Dinosaurs are one of the most fascinating animals that ever roamed the earth. Ever since their remains have been discovered, dinosaurs have captured the imagination of many. They are featured in museums and exhibits around the world and have been embedded in our pop culture.
Dinosaurs were estimated to have lived between 245 to 66 million years ago, a time known as the mesozoic era. Because we can only study fossils or the remains of dinosaurs, there is still so much to learn about them.
One of the things that baffled many is what type of animal are dinosaurs. Can they be considered as reptiles or are they an entirely separate group of animals altogether?
Before we can answer the question, “are dinosaurs reptiles?”, we must first define what a reptile is.
What are Reptiles?
You probably know that lizards, snakes, turtles, and crocodiles are reptiles. They are a group of animals that share the following characteristics.
- Reptiles are vertebrates, meaning they have internal backbones.
- Most reptiles lay eggs.
- Reptiles are tetrapods (four-limbed). Although snakes are limbless, they are still considered tetrapods because they are descended from four-legged creatures.
- Reptiles have dry, scaly skin, unlike amphibians which have smooth and slimy skin.
- Reptiles breathe with their lungs.
- Reptiles are cold-blooded animals, meaning they don’t have the ability to control their body temperature and rely on the environment to cool down or warm-up.
So, are dinosaur reptiles?
Dinosaurs have all the above characteristics of reptiles, except for one. Dinosaurs were once thought to be cold-blooded, but recent studies suggest that they were probably warm-blooded.
However, dinosaurs are still considered reptiles because they shared many characteristics with other reptiles.
Furthermore, there are two approaches when it comes to classifying animals. The first one, is by grouping animals according to their common characteristics, like what we did above. The second, more modern approach is by grouping animals according to their evolutionary history.
Using the second approach (phylogenetic classification), dinosaurs will still fall into the reptile category because the reptiles that we know today share a common ancestor with the dinosaurs.
What makes a dinosaur a dinosaur?
Now that we have established that dinosaurs were indeed reptiles, the next thing we can ask is how are they different from the other reptiles? How can you tell whether a certain reptile is a dinosaur or not?
If it is big, scaly, and a prehistoric animal, it must be a dinosaur, right? Not necessarily. Let’s learn more about dinosaur characteristics.
Dinosaurs had two holes in each side of their skulls
Jaw muscles went through these holes called temporal fenestra to attach directly to the top of the skull. This allowed the dinosaur jaws to clamp down with more force. Dinosaurs share this characteristic with modern crocodiles and alligators.
Dinosaurs had holes in front of their eye socket called antorbital fenestra
Nobody knows for sure what these holes are for, but dinosaurs and other prehistoric animals had them.
Dinosaurs had an upright stance
One thing that sets dinosaurs apart from other modern and prehistoric reptiles is that they had an upright stance with their limbs perpendicular to their body. This posture allowed them to support their big bodies and move faster than other animals of the same size.
Modern-day reptiles like the lizards, tuataras, turtles, and crocodilians (crocodiles, alligators, and gharials) have legs that sprawl out to the side with their thigh bones almost parallel to the ground.
Dinosaurs had distinctive skeleton features not found in other reptiles
Dinosaurs had holes on their hip sockets and had a long crest on their upper arm bone. Their ankles can bend in a single plane like a hinge.
What are the different types of dinosaurs?
Dinosaurs were a diverse group of reptiles. Some walked on all fours, others were bipedal, meaning they walked on two legs. Some were carnivores and some were herbivores. Most were big, based on our current standards, but some were not so large. Some had body armour and some did not.
Dinosaurs are classified into three main groups.
The Ornithischians were a group of plant-eating dinosaurs that included the Triceratops, Stegosaurus, and Ankylosaurus.
The name Ornithischians came from the word ornith meaning “of a bird” and ischion meaning “hip-joint.” They were so named because their hip joints resembled that of a bird. Birds however, are more related to another group of dinosaurs, the theropods.
Another distinguishing feature of ornithischians is their beak-like mouth which was probably used to clip off plant material.
Some Ornithischians were bipedal (walks on two hind legs) while others were quadrupedal (walks on all fours).
The Sauropods were a group of dinosaurs that were large, had long necks and tails, small heads relative to the body, and a four-legged stance. Like the Ornithischians, they were also plant eaters.
This group included the Brontosaurus, Argentinosaurus, Brachiosaurus, and more.
The Theropods were a group of dinosaurs that is characterised by their bipedal stance and short forelimbs. They also had hollow, thin-walled bones, three-toed limbs, and wishbone -- characteristics that they share with present-day birds.
Most theropods were carnivores.
The Tyrannosaurus Rex, the Velociraptor, and the Giganotosaurus belonged to this group of dinosaurs.
Prehistoric animals that were NOT dinosaurs
Some prehistoric animals are usually lumped together with dinosaurs just because they lived around the time of the dinosaurs. But technically, they belong to different groups of prehistoric animals. Let’s get to know them.
The pterosaurs were flying reptiles that lived in the mesozoic era that are often mistaken for dinosaurs.
Both the dinosaurs and pterosaurs are nested within another larger group of animals called the archosaurs which also included the extinct relatives of crocodilians, as well as the modern day crocodilians and birds. This means that all these animals shared a common ancestor.
Since pterosaurs had a common ancestor with the dinosaurs, they did have some similarities with the latter like the presence of temporal and antorbital fenestrae or the holes in their skulls.
But pterosaurs also had unique anatomical features that differentiate them from the dinosaurs.
Unlike the dinosaurs, they did not have holes in their hip sockets and had no crest in their upper arm bone.
Also, many pterosaurs had crested heads. Depending on the species, these crests can be bony or fleshy.
Another distinctive feature of pterosaurs were their super long fourth digits that extended to the tip of the wings. One of the most popular species of pterosaurs, the pterodactylus, is named after this feature: ptero means wings and dactyl means fingers.
The pterosaurs’ wings ran along the sides of their bodies and may have been connected to their ankles. Layers of muscles, blood vessels and actinofibrils (chord-like fibres) made up the wing membrane of the pterosaurs. Scientists believe that pterosaurs were capable of powered flight (by flapping their wings in contrast to just gliding) like the bats and birds.
The pterosaur's wings were not only used for flight but also for walking on all fours!
Another unique characteristic of pterosaurs is their oddly proportioned bodies with very long necks and big heads.
Aside from the Pterodactyl, pterosaurs include the Pteranodon, Quetzalcoatlus, Cearadactylus, and many more.
Dimetrodons are often mistaken for dinosaurs because of their reptilian-like characteristics and tall sail on their back which looked somewhat similar to that of the spinosaurus.
However, dimetrodons and their relatives lived during the Permian Period and became extinct even before the first appearance of dinosaurs.
Another tell-tale sign that they were not dinosaurs is their skull. Dinosaurs had two holes on each side of their skulls and thus are classified as diapsids. Dimetrodons only had one hole on each side making them synapsids.
Likewise, dimetrodons’ legs are sprawled to the sides unlike dinosaurs’ legs which are directly under their bodies.
The mosasaurs comprise a group of large marine reptiles from the late Cretaceous period. Being reptiles, mosasaurs need to come up to the surface of the ocean for air.
Mosasaurs had double hinged jaws and flexible skulls like snakes which allowed them to swallow their prey almost whole. Fossil skin impressions of mosasaurs show that they had scaly skin.
Scientists believe that mosasaurs had shared an ancestor with snakes and monitor lizards.
As you can see the question are dinosaurs reptiles is not exactly as simple as it sounds! We hope you have learned something from reading this article and that you share this information with your friends!