Because people kept finding their fossilized bones as well as complete animals frozen in the permafrost of Siberia. There aren't any of those animals living now so they must be extinct.
About 350 kilograms. The better known fibulasaurus weighs about 200 kilograms. Both were extinct by the time other large land animals evolved.
No one knows for sure how the dinosaurs went extinct. However, some of the theories are a dramatic climate change, or a large meteorite impact.
Early humans only killed animals to eat. When they killed all of the animals, they would have to move to other places. They would start making small community's and eventually, when their towns became too large, it became too difficult to move. They had to find an easier way to get around. When they trapped their horse like animals, they decided not to kill them. They tried to train the animals to help them carry their belongings. When this proved successful, they moved on to larger animals like elephants. Soon they started to domesticate animals left and right. First they domesticated only useful animals. Then they would make pets out of some of them.
Well, the pollution in the sea actually kills animals. Think about it, if you were in a polluted sea, how would you even live? The answer is, there is no way to live. Toxic, toxic water pollution by large industrial companies who spill oil and waste and individuals who dump trash when they go to the beach.
Mammoth
The large rodents became extinct due to evolution. This can happen to many different types of animals not just rodents.
Saber toothed cats (tigers) became extinct 11,000 years ago. Food sources were large animals such as elephants, rhinos and colossal herbivores of the era
The heat was drying up the water so animals could no survive .
The 12 animals that people should be glad are extinct are;giant crocodiles, 3 ft long scorpions, extremely large millipedes, spiders that sting, extremely large sharks, a hybrid scorpion and millipede, large piranhas, snakes larger than anaconda, large dragonfly, and prawns with teeth.
They hunted large animals, like horse, bison, mammoth, deer, aurochs (extinct wild cattle), etc.
All of their prey (large mammals) had vanished and had been replaced by smaller faster mammals like deer. The saber tooth cats were specialised in bringing down large animals and were not long distance runners so they found it very hard to catch the fast prey. They could not get enough food and became extinct :)
The primary prey of saber toothed tigers were big game animals. They would have hunted deer, bison, camelops (an extinct species of North American camel), and even mammoths and giant ground sloths. At the end of the ice age, many of these large prey animals that the saber toothed cat depended on died out, and the saber toothed cat became extinct.
At the time of the dinosaurs, most large animals were reptiles and the dominant trees were conifers. Today, most large reptiles have been long extinct, and most large animals are mammals. The dominant plants are now flowering plants.
Megafauna means large animals. Sometimes, it is used to refer to the unusually large animals of the last ice age, such as mammoths. Sometimes, it is used to refer to large, extinct animals, such as the short-faced bear or the sabre-toothed cat. Sometimes, it is used to refer to dinosaurs. Sometimes, it is used to refer to large, modern animals, such as polar bears and hippopotami.
Nobody knows how any dinosaurs became extinct but the most likely explanation is that a 10Mile big meteorite smacked into the Earth
Nobody is certain why the saber toothed cats died out. They probably became extinct, however, because many of the large prey animals that saber toothed cats depended on died out. Theories for why this happened include climate change, overhunting by humans, and human induced diseases.
There are none alive today. Saber tooth tigers were prehistoric animals and are now extinct. Only their fossilized remains can be found. You can find a link below for more information.