DINOSAUR FOSSILS

How do paleontologists identify species of dinosaurs from other fossils?

One of the best ways to identify dinosaur fossil bones is by size, as many of the bones are huge. For example, the upper leg bone, or femur, of an adult Apatosaurus often measures over 6 feet (1.8 meters) long.

But size is not everything, as many dinosaurs were the same size as a chicken or cat. The way scientists detect the differences between dinosaurs and other animal species is by the construction and orientation of their bones, including heads, tails, and hipbones. In addition, dinosaur fossils are often found in association with other dinosaurs at a site. Many times these fossils represent dinosaurs from meat- eaters to plant-eaters that gathered together along the shore of a lake or ocean. The dinosaurs were all searching for food along the banks of the water, a place that would attract many animals and plants.

Of course, not all dinosaurs are found in the conventional way. In 1998, an amateur fossil collector saw the movie Jurassic Park, and recognized that a fossil he had (which he thought was a bird) was actually a dinosaur. The specimen was found in Italy and measures only 9.5 inches (24 centimeters) long; scientists now know it was a young dinosaur (a theropod named Scipionyx samniticus) that had just hatched before it died. In this case, the dinosaur remains probably washed into oxygen-starved waters, where it was quickly buried. This may be one of the most important dinosaur fossils ever found, as many of its soft body parts were preserved, including the intestines, muscle fibers, and what appears to be the liver.

When was the first dinosaur bone collected and described?

The fossilized bones of dinosaurs have probably been found throughout human history, but for much of this time people did not realize what they were. Therefore, no records or descriptions were kept until fairly recently. References to fossilized sharks teeth and shells are recorded from the European medieval period, but because they believed that no animal or plant made by God could become extinct, they explained them in other ways. For example, many of the fossils were interpreted as the remains

of modern species as opposed to ancient, extinct species; others were thought of as merely pebbles that resembled the remains of animal and plant species.

The first recorded description of a dinosaur bone was made in 1676 by Robert Plot (1640-1696), a professor of chemistry at the University of Oxford, England, in his book The Natural History of Oxfordshire. Although he correctly determined that it was a broken piece of a giant bone, Plot did not know the bone came from a dinosaur. Instead, he felt it belonged to a giant man or woman, citing mythical, historical, and biblical sources. In 1763, the same bone fragment was named Scrotum humanum, by R. Brookes, to describe its appearance, but the name never gained wide, or serious, acceptance. Based on Plots illustration, modern scientists believe the bone fragment is actually the lower end of a thigh bone from a Megalosaurus, a meat-eating dinosaur from the Middle Jurassic period that roamed the area now known as Oxfordshire.

In 1787, American physician Caspar Wistar (1761-1818) and Timothy Matlack (better known as a statesman and patriot during the American Revolution; 1730-1829) discovered a large fossil bone in the state of New Jersey. Although they reported their finding, it was ignored and unverified; it may have been the first dinosaur bone ever collected in North America.

What are some of the oldest dinosaur fossils found to date?

There are several dinosaur fossils claimed to be the oldest ever found, a claim many scientists have made in recent years. The oldest dinosaur bones and skulls found to date may be of a small genus of meat-eating animal measuring about 6.5 feet (2 meters) in length, but some scientists believe it was another type of reptile called a thecodont. The fossils were discovered in Brazil and are thought to be 235 to 240 million years old.

Previously, an Eoraptor, a 228 million-year-old meat-eating dinosaur, was found in Argentina. More recently, paleontologists also discovered the fossilized bones of three prosauropods, plant-eating dinosaurs that lived approximately 220 million years ago in Santa Maria, an area of southern Brazil. And finally, another claim to the oldest-known dinosaurs (or precursors) were prosauropods from Madagascar thought to be 230 million years old. The Eoraptor was dated using radio-isotope analysis, whereas index fossils or the use of surrounding fossils to date a dinosaur were used to date the fossil in Madagascar.

 
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