The Great Fossil Enigma (33 page)

The initial optimism that had accompanied the rise of paleoecology had begun to wane. One major textbook noted, “Paleoecology, which during the 1960s occupied center stage in the paleontologic theatre has matured as a subdiscipline but has also lost some of its luster; appreciation of the incompleteness of the invertebrate fossil record has led to a general narrowing of goals in the study of ancient marine communities.” Joel Hedgpeth, who had pioneered the field in the 1950s, found ecology undergoing significant change and palaeoecology often in possession of old ideas, unable to keep up.
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In 1978, Gil Klapper and James Barrick also asked whether it really was possible to infer lifestyle from the distribution of conodont fossils in the rocks.
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Reviewing a number of marine animals, they became convinced one could not. Seddon and Sweet's favored chaetognath analogue, for example, did not show simple depth stratification after all but reflected the complexities of temperature and salinity, which actually produced
lateral
variation. Indeed, bottom dwellers and swimmers were capable of leaving the same record. Only the presence of conodonts in black shales, which were devoid of bottom dwellers, strongly suggested a swimming or floating animal of the open sea. They concluded that since conodonts seemed to be confined to the continental shelf, it would be better to draw on modern analogues to visualize the ways in which they might have been distributed in life. These reflected changes in key environmental variables in relation to the coast (
figure 9.1f
). Like many living animals, conodonts had a few specialist species able to survive the difficult conditions of the nearshore; their diversity increased away from the shore. This was another model, but it removed the need for a bottom-dwelling lifestyle yet could still produce the observed lateral changes and overlaps. It also captured that reciprocal relationship between genera, which Weddige and Ziegler, Merrill, and even Rexroad had written about.

9.1.
Modeling the ecology of the animal. Deducting lifestyle from the distribution of fossils in the rocks. The triangles represent the sea in section, showing increasing depth and distance from shore. The patterns represent different genera of conodont animal: (a) Druce saw lateral distribution in his reef limestones; (b) Seddon introduced a one-way depth-controlled filter; (c) Druce adopted Seddon's model but argued that nearshore population densities were higher; (d) Weddige and Ziegler saw water clarity and oxygenation as differentiating
Icriodus (left
) and
Polygnathus (right);
(e) examining other environments, Barnes and Fåhræus saw clear banding of animal communities, suggesting they were bottom dwellers; and (f) reviewing the evidence in 1978, Klapper and Barrick showed that the distribution of marine animals was governed by complex factors and that the record of the rocks could be explained in multiple ways.

There were, then, repeated attempts to adjust the theory to the limitations of the data but no wholesale retreat from a line of enquiry that had certainly delivered results. New data continued to reinforce Bergström and Sweet's provinces. Indeed, provinces became established in other periods, too, but turned out not to be universal. In the Devonian, at least, it was understood that conodonts were probably confined to tropical latitudes. Of these,
Icriodus
returned to favor, finding its own parallel zonation to mirror the one Ziegler had developed using
Palmatolepis.
This work revealed that
Icriodus
had become extinct rather earlier than assumed and that an impostor had evolved from
Pelekysgnathus.
The first
Icriodus
was quite well distributed in the upper, highly illuminated waters of the coastal zone, but its impostor, known as
“Icriodus,”
was more restricted in its distribution.
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A reversal of expectation had taken place. Having believed in universalism, workers increasingly expected environmental control.

 

THROUGH THE 1970S, PALEONTOLOGY ACQUIRED AN
increasingly global outlook as geology as a whole embraced the unifying ideas of plate tectonics. The conodont workers felt this sense of the global even more profoundly as its field of study spread to every corner of the earth. In this period, the living animal became a mobile entity inhabiting clearly defined niches and repeatedly evolving similar anatomies to deal with the return of particular environmental conditions. Progress for the conodont workers, as for most of paleontology, had been logical and incremental. But then two unexpected events forced them to look and think differently, and even to imagine the unimaginable.

The first, which occurred in 1974, resulted in the discovery of unforeseen utility in the conodont fossils' strikingly varied colors. It indicated that even when dead, buried, and fossilized, this remarkable animal could bear witness to changes going on around it. The second event was considerably more dramatic and occurred at a precise moment in 1980: An asteroid came crashing in, turning the paleontological community upside down. No one saw it coming, but no one could ignore it. Scientists from many different fields came together to understand it and its consequences. In that drama, the conodont played a bit part, valued particularly for the manner of its dying. In this period the geological community as a whole entered its most speculative and imaginative phase, and conodont workers, who were never immune to outside influence, soon developed a wonderful facility for thinking fantastic thoughts.

In this chapter we will explore how this thinking continued to shape the animal in its world. In the
next chapter
we will begin the final phase of this book and start to follow the scientists as they close in on the animal itself.

In a science so attuned to shades of brown and gray, the conodont's yellows, oranges and blacks, when combined with their beautiful translucence and miniscule but finely detailed form, had an aesthetic effect on all who studied them. These facets contributed to the objects' attractiveness and amazingly – when you think about it – encouraged so many people to place these objects at the center of their lives. Pander had, at the outset, thought the color of conodonts both remarkable and important, but no one made anything of it until the U.S. Geological Survey's Anita Epstein, later Anita Harris, did so in the late 1960s.

Epstein – a product of Sweet's “conodont factory” – owed rather more of her character to her origins in the tenements of the Williamsburg neighborhood of Brooklyn. The daughter of an immigrant Russian Jew, she saw geology as a means of escape from the poverty of New York. Tough and determined, she talked geology as one who lives and breathes it. “She is one sharp cookie, as we say,” Sweet remarked. “She has a photographic memory and is as hard a worker as anyone I know.” In his road trip with Epstein, described in his book
In Suspect Terrain
, published in 1982, John McPhee introduced the conodont, the subject of Epstein's great innovation, to his general readers using descriptive prose that seemed to be haunted by the ghost of Charles Moore: “At a hundred magnifications, some of them looked like wolf jaws, others like shark teeth, arrow heads, bits of serrated lizard spine – not unpleasing to the eye, with an asymmetrical, objet-trouvé appeal.”
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In 1967, Epstein had noticed that there was a correlation between the color of the conodont fossils she was finding and the depth to which they had been buried. By buried, here, I mean geological burial beneath perhaps hundreds or thousands of meters of rock. As the conodonts showed a color range much like that seen in butter heated in a pan, she imagined that the color of the fossils might be used as an indicator of the maximum temperature experienced by the rocks in which they were found, as temperatures underground increase with depth. However, finding no encouragement at the Survey, she quickly dropped the idea. It was a chance meeting and conversation with Leonard Harris (later to be her second husband), six years later, that re-awoke this thought with something of a start. An oil geologist, he told her that oil companies had been using color changes in pollen and spores in this way for many years. The color range was exactly like that Epstein had seen in her conodonts. This was a moment of revelation. But when she told him that conodonts performed the same trick, it was he who was surprised.

Epstein's discovery meant that this abundant and extraordinarily ancient time marker might possess a wholly new dimension of meaning. In an era of oil shortages, if Epstein's hunch proved correct, the conodont would offer an easy means to locate rocks that might hold oil. Oil forms from marine algae at depth in rocks exposed to certain temperatures. If the temperature is too low, oil does not form; if it is too high, oil is lost. Epstein now spent much of her spare time experimenting on relatively unaltered conodonts from Kentucky supplied to her by Stig Bergström. These were the same conodonts he and Sweet had used in their groundbreaking 1966 paper. Epstein heated the conodonts to temperatures from three hundred to six hundred degrees Celsius over a period of ten to fifty days, removing samples at regular intervals to record their color. She found that the fossils' color altered in a “progressive, cumulative, and irreversible”
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way and was the direct product of time and temperature. Reassuringly, the colors produced in those she had cooked were exactly like those found in the field.

Working with her husband, Jack, and Harris, she extrapolated this experimental data so that the relationship between temperature and color could be understood on the scale of geological time. Now the color of the conodonts could be used to indicate the burial history of the rocks that contained them. Announced to the world in 1974, with full results published in 1977, this discovery changed her life and expanded the meaning and importance of the fossil considerably: “This study increases their use from index fossils to metamorphic indexes and demonstrates their application to geothermometry, metamorphism, structural geology, and for assessing oil and gas potential.” The scale of color change became known as the “color alteration index,” or
CAI
, and it drew in new kinds of conodont workers. This was yet another case of these tiny things participating in science on the grand scale and, in this case, in science that was really useful to everyday concerns. A fascinating episode in and of itself, which opens up an entirely new story arc, we must, however, leave it here because it tells us nothing of the animal itself.
CAI
records only aspects of the postmortem existence of the animal. We must turn our attention now to the world of the living animal, though in doing so we will primarily concern ourselves with its death.

The 1980 asteroid, or meteorite, that once struck earth and now, in a metaphorical sense, impacted the scientific community was delivered by Nobel laureate physicist Luis Alvarez and his geologist son, Walter, along with chemists Frank Asao and Helen Michel. It arose from work Walter Alvarez had been conducting at the Cretaceous-Tertiary boundary at the ancient town of Gubbio in Umbria, Italy. Measuring the trace element iridium, which is constantly falling to Earth as meteoric dust, he postulated that its degree of dilution in marine sediments would indicate how rapidly the sediment had been deposited. The sedimentary dilution of a constant – such as Merrill's dying and fossilized animals, discussed in the
previous chapter
, or meteoric dust falling to Earth – had long been used to deduce the relative rates at which rocks were laid down. The sediment that interested Alvarez marked the end of the Cretaceous, that remarkable moment when the dinosaurs and many other kinds of animal became extinct. However, it was not dinosaurs that first caused Alvarez to stop and think, but the near extinction of those tiny amoeba-like animals with delicate and intricate shells known as foraminifera. At Gubbio, a centimeter-thick layer of clay divides the extraordinarily different foraminifera of the Cretaceous from those of the overlying Tertiary. Alvarez asked, “Has this mass extinction occurred in a human timescale or a geological one?” In order to answer this question, he needed to know how rapidly the clay had been deposited.
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As it turned out, the iridium performed better than he had hoped, for rather than simply giving Alvarez the rapidity of change, it also gave him a cause. What he found were extraordinarily high amounts of this element (in relative terms at least). After much deliberation, the team felt this could only be explained by a huge meteorite impact. Astronomy, that esoteric science of other worlds too distant to really know, now became central to understanding the history of life on Earth. Newly globalized, geology now found itself a science of planets.

The idea was a “bombshell” that caused an explosion of papers and conferences – and some bizarre theoretical imaginings, including a death star called Nemesis and an equally deadly Planet x. Supportive speculation and doubting cynicism developed in parallel, but increasing amounts and types of data seemed to confirm this radical and seemingly improbable alien visitor.
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The impact on science was so great that it is easy to imagine geologists now talking new talk and thinking thoughts that had never previously crossed their minds. But this was not entirely what happened. Their initial response was to work with what they knew, to marry this new idea with existing data. In this respect the asteroid became a new pair of interpretive spectacles through which to look afresh at old things. These glasses would also encourage geologists to seek out obscure and esoteric work that at one time seemed to make little sense. Perhaps it would do so now. In some cases, yesterday's nonsense and self-indulgence suddenly became prophetic. Some on the edge of the community now found themselves treated as oracles and placed at the center of this new debate.

Otto Walliser was among those who welcomed the meteorite, or rather the change of thinking it brought about. He never found a need for the meteorite itself. It might be recalled that Walliser had played a singular role in establishing the conodont in Silurian stratigraphy in the early 1960s. With no good Silurian sections in West Germany in which to continue these studies, he simply left the field. He had moved to Göttingen, and while he retained an interest in conodonts, he did so no more than in the cephalopods that had first attracted him to the science. Trained by Otto Schindewolf who for a time was the leading light in German paleontology, Walliser had acquired an interest in the global aspects of the science long before the Alvarez meteorite hit. Indeed, back in 1954 and again in 1962, Schindewolf had suggested that cosmic radiation from a supernova could cause catastrophic extinctions of life on Earth. Such extinctions, he said, would be followed by a burst of evolution and diversification among the survivors. Schindewolf claimed that these catastrophic events could be read in the rock record because that record was sometimes complete; there were no gaps in the sequence at those moments of catastrophe. At the time, the idea of mass extinction was too much for many paleontologists. Extraterrestrial causes simply added to a sense that this was mere fantasy. To their eyes, species were lost gradually – as they seemed to be at the present day. Any apparently sudden loss was merely an artifact of missing or eroded strata. Unsurprisingly, then, Schindewolf's views did not find much support, even among those, like Norman Newell, who did much in the 1960s to demonstrate the reality of mass extinctions. Newell had taken a rather different approach and had plotted the diversity of life against time to reveal the truth of these extinctions, though the coarseness of his methods concealed the true prevalence of such events.
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