Scientists believe that they first appeared about 245 million years ago, at the beginning of the Middle Triassic Epoch, and existed for about 180 million years, going extinct about 66 million years ago, at the end of the Cretaceous Period.
The period when they lived is called the Mesozoic Era. During this time, they went through many changes, and various species of dinosaurs replaced other species.
Some dinosaurs were bipedal, meaning they walked on two legs, and some were quadrupedal, meaning they walked on all fours.
Some switched back and forth. Some were covered with feathers, while others had what was almost like body armor. Some ran fast, and others were slow; most were herbivores, but some were carnivores.
It is estimated that there were at least seven hundred species of dinosaurs, and possibly more than one thousand.
There were big biotic changes at the end of the Cretaceous Period, and many other animals and plants died at that time as well.
There are many theories as to why dinosaurs died out, including disease, heat waves, cold spells, changing sea levels, a large amount of volcanic activity, the emergence of egg-eating mammals, or from X-rays from an exploding supernova.
One other common theory is that an asteroid smashed to earth, spread ash widely, and shifted the earth's climate. However, it is not believed that all dinosaurs died out at the same time.
Rather, it is believed they had been declining during the last part of the Cretaceous Period. Scientists also believe that some dinosaurs may have evolved into birds.
In 1842, English biologist, comparative anatomist and paleontologist Sir Richard Owen came up with the word "Dinosauria".
The word comes from the Greek word "deinos," meaning "terrible" or "fearfully great", and "sauros," meaning "reptile" or "lizard".
The word comes from the Greek word "deinos," meaning "terrible" or "fearfully great", and "sauros," meaning "reptile" or "lizard".
He applied the term to three animals that fossilized bones had been found over the previous few decades. The remains came from reptiles that were both larger and had more vertebrae than any found before.
The earliest known published record of dinosaur remains was in 1820, and many fossils were found in the 1820s and 1830s.
Many other kinds of dinosaurs were found in the years following the 1842 naming as well. Fossils of dinosaurs have now been found on all seven continents.
Many other kinds of dinosaurs were found in the years following the 1842 naming as well. Fossils of dinosaurs have now been found on all seven continents.
HOW TO OBSERVE
The best way to celebrate the day is to visit a museum or other dinosaur-related attraction, where fossils or bones may be viewed.
You could also watch a documentary about dinosaurs, or a film that features dinosaurs, such as Jurassic Park. If you have children, there are many dinosaur related activities they could do today.
What is your favorite dinosaur(s)?
#InternationalDinosaurDay
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