The Great Fossil Enigma (11 page)

But not everyone was enamored with the Missouri conodont factory. Ulrich and Bassler's disciple, Chalmer Cooper, must have felt his own work had been devalued by Branson and Mehl's proof that the Washington men had been wrong. In a review of
Conodont Studies
, Cooper found every possible excuse to complain: about their preference for mass processing, their re-identifications, their use of broken specimens so “valueless to other workers,” and their splitting of fossils into narrowly defined species and genera “to a degree that makes it difficult to recognize them.”
²⁷

At Indiana University in Bloomington, the young John Huddle also grew concerned about the new Missouri orthodoxy. While Branson and Mehl were wrestling with the Grassy Creek, Huddle had been completing his doctoral thesis on the New Albany Shale of Indiana.
²⁸
Like the Grassy Creek, this was a disputed sequence. Most thought it entirely Devonian, but in 1911, Ulrich had suggested that it might be part Mississippian. Bassler had then supported this view.

Huddle had entered this disputed territory quite by accident, having been shown some Devonian brachiopods from near the top of the shale. This seemed to challenge Ulrich and Bassler's claim. It was while Huddle was investigating the source of these fossils that he came across some conodonts that he knew from Ulrich and Bassler's recent work might resolve matters. He began his fieldwork in the summer of 1932 and was soon corresponding with Bryant and Cooper. This “brownish to black in color, more or less massive, hard, brittle” shale becomes fissile when weathered and is easily split, giving it its local name of “black slate.” But Huddle found it resisted bulk processing. It was a technique Huddle distrusted anyway, having found that it destroyed the most delicate species. Instead, he painstakingly extracted or revealed his fossils using needles, in the process producing one of the most thorough investigations of those early years. Nevertheless, Huddle felt disappointed with his results. Of the 158 species he described, only 37 had been found previously. Only they would offer any chance of correlating these rocks with others, thus proving their age. He had no contact with Branson and Mehl and knew nothing of their Grassy Creek work. Huddle tentatively concluded that the lower part of the shale seemed to correlate with the Devonian Genesee. Those conodonts from the middle were most like those of the Hardin and Chattanooga but were also associated with a few Portage and Genesee species. These were found well below the Devonian brachiopods and proved that Ulrich and Bassler's supposedly distinctive Chattanooga species were not Mississippian. Conodonts from the upper part of the rock included the most new species, and while he found Chattanooga and Hardin species among them he could not say that the Mississippian had been reached. He did, however, find a shark's tooth, which Bryant suggested might indicate a possible Mississippian age. Huddle had independently and simultaneously reached the same conclusions as Branson and Mehl: Ulrich and Bassler were wrong. Cooper, who was now at the Walker Museum in Chicago and working on his own doctorate degree, remained oblivious to these new discoveries and continued to work on the Oklahoma rocks in the belief that Ulrich and Bassler were right.
²⁹

Branson and Mehl soon consolidated the position of their “index genera.”
³⁰
The “index Devonian genera” were now
Icriodus, Palmatolepis, Ancyrognathus, Polylophodonta
and
Ancyrodella.
The “index Mississippian genera” were
Pseudopolygnathus, Siphonognathus, Pinacodus
and
Solenognathus.
Such clear presence-absence criteria were a stratigraphic ideal, and among them there was one particularly widespread Devonian form,
Icriodus
, the various species of which also permitted the division of the Middle and Upper Devonian. There was nothing like it in the Mississippian and it appeared to have no descendants. There was no ambiguity about this fossil, and to prove their point they revisited some disputed and imperfectly understood black shales, including those studied by Cooper and Huddle (they did not mention Cooper by name, perhaps wishing to avoid a personal dispute). They confirmed that the upper beds of the New Albany Shale were indeed Mississippian and moved all Cooper's Mississippian rocks into the Devonian. Now it seemed they were able to resolve the black shales problem on the basis of a single type of conodont.

Remarkably, this advanced state of knowledge was achieved in 1938. But by then even Branson and Mehl knew that progress had been at the expense of a chaotic proliferation of names. Unrestrained by any biological paradigm, workers had attempted to locate as many distinctive species as possible. Now a new rationalism broke out, led by the soft-spoken and self-contained Will Hass. Hass had moved to the National Museum in 1935 to work with the
USGS
. Here Girty trained him in the art of micropaleontology and Roundy gently directed him toward the study of conodonts. In 1938, Hass coauthored an account of some Montana conodonts, calling on Cooper to help with his identifications. In all Hass identified forty-six new species. Here, a little naïvely, he took a swipe at Branson and Mehl's index genera – a division Stauffer had recently and unknowingly confirmed. Hass claimed that Branson and Mehl's Mississippian
Siphonognathus
also occurred in the Devonian, while their Devonian
Palmatolepis
could be found with two of their Mississippian indicators. Branson and Mehl told Hass that he must have used contaminated samples, but Hass thought the associations a “curious coincidence.”
³¹

In the following year, Cooper was bedazzled by 256 remarkably preserved conodont species in an eleven-inch-thick Mississippian (so he believed) shale, “the most striking assemblage of these forms encountered in my experience,” he noted. “Some species are so preserved that they are almost transparent and appear as though constructed of cellophane, giving the appearance of artificiality.” As we shall see in the
next chapter
, this extraordinary material permitted Hass to undertake internal investigations of conodont fossils and reveal the true extent of the name proliferation. It fundamentally altered Hass's outlook, and in 1943 he returned to his Montana specimens and decided that he had not found a single new species.
³²

Two years later, Branson and Mehl began to talk defensively about the actions they had taken. Critics were all too ready to forget the wilderness out of which the two men had led the conodont. Branson and Mehl argued that without names there could be no progress, even if the full history of a form remained unknown at the time. Each named species then existed as a discrete entity in time and space. It possessed no future, no past, and no geography. It was from such flags in the ground that science built its knowledge, and inevitably it would then need to make corrections. It was to be expected that, as knowledge matured, a period of name inflation would be followed by deflation as they realized that the same fossil found in different rocks had been given different names.
³³

The other source of error was contamination, which Branson and Mehl wrote about at length in 1941, using examples from Huddle, Cooper, and Stauffer. Detection, they said, in a rather circular argument, relied upon “knowledge of conodont successions rather than in field evidences.” There were, they said, such self-evident reports of mixing as the discovery of unworn conodonts in the Triassic of Germany that the problem could not be denied. Branson's son, Carl, had been one of the first to find Permian conodonts in the United States and fancied he saw the “senile specializations of a rapidly declining group.”
³⁴
Branson and Mehl thought the German fossils looked like those found in the American Pennsylvanian and Permian and must therefore result from contamination of the overlying Triassic rocks. To have persisted into the Triassic, these animals would have survived the great extinction that took place at the end of the Permian and crossed from the Paleozoic world into the Mesozoic virtually unchanged. The idea seemed impossible.

At the heart of the contamination argument was a growing feeling, which had certainly taken hold by 1938, that the conodont fossils showed progressive advancement over time. One could guess the age of these fossils simply from how advanced they seemed. It was a powerful idea. One that would prove irresistible to later generations and that, in this era, caught the imagination of Bill Furnish, a young doctorate student at the University of Iowa. Here a hard-working cephalopod paleontologist, A. K. Miller, was pulling together the beginnings of one of the most influential conodont research schools of the mid-twentieth century. To achieve this, Miller, a former student of Ted Branson, drew upon the influence and encouragement of his Missouri and Minnesota neighbors. Furnish was the first product of this new school and was already examining some of the oldest faunas and giving serious consideration to classification. He concluded that the fossil record indicated “beyond reasonable doubt that compound teeth were derived by several distinct lines of evolution.”
³⁵
In other words, and contrary to what most believed, there was no single evolutionary progression; development had followed a number of parallel paths. This meant that Ulrich and Bassler's classification, which had grouped together “teeth” on the basis of superficial resemblance, was no more reliable than Pander's. These “lines of evolution” were, Furnish believed, open to interrogation and would permit a truer classification. Only by this means could the science move beyond the connoisseurship of abstract forms. But in order to achieve this, further action was needed to tackle the proliferation of names.

Resolution of this problem required a curatorial mind – someone who could collate, distinguish, and arrange. Fortunately such a mind was possessed by Mehl's doctorate student and protégé, Sam Ellison. Ellison sought to bring order to the Pennsylvanian.
³⁶
Reviewing thousands of specimens, when his predecessors Gunnell, Stauffer, and Plummer possessed only a few hundred, he could confirm that minute differences of form were an irrelevance. With this he began a mass extermination of species. Whole lists of names were now vaporized as one name came to define what had previously required a dozen or more. This was in 1941.

Delighted with his results, Ellison now turned his attention to the whole of the Paleozoic. In 1944, his former mentors, Branson and Mehl, had summarized the state of knowledge in Shimer and Shrock's definitive
Index Fossils of North America.
³⁷
Frequently cited, the book nevertheless lacked the clarity and security of argument that Ellison, then at Stanolind Oil and Gas in Midland, Texas, would find just two years later. Extracting the stratigraphic ranges of some fifteen hundred species mentioned in more than 180 papers, Ellison mapped the ranges of those genera he considered valid on charts ranging from the Lower Ordovician to the Upper Permian. The result had a clarity and logic never before seen in conodont studies. In this respect it was much like earlier pictorial arguments. It spoke directly of the wonderful utility of these fossils and their seemingly distinctive forms. It seemed to offer an almost perfect portrayal of their progressive evolution: “The fibrous and non-fibrous conodonts develop in form from simple cones through the bladed and bar stages to the platform types. The simple cones give rise to blades and bars by addition of denticles to the basic cone. The basic cone becomes the apical or largest denticle. Bladed and bar forms give rise to platforms by a process of lateral thickening of the blade or bar…. Such excellent examples of evolution impress the idea that the conodonts are among the best fossils for family tree studies.”
³⁸
Here was the key to a new utilitarian future: abstract things on an evolutionary journey that left behind the footprints of their development.

2.1.
The solution to the black shales dispute. Ellison's mapping of the stratigraphic ranges of conodont fossils demonstrated the fossils' utility at a time when most paleontologists knew little about them. This part of the chart, illustrating Branson and Mehl's index genera, showed that conodonts permitted the detection of boundary between the Devonian and the Mississippian. From S. P. Ellison,
Bulletin of the American Association of Petroleum Geologists
30 (1946).
AAPG
©1946, reprinted by permission of the
AAP G
, whose permission is required for further use.