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| | Descendants of the Thecodonts are conservative groups of crocodiles and flying pangolins- Pterosauria. Saurischia and Ornithischia also derived from the Thecodonts.
Though the Euparkeria is slightly similar to the small dinosaur, it differed from dinosaurs substantially. The limbs of Euparkeria were located on the sides of the body as can be noticed in other reptiles. The limbs of Saurischia and Ornithischia dinosaurs were directly beneath the body as they are found in mammals. This indicates that the feet of dinosaurs could sustain the weight of a very big body. Lizards too can never grow too big since their limbs are positioned sideways from the body and the body is suspended between the limbs. This gives a clumsy gait to lizards and such design of limbs is simply not suitable for supporting huge bodies. On the contrary, dinosaurs could be very heavy because their trunk was positioned vertically on feet and rested on them. Vertically positioned limbs are capable of supporting large body weight; imagine the heavy carcass of an elephant, which is supported by column-shaped feet. Such a structure is rather functional. Without it, the animal should simply collapse to the ground! Particularly, the vertical arrangement of limbs allowed some dinosaurs to grow up to vast sizes.
Saurischia and Ornithischia dinosaurs differed from each other by the shape of their hip bones. The pelvic arch in the Saurischia was triactinal and it consisted of paired flat huckle bones, paired sciatic bones and also pubic bones. In the Saurischia, the paired flat huckle bones are positioned in the upper portion of the pelvis and attached to the backbone, the paired sciatic bone deviates from the depression of the thigh joint and directed downwards and back and the pubic bones deviate from the depression of the thigh joint and are directed forward and down. The Saurischia were the first carnivorous dinosaurs. They moved on two limbs leaving free the fore limbs to catch a prey. While resting, the body rested on the ground by leaning on the powerful pubic bone.
Herbivorous Saurischia dinosaur's originated from similar creatures. Since herbivorous animals require much larger intestines than carnivorous animals, their bodies, naturally, should be much bigger. Herbivorous dinosaurs had such a pot-belly that they could not stand on two limbs even for an insignificant amount of time. It forced them to once again move on four legs. The predatory Saurischia dinosaurs were called “THEROPODA” whereas heavy long-necked herbivorous Saurischia dinosaurs were called “SAUROPODA”.
In the Ornithischia pangolins, the pelvis was quadriradiare due to the other arrangement of the hip bones. Thus, the position of the huckle and sciatic bones was the same as in the case of the Saurischia dinosaurs but the pubic bones stretched backwards parallel to the sciatic bones. Owing to this, a huge gap appeared between the bones in the bottom portion of the pelvis. Since all the Ornithischia dinosaurs were herbivorous, they had a large intestine which could position into this gap i.e. the stomach was located between the hind legs. Therefore, Ornithischia dinosaurs could eat vegetative food and steadily stand and move on two limbs.
Ornithopods (“bird feet” dinosaurs) looked particularly like that. Later on, Ornithischia pangolins started moving on four limbs and acquired “weapons” and armor. Spikes and plates were found on the spine and tail of the Stegosaurus (“roof-lizard” dinosaurs), the body was crustaceous in the Ankylosaurus (armor-clad dinosaurs) and the Ceratops (horned dinosaurs) had armor and horns on their head. A difference in skull structure is noticed between the Saurischia and Ornithischia dinosaurs. An additional predentary bone, which supported the horned beak, was found in the bottom jaw in the skull of Ornithischia dinosaurs.
As in the case of birds, the quadriradiare pelvis of dinosaurs, possibly, occurred from the traradiate pelvis of Saurischia dinosaurs. However, the quadriradiare structure of the hip bones of bird types, apparently, occurred in evolution several times independently from each other. Recently found groups of predatory pangolins obviously had the quadriradiare bird's pelvis structure, though they were, undoubtedly, Saurischia dinosaurs. During the Jurassic period one more group of animals with a bird's type of pelvis originated from the Saurischia dinosaurs. They were birds. |
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It has been long accepted that all modern birds evolved from dinosaurs. Now the recent discovery shows that more dinosaur kinds had feathers than previously thought. The newly discovered dinosaur fossil with feathers was found in China. This species lived 198 million years ago in the Cretaceous Period. Scientists affectionately call all dinosaurs with feathers "fuzzy dinosaurs".
