Dinosaurs

We use dinosaur as a general term describing animals that had certain reptile-like characteristics and gained huge proportions. But scientists have narrowed down the definition a bit. A dinosaur is said to have possessed upright limb posture (allowing them to use their "hands" for purposes other than running), a ball-like top to the femur with an open hip-socket in the pelvis (allowing a greater range of motion in the back legs. Other characteristics of their bones include special requirements for hands and vertebrae. Some of these defining characteristics could be defined to humans (even though we are not related except in the remotest sense). Perhaps the most famous of the dinosaurs is Tyrannosaurus Rex whose upright stance is quite pronounced. Rather than four legs, he has two legs and two arms.

Dinosaurs are said to be descended from the Archosaurs (from whom are also descended our Crocodiles and Alligators). Dinosaurs began their existence in the Triassic Period (The Mesozoic Era is divided up into three periods, similar to the way a week is divided in to seven days). Many dinosaurs were quite small often weighing less than humans and frequently as small as a human's hand (like the Lagosuchus). The dominant dinosaur type was the prosauropod which were small and lightly built, with long necks and tails. They fed on both plants and animals.

The Jurassic Period came next and is when large dinosaurs began their rule of the Earth. Climatologists believe that the world was still hot and arid at this time, but becoming increasingly wet, so there were more and more jungles and green habitat. The giant sauropods (like the Apatosaurus) began to take over from the prosauropods. Armored dinosaurs like the Stegosaurus also appeared on the scene. The armor is thought to have been a way for plant eaters to protect themselves from the ever larger meat eating dinosaurs like the Allosaurus. The tallest of the dinosaurs, the Brachiosaurus, also munched its way through this period.

Very high sea levels and humid, warm temperatures marked the subsequent Cretacious Period. This has been marked as the heyday of the dinosaurs. Many new species, like the Spinosaurus and the Parasauralophus appeared, perhaps in response to the evolution of flowering plants. In the oceans the Plesiosauruses made their presence felt. One of the most remarkable dinosaurs of the period was Triceratops where a large neck frill provided both protection and an opportunity for display. Some plant-eaters also developed armor on their backs and even club tails that allowed them to counter attack against the pursuing carnivores.

The Cretacious Period ended with a mass extinction that completely wiped out the dinosaurs. No one is quite certain as to the cause. Some conjecture that an asteroid may have struck the Earth or that some other event came along to create a severe climate change. Some believe that such a thorough destruction of a whole group of creatures was more likely the product of a virulent virus that evolved and was likely passed along by flying creatures as well as insects which were also becoming more and more pervasive during this time in geologic history.

There are some misconceptions about pteranadons being flying dinosaurs. Pteranadons were not dinosaurs per se. They were a separate branch of the family tree. Flying dinosaurs though did exist and may have descended from small, fast running maniraptor dinosaurs. They would eventually become birds. The first bird/dinosaur is thought to be the Archaeopteryx. Because of their size Mammoths are sometimes lumped together with dinosaurs. However, Mammoths lived much later and were mammals.

Scientists learn more and more about dinosaurs every day, but the fact is that evidence about these creatures is millions of years old. It is, at this point, impossible to know what most of the creatures looked like other than in outline. Feathers, skin and flesh seldom survived the ravages of time to our own geologic era. Also, the number of skeletons available for study, though growing, is not vast. Thus, much of what is thought about dinosaurs is not actually "known" about dinosaurs. Because of this, there is still much debate over such issues as whether dinosaurs were warm or cold blooded. How intelligent were they? Did they have a herd instinct? Were they generally drab like lizards or bright and colorful like birds? The answers to these questions and many more will likely find answers as science continue to quest into the past, into the world of the dinosaur.

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W.J. Rayment

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