The type locality of Seismosaurus in the Ojito Wilderness Study Area northwest of Albuquerque, New Mexico, and the Dry Mesa Quarry southeast of Delta, Colorado—the type locality o/Ultra-saurus macintoshi, Supersaurus viviani. and Dystylosaurus edwini.
The giants were common, the supergiants rare. Brachio-saurus is the best known of the supergiants. It weighed about twice as much as Apatosaurus — about seven to eleven times that of an elephant. With long neck and forelegs, it had a more giraffelike build than the other sauropods. Also among the supergiants were Ultrasaurus, a close relative of Brachiosaurus, and Supersaurus, more closely related to Diplodocus. Ultrasaurus and Supersaurus are both known only from Dry Mesa Quarry in Colorado. A third Dry Mesa supergiant, Dystylo-saurus, rivaled the others in size, but like Supersaurus and Ultrasaurus it is known only from isolated bones. Seismosaurus is the fifth supergiant sauropod—and the only one besides Brachiosaurus known from partial skeletons.
Skeletons of the giants (Camarasaurus, Apatosaurus. Diplodocus, Barosaurus) suitable for display in the great museums were among the trophies sought by collectors during the rush for dinosaurs in the American West during the late 18oos and early 1900s. Casts of Diplodocus were traded to museums around the world, making it one of the most well-known dinosaurs. Today, visitors can see partially articulated skeletons of these and other dinosaurs on display in situ, locked into the sandstone from the Jurassic river bed in which they were buried.
Skeletal reconstruction o/'Diplodocus carnegii, probably the closest known relative o/Seismosaurus. This slender sauropod is known from essentially complete skeletons from the Morrison Formation. Its skeletal anatomy is well established, and it formed the basis for most comparisons with Sam's skeleton.
This spectacular demonstration of dinosaur hones at Dinosaur National Monument, on the border of Utah and Colorado, documents one of the most productive sites for Jurassic dinosaurs in the world.
Mounted skeletons of sauropods now grate the halls of museums around the world. Increasingly, these skeletons are replicas made from original reconstructions. And original reconstructions themselves are not the real thing; they are most often a potpourri, a single skeleton made from isolated bones — often from several individuals. Reconstructions of skeletons are not the same as restorations. These two terms have very different meanings. For example, John Harris distinguishes them in this way: "the term reconstruction is used in the sense of piecing together the original but often fragmentary fossilized parts of extinct animals, whereas restoration is used to describe the depiction of their original appearance — muscles, flesh, skin, and all." Thus, a reconstruction is a skeleton, and a restoration is the animal in the flesh, as though living. Animated restorations, which depict dinosaurs in their flesh-and-blood glory with movements controlled by computers, draw huge crowds. Artists' paintings, meanwhile, have long re-created the living animals in their habitats — giving them a lifelike quality that is sometimes
so realistic that they seem to be photographs taken by a camera loaded with fast, color-saturated film.
But the real nuts-and-bolts of the dinosaur world is skeletons and the sites from which the skeletons have been recovered. The real natural history of dinosaurs resides there, in the bones and the collecting localities, the only sources for the raw material of dinosaur studies. The Smithsonian grant gave me the opportunity to study the real bones of some of Sam's relatives. This award was pivotal in the project, and it led to the other, larger grants that made excavation beyond the discovery stage possible.
Before I went to the Smithsonian, I thought Sam was a member of the genus Diplodocus, a well-known and widespread dinosaur in the Morrison Formation of Utah, Colorado, and Wyoming. But I had trouble matching the eight tail vertebrae we had collected during our initial excavation to known tails of Diplodocus. The proportions were off, the dimensions were too large, and the anatomical details were different enough to question the identification of Sam as Diplodocus. The possibility surfaced: maybe it's a new dinosaur. The fact that the site is hundreds of miles from other Diplodocus localities in the Morrison Formation added to the uncertainty.
Muscular anatomy o/Diplodocus car-negii. This kind of drawing is a prerequisite for producing a reasonable in-the-flesh restoration. Seismosaurus was similar, but had more massive hips, stouter (but not longer) legs, and a tail that differed in some important ways.
Eventually I came to believe that Sam could not be Diplodocus or kin such as Barosaurus or Apatosaurus. The tail bones of Apatosaurus do not have a deep concavity on their undersurface. The tail bones of Barosaurus have the deep concavity, like Sam's, but the vertebrae are relatively short. The closest resemblance was to Diplodocus, but the differences were still too great. Notably, Sam's vertebrae are proportionally longer and taller, and the dorsal spines are nearly erect, quite in contrast to the tail vertebrae of Diplodocus. When I consulted with other sauropod specialists, they were unable to offer any new information or interpretations that I had not already considered. I thus concluded that Sam belonged to a hitherto unrecognized species of dinosaur.
When the New Mexico Museum of Natural History decided to announce the existence of this new and impressive dinosaur to the public later in 1986, I faced a dilemma. We needed a name for the skeleton, and I could not assign it a name based on any known dinosaur.
The paleontologist who first describes a fossil as a new species has the singular responsibility and honor of selecting the name. By international convention, the name should be latin-
i/ed according to a universal standard adopted l>v all zoologists, The International (lode of Zoological Nomenclature. Its contents read like a legal document, and issues related to naming of animals resemble court cases.
The choice of name — the technical name — lor a dinosaur, or any fossil organism, is as important to a paleontologist as naming a newborn is to a parent. We cannot take the matter lightly, because the technical name will stay with the species forever. Sam and all Sam's kind would be known by the technical name. The name should have meaning; ideally il should also be easy to remember and pronounce. And it should be constructed using the agreed-upon rules designed just for this purpose. In some ways the honor of coining the name is the most pleasant of our responsibilities.
That summer, before the press conference organized by our museum staff, I lay awake at night in my cabin in the mountains east of Albuquerque, deliberating. I pored over my dictionary of scientific names, seeking an appropriate root to combine with -saurus in keeping with the tradition of Apatosaurus, Barosau-rus, Camarasaurus, and dozens of other dinosaurs named under this convention.
After several weeks of searching for a name, I made a decision. I chose Seismosaurus. Seismo is the Latin root for "shaking." It is familiar in words like seismicand seismology, all relating to ground-shaking generated by earthquakes or underground blasts. Sam would be the earth-shaking dinosaur. I searched the technical literature to ensure that this name had not already been taken; if so, the name would have been "preoccupied" and not available for any newly discovered species.
1 was luckv. Seismosaurus hadn't been used before; mv fust choice was available. As long as I didn't attach a species name to this informal genus, any publication ofthe name in print would be safe from technical nullification— provided I was right that Sain was a new genus. I would use this name in the press conference.
Restoration of the in-the-flesh anatomy o/Diplodocus carnegii. (Color patterns are conjectural.! In life. Diplodocus would have been hard to distinguish from Seismosaurus except that the largest adults among the latter were probably 20 to 50 percent longer, with a disproportionately long neck and tail and stouter legs.
Floodlights blinded me, and the array of microphones seemed like menacing tentacles of a giant octopus. Paleontologists are not trained in graduate school for press conferences. I briefly explained what we had found, unveiled the bones, and revealed the new informal name. I reported that this individual ol Seismosaurus was probably at least l t o feet long, comparing it with our own mounted skeleton of Camarasaurus (which is only
about 50 feet long.) This put Sam in the ranks of the super-giants, not the giants.
I then demonstrated how I made that calculation by direct proportions with Sam's closest relative, Diplodocus. Each vertebra was at least 20 percent longer than corresponding vertebrae in Diplodocus, and with the disproportionately tall neural spines, there was the possibility that the overall length of the tail (and indeed the entire body) was also disproportionately long. Although I had data in hand that indicated a more likely length of 120 feet or more, I chose to conservatively estimate Sam's length at 1 10 feet —which is longer by 23 feet than the longest specimen of Diplodocus, the previously accepted longest dinosaur. (Later I would revise these figures upward.)
Questions came from all directions as each reporter sought a different angle to develop. Sam's new name, Seismosaurus, caught on immediately, capturing the reporters' imaginations. One reporter asked rhetorically why I didn't select a name like Superdoopersaurus to follow the recently invented names Supersaurus and Ultrasaurus for two supergiant dinosaurs that were discovered in Colorado. That quip lightened up the discussion.
We had prepared an exhibit case for the four vertebrae, set beneath the Camarasaurus skeleton for comparison with its tail
First display of the tail vertebrae at the .Vni Mexico Museum of Natural History, Albuquerque. This vertebra is no. 20, counting from the base of the tail. It was the anterior-most of the original eight excavated in 1985.
vertebrae. Comparison with a skeleton of Diplodocus or Apa-tosaurus would have been more appropriate, since Seismosau-rus belongs in the same family with these two familiar dinosaurs, but the Camarasaurus skeleton was the closest comparison we could make with the exhibits available. The corresponding vertebrae in the tail of the Camarasaurus skeleton are ridiculously small by comparison. The display emphasized the extraordinary size of the new dinosaur, even though we had only four bones to present to the public.
The press conference generated a surge of media attention, more than I ever imagined. Sam (rather, Seismosaurus) was spectacular.
My allusion to "earth-shaking" proved ironic, for the next year we would initiate experiments in remote sensing to look for more of Sam's bones hidden deeper in the mesa. Artificially generated sound waves (from a fancy shotgun) would help us "see" bones without digging. That technology was called seismic tomography.
To formalize the name Seismosaurus I needed to fully describe the eight tail vertebrae on which the determination had been made. This description had to be published in a technicaljournal. I had to distinguish the bones from all other dinosaurs, including Sam's closest relatives, Diplodocus, Apatosaurus, and Barosaurus. This might appear to be a dry and simple task, but technical descriptions of new species are difficult and demanding. Putting into words the description of a bone or skeleton is an extraordinary challenge of communication in the use of our wonderfully versatile language. To succinctly describe an object that is as irregular as a bone, and to do so in words that others can understand without ever seeing it, is immensely satisfying. I, of course, had a science illustrator draw the bones from various perspectives, but in a scientific journal the words are definitive.
Formal description would not be done overnight. What is more, I knew that if I waited I would almost surely have more bones upon which to base the genus-making description. Publication would therefore wait.
Seismosaurus was not, however, a complete name for formal publication. Living and extinct organisms are given binomial names. The principle of binomial nomenclature is that every organism is given a pair of names: a genus name that is capitalized and a species name that is not. Humans belong to the genus Homo. We share this genus with no living species but with several extinct hominid species — Homo erectus, for example. Our species is sapiens. We are therefore Homo sapiens— presumably, "wise" humans.
The informal name Seismosaurus established at the press conference could not be formalized without a species name to follow it. That left me with another decision: what to call Sam's species in the formal description.
Sometimes a species name is coined for an anatomical feature, or for a locality, or for a person, such as the discoverer or a patron of the project. Several times I half-j okingly offered to name the species after anyone willing to donate half a million dollars to the project, and the genus after anyone willing to donate a million dollars. My circle of friends is not wealthy; I got no takers.
I considered naming the species for Arthur Loy and Jan Cummings, who together found the bones. In fairness, however, I recognized not only Arthur and Jan as the discoverers but also their friends Frank Walker, who brought the bones to my attention and showed them to me, and Bill Norlander, the fourth member of this fraternity ofhiking buddies. I couldn't name the species for all four, and naming it for one wouldn't be fair to the others.
What about geography? The correct latinization of ojito, for the site in the Ojito Wilderness Study Area, would be ojitoensis. The pronunciation would thus be a puzzle to everyone not familiar with Spanish etymology, and I dislike tongue-twister names anyway.
What about anatomy? Most of Sam's anatomical features are subtle and I couldn't find any one trait in particular that would by itself characterize the species. I thought about referring to the size of the new species by using longus or colossus, but these names didn't seem appropriate either.
I settled on naming the species for the Reverend James Hall, director of the Ghost Ranch Conference Center, and his wife Ruth Hall, an amateur paleontologist who inspired several professional careers by her teaching. Ghost Ranch is in northern New Mexico, a study center owned by the Presbyterian Church in the canyonlands north of Santa Fe made famous by the artist Georgia O'Keeffe. On its 23,000 acres is one of the richest and most spectacular dinosaur sites in the world, a quarry where at least a thousand individuals of the little predatory dinosaur Coelophysis have been excavated. Jim and Ruth together sup ported paleontology in and around Ghost Ranch and northern New Mexico for a quarter century. I began working there in 1985 and continue with several active projects related to the Coelophysis quarry. Ghost Ranch has since established the Ruth Hall Museum of Paleontology, organized by Lynett Gillette, the museum's first curator.
Seismosaurus would thus bear the simple species name "halli." Seismosaurus halli, or "Hall's earth-shaker dinosaur," it would be.
I now had the name necessary for publication, and soon I had more bones. I submitted my description to the Journal of Vertebrate Paleontology in 1989. The review process stretched on, however. Scientists are naturally skeptical of claims of new species (and, even more so, genera), and the peer reviewers of my paper took their task seriously. I had to respond to their criticisms; producing acceptable revisions added another year to the publication date. The descriptive paper was finally published in 1991. Prior to that time, I had given a talk at a scientific symposium (1986) and had published a short abstract (1 987), referring to Sam as "a giant sauropod" or "a new giant sau-ropod" from the Morrison Formation of New Mexico. I had also written a popular article on the excavation for the Ghost Ranch Journal. But publication of a formal description and a full scientific name in the Journal of Vertebrate Paleontology made it official.
To paleontologists the full and correct name for the new species is now "Seismosaurus hallorum Gillette 199 1." My initial name proved to have an incorrect Latin ending of a genitive singular —a mistake recognized by George Olshevsky, a dinosaur classification aficionado. So it was changed to the plural form. I formally assigned it to the family Diplodocidae, the family that includes the giants Diplodocus, Barosaurus, and Apatosaurus and the supergiant Supersaurus, all from the Morrison Formation of western North America.
From my original coining of the name Seismosaurus to technical publication of the name Seismosaurus halli (more properly, Seismosaurus hallorum) took five long years. With the formal publication of the name and the description of Sam's bones as the basis for the new species, our initial goals had been achieved: we had defined the species, identified its distinguishing characteristics, established the geologic age in which the animal lived (late Jurassic) and the geographic position of the site (the southern end of the Morrison Formation), and presented the data and the interpretive calculations that would verify Sam's size — then calculated as between 128 and 170 feet, or between 39 and 52 meters —in the technical literature, through the rigors of peer review.
Sam's position in the scheme of classification of animals can be succinctly summarized. The fundamental unit of classification is the species. Taxonomic categories above the species level are increasingly subjective, generally arranged in hierarchical order. For Sam, the full classification using traditional ranks is as follows:
Subphylum Vertebrata (all animals with backbones)
Class Reptilia (all reptiles including dinosaurs)
Order Saurischia (the giant quadrupedal herbivorous dinosaurs and the bipedal carnivores) Suborder Sauropoda (the giant quadrupedal, long-necked herbivores)
Family Diplodocidae (relatives of Diplodocus) Genus Seismosaurus
Species hallorum, correctly expressed as the binomen Seismosaurus hallorum.
Some paleontologists prefer to separate dinosaurs from the reptiles into a distinct class: Dinosauria. Usually, by that convention, Dinosauria includes only dinosaurs, but some paleontologists place birds in the same class, subsuming the traditional class Aves into Dinosauria. At issue are the questions of origins and the philosophy of establishing these evolutionary hierarchies. In recent years applications of the principles of cladistics, and with them a new system of nomenclature, have clarified many questions of ancestry, but the basic unit of classification, the binomial (genus and species) remains largely unaffected.
This naming, this classification, this identification and formal description of Sam depended ultimately on the bones. How does one find more bones hidden, and perhaps scattered, inside a mesa?
In 1 985 the curators of the soon-to-open New Mexico Museum of Natural History were each invited to present a short seminar at nearby Los Alamos National Laboratory. Expecting that the scientists attending my presentation would have little interest in the anatomy of Ice Age glyptodonts or the biogeography of Miocene sharks in the Caribbean (two of my research projects to date), I chose instead to discuss local paleontology. More important, I decided to share two problems. These were not paleontological problems in the usual sense, but problems that had bothered me since I began fieldwork as an undergraduate student in 19 6 7.
Usually, when invited to present a seminar, scientists talk about their latest achievements. That is, after all, a good way to inform others about our work. Often, however, our goals are more subtle: we also intend to impress the audience, our peers, with our prowess. This professional exposure is important, and promoting one's work in hope that it will be useful to (and, ultimately, cited by) others is a stimulus to scientific advance. And if our presentations yield additional benefits, such asjob offers or a more enthusiastic review of a proposal for funds, so much the better.
To present problems at a seminar is unorthodox, because in so doing we reveal our weaknesses. Often in technical seminars, members of the audience take great delight in publicly pointing out deficiencies or inconsistencies in the presenter's research, exposing weak points in methodology or logic. Nevertheless, I did just that: I confessed my lack of knowledge on two pe ripheral but bothersome subjects, thinking maybe my talk would spark some interest or even lead to ideas for technological applications I had never considered. This was, after all, Los Alamos National Laboratory —the place where the atomic bomb was born, and the place that had continued to bring in brilliant scientists to fight the Cold War.
I stood in the auditorium before a gathering of about a hundred scientists and technicians, hoping that the combination of "big dinosaur," "local excavation," and "looking for technological ideas" would pique their interest. I posed two specific questions. First, is it possible to see traces of soft tissue that may be preserved next to the bones, perhaps as unseen chemical signatures of the outline and position of muscles or stomach?
Occasionally soft parts of vertebrate animals are preserved with bones: fossil tendons are common; wing membranes of pterosaurs and bats have been recognized with some skeletons; feathers have been found with fossil birds. In a few cases, contents of the body cavities have been preserved. As a graduate student I had published a paper that described three Cretaceous fish fossils as containing probable egg masses (in a research project where I puzzled over the chemistry ofpreserva-tion). And I am still intrigued by the problems of chemical alteration in fossilization.
The idea that ghost outlines might be preserved with a skeleton drew considerable interest at the seminar. I could feel the abrupt change of attention in the audience. No longer were they polite and dutifully courteous. Here was a problem these scientists could relate to, a challenge that might bridge the gap between my Victorian-style approach to fossils and their world of high technology. I sensed their tension, and my confidence grew. I went into more detail than I had planned: I gave an overview of the problems of preservation chemistry. How, in fact, do bones become fossilized?
My allotted time was short, however. I moved on to my second question: Is there any way to "see" into the ground before excavating a skeleton? Is there some technology that can give me a kind of X-ray vision so I can know whether and where to dig?
I told them why I was interested; I told them about the gigantic tail vertebrae that had been discovered an hour's drive of Albuquerque. I told them why the articulated character of the bones made them specially valuable —and seductive. And I told them of my hopes of following the tail forward, into the mesa with its ten-foot cap of sandstone.
I knew it was a ludicrous wish: to see a skeleton beneath the ground before striking the first rock with a pick-axe. With the frustrations of a century of paleontologists before me, I conveyed to my audience the difficulties we faced in excavating this exceptionally large sauropod: a ten-foot wall of sandstone to move, wilderness advocates demanding minimum disturbance and no mechanized equipment, and the likelihood of needing to race to complete the excavation before the area becomes a formally designated wilderness. If we could see the buried bones in the ground before excavating, we could dramatically improve our efficiency and minimize the disturbance.
At the conclusion of my fifteen-minute presentation, I asked for help. I expected one or two takers. Instead, I was swamped with volunteers and ideas. They overwhelmed me with enthusiasm. That seminar proved to be the most productive quarter-hour talk in my career.
Los Alamos scientists took up the challenge. On a field trip to the site, Nate Bower, a contract researcher from Colorado College, found a bone chip that he took back to his lab for chemical analysis —the results would prove surprising. Carrie Neeper, a microbiologist from the city of Los Alamos (but not at that time employed by the lab), became one of the local coordinators for volunteers and information sharing. Later, geologist Kim Man-ley, also from the town of Los Alamos, took an interest in gastroliths.
News of my talk and my challenging questions went beyond Los Alamos. Roland Hagan, an electronics technician at Los Alamos, enlisted the collaboration of Cliff Kinnebrew and other scientists from Sandia National Laboratory in Albuquerque to join with Los Alamos in their radar experiments. Later, Roland invited scientists led by Alan Witten from Oak Ridge National Laboratory to try their hand with technology still under de velopment for locating buried hazardous wastes and other classified applications. By 1987 the friendly rivalry between the scientists from these three national laboratories seemed to be producing tangible ideas for assisting the excavation of Sam.
The Seismosaurus excavation had become THE SEISMO-SAURUS PROJECT, a multifaceted experiment involving not just traditional paleontology, but also chemistry, physics, engineering, electronics, and a little bit of magic — magical science and magical friendships.
On one visit to the site by Los Alamos scientists, chemist Shaun Levy took hold of the fact that dinosaur bones are often preserved with relatively high concentrations of uranium. An earlier analysis at Los Alamos established that Sam's bones contain a small amount of uranium, too. The origin of this uranium is somehow related to percolation of ground water long after burial, but the actual process ofdeposition and concentration is problematic. Because some uranium-containing minerals fluoresce under ultraviolet light, we wondered whether Sam's bones had adequate concentrations of uranium and the right minerals to fluoresce.
We collected a fist-size fragment of bone on-site, and I accompanied the group back to Los Alamos to witness this test of fluorescence. We needed only an ultraviolet lamp and a place dark enough to conduct the experiment. Someone suggested the men's room. It's only big enough for two people, or uncomfortably, maybe three, but it can be made absolutely dark. So, several of us crowded in, turned on the ultraviolet lamp, and turned off the lights.
The fossil bone glowed. Whether the fluorescence came from the uranium was still uncertain, but at least we had discovered an unusual and potentially important property of Sam's bones, and perhaps many fossil bones.
Our discovery that dinosaur bones can fluoresce, we learned later, had been made by rock hounds long ago. This fact was well known by amateur collectors, a spin-offfrom the widespread use of ultraviolet lights to prospect for certain minerals in mines and caves. This fluorescence was new to us, however, and we soon learned that the glow comes not from uranium minerals in the fossil bone (uranium is there in significant concentrations, to be sure, but not in minerals that fluoresce), but instead from the natural fluorescence of the hydroxyapatite, a crystalline mineral found in all living bone—and, incidentally, probably all fossil bone in its original or nearly original state.
The discovery of fluorescence in Sam's bones suggested an immediate practical application. Because the bones were buff-colored and difficult to distinguish from surrounding rock, perhaps we could use ultraviolet light to prospect for more bone. So on a dark, moonless night our team of prospectors waited until nearly midnight to try so-called black lights we brought from Los Alamos. In three small groups, armed with flashlights to guide us to the broken cliff face and black lights to search for bones, we spread out over the site. One group searched where bones had already been excavated. Another searched where bone fragments were known to be exposed —and which we had specifically marked for testing that day. The third group searched on the face of the cliff.
The experiment was wildly successful. We found bone everywhere— most of it in small fragments that had weathered out and disintegrated over the past thousand years. Some of the bone we hadn't seen before, but none of the discoveries actually led to new intact bones in the mesa. Nevertheless, I was delighted. The night's work had made me confident that the skeleton had not been exposed and eroded away with boulders and rocks and pebbles in the cascade of rubble on the hundred-foot slope beneath the site. Rather, if more bones did accompany the eight tail vertebrae, then they were still safely preserved within the mesa — albeit beneath a cap of rock that would make life difficult for the excavation crew.
Another spin-off from this discovery of fluorescence helped us improve our laboratory preparation of several of Sam's vertebrae. One vertebra from the tail was encased in rock that was especially hard. Removal of that rock would be difficult; the work would be slow and tedious, progressing by only a few square centimeters a day. The problems were compounded by the intricate folds and projections of the bone, which were tough to follow without damaging the bone's surface. More frustrating, however, was a peculiar condition of preservation that we found on many of the upper surfaces of the bone throughout the skeleton: the sandstone rock actually penetrated the fabric of the bone, through an interval of several millimeters, destroying the naturally sharp contact between bone and rock that is common to most fossil bone. To make matters worse, the rock and the bone were identical in color, and almost identical in texture. We found that a technician could easily dig right through the bone structure and never realize it.
To solve that problem we improvised an experiment using ultraviolet light to see whether we might readily distinguish bone from rock in the laboratory, where the majority of bone extrication must be done. In the makeshift black box, which blocked out all ambient light and allowed only ultraviolet light from an overhead fixture, the bone glowed a brilliant blue and orange lint. The surrounding sandstone remained dark and unreflective. With the aid of the black light in otherwise total darkness, Wilson Bechtel prepared that vertebra with delicate accuracy and efficiency; the rate of exposing the bones improved to as much as a square inch a day, sometimes even more. We were elated.
These modest beginnings eventually led to a major research investigation of the chemistry of fossil bone preservation, including the vexing problem of why uranium accumulates in fossil bone. A preliminary chemical analysis of the fossil bone fragment I had casually given to Nate Bower was surprising: a
A partially prepared Seismosaurus caudal vertebra. The sandstone in which this bone was encased was so perfectlv matched in color and texture that distinguishing bone under ordinaix lighting conditions (such as photographed here) was almost impossible.
The same vertebra under low-intensity ultraviolet light and reduced natural lighting.
Close-up of ultraviolet image. The brilliant fluorescing purple is bone and the nonfluorescing material is sandstone. Wilson Bechtel completed the meticulous preparation of this vertebra in a makeshift box that was illuminated only by ultraviolet light. This visual enhancement doubled or even tripled his efficiency. Courtesy of Wilson Bechtel.
dozen major elements in the composition of Sam's hones wire of the same concentrations as that in samples of modern bone. The match was, in fact, almost identical. The conclusion was inescapable: the dinosaur bones could not have been replaced by secondary minerals. These were not stone bones; these were real bones. A large portion of what remained of Sam must be original material.
Research concerning preservation chemistry began with Nate Bower's report, which stimulated Los Alamos to get further involved. They, in turn, recruited colleagues to take up the challenge I had presented in seminar several months before —
now modified to address the entire question of geological processes that lead to bone preservation. I remember having been taught about the mysterious process of "molecule-by-molecule replacement" believed to occur in fossilization. But when pressed, I could only confess confusion.
From these rather casual beginnings George, Roland, their colleagues, and I began to identify specific problems that required carefully controlled experiments. We recruited other scientists, asked for advice, held rump session seminars, and prodded colleagues well beyond the bounds of New Mexico to lend a hand. But research into chemical preservation of fossils was not the only spin-off of my Los Alamos seminar.
A century ago during the golden age of dinosaur excavations, and even thirty years ago, the principal or even sole objective in dinosaur excavations was the procurement of exhibit specimens. Today, however, the sedimentary context holds equal importance to the bones. Paleontologists now give attention to habitat interpretation (largely for improving our understanding of behavior). And we try to accurately correlate the stratigraphy of a new site with previous excavations (as precise data can be used to understand regional or even global biotic changes such as migration and extinction).
Whereas our objectives are different today, the techniques of excavation have changed little in the past century. We still use hammer and chisel, pickax and shovel —all powered by muscle and cooled by sweat. Sometimes now we do use jackhammers, driven by generators and compressors. Plaster-and-burlap bandages, often reinforced with lumber and steel, have replaced rice paper and flour paste for stabilizing bones. But, overall, we use the same procedures for finding and digging bones.
Every field paleontologist has a sad tale of discovering a portion of skeleton and launching an excavation only to find that the specimen was at the end of its erosional history, not the beginning. The only bones there were the ones exposed; the skeleton did not "continue into the hill." The immense disappointment may, however, be forgotten in the quest for another skeleton, but we all want to use our time and budgets efficiently.
Our big problem, our perpetual frustration is that we can not see into the ground. We use experience and intuition to predict more bones below or beyond the ones that lured us there in the first place. But the only way to test such predictions is to dig. No amount of wishing or dreaming can determine how much of the skeleton is still buried, locked in the rocks beneath our feet.
No rock is too hard, no mesa too tall, to deter us once we declare a skeleton important enough to excavate. Sam's bones, encased in some of the hardest rock I have ever experienced in an excavation, and buried by ten feet of sandstone cap rock, presented a real challenge. Because Sam's tail bones were articulated and the skeleton was lying in a position that indicated curvature going into the hillside (rather than out of the hill — that is, eroded away and disintegrated into fragments in the rubble at the foot of the mesa), I was convinced that excavation was in order.
Even ifSam were not new to science, the skeleton deserved complete excavation just because the bones were connected, a rare situation. Surprisingly few dinosaurs, even the famous ones, are known from reasonably complete skeletons. But here was a skeleton only an hour's drive from our museum, belonging to a dinosaur new to the state, and in an exquisite state of preservation. We launched the excavation, with outside funding assistance, and with quiet resolve to find every bone and to carry the work to a reasonable completion.
My determination was edged with apprehension as we laid out the excavation plans. Sam's skeleton might continue for fifty or sixty feet into the mesa, and we couldn't predict with any real confidence its orientation —beyond the rather safe conclusion that it indeed went in. The skeleton might be disarticulated and its bones scattered. Predicting where to dig would require me to call on all my experience. But there would also be a lot of guesswork, and perhaps uncalled-for conviction —and (I hoped) a good measure of luck.
With measuring tapes we determined the projected depth of the bones beneath the cap rock: ten feet at least and perhaps as deep as fourteen feet (depending on the orientation or trend of the skeleton). On top of the mesa, we laid out a rectangular area that I predicted should contain the skeleton. The quarry site would penetrate sixty feet into the mesa, leaving a gap thirty feet wide.
If only we could see into the ground and know exactly where to dig before commencing the excavation, we could calculate how much rock to move, the limits of the quarry, the projected costs and duration of the work. This is a paleontologist's dream.
But "seeing" into the ground had become reality for field-workers in other professions. Archaeologists had pioneered stunning field applications of technology in the past two decades in their searches for buried pyramids and pueblos. Geologists had developed sophisticated techniques to follow buried river beds in the Sahara, or to detect fault lines invisible to the unaided eye. Why not try to find buried dinosaur bones? I knew the principal difference in my plea was a matter of scale: dinosaur bones, even the largest bones of a skeleton, were two or three orders of magnitude smaller than the underground targets archaeologists and geologists had set their sights on. At best, we might expect a cross-sectional diameter of a meter for the largest bones; most would be smaller.
Sam, however, proved to be an ideal dinosaur for a set of experiments conducted by several teams of scientists from Los Alamos National Laboratory, Sandia National Laboratory, and Oak Ridge National Laboratory in Tennessee. The skeleton was buried beneath a relatively uniform sandstone, without intervening layers of other kinds of rock; it promised to be articulated and relatively easy to follow into the mesa with excavation; and the bones were among the largest known. For a smaller dinosaur, at a different site, we would surely have encountered many more variables and we would have demanded even higher resolution than needed to detect Sam's bones. These were fortuitous advantages.
In effect, I was asking these scientists as volunteers on their off-duty time from their national laboratories not only for a novel application of their expertise and equipment. I was also asking them to push the resolution of their technologies and their interpretations to ridiculously small dimensions. But the teams took up the challenge.
Los Alamos scientist Roland Hagan was the first to propose a working plan for using applied technology to look for more of Sam's skeleton. In his lab he had a new piece of equipment designed for just the kind of problem I posed: locating shallow buried objects. He had designed the equipment specifically for locating the 55-gallon drums that might signify hazardous waste buried in a land-fill.
Roland told me that his "ground penetrating radar" equipment had been used already with some success at archaeological sites and that it might be useful at the new dinosaur locality. He asked for details about the bone and the rock: how large were the bones? what was their density and mineral composition? what was the nature of the sandstone surrounding the bones? would the skeleton be articulated? would there be iron or other metals concentrated in the bones? I couldn't answer any of these questions satisfactorily. But Roland threw himself into the project with enthusiasm.
The device sends radio-frequency impulses into the ground; the reflections back to the surface are recorded for later analysis. The radar reflections mirror the layering in the subsurface. Under the right conditions the recorded data will indicate the presence of objects different from the surrounding matrix of rock.
I was enthralled with the idea of looking for more of Sam with this ground penetrating radar. I was also puzzled, however, because radar, as generally used, measures a time lapse between transmission and reception of the reflection. How could a sta-
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