The Great Fossil Enigma (10 page)

Fired up by Gunnell's discovery of conodonts in the neighborhood of Columbia, his colleagues, Ted Branson and “Doc” Mehl, hatched a plan to reveal the stratigraphic utility of the conodont completely. They were to do what Gunnell had began to do but on a grand scale. Both were former students of Samuel Wendell Williston, who himself was a former assistant of dinosaur addict Marsh. Williston had risen to a position of distinction as a vertebrate paleontologist, and Branson had followed him from Kansas to Chicago in order to continue his studies. The first to arrive in Missouri, Branson had orchestrated a renaissance in the Geology Department's fortunes. Ambitious, and still known as a fish paleontologist, the conodont fish must have come to him as something of a revelation. No other fish fossils held this kind of stratigraphic potential. Branson's collaborator, Maurice Mehl, had as a young man teaching in Oklahoma been active in the founding of the
AAPG.
They made a good team. Branson was a man of ambition and strategy, while Mehl was regarded as an exemplary scientist.
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Their extraordinary conodont odyssey started in 1930, when the two men, with the help of their students, began an assault on the Missouri strata. They published as they went, mapping a geological landscape strewn with the teeth of thousands of corpses and fundamentally altering the animal and its utility. “We discover new conodont localities and horizons nearly every week,” they reported in 1933.
²⁴
Their data began to accumulate so rapidly that they, rather remarkably, acquired permission to fill all four issues of the university's research journal,
University of Missouri Studies
, with conodonts. At 349 pages in length and published between June 1933 and October 1934 under the title
Conodont Studies
, this was the first book-length treatment of these fossils.

Like Ulrich and Bassler, Branson and Mehl believed conodonts were the teeth of more than one group of primitive fish. It was the finding of bony material attached to some conodonts around this time that convinced them that this was the case, not the weak arguments that had come from the National Museum. They also differed from the Washington men on one other important point: They believed “the teeth in some species were arranged shark-like with two or more kinds in the same mouth.” But, ever the utilitarians, they recognized that the “likelihood of finding the teeth in their original associations is remote.” They used this to justify giving each kind of tooth its own species name, and in doing so they included the leaf-like forms Ulrich and Bassler had considered dermal plates. These were now thought to be “crushing teeth” and were to become particularly important. While praising the “epoch-making contributions” of Ulrich and Bassler, they thought the Washington classification premature and refrained from using it. Branson and Mehl were their own men and were determined to forge their own way. They saw conodont studies as a blank slate and made it their mission to fill it. They wished to create a new research field and place themselves at the head of it.

They realized that this would involve both evangelism and education and so began
Conodont Studies
with a “how to do it” guide. It gave assurances to those who doubted they would be able to find what were still largely unknown fossils. Branson and Mehl encouraged these novices to exploit plastic and sandy clays, suggesting that they were often more productive than many shales. They also implied that limestones were often devoid of conodonts, so making their investigation unattractive. Instead, readers were advised to adopt mass-processing techniques that involved boiling samples of sediment, sieving the results, and then separating fossils from the remaining sediment on the basis of their differing densities using heavy liquids, before finally picking over the resulting residue to extract the fossils. This, they claimed, was far more reliable than picking individual conodonts off bedding planes by hand. “Starting with a meagre knowledge of general micropaleontological technique” and unable to draw upon the technical expertise of “industrial organizations” (oil companies), who saw such information as commercially sensitive, they pulled together an arsenal of methods from their own innovations and borrowings. Among these was the innovative use of stereoscopic photography to study the fossils. They even went so far as to publish stereoscopic images, thus enabling their readers to see the fossils in 3D and better understand their complexity.

Branson and Mehl's optimism for these new fossils was, however, overshadowed by one great fear: contamination. They worried that their samples might be corrupted by splashes from boiling pots and residues left on sieves. But with care they knew they could avoid these problems. They were rather more concerned about natural contamination resulting from older rocks and fossils being eroded and redeposited as younger rocks, and so mixing together conodonts belonging to different periods. They also imagined younger deposits containing conodonts penetrating cavities in older rocks, much as Moore's Triassic mammals had fallen into fissures in the older Carboniferous Limestone. What they did not consider was that their minds could also become contaminated as a result of this obsession. It affected their ability to see. An unexpected conodont was, for them, always an error and never simply a rarity. But perhaps they did not have the luxury to think otherwise in a science so new.

Branson and Mehl's “how to do it” guide was followed by papers discussing rocks ranging in age from the Lower Ordovician to the Lower Mississippian. In these, the two men demonstrated how conodonts could be used to solve existing stratigraphic problems. The Ordovician Harding Sandstone, for example, was problematic because it held Ordovician invertebrate fossils and fish fossils that looked rather Devonian. The conodonts alone proved that this sandstone could be correlated with the Middle Ordovician Joachim of Missouri. The fish were merely deceptive. The conodonts were, in contrast, quite distinctive: dull and amber colored, “a very primitive group” that possessed what is “best described as ‘fibrous' structure” that splits lengthwise. They seemed to be fused to parts of the animal's jaw.

In the Lower Ordovician Jefferson Formation of Missouri, they found their oldest conodonts. They were simple, diverse, and distinctive, and they offered the possibility of correlating this rock for the first time. An examination of the Silurian Bainbridge Formation of Missouri produced rather different results. Here they were pushed to find any conodonts at all, but when they did they were a predictable mix of “typical Ordovician genera” and “obvious forerunners of typical Devonian and Mississippian genera.” Although these rocks were positioned between the Ordovician and Devonian, they could not connect these two groups of conodont fossils. Indeed, their difficulties in finding conodonts suggested to them that the Silurian was a low point in their history.

As they worked their way through the stratigraphic column, a more comprehensive picture of changing conodont faunas began to emerge in their minds and it became possible to guess the relative age of the strata on this basis. Locating rocks of equivalent age was not, however, as easy as might be imagined. The geological map of America, which can so easily be painted in large blocks of uniform color, conceals a complex, three-dimensional patchwork of rocks. It was from the pieces of this jigsaw that Branson and Mehl extracted their fossils and thus began to solve the puzzle of their age relationships. It was to their advantage that they treated their subject abstractly, as by removing their samples to the laboratory, they also removed themselves from the problems and complexities of the field. It simply became a matter of matching fossils at different sites. This also helped them to imagine the conodont fossils as an evolving continuum of forms and to guess the form of those conodonts that occupied gaps in their knowledge. They became connoisseurs of their fossils, and this gave them an ability to predict.

Before long, Branson and Mehl's climb up the stratigraphic ladder led them to consider those conodonts that marked the division between the Devonian and Mississippian – those contentious rocks Ulrich and Bassler had claimed to have tamed using conodonts. To aid their interpretations, Branson visited Hinde's type specimens at the British Museum in London. With a lack of empathy for a science still in its early days, Branson was rather dismissive of Hinde's achievement: “He spent twenty days in making the study and it was far from thorough in many respects.” Hinde's material was embedded in matrix, and for this reason Branson considered it imperfect, but it had been supplemented by specimens from Bryant. Branson also had some five hundred specimens of his own from Eighteen-mile Creek, which his son Carl had collected. Armed with this material, Branson and Mehl now entered this contentious terrain.

Their study, and the whole of the third issue of
Conodont Studies
, published in June 1934, concerned the Grassy Creek Shale of Missouri. Branson and Mehl's conodonts correlated it with the Chattanooga, the low Huron of Ohio, the Portage, the Hardin, and the Woodford; across them all there was a fairly consistent and distinctive fauna very much like that Bryant had described for the Genesee, which they took to mean that all these rocks were Upper Devonian. Ulrich and Bassler had claimed the Chattanooga and Hardin as undoubted Lower Mississippian precisely because they had not found Genesee or Portage conodonts. Branson and Mehl, however, drew upon their superior connoisseurship to claim that the faunas found in these different rocks were more closely related to each other than to those of undoubted Middle Devonian or Mississippian rocks. Indeed, they felt that distinctive faunas marked the Devonian-Mississippian boundary and these were not those claimed by Ulrich and Bassler. They also pointed out that Ulrich had foolishly dismissed the evidence of Devonian fish fossils. Ulrich's blinkers were now fully exposed, his godlike command of nature a matter of self-delusion.

Branson and Mehl's new faunal criteria boiled down to just six seemingly diagnostic groups of conodonts: The
“Polygnathus-like
genera,
Polylophodonta, Ancyrodella, Ancyrognathus
, and
Palmatolepis”
were restricted to the Upper Devonian and were only ever found in the Mississippian as contamination. They were replaced in these latter rocks by
Pseudopolygnathus
and
Siphonognathus.
All of these kinds of conodont would become known as “platforms.” Ironically, Ulrich and Bassler had dismissed them as being “dermal plates,” not conodonts. Now they were the most important conodonts of them all.

Branson and Mehl were in awe of the Grassy Creek conodonts, which were “in a highly plastic stage of their development.” The distinctive forms of major groups seemed to merge seamlessly one into another. Some genera, such as
Polygnathus
, were so variable that species could not be distinguished. Small forms could not be related to larger ones. The sheer variety and blending of form was perplexing and yet marvelous. And alongside these remarkable forms were other conodonts that seemed to belong to an earlier era. Branson and Mehl thought they must be contamination and they established a principle to guard against it: “It is the new elements that determine the age.”
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Old ones, they presumed, may result from erosion and redeposition.

As the final issue of
Conodont Studies
was packaged up for the presses, Branson and Mehl must have realized the enormity of what they had achieved. They, rather than Ulrich and Bassler, had laid the bedrock for a new science, and across the American landscape they had left markers others could now use to locate the age of their own rocks using conodonts. Ulrich and Bassler may have asserted the utility of these new fossils, but in doing so they merely echoed Kindle's call. The proof of the method had not been theirs; they had merely stated what they thought they knew. The proof belonged to Branson and Mehl, who now said it was only necessary to identify a few kinds of conodonts in order to resolve the problem of the black shales. As a consequence of this work, in 1935, Stauffer felt it was possible to say that “Conodonts in Paleozoic sediments assume much of the importance of the Foraminifera in later sediments.”
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