Dinosaurs - origin and facts

Dinosaurs lived on earth for about 165 million years during Mesozoic Era, the age of reptiles and mysteriously went extinct 65 million years ago leaving back their gigantic bones as an evidence of their existence. People studying dinosaurs believe that they live even today as birds and this conclusion was based on the feathers on their skeletons. The term "Dinosaur" evolved from a scientific term,"Dinosauria" (a varied group of animals with widely different modes of living). Dinosaurs were a specific subgroup of the archosaurs, a group that includes crocodiles and birds. The dinosaurs of Mesozoic Era left behind many clues about what they looked like and how they lived. Their fossils give us clues about their lifestyles. Some of the dinosaurs had thick, bumpy skin and some even had primitive feathers.

Most of the dinosaurs were hatched from eggs, and they could neither fly nor live in water. They were fast and energetic creatures. It is said that some dinosaurs were tall and others small but most of them were medium-sized. The largest dinosaur is 100 feet long and the smallest, size of a chicken. Even after extensive research and observations, researchers say that it is very difficult to figure out their behavior, mating and color. It is difficult to determine whether a dinosaur is a male or a female from its fossil. Dinosaur fossils had been known for centuries as "dragon bones" or the remains of giants. Different types of dinosaurs lived at different times. Some walked on two legs (called bipedal) and some on four legs (called quadrupedal).

Dinosaur diets can be determined from their tooth structure (Dentition) and the contents of their stomach. Well-preserved dinosaur skeletons sometimes have traces of apparent food items preserved in their abdominal cavity, where it's safe to assume that they had a stomach. Some of their stomachs had well-rounded stones, called gastroliths that were probably used to grind food in a muscular crop or gizzard, like some birds (and crocodilians) do. Most of them were plant eaters (herbivores) and some, meat eaters (carnivores).

Based on the sequence of their footprints (Trackway) and the fact that crocodiles were dinosaurs' closest living relatives and birds being their living descendants, the following conclusions can be drawn:

1) Parental care was involved in their lifestyle.
2) They are extensive nest builders.
3) Some non-avian dinosaurs traveled in large groups.
4) Non-avian dinosaurs moved with their feet held underneath their body (as birds and mammals do).
5) Some non-avian dinosaurs moved rather quickly, but some plodded along at a more leisurely pace.
6) Some say that dinosaurs were complete endotherms just like birds while others say that they had an intermediate type of physiology between endothermy and ecothermy but it is believed that they were mostly inertial homeotherms; they were ectothermic but maintained a constant body temperature by growing large.
7) From the preserved footprints, it is possible to determine how fast that particular creature was traveling at that moment. This method uses simple equations based on the distance between footfalls and the size of the feet. The fastest speeds evident from dinosaur tracks (a medium-sized theropod in this case) are about 12 meters per second (about 27 mph).

Dinosaurs are vertebrates and stood erect (like birds and most mammals); they did not keep their legs sprawling out to the side of their body like most lizards and salamanders do. Also, from the trackways of dinosaurs, we know that they rarely dragged their tail on the ground. So, mammals and birds are probably better models for understanding dinosaur locomotion than lizards are (but all are useful to some degree, and all are limited in their usefulness).

Although dinosaur remains had been found earlier elsewhere, it was the discoveries of dinosaurs in North America in the second half of the 1800s that provided the first real glimpses of what these animals were like, and gave paleontologists some clues about the past diversity of life on Earth. The late 1800s were the "golden age" of dinosaur paleontology, when many animals that you might be familiar with were discovered and named. Today we seem to be in another "dinosaur renaissance".