The Great Fossil Enigma (26 page)

The conodonts had not been the subject of Eldredge and Gould's attack. Indeed, they admitted to knowing little about these fossils. But Gil Klapper was intrigued. Having worked on species variability, he had, in 1969, supplied Alan Shaw with Devonian conodonts for his presidential address to the Society of Economic Paleontologists and Mineralogists. In his speech, Shaw was at his most provocative, attacking the utility of the species concept and using Klapper's fossils to make the point. What becomes a species, he said, is the result of a “non-objective art”: “Each paleontologist puts out his own work of art – that is, his species concept – in the hope, or faith, that his particular form of non-objectivity will find favor among his fellow artists.” Success relied upon salesmanship, and lists were only trusted if the author's name was known. Shaw suggested that paleontologists would be better recording morphological change and dispensing with species names altogether. As an oilman, he was interested in the utilitarian possibilities of fossils and was asserting a view that built upon those charts of variability that Austin thought so empowering. It was the antithesis of Gould's view. Gould was absolutely wedded to the notion of species being fixed and knowable, and he and Eldridge ridiculed all the doubting – this crisis of confidence in species – as being “unsurpassed in the annals of paleontology for its ponderous emptiness.”
³⁷

Klapper, with Glenister, introduced Gould and Eldredge's ideas into their teaching, and with David Johnson, Klapper set about using conodont data to test punctuated equilibria. They published a description of the Y-shaped branching of populations into two species – the kind of branching epitomized by Helms's diagram – locating intermediate forms that suggested gradualism. Gould and Eldredge responded, proposing that these intermediate forms might be hybrids rather than moments in evolution. They suggested that Klapper and Johnson might have engaged in circular reasoning and selected their ancestors having started with this gradualistic trajectory in mind. Gould and Eldredge remarked, “We cited the evidence of…
Polygnathus
in detail not primarily to reveal the fragility of stories built upon it; for most ‘phylogenies' based on fossils rely on flimsy data. Rather, we wish to demonstrate that most cases presented as falsifications of punctuated equilibria are circular because they rely, for their gradualistic interpretations, not upon clear evidence, but upon the gradualistic presuppositions they claim to test.” They continued, “Klapper and Johnson epitomize their conclusions in an evolutionary tree, unambiguously presented. These are diagrams that work their way into textbooks, there to convince the uninitiated that paleontologists can specify with assurance the (gradualistic) history of life.”
³⁸
Though Gould and Eldredge were fundamentally opposed to the views adopted by Shaw, they were no less of the opinion that there had been rather too much interpretive “art.” Klapper, who was already convinced that Gould and Eldredge's model operated in some circumstances but not all, communicated directly with Gould and became even more convinced by these new arguments.

A second paper by Eldredge and Gould in 1977 continued this program for change. Perhaps they were now less ignorant of the conodont as the fossil equivalent of
Drosophila
, for they wrote, “Populations evolve, not individuals or, still less, anatomical parts of individuals.” The universal evolutionary change that underpinned the conodont workers' ambitions and had so effectively produced global correlations was theoretically incomprehensible to Gould: “If such problems as these routinely occur when we deal with closely related population samples within a single depositional basin, then the wholesale application of such a research strategy to problems of international correlation (as Shaw, 1969, and Barnett, 1972, have recently done with conodont data) presents many problems and carries little prospect that self-correcting results can emerge. The assumptions underlying such a procedure are simply too vast and too ill-founded. It can't work.” Eldredge may, however, have empathized a little with conodont workers, as he too had utilized the “stage of evolution” argument in his studies of trilobites.
³⁹
Gould, however, was firmly of the opinion that such interpretation illustrated “the most pervasive and nefarious influence that phyletic gradualism has had on the development of biostratigraphic methodology.”

Gould was at this time pioneering a view of evolution as a succession of particular, unique, and unrepeatable events: “Infraspecific trends in vertical outcrop of one local area may not be repeated in an adjacent region.”
⁴⁰
Replay the history of life, Gould believed, and an entirely different tree of life would take shape. Gould's interest in history would have told him that the past was contingent on particular conditions and events. He saw the history of life in similar terms.

Like many areas of paleontology, conodont studies possessed a resilience in these debates because the rock record provided the ultimate truth. Only here might one locate objective fact. So as these arguments raged, most in the conodont community were untouched by them. That is not to say that they were not interested but simply that the arguments had little direct impact on their work. At that moment, the finishing touches were being put to the second appearance of conodonts in the
Treatise on Invertebrate Paleontology
– now these fossils occupied a whole volume. Here Helms's evolutionary tree, coauthored with Ziegler, was updated but little altered. Gradualism stood its ground here at least, and it did so by turning a blind eye. Conodont workers were already reflecting upon the success that had resulted from their own way of looking: “The first job of conodonts was to demonstrate the value of “nuts and bolts” in stratigraphy. This is being done and on a larger scale than many paleontologists would have guessed. A complete reliable and world-wide zonation of Middle Cambrian to Upper Triassic strata based on conodonts may be possible.” But this
Treatise
would suffer the fate of the first one: Delayed in publication, it too would be out of date by the time it finally appeared in 1981.

The revolution that had taken place in the 1960s permitted the conodont to come of age as a scientific object. The animal itself had acquired an evolutionary identity that had been mapped perfectly across time and was second to none. But in this decade, there were tremors that had their origins in earlier times, when Branson and Mehl, and American science in general, decided to deny the truth of the assemblage. Ziegler had risen to the top of conodont stratigraphy by a refined use of the kind of study these Missouri workers had undertaken. But as he rose to the top on the basis of mapping individual conodont fossils, the biological truth of the animal continued to seep out into the everyday of conodont science. It seemed almost inevitable that the abstract basis on which Ziegler's science was based would be challenged.

 

IN 1967, WILLI ZIEGLER STOOD ON THE SUMMIT OF A
utilitarian mountain. Now, as he surveyed the world's Devonian rocks, he fancied that he had within his grasp the means to correlate them all. This mountain had been built through the efforts of generations of stratigraphers who had turned the conodont into an abstract timepiece. Buried somewhere near the mountain's base were Kindle's call to action and Ulrich's erroneous assertions. The greater mass was American and had been shaped by Branson and Mehl and few others. The summit, however – where Ziegler now stood, flag in hand – was largely German. Here, inspired by Beckmann's proof of the conodont's potential in the German Devonian, a whole generation had raced for glory, their heads filled with thoughts of mapping the evolution of animal parts. Only on the upper slopes did Ziegler scramble ahead, driven by ambition, extraordinary resources, and sheer hard work.

The practical science that had built this mountain had found no need for the animal, but after 1950, its biology was hard to ignore; the assemblage had become, for almost everyone, an undeniable truth. It was now impossible to look into drawers of these fossils and not see a deception, an act of denial, a piece of non-science – perhaps even pure nonsense. Matters had not been helped by the willingness of those who had believed in the assemblage to nevertheless toe the line. But then, in the 1950s, everyone also knew that the conodont was important only for the huge stratigraphic potential it possessed. This, however, produced a seemingly insoluble dichotomy: Should they keep the fossil as an abstract tool and in so doing deny the animal its biology or should they adopt the animal as the essential basis for rigorous science but then risk shaking this mountain to its core? The conodont workers had cleverly thought they might “have their cake and eat it.” Better to change the law, they thought. But when the parataxa plan failed, Raymond Moore – frustrated by the conodont workers' nonconformism – thrust his own solution upon them, effectively telling them to let the animal sleep and continue their old utilitarian ways. Moore was, however, no conodont worker, and he did not have to deal with the contradictions and unrealized potential that daily faced those who were. Inevitably, among some of those studying these fossils there developed a creeping sense that the science could not go on living a lie. It was the animal itself that told them this, for in tantalizing glimpses it began to reveal sufficient of itself to challenge the charade. Gently, it seemed to push for its own recognition. In time, surely someone would take a stand?

The first cracks appeared in 1954, when Rhodes answered Branson and Mehl's test. It will be recalled that these men had challenged Scott to find isolated conodont fossils in the same proportions as seen in natural assemblages. Branson and Mehl must have known this was a mischievous test as the assemblages were composed of both robust and delicate elements, making it almost impossible to imagine nature preserving their natural ratios so perfectly. Yet against all the odds, this is precisely what these durable and abundant little fossils revealed. It enabled Scott, Du Bois, and Rhodes to emphatically reaffirm the truth. But in 1954, there was no longer any need to answer this test, as Rhodes's arguments had already won the day and, anyway, Branson was dead.

Now Rhodes realized that the test held other potential, for the search for ratios had forced him to think of fossil elements not in terms of species but as components. The animal was, to this way of looking, like an Airfix kit composed of the anatomical equivalents of wings, rudder, and fuselage. One only need find and recognize these components and construction could begin of assemblages that had never been found in any coherent form. So Rhodes divided the fossils into a handful of types, easily understood in the everyday language of bars, blades, platforms, and so on. Seeing these as different kinds of component, he looked again at the assemblages he had found and named, and discovered that each contained the same component parts. This suggested that the basic plan conformed to Scott's
Lochriea
, which Rhodes had rearranged so that it looked broadly similar to Schmidt's reconstruction. The only assemblage that did not adhere to this plan was
Duboisella
, which Rhodes used as the basis for another standard pattern. These now became the equivalents of box-lid illustrations, useful for guiding the construction of previously unseen assemblages from their components. By tracing the history of each component type so as to discover which coexisted, Rhodes could also say, with some certainty, that assemblages similar to
Lochriea
could be traced from the Silurian onward and those similar to
Scottognathus
– which shared the same broad body plan as
Lochriea
– from the Upper Devonian to the Lower Mississippian. The
Duboisella
type, in contrast, had existed from the Silurian to the Permian.
¹

Rhodes knew, however, that this picture was incomplete, that there were other kinds of assemblage for which there was still insufficient data to begin to reconstruct them. No complete assemblages had been found in the Devonian, for example, and Müller was, in 1956, struggling to imagine what they might look like. His collections suggested that the preponderance of elongated blades seen in Carboniferous assemblages had been preceded by a prevalence of platforms in the Devonian animals. But puzzlingly, some rocks from the Middle Devonian produced
Icriodus
platforms and nothing else.
²

Hermann Schmidt was, in that year, in that same quarry that had first furnished him with assemblages. Here, with the help of three of his students, he spent eight days searching for yet more. In what Müller recalled as a difficult collaboration, he helped Schmidt to interpret what had been found.
³
It was now that Müller realized that his problems imagining Devonian assemblages resulted from the incomplete survival of the different kinds of element. He warned others to beware – building assemblages, in the way Rhodes had began to do, held grave risks.

Schmidt and Müller's paper did little to progress the study of assemblages, not least because these were types already well known. But the work also held other difficulties, for while the men could agree on the basic facts, they could not agree on what they meant. As a result, the paper, like a film with a choice of endings, supported two contrasting interpretations. But Müller did not mind too much; he had already decided that assemblages were relatively unimportant. Perhaps the most interesting outcome was a decision to return Schmidt's
Westfalicus
– a name invented to satisfy conventions being introduced with parataxa – back to its original name,
Gnathodus.
It will be recalled that this name had been chosen by applying the rules of zoological nomenclature. It was once again the only assemblage to be named in this way and a direct challenge to Moore's proposal for interpretive myopia.
⁴

Back in the 1950s, Müller had also wondered if assemblages were symmetrical. From the 1920s, it was believed that elements existed in mirror pairs, left and right. Thoughts of the fish made this as an expectation, but Müller believed that Chalmer Cooper had found an unpaired element in an assemblage in the 1940s. It seems probable, however, that Cooper was merely complaining that an assemblage was incomplete. Nevertheless, Müller used this new piece of information to suggest that an unpaired element was missing from Rhodes's
Duboisella.
Soon, and independently, Lindström, Adolf Voges, and Bergström and Sweet were also reporting unpaired elements. It was easy for this idea to take hold now that Walter Gross had demonstrated that the animal was neither fish nor worm, and that the elements were not teeth. Indeed, the thought of unpaired elements encouraged the ever-imaginative Lindström to wonder if the animals were always bilaterally symmetrical. He felt he had evidence to suggest that sometimes they were not. He consulted Carl Rexroad and Sam Ellison, who concurred; they too had platform elements that did not consist of mirror pairs. Lindström was then trying to imagine the animal for his book and speculated, “Some might have floated passively, perhaps even in colonies.”
⁵
He was, however, alone in having any thoughts of the animal.

While Lindström pondered the architecture of the assemblage and what it meant for the biology of the animal, others were trying to see assemblages in collections of discrete fossils. At Marburg, Reinhold Huckriede thought he could see the appearance and disappearance of whole groups of conodont fossils in his relatively sparse Triassic collections. He pulled these associations together, calling them “Satze” (sets) guided by the assemblages Schmidt and Rhodes had described. Similarly, in his 1964 paper on the Silurian of the Carnic Alps, Otto Walliser produced nine “apparatuses,” giving each an identifying letter, A to J, but no name. He knew that to name them according to rules of zoological nomenclature, as Eichenberg and Schmidt had done, would be to isolate his work. He also knew that the resulting names would reflect a random and curious history of discovery rather than the zoological logic of the apparatuses. “It would be difficult to convince colleagues,” he recalled. “I didn't dare to do this.”
⁶
To advance science, Walliser realized, it was necessary to play ball, even if that meant ditching a few scientific ideals. For the moment his apparatuses remained convenient and practical associations.

Walt Sweet and Stig Bergström also hinted in 1962 that a more natural taxonomy was desirable. Sweet had long been cultivating an interest in conodonts in his students. It was, however, with the arrival of some samples from Arthur Cooper at the U.S. National Museum that conodont science at Ohio State University took a new turn. Cooper had been using acids to extract fossil brachiopods from a thin Middle Ordovician limestone from near Pratt Ferry in Alabama and he sent the residues left behind to Sweet and Bergström for them to pick over in search of conodonts.
⁷
As the two men examined the fossils, they detected a similar number of “right” and “left” elements and noticed that different kinds of element occurred in approximately the same numbers. With a large number of conodonts fossils at their disposal, these facts suggested that it would be possible to unite the elements in “natural species,” but they stopped short of doing so. Instead they held onto the hope that an Ordovician assemblage that would “ultimately indicate which of several possible combinations existed in fact” would be discovered. They had no thoughts of rocking the boat. Now converts of Cooper's “acidizing,” Bergström started to digest great volumes of rock.

While these discoveries were being made, Lindström was quietly writing his book, but as he did so he became increasingly of the view that the science could only ignore the animal at its peril. Only a few years before, he had been a strong advocate of the utilitarian approach, but as he looked at his fossils he noticed that some could be arranged into gradational series, each element changing slightly as its lines of symmetry shifted and parts of the element were extended. These were fossils of precisely the same age; he was not looking at evolutionary change over time. Lindström called these “symmetry transition series” and found that they only affected certain element types. They were not found among the platforms, for example. He recognized that these transition series reflected the positioning of each element in the assemblage and suggested that unpaired symmetrical elements might once have occupied the midline of the animal.
⁸
Lindström's arguments were deep and complex, and a little hard to follow, but they provided a vital key for the reconstruction of apparatuses. They gave the apparatus an anatomical logic but made a mockery of naming individual elements as if they were species. When he told Ziegler this, Ziegler responded, “Yes, so what?” They had been firm friends since 1962, and Ziegler's unwillingness to make any concessions to the biological truths of the animal only encouraged Lindström to take the opposite view.