The actual hardened remains of an animal’s skeletal structure and an impression of an insect or leaf on a muddy or other surface that now is stone are known as fossils. It is the hardened forms of fossil-bone turned to stone-that has given paleontologists the most information about primate evolution.
When an animal dies, the organic matter that made up its body quickly begins to deteriorate. The teeth and skeletal structure are composed largely of inorganic mineral salts, and soon they are all that remains. Under most conditions, these parts eventually deteriorate too.
But once in a great while conditions are favorable for preservation for instance, when volcanic ash, limestone, or highly mineralized ground water is present to form a high mineral environment. If the remains are buried under such circumstances, the minerals in the ground may become bound into the structure of the teeth or bone, hardening and thus making them less likely to deteriorate.
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Discovery of Fossils:
Paleontologists can tell a great deal about an extinct animal from its fossilized bones or teeth, but reading the fossil record is not easy. For one thing, the very formation of a fossil depends a good deal on chance; the fossil record contains remains of only a small proportion of all the animals and plants that ever lived.
Chance also plays a large role in the discovery of fossils, although paleontologist often knows on the basis of geological evidence where fossils of a particular age might be found. Rock that was laid down millions of years ago will be visible only if uplift reveals it or erosion has removed what was laid down over it.
In addition, fossils are often fragmented or damaged, and judgments about what the organism looked like may be based on one or just a few pieces. Although, we can tell the age of a fossil with some accuracy, methods of dating are not always exact enough for the paleontologist to determine whether a fossil is older than, contemporaneous with, or more recent than other fossils. For this reason too, evolutionary lines are difficult to trace.
A further complication is an artificial one: the problem of taxonomy, or classification. Over the period that paleontologists have been discovering primate remains, different assumptions have
guided scientists in making judgments about the taxonomic status of fossils.
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Even when paleontologists agree in theory, they often have honest differences of opinion about the status of a fossil. After all, we cannot conclude without doubt that two similar fossil forms belonged to separate species, because we cannot know whether or not they interbred.
Importance of Fossils:
Despite all these problems, fossils do provide a wealth of information. In studying primate evolution paleontologists ask two basic questions as they examine an animal fossil: What was the animal’s means of food-getting? And what was its means of locomotion? Often the answers to both questions can be determined from a few fragments of bone or teeth.
Much of the evidence for primate evolution comes from teeth, which along with jaws are the most common animal parts to be preserved as fossils. Animals vary in dentition, the number and kinds of teeth they have, their size, and their arrangement in the mouth.
Dentition provides clues to evolutionary relationships because animals with similar evolutionary histories often have similar teeth. Dentition also suggests the relative size of an animal and often offers clues about its diet.
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Paleontologist can tell much about an animal’s posture and locomotion from fragments of its skeleton. They can often judge whether the animal was a brachiated and whether it walked on all fours (Quadrupedalism) or upright (bimetallism).
The bone structure also tells much about the soft tissues. The form and size of muscles can be estimated by marks found on the bones to which the, muscles were attached. Finally, fragments of the skull or vertebrae provide clues about the proportions and structure of the brain and spinal cord. From such evidence, scientists can tell whether areas of the brain associated with vision, or smell, or memory were large or small.