The Great Fossil Enigma Page 12

  Scott had sufficient material to define two genera. One – Lochriea – was composed of two species, and he remarked that it was possible to distinguish these on the basis of an individual “tooth,” as he still called them. He also described another genus, which he named Lewistownella. These were new names, and as such they broke the zoological rules, for his named assemblages were composed of conodonts that themselves already possessed names. He had decided not to take – for the name of the animal – the oldest established name, as Schmidt and Eichenberg had done. Rather, he argued that he could not be certain that that name belonged to precisely the same element and thus animal. Perhaps that name was associated with a slowly evolving “tooth,” while the animal itself, as understood from its apparatus, showed much more rapid change. How could that unadventurous tooth really help distinguish the different animals? It was clear to Scott that to follow the rules would be to throw conodont studies into “utter confusion.” Instead, he introduced a dual system. The names of isolated conodont fossils were now to be understood as artificial “form genera” and “form species.” It was these that the stratigraphic community would continue to use, but he could not use them as names for the elements within his assemblages. Instead, he took a form name, such as Hindeodella, and turned it into a noun (hindeodell) or adjective (hindeodellid) to describe the component elements. Although this approach was a radical step, it seemed logical to Scott, who had established a similar system for the spicules (the tiny skeletal components) of sponges back in 1936. It was a compromise that permitted both camps – the utilitarians and the biologists – to “have their cake and eat it.” It also showed that Scott possessed a very sophisticated understanding of the problem.

  Over at the Illinois State Geology Survey in Urbana, another disciple of Croneis, Ernest Paul Du Bois, was developing his own views on “the riddle of conodont origin,” which he had first presented back in 1941 at the Illinois Academy of Science.6 It may have been this that finally pushed Scott into press, as Du Bois was an able worker who possessed some extraordinary Illinois material. Du Bois had collected, split, and sorted some three hundred pounds of shale, locating five hundred individual conodont fossils and seventy-five assemblages, including one much like Schmidt's best specimen. He agreed in part with the German interpretation of their function: “The polygnathids perform the preliminary mastication, and the hindeodellids the final comminution or straining.” This did not, however, mean that Du Bois looked at these fossils and saw a German fish. In one of his specimens there were “impressions” associated both with the conodont fossils and with a “brown carbonaceous film,” which Du Bois interpreted as “a fossilized portion of the cuticle of some worm-like creature.” He continued, “It is believed that the conical structures pictured here represent parapodia or cirri. Not shown in the figure is a hindeodellid which was ‘sandwiched’ in between two layers of the membrane and which may indicate in a more positive manner the origin of conodonts.” Parapodia are foot-like projections seen on the sides of some worms which assist in locomotion. The common association of particular types of conodont pairings in some of the finds, where other elements were missing, further suggested to Du Bois that they must have been connected by muscle.

  Reflecting on the affinity of the animal, he concluded that there were three possibilities: an unrecognized group of vertebrates, an unrecognized group of invertebrates, or annelids. He thought the latter most likely and felt that his finds suggested two different species, but he did not name them. The big stumbling block with this conclusion was, of course, the conodont's chemistry. But here Du Bois offered a new explanation. It drew upon information published by Frank Clarke, chief chemist to the U.S. Geological Survey, which stated with some surprise that some annelids, particularly tube-dwelling forms, were rich in phosphorus.7 Du Bois postulated that an outer phosphorus-rich sheath or tube might, during evolution, have been turned in upon itself to form the mouth cavity of the animal and thus also the conodont elements.

  In Du Bois's mind the animal achieved more solid form: “If it is assumed that conodonts are associated with both the problematic parapodia and the worm trails, it is possible to erect a picture which may represent the appearance in life of the animal which bore the teeth. The adult was an elongate worm, seldom more than three millimeters in width, with a length of at least three centimeters, and probably five or more. It probably possessed a ventral nerve cord and resembled modern annelids in many other internal structures. Metamerism [i.e., serial segmentation] may have been indicated by the serial development of the jaws, in which each type of tooth was restricted to a separate metamere, and by the presence of regularly arranged parapodia.” He continued, “The anterior part of the digestive tract was divided into buccal and pharyngeal regions. The buccal cavity [“mouth”] had a single (but perhaps more in some cases) polygnathid on either side, with the blade directed anteriorly. These jaws were probably covered with hypodermis and cuticle so that only the actual cusps were visible. Protractor and retractor muscles supported and moved the teeth. Anterior to the polygnathids there may have been one or two teeth of the symmetrical type illustrated in Scott's figure 3c (1935 [1934]). The pharyngeal region [“throat”] supported the hindeodellids which probably functioned in the final straining or comminution of the food.”

  This was new. Based on the evidence and some good zoological reasoning, Du Bois had taken the argument to a new level of anatomical sophistication.

  By 1944, Branson and Mehl were making accommodations. In their important summary of the stratigraphic significance of conodonts published in that year, they indicated that the jury was still out on affinity: “Most investigators assume that they represent jaw armor of an extinct order of primitive fishes.” This was hardly an emphatic assertion of their own beliefs and appeared in a paper that was balanced and tentative on those many aspects in dispute. In this paper, they confusingly placed the conodonts in the Order Conodontophoridia, which differs from Eichenberg's grouping only by the addition of a single letter. It has been assumed that Branson and Mehl used this term to refer to a group of fish, but nowhere do they make this explicit. They seemed to be approaching the point of being able to accept assemblages but were still cautious: “Granting, for the purposes of illustration, that more than one so-called genus [of fossil] represents one individual, the stratigraphic range of any distinctive part of this composite, the so-called species, loses none of its value. The only offense of such usage is against biological veracity.” Their classification was based on grouping similar forms together “in an attempt to indicate genetic relationships,” but they admitted to rising taxonomic uncertainty, noting that “specific values are not agreed upon.” As to the animal itself and its mode of life, they had yet to read Du Bois and could only draw information from the lithologies in which the fossils were found: “It is reasonably certain that the normal conodont environment was near shore in moderately shallow marine waters containing some clay, possibly somewhat modified by fresh waters around debouchures of streams.” It was an ecological interpretation the ambitious Sam Ellison sought to imitate. But this simply revealed that virtually nothing was known; Ellison could write just seven sentences on the subject.8 This did, however, suggest to him that the animal was not as restricted to particular environments as Branson and Mehl believed. In particular, Ellison was unconvinced by their assertion that conodonts were rare in limestones. His own literature review suggested that the fossils were found in almost every kind of sedimentary rock and that the animals were probably free swimmers.

  The animal continued to develop in American minds during the war, but in Europe the conodont had been sleeping, locked up in unseen books or buried beneath the rubble of German cities. For fifteen years from 1934, conodont studies in Germany had ceased. Then, in 1949, an emergency committee, the Notgemeinschaft der Deutschen Wissenschaft, was established – as one had been after World War I – to mastermind science's recovery. The war had taken its toll on the universities, though sometim
es that toll was more imagined than real. Schmidt's important specimens, for example, were believed by some to have been lost when really they remained untouched in Schmidt's office in a Göttingen, which had avoided destruction.9 As the German paleontologists woke up from their self-induced nightmare, they believed the world was as it had been when they had fallen asleep. They had no idea of the progress the Americans had made. Thus in his Outline of Historical Geology, published in 1948, Roland Brinkmann adopted H. A. Pilsbry's never-fashionable molluskan teeth as an explanation for the conodont.10

  The German recovery in conodont science was more properly led by Heinz Beckmann, a former student of oil geology at Cologne, who returned from the war to begin a doctorate on conodonts at Marburg. Beckmann first found conodonts accidentally, when working on Devonian brachiopods, and “immediately fell under the spell of these puzzling fossils.” Unable to access the modern literature, and largely unsupervised but possessing exceptionally preserved local conodonts, “shining green, grey-blue with whitish, and often reddish, decomposition,” he began a study of the inner structure of the conodont unaware of what Hass had achieved. During the war the zoological affinity of the conodont had become less certain, but Beckmann continued the prewar belief that he was looking at Schmidt's fish, so much so that he grouped his fossils anatomically: mandibles, hyaline teeth, and gill apparatus.11 It was a wise move, as Schmidt, who was regarded as “the only conodont connoisseur in Germany,” became Beckmann's examiner. In many respects, Beckmann discovered what Hass had already demonstrated, such as the importance of the pulp cavity. But he also found clusters of “fine hair tubes” in the white matter – also seen by Zittel and Rohon – which suggested that material might be delivered to the surface of the tooth from the pulp cavity and permit surface growth like the dentine in vertebrate teeth. However, he noted that continued growth resulted in the pulp cavity being closed off, and thus: “The arrangement of the cavities and lamellas forces us to accept that the outside lamella is not substantially older than the inside and proves the dentine structure of the conodont.” Despite his intellectual isolation, or perhaps because of it, Beckmann's work threw up new ideas that both confirmed and contrasted with Hass's conclusions. It also demonstrated that Pander's anatomical descriptions remained, for the most part, robust. Yet Beckmann knew there was more to be understood, if only the technology was more advanced.

  Schmidt again published on conodonts in 1950, following up his groundbreaking paper of 1934.12 But like Beckmann, he found himself without the modern American literature and thus arguing with the past and with a Scott of sixteen years earlier. In his ignorance of Scott's more recent reconstruction, he made his own from Scott's published figures, in effect inserting another pair of conodonts into his own apparatus. In doing so, Scott's material was assured of a supporting role. The only recent paper to which Schmidt had access was Beckmann's, with its case for dentine tubes that simply strengthened Schmidt's conviction that the animal was a fish. Of course, Beckmann had begun by believing in Schmidt's fish, and the interpretation of his dentine tubes relied upon it. There was, then, a certain reinforcing circularity to German interpretations, which had probably accompanied the German fish from the moment it left Eichenberg's mind.

  However, this particular fish did not have long to live. A new wave of conodont workers was waiting in the wings, and they would take possession of the fossil completely and remake it for modern science. The conodont assemblage might have been on the verge of acceptance, even among the most conservative of American stratigraphers, but it would take this new wave to deliver the final knockout punch. That punch came from an Englishman, one of the first Fulbright Scholars, who arrived in Urbana to work with Harold Scott. A precocious, young postdoctoral student, Frank Rhodes began his time in Illinois with an unexpected education; having arrived skeptical of conodont assemblages, he was soon converted and then became a great evangelist for them. Rhodes had recently completed his PhD at the University of Birmingham in the UK, the topic of conodonts having been suggested to him by Harry Whittington, then of Harvard University and later portrayed heroically in Stephen Jay Gould's Wonderful Life.13

  In the early 1950s, Rhodes published a flurry of papers reviewing many aspects of conodont science. While most paleontologists only made excursions into conodonts (Branson and Mehl were exceptions), Rhodes was the first high-flying paleontologist to give them focused attention. Scott's mentoring hand can be seen as Rhodes launched himself into an attempt to “build up a detailed natural classification treating such assemblages as biological units” based on existing finds and some of Rhodes's own from Illinois and Kentucky. In doing so, Rhodes followed Scott in believing in the necessity of maintaining form species, and like Du Bois and Scott before him, he hammered home those proofs that demonstrated Branson and Mehl's skepticism had been ill founded.14

  Following the precedent established by Scott, Rhodes introduced three new genera, and as he did, he shifted authority away from Schmidt, who, unknown to Rhodes, had recently put the Americans in a supporting role. Now Rhodes usurped Schmidt's original invention and made it American. He had not read Schmidt's recent paper and perhaps did not know whether Schmidt had survived the war; to Rhodes, Schmidt was a historical figure and perhaps as a result Schmidt did rather badly in Rhodes's review. Rhodes named Scottella, for example, in honor of his mentor, but it was essentially a new name for Schmidt's Gnathodus, which Schmidt had named according to the zoological rules. Rhodes believed Schmidt had wrongly identified the Gnathodus elements making up the assemblage, but this was perhaps a small point. Rhodes wanted an idealized and consistent natural classification; he wanted to make scientific sense and he saw that sense in the Scott's rationale for a separate system for assemblages. But soon Rhodes had to backtrack: Schmidt was alive and had not made a mistake. In any case, the name Scottella was already in use for another animal. Rhodes came up with a replacement, Scottognathus, which performed the same feat, but it too would be no permanent memorial to Scott. And if Schmidt had reason to be upset, Du Bois also had no reason to celebrate, for nearly all of his assemblages, which he had not named, were also accommodated within Scottella/ Scottognathus. The great irony here is that both Du Bois and Schmidt had described essentially the same assemblage – which was closely similar to the one Rhodes now recognized. Rhodes's interpretation, however, maintained the overall architecture but reversed the direction of each element.15 In contrast, Scott's assemblage was strikingly different and largely speculative. Du Bois was, however, honored, in Duboisella, a name used to refer to the assemblages Du Bois had considered atypical. A third genus honored the state: Illinella.

  Rhodes had thus manufactured a redistribution of honors, which echoed the spoils of war, but his rewriting of history would not stop there. He found the conodonts making up the assemblages graded from one form species into another, their distinctive names reflecting stratigraphers’ desire to highlight difference rather than any biological truth. To Rhodes, these differences were merely a reflection of natural variation. In other words, they were all synonyms, and in a single stroke the taxonomic efforts of Stauffer, Plummer, Gunnell, Branson, Ellison, and others could be subsumed into a few form species.

  On the matter of the animal's zoological affinity, Rhodes's open mind was also affected by the Illinois air: “Until more definite evidence is forthcoming no final opinion can be given…although the writer is of the opinion that evidence afforded by the study of assemblages tends to support their association with an extinct group of annelids.”16

  Rhodes's contribution formed a point of closure in the debate over whether to accept the reality of assemblages. In one short paper, he had traveled from skeptic to self-made authority. Now others would follow. By admitting to his skepticism and then conversion, he built a bridge between the two opposing camps. For twenty years, conodonts had apparently existed within numerous overlapping and interwoven paradigms, which shaped the objects into different associations and configurations and dressed them
in rather different flesh. For much of that time, the sheer momentum of microfossil-based stratigraphy permitted an uncomplicated view to dominate, and, in the United States at least, even those possessing contradictory evidence did not attempt to counter it. The new Journal of Paleontology provided the vehicle for this American debate and a yardstick against which to measure progress, but as it was driven by the burgeoning oil industry it was also the voice of rational utilitarianism. Consequently, the question of biological affinity became secondary. It was a fascinating and attractive conundrum, which drew in its own workers, but it was also theoretical and contentious, and of little practical value.

  In Europe, the situation was entirely different. The biological aspects of paleontology dominated and the affinity of the conodont animal was not in dispute. Conodont stratigraphy was yet to begin and there was no crisis – other than that determined by actions on the other side of the Atlantic. The arrival in the United States of a new generation of conodont specialist, epitomized here in the form of Frank Rhodes, meant that the two worlds would be forced into some kind of reconciliation. But this moment of reconciliation also added to a sense that the science was mired in a taxonomic mess of epic proportions.