The Great Fossil Enigma (16 page)

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.
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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.
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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.
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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 sometimes 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.
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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.
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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.
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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.
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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.
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