the embryo develops inside the mother into a young. Hence, most mammals give birth to mostly-developed live young. One of the most significant features of mammals is the presence of mammary glands, a type of enlarged sweat glands, to breastfeed the young. Placentals, marsupials, and monotremes are the three types of mammals.

Reptiles – Definition, Facts, Characteristics

Reptiles are cold-blooded, vertebrate animals who possess a dry, scaly skin and lay shelled-eggs on the land. The regulation of the body temperature of reptiles mainly depends on the external temperature of the environment. The skin of reptiles is water-tight due to the presence of horny epidermis layer. Some reptiles such as turtles have a hard shell. Others have soft or hard scales. The vision of most reptiles is adapted to daylight. Their visual depth perception is more advanced than that of amphibians and mammals. Most reptiles are tetrapods. However, some reptiles such as snakes do not have limbs. Their spinal column aids in locomotion. Reptiles have a large cerebrum and cerebellum.

Main Difference - Mammals vs Reptiles

Figure 2: Lizard

Reptiles lay eggs that are covered either with calcareous or leathery shells. They feed their young mainly through hunting. The tail of some reptiles can be shed as a defense mechanism. The principal defense mechanism of snakes is the delivery of venom to the enemy.

Similarities Between Mammals and Reptiles

  • Mammals and reptiles are two classes of the phylum Chordata.
  • The nerve cord of both mammals and reptiles are protected by a nerve cord.
  • Both mammals and reptiles have a sophisticated nervous system.
  • Both mammals and reptiles have bilateral symmetry.
  • Both mammals and reptiles are tetrapods, having four limbs.
  • Both mammals and reptiles breathe through lungs.
  • The respiratory system of both mammals and reptiles have a pharynx.
  • Both mammals and reptiles have a closed circulatory system with a heart.
  • Both mammals and reptiles have a complex exoskeleton made up of bones.
  • Both mammals and reptiles have well-developed sense organs.
  • The reproductive and excretory systems overlap in both mammals and reptiles.
  • Both mammals and reptiles undergo sexual reproduction as the major method.
  • Both mammals and reptiles are unisexual animals with internal fertilization

Difference Between Mammals and Reptiles


Mammals: Mammals are warm-blooded animals that nourish their young with milk secreted by mammary glands and have skin more or less covered by hair.

Reptiles: Reptiles are cold-blooded, vertebrate animals who possess a dry, scaly skin and lay shelled-eggs on the land.


Mammals: The epidermis of mammals is covered with hair.

Reptiles: The epidermis of reptiles is covered with scales.


Mammals: The heart of mammals consists of four chambers; left atrium, right atrium, left ventricle, and right ventricle.

Reptiles: The heart of reptiles consists of three chambers; left auricle, right auricle, and ventricle.


Mammals: Mammals are warm-blooded animals.

Reptiles: Reptiles are cold-blooded animals.


Mammals: Mammals have a diaphragm that assists respiration.

Reptiles: Most reptiles lack a diaphragm.

Metabolic Rate

Mammals: Mammals have a high metabolic rate.

Reptiles: Reptiles have a low metabolic rate.

Mode of Reproduction

Mammals: Mammals are viviparous, the young develop inside the mother’s womb and give rise to the live young.

Reptiles: Reptiles are oviparous animals, who lays eggs.


Mammals: Mammals develop a placenta.

Reptiles: Reptiles lack a placenta.

Mammary Glands

Mammals: Mammals have mammary glands that produce milk.

Reptiles: Reptiles lack mammary glands.

Care of Young

Mammals: Mammals care for the young for a longer period of time.

Reptiles: Reptiles care the young for a short period of time.


Mammals: Mammals have a limited growth after adulthood.

Reptiles: Reptiles have a continuous growth.


Mammals: Mammals have a skull with an expanded brain case.

Reptiles: Reptiles have a skull with a small brain case.

Occipital Condyle

Mammals: Mammals have two occipital condyles in their skull.

Reptiles: Reptiles have single occipital condyle in their skull.


Mammals: The cerebrum of mammals is larger and convoluted.

Reptiles: The cerebrum of reptiles is relatively small.

Cognitive Ability

Mammals: Mammals have high levels of cognitive ability.

Reptiles: Reptiles have low levels of cognitive ability.


Mammals: The jaw of mammals is formed by a single bone.

Reptiles: The jaw of reptiles is formed by several bones.

Middle Ear Bone

Mammals: Mammals have three middle ear bones: malleus, incus, and stapes.

Reptiles: Reptiles have a single middle ear bone: columella that resembles stapes.


Mammals: Two sets of teeth occur during the lifetime of mammals; deciduous and permanent. Mammals have complex cheek teeth.

Reptiles: The teeth of reptiles are continuously-replaced by simple cheek teeth.

Bony Plate

Mammals: The bony plate of mammals separates the mouth from the nasal passages completely.

Reptiles: The bony plate of reptiles is incomplete.


Mammals: Mammals have ribs confined to thoracic vertebrae.

Reptiles: Reptiles have ribs on all vertebrae.

Pelvic Bones

Mammals: The pelvic bones are fused in mammals.

Reptiles: The pelvic bones are separated in reptiles.


Mammals: Mammals have limbs directly beneath the body.

Reptiles: Reptiles have limbs emerging horizontally from the body.


Mammals: Mammals have an upright stance-locomotion.

Reptiles: Reptiles have a sprawling gait.


Mammals and reptiles are two classes of chordates that have a vertebral column, covering the nerve cord. Mammals give birth to live young, and they have mammary glands to feed their babies. They also possess hair all over the body. Reptiles lay eggs and feed their babies by hunting food. The body of reptiles is covered with scales. The main difference between mammals and reptiles is the mode of reproduction.


1.“Mammals.” National Geographic, .
2.“Reptiles”. Saint Louis Zoo, .

Image Courtesy:

1. “1026395” (CC0) via
2. “2354834” (CC0) via

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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