Part 2

In 450 B.C., Herodotus noticed fossils in the Egyptian desert and correctly concluded that the Mediterranean Sea had once been in that area.

Aristotle in 400 B.C. stated that fossils were organic in origin but that they were embedded in the rocks as a result of mysterious plastic forces at work within the earth. One of his students, Theophrastus (about 350 B.C.), also believed that fossils represented some form of life but thought that they had developed from seeds or eggs that had been planted in the rocks.

Strabo (about 63 B.C. to A.D. 20) was another important Greek scholar who attempted to explain the presence of fossils. He noted the occurrence of marine fossils well above sea level and correctly inferred that the rocks containing them had been subjected to considerable elevation.

During the “Dark Ages” fossils were alternately explained as freaks of nature, the remains of attempts at special creation, and devices of the devil which had been placed in the rocks to lead men astray. These superstitious beliefs and the opposition from religious authorities hindered the study of fossils for hundreds of years.

In approximately the middle of the fifteenth century the true origin of fossils was generally accepted, and they were considered to be the remains of prehistoric organisms which had been preserved in the earth’s crust. With the definite recognition of fossils as organic remains, many of the more primitive theories were discarded for one just as impractical—these remains were considered remnants of the Great Flood as recorded in the Scriptures. The resulting controversy between scientists and theologians lasted for about 300 years.

During the Renaissance several of the early natural scientists concerned themselves with investigations of fossils. Noteworthy among these was Leonardo da Vinci, the famous Italian artist, naturalist, and engineer. Leonardo insisted that the Flood could not be responsible for all fossils nor for their occurrence in the highest mountains. He reaffirmed the belief that fossils were indisputable evidence of ancient life, and that the sea had once covered northern Italy. Leonardo explained that the remains of the animals that had inhabited this ancient body of water were buried in the sediments of the sea floor, and that at some later date in earth history this ocean bottom was elevated well above sea level to form the Italian peninsula.

In the late eighteenth and early nineteenth centuries the study of fossils became firmly established as a science, and since that time fossils have become increasingly important to the geologist.

THE STUDY OF FOSSILS

The study of fossils is called paleontology (Greek palaios, ancient; ontos, a being; logos, word or discourse). Information gathered with the help of paleontology has greatly increased the knowledge of ancient plants and animals and of the world in which they lived.

Fossils represent the remains of such great numbers and various types of organisms that paleontologists have found it helpful to establish four main divisions within their science.

Paleobotany

Paleobotany deals with the study of fossil plants and the record of the changes which they have undergone.

Invertebrate Paleontology

This is the study of fossil animals without a backbone or spinal column. These include such forms as fossil protozoans (tiny one-celled animals), snails, clams, starfish, and worms, and usually represent the remains of animals that lived in prehistoric seas.

Because invertebrate remains are the most common fossils in Texas, this book is devoted largely to the discussion of invertebrate fossils and their method of collection.

Vertebrate Paleontology

The vertebrate paleontologist studies the fossils of animals which possessed a backbone or spinal column. The remains of fish, amphibians, reptiles, birds, and mammals are typical vertebrate fossils.

Micropaleontology

Micropaleontology is the study of fossils that are so small that they are best studied under a microscope. These tiny remains are called microfossils and usually represent the shells or fragments of minute plants or animals. Because of their small size, microfossils can be brought out of wells without being damaged by the mechanics of drilling or coring. For this reason microfossils are particularly valuable to the petroleum geologist who uses them to identify rock formations thousands of feet below the surface.

PRESERVATION OF FOSSILS

The majority of fossils are found in marine sedimentary rocks. These are rocks that were formed when salt-water sediments, such as limy muds, sands, or shell beds, were compressed and cemented together to form rocks. Only rarely do fossils occur in igneous and metamorphic rocks. The igneous rocks were once hot and molten and had no life in them, and metamorphic rocks have been so greatly changed or distorted that any fossils that were present in the original rock have usually been destroyed or so altered as to be of little use to the paleontologist.

But even in the sedimentary rocks only a minute fraction of prehistoric plants and animals have left any record of their existence. This is not difficult to understand in view of the rather rigorous requirements of fossilization.

REQUIREMENTS OF FOSSILIZATION

Although a large number of factors ultimately determine whether an organism will be fossilized, the three basic requirements are:

1. The organism should possess hard parts. These might be shell, bone, teeth, or the woody tissue of plants. However, under very favorable conditions of preservation it is possible for even such fragile material as an insect or a jellyfish to become fossilized.

2. The organic remains must escape immediate destruction after death. If the body parts of an organism are crushed, decayed, or badly weathered, this may result in the alteration or complete destruction of the fossil record of that particular organism.

3. Rapid burial in a material capable of retarding decomposition. The type of material burying the remains usually depends upon where the organism lived. The remains of marine animals are common as fossils because they fall to the sea floor after death, and here they are covered by soft muds which will be the shales and limestones of later geologic periods. The finer sediments are less likely to damage the remains, and certain fine-grained Jurassic limestones in Germany have faithfully preserved such delicate specimens as birds, insects, and jellyfishes.

Ash falling from nearby volcanoes has been known to cover entire forests, and some of these fossil forests have been found with the trees still standing and in an excellent state of preservation.