Other kinds of fossil

Bones are not all that is left of dinosaurs. Occasionally the fossilized feces of dinosaurs and other vertebrates are found. Called coprolites, these sometimes-impressive relics can give an intestine's-eye view of dinosauri-an diets. Likewise, as we shall see later in this book, eggs and skin impressions have also been found.

Still, the single most important type of dinosaur fossil, other than the bones, themselves, are trace fossils. Dinosaur trace fossils (sometimes also called ichnofossils; (ichnos - track or trace)) are most commonly isolated footprints or complete trackways. Figure 1.3 shows a track left by a dinosaur. To be produced, the footprint must be made in material that can hold an impression (mud or fine sand). Again, rapid burial is a good way to ensure that tracks and trackways stick around. One finds molds that, in the case of tracks, represent the original impression itself, and casts, which are made up of material filling up the mold. Thus, a cast of a dinosaur footprint is a three-dimensional object that formed inside of the impression.

It would be terrific if we could link tracks with dinosaurs known from bones. But we can't; sometimes we can identify the trackmaker by a broad category like, for example "theropod." For this reason, footprints have their own names, and are classified separately as ichnotaxa, or footprint types. This may seem at first to complicate the number of

4 Mayor; A. 2000. The First Fossil Hunters.'Pnnceton University Press, Princeton, NJ, 361 pp.

Figure 1.3. Theropod dinosaur footprint from the Early Jurassic Moenave Formation, northeastern Arizona, USA. Human foot for scale.

dinosaurs out there, but in fact it is an important way of keeping different lands of data distinct.

While historically trackways have tended to be undervalued by vertebrate paleontologists, in the past 15 years their importance has become recognized. Trackways have demonstrated that dinosaurs walked erect, much as mammals and birds do today. Moreover, the trackways have shown the position of the foot: up on the toes in some cases and flat-footed in others. The speeds at which dinosaurs traveled (see Box 15.3) have been calculated using trackways: we can actually assess the possibility of T. rex running down a Jurassic Park Jeep. Trackways can give some indication of the faunal composition of a particular locality. Trackways have been used to document a predator (in this case, a theropod) stalking a herd of sauropods. The very idea of dinosaur herds has been supported by trackways. Trackways, therefore, are important clues to dinosaur behavior, and we will have recourse to them throughout the pages of this book.

Collection The romance of dinosaurs is bound up with dinosaur collection: one travels to far-flung locales, undergoes heroic field conditions and, like Dr Seuss' Gerald McGrew, manfully extracts exotic beasts. Regardless of romance, dinosaur collecting turns out to be non-trivial. The first step is prospecting; that is, hunting for them. The second step is collecting them, which means getting them out of whichever (usually remote) locale they are situated. The final step is making them available for study and/or display in a museum. This last step involves preparing and curating them; that is, getting them ready for viewing and incorporating them into museum collections. These steps involve different skills and commonly different individuals.

How deep is your wallet? Let's say that you decided to bag a Triceratops, a moderately large but common (finding it would not be extraordinarily difficult) herbivorous dinosaur from the western part of the USA. Presuming you have elected not just to buy the fossil outright (its ±$1,500,000 price tag might prove a small stumbling block), you should budget 1-1.5 months for prospecting (if you and your crew know what you are doing), about 2.5 months for collecting (because the bones will be spread out all over the ground), and somewhere between 8 and 12 months for preparation and for mounting the specimen for display. More than one person will be involved in all of these steps, and it is likely that, after salaries (for your field crew and preparation staff), equipment, transportation, and preparing the display, your dinosaur would cost you upwards of $300,000 to $500,000. Maybe you should go back to trilobites.

Prospecting A question that is commonly asked of paleontologists is "How do you know where the dinosaur fossils are?" The simplest answer is, "We don't." There is no secret magic formula for finding dinosaurs, unless long hard hours of persistent searching qualify as a secret magic formula. On the other hand, you can make a well-educated guess about where you might search, and in doing so you can greatly increase your odds of finding dinosaurs. Some collectors fare better than others, and a "feel" is surely involved in finding bone, as well as an experienced eye and plain luclc (Figure 1.4).

Some basic criteria constrain the search. These are:

1 the rocks must be sedimentary;

2 the rocks must be of the right age; and

3 the rocks must be terrestrial.

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