Dinosaurs were a very large and varied group of prehistoric reptiles that dominated the Earth millions of years ago, long before humans were even about to appear. These animals populated all the habitats on the planet: the oceans, the mainland and even crossed the air, throughout 135 million years, from their appearance in the Upper Triassic period until their extinction at the end of the Cretaceous period.
How do we know that dinosaurs existed?
We know that dinosaurs existed because we have found their Fossil remains, that is, their skeletons, their footprints or parts of their bodies, preserved in different mineral substances such as stone or amber.
These remains are obtained underground and have been found since the 19th century, showing us extinct creatures but very similar to those that exist today. Thus, over two centuries of study, much is known about these ancient creatures.
What were dinosaurs like?
The term “dinosaur” already tells us a lot about what these animals were like: it is made up of the Greek voices deinos (“Terrible”) and sauros (“Lizard”), from which we can conclude that they were reptiles very different from the ones we are used to. This is because many of the first fossils found revealed large creatures, so much so that many of their early researchers took them for ancient monsters, like those that appear in the Bible.
The truth is that dinosaurs were a very large and diverse group of animals, of which Today we know more than a thousand different species, from all corners of the planet. Some walked on two or four legs, were herbivores, piscivores, omnivores or carnivores, and competed with other species of prehistoric marine and even flying reptiles, but which are not considered (strictly speaking) as dinosaurs.
Like modern reptiles, dinosaurs laid eggs and probably created nests; but unlike them, the dinosaurs they had an upright posture, with their legs perpendicular to the body instead of to their sides. And although it was thought that they were slow and cold-blooded beings, many findings seem to indicate that they were much more active and dynamic animals.
What kinds of dinosaurs do we know?
The task of classifying dinosaurs and trying to reconstruct their evolutionary history falls to paleontologists, and it is not an easy task. First of all, because all the information we have about dinosaurs comes from the fossil record, so in many cases it is incomplete, fragmentary.
Fortunately, its similarity with the species that accompany us today allows us to make comparisons and deductions, and thus we have been able to establish a classification of known dinosaurs.
This classification depends on the structure of the hip bones of the fossils found and distinguishes between two orders of dinosaurs: the saurischians (Saurischia, which means “lizard pelvis”), whose bones are more similar to those of their ancestors, and ornithischians (Ornithischia, which means “bird pelvis”), which have a more modern structure.
In each of these orders we can find different genera and species of dinosaurs, as follows:
- Saurischian dinosaurs:
- Theropods. Mostly bipedal carnivores, that is, predators that walked on their hind legs, such as the ferocious Tyrannosaurus rex.
- Sauropods. Mostly quadruped herbivores with long necks and very bulky bodies, such as the gigantic Apatosaurus ajax.
- Ornithischian dinosaurs:
- Thyrophores. Quadruped herbivores endowed with a powerful bone armor whose plates covered specific parts of the body, such as the Stegosaurus armatus.
- Neornitischios. Quadruped herbivores that had a thick enamel beak in their mouth (like a parrot beak) and different defensive formations on the skull, such as the Triceratops horridus.
Why did dinosaurs disappear?
There are different possible explanations for the sudden massive disappearance of the dinosaurs, which took place in the late Mesozoic era, 66 million years ago. At that moment 75% of life on the planet was suddenly lost, in what is known as the Cretaceous-Tertiary (or KT) mass extinction event.
The hypotheses handled by the scientists point to some type of global climate catastrophe, the product of a sudden and intense seismic and volcanic activity, or consequence of the impact of an asteroid or meteor in the region that we know today as the Yucatan peninsula, in Mexico. This last explanation is the one that enjoys the greatest acceptance among specialists.
What is an informational text?
An informative or expository text is one whose purpose is to provide the reader with data, observations and other information in an objective, concrete and formal way, without giving room for opinions, arguments or stories in its content. It is a very common type of text in the educational world, for example, or in the informative world, such as encyclopedias, textbooks or scientific articles.
Depending on the level of complexity of its language, an informative text can be aimed at any type of person (that is, informative texts) or a professional sector that handles technical knowledge (that is, specialized texts).
References:
- “Dinosauria” in Wikipedia.
- “Informative text” in Wikipedia.
- “The dinosaurs” in Educ.ar.
- “What are Dinosaurs?” at National History Museum (UK).
- “Dinosaur (fossil reptile)” in The Encyclopaedia Britannica.