The landscape of southwestern Wyoming around the ghost town of Fossil is beautiful but harsh; a dry, high mountain desert with cool nights and long, cold winters inhabited by a sparse mountain desert community. But during the early Eocene, more than fifty million years ago, it was a subtropical lake, surrounded by volcanoes and forests and teeming with life. Buried within the sun-baked limestone is spectacular evidence of the lush vegetation and plentiful fauna of the ancient past, a transitional ecosystem giving us clues to how North America recovered from a great extinction event that wiped out dinosaurs and the majority of all species on the planet.
Paleontologists have been conducting excavations at Fossil Butte for more than 150 years, and with The Lost World of Fossil Lake, one of the world’s leading experts on the fossils from this spectacular locality takes readers on a fascinating journey through the history of the discovery and exploration of the site. Deftly mixing incredible color photographs of the remarkable fossils uncovered at the site with an explanation of their evolutionary significance, Grande presents an unprecedented, comprehensive portrait of the site, its treasures, and what we’ve learned from them. Grande presents a broad range of fossilized organisms from Fossil Lake—from single-celled algae to palm trees to crocodiles—and together they make this long-extinct community come to life in all its diversity and splendor. A field guide and atlas round out the book, enabling readers to identify and classify the majority of the known fossils from the site.
Lavishly produced in full color, The Lost World of Fossil Lake is a stunning reminder of the intellectual and physical beauty of scientific investigation—and a breathtaking window onto our planet’s long-lost past.
|Publisher:||University of Chicago Press|
|Product dimensions:||8.30(w) x 10.30(h) x 1.40(d)|
About the Author
Lance Grande has been doing paleontological fieldwork in the Fossil Butte Member of southwestern Wyoming for more than thirty years and is one of the world’s foremost authorities on this amazing locality. He is also a curator at the Field Museum of Natural History, Chicago, where he conducts research on fishes, paleontology, geology, and evolutionary biology. He is the award-winning author of more than one hundred books and scientific articles, including The Lost World of Fossil Lake: Scenes from Deep Time and Gems and Gemstones: Timeless Natural Beauty of the Mineral World, both published by the University of Chicago Press. Gems and Gemstones won the 2009 PROSE Award in Earth Sciences, and in 2012 he received the Robert H. Gibbs Award for an Outstanding Body of Published Work in Systematic Ichthyology. He is a Lecturer at the University of Chicago, and an Adjunct Professor at the University of Illinois. At the University of Chicago he also serves on the Council of the Graham School, and on the Committee on Evolutionary Biology. He is a board member for the Chicago Council on Science and Technology, and serves on the Executive Steering Committee for The Encyclopedia of Life.
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THE LOST WORLD of FOSSIL LAKE
Snapshots from Deep Time
By LANCE GRANDE, John Weinstein
THE UNIVERSITY OF CHICAGO PRESSCopyright © 2013 Lance Grande
All rights reserved.
In the Beginning
Every story must have a beginning, and this one starts in the middle of the Cretaceous period, about 90 million years ago. By that time, rising sea levels had created the great Western Interior Seaway, dividing the North American continent into distinct eastern and western subcontinents that would remain separated for the next 25 million years. This immense marine waterway was 762 meters (2,500 feet) deep and hundreds of miles wide in places. It connected the Arctic Ocean in the north to the Gulf of Mexico in the south, and it served as an impenetrable barrier to the dispersal of most freshwater and terrestrial plants and animals between the eastern and western North American subcontinents (fig. 1). The effects of this long continental division—together with a solid land connection between the western subcontinent and Asia—greatly influenced the early development of the North American fauna and flora. The BIOGEOGRAPHIC influence from Asia was still very strong in the Eocene Green River Formation of western North America (MacGinitie 1969; Grande 1994b).
Time Changes Everything
From the Late Cretaceous into the Early Cenozoic, Earth and its inhabitants went through a severe transformation. A huge impact from the Chicxulub asteroid off the coast of Mexico's Yucatán peninsula caused widespread, massive extinction at the end of the Cretaceous, wiping out an estimated 75 percent of all living species on the planet. The great seaway disappeared due to plummeting sea levels and mountain uplift; and along with it, all pterosaurs, marine reptiles, ammonites, and dinosaurs became extinct, except for a single surviving dinosaurian lineage: birds. The post-Cretaceous world had gone through tremendous change in its physical topography and suffered a profound loss of biodiversity; but now in the Early Cenozoic, Earth's biota was in the process of renewing itself in a different form. The age of mammals arrived on land with a vengeance and overtook the long rule of reptiles. Flowering plants and broad-leafed trees diversified, as did the animals that pollinated and fed on them. Birds and bats were also becoming more diverse and now controlled a sky devoid of pterosaurs. Teleost fishes (the group containing 96 percent of all living fishes today) expanded their dominance in both marine and freshwater environments, and numerous freshwater lake systems formed in the western part of a North American continent no longer divided by a seaway.
One of the most remarkable western lake systems to appear was the Early Cenozoic Green River Lake System (figs. 2 and 3). This great lake complex was comprised of three lakes at its peak; Lake Uinta, Lake Gosiute, and the subject of this book: Fossil Lake. The earliest appearance of this lake system began in the late Paleocene as a result of regional uplift. As the mountains rose over time, the areas between them warped downward into basins that collected runoff from the surrounding highlands. The lake system eventually formed from thousands of years of drainage and runoff and persisted for a very long time (figs. 2 and 3). This was a true great lake system with one of the longest durations of any known lake system on Earth. One of its lakes, Lake Uinta, lasted well over 10 million years. There are no North American lake systems today that have anything close to the maturity reached by the Green River Lake complex. The North American Great Lake System that exists today is only about 10,000 years old.
Dating techniques for the Green River Formation sediments continue to be refined, and time estimates used here represent revisions of previous work (e.g., Grande 1984, 1994b). Most of the dates for the beginning and end of each Green River lake are based on correlations of INDEX FOSSILS AND STRATIGRAPHY rather than ABSOLUTE DATES. Within the Green River Formation, only a few absolute dates (based on radiometric data) have been determined, but one that is well established is for the K-spar tuff bed near the top of the FBM (fig. 4) dated at about 52 million years before present (data repository of Smith et al. 2010). There is still much that needs to be done to definitively date the origin and extinction dates of the three lakes.
Although the Green River Lake System persisted over a period of millions of years, it was not a continuously stable freshwater environment for all of that time. Geological evidence indicates that all three of its lakes went through drying phases in which shorelines fluctuated wildly and salinity concentrations rose to levels lethal to most freshwater fish species. The few species of fishes and other freshwater aquatic organisms that survived such periods must have retreated up the tributaries that fed the lakes in order to survive. Some probably just became extinct, because the aquatic diversity of freshwater fishes achieved within the FBM is never seen again in the Green River Lake System.
The long-buried SEDIMENTARY ROCK left from the Green River Lake System, particularly the Fossil Butte Member of southwestern Wyoming deposited by the middle phase of Fossil Lake, provide a window into the deep past—an unprecedented comprehensive picture of the North American biota transitioning between the Mid-Cretaceous and the present day. This book will focus only on the paleontology of the Fossil Butte Member of the Green River Formation (here abbreviated as the FBM). A few older post-Cretaceous formations (e.g., the Tongue River Formation) as well as older members of the Green River Formation (e.g., the Flagstaff Member) show sporadic occurrences of fossils or an abundance of specific types of fossils (Estes 1976; La Roque 1960), but the FBM provides the earliest comprehensive look at a post-dinosaur community in graphic, visually revealing detail. It provides natural portraits of an entire community, long since extinct. A few younger members within the Green River Formation show great diversity of insect and plant fossils, but they lack the overall biotic diversity known from the FBM.
The Larger Stratigraphic Context: The Relationship of the FBM to the Other 13 Members of the Green River Formation
The source of the FBM, Fossil Lake, was part of a unique PALEOGENE lake system of three lakes that produced the Green River Formation. The great longevity of the Green River Lake System (particularly Lake Uinta) made the Green River Formation one of the largest documented accumulations of lake sediments in the world. This enormous FORMATION extends over an area of more than 65,000 square kilometers (25,000 square miles) and over much of its geographic expanse it is 600 meters (2,000 feet) or more in thickness.
Today the Green River Formation is divided into 14 different subdivisions called MEMBERS (fig. 5). Each of the three lakes that created the formation had a different duration (figs. 2 and 3). Lake Uinta—whose lithified sediments are located in the Uinta Basin of Utah and the Piceance Basin of Colorado—was the largest of the three Green River lakes. It was the first to form and the last to disappear, lasting at least 12 million years, and is today represented by six members. The earliest stage of its history was originally referred to as a separate lake called Lake Flagstaff. Later geologists found that the Lake Flagstaff history was continuously connected with that of Lake Uinta, and thus considered it to be synonymous with Lake Uinta. Fouch (1976) subsequently downgraded the Flagstaff "Formation" to "Member" status within the Green River Formation (e.g., now the Flagstaff Member of the Green River Formation).
Typically, Lake Uinta was LAGOONAL to very shallow LACUSTRINE, represented today by mudstones, sandstones, siltstones, and shales (Baer 1969). The Flagstaff Member of Lake Uinta formed in what is now central Utah during the late Paleocene. Eventually, in the latest part of the Paleocene, Lake Uinta dried up in its southern end while expanding eastward into what is now Uinta Basin in Utah and Piceance Basin in Colorado. At the same time, Lake Gosiute and Fossil Lake were forming in Wyoming. The sedimentary rock left by Lake Uinta represents one of the thickest documented accumulations of lake sediments in the world, with thicknesses greater than 2,100 meters (7,000 feet) in places (Cashion 1967). The shales left by Lake Uinta are rich in fossil fuels, containing an estimated 1 trillion barrels of oil (Pitman, Pierce, and Grundy 1989). Lake Uinta deposits (from youngest to oldest) consist of the Parachute Creek Member, the Garden Gulch Member, the Douglas Creek Member, the Anvil Point Member, the Cow Ridge Member, and the Flagstaff Member (fig. 5). The sedimentary rocks from Lake Uinta do not contain a very diverse vertebrate fauna, and fishes are far less common than in the FBM of Fossil Lake or the Laney Member of Lake Gosiute, but the Lake Uinta deposits contain some of the most productive plant and insect fossil localities within its Parachute Creek Member, near Douglas Pass, Colorado, and Bonanza, Utah (e.g., MacGinitie 1969).
Lake Gosiute, whose LITHIFIED sediments are found in Green River Basin directly east of Fossil Basin, was the second largest of the Green River lakes. Its deposits formed five different members in the Green River Formation (from youngest to oldest): the Laney Member, the Wilkins Peak Member, the Fontanelle Member, the Tipton Shale Member, and the Luman Member (fig. 5). Longer lived than Fossil Lake, but shorter lived than Lake Uinta, Lake Gosiute is thought to have been shallow with a fluctuating shoreline throughout its history. During periods of contraction, the lake often became saline, and the fishes retreated to freshwater tributaries, marshes, and ponds that fringed the lake (Buchheim and Surdam 1981). There were also periods during deposition of the Laney Member Lake Gosiute deposits when the lake was freshwater, indicated by abundant ictalurid catfishes (Ictaluridae) and suckers (Catostomidae), two PRIMARY FRESHWATER FAMILIES of fishes. Ictalurid catfishes and suckers, which are bottom dwellers, are curiously absent from the FBM deposits, probably due either to ecological conditions (Fossil Lake possibly being less hospitable to bottom dwellers than Lake Gosiute) or differing age (the FBM deposits are about 3 million years older than the Laney Member deposits, perhaps indicating that ictalurids and suckers did not penetrate the Green River Lake System until after Fossil Lake had become saline or dried up). The fish assemblage of the 49-million-year-old Lake Gosiute deposits (the Laney Member) was very different from that of the 52-million-year-old Fossil Lake deposits (the FBM) (Grande 1994b, table 2).
The third lake represented by the Green River Formation was Fossil Lake, part of which is the subject of this book. At its peak, Fossil Lake also extended into the northeastern corner of what is now Utah and the southeastern corner of what is now Idaho (fig. 7). This lake has also been referred to as "Unnamed Green River Lake West of Gosiute Lake" by Bradley (1948) and "Fossil Syncline Lake" by McGrew (1975). Fossil Lake is represented in the Green River Formation by three members (from youngest to oldest): the Angelo Member, the Fossil Butte Member, and the Road Hollow Member (Buchheim and Eugster 1998; Buchheim, Cushman, and Biaggi 2012). The Road Hollow Member represents the earliest formation of Fossil Lake and is the thickest of the three members that contain deposits from Fossil Lake. It is the time equivalent of part of the Luman Member of Lake Gosiute (Buchheim, Cushman, and Biaggi 2012). It originated in the southern part of Fossil Basin as a floodplain that gradually migrated northward and deepened as the lake evolved. The Angelo Member is the youngest member and records the latest phase and eventual demise of Fossil Lake. It is the time equivalent of the Wilkins Peak Member of Lake Gosiute (Buchheim, Cushman, and Biaggi 2012). In the Angelo phase, the lake became saline, and there was a general disappearance of fishes and other aquatic organisms. The rest of this book and all the fossils illustrated in it will focus on the thinnest but most fossiliferous of the three members, the Fossil Butte Member (FBM), which was sandwiched between the Road Hollow and Angelo Members. The FBM ranges from only about 22 meters in thickness in the nearshore deposits to about 12 meters in thickness in the mid-lake quarries, and it represents only about 9 percent of the stratigraphic thickness of the Fossil Lake deposits. For more information on the stratigraphy of the Fossil Lake members, see Buchheim, Cushman, and Biaggi (2012).
Sweet Spot in the Eocene: The Relatively Short but Productive Duration of the FBM
The FBM is only a tiny slice of the Green River Formation. To put it in perspective, the Green River Lake System lasted at least 12 million years, and Fossil Lake appears to have lasted for less than 2 million of those years. And of that 1 to 2 million years, the FBM represents less than 9 percent of Fossil Lake's stratigraphic record (Buchheim, Cushman, and Biaggi 2012, fig. 2). Thus, the FBM probably represents only a few tens of thousands of years at most, which in the context of GEOLOGIC TIME is a blink of an eye.
The FBM represents Fossil Lake in its largest, deepest, and freshest stage. The southeastern end of the FBM connects to the Wilkins Peak Member of Lake Gosiute in places, indicating a brief, narrow connection between Fossil Lake and Lake Gosiute in the early Eocene (Buchheim, Cushman, and Biaggi 2012). If fishes from Fossil Lake were able to enter Lake Gosiute via this connection, they were later wiped out in Gosiute during deposition of the Wilkins Peak Member (fig. 5) when Lake Gosiute dried and became hyper-saline and toxic to fishes. The later Gosiute fish assemblage of the Laney Member is a very different one than that of the FBM assemblage from Fossil Lake, with only a few overlapping genera (Atractosteus, Amia, Knightia, Diplomystus, Asineops, and Phareodus). (Dagger symbols indicate extinct groups or taxa.) Although Grande (1994b, table 2) listed the percoids Priscacara and Mioplosus as rare occurrences in Laney Member deposits, rechecking the original reports of these genera from the Laney indicate that these reports are in error. It appears that percoids are absent from most, if not all, of the Laney Member localities.
The known aquatic biodiversity of the FBM exceeds that of the other 13 members of the Green River Formation combined. In part this was probably due to the variety of well-preserved habitats in these deposits. It is also due to the intense level of fossil excavation from the Fossil Butte Member over the years. Grande and Buchheim (1994, 34) estimated that over half a million fossil fishes were excavated by commercial quarries from 1970 through 1994—mostly complete to nearly complete skeletons. Another million incomplete or damaged fishes were excavated and discarded during the same period. I estimate that now over 200,000 specimens are excavated annually. After more than a century of collection, millions of fossils have been recovered from the FBM, so even proportionately rare elements of the overall fauna and flora (e.g., birds, bats, etc.) are now known by numerous specimens. And the diversity continues to climb. It wasn't until 1998 that a member of the pike and pickerel family (Esocidae) was discovered in the FBM. Out of a million-plus fishes that have been excavated over the last century from the FBM, this unique specimen is the only one of its kind (fig. 78). Large sample size is a definite advantage for deciphering past biodiversity based on fossil localities. But regardless of sample size, the biodiversity of aquatic vertebrates in the FBM is unmatched in any other part of the Green River Formation, because even the diversity of common fish species is high.
Within the FBM, some of the most productive fossil localities are located within a relatively narrow zone of CALCIMICRITE limestone including the "18-inch layer" and the underlying "sandwich beds" (described on pages 10–15), together representing what is probably only a few thousand years of the lake's history at most. Other highly productive zones are the so-called "mini-fish beds" near the K-spar tuff bed (figs. 4, 74, and 83, bottom). It is the K-spar tuff that has been RADIOMETRICALLY DATED to be about 51.97 years old (Smith et al. 2010, data repository). As explained on page 8, all of the fossils illustrated in this volume are from the FBM, and nearly all are from either the 18-inch layer or the sandwich beds of this member. Green River Formation fossils from members outside of the FBM (some of which are millions of years younger or older than the FBM) were excluded from this book to provide a more contemporaneous community picture. It is the snapshot-like aspect of a relatively contemporaneous extinct biota that continues to attract my interest to the FBM. In fact, the FBM contains such a diversity of fossil organisms that it is hard to do it complete justice in a single volume, so there are references cited throughout this text for further reading.
Excerpted from THE LOST WORLD of FOSSIL LAKE by LANCE GRANDE. Copyright © 2013 by Lance Grande. Excerpted by permission of THE UNIVERSITY OF CHICAGO PRESS.
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Table of Contents
In the Beginning
Fossils from the FBM: History, Controversy, and Quarry Life
Exposing the Record of Past Life: Fossil Preparation
Classification of Fossils and Their Place in the Web of Life
Arthropods (Phylum Arthropoda)
Mollusks (Phylum Mollusca)
Vertebrates (Phylum Chordata, Subphylum Vertebrata)
Cartilaginous Fishes (Superclass Chondrichthii)
Ray-Finned Fishes (Superclass Actinopterygii)
Abundance and Distribution of Fish Species
Tetrapods (Superclass Sarcopterygii)
Amphibians (Class Amphibia)
Non-Avian Reptiles (Class Reptilia; Superorders †Paracryptodira, Cryptodira, Squamata, and Crocodylomormha)
Birds (Class Reptilia; Superorder Aves)
Mammals (Class Mammalia)
Green Algae (Phylum Chlorophyceae)
Ferns and Horsetails (Phylum Filicopsida and Phylum Equisetopsida)
Conifers (Phylum Coniferophyta)
Non-Eudicot Flowering Plants (Phylum Angiospermophyta; Subclasses Magnoliids, Monocotyledons, and Ceratophyliids)
Eudicot Flowering Plants (Phylum Angiospermophyta; Subclass Tricolpates)
Reading the Pages of Deep History
Appendix A: Key to the Major FBM Localities
Appendix B: Summary List of FBM “Fish” Species
Appendix C: Summary List of FBM Bird Species
Appendix D: FBM Fossils That Have Been Enhanced, Restored, Inset, or Faked
Appendix E: Using This Book and Comments on Bulletin 63
Appendix F: Sources of Phylogenies Used in This Book
List of Institutional Abbreviations Used in This Book