There are few places more interesting or awesome to visit than a museum of natural history. These institutions that preserve the past can open up a window on the world of the prehistoric Earth and its inhabitants. Dinosaurs, mammoths, ancient whales, and other extinct creatures are displayed for all to see. Fossil bones and replicas of immense, extinct creatures are amazing and scary at the same time. These creatures are the subject of wild imaginings as well as best-selling books and movies.
What is a fossil anyway? Are they really rocks? Where do you find fossils? How do fossils form?
In this chapter, we’ll look at fossils with the view of how they fit into the Earth’s geology and history. The books listed in the references provide a good start to the study of dinosaur types and lifetimes. For a complete study of dinosaurs, marine life, and other prehistoric creatures and fossils, the following Internet websites provide more information:
It has only been within the past 200 years that fossils were recognized for what they are. Before that, people thought strange-shaped rocks that looked like shells, wood, lizards, and other creatures were just oddities of nature, like a rock formation that looks like a bear or the face of a person.
Since most people today read about and play with toy dinosaurs from childhood, it’s hard to imagine a time when no one really knew what fossils were or how they were formed. Usually, depending on where they were discovered, creative explanations thrived. It was not until Darwin published, On the Origin of Species by Means of Natural Selection in 1859 (a best seller at the time), that the idea of extinct ancestors of modern plants and animals seemed possible.
The field of paleontology began about this time. A paleontologist is a scientist who studies fossils. Paleontology includes all fossils, not just dinosaur bones.
A fossil is the remains of a once-living plant or animal whose hard parts (those resistant to decay, like shells, bones, claws, and teeth) have been preserved within the Earth. Clams and mammals, then, have a better fossil record than soft creatures like worms or slugs.
A fossil is formed from the remains or traces of plants and animals preserved by natural causes in the Earth’s crust.
The key to fossil preservation and dating is decomposition. If a living organism is buried quickly before oxygen and microorganisms can break it down, it has a good chance of being preserved. Since shells and bones are fairly porous, minerals from surrounding sediments are deposited in open areas where the once fleshy parts have dried or disintegrated. Geologists find the age of fossils by radioactive dating. The better preserved the sample, the more accurate the dating within certain margins of error.
Skin imprints, tracks, and feces (called coprolites ) from ancient organisms are also considered to be fossils. Can you think of any other profession where the rock-hardened waste from ancient animals is considered a real find?
By studying petrified stomach contents and coprolites (measuring from less than a centimeter to over 30 cm) from dinosaurs, paleontologists have gotten information about the diet of dinosaurs. Because some plants are tough and resistant to digestion, some coprolites are pretty intact. Several plant-eating dinosaurs had a wide diet by today’s salad standards.
Tooth shape also gives clues as to diet. Scientists look at modern animals’ tooth shape for eating habit and diet comparisons. Broad, grinding teeth seem to point to plant eaters, while jagged, sharp teeth are used by meat-eating predators. Figure 10-1 gives you a sampling of different dinosaurs that have been categorized into plant eaters, meat eaters, or omnivores (eats both plants and animals).
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