How to tell if a fossil belongs to a dinosaur


If you saw a huge lizard-like skeleton, chances are, you would assume it is a dinosaur. That is not the answer in many cases. Animals existed before dinosaurs did. There were primitive birds, stem mammals, mammals, reptiles, Mosasaurs and Pterosaurs, living before and with dinosaurs. They too have fossilized over years. To an untrained eye, most of these prehistoric species might look like a dinosaur. Hence learning what makes a dinosaur different is crucial, as explained in this article

Life on Earth started 3.8 billion years ago. Different forms of life emerged in different epochs. Dinosaurs remained a dominant life form in this enormous timeline for almost two hundred million years. This time period was called Mesozoic and it was divided into three parts: Triassic, Jurassic and Cretaceous periods. All non-avian dinosaurs disappeared because of a huge asteroid impact 66 million years ago in present-day Yucatan Peninsula. There must have been a chain of other events too that meant destruction to non-avian dinosaurs. But a group of dinosaurs managed to evolve into organisms that make up modern birds. But two hundred million years is so little in this massive 3.8 billion years of timescale. Complex organisms existed before dinosaurs and were a dominant species in their timeline. Following are the eras in which life was classified:

  1. Cenozoic era started 66 million years ago and extends to the present day. Rapid speciation of mammals and birds began in this era.

  2. Mesozoic era started approximately 252 million years ago and ended with dinosaurs at 66 million years ago. Dinosaurs, Pterosaurs and Mosasaurs ruled the planet in this era.

  3. Paleozoic era started 542 million years ago and ended with the advent of dinosaurs at 252 million years ago. This era consists many time periods in which life underwent a revolution
  4. .

Before we start, why should one learn about dinosaurs? It is not like we are going to excavate a fossil suddenly, right? Ever wondered why the number of fossil excavations and findings sky-rocketed since the 1860's? The need for coal and oil pushed humans to dig more. As we dug deeper we found fossilized remains coincidentally. Kids playing in their garden have found fossils. Construction workers have found fossils. In the modern era, anyone could be a possible excavator of a fossil. So we need to be sure of our findings. Moreover learning these differences between dinosaurs and other prehistoric creatures can help you understand evolution better.

To understand the scenario better, lets list out the animals that look like dinosaurs and can confuse many.
  1. Pterosaurs

  2. Pterosaur(Image credits: nationalgeographic.com)

  3. Mosasaurs

  4. Mosasaurs(Image credits: Fossilera.com)

  5. Dimetrodon

  6. Dimetrodon(Image credits: Wikipedia.com)

  7. Plesiosaurs

  8. Plesiosaurs(Image credits: thoughtco.com)

  9. Sarcosuchus

  10. Saurasuchus (Image credits: Wikipedia.com)

  11. Glyptodon

  12. Glyptodon(Image credits: thought.co.com)


So why are the animals above not dinosaurs when they reciprocate our idea of dinosaurs so well?

  • Pterosaurs are flying, gliding reptiles, who deserve their own family. They were distant relatives of dinosaurs. They mostly flew in the Mesozoic skies and hunted smaller dinosaurs and other creatures.

  • Mosasaurs had double hinged mouths, like modern snakes. They thrived in late Cretaceous and went extinct with dinosaurs 66 million years ago. These sea-dwelling monsters were the apex predators of their time and they gave birth to living young, like us mammals. Their closely related living organisms are snakes and monitor lizards.

  • Dimetrodon is more closely related to mammals than dinosaurs. They lived in the early Permian period of Paleozoic era hunting fish, reptiles and smaller vertebrates. They are Therapsids, a link between reptiles and mammals. Therapsids are recognized by their legs which extend vertically beneath their bodies. Dimetrodon had many other mammal-like features too, such as having a single opening in skull apart from eye sockets and two different sets of teeth. But because of their sail and their anatomy, they are quite often confused with dinosaurs. But those two didn't even exist in the same era. Dimetrodons died out in Permian-Triassic extinction event and led way for dinosaurs to take over.

  • Plesiosaurs were sea-dwelling reptiles too that lived hunting fish. They too gave birth to their living young ones. They lived in the early Jurassic period of Mesozoic. They had long necks and paddle-like fins. They might have shared their feeding grounds with Mosasaurs and went extinct with them 66 million years ago.

  • Sarcosuchus belonged to the family of crocodiles. Glyptodon was a furry mammal which is related to modern armadillos. In fact Glyptodons lived alongside humans and humans hunted them to extinction.


As one can see, there lived a very diverse amount of animals in prehistoric eras. The earliest species of dinosaurs was Eoraptors, who lived 230 million years ago. The age of dinosaurs followed from since to 66 million years ago. Dinosaurs could only take over the world because of a catastrophic event called Permian extinction. Permian extinction was so massive that it killed off 90% of the denizens of Earth at its time. It is believed that a chain of volcanic eruptions caused this extinction. Dimetrodon and other prehistoric animals along with it were wiped out too. This allowed the dinosaurs to take over the ravaged planet and occupy the niches. Now that explains why dinosaurs had so many species.

Life on Earth is approximately 4 billion years old. Species had an ample time to develop. Before dinosaurs there lived, crocodile-like salamanders, sabre-toothed Gorgonopsids, a meat-eating Dimetrodon, eagle-sized Dragonflies and etc. Life before dinosaurs is just as interesting as the life of dinosaurs.

How to tell if a fossil belongs to a dinosaur?

  1. There were few dinosaurs that could fly. They are called Avian dinosaurs. Other than them, all non-Avian dinosaurs lived on land. There are no fully aquatic dinosaurs. There are semi-aquatic kinds such as Spinosaurus that lived off fish but no dinosaurs went fully aquatic.

  2. Dinosaurs and other reptiles are Diapsids. They have two holes other than eye sockets in their skull. This helps them to force shut their jaws.

  3. Dinosaurs were the first to develop hips. By looking at their pelvis you can determine if you are looking at a dinosaur.

  4. Fossils are formed in layers of soil. As the earth ages, newer soil keeps accumulating over the older layers. So you'll never find a skeleton of a woolly mammoth alongside a dinosaur because they lived millions of years apart. By examining the layer of the soil, we can find out if a fossil belongs to a dinosaur.

  5. It was the mammals that developed different sets of teeth. Prehistoric reptiles and dinosaurs had only one kind of teeth according to their diet. So by examining a fossilized tooth, you can differentiate a dinosaur from other prehistoric animals.

Using the above-mentioned traits that only dinosaurs possessed, you can differentiate dinosaurs from other prehistoric animals easily. But fossils that are available only in fragments make it difficult even for experts to be sure of their findings. This was a brief article explaining the differences between dinosaurs and other prehistoric reptiles and stem mammals. Earth had a rich biodiversity in all eras.


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