| Dinosaurs (“terrible pangolins”) are animals belonging to the reptile class (Reptilia), and the subclass Archosauria. The range of distinctions between dinosaurs was so great that it is very difficult to establish sibling connections between them. They could be the size of a cat or a hen and could reach the sizes of huge whales. One of them moved on four limbs and others ran on their hind legs. Clever hunters and bloodthirsty predators were found amongst the dinosaurs but harmless vegetable-feeding animals were also found amongst the dinosaurs, some of which have become aqueous animals. The most obvious difference of dinosaurs from other reptiles is the arrangement of their limbs. They are directly under the trunk of the dinosaur, as in the case of mammals.
The term “Dinosaur” (Dinosauria; from Greek. deinos – terrible, awful and saurus –pangolin) was introduced by the English zoologist Richard Owen in 1842. He named such an order in which he combined various reptiles known at that time according to fossil bones from Europe and North America. Since then, any large extinct pangolins are called dinosaurs. However, such wide use of the term is incorrect, since not all gigantic terrestrial reptiles of the mesozoic era were dinosaurs and some dinosaurs were smaller than a cock in size.
For almost 140 million years these animals dominated the planet. They were found on all the continents and adapted to life in different conditions. It is accepted to divide the Mesozoic or “an era of average life” into three periods when dinosaurs lived on Earth: Triassic, Jurassic and Cretaceous. Dinosaurs appeared on Earth about 200 million years ago in the Triassic period. At that time, modern continents were shifted and formed a single entity. The climate was hot and dry and consequently extensive lands reminded as deserts. Ferns and horsetails grew on moist lowlands in valleys of rivers and on the coasts of oceans tree ferns and coniferous trees grew in forests. In the Jurassic and Cretaceous periods, dinosaurs were very large in numbers and of varied typess. They dominated the terrestrial vertebrates and played an important role in the water ecosystems and even mastered airspace. About 65 million years ago the extinction of dinosaurs occurred at the end of the Cretaceous period.
Primitive Archosauria were combined into the thecodont’s group. Crocodiles and flying pangolins (Pterosauria) were dinosaurs belong to this subclass and in some classification charts, even birds belong to this class. Only birds and crocodiles survived until now.
It is accepted to divide dinosaurs into two groups - Saurischia and Ornithischia. Earlier it was assumed that they were derived from the Thecodont predecessor’s independent from each other. Thus, the word “dinosaur” lost its initial taxonomic sense and remained only the convenient popular designation of extinct Saurischia and Ornithischia reptiles.
However, a more detailed analysis allowed to ascertain a unique set of features, characteristic for both of the groups and now it is considered that all dinosaurs came from one common predecessor, i.e. the monophyletic group or clad ( the branch of the family tree of animals).
The Saurischia were named due to the similarity of their pelvis with the pelvis of the majority of reptiles. Predators as well as vegetable-feeding forms were found amongst them. In this order, probably, gigantic vegetable-feeding sauropods with a length of up to 24m and above are quite popular. Monstrous biped predators with huge skulls, jaws and teeth were also impressive.
The Ornithischia differ by the shape of the pubic bones of the pelvis, as in birds which have a long appendage directed more or less parallel to the ishiadic bone. In the majority of reptiles, pubic and ishiadic bones diverge at a significant angle. All Ornithischia dinosaurs are vegetable-feeding animals.
Many early representatives of both the Saurischia and Ornithischia were biped animals. However, some of their descendants in both groups have mastered once again moving on four legs.
Fossils of dinosaurs were found in many areas of North America. Rocks from the Triassic age (the beginning of the Mesozoic era) have foot imprints of dinosaurs in the east of the USA in a valley of the river Connecticut. By studying such footprints, it is possible to know how the dinosaurs moved and which of their forms inhabited together. A vast cemetery of dinosaurs of the Jurassic Period (in the middle of the Mesozoic era) was unearthed in the Uinta Basin near Vernal (in the state of Utah). Many gigantic vegetable-feeding sauropods, the largest terrestrial reptiles are amongst the displayed types of dinosaurs. Many fossils of dinosaurs of close age were found in Como-Bluff (Wyoming State) near Medicine Bow. The fossils are very well presented in the layers of later age, belonging to the Cretaceous period, i.e. by the end of the Mesozoic era in the State of Montana and in the west of Canada.
Certainly, not all dinosaurs are gigantic pangolins. Small forms are interesting in and what is important is that some of them specify link this group with earlier, archaistic organized reptiles. Primitive dinosaurs, the earliest of which are known from the Upper Triassic (approx. 200 million years ago), have only continued the history of reptiles, which began at least 150 million years prior to their period.
Then, what are dinosaurs? The term “Dinosaurs” is not simple to explain and even now, it even does not have accurate scientific importance. Two different reptile orders are combined under the name dinosaurs – the Saurischia order and the Ornithischia order, which have close sibling connections with the other order of reptiles the extinct Pterosauria and crocodiles, which survived till now. These four orders – Saurischia, Ornithischia, Pterosauria and crocodiles are considered to be a single reptile order - of the subclass Archosauria, which if translated means “Dominating Pangolins”. |
Despite the popular notion that dinosaurs were big mean creatures, there were many "dwarf" dinosaur species about the size of modern dogs. Scientists are not sure whether these small dinosaurs ever wagged their tails like dogs, but judging by their vegetarian food habits, these dog-dinos were friendly creatures.
