Around 130 million years ago, a branch of the reptile family split off and a tiny, mouse-like creature emerged: Introducing the first mammal! From that early beginning have evolved approximately 6,500 different species of mammals living today.

Evolution: From Reptiles into Mammals

post dinosaurs
After dinosaurs went extinct, small mammals evolved into much larger animals such as the Hyracodon.

Most reptiles are warm blooded and need warmth from the sun in order to be active. Mammals evolved several new strategies for conserving body heat.

The platypus is an early type of mammal that still has some reptilian traits. Species, like the platypus help us see the evolutionary link between mammals and reptiles. Even though the platypus has hair like a mammal, it lays eggs like a reptile.

Full mammals have a spiral-shaped cochlea as part of their inner ear. Reptiles also have the capacity to hear, and have a cochlea, but the reptilian cochlea is shaped more like a banana. The platypus does not have a spiral shaped cochlea, but instead, has a cochlea that also has a banana shape.

Mammals: Living with Dinosaurs

Megazostrodon, one of the earliest true mammals, only came out at night in order to avoid dinosaurs.
Megazostrodon, one of the earliest true mammals, only came out at night in order to avoid dinosaurs.

Mammals and dinosaurs shared the same ecosystems for around 150 million years.

These warm-blooded creatures lived in nests and burrows, venturing out to forage after dark when the dinosaurs were sleeping.

Mammals: The Night Life and Hearing

Early mammals were nocturnal and relied on excellent hearing. Their finely tuned ears helped them to navigate in the dark, as well as communicate with each other through squeaks.

Mammals: Mama’s Warmth and Nourishment

Piglet feeding... while mama does, too!
Piglet feeding... while mama does, too!

Fish and reptiles lay eggs, but baby mammals grow inside the mother’s womb and, during infancy, are fed with their mother’s milk.

This early dependence is the basis for a social species with complex relationships.

Mammals: External Protection

While reptiles and mammals have similar body plans, one big difference is that mammals have fur instead of scales. This helps keep mammals warm and protects them from hazards in the environment.

Mammals Survive the Asteroid Hit

Around 66 million years ago, the dinosaur party abruptly ended when a giant asteroid hit the Earth, setting off a mass extinction.

Echidna quills are actually modified hairs
Echidna quills are actually modified hairs.

While most of the larger life forms went extinct, the small, smart, adaptable foragers–mammals–managed to survive the crisis.

A branch of the mammal family split off as it evolved hands with fingers and thumbs.

What do You have in Common with Early Mammals?

Like these early mammals, you have highly sensitive hearing. You use the sounds of language to communicate with your family.


A branch of the mammal family split off and evolved into primates.

Basic characteristics of mammals

Looks good, but not able to make link work

Good basic info plus fun facts

Eight main mammal traits, excellent diagram