Birds are dinosaurs.
There, I said it.
But, as I sit watching a flock of finches, it’s hard to see the resemblance.
How could this bird, no larger than a tennis ball, be related to the mighty T-rex?
Recent discoveries in paleontology have reshaped our understanding of dinosaurs, revealing their surprising connection to the birds we see today.
Far from being just “terrible lizards,” many dinosaurs could have been feathered, warm-blooded, and displayed behaviors remarkably similar to modern birds.
Sinosauropteryx was a small, bipedal dinosaur with short arms, a large thumb, and a long tail. It was the first feathered dinosaur discovered that wasn’t directly related to birds, and its discovery in 1996
This article will aim to explore the relationship between birds and dinosaurs and how evolution shaped the way birds now exploit nearly all environments on our planet.
Evolutionary Tree of Dinosaurs and Birds
Biology can be confusing. No doubt about it.
Especially when all life, both extinct and living, is categorized into groups.
Knowing where each animal fits into specific groups can be a challenge.
Phylogenetic trees, also known as evolutionary trees, can help scientists understand the relationship between a group of organisms.
So, where do dinosaurs and birds fit into this evolutionary tree? Buckle up and pay attention, you’re in for a ride.
Amniotes are tetrapod animals with a backbone. This group comprises the vast majority of living terrestrial and semiaquatic vertebrates.
Amniotes can then be further split into mammals and sauropsids.
Sauropsids are reptiles, and include all living and extinct groups.
Within sauropsids, the squamates (lizards and snakes) and the testudines (turtles) diverged first. This was followed by the divergence of the archosaurs, which included the dinosaurs.
Still with me?
Although the dinosaurs are no longer with us, we still share our planet with living archosaurs: birds, crocodiles and their relatives.
Okay. That’s the complicated classification bit out of the way. Now, let’s explore the archosaurs in more detail. What is a dinosaur and how are birds related to this ancient group?
What Is A Dinosaur?
“Welcome to Jurassic Park”.
An iconic line from an iconic film that shaped the modern mind on our perceptions on what dinosaurs should look like.
But let’s be real. No one really knows what a dinosaur looks like.
One of the smallest dinosaurs known, Compsognathus grew only about as large as a chicken
For all we know, they could have been little feathered things, no larger than a chicken…
Using fossil records and fancy technology, scientists have discovered some species were in fact little feathered things the size of chickens. Who’d have thought it?
Of course, like any other animal group, dinosaurs were diverse. They evolved an array of shapes and sizes, from the aptly named Giganotosaurus, to the hummingbird-sized Oculudentavis.
But what makes a dinosaur a dinosaur?
Well, there are two main factors to consider:
- Dinosaurs are reptiles
- Dinosaurs have an upright stance
Dinosaurs Are Reptiles
First and foremost, dinosaurs are reptiles. Their name quite literally translates to “terrible lizard”.
They first appeared about 251 million years ago, near the start of the Triassic Period.
But isn’t this article about birds and their relationship to dinosaurs? How can birds be related to these ancient reptiles?
Well, that brings us onto the second defining characteristic.
They Have an Upright Stance
Some reptiles, such as crocodiles and lizards, have legs that sprawl out to the side. Their thigh bones are almost parallel to the ground creating a side-to-side motion when they move.
Dinosaurs, on the other hand, stand with their legs positioned directly under their bodies. A hole in the hip socket permits this upright stance.
Birds also have their legs positioned under their bodies. Coincidence?
Most dinosaurs went extinct by the end of the Cretaceous Period, about 66 million years ago, but there’s evidence that one lineage evolved into birds about 155 million years ago.
Dinosaurs May Have Been Warm-Blooded
An age old question – were dinosaurs warm or cold blooded?
It’s easy to default to “dinosaurs were cold-blooded because they are reptiles”.
And sure, our modern-day reptiles are cold blooded, whilst birds are warm blooded. So where do dinosaurs fit into all this?
Well, that’s where science comes in.
Using fancy sciencey techniques, such as infrared spectroscopy, a group of scientists identified an abundance of molecules produced as waste during oxygen inhalation.
To do this, the scientists used fossilized thigh bones from a range of extinct dinosaur species, as well as their living relatives – birds.
You may be thinking “And, so what?”
A higher abundance of these molecules suggests high-powered metabolism – something we see in modern day warm blooded animals to regulate their body temperatures
This isn’t an isolated study.
Other scientists have taken bone fragments and, where possible, soft tissue records, and discovered that not only did certain species grow remarkably fast, many also had insulating feathers – an adaptation used by some warm blooded animals to maintain a constant temperature.
Nifty tricks from the dinos.
Yet, despite the data, our knowledge is still limited. We simply don’t have conclusive evidence about dinosaur metabolism as we don’t know how their internal mechanisms worked. A classic “pinch of salt” scenario.
Other Similarities Between Birds And Dinosaurs
Warm-bloodedness and bipedalism are sure signs of the relatedness between the two groups.
But are there other similarities between birds and dinosaurs?
Absolutely.
Dinosaurs and Birds Both Laid/Lay Eggs
As far as scientists are aware, all dinosaurs, both living and extinct, hatch from eggs.
However, unlike most other reptiles, which lay soft and leathery eggs, theropod dinosaur eggs were believed to be hard-shelled – much like our modern day bird eggs.
Many fossilized nests have been found across the globe, with egg fragments laying close to the nest sight. This suggests hatchlings crushed the egg shells whilst either emerging, or moving around the nest.
But Dinosaurs Don’t Have Beaks
How did a set of dinosaurian jaws, complete with an array of different tooth types evolve into the toothless jaws of modern birds?
Simple – the suppression of the teeth and growth of the beak.
Why dinosaurs started to lose teeth and develop beaks isn’t clear. However, scientists speculate that there are two main reasons: faster development and new feeding opportunities.
Tooth development can take up to 60% of incubation time. By hatching faster, survival rates are improved, as hatchling can avoid potential predators or natural disasters.
Using our trusted fossil records, scientists discovered how beaks in some dinosaurs and bird relatives originally expanded backwards as the animals grew up and tooth sockets closed off.
Eventually, this process happened earlier and earlier in the developmental cycle until hatchlings emerged with beaks and no teeth.
Modern day birds still have the bone gene BMP4. So, in theory, they do still have the ability to grow teeth.
Birds Share Similar Weaponry to Dinosaurs
We don’t tend to think of birds as overly aggressive animals.
Yet, when threatened, some birds have a few tricks up their wings – quite literally.
The spur-winged lapwing is one such bird.
When threatened, they use spurs like tiny clubs to fend off predators, guard their nests and compete with mates.
This behavior can be seen in some dinosaur species, such as Ankylosaurus and Stegosaurus.
Some Dinosaurs Had Feathers
Feathered dinosaurs? Have I gone mad?
As crazy as it sounds, many scientists believe that the most prominent feature of birds – feathers – evolved in non-avian dinosaurs long before the earliest birds.
These feathered dinosaurs, or Theropods, are characterised by having three forward-facing toes and walking on two legs. Sounding familiar?
Velociraptors are part of this group.
Unlike Spielberg’s famous portrayal of these ferocious dinos, there is evidence that they were feathered. But these feathers were used for insulation, rather than flight. A glorified turkey.
The First Bird
Using fossil records, the origins of birds can be traced back to the time of the dinosaurs – some 165 – 150 million years ago.
This was a very different time, and these early birds are unrecognizable from today’s avians.
The iconic Archaeopteryx, discovered in 1861, has long been considered as the first bird. It is thought to have lived in the Jurassic period, some 150 million years ago.
Although it had many bird-like qualities, such as feathers and the presence of a wishbone, Archaeopteryx also had many reptile-like qualities that we don’t see in modern birds. This includes sharp, pointy teeth, a long, bony tail and long claws on its hands.
Scientists also speculate whether Archaeopteryx could fly. But if penguins and ostriches have taught us one thing, it’s that the ability to fly isn’t a defining characteristic of birds.
Whether Archaeopteryx was the first bird is still debated today.
However, the earliest modern bird fossil, that majority of scientists agree on, is that of Asteriornis maastrichtensis – more popularly called the wonderchicken.
Fossils of the wonderchicken date to 66.7 million years ago, just 700,000 years before the mass extinction that killed off the non-avian dinosaurs.
The wonderchicken is thought to have been a small, ground-dwelling bird, much like a rail/duck/chicken hybrid.
Their fast reproduction rates and ability to fly may have helped it survive the devastating extinction event, which wiped out 75% of all life on Earth.
The Evolution Of Flight – Why Do Birds Fly?
Flight is a unique adaptation which has allowed some taxonomic groups to evolve great diversity.
Birds have been largely influenced by flight – their anatomy, physiology and behaviour are adapted to this complex mode of locomotion.
Using flight, birds are able to forage on extensive areas, they can migrate over long distances and they are able to colonize all terrestrial habitats on Earth including high elevations, polar regions and distant islands.
But how did they get there from ground-dwelling reptiles?
Birds, like theropod dinosaurs, are bipedal. This means they walked upright on their hindlegs.
With their hindlegs occupied, their forelimbs were free to evolve to help them exploit a particular niche. Unlike bats, which are mammals and have both their forelimbs and hindlegs attached to a wing membrane, birds evolved wings independently.
Can Birds Survive Another Mass Extinction?
Here we go. Doom and gloom time.
The current biodiversity crisis, often referred to as the sixth mass extinction, is happening at an alarming rate – much like the one that killed off the dinosaurs.
But this time, there’s no meteor hurtling towards Earth.
This extinction event is anthropological – we humans are accelerating the effects.
We’re losing species at a rate like never before.
Climate change, habitat loss, introduced species. The list goes on.
But birds survived once before. Can they do it again?
Unfortunately, it’s looking unlikely.
Since the 1500’s, an estimated 182 bird species are believed to have become extinct due to human actions. This figure could be grossly underestimated, with the actual statistic being closer to 1,500 species.
However, some bird species are adapting to a human-modified world. Species have adjusted their feeding habits, nesting locations, as well as songs and calls in response to human expansion and urbanization.
Final Thoughts on Whether Birds Are Dinosaurs
Birds are living dinosaurs – think more “astonishing avians” rather than “terrible lizards”.
Modern-day birds retain many dinosaurian traits – bipedalism, feathers, egg-laying, and perhaps even warm-bloodedness.
Over millennia, birds evolved strategies to help exploit specific niches. They became smaller and adapted to fly, both of which could explain how early birds survived the mass extinction.
Yet today, birds face their biggest threat: humanity.
By monitoring birds and their populations, scientists can understand the broader ecological challenges they face. While mass extinctions in the past allowed life to recover over millennia, today’s crisis demands immediate action to protect ecosystems and species.
