Criterion

Dinosaurs were terrestrial beasts through and through, which means that their bones will generally be found in river systems, deserts, and deltas. Dinosaur remains, however, are known from lake deposits and from near-shore marine deposits. Clearly they lived neither in lakes nor in the ocean. In such cases, if the bones are articulated, the bloated carcasses may have floated out into the water, and eventually sunk and been buried. If not articulated, they may have been washed out of the mouths of rivers into the lakes and oceans.

Many of the richest fossil localities in the world are in areas with considerable rock exposure, such as badlands. Fossil localities are common in deserts; plant cover on the rocks is low, and the dry air slows down the rates of weathering so that, once a fossil is exposed, it isn't chemically destroyed or washed away. Paleontologists, therefore, don't often find themselves in the jungle looking for fossils; the weathering rates are too high and the rocks are poorly exposed. Instead, they commonly toil under the sun (because few plants means little shade) in deserts, or at least fairly dry regions.

This is not to say that all dinosaur material has been found in badlands or in deserts; far from it. As long as the three criteria above are met, there is a possibility of finding dinosaurs, and that's usually reason enough for going in and taking a look.

Once we find rocks that match the criteria above, we simply start searching for bone weathering out of the rock.5 Despite the promise of high-tech gadgetry such as the ground-penetrating radar used in Jurassic Park I, there has not yet been found any substitute for a well-trained eye. You walk, head down, covering as much area as efficiently as possible, looking for exposed bone. If you're lucky and/or have a good eye, you'll spot something. Now what?

Collecting Collecting is the arena in paleontology in which finesse meets brute force. Delicacy is required in preparing the fossils for transport; raw power is required for lifting blocks of bone and matrix (the rock which surrounds the bone) - commonly weighing many hundreds of kilograms - out of the ground and into a truck or some other means of transportation. So that it can be moved safely out of the field, the fossil is encased in a rigid jacket, or protective covering. Figure 1.5 shows how this is done.6

Transport out of the field can be difficult or not, depending upon the size (and weight) of the jackets. A small jacket (soccer ball size) can be carried out easily enough. Many jackets, however, are considerably larger, and there are times when braces, hoists, winches, cranes, flatbed trucks, front-end loaders, and even helicopters are necessary. A rule of

5 Notice that the term dinosaur "dig" is a misnomer: Nobody digs into sediment to find bones; bones are found because they are spotted weathering out of sedimentary rocks.

6 Purchasing toilet paper for this purpose provokes raised eyebrows. Consider this often-repeated scene: a paleontologist and her two- or three-member crew walk into a small town in a remote part of the world.They go to the local market and purchase a couple of cases of toilet paper rolls."How long do you plan to be in the field?"the bewildered shopkeeper asks."Oh, maybe a couple of weeks," the paleontologists reply.The shopkeeper is very impressed.

Figure 1.5. Jacketing, (a) A fossil is found sticking out of the ground; now it needs to be cleaned off so that its extent can be assessed. Exposing bone can be done with a variety of tools, from small shovels, to dental picks, to fine brushes. As the bone is exposed, it is "glued"; that is, impregnated with a fluid hardener that soaks into the fossil and then hardens. (b)The pedestal. When the surface of the bone is exposed, the rock around it is then scraped away. For small fossils, this can be quite painless; however; for large fossils, this can mean taking off the face of a small hill. This process continues until the bone (or bones) is sitting on a pedestal, a pillar of matrix underneath the fossil, (c) Toilet paper cushion. Padding is placed around the fossil to cushion rt.The most cost-effective cushions are made from wet toilet paper patted onto the fossil. It takes a lot of toilet paper; for example, a I m thigh bone (femur) could take upwards of one roll. On the other hand, this is not a step where one should cut corners, because returning from the field with a shattered specimen, or one in which the plaster jacket is stuck firmly to the fossil bone is not so good, (d) Plaster jacket. Jackets are made of strips of burlap cloth soaked in plaster and then applied to the toilet paper-covered specimen. A bowl of plaster is made up and then precut; rolled strips of burlap are soaked in it and then unrolled onto the specimen and the pedestal, (e) Turning the specimen. After the plaster jacket is hardened, the bottom of the pedestal is undercut, and the specimen is turned; that is, separated at the base of the pedestal from the surrounding rock, and turned over This is a delicate step in which the quality of the jacket is tested. (f)The top jacket. More plaster and burlap are then applied to the open (former) bottom of the jacket, now its top. At this point, the fossil is fully encased in the plaster-and-burlap jacket and is ready for transport from the field. (Photographs courtesy of D, J. Nichols.)

Figure 1.6. Scenes from a prep lab, in this case, that of the

Museum of Northern Arizona in Flagstaff.

Figure 1.6. Scenes from a prep lab, in this case, that of the

Museum of Northern Arizona in Flagstaff.

(a) Foreground: a large plaster jacket containing the dinosaur Coelophysis. Background: sand tables for stabilizing specimen fragments (to be glued), open jackets, storage shelves, and grinding equipment.

(b) The jacket shown in (a). A specimen of the dinosaur Coelophysis is visible in the foreground.The arms and hands are to the left; the pelvis, legs, and tail are visible to the right.

(c) A dinosaur skull (Pentaceratops) laid out for study. In the background are the large bays in which specimens are stored.

thumb is that the better the fossil, the less conveniently located it is: more than one paleontologist has actually had to cut a road into the middle of nowhere to get a truck to a remote specimen.

Back at the ranch The fossil dinosaur bone is out of the field and back at the museum.

The jacket must be cut open, and the fossil prepared, or freed from the matrix. This is done in a laboratory, universally called a prep lab (Figure 1.6). This turns out to be a complex process, for which there is a variety of techniques from the simple to the highly sophisticated. Some fossils require little effort: soft matrix is literally brushed away from the side of the well-preserved bone. In other cases, carbide-tipped needles must be used under a microscope, as the matrix is painstakingly chipped away from the fossil. In still other cases, special air-powered vibrating scribes, called "zip scribes," are used to free the bone. Sometimes an "air dent," a kind of miniature sand-blaster with a very fine spray of baking soda, is used to clear the matrix. A version of this tool is used in some dentists' offices to whiten teeth after cleaning. Finally, in certain circumstances, the matrix can be removed by "acid etching"; that is, dissolution in a bath of weak acid.

It gets tricky when the bone is softer than the matrix, because all those wonderful tools can damage bone more efficiently than they can remove the matrix. A variety of techniques, therefore, is available for hardening the bone. None of these can be too destructive; the preserved fabric and microscopic detail of the bone cannot be destroyed, or the scientific value of the fossil is compromised. Chemically sophisticated low-viscosity hardeners, such as those used in the field, are dripped onto the bone, soak in, and harden. Sometimes the specimen is heated, impregnated with carbowax, cooled, prepared, and then the carbowax removed. There is almost no limit to the ingenuity required for preparation and, in the end, the success of the preparation is measured only by whether the fossil is freed from its matrix undamaged by the process.

Fossils are commonly fragmented and part of the preparation is to put the pieces back together. Sometimes this is rather like a jigsaw puzzle, but sometimes the jacket holds adjacent pieces right next to each other and, by opening the jacket carefully, much of the jigsaw puzzle guesswork is removed. Pieces are stuck together by virtually any glue imaginable (depending upon the requirement): epoxies, superglue, and white, water-based wood glue. Interestingly enough, specimens are not always glued together when broken. This is because broken specimens can permit access to detailed parts of the skeleton - for example, the braincase - that would be very hard to study if the specimen were intact.

We often expect that the preparation process is completed only when a specimen is mounted as a freestanding display in a museum. Although this is the way things were done once, it is no longer the most modern approach to dinosaur fossils. Mounts are admittedly attractive, but using real bone in them presents some serious problems. First, real bone is delicate and needs to be supported. For this reason, a metal frame must be welded to support the bones, a process that is time-consuming, costly, and ultimately destructive to the fossil. In addition, when the specimens are mounted, they cannot be moved around easily and examined for study. Finally, mounted specimens commonly undergo damage over time; slight shifts in the mounts because of the extraordinary weight of the fossil bones, or vibrations in the buildings in which the bones are housed, or museum patrons lifting apparently "insignificant" bits7 all diminish the quality of mounted specimens.

Most museums, therefore, have begun to cast the bones in fiberglass and other resins and mount the casts. Such mounts are virtually indistinguishable from the originals if done correctly. Casts are lighter and allow for internal frames, and permit spectacular, dynamic, and realistic mounts (Figure 1.7). Finally, mounting casts frees up the actual fossils so that the bone can be optimally protected and studied under the most ideal conditions.

7 At the American Museum of Natural History in New York, tail vertebrae of a number of the mounted specimens keep having to be replaced, as some dinosaur enthusiasts have been known to take them home.

Figure 1.7. A spectacular mount of the sauropod Barosaurus and the theropod A//osourus.This mount is made of fiberglass and epoxy resin, cast from the bones of the original specimens. A dynamic pose like this would not have been possible using the original fossil bones. (Photograph courtesy of the American Museum of Natural History.)

Figure 1.7. A spectacular mount of the sauropod Barosaurus and the theropod A//osourus.This mount is made of fiberglass and epoxy resin, cast from the bones of the original specimens. A dynamic pose like this would not have been possible using the original fossil bones. (Photograph courtesy of the American Museum of Natural History.)

Some museum curators fear that displaying mounted casts (instead of mounting the fossils themselves) somehow cheats the public of its right to see the originals. A cast, however, is not a poor substitute for the real thing. Leaving the bones disarticulated, properly curated, and available for study maximizes returns on the very substantial investments that are involved in collecting dinosaurs. Paleontology is carried out in large part by public support, and mounted casts give the public the best value for its money.

Important readings Behrensmeyer, A. K. and Hill, A. P. (eds.) 1980. Fossils in the Making.

University of Chicago Press, Chicago, IL, 338pp. Cvancara, A. M. 1990. Sleuthing Fossils: the Art of Investigating Past Life. John

Wiley and Sons, New York, 203pp. Gillette, D. D. and Lockley, M. G. (eds.) 1989, Dinosaur Tracks and Traces.

Cambridge University Press, New York, 454pp. Kielan-Jaworowska, S. 1969. Hunting for Dinosaurs. Maple Press,

Pennsylvania, 177pp. Lessem, D. 1992. Kings of Creation: How a New Breed of Scientists is Revolutionizing our Understanding of Dinosaurs. Simon and Schuster, New York, 367pp.

Mitchell, W. J. T. 1998. The Last Dinosaur Book. University of Chicago Press,

Chicago, IL, 321pp. Moore, R. C., Laiicker, C. G. and Fischer, A. G. 1952. Invertebrate Fossils.

McGraw-Hill Book Company, Inc., New York, 766pp. Parsons. K. M. 2002. Drawing Out Leviathan: Dinosaurs and the Science Wars.

Indiana University Press, Bloomington, IN, 210pp. Preston, D. J. 1986. Dinosaurs in the Attic: an Excursion into the American

Museum of Natural History. St Martin's Press, New York, 244pp. Sternberg, C. H. 1985. Hunting Dinosaurs in the Bad Lands of the Red Deer

River, Alberta, Canada. NeWest Press, Edmonton, Alberta 235pp. Walker, R. G. and James, N. P. (eds.) 1992. Fades Models: Response to Sea Level Change. Geological Association of Canada, St Johns, NL, 409pp.

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