Difference Between Reptiles And Mammals

Mammals and reptiles are two classes of animals that are abundant and diverse classes of chordates and vertebrates that are members of the phylum Chordata. While there are a few anatomical similarities between mammals and reptiles, although you may ask, what is the difference between mammals and reptiles?

Mammals and reptiles exhibit profound differences that differentiate them into distinct classes with unique adaptations. Understanding the difference between similar terms and functions allows you to gain key insights into vertebrate evolution.

In our guide, you can learn more about the many differences between mammals and reptiles. By the end, you’ll better understand the other diverse group than mammals that reptiles make up.  You’ll also see how mammals are warm-blooded animals and reptiles are cold-blooded animals and how this adds more differences between mammals vs reptiles. (Read 75 Gallon Tank For Bearded Dragon)

Reptiles and Mammals

Overview of Reptiles and Mammals

Mammals and reptiles belong to the phylum Chordata. This phylum contains all vertebrate animals, meaning those with a backbone. Within the phylum Chordata, reptiles and mammals fall under different classes:

Reptiles are members of the class Reptilia. This diverse group includes turtles, snakes, lizards, crocodiles, and more. There are over 10,000 species of reptiles.

Mammals belong to the class Mammalia. There are around 6,000 species of mammals, including humans. Well-known examples include dogs, cats, horses, whales, bats, and primates like monkeys and apes.

So while reptiles and mammals are both vertebrates, they represent two distinct classes of animals with many differences.

Classification Difference Between Mammals and Reptiles

There are fundamental differences in the biology, anatomy, and evolutionary history of reptiles and mammals since they are categorized into different taxonomic classes. Look at how the two classes are separated in more detail below:


Classified based on physical traits, reptiles have scales, and female reptiles are egg-laying. The class Reptilia consists of cold-blooded vertebrates with scales or scutes on their skin that reproduce by laying shelled eggs on land.

This unites snakes, lizards, turtles, crocodilians, and extinct species like dinosaurs. (Read Can Bearded Dragons Eat Ladybugs)



Mammals also share traits like hair and milk production. Mammalia consists of warm-blooded vertebrates distinguished by hair, three middle ear bones, and mammary glands that produce milk to feed young. This includes diverse species like platypuses, bats, whales, and primates.

So reptiles are defined by egg-laying, scales, and cold blood; experts believe the lower jaw bone of reptiles is made up of three bones. In mammals, this is firmly attached to the skull have evolved into the three middle ear bones.

Also, mammals are united by warm blood, fur/hair, milk, and a sophisticated middle ear that reptiles lack.  You can also find well-developed sense organs and reproductive and excretory systems overlap, and each has a sophisticated nervous system. Yet warm-blooded animals possess many traits reptiles do not possess.

Physical Differences

Reptiles and mammals have distinctly different physical characteristics due to their evolutionary histories. Here are some of the major physical differences:


Reptiles are covered in tough, dry scales or scutes. Mammals have skin covered by hair and often fur.

Temperature regulation:

Reptiles are ectothermic or “cold-blooded” – they rely on external sources like the sun to maintain their body temperature. Mammals are endothermic or “warm-blooded animals” – they maintain a constant body temperature. (Read What Is The Difference Between Goose And Geese)


Even though their sizes may vary, reptiles have uniform-shaped teeth. Mammals grow only two sets of teeth throughout their lives, whereas reptiles’ teeth continue to grow throughout their lifetimes. The initial set, also called milk teeth, is unique to mammals.


Many mammals have a highly developed sense of smell, while reptiles rely more on vision and sensing vibrations.


Reptiles have short limbs or none at all (snakes). Mammals generally have longer limbs adapted for running, climbing, digging, swimming, or grasping.

Eggs vs. live birth:

Nearly all reptiles lay eggs. All mammals give live birth to young (except monotremes like platypuses). These are just some of the major physical differences that set reptiles and mammals apart. The mammal body plan is specialized for a high metabolism, mobility, and care of offspring.

Reproduction Differences

When it comes to reproducing and caring for offspring, reptiles, and mammals have markedly different strategies:

Eggs vs. live birth:

As mentioned, nearly all reptiles lay eggs covered by a protective shell and membrane. Mammals give birth to live young, providing nourishment through a placenta.

Amniotic eggs:

Reptiles lay eggs that are covered in leathery or calcareous shells. The reptile eggs contain embryos in a self-contained environment providing food and oxygen. The significant difference is mammals are viviparous, and the mammal fetus develops in the mother’s womb, unlike reptiles.

Parental care:

Most reptiles abandon eggs after laying them. Mammals care for their young through nursing, nurturing, and teaching behaviors.


Reptile hatchlings are immediately independent. Mammal newborns are dependent on their parents for an extended period.

Mammary glands:

Mammals have the presence of mammary glands to feed their young with milk from mammary glands, and also female mammals give birth to their young ones.

Overall, reptile reproduction relies on producing numerous eggs with little parental care who mostly abandon their young after hatching. Mammal reproduction involves fewer young but extensive care to raise and nurse them.

Sweat Glands

The substance keratin gives scales and hair their respective textures, unlike mammals, who have hair or fur and also have sweat glands beneath.

Behavioral Differences of Mammals Vs. Reptiles

Reptiles and mammals have very different patterns of behavior and activity:

Cold- vs. warm-blooded:

As ectotherms, reptiles’ behavior is strongly influenced by external temperatures. Most are inactive at cooler temperatures. Endothermic mammals maintain activity even in cold climates.


Most reptiles are solitary and only interact for mating. Many mammals (like wolves, primates, and elephants) have complex social structures.


Reptiles rely heavily on visual displays and scent markings. Mammals additionally use vocalizations like barks, cries, or songs to communicate.


Reptiles are primarily ambush predators, waiting motionless for prey. Mammals are more active hunters relying on stamina and speed.


Mammal brains are generally larger and more complex. Some mammals, like primates, show advanced cognition and problem-solving skills. So mammals exhibit more complex behaviors facilitated by their sophisticated brain, vocalizations, warm-blooded metabolism, and parental care strategies.


Similarities Between Mammals and Reptiles

Although reptiles and mammals are very distinct types of animals, they do share some basic similarities since they both evolved from earlier vertebrates:

  • Both tetrapods: have four limbs or descended from four-limbed ancestors.
  • Both are amniotes: their eggs contain protective membranes and nourishment for developing embryos.
  • They have a similar body plan: distinct head, neck, trunk, and tail regions.
  • As chordates, they possess a notochord and dorsal hollow nerve cord at some point in development.
  • Hearts in mammals consists of four chambers, two ventricles, and two atria. By contrast, reptiles’ hearts consist of three chambers, two ventricles, and one atrium to direct blood to the lungs.

So reptiles and mammals share broad traits reflecting their common evolutionary origins. But the differences outlined above separate them into very distinct classes of animals. (Read Why Does My Goats Poop Look Like Dog Poop)

Conclusion: Mammals Are Warm-Blooded

In summary, reptiles and mammals exhibit profound differences justifying their separation into distinct classes of vertebrates. From scales versus fur to egg-laying versus live birth, reptiles, and mammals have evolved divergent reproductive and developmental pathways.

Their disparate approaches to thermoregulation, metabolism, cognition, and sociality reflect 300 million years of separate adaptation. However, reptiles and mammals retain similarities in their body plans, heart structure, and embryonic development as products of vertebrate evolution. Appreciating the contrasts and parallels between reptiles and mammals provides insight into the forces shaping vertebrate biodiversity.

By analyzing two of the five classes of vertebrates, mammals and reptiles, are among the most complex animals on Earth.


Here are answers to some common questions about the differences and similarities between reptiles and mammals:

Are whales considered reptiles or mammals?

Despite living an aquatic lifestyle, whales are definitively mammals. They breathe air, are warm-blooded, give live birth to young and nurse them with milk from mammary glands. Their fish-like appearance is an adaptation to ocean environments.

Which group contains more species – reptiles or mammals?

There are over 10,000 known species of reptiles which outnumbers the approximately 6,000 species of mammals. However, many reptile species are small lizards and snakes that are poorly studied. New mammal species continue to be discovered but at a slower rate than reptiles.

Do any mammals lay eggs?

While nearly all mammals give live birth, the platypus and four species of echidna are exceptions. These monotreme mammals from Australia and New Guinea lay eggs rather than give birth to live young. The eggs hatch outside the mother’s body. But the mothers do produce milk to feed their young.

What are the most intelligent reptile and mammal species?

Among reptiles, monitor lizards and tegu lizards are considered the most intelligent and can be trained to recognize owners. Among mammals, elephants, cetaceans (whales and dolphins), and primates (monkeys, apes, humans) are considered the most intelligent.

Which mammal characteristics are absent in even the most primitive mammals?

Even the most primitive mammals have hair on their body, produce milk, are endothermic, and mammals have specialized teeth that distinguish them from reptiles. All mammals share these core characteristics.

What is the biggest difference between reptiles and mammals?

The most fundamental difference is their metabolic strategy. The main characteristic feature of mammals is that they are endothermic, meaning they regulate a constant internal body temperature.

Reptiles are ectothermic and rely on external heat sources like the sun to regulate their body temperature.

Difference Between Reptiles And Mammals

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