The Great Fossil Enigma Read online

  Pander soon discovered that he had been a little naïve in permitting examples of his fossils to circulate in the jealous scientific communities of Paris and London before his detailed analysis was published. It left him exposed to a preemptive strike – one his friend, Murchison, was already primed to make. Murchison was then preparing his Siluria: A History of the Oldest Known Rocks Containing Organic Remains, a book he aspired to make definitive. Pander's teeth were something of a problem, and particularly so if they might be used to claim a fossil-bearing system older than the Silurian. Were this to succeed, Murchison's book and his Silurian would be seriously challenged. So he called upon the expertise of Barrande and William Carpenter, professor of physiology at the Royal Institution in London, and the superior technology of their “powerful microscopes,” in the hopes of causing a little tooth decay. He was in luck. With no evidence of bone, Pander's fish teeth, “not larger than pin heads,” could be dismissed as mere fragments of trilobites.11

  It was Pander's reading of these objections, two years before his own book was published, that spurred him on to develop a fully argued case for the fish. But Pander was perhaps too open in even this analysis as his unsympathetic colleague in St. Petersburg, Karl Eichwald, turned Pander's own doubts about the conodont's peculiar construction against him and suggested that the conodont fossils came from the skin covering of that sausage-shaped relative of the sea urchin, the sea cucumber.12

  The debate concerning the identity of the fossils took a new turn, however, when, in the late 1850s, some English analysts discovered that conodont fossils contained traces of calcium phosphate, the material which makes up vertebrate bone and teeth. Pander now felt even more confident about his conclusions. Murchison, the self-proclaimed historian of the oldest fossiliferous rocks, was once again on the back foot and now called upon the distinguished British anatomist Richard Owen to provide a definitive diagnosis. Owen, who had taken charge of the natural history departments of the British Museum in the year Pander's book was published, was a human encyclopedia of animal physiognomy, expert in both vertebrates and invertebrates, living and fossil, and a student of teeth. It was reasonable to believe that he was the man in all Europe most capable of solving the riddle.13 Pander himself had used Owen's work to interpret these tooth-like fossils.

  Owen approached the problem with an open mind. He knew that recent decades had brought to light “every type of invertebrate animal” in the older rocks and that the development of life appeared to follow a non-evolutionary progressive and branching course. At first this growing list of very ancient animals had caused surprise, but now Owen was willing to consider the possibility of vertebrates also being present in these older rocks. At the time, the earliest fishes came from the Upper Silurian. Pander's discovery pushed them back into the Lower Silurian, or what we would now know today as the Lower Ordovician (a term introduced later in the century to resolve the disputed overlap between Sedgwick's Cambrian and Murchison's Silurian).

  Owen examined Pander's “minute, glistening, slender, conical bodies” under his microscope and published essentially the same report three times between 1858 and 1861, making only minor alterations with each new revision.14 In 1860, for example, and perhaps in deference to Murchison, Owen described Pander as an “accomplished naturalist and acute observer” and his book as “an important work.” But in 1861 he found no place for these compliments. In 1860, he raised the possibility that a few of Pander's fossils might have claim to “vertebrate rank” but then admitted “that the parts referred to jaws and teeth may be but remains of the dentated claws of Crustacea.” The recent recognition of calcium phosphate caused Owen to give greater consideration to the vertebrate origin of conodonts in that year. Here, Owen alighted upon a new analogue, the whale shark (Rhinodon), which although typically nine meters in length has rows of thousands of two-millimeter-long teeth. But Owen agreed with Pander that these teeth were never attached to bone. So he considered Pander's hagfish theory but here felt the conodonts were “much smaller, slenderer and far more varied” than the teeth of that group of fishes. Then he asked, if they did need to be attached to a “soft substance,” then why not a “soft Invertebrate genus”? Certainly they seemed not to belong to an animal with a shell (because no shells had been found), and by a process of deduction, and not finding any perfect solution himself, he concluded that “they have most analogy with the spines, or hooklets, or denticles” of the slug-like naked mollusks or worms. Owen offered these as the least problematic and contradictory possibilities. He certainly saw no grounds for Pander's more narrow interpretation: “The formal publication of these minute ambiguous bodies of the oldest fossiliferous rocks, as proved evidences of fishes, is much to be deprecated.”

  For some, Owen's verdict was definitive, his scientific indecision concealed behind his clear preference for an unproblematic invertebrate. Beyond the inner circles of metropolitan science, Owen's self-styled greatness was received wholesale, even if many in the city, such as the young Thomas Huxley, “feared and hated” him: “He can only work in the concrete from bone to bone, in abstract reasoning he becomes lost.”15 Pander's fish had relied upon Pander's imaginative capabilities, and in Huxley's view this was a facility Owen lacked.

  In June 1861, when Owen's most recent opinion was published, Huxley was engaged in the Panderian act of studying the embryology of the chick's skull. He, too, would soon be called upon to ponder the conodonts. As secretary of the Geological Society of London, he presented a paper on these fossils written by his associate, John Harley of Kings College, a Ludlow fossil collector who had earlier provided fossils for Huxley's investigation of giant fossil “sea scorpions,” or eurypterids. Believing Murchison's Silurian to be “the Crustacean Age,” Harley had gone in search of crustaceans in the Ludlow Bone-Bed, a deposit made famous by Murchison, who described it as “a matted mass of bony fragments, some of which are of a mahogany hue, but others of so brilliant a black, that, they conveyed the impression that the bed was a heap of broken beetles.”16 Murchison interpreted these fossils as the remains of primitive fish and thus possibly the earliest record of vertebrate life, but he could not get any good specimens of these fish and so could say little about them.

  Harley's solution was to break and wash pieces of the bed. It was by a similar technique that Pander found his first conodonts. Now Harley found “minute bodies,” too, and looking at them through his microscope, he thought they were like those described by Pander, a fact that seemed to be confirmed when Huxley gave Harley two of Pander's own specimens. But Harley, who looked with crustacean eyes, could see nothing piscine in his specimens or in Pander's, only the spiny protection of the modern horseshoe (or king) crab (Limulus). He concluded that all his finds, including the conodonts, came from crustaceans and in all probability from the shrimp Ceratiocaris, on which the conodonts performed as “minute spines which were attached to the tail-spines.” He convinced himself that this was the case by examining specimens of mantis shrimp in the collections of the Museum of Comparative Anatomy at King's College in London. Sure in his conclusions, Harley set up a new genus to accept all his material: “Astacoderma is a name I would give this genus, in which I would also include the whole of the so-called Conodonts, and thus give them at once a natural association, and a more appropriate name.”

  By coincidence Dr. Alexander von Volborth of St. Petersburg was making a short visit to London at the time. In conversation with Murchison and Huxley at the Museum of Practical Geology, he told them that he was convinced that the conodont was no limited phenomenon but was to be found wherever the Silurian occurred. Huxley told Volborth of Harley's discovery, and this sent Volborth in search of the author. On viewing Harley's collection, Volborth was convinced that a small tooth was indeed one of Pander's conodonts. Making the long trip up to Ludlow, he too found conodonts in the rock, hundreds of them, he said. But these were quite unlike those he knew in St. Petersburg: They were white, opaque, dull, and brittle. Nevertheless, when P
ander saw them, he felt he could confirm the conodont's peculiar internal structure. Volborth also found conodonts on the Swedish Baltic island of öland, though these were of the familiar kind.17 Whether Harley's rather odd fossils really were conodonts was, however, not beyond doubt. Certainly those he figured looked nothing like them, but then no one was quite sure how varied these new fossils could be.

  By the end of 1861, the conodont had at least six possible identities: fish, sea slug, marine worm, sea cucumber, trilobite, and now crustacean. Each was the product of a rather different outlook. Pander had unquestioningly been rather narrow in the kinds of animal he considered but had been very open and imaginative about the anatomical possibilities of vertebrate life. One might expect a fish paleontologist who had in his lifetime seen the discovery of the most remarkable and unexpected fossil fishes to have this open mind. Owen was by comparison an encyclopedist. If this permitted him to admit a huge diversity of animals into his analysis, it by implication made him rather more the generalist and content to work within the known categories of life. He was not one to think very far beyond the apparent natural order of things. Harley was an entirely different kind of naturalist: an enthusiast, rather less informed and as a result having a tendency to naïve assumptions and conclusions. To these we might add Carpenter and Eichwald. With the mythologizing of the animal, the varying capabilities, scientific status, and outlook of these authors would be overlooked; all views would be considered equally valid. By 1861, the extraordinary riddle of the animal's identity was becoming the fossil's most important feature. The conodont was acquiring the mantle of perpetual uncertainty, which others would recognize and develop. As its mythological status developed, so it acquired a long tail of speculation. It became the very portrait of puzzlement.

  Nevertheless, each actor who confronted the problem thought he possessed the solution. In the 1867 edition of Siluria, for example, Murchison published Owen's 1858 opinion and stated with satisfaction that “the question [of the conodont] is completely set at rest.”18 It wasn't that Murchison believed the issue of affinity settled – he knew Owen was tentative on that point – but that science could now be sure that these were not the remains of vertebrates. This was the critical point for both Owen and Murchison. It was a rather secondary concern to know what the conodont actually was.

  However, even if paleontologists like Owen had grown accustomed to the strangeness of the fossil past, the conodont could not easily be pushed into the shadows, for whenever these evocative little things came to light, usually as unexpected and chance finds, they astonished the finder. Throughout the nineteenth century conodont fossils were sufficiently rare to produce in collectors those same feelings of wonder and amazement that had once affected Pander. These were precisely what Bath amateur geologist and fossil collector Charles Moore felt when he found them.

  Moore had long collected from the Carboniferous Limestone and had, by washing debris found in fissures in the rock and sorting them under his microscope, made the sensational discovery of Triassic mammalian teeth.19 Nevertheless, he was not prepared for the sight of conodonts when this same technique turned them up in the late 1860s. These were quite unlike those Pander had seen: “Their forms are about as eccentric as can be imagined.”20 Rather than illustrate these fossils, he painted a word picture that began with teeth that were remarkable for their scale and imitation of a larger form. It ended with forms that to this seasoned collector seemed utterly bizarre: “a minute conical fish-tooth”; another “not unlike the central cusp of a hyboid tooth”; another with “teeth arranged on an irregular or waved platform…too eccentric for description”; “nine curved teeth, arranged somewhat symmetrically, graduating in height from the centre, but with a much larger fang at one end”; “a long curved tooth at one end, throwing off a semicircular spur, which passes under a base-line, on the top of which follow numerous small depressed regular teeth”; “some instances with serrations as close-set and minute as are the bristles on an insect's limbs”; like “an old-fashioned rat-trap.”

  Moore had discovered an Aladdin's cave of organic wonders, and it was to Murchison's Siluria, and particularly to Owen's diagnosis of Pander's “curious fossils,” that Moore now turned in an attempt to explain his own finds. He believed that he was the first to find these fossils above the “Lower Silurian.” Certainly the 1867 edition of Murchison's Siluria recorded that Pander and others had found them from the Upper Silurian, Devonian, and Carboniferous Limestone. As to what the fossils were, Moore agreed with Owen but added, “One objection to it is the variety of forms they present, and that we have no existing analogues.” Moore's bizarre specimens seemed to remake the imagined animal. It now appeared even less certain.

  As the controversy entered the mid-1870s, so its center moved from Britain to North America. As it did so, it could be said to have progressed in a limited way. First, Charles Moore was certain that conodonts were restricted to the Paleozoic era – a period of geological time stretching from the Cambrian to the Permian and typified by particular forms of life. Second, Pander's fish was dead. The animal that had left behind these peculiar fossils was an invertebrate. Moore might also have recognized that while many possibilities could be eliminated, no prime contender had been found. Owen's two favorites were attractive as much for what they lacked – a hard shell, skeleton, or backbone that might become fossilized and associated with the teeth – as for any morphologically similar thing they possessed. This is how things looked in Britain; this is what science could be said to have deduced from the evidence. However, no sooner did the conodont arrive in America than it found itself, once again, a fish.

  The North American awakening owed much to the booming city of Cincinnati in Ohio, which drew in immigrants from across America and Europe. Here, in response to the local abundance of fossils, there emerged a group of avid collectors later known as the Cincinnati School of Paleontology. The Cincinnati Society of Natural History became the hub of the school's activities and spawned many eminent geologists, important papers, and fine collections.21

  The conodonts, when they arrived, entered the American consciousness with something of a jolt. As rising Cincinnati geologist Edward Oscar Ulrich recalled in 1878, “Somewhat more than a year ago, the paleontologists in the vicinity of Cincinnati were considerably disturbed by the announcement then made, that fish jaws had been discovered in large numbers in rocks of the Cincinnati group. Two of the collectors here sent specimens of the supposed fish jaws to Dr. Newberry, and in a letter to me, he stated that he considered them to be identical with Pander's Conodonts.”22

  John Strong Newberry was director of the second Ohio Geological Survey and professor of geology and paleontology at Columbia University in New York. An Ohio man from Cuyahoga Falls, south of Cleveland, he had studied in Paris under the great French paleontologist Adolphe Brongniart and explored the famous Eocene fish excavations at Monte Bolca in Italy. He could claim the pioneering American geologist James Hall among his early influences and had shown considerable talent on expeditions into the West, most notably in establishing initial stratigraphic sections of the Grand Canyon. At the Ohio Survey, he was working on a nine-volume series giving the first comprehensive account of the state's abundant fossils, and it was in one of these volumes, published in 1875, that he described the first American conodonts, which came from the Cleveland Shale at Bedford. To him they seemed so like, and yet so unlike, fish teeth. Like Murchison before him, Newberry needed to resolve the matter of their identity if he was to achieve his goal of producing a definitive account of the state's fossils. If not the most important fossils he would describe, these were certainly the most controversial, as they had profound implications for determining the history of life on Earth. So he sought the assurances of America's greatest experts in those fields that encompassed the debate in Britain. Surely they would recognize whether these things came from a vertebrate or invertebrate animal? If only the problem were that simple. Harvard professor Louis Agassiz, a native
of Switzerland and a leading figure in American science, and possibly the greatest living fish paleontologist, thought the fossils were the remains of sharks and rays. In contrast, Edward Morse, an authority on the structure of invertebrates, thought them very like mollusk teeth and could imagine them belonging to the ancestors of living species. William Stimpson, America's foremost – and soon to be deceased – expert on crustaceans, could at least confirm that conodonts were not part of the armament of his group of animals. He, too, thought they might be the lingual teeth of mollusks.23

  Newberry's consultation had done nothing to resolve matters. American opinion was now divided along exactly the same lines as in Europe. Was it a fish? Was it a worm? No one could tell him. He had to make his own call, and being rather more an expert in fish than an encyclopedist, he tended to see the problem as Pander had. He could see that conodonts were quite unlike shark's teeth: They had no enamel, or dentine with radiating and ramifying canals, nor a distinctive base (though he knew this latter was often lost in fossilization), and could not have been set in a jaw. But his point-by-point analysis of the possibilities fell short of Owen's overview, and before long he began to speculate – “I take the liberty of offering, as a possible and plausible explanation of the enigma” – that the animal might indeed be a relative of the hagfish. While he admitted there were problems with this view, not least the “horny or chitinous” chemistry of the hagfish's teeth, he challenged anyone to compare the teeth of these two animals and not see “a very close and remarkable similarity between them.” He became captivated by the thought that he possessed in his hands, in great variety, “the first fishes that existed on the globe.” Although his final diagnosis relied rather more on his own gut instinct than on the opinions of the great men he had consulted, nevertheless, their names certainly gave his conclusions a sense of weight.