The Great Fossil Enigma (27 page)

The problem remained that only from the Carboniferous was there good evidence of the nature of assemblages. Then, in 1964, Carl Rexroad and Robert Nicoll of the Indiana Geological Survey published a paper describing two pairs of elements that had been fused together (
figure 8.1
). Each of these preserved a different element pairing and seemed to reflect the relative positions of the elements in life. These came from a drill core through the Silurian Kokomo Limestone near Logansport in the north of the state. As no natural assemblages had ever been found in rocks this old, the two men thought these new finds offered important clues to the animal's anatomy. The “fused clusters,” as they called them, had survived bulk processing because they were bound together with exactly the same material that made up the elements themselves. Rexroad and Nicoll had never seen anything like them, and they consulted Lindström, Collinson, and Klapper. Only Klapper recalled seeing something similar. Rexroad and Nicoll concluded that the animals must have befallen a “pathologic mishap” and had perhaps suffered a tetanus infection.
⁹

By the end of 1964, then, a number of authors were, in their own quiet ways, exerting pressure on the mountain Ziegler was scaling. They were producing small cracks and voids. Certainly, we can say that a number of conodont workers were beginning to see their fossils through the lens of the assemblage, and in complementary studies they were acting like catalysts one upon the other. Nevertheless, this remained simply a way of looking; it had not yet become a political movement for change. In that year, no one sensed the coming revolution, even if the germ of that revolution was already in the minds of Bergström and Sweet.

8.1.
Rexroad and Nicoll's fused conodont clusters. In one pair the left element overlaps the right; in the other the reverse is true. Reproduced with permission from C. B. Rexroad and R. S. Nicoll,
Journal of Paleontology
26 (1964).
SEPM
(Society for Sedimentary Geology).

In the summer of 1961, Bergström and Sweet had made a “grand traverse of the Ordovician exposures of the eastern Midcontinent.” This gave them a panoramic outlook that would affect their work together over the coming decade. With Sweet's other students, Bergström had been gathering and processing hundreds of samples from the Middle Ordovician Lexington Limestone in Kentucky, Ohio, and Indiana. This rock was extraordinarily rich in conodonts: “There were thousands and thousands and thousands of them.” Sweet insisted that Bergström tabulate the numbers and occurrences of those he found, sample-by-sample. This work began but was interrupted, in the fall of 1961, when Bergström had to return to Lund in the hope of securing an academic appointment there. Nevertheless, the two men continued to work on their report by mail. Then Sweet attended a lecture on pollen: “Sometime in 1964, I was struck by the similarity of our work to that of Aureal Cross, a palynologist from Michigan State and I went back to my office after this lecture and began to plot the frequencies of the most common Lexington conodonts on Cross-like relative abundance graphs. The results convinced me beyond the shadow of a doubt that 4 of the element types Stig and I (and my other students) had been treating as representatives of 4 separate species, were, in fact, components of a single ‘apparatus' which should be regarded as that of just one conodont species.”
¹⁰

The paper was then already close to completion, but based on single element species. Bergström was busy in Lund preparing the illustrations. However, Sweet was now convinced they could and should do the job properly, that they should locate and name the natural species they had found. He wrote to Bergström, telling him that if they continued along their present course the paper would be out of date from the day it was published. When Bergström returned to Columbus from May to September 1964, they undertook a complete revision of the paper, piecing together natural species on the basis of size, color, secondary structures (like denticles), ornament, geographic and stratigraphic range, ratios of components, and so on. As no Ordovician assemblages had been found, they possessed no architectural plan and had to rely instead on the certainties that come with huge collections. In this regard, at least, they were extraordinarily fortunate, for they possessed about a quarter of a million conodont elements! They became connoisseurs: “We found that it was often possible to predict with uncanny accuracy the ultimate composition of a collection after just the first few specimens had been sorted from the residue.”
¹¹
The result of this colossal effort was the detection of what they considered to be twenty-three truly biological species. Twenty of these were composed of different kinds of elements and three of only one kind. Far from undermining the simple evolutionary model so effectively exploited in Germany, Bergström and Sweet found these associations gave new evolutionary insights. Now long-ranging elements became inextricably associated with short-lived and rapidly evolving ones. The critical step Bergström and Sweet took, however, was not merely to detect what they thought were natural species but to actually name them. No one had dared do this since Schmidt: “So we messed around with it. We didn't get it all right and there were some people who thought we didn't get any of it right!”
¹²
The paper was completed in 1965 while Sweet was visiting professor at Lund. It would be published the following year.

Sweet, Sweet's doctoral student, Tom Schopf, and Minneapolis student Gerald Webers gave the first indications of this approaching storm at the annual meeting of the Geological Society of America in 1965. All three had papers in press that in some degree promoted this new way. Between them, they had amassed three hundred thousand conodont fossils – a body of evidence vastly superior to any previous study. Inspired by the statistical predictions of Scott, Du Bois, and Müller, Webers had began his research in 1959 and had, without the slightest hesitation, adopted the rules on zoological nomenclature and used the earliest established element species to name his natural species.
¹³
He possessed the smallest collection – thirty-five thousand fossils – but this was nevertheless a huge amount of data. He wasted little time reviewing the failed attempts of others to find alternate solutions and felt sure that this new way would find support and generate fewer problems than had been predicted. Webers and Sweet had met on occasion but Webers's project was totally independent. Schopf's project, in contrast, had been suggested to him by Sweet. He possessed some fifty-five thousand specimens in 1962, but while he was happy to discuss recurrent groups, he stopped short of naming natural species.
¹⁴

When Bergström and Sweet's Lexington paper appeared in 1966, it was, for Ziegler and others, as if a 100-megaton bomb had been dropped on the conodont community. The paper itself was about the stratigraphy of the Lexington Limestone; the new taxonomy was merely a necessary underpinning. To some degree Bergström and Sweet attempted to protect themselves by downplaying this innovative aspect: “The taxonomic philosophy involved is not new, nor is it novel in the interpretation of collections of discrete conodont elements.”
¹⁵
Nevertheless, “we understood this might be Revolutionary,” Sweet later remarked.
¹⁶
It shook the science out of its comfort zone and demanded that it think of the conodont as a biological entity. If this in itself was not challenge enough, it also demanded that the science learn a new language and transfer names that once spoke of individual elements to associations that were then to be understood as natural species. As we shall see in the
next chapter
, this paper was, in all respects, conceptually grand and, in so many ways, startlingly original. It was one of the masterpieces of conodont science.

8.2.
Revolutionaries Walt Sweet (
left
) and, in a more recent picture, Stig Bergström. Photos: Dick Aldridge and Jeff Over, respectively.

Bergström, Sweet, and Webers now found themselves “plunged headlong into the jungle so neatly avoided by Huckriede, Walliser, and Lindström.”
¹⁷
As Bergström and Sweet noted, “The revised taxonomy was not greeted with enthusiasm, to say the least!” But Sweet could not have been surprised. He never seemed to shrink from what he considered the proper scientific course. Indeed, the two men continued their rebellion in the small print, too, pointing out that since the conodont fossils were no longer considered the teeth or jaws of vertebrates, terms like “tooth, jaw, oral, aboral, pulp cavity, fang, ramus” should also be ditched.
¹⁸
They now reintroduced the concept of “form species” to describe individual elements; the only proper species names were those attached to element associations.

The mountain was truly shaken. A fault line now ran through it and intersected with the long-ignored animal. Published just four years after the first
Treatise
, this new thinking would render that earlier work completely obsolete if it took hold. Rhodes, who was visiting professor at Ohio State University in 1966, liked the paper and “did a lot to calm the ire of the vast majority.”
¹⁹
Ziegler, however, was annoyed. He could not help but see this as a challenge to a lifetime's work. It complicated a system that worked so perfectly, easily, and usefully, and it came at a moment when Glenister and Klapper had replaced Ziegler's names with numbers and, as we shall see, when other studies were threatening to topple Ziegler's position. Ziegler must have feared that he would need to start his research from scratch, but he also knew that his collections did not hold sufficient evidence to reconstruct Devonian assemblages. The threat to his position was very real.

Although Bergström and Sweet's stand was greeted with fierce opposition from nearly every quarter, a few looked at what they had done and hardly blinked. Chris Barnes, at the University of Waterloo in Ontario, for example, used Bergström and Sweet's new species to interpret an unexpected cluster of elements from the Middle Ordovician. These convinced him that these four variously sized conodonts of the same type, all oriented in the same way and stacked one upon the other, belonged to the same animal and seemed to reflect their positions in life. The discovery appeared to confirm that Ordovician assemblages were rather different from those that had been found in the Carboniferous. Two years later, in 1969, Austin and Rhodes reported a strange fused cluster from the Carboniferous of the Avon Gorge, near Bristol, England. It was made up of an interlocking arrangement of conodonts of the same kind but of different sizes. They, too, thought these elements had belonged to the same animal and reasoned – like Barnes – that the differing sizes possibly reflected continual replacement of old elements by new or, more likely, the presence of different sized elements in the same animal.
²⁰