The Great Fossil Enigma (32 page)

Merrill believed that the richness of modern data was permitting conodont workers to see subtlety and complexity, displacing beliefs in the universal. He put it metaphorically: For so long it had been possible only to hear the orchestra; now they were beginning to hear the individual instruments themselves, even if “the composition and the composers are unknown.”

In the 1970s the science possessed for the first time the makings of a global database of information on conodont distribution in space and time. It was already altering perceptions. For example, simple cone-shaped conodont fossils, which were considered mere contaminants in the Devonian in 1957 and questioned as such two years later, were in 1973 mapped by as a true but progressively declining component in that fauna.
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In this incremental way the whole data set was changed and extended, knowledge shifted, and interpretations were reformulated according to new and, as we shall see, increasingly spatially aware criteria.

This new trend in conodont studies really took off as geology in general embraced the unifying theory of plate tectonics. It was a theory that gave the earth a fluid geography of mobile continents and spreading oceans. It encouraged the sometimes near-sighted paleontologist to think big as it gave new explanation to the comings and goings of oceans and the appearance and disappearance of animals and plants over time. The idea that the continents drifted over the surface of the globe had been debated for much of the twentieth century, but it was only in the late 1960s that all the components of the theory were locked together into a convincing whole. It became the new paradigm. But not everyone felt the need for an imposing theory. The science had, after all, gained nearly all its intellectual possessions by hard graft in the field or through instrumentation. Conodont worker Anita Harris – a onetime PhD student of Walt Sweet – certainly belonged to this proud tradition. Back when the theory was still fresh, she told popular geological writer John McPhee, in a book in which she was the main actor, “The plate-tectonic model is so generalized and used so widely…. People come out of universities with PhDs in plate tectonics and they couldn't identify a sulphide deposit if they fell over it. Plate tectonics is not a practical science. It's a lot of fun and games but it's not how you find oil. It's a cop out. It's what you do when you don't want to think.”
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Conodont science was indisputably practical, and Harris had by then, as we shall see, made a major contribution to that practicality. She had done so by paying her dues in the field, not by theorizing. Her comments indicate how fundamentally geology was changing, and she in time would adjust to it once all the hullabaloo settled down. The new tectonic theory rapidly found its way into the interpretative armory of practical geologists, particularly those concerned with the spatial dynamics of the earth. Leading paleoecologist James Valentine at the University of California in Davis, for example, combined the new theory with evolutionary concepts to revolutionize the way paleontologists thought about the distribution of life over time.
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Drawing on these new theoretical and interpretive resources, it was again possible to think differently. Geology received a shot in the arm as the developing theory gave explanation to phenomena that had long been puzzling. Perhaps it was coincidence, but just as the conodont workers began to possess global data about their fossils, so the geology as a whole started to think global thoughts.

Chris Barnes of the University of Waterloo in Ontario was certainly among those who thought these new theoretical ideas powerful interpretive tools. Valentine's work was in his mind when he teamed up with Rexroad and Cambrian specialist James Miller of the University of Utah to consider the global pattern of conodont communities and provinces during the period when these communities first appeared and experienced explosive diversification.
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They reasoned that for this diversification to have occurred there must have been ecological niches available for exploitation by different species. Valentine's refined definitions of province and community suggested a spatial continuum of environments and a way to relate diversity to a changing world. It gave them a means to reinterpret Bergström and Sweet's provinces and subprovinces and attempt to locate communities within them. These communities, they believed, were distributed as a series of lateral bands parallel with the shore and extending into deeper water. Using the brand-new understanding of continental margins, they set these bands in the context of plate-tectonic theory. It gave their ecological niches a theoretical rationale and a new global context. But Sweet and Bergström simply could not agree and recalled a paper in press to add a short addendum critical of this interpretation. It was, however, a sign of the times: “The concepts and ideas of the theory of global tectonics have proven to be a virtual panacea for geologists.”
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Many of the ideas developed in this first paper were extended and given greater clarity when, three years later, Barnes and Lars FÃ¥hræus of Memorial University of Newfoundland in St. John's reviewed the growing literature to propose a “unifying model of the major habitats” of Ordovician conodonts.
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Seddon and Sweet had imagined a weakly swimming or floating animal, but Barnes and Fåhræus reassessed the evidence and suggested a bottom-dwelling animal that was in control of its own movements. The lateral banding of fossils was so clear, they felt it was possible to predict neighboring communities. There were, they admitted, some simple species that transgressed these bands that probably represented swimming forms, but these were less numerous (
figure 9.1e
).

Barnes and FÃ¥hræus then took Bergström and Sweet's two provinces and rotated them in order to understand their relationship in Ordovician times. East-west now became north-south. The Appalachian or North Atlantic Province was understood to represent a normal marine environment with a “virtually cosmopolitan” fauna. The midcontinent fauna was, by contrast, seen as being restricted to a “fairly narrow equatorial belt” and adapted to higher temperatures and salinities.

Using these ideas, they now reimagined Bergström and Sweet's panoramic view of mobile populations of animals with ideas that integrated time and community with the province. The controlling factor was a relative change in sea level. In the lowermost rocks of the midcontinent, the animals held simple cone-shaped elements. They showed no lateral segregation. However, during the Middle Ordovician, major transgressions flooded the midcontinent from the direction of the Appalachian province. Habitats and communities diversified and ecologically specialized faunal belts developed. In this manner, Barnes and Fåhræus gave a sophisticated and detailed reading of the history of a group of animals experiencing environmental change. They, too, were sure that the form and shape of individual conodont elements and assemblages reflected particular lifestyles. Increasingly, they felt it was possible to talk with reasonable certainty about the life requirements of particular genera and species. Drawing upon a sizable literature, they had pieced together a rich, complex, and changing conodont world. One could almost imagine the animal.

Barnes and Fåhræus's paper appeared in April 1975. A month later, Barnes played host to a paleoecology-themed meeting of the Pander Society in Waterloo, Ontario. The meeting showed how the field had diversified.
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The idea that environments could be read merely from the shape of these tiny fossils was then in the ascendancy.

One of the more extraordinary papers was by Jeppsson, who had been inspired by science fiction writer and acclaimed Ice Age mammal specialist Björn Kurtén. Kurtén had attempted to go beyond the descriptive essentials of paleontology, measuring bones in order to interpret communities. Jeppsson transferred the method to the deep past and took to measuring almost immeasurably small processes on these tiny fossils. He considered the possibilities of the animal having a spawning season and seasonal migrations.
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Barnes thought the paper both speculative and intriguing. It was typical of Jeppsson's individualistic approach to his science but it also marked a wider desire to give these animals biological clothes of some kind.

While an increasing number of conodont workers were becoming rather theoretically minded, Dick Aldridge of the University of Nottingham in the UK was not alone in treating his piece of geological time with historical specificity. Believing each period to be distinctive and affected by particular influences, Aldridge thought the existing models rather simplistic in their assumptions of cause and effect when so many environmental factors were known to be at play.
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Many others discussed the various models, though the latest by Barnes and Fåhræus was simply too new to attract much attention. Opinion remained mixed; some testing had taken place, but it was inconclusive.

Karsten Weddige and Willi Ziegler, being dissatisfied with the explanatory power of the models produced to date, came up with yet another (
figure 9.1d
). They did not believe that depth and distance from shore were responsible for the observed distributions of fossils. Indeed, the models seemed too static; the ocean was a dynamic environment and other factors were at play.
Icriodus
, they said, preferred turbulent, oxygen – and carbonate-rich waters, while
Polygnathus
preferred quieter conditions associated with muddier sediments.
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Riding the wave of ecological optimism, Fåhræus and Barnes rushed a second paper into print in the distinguished science journal
Nature.
Their vision was nothing short of oceanographic. The conodont was to be a tool in “studies involving the extent and relative depths of sedimentary basins; for unraveling patterns of transgressions and regressions; as aids in the recognition of depositional environments characterized by raised temperature and salinity; and in understanding palaeogeographic and tectonic changes.”
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They demonstrated this by examining the relative abundance of two genera thought to occupy adjacent and overlapping communities:
Phragmodus
, which occurred offshore, and the nearshore form,
Plectodina.
The changing relative abundance of these in a geological section would indicate transgressions and regressions. It was a view not far removed from Merrill's. But FÃ¥hræus and Barnes now saw the conodont as a precision tool for plotting major global change: “Thus, initial destruction of this ancient continental margin can be dated with considerable precision.” In taking this view, Barnes acknowledged the debt they owed Sweet and Bergström whose data they had turned to their own ends.

Barnes and FÃ¥hræus were not alone in considering major events in the earth's history. Across the Atlantic, Otto Walliser was having similar thoughts. The science was continuing to change, and as it did so it would move the cutting – or at least fashionable – edge away from ecology. The late 1970s marked a point of reflection for those who had looked at palaeoecology as holding promise. The conodont workers certainly felt they had achieved new understanding, but this was not the view of Smithsonian foraminifera specialist Martin Buzas when he reluctantly took up the task of reviewing the book that came out of the Waterloo conference. In that review, titled “On the edge of the unknown,” he admitted to knowing nothing of conodonts or of the rocks in which they are found. He could, however, reflect upon the distribution of foraminifera in rocks, and he remarked how little indication this gave of their distribution in life. He wondered, given the data they possessed, how conodont workers could deduce an open-water swimming lifestyle and distinguish it from an animal that lived on the seafloor: “I conclude conodonts were some strange animals but don't venture a guess as to where they lived.”
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