Are Birds Related To Dinosaurs? (Complete Guide)

Birds are one of the most successful groups of animals on the planet today. Depending on the time of day, you can probably see or hear a bird from wherever you are reading this article! It seems almost unbelievable that these busy, two-legged flying creatures could be related to the big scaly dinosaurs we’ve seen in books and movies.

Birds aren't just related to dinosaurs, they are technically dinosaurs. The first birds evolved from theropod dinosaurs over 150 million years ago. Their evolution was not an event, but rather a gradual process of adaptation and mutation that involved many increasingly bird-like species.

Paleontologists and ornithologists agree that avian birds lived with dinosaurs before the great extinction event of 66 million years ago, and were the only dinosaurs to survive the catastrophe. Put simply, birds are a group of living dinosaurs!

The first flying reptiles were the Pterosaurs (Pterodactyls). They were not technically dinosaurs and were unrelated to the evolving birds they shared the planet with for millions of years. Theropod dinosaurs looked very different from modern birds. They also had many undeniable similarities, however.

Illustration of a Pterosaurs, commonly known as a Pterodactyl

Some dinosaurs developed feathers and small wings long before they gained the ability to fly. But why would dinosaurs give up arms for wings that could not be used for sustained flight?

Flight may have evolved in dinosaurs in some surprising ways. Studies at the University of Montana have shown that even poorly developed wings can be useful.

Ground birds, for example, are able to run up near-vertical surfaces without actually flying. Other examples include ducks that can use their wings to move faster over the surface of the water or chicks that can jump to the ground from great heights by using their wings to parachute their fall and coordinate their landing.

Read on to learn more about how birds evolved into what they are today and how they survived the asteroid that killed all other dinosaurs.

Tufted Duck flying low above the water

How are birds like dinosaurs?

Birds evolved from a suborder of two-legged dinosaurs known as the theropods. This group of dinosaurs contained well-known species like Tyrannosaurus rex and velociraptors.

Birds are technically modern dinosaurs and therefore share many traits with their extinct ancestors. Some of the most notable similarities are in the hand and foot structure, the metabolism, the gait, and even the presence of feathers.

Let’s take a look at some of the things dinosaurs and modern birds have in common:

Warm blood

Dinosaurs are believed to have been warm-blooded (homeothermic), just like modern birds are today. This is different from reptiles, amphibians, and fish which are generally cold-blooded (ectothermic).

Bipedalism

Birds are bipedal, which means they walk, run, and hop on two legs just like us. Theropod dinosaurs were also bipedal, although many other dinosaur groups walked on four legs.

Feathers

Some therapods even had feathers, even though they were not able to fly. Feathers have excellent insulating properties, so they may have developed for keeping dinosaurs warm. Their feathers did not necessarily cover their entire bodies, however, and were often limited to their tails and forelimbs. Dinosaur feathers also served a display function in some cases and were used for attracting mates or intimidating rivals.

Foot Structure and Hand Structure

Theropod dinosaurs like Tyrannosaurus had three forward-facing toes and one small backward-facing digit. Sound familiar? That’s because most modern birds have the same arrangement. The podotheca, the scaly covering that birds have on their feet, also first developed in theropods.

While theropods might not have had wings, there are obvious similarities between their forelimbs and the wings of birds. Later theropods also had just three digits in their hands, just as modern birds have three fingers in their wings.

Special bones

Theropod dinosaurs also had hollow bones and a furcula (wishbone), just like modern birds do today.

Foot structure is one of the biggest similarities to dinosaurs

Evolution of birds timeline

The birds we know today did not evolve overnight. Selective pressures from competition with other animals, the environment around them, their food sources, and other factors shaped them through the process of natural selection and evolution over hundreds of millions of years.

Our insights into their evolutionary progress come chiefly from the fossil record. Here are some of the major milestones in bird evolution:

• 230 million years ago: Eodromaeus, the first known theropod hunts in what is modern-day Argentina.
• 150 million years ago: Archaeopteryx lithographica, a dinosaur that many consider as the first bird, flies through the forests of what is present-day Germany. Archaeopteryx has a long tail and a tooth-filled mouth but is undeniably bird-like.
• 120 million years ago: Confuciusornis, the earliest toothless bird lives in present-day China. It is about the size of a crow and looks very much like a modern bird.
• 66 million years ago: An asteroid measuring about six miles across strikes the earth off the Yucatan Peninsula of Mexico creating the Chicxulub crater. A few bird species survive the impact and after-effects but all other dinosaurs go extinct.
• Present: Birds have speciated (evolved) into between 10,000 and 18,000 bird species. They have not grown to the size of other extinct dinosaurs but are a remarkably diverse and successful group of animals, occurring on every continent as well as the skies and oceans.

Archaeopteryx, bird-like dinosaur from the Late Jurassic period around 150 million years ago

How did birds survive the dinosaur extinction?

A massive asteroid struck the ocean just off Mexico’s Yucatan Peninsula about 66 million years ago. This asteroid strike is known as the Cretaceous–Paleogene (K–Pg) extinction event.

The dust kicked up by the impact smothered and killed plants, the basis of the food chain. As the cloud of dust hung in the air, sunlight was blocked and the earth grew cold.

As much as 75% of all species are thought to have gone extinct, but some birds found a way to make a living in what must have been a desolate wasteland. These avian dinosaurs were the only dinosaurs to survive.

The great majority of avian dinosaurs perished and their many species, the culmination of millions of years of evolution, were lost. A few ground and water birds did survive, however.

We don’t know exactly why birds were the only dinosaurs to survive the K-Pg extinction event, but the following factors might hold the answer:

• Birds are small and could breed and repopulate faster than non-avian dinosaurs.
• Birds can survive on smaller amounts of food. This would have been important when resources were scarce.
• Birds are highly mobile, meaning they could forage over wider distances and move out of the worst affected areas.
• Birds had adapted to feed on a variety of different food types. Fresh vegetation, insects, and small animals would have become very scarce, but seeds persisted, providing a very long-lasting food source that birds could exploit.

The Cretaceous–Paleogene (K–Pg) boundary of Zumaia (Spain)

What bird is most closely related to dinosaurs?

Modern birds are not just closely related to dinosaurs, they are technically dinosaurs. The great extinction event that occurred about 66 million years ago wiped out all non-avian dinosaurs, as well as most of the bird species that were alive at the time. All the modern-day bird species have since evolved from those few survivors and we now have over ten thousand bird species on the earth today.

Some birds certainly do seem more primitive than others, however. The topic is a great conversation starter because it’s completely open to interpretation but the following birds certainly seem pretty close to the classic depiction of dinosaurs:

• Vultures and condors - The large size and naked heads and necks of these birds give them a very dinosaur-like look. The California condor and lappet-faced vultures are great examples.
• Cassowaries and other ratites - Many of these giants of the bird world have naked heads and necks, walk upright on two legs, and lack the ability to fly. If you squint your eyes a little, they could look just like a modern-day theropod! Interestingly, these ground birds have evolved from birds that could fly.
• Hoatzins - These clumsy South American birds lack feathers on their faces. While the adults can fly, the babies use the well-developed claws on their wings to climb through the branches of trees.

Close up of a perched California Condor