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| | Descendants of Thecodonts are conservative group of crocodiles & flying pangolins- Pterosauria. Saurischia & Ornithischia also derived from Thecodonts.
Though Euparkeria slightly reminded small dinosaur, it differed from dinosaurs substantially. Limbs of Euparkeria were located on sides of the body as it can be noticed in other reptiles. Limbs of Saurischia & Ornithischia dinosaurs were directly beneath the body as they are found in mammals. This indicates that feet of dinosaurs could sustain the weight of very big body. Lizards too can never grow too big since their limbs are positioned sideways from the body & the body is suspended between the limbs. This gives clumsy gait to lizards & 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 vertical on feet & 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 structure is rather functional. Without it, the animal should simply collapse on ground! Particularly vertical arrangement of limbs allowed some dinosaurs to grow upto vast sizes.
Saurischia & Ornithischia dinosaurs differed from each other by the shape of hip bones. Pelvic arch in Saurischia was triactinal & it consisted of paired flat huckle bones, paired sciatic bones and also pubic bones. In Saurischia, the paired flat huckle bones are positioned in upper portion of pelvis & attached to backbone, paired sciatic bone deviate from depression of thigh joint & directed downwards & back & pubic bones deviate from depression of thigh joint & directed forward & down. Saurischia were the first carnivorous dinosaurs. They moved on two limbs leaving free the fore limbs to catch a prey. While resting, body was rested on ground by leaning on powerful pubic bone.
Herbivorous Saurischia dinosaurs derived from similar creatures. Since herbivorous animals require much larger intestines than carnivorous animals, their bodies, naturally, should be much bigger. Herbivorous dinosaurs had such pot-belly that they could not stand on two limbs even for insignificant time. It forced them to once again move on four legs. Predatory Saurischia dinosaurs were called “THEROPODA” whereas heavy long-necked herbivorous Saurischia dinosaurs were called “SAUROPODA”.
In Ornithischia pangolins, pelvis was quadriradiare due to other arrangement of hip bones. Thus, position of huckle & sciatic bones was same as in the case of Saurischia dinosaurs but the pubic bones stretched backwards parallel to sciatic bones. Owing to this, huge gap appeared between the bones in bottom portion of pelvis. Since all the Ornithischia dinosaurs were herbivorous, they had large intestine, which could position in this gap, i.e stomach was located between the hind legs. Thus, Ornithischia dinosaurs could eat vegetative food & steadily stand and move on two limbs.
Ornithopods (“bird feet” dinosaurs) looked particularly like that. Later on, Ornithischia pangolins started moving on four limbs & acquired “weapon” & armor. Spikes & plates were found on the spine & tail of Stegosaurus (“roof-lizard” dinosaurs), body was crustaceous in Ankylosaurus (armor-clad dinosaurs) & Ceratops (horned dinosaurs) had armor & horns on head. Difference in skull structure is noticed between Saurischia & Ornithischia dinosaurs. Additional predentary bone, which supported horned beak, was found in bottom jaw in the skull of Ornithischia dinosaurs.
As in the case of birds, quadriradiare pelvis of dinosaurs, possibly, occurred from traradiate pelvis of Saurischia dinosaurs. However, quadriradiare structure of hip bones of bird type, apparently, occurred in evolution several times independently from each other. Recently found group of predatory pangolins obviously had quadriradiare bird's pelvis structure, though they were, undoubtedly, Saurischia dinosaurs. During Jurassic period, one more group of animals with bird's type of pelvis derived from 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".
