Featuring specimens from Bohemia to Newfoundland, California to the Tucson Gem and Mineral Show, and Wales to the Anti-Atlas Mountains of Morocco, Levi-Setti’s magnificent book reanimates these “butterflies of the seas” in 235 astonishing full-color photographs. All original, Levi-Setti’s images serve as the jumping-off point for tales of his global quests in search of these highly sought-after fossils; for discussions of their mineralogical origins, as revealed by their color; and for unraveling the role of the now-extinct trilobites in our planetary history.
Sure to enthrall paleontologists with its scientific insights and amateur enthusiasts with its beautiful and informative images, The Trilobite Book combines the best of science, technology, aesthetics, and personal adventure. It will inspire new collectors for eras to come.
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About the Author
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The Trilobite Book
A Visual Journey
By Riccardo Levi-Setti
The University of Chicago PressCopyright © 2014 The University of Chicago
All rights reserved.
INTRODUCTION: WHY COLOR?
As we split open a slab of shale, especially if it is of Cambrian age, trilobites often appear in brilliant shades of ochre, against a gray-greenish background, the color of the matrix encasing them. The color of the trilobite shell, or carapace, has little to do with the original color of the living trilobite. It is the result of chemical processes, such as mineralization, which took place after the burial and decay of the dead animal or its molting exuviae. These processes are called diagenesis and are part of a broader set of burial events that depend on the environment and fall under the comprehensive name of taphonomy. Taphonomy involves the nature of the minerals making up the shale and of those dissolved in the surrounding water or infiltrated after burial and fossilization. And yet, the color that our vision perceives has an emotional impact that makes our "treasure hunt" for trilobites both attractive and addictive.
Unfortunately, the rigor of the scientific paleontological literature has predominantly denied such emotional responses by erasing any trace of color with whitening coatings, which reduce the graphical reproduction of the subject matter to black-and-white photography. However, there is a reason for the whitening process: the aerosols used for the whitening carry an electrical charge that makes the coating stick preferentially to the tips of protruding details, thus enhancing somewhat the resulting informative three-dimensional contrast. Such whitening has been the fate of many images presented in my earlier trilobite books.
The rise of digital photography and the fact that color printing is now more affordable make it possible to exploit to its fullest the splendid complexity of human vision, which, with its trichromatic sensitivity, unique among primates, connects directly to the emotional response that color images may elicit as well as to artistic expression. Is this of added value over black-and-white images when looking at trilobites? It is my contention that, indeed, color images of trilobites convey more information about the fine structure of the object, such as that enhanced by aerosol whitening, than is usually appreciated. Under illumination of a color reproduction similar to that used in taking the picture (e.g., daylight or halogen lighting,), the response of the eye retina contains a subtle contribution from a phenomenon called chromostereopsis. The latter is an optical phenomenon whereby different colors may elicit different depth perceptions. Much has been discussed in the literature in regard to this phenomenon and how the brain processes the signals from the retina in regard to color processing hand in hand with the perception of form and boundaries. The net result is that color images seem to stand out with some illusion of relief. (An excellent and updated summary of this visual phenomenon can be found on the web under "Chromostereopsis" in Wikipedia, The Free Encyclopedia.)
My input on this issue is a comparison I made between black-and-white images of trilobites whitened with white aerosols of magnesium oxide (the old trick to enhance 3-D contrast mentioned above) and color images of the same prior to whitening (an example of this comparison is shown in plate 1). This comparison showed clearly that the structural information delivered by both images is essentially identical, thus confirming that the color image does provide the relief evidence sought by paleontologists for publication. On this ground, to publish my trilobite pictures in color has more to offer than just the entertainment of browsing through a coffee-table book.
Now I must turn to the choices I made about which trilobite images to include and which of their geographic origins to highlight. On both grounds, my choices were greatly biased. As to the choice of depositional location, this was dictated by preconceived notions of accessibility, renown, and sometimes also by exotic appeal. A certain predilection for the most ancient geological settings, the Lower and Middle Cambrian, will transpire here—a predilection perhaps fostered by my encounters with my mentor, the late Franco Rasetti, who regarded Cambrian trilobites as the most rewarding of his attention. However, the principal bias results from my choice of illustrating complete, fully articulated trilobite specimens. Complete specimens are a rare occurrence in the fossil record of trilobites, which restricts greatly the taphonomy of their burial, which, in turn, is responsible for their ultimate appearance, inclusive of their color. Complete outstretched trilobites, with all sutures intact, indicate sudden burial of living individuals in a tranquil environment, at some depth in the sea, remote from the disturbance of wave motion. Such episodes of sudden burial are known to occur as a result of gentle but massive deposition of silt in suspension in so-called turbidity waves, the result of surface storms and sometimes volcanic ash fallout. The sediments often reveal a cyclic or rhythmic alternating repetition of mineral content, as documented, for example, in the layers of the Manuels River Formation of Conception Bay, Newfoundland—which I studied long ago with my colleague Jan Bergström of Sweden. After the death of a trilobite, several pathways lead to fossilization of the remains, which depend critically on the chemistry of the local environment. With few by now famous exceptions, like the Burgess Shale of British Columbia and the Chengjiang fauna of China, where soft tissues are beautifully preserved, the decay of the biopolymers making up the soft tissues, generally fostered by bacterial action even in anaerobic marine sediments, leaves no trace of internal, nonmineralized structures. Only the trilobite exoskeleton, the carapace, partially mineralized by calcite, often escapes complete dissolution, and this may survive unaltered over geological eras. However, over time, mineralogical alterations, diagenesis, still conspire to modify the chemical nature of the fossilized carapace, leading to a multitude of final appearances, and in particular colors, of the fossil trilobite.
Thus, the brilliant ochre colors frequently encountered in the carapace of trilobites preserved in clay-mineral shales are the result of a three-step taphonomic-di-agenetic process, favored by a marine environment rich in dissolved iron hydroxide and oxygen starved. In the first step, residual organic matter is digested by sulfate-reducing anaerobic bacteria yielding hydrogen sulfide (HS-). In the second step, HS- combines with iron ions (Fe2+) to yield iron sulfide FeS2 (the mineral pyrite, fool's gold). These two steps may occur within a few weeks after burial. The third step, which may occur over millions of years, involves the oxidation of the pyrite to the minerals limonite (FeO2, yellow ochre) and hematite (FeO3, red ochre). Sometimes, the pyrite replacement survives over eons, and we find the trilobites amidst a multitude of pyrite nodules, in particular in carbon-rich black shales.
Particularly striking yellow and red ochre carapace coatings are encountered in the Middle Cambrian Paradoxides of the Manuels River Formation of Newfoundland; Lower and Middle Cambrian, Ordovician, and Devonian of Morocco; the Ordovician of China (see plates 1 and 220); and the Lower Cambrian of California and Nevada. Very attractive coloring is found in the Olenelloid trilobites of the top Lower Cambrian layers at Ruin Wash, in the Chief Range of Nevada. Here the dark trilobite exoskeletons, replaced by chlorite (a clay mineral), are embedded in a wafer-thin medallion or halo of yellowish calcite, and the ensemble is further colored by scattered remnants of iron, sometimes manganese oxides, the result of a multistep taphonomy and diagenesis. This process was studied in detail by my University of Chicago colleague Mark Webster.
A different pathway to preservation of the exoskeletal cuticle, which occurred for the Middle Cambrian trilobites of the Wheeler Shale in Utah's House Range, leads to a black, somewhat shiny color. Here again the prevalent taphonomic environment seems to have prevented the complete bacterial digestion of the non-mineralized components of the cuticle, which were preserved as black kerogenized carbon films. In addition, due to the proximity of abundant calcium carbonate in the sediments, a peculiar growth of laminar calcite developed, extending for a few millimeters on the ventral side of the carapace, in the so-called cone-in-cone habit. These black "padded" trilobites, among them Elrathia kingii and Asaphiscus wheeleri, became the most collectible and sturdy mementos of an excursion to the Wheeler Amphitheater.
There are many other "taphofacies" that may determine the color appearance of the preserved trilobites, ranging from the extreme cases mentioned above to the total absence of color differentiation between the fossil and the sediment matrix. The latter presentation occurs when the entire body of the buried trilobite is dissolved by decay and the resulting cavity is filled by the same minerals making up the sediment. This leads to the presence of an external impression or mold of the original body surface and to an internal impression (steinkern) of the inside surface of the trilobite exoskeleton, if still present. The filling of either impression by sedimentary material forms a cast, which is a replica of the original body. At times, a thin gap is left between internal and external molds in the space that was occupied by the exoskeleton, the last part of the body to be dissolved. This void gap is sometimes encrusted with tiny crystals of calcite or dolomite in calcareous rocks. Color, if any, may result from minerals that may have infiltrated the void gap.
There is a notable exception to all of the above when focusing on the visual system of trilobites, the earliest known in the animal kingdom. Escaping decay and diagenesis, the lenses in the compound eyes of trilobites were made of oriented calcite crystals, already fossils in vivo. Such lenses are generally colorless and often still transparent. As described in detail in my previous trilobite books, some, like those of the Phacopids, had sophisticated and optimized doublet optics that corrected the chromatic aberration of thick spheroidal lenses. When we look at these eyes, we feel as if they were looking at us in their whimsical eternity.CHAPTER 2
The Bohemian Karst, a picturesque region southwest of Prague in the Czech Republic, has been immortalized by the blazing paleontological work of a French engineer, Joachim Barrande, who established himself in Prague in the middle of the 19th century. I first became familiar with his unparalleled scientific observations and descriptions of the trilobites of Bohemia when I perused the introductory volume of his series entitled Système Silurien du Centre de la Bohème among the dusty collections of the old geological library at the University of Chicago. I was struck by the magnificent lithographic plates of his descriptive documentation. And finally, in the mid-1990s, I found myself in the very locales of Barrande's discoveries in Prague and the Bohemian Karst, the latter now referred to as the Barrandian. Barrande's tangible legacy, his trilobite collection, is displayed at Prague's National Museum, where I spent many enraptured hours.
My visit to some of the historical Barrandian trilobite localities was greatly helped by the generous assistance of several scientists of the Geological Institute and the Czech Geological Survey. Among them, Petr Storch, Petr Budil, and the late Ivo Chlupác. In addition, Vratislav Kordule, an enthusiastic and knowledgeable amateur with an impressive trilobite collection and publication record, joined my quest on several occasions.
After absorbing the initial wonderment at the fairy-tale views of the Staré Mesto, Prague's Old Town, and becoming less inhibited at driving through the local traffic, I ventured toward my first field trip through the Bohemian Karst, kindly guided by Petr Storch. We exited a comfortable expressway at Beroun, and our first stop was Lodenice, where, climbing through a wooded slope, we reached the remnant of a famous Middle Silurian exposure, which in the past yielded the delightful Odontopleura and Miraspis trilobites shown in my previous books. These specimens were on loan from the Harvard Museum of Comparative Zoology and were part of the Agassiz Collection, acquired in the 19th century from a Bohemian source. Because they are irreplaceable, they will appear once more here, this time in color. What was left of the original excavations was only a thick layer of detritus, hiding the bedrock layers, and only a few small, yet beautiful, specimens of Aulacopleura could be obtained by splitting leftover chips.
Our trip continued, through attractive old villages and idyllic vistas, toward Jince, another historical locality noted for its Middle Cambrian Paradoxides beds. Above the Jince cemetery, a path through wildflower meadows brought us to a prolific Paradoxides gracilis locality, where I could extract a number of well-preserved exuviae. For me, it was a dream come true, as if Barrande's beautiful lithographs had come back to tangible reality in my hands. Somewhat further, in a pine forest, a quarry still yielded slabs containing assemblages of Ellipsocephalus hoffi, another abundant Middle Cambrian trilobite.
Appeased with the above introduction to the Barrandian, I was kindly introduced by Petr Storch to the scientists at the Czech Geological Survey (CGS) in Prague, located in an imposing building at the foot of the steep climb toward the Prague Castle and St. Vitus Cathedral. This building formerly housed a hospital retreat. After Petr Budil showed me several trilobite collections, he brought me to see the CGS library. To my surprise, I found myself on a balcony perched on the wall of a chapel adorned with beautiful frescos, remindful of the Sistine Chapel of the Vatican, overlooking a floor densely packed with book stacks, which had replaced the original pews. After absorbing this unexpected view, I was asked by Petr Budil if I wished to go for a quick trilobite hunt, another unexpected surprise, and he provided me with a geological hammer. I followed him for a short walk around the building, and found myself on a steep forest incline jutting on a rocky exposure, and we both started rummaging through the underlying detritus. Believe it or not, we were finding exuviae of Ordovician Trinucleid trilobites with pitted wide fringes in the middle of Prague!
The memories of my encounters at the CGS do not stop at this adventure. In a subsequent visit, accompanied by my colleague and longtime friend Mark Utlaut, which took place on the occasion of my 69th birthday, we were summoned to the office of the CGS director, Zdenek Kukal, together with Petr Budil and Ivo Chlupak, as well as several other CGS researchers. An imposing grand piano was part of a sumptuous decor. After the initial salutations, the director sat at the piano, and with his accompaniment, everybody erupted in a festive "Happy Birthday to You." It was an emotional moment.
My exploration of the Barrandian was further broadened with the generous help of Ivo Chlupak, who brought me and Mark Utlaut above Rejkovice on the way to Jince, up the mountain to a secluded exposure rich in Paradoxides gracilis, inclusive of several juvenile specimens, as well as Conocoryphe sulzeri. In a later comprehensive tour, we stopped at Skryje, where an imposing bronze likeness of Joachim Barrande commemorates his discoveries in the region, and went to dig on a nearby steep ravine where bright-yellow exuviae of Hydrocephalus carens could still be extracted from the exposed shale bedrock. We continued to Tyrovice, where another ravine yielded a collection of the remnants of more Middle Cambrian trilobites.
The next experience brought us to Pribram, where we met with Vratislav Kordule, who guided me to several further localities. Vratislav Kordule was instrumental in obtaining for me, Mark Utlaut, and a Milanese friend, Bruno Corti, permission from the local environmental protection authority to visit and collect at protected classical localities. In a memorable outing, an agent of the environmental protection authority guided us to a famous, now-hidden excavation at Vinice, at the periphery of Jince, on a densely forested right bank of the Litavska River. We were struck by the demure behavior of our guide, a burly, mustachioed, authoritative young man with a gentle touch, who kept checking wildflowers for evidence of parasites, while we traipsed through meadows leading to the river. After a barefoot crossing of the Litavska, there we were, next to a wall of black rock that most likely yielded some of Barrande's discoveries. The rock wall was not as impervious as it looked, and sizeable blocks could be eased out for further splitting. Soon we augmented the underlying heap of prior chippings, amidst exclamations of success in finding shining bodies of Paradoxides gracilis and Conocoryphe sulzeri. The black sheen (probably due to surface diagenesis of the carapace into hematite) against the black matrix did represent a later challenge to my photography.
Excerpted from The Trilobite Book by Riccardo Levi-Setti. Copyright © 2014 The University of Chicago. Excerpted by permission of The University of Chicago Press.
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Table of ContentsPreface
1 Introduction: Why Color?
2.2 Morocco Cambrian Ordovician Devonian
2.3 Western North America
Cambrian Ordovician Silurian Devonian
2.4 Eastern Newfoundland
2.5 Great Britain
2.7 Tucson Gem and Mineral Show
Reputable Originals of Moroccan Trilobite Assemblies and Single Specimens Moroccan Trilobite Reproductions (Fakes) Trilobites from Other Reputable Worldwide Sources
3 The Eyes of Trilobites Acknowledgments References Index to Genera