The Great Fossil Enigma

by Simon J. Knell

  …and the discovery of the Golden City, or El Dorado – believed by him to be situated in Guyana – and the conquest of that country, occupied his mind; but which appear to have been some time before in his contemplation, and required only the circumstances in which he was now placed, to give them life and activity to exert a controlling influence over his thoughts.

  Account of Sir Walter Raleigh's search for El Dorado,

  JACOB ADRIEN VAN HEUVEL, El Dorado (1844)

  THIRTEEN

  El Dorado

  FOR THOSE WHO WENT IN SEARCH OF PANDER'S EL DORADO, that distant city of gold was where the extinct mythological beast lay at rest, its flesh sufficiently preserved to at last reveal the truth.1 In 1923, Macfarlane had dreamed of such a place, “that some layer of subaquatic volcanic ash may yet be discovered.” Many had dreamed, but the animal had not revealed itself. Few, if anyone, had imagined that this sacred place might be a shelf, box, package or drawer. But there it was, this Holy Grail of science. And there it had been for some sixty years. Hidden from view and beyond the reach of all earlier attempts to find it, it might just as well have been lost in the mountainous jungles of Guyana. Then, in 1982, Euan Clarkson found it – though at first he did not know precisely what he had found. A paleontologist at the University of Edinburgh, he had been searching for fossil shrimps in the Granton Shrimp Bed. This rock outcrops where that city meets the sea, but Clarkson was not braving the Scottish weather. He was working his way through old collections held by the British Geological Survey in Edinburgh, much of which had been collected by the Survey's fossil collector, David Tait, early in the twentieth century.

  A shrimp bed had been first discovered at Cheese Bay in East Lothian, some twenty-five miles from Edinburgh, in 1903, but was soon exhausted as a result of the attention paid to it by collectors and the Survey's paleontologists. It contained a single kind of shrimp but no other fossils. Collectors then made their way along the coast in search of further outcrops. In 1917, Tait at last found one: a finely laminated limestone, forty-five centimeters thick, in a coastal section dominated by Carboniferous black shales. The limestone was unique and quite different from that at Cheese Bay, for despite its considerable age, it preserved the soft and delicate structures of shrimps, worms, and a host of other animals.2 Tait gathered up small slabs of this precious rock and placed them into the protective care of the Survey, there to serve science as and when they were needed.

  At that moment, of course, on the other side of the Atlantic, Edward Kindle, E. O. Ulrich, and the others were just beginning to believe that the conodont might resolve the dispute over the black shales – rocks roughly contemporary with those at Granton. But in 1919, those thoughts were still immature and micropaleontology itself a thing of the future. Ulrich and Ray Bassler had not then split the conodonts into a myriad different fishes, nor had they or Ted Branson and Maurice Mehl proven their utility. For Tait, working in the practical world of Survey geology, the conodont lay beyond his field of vision. Among all those smudgy suggestions of life, the tiny animal was in so many ways invisible.

  Clarkson lived in a different world. He belonged to that postwar generation that had aspired to a new paleontology and in recent decades had gained a new optimism following the discovery that Lagerstätten were not as rare as previously thought. A science built largely on the evidence of bones and shells, these remarkable deposits provided “windows” through which lost worlds could be seen in all their ecological and anatomical glory. They made it possible to both imagine a deep past clothed in flesh and aspire to the invention of that long desired science of palaeobiology.

  Among those who had pioneered this new vision was Clarkson's collaborator in the shrimp project, Derek Briggs, a paleontologist at Goldsmith's College in London. In the 1970s, Briggs and Simon Conway Morris had been part of a three-man research team, led by Harry Whittington, that re-examined the oldest and most extraordinary Lagerstätte then known, the Burgess Shale of British Columbia in Canada. Using the evidence of rare and fragmentary fossils, they conjured up a previously unimaginable world, for the rocks seemed to record a great biological experiment that had taken place at that very moment when life had acquired its anatomical complexity. The old orthodoxy, which they were now displacing, suggested that life had been born into a number of biological groups (mollusks, echinoderms, annelids, etc.) that persisted through the millennia. Animals had continued to evolve, but they had done so within the constraints of this natural order. It was this knowledge that encouraged paleontologists to pigeonhole their finds and believe that all life must fit somewhere in this ordered world. And it was this expectation that had made the conodont so remarkable, for it had repeatedly resisted all attempts to pin its biology down. Many of the new Burgess Shale animals were similarly resistant, prompting the idea that their early extinction recorded “failed experiments” in the diversification of life. This brilliantly evocative notion would find support over the course of the following decade and become celebrated in 1989 in Gould's bestseller, Wonderful Life. Immortalizing Briggs, Conway Morris, and Whittington as the heroic architects of this new vision, Gould promoted the idea that life in the deep past was considerably more exotic and varied than it is now, and that it was only a matter chance that those animal groups we know today survived this moment of experimentation. If one could replay time, he said, a rather different biological world might evolve – one that was truly alien. There was no natural order and evolution would not repeat itself. This was a radical and exciting new way to think about the past, and it gave the conodont a new lease of life, for it could now be considered a strange survivor from that moment of experimentation.

  Clarkson had tried to find the Granton bed from about 1980 onward: “Went searching on Sunday mornings when my elder sons were playing rugby. I found many loose blocks and then the ‘mother lode.’ Briggs and I had collected quite a lot of material before I searched the Survey collections in 1982.” When he did search those collections, Peter Brand, the curator, handed him this curious specimen. As Clarkson looked closely, he could see a wormlike animal – just four centimeters long and two millimeters wide, preserved on opposing limestone slabs. It had what looked like fins, a bi-lobed head structure, and tiny teeth. “Was this an ancestor to the modern hagfish or lamprey?” he wondered. If so, then it would be an important find as these boneless animals had left almost no fossil record. Briggs sent Clarkson a paper describing a fossil lamprey from the Mazon Creek Lagerstätte in Illinois. As it too had come from the Carboniferous, it was reasonable to expect that the two fossils would show similar features, but Clarkson's had none of the head cartilage seen in the American specimen yet nevertheless looked rather more lamprey-like in overall morphology. Clarkson was also perplexed by his animal's teeth, which were quite different from the peg-like structures found in modern lampreys. He wondered if they might find a better analogy in the hagfish, as part of “some kind of armoured protrusible pharynx.” The fossil seemed to be new to science and he needed additional opinions. Using a camera lucida to superimpose an image of the fossil onto his paper, he produced accurate drawings and sent them to Briggs in January 1982, telling him, “Tooth structure is really much more reminiscent of those of hagfish – see enclosed diagrams – increasingly this impresses me.” He appended the opinions of his zoological colleagues. They had suggested that he had a larval stage or that the “teeth” might actually be gill rakers or part of the branchial basket. Even before Clarkson realized what he had found, his conversations were unknowingly revisiting earlier ideas about the conodont animal. It was as if the enigma, soon to enter its death throes, was reliving its past existence one last time.

  When the drawings arrived in London, a new rumor began to develop. Now, and from Clarkson's drawings rather than from fossil or rock, the conodont animal began to emerge and acquire flesh. When the news reached Bev Halstead at the University of Reading, one of Britain's best known paleontologists, he urged Clarkson to announce the discovery in Nature, the p
remier vehicle for breaking scientific news. Halstead had a penchant for sensation, but on this occasion he was working on a volume on fossil fishes in which he would have liked to illustrate the new animal: “So please a preliminary description, illustration and name. ASAP.” Clarkson was rather more circumspect: “For the moment I am quite uncertain about the spiny things inside the mouth. They look like conodonts, yes, but I would not go so far as to say they are – their story has grown a bit in the telling thereof!” Clarkson remained calm. He knew others had believed they had seen the animal, only to be greeted with ridicule and scorn. In two weeks he would be in London, there to spend a week in Briggs's company writing up the Granton “shrimps.” He could wait until then to decide the matter and then publish a note on the fossil. He sent Halstead some photographs and a copy of the drawing, telling him, “The creature is clearly a cyclostome.”

  By the time the two men met, the seed of the idea had matured; the conodont animal was taking on definite form. Briggs teased grains of sediment away from concealed elements using weak acid, as the two compared the new fossil with natural conodont assemblages. Still they could not be absolutely sure. They needed an expert view. Fortunately, on Wednesday, March 17, 1982, Briggs was to attend a meeting of the Council of the Palaeontological Association at the Natural History Museum in London. He knew Nottingham University's conodont specialist, Dick Aldridge, would be there. An authority on conodont palaeoecology and Silurian stratigraphy, Aldridge had not researched or pursued the conodont animal or the Carboniferous rocks in which this Scottish fossil had been found. The only expertise Briggs and Clarkson required of him, however, was the ability to identify conodont fossils. When Aldridge got up that day, he had no idea that his life was about to change forever. “If there was ever a case of being in the right place at the right time, this was it,” he later recalled.

  After the meeting, Briggs asked Aldridge if he would take a look at a fossil. When the two met with Clarkson, Aldridge still had no idea what he was about to be shown. The rumors had certainly not reached Nottingham. Asked to look at the fossil through a binocular microscope, he soon confirmed that the amber tooth-like structures were indeed conodont-like. Looking at part and counterpart together, he could also clearly see that a conodont apparatus was preserved. Aldridge took his time to consider the possibilities. Like Clarkson, he was not one to jump to conclusions. Possibilities had to be weighed up, probabilities considered. Could this be one fossil (a worm, say) superimposed on another (a conodont apparatus)? He thought that idea most unlikely, because the elements were enclosed within the fossil impression. Was this a case of a conodont animal merely having been eaten by Clarkson's beast? With no disruption to the conodonts, and no further remains of the dead animal, this again seemed unlikely given the high quality of preservation. All the components seemed to fit together: The conodont fossils were in the right place and undisturbed and the animal was of the right scale. The realization began to dawn. He really was looking at the conodont animal!

  Aldridge was numbed. That evening began to pass in a dream. Had he remained in this dream, his role in this story would have amounted to little more than a footnote. But on the train home he woke up and jotted down his observations. The next morning he wrote a two-page letter to Clarkson, copying it to Briggs, comparing the animal's apparatus with recent bedding plane assemblages described in Rod Norby's unpublished doctoral thesis at the University of Illinois in Urbana. He also included copies of a number of illustrations of schematic arrangements of conodont elements and natural assemblages. Aldridge knew far better than the other two that a rich and complex body of arcane knowledge surrounded this animal and its anatomy, but this remained implicit and unspoken in the letter; Aldridge was just giving them a few pointers. He ended, “I hope these rather garbled comments are of some help. Perhaps my enthusiasm and excitement are coming through; the more I think about it the closer I get to being happy that you've really found it. I suppose one reason is that your animal fits my prejudices much better than any previous contender, but the evidence is also looking stronger all the time. Can't wait to see it in print. Thanks for showing it to me.”

  Clarkson and Briggs immediately got down to writing a short account of the discovery for Nature titled “The conodont animal is a chordate” and asked Conway Morris and Aldridge for comments. Clarkson and Briggs also had a rather more generous offer to make Aldridge: “Euan and I have had lengthy discussions about a subsequent more detailed paper and, as I told you on the telephone, we would be delighted if you would cooperate as a joint author.” He added, “To avoid any subsequent misunderstanding I should say at the outset that we have decided that the most appropriate authorship would be Briggs, Clarkson and Aldridge, in that order, and we hope that you will be happy with this. It is likely, in any case, that among conodont workers yours will be the name that will spring to mind as author of the conodont animal, once the larger paper has appeared!” The plan was to get the paper written before the summer and submit it to the journal Palaeontology. Aldridge was delighted. It had been pure chance that led him to the fossil, but it was the writing of his letter that changed his life so fundamentally. His expertise was indispensible, and if Briggs and Clarkson were not already convinced of this, Conway Morris told them this straight when returning comments on their proposed paper for Nature: “Even with my limited experience of conodonts I found the relevant parts of the discussion somewhat simplified; might I suggest that Dick Aldridge joins you in this description rather than waiting for the full blown account later.” When they received Aldridge's “friendly amendments,” their insecurities must have been further amplified, for Aldridge wrote in the arcane code of conodont elements – “Sc,” “Sb,” “Pb,” “M” – and transition series elements. On that same day, Stefan Bengtson in Uppsala, Sweden, where Conway Morris was at the time, wrote a long detailed critique of their proposed paper: “If the conodonts are in situ, which seems likely although not proven, the elusive conodont animal has finally been caught, however badly battered. But is it a chordate?” After a detailed critique of this idea, he wrote, “Obviously, in a poorly preserved fossil one may to a certain extent see what one wants to see. You want to see a chordate, I want to see a chaetognath, and maybe none of us is right. But I find it to be a major weakness of your paper that you herald your fossil as a chordate without giving attention to alternative explanations. (Maybe it is a characteristic of the conodont animal that it leads its investigators to jump to conclusions too quickly. Melton & Scott certainly did so with their zeppelins, I think Simon did so with Odontogriphus, I think you are doing so with the present animal – and just now I have to admit that I feel enchanted by the prospect of identifying the same beast as a chaetognath!).” He continued, “I advise you not to stick out your much to[o] valuable heads with assertions on the conodont animal as a filter-feeding chordate.” He then asked them to consider publishing a revised version of the paper in the paleontological journal Lethaia, which he edited, rather than Nature. “This is clearly a scoop,” he added, “and it could be taken into the next available issue outside the normal waiting list.” Clarkson was then a new associate editor at the journal, and Bengtson also pointed out that Lethaia had carried much of the recent debate on conodont biology.

  When Clarkson received Bengtson's letter, he was quite taken aback and responded, “I confess that I simply had not thought of the animal as anything but a chordate, because of the apparent myomeres [muscle segments] and the ray-supported structure of the tail. But as you have shown clearly, these do not unequivocally indicate that the animal is a chordate.” He told Bengtson they were still deliberating on whether to publish in Lethaia, believing that Nature would permit rapid dissemination, but Bengtson told him his journal would not be far behind and would offer a much better vehicle for the discovery. He did the hard sell.

  This put Briggs and Clarkson in a difficult position. If they went with the Swedish journal it would mean a full account rather than a piece of breaking new
s. That would leave virtually nothing for the paper in which Aldridge was to be involved. Briggs asked Aldridge how this might be resolved, but Aldridge simply refused to be part of that discussion. It was for Briggs and Clarkson to decide. He was happy either way, and now also a little bemused because news of the animal had spread like wildfire across Sweden – Lennart Jeppsson had invited Aldridge to speak on the animal at a forthcoming meeting. This put Aldridge in a difficult position. He told Briggs, “I'll have to talk to yourself and Euan about how much or how little you are prepared for me to reveal.” Aldridge was then dissolving rock Clarkson had sent him and despite early doubts managed to find conodonts and clusters. These would help to confirm that this really was the conodont animal. On May 26, 1982, Briggs and Clarkson finally decided to change their plans and invited Aldridge to accompany them in extending their five-thousand-word paper into a full account titled “The conodont animal” to be published in Lethaia. They also told Aldridge, recognizing that only he among them had a specialist interest in the animal, “You will be free to write a follow-up in due course. Either or both of us, hope to cooperate on this in any way (compaction of assemblages, stratigraphy, associated faunas) that seems appropriate, but leave this open to discussion.” Aldridge immediately thought about getting a research student working on the topic, but Briggs asked that this be delayed; he was still hopeful that other opportunities might arise from the bed and he and Clarkson did not want to relinquish ownership. Briggs finished, in a manner reminiscent of Scott's advice to Melton, “We look forward to hearing from you about developments but counsel that you keep the specimen reasonably “close to your chest” until our joint paper is out. I guess that discoveries such as this make us all a bit paranoid!”