Are Dinosaurs Reptiles or Birds?

Most dinosaurs became extinct 65 million years ago. It is likely that an asteroid hit Earth, destroying many types of creatures. Before this, dinosaurs lived for 165 million years on Earth. We know this because of scientists called paleontologists who study the past through fossil records. Fossil records gained popularity with Mary Anning’s work. 

Scientists have since learned more about dinosaurs, piecing together whole exhibits that show us what they looked like and how they may have behaved. But how do we know exactly what dinosaurs looked like with only their bones as a reference?

An illustration of an asteroid hitting Earth
An illustration of an asteroid hitting Earth, Credit: Wikimedia/Fredrik

Table of Contents

How are creatures classified?

To help us understand what dinosaurs looked like, it is important to know how animals are classified. In other words, creatures are put into categories based on how similar they are to other creatures. For example, dogs and wolves are more similar to each other than dogs are to fish. This example is obvious partly because we see dogs, wolves, and fish on Earth today. So, how do we classify creatures that went extinct a long time ago?


Paleontologists find clues about creatures from the past. Bones are a great hint to help understand what extinct species looked like. But how do we know if dinosaurs were covered in scales or feathers? Some dinosaur fossils have been found with the impressions of feathery details in the stone, while others have been found with scale-like details. A famous fossil of Archaeopteryx clearly showed teeth and a muscular tail like a dinosaur but feathered wings like a bird. There are also some parts of dinosaur bones where feathers could have attached.


But feathers are not the only thing that make an animal bird-like. Paleontologists have also suggested that some dinosaurs had similar respiratory systems to birds, which helped them to breathe differently than other animals. Scientists also believe that some dinosaurs could have been warm-blooded, rather than cold-blooded like today’s reptiles.

Pyroraptor olympius dinosaur covered in feathers
Pyroraptor olympius dinosaur covered in feathers, Credit: Wikimedia/Mette Aumala

How do we know if dinosaurs were reptiles or birds?

Today’s reptiles have specific features that make them different from birds. For example, reptiles normally have scales and are cold-blooded animals. Birds can have feathers and are warm-blooded animals. But dinosaurs are often considered reptiles, because reptiles of the past did not all look like reptiles of the present. Dinosaurs were a complicated group of animals and did not all fit into the same category! As a class of animals, their sizes and features ranged widely.


Recently, a very small dinosaur called the Oculudentavis khaungraae was discovered. This little reptile was as small as a hummingbird. On the other hand, the largest dinosaur may have been over 100 feet long and has been named the Titanosaur.

Oculudentavis khaungraae drawing
Oculudentavis khaungraae drawing, Credit: Wikimedia/SpinoDragon145

Between the tiniest and the largest dinosaur are species of all sizes and types. We know now that some warm-blooded dinosaurs had wings and feathers, as well as complex respiratory systems. Not all of these warm-blooded dinosaurs had feathers. One warm-blooded dinosaur that we know well is the Tyrannosaurus rex. But some cold-blooded dinosaurs had scales and looked more like the reptiles we know today. For example, we know that the Triceratops was likely cold-blooded.

Titanosaur skeleton at the Field Museum of Natural History in Chicago, IL.
Titanosaur skeleton at the Field Museum of Natural History in Chicago, IL., Credit: Wikimedia/Zissoudisctrucker

What makes dinosaurs similar to one another?

If some dinosaurs were small and feathery, while others were large and scaly, why do we classify them all together? Over the course of history, all living creatures developed from the same ancestors. You and your cousins may look different from one another, but you share a pair of grandparents . In the same way, today’s birds and reptiles are very different from one another, but they share the same long-lost relatives.


Over 200 million years ago, a creature smaller than your hand existed. The Kongonaphon kely was a tiny, fuzzy reptile that ate insects. Over millions of years, some descendants of the Kongonaphon became larger, and their features started to range widely, including some with feathers and others with scales. This was the ancestor to all dinosaurs. Today, hundreds of millions of years later, animals look even more different than the dinosaurs of our past. This is partly because many dinosaurs did not survive the mass extinction event 65 million years ago. The animals that did survive look more like the animals we see today.

Kongonaphon kely drawing
Kongonaphon kely drawing, Credit; Wikimedia/Fanboyphilosopher (Neil Pezzoni)

Are birds descendants of dinosaurs?

We know that dinosaurs could be scaly or feathery, warm-blooded or cold-blooded. Only some of these species survived the mass extinction, including certain bird-like creatures. So, are today’s birds really dinosaurs? Birds descended from dinosaurs. When dinosaurs existed, there were likely some that looked similar to the birds we see today. The ones that survived have now grown into species ranging from hummingbirds to ostriches. So, although birds do not look like today’s reptiles, they are descendants of reptiles from the days of the dinosaurs. Some might even say they can still be classified as dinosaurs today.

Archaeopteryx — the missing link between dinosaurs and birds, Credit: Wikimedia/H. Raab


Paleontologists: scientists who study fossils


Classification: the way that we put animals into categories according to their similarities and differences


Respiratory Systems: breathing systems of different types of animals


Dinosaur Species:


– Oculudentavis khaungraae: the smallest known dinosaur
– Titanosaur : the largest known dinosaur
– Tyrannosaurus rex: A large, warm-blooded dinosaur
– Triceratops: A cold-blooded dinosaur
– Kongonaphon kely: The ancestor to all known dinosaurs

Flesch Kincaid Grade Level: 8.6


Flesch Reading Ease Score: 57.8


  • Tess Bub
    : Author
    Tess Taggart Bub has a bachelor’s degree in biochemistry and a minor in data science from Houghton College. During her undergraduate studies, she conducted research in the areas of climate science, ecology, and muscle biology. She is currently a PhD candidate at the University of Tennessee Health Science Center studying host cellular response to viral infection. She is a strong believer that science can change the world, especially when it’s shared. In her free time, she loves communicating science, playing guitar and piano, and running. Writing for smore gives Tess the opportunity to help inspire a new generation of women in STEM.

Copyright @smorescience. All rights reserved. Do not copy, cite, publish, or distribute this content without permission.

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