Part 5

Thus, the study of a series of dinosaur tracks would not only indicate the size and shape of the foot but also provide some information as to the weight and length of the animal. In addition, the type of rock containing the track would help determine the conditions under which the dinosaur lived.

Some of the world’s most famous dinosaur tracks are to be found in the Lower Cretaceous limestones in Somervell County, Texas. These footprints, which are about 110,000,000 years old (Pl. 4), were discovered in the bed of Paluxy Creek near the town of Glen Rose. Large segments of the rock containing these tracks were collected by paleontologists of the American Museum of Natural History in New York City and the Texas Memorial Museum at Austin. Great slabs of limestone were transported to the museums, replaced in their original position, and are now on display as mute evidence of the gigantic size of these tremendous reptiles.

Invertebrates also leave tracks and trails of their activities, and these markings may be seen on the surfaces of many sandstone and limestone deposits. These may be simple tracks, left as the animal moved over the surface, or the burrows of crabs or other burrowing animals. Markings of this sort provide some evidence of the manner of locomotion of these organisms and of the type of environment that they inhabited.

Coprolites

Coprolites are fossil dung or body waste (fig. 1). These objects can provide valuable information as to the food habits or anatomical structure of the animal that made them.

Gastroliths

These highly polished well-rounded stones (fig. 2) are believed to have been used in the stomachs of reptiles for grinding the food into smaller pieces. Large numbers of these “stomach stones” have been found with the remains of certain types of dinosaurs.

PSEUDOFOSSILS

Among the many inorganic objects formed by nature there are some that bear superficial resemblance to plants or animals. Because they are often mistaken for organic remains, these objects have been called pseudofossils, or “false fossils.”

Dendrites

Although these closely resemble the remains of ferns or other plant material (fig. 3), dendrites are actually thin incrustations of manganese dioxide. They are often found along the bedding planes of Cretaceous and Paleozoic (geologic time scale, Pl. 1) limestones in many parts of Texas.

Slickensides

These are striations that are produced when rock surfaces move past each other while being fractured. Slickensides may superficially resemble certain of the Pennsylvanian coal plants of Texas.

Since slickensides are commonly at an angle to the bedding plane and plant remains lie parallel to the bedding plane, the two are usually easily distinguished.

Concretions

Many shales and sandstones contain hardened masses of minerals and rock that are often mistaken for fossils. These masses, called concretions, are usually found weathered out of the surrounding rock and may assume the shape of bones, flowers, vegetables, turtles, etc. Although these concretions do not represent organic remains, it is sometimes possible to find true fossils inside them.

WHERE AND HOW TO COLLECT FOSSILS

In fossil collecting, as in most “collecting” hobbies, the key to success lies in knowing where to look, what equipment to use, and the most effective methods of collecting.

COLLECTING EQUIPMENT

Fossil collecting is a relatively inexpensive hobby because it requires a minimum of supplies and equipment. However, as in almost any hobby, there are certain basic items of equipment that must be acquired.

Hammer

The hammer is the basic tool in the collector’s kit. Almost any type of hammer is satisfactory, but as collecting experience is gained it may be desirable to get a geologist’s hammer. These hammers, also called mineralogist’s or prospector’s picks, are of two types. One type has a square head on one end and a pick on the other (Pl. 5): the other type is similar to a stonemason’s or bricklayer’s hammer and has a chisel end instead of the pointed pick end. The square head of the hammer is useful in breaking or chipping harder rocks, and the chisel or pick end is good for digging, prying, and splitting soft rocks.

Collecting Bag

It will be necessary to have some type of bag in which to carry equipment, fossils, and other supplies. A Boy Scout knapsack, musette bag (Pl. 5), hunting bag, or similar canvas or leather bag is suitable.

Chisels

A pair of chisels is useful when fossils must be chipped out of the surrounding rock. Two sizes, preferably ½ and 1 inch, will usually suffice. A small sharp punch or awl is effective in removing smaller specimens from the softer rocks.

Wrapping Materials

Some specimens are more fragile than others, and these should be handled with special care. Several sheets of newspaper should always be kept in the collecting bag, and each specimen should be wrapped individually as it is collected. Such precautions taken in the field will usually prevent prized specimens from being broken or otherwise damaged. In addition to newspaper, it is wise to carry a supply of tissue paper in which to wrap more fragile specimens.