(English: Dinosaurs) are extinct reptiles that appeared on Earth in the Late Triassic period, approximately 245 million years ago. Two Greeks, the first dainos (Greek: δεινός) meaning great, or colossal, and the second, Soros (Greek: σαύρα), meaning lizard. see more here www.pets-home.net
There are approximately 700 known species of extinct dinosaurs that scientists have identified from fossils found on the seven continents, which include bones, teeth, and eggs of dinosaurs, in addition to footprints, their movement paths, and the skin impressions they left behind.
Dinosaurs are among the huge animals on earth, and they are predatory animals, carnivores and herbivores at the same time, they lived on the continents of the world in Antarctica and North America
It is one of the groups of the animal world that became extinct and disappeared from existence millions of years ago, and it first appeared 233-243 years ago in the Triassic period and was one of the dominant animals on the surface of the earth at that time, and its dominance continued during the Cretaceous period
and its fossils were found for the first time in The beginning of the nineteenth century, and since that time to this day more than 500 genera of these organisms and more than 1,000 species have been discovered, of which 1,047 species were named by 2008, and the reason for its name is that of the two Greek words “dino” which means strong and “Sauro” which means reptile or lizard.
Information about dinosaurs
Dinosaur is a name given to some types of reptiles, especially large ones, and these reptiles first appeared about 245 million years ago, and spread throughout the world for nearly 180 million years.
These organisms became extinct about 66 million years ago, but there is some evidence Which shows that one lineage of them evolved in the form of birds about 150 million years ago.
The first appearance of the term dinosaur was in 1842 by Richard Owen, and the extinction of dinosaurs was not sudden and at the same time, but their numbers began to decline and decline as a result of some complex factors and causes that made it difficult Link them to one source to understand this phenomenon.
Reasons for the extinction of dinosaurs
65 million years ago, the Cretaceous period ended with the disappearance of half of the living species on Earth, so most of the reptiles, mammals, crocodiles and many others disappeared, and this disappearance formed a mysterious mystery to scientists.
Scientists have presented two assumptions to explain this extinction, the first of which is an impact that came from outside the Earth, such as an asteroid or comet, and the other is related to the huge eruptions of volcanoes on Earth that wiped out life in it.
Both explanations show that the sky was filled with smoke that blocked the sun’s rays, and thus affected the photosynthesis of plants, which led to an imbalance in the food chain.
Others believe that the real cause of extinction is related to changes in the climate and a change in the levels of oceans and seas.
Definition of dinosaurs
Dinosaurs (English: / Dinosaurs) are extinct reptiles that appeared on Earth in the late Triassic period approximately 245 million years ago, and the term Dinosauria (English: / Dinosauria) appeared for the first time by the English ecologist Richard Owen in 1842 AD, and the term was derived from Two Greek words, the first dinos (Greek:/ δεινός), meaning great, or enormous, and the second, Soros (Greek:/ σαύρα), meaning lizard.
There are nearly 700 known species of extinct dinosaurs that scientists have identified from fossils found on the seven continents.
These include bones, teeth, and eggs of dinosaurs, as well as footprints, their movement paths, and the skin impressions they left behind.
Types of dinosaurs
In the middle of the Jurassic period, the earth was greener, and it had begun to split, which led to the creation of diverse environments that were the reason for the emergence of more varieties and types of dinosaurs.
Ornithischia is characterized by the presence of a pelvis that resembles a bird’s pelvis, so that its pelvis or part of it is low down, and its bones are not double, and that they are hollow covering the front of the lower jaw. And one of the most famous types of hip ornithischians: / Lesothosaurus (English: / Lesothosaurus): It is a small plant dinosaur, with long limbs, that lived at the beginning of the Jurassic period.
Dinosaurs that lived about 100 million years ago and produced 50 species, thanks to their defense strategy.
This group is characterized by the presence of bones embedded in the skin, extending from the neck to the back to the tail.
The most famous of them
Stegosauria (English: Stegosauria)
They are medium-sized dinosaurs, three to nine meters long, and weighing from 300-1500 kg, and their bones embedded in their skin have developed into thorns and plates.
These dinosaurs have four feet, Ankylosauria
The skins of these dinosaurs are covered with bony plates and spines, connected with adjacent plates together to form a shield that extends across the neck, throat, back and tail, and its head is low.
They feed on terrestrial plants. They are of medium size, not exceeding five meters in length. Marginocephalia: These dinosaurs have a chain of bones in the back of their skull, and they have one or several horns. Different skulls, and did not appear except in the Cretaceous period.
Among the most important types:
Pachycephalosaurus (English:/ Pachycephalosaurus)
It has a thick skull roof, and it feeds on plants, and it has small teeth, some of which bear coarse teeth to pierce the leaves of the plant or the fruits./ Ornithopods (English: Ceratopsia): resembles a rhinoceros horn, it has horns, and weighs six or seven tons, including a small type that appeared in the Cretaceous period, weighing no more than 200 kg, and it does not have any horns
Ornithopods (English: Ornithopoda)
It is considered one of the most diverse and long-lived groups, it appeared in the Jurassic period and continued until the end of the Cretaceous period, and one of the most famous types of hadrosaurids (English: / Hadrosaurids).
Then it evolved until it reached 12 meters. It has strong wrists and hands with thick nails. It feeds on herbs and low foliage. It has four legs and a long tail.
The collision accident
The scientist Walter Alvarez suggested in the seventies of the last century that the extinction of the dinosaurs was caused by the collision of a meteorite or an explosive meteor ranging from 5 to 15 kilometers wide to the Earth, and it is believed that the collision occurred in the vicinity of the Yucatan Peninsula, which created a crater Chiciclesole, which is 170 km long in the Earth, Alvarez demonstrated his theory that the Earth’s layers during the extinction period showed a sudden rise in iridium levels.
Scientists differed about the impact of the collision on the temperature. Some scientists believed that the collision caused a sharp drop in the air temperature, while others believed that it caused the emergence of a heat wave that swept the Earth.
Scientists suggested that the intense heat resulting from the collision caused the death of part of the dinosaurs directly. And the death of the rest of the dinosaurs indirectly due to the hypothermia resulting from blocking the sun’s rays by the impact of materials ejected from the impact crater.
This theory suggests that instead of a single meteor colliding with the planet, it was separated from the Oort cloud that surrounds the Earth by several comets due to the refraction of gravity caused by the passing of a passing star and collided with the Earth, which led to a sharp drop in temperatures followed by a cooling period long, which caused the extinction of the dinosaurs.
Some scientists suggested that the dinosaurs became extinct as a result of their inability to adapt to the changes that occurred in the environment and the atmosphere.
It is now, and the temperature differences between the equator and the poles did not exceed 25 degrees Celsius, as for the gases of the Earth’s atmosphere, the level of carbon dioxide was 12 times higher than the current level, and oxygen constituted between 32-35% of the gases in the atmosphere Atmospheric, compared to 21% today, and these environmental changes in addition to the lack of oxygen level that deprived the dinosaurs of obtaining their enormous needs of oxygen to their extinction.
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