The Great Fossil Enigma (51 page)

Scott had experienced similar empowerment when he possessed the animal, but he was more vulnerable to poaching and, being less of a conodont specialist than he claimed, he found himself somewhat isolated. Sweet and Bergström, Zeigler, Branson and Mehl, and a few others, had also shown similar determination, knowing that to win one needed both rigorous science and a willingness to see through a campaign. Not all conodont workers adopted these roles. In this small community there were really only a few combatants, and as Sweet recalls, in this close-knit world this combat was almost always chivalrous.

The British team was also large enough to internalize some of the debate, to test ideas and remove risk and uncertainty and join minds before airing results. This also gave its members extraordinary intellectual resilience. It permitted them to travel that edge where doubt lurked. They also shared an advantage over others linguistically as this science, like all science, increasingly conducted its conversations in English. Russian conodont research, which had begun the science, had long been locked behind the Iron Curtain. It found itself liberated in 1989, when the Berlin Wall fell, but then discovered another barrier stood in its way: language.

As the British conodont animal workers reorganized themselves, Theron and Pedro were hard at work in South Africa looking for new sites. They found several, the most important being some seventy kilometers to the south of the first. Aldridge and Gabbott joined Theron and his wife Elmarie there on the last couple of days of a three week collecting trip in May 1994. It was, Aldridge later recalled, an impressive spot: “The farm of Sandfontein is set in idyllic surroundings overlooked by high mountain crags. The sandstone rocks of the Table Mountain Group are weathered into stone pinnacles, in which the imaginative eye can discern the shapes of people and animals. There are few people in the area, only the local farmers and their field hands, and the skies are regularly patrolled by black eagles and jackal buzzards.” In Aldridge's words, there is something of the romance of the field that has been associated with geology since its early days, but from his description we might also understand something of the work, he, Theron, and Gabbott were involved in. Fossils are not common in the Soom Shale, and excavation can soon become an unrewarding daily grind of splitting rocks. The excavation begins with its participants believing that on each next hit something remarkable will appear. Each time, anticipation is followed by disappointment or unremarkable results. After half a day, anticipation and belief become tested, and as the days go by, sights beyond the immediacy of the excavation begin to catch the eye. Soon things outside the excavation can become more attractive than those within. At Sandfontein, the rocks were blacker, less weathered, less willing to split, and less willing to give up their treasures. Inevitably, perhaps, sharing the toil of hard labor, in these pleasant surroundings, the excavators indulged in leg pulling as a way to mitigate the tedium.

The 1994 collecting trip had been a pleasant three weeks that were not in any sense unproductive, but they had not found a specimen that really stepped up the game. They began to wind down on the last morning, but then, as in the best adventures, something happened. Aldridge again: “We had dug quite an impressive trench, and I hacked out a few last slabs of rock and passed them out to be split. Inevitably, as the field season wound down, our concentration had been waning and we had been enjoying the sunshine and the banter, so we thought that Sarah Gabbott was attempting to repay Hannes for one of his jokes when she cracked open one of these final blocks and announced that she had found a conodont animal.” She had! It was the animal they had been searching for. A giant, which although not complete, possessed its eyes, feeding apparatus, and about ten centimeters of its trunk.
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Their luck had held – or rather, their sheer hard graft had finally paid off. They left knowing that the Soom had given them a hundred apparatuses, many with associated head structures. Gabbott's fossil, however, trumped them all.

Elsewhere the debate concerning the animal's vertebrate characteristics had been heating up. The decade had begun with the British proposition that the animal might indeed be a chordate, and this notion was at last finding a tiny place in reviews of the vertebrate literature. Some of those looking at primitive near-vertebrates in the field of biology held out a welcoming hand to Aldridge and his collaborators. Although related, conversations do not flow naturally between the fields of paleontology and biology; as George Simpson recognized long ago, they produce their animals using rather different materials. But the history of conodont studies also shows us that this fossil periodically attracts the attention of outsiders, and now a few biologists were beginning to take note and offer some insights on the flesh of the animal. Among them was Richard Krejsa in California, from whom Aldridge sought information about hagfishes back in 1986. Krejsa and his associates, in 1990, tried to resolve some of the outstanding issues surrounding the conodont animal – many of which had arisen in the decades before the animal had been found – by referring to living juvenile hagfishes.
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This line of argument, however, was complicated by the fact that the hagfish were then treated by many as an encampment on the periphery of vertebrate city. Inexplicable in their form, they were regarded by some as degenerate – vertebrates that had lost many of their key vertebrate characteristics. In that idealized picture of evolution that envisaged the advancement of life, the hagfish seemed to have gone backward. By moving in next to the hagfish, the conodont animal found itself embroiled in the politics of vertebrate ancestry, a debate centered on inclusion and exclusion. The Californian team was certainly on the side of the hagfish, suggesting there was more to this animal than was commonly believed. Indeed, they argued that much existing belief relied upon old literature, old ideas, and consequently old prejudices. They felt the “teeth” of the hagfish and the conodont animal shared structural similarities, such as bubbles and tubules, even if composed of rather different materials. These bubbles occurred in the white matter in the conodont elements and had led Lindström to suggest that white matter was formed through resorption of the material making up the lamellae. Krejsa and company felt this could now be refuted. Noting that enamel and dentine grow away from each other, they thought Walter Gross's objections, to conodont elements being tooth-like, also wrong; the elements were very much like teeth. And since hagfish teeth are replaced as new ones erupt beneath them, they wondered if conodont teeth did the same.

As biologists looking in from the outside, Krejsa and his colleagues saw a field shaped by “orthodox conodontological theory.” Now, with the animal found, it was difficult to understand why some of these old orthodoxies had not fallen. And while some of these arguments from California could easily be dismissed by experienced conodont workers, these biologists did the conodont workers the service of asking them to question their beliefs and offered a friendly hand of support.

Further assistance came in the form of a review of vertebrate ancestry that at first dismissed the conodonts. In 1990, Moya Smith, an expert in the structure and evolution of teeth at Guy's and St. Thomas' Hospitals in London, and Brian Hall, who was on a sabbatical there from Dalhousie University in Nova Scotia, produced a major review of the origins of the vertebrate skeleton. Nearly one hundred pages in length, this was a monumental work, and one that, during its preparation, they had discussed with Philippe Janvier and Derek Briggs. It touched more broadly on the work of Pander but denied the conodont animal its vertebrate status. For Smith and Hall, the conodont animal existed in a special place: It was a craniate (it possessed components of a skull) but it did not possess real teeth: “They simulate teeth but are not homologues of teeth” (they are not related in an evolutionary sense).
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They thought this true of the hagfish's teeth, too, and pointed out that the platypus has horny teeth, warning against simplistic evolutionary assumptions based on form. Their dismissal of conodonts, however, confirmed a widely held view among those studying early vertebrates: “Though opinion seems to be divided as to whether conodonts are chordates or members of an invertebrate group…it is at least clear that they are not vertebrates.”
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This paper, and a number that followed in its wake, produced a serious challenge for “the animal that would be a vertebrate,” but it gave the animal's proponents clear points of focus for future research. Objections, such as those in this paper, were always based on weaknesses and inconsistencies, which were easily identified and then attacked. It was clear from Smith and Hall's paper that ascent to vertebrate status depended on the detection of key vertebrate building blocks: cellular bone, enamel, and dentine. It was necessary to know once and for all of what the conodont elements were composed.

Fortunately, Ivan Sansom and Paul Smith in Birmingham were already on the case. While working on his doctorate degree at the University of Durham in 1990, Sansom had used a new acid-etching technique to decalcify conodont elements. He showed the scanning electron microscope images of the results to Angus Parker and Trevor Booth at the medical school at the University of Newcastle, and they “immediately identified the fossil tissues as the enamel, calcified cartilage and cellular bone which is typical of living vertebrates.”
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(Sansom showed Aldridge these images of spheroidal or globular bodies in 1991, and Aldridge thought they might also explain those curious conodont pearls.) Sansom's work at Birmingham was supervised by Paul Smith and former Nottingham PhD and established Durham academic Howard Armstrong. As with much PhD work in the sciences, there is a strong collaborative element, but, unusually, Paul Smith was keen to see that his doctoral student, Sansom, featured as lead author in their published outputs. They were now joined by Moya Smith. Sansom's task was to demonstrate that conodont elements really were directly related to vertebrate teeth and not mere imitators.
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Moya Smith's expertise was central in this regard; above all else he needed to convince her. If she was convinced, then the opposition, who had used her review as a weapon to deny the vertebrate, would be considerably weakened.

Sansom had compared the material making up conodont elements with some of the oldest materially intact vertebrate fossils then known. These were Charles Walcott's fossil fishes from the Ordovician Harding Sandstone of Colorado – rocks and fossils, it might be remembered, that had nurtured Kirk's influential claim for the conodont fish back in 1929. Sansom and his collaborators found that conodont white matter contained spaces interconnected by irregular and radiating tubules that were identical to, and considered homologous with, those found in fossil and recent cellular bone. This, in some respects, echoed Beckmann's discovery in the late 1940s. Like Krejsa and his collaborators, Sansom and colleagues believed white matter a primary structural building material, not a later addition. They interpreted the white matter as bone. Additionally, the lamellae showed incremental growth lines, which they considered, by reference to Moya Smith's work, typical of “tissues such as enamel.” And, finally, the globular structure of the material making up the basal part of the conodont had, they felt, a striking resemblance to calcified cartilage found in some vertebrates.