Paleontological studies at Florissant have been ongoing for more than 13 decades. As the focus of these studies has shifted through this time, the site has provided important insights into the evolution of paleontology as a science from its beginnings in the nineteenth century through its subsequent development. Early studies focused on the description of new taxa from collections that were being made by the early scientific surveys of the American West, particularly the Hayden Survey during the early 1870s and an expedition from Princeton in 1877. The first studies and descriptions of these fossils were by Leo Lesquereux on the fossil plants, S.H. Scudder on the fossil insects, and E.D. Cope on the fossil vertebrates. At the beginning of the twentieth century, T.D.A. Cockerell conducted field expeditions in 1906–1908, and subsequently published ∼130 papers on fossil plants, insects, and mollusks. Work by these early researchers was the first to consider the implications of the Florissant fossils for evolution, extinction, biogeography, and paleoclimate. Even greater emphasis on these broader implications began when H.D. MacGinitie made excavations during 1936–1937 and published a comprehensive monograph on the fossil flora in 1953, including numerous taxonomic revisions and detailed interpretations of stratigraphic context, paleoecology, paleoclimate, paleoelevation, biogeography, and taphonomy. Other workers during the late 1900s initiated the first studies on pollen, dicotyledonous woods, and multiple organ reconstructions of extinct plant genera, and developed more quantified methods for determining paleoelevation and paleoclimate. Current work emphasizes plant-insect interactions, the use of diatoms as fresh-water paleoen-vironmental indicators and as agents in macrofossil taphonomy, and the use of insects as terrestrial environmental indicators.

The biogeographic affinities of the Florissant flora are in need of reevaluation. We give a critical review, based on megafossil and pollen records representing genera whose affinities we accept as well founded. The Florissant assemblage includes taxa of diverse modern geographic distribution. The flora is composed mainly of Laurasian elements, some of which are now confined to Asia ( Ailanthus , Dipteronia , Eucommia , Platycarya , Pteroceltis ) and a wide number co-occurring in the eastern United States and Asia. Others are now confined to western North America ( Sequoia , Cercocarpus , Sarcobatus ) and many occur in Mexico. The major geographic affinities of the Florissant genera discussed here are broad and include the present-day warm temperate and subtropical floras of Mexico, central and southern China, and the southeastern United States. Many taxa appear to have been shared between North America and Asia by Eocene time. The Rocky Mountain flora was distinct from that of the southeastern United States, probably because of the barrier represented by the Cannonball epeiric sea that traversed the Midcontinent in the Paleocene. Similarity of Florissant taxa to the South American flora is low. The deterioration of climate after the time of Florissant deposition represents one of the most significant decreases in temperature of the entire Tertiary. Following the warm interval of the latest Eocene, a few Florissant genera were locally extirpated, a few became extinct, some were already at or dispersed to lower-elevation regions, and others persisted in the southern Rocky Mountains. Over longer geologic time spans, some taxa seem to have persisted on the West Coast of North America through the Miocene, and in a few cases even up to the present. Many deciduous taxa have persisted in the summer-wet climate area of the eastern United States.

Abstract This field trip in the vicinity of the Florissant fossil beds includes five stops that examine the Precambrian Cripple Creek Granite and Pikes Peak Granite, and the late Eocene Wall Mountain Tuff, Thirtynine Mile Andesite lahars, and Florissant Formation. The Cripple Creek Granite and Pikes Peak Granite formed in balholilhs ca. 1.46 and 1.08 Ga, respectively. Uplifted during the Laramide Orogeny of the Late Cretaceous and early Tertiary, the Precambrian rocks were exposed along a widespread erosion surface of moderate relief by the late Eocene. The late Eocene volcanic history of the Florissant area is dominated by two separate events: (1) a caldera eruption of a pyroclastic flow that resulted in the emplacement of the Wall Mountain Tuff, a welded tuff dated at 36.73 Ma; and (2) stratovolcanic eruptions of tephra and associated lahars from the Guffey volcanic center of the Thirtynine Mile volcanic field. This volcanic activity from the Guffey volcanic center had a major influence on the development of local landforms and on sedimentation in the Florissant Formation, which was deposited in a fluvial and lacustrine setting and is dated as 34.07 Ma. The Florissant Formation contains a diverse flora and insect fauna consisting of more than 1700 described species. Most of these fossils are preserved as impressions and compressions in a diatomaceous tuffaceous paper shale and as huge petrified trees that were entombed in a lahar deposit.

ABSTRACT Florissant fossil beds ranks among the best documented Cenozoic fossil deposits in the world in number of scientific publications and named species. The history of geoscience research on the Upper Eocene Florissant Formation spans nearly one and a half centuries. New excavations and transfers of historic collections have spread Florissant fossils to nearly 30 natural history museums during that period. The history of acquisition, conservation, and taxonomic study of each museum’s collection is unique, so Florissant collections provide examples of how taxonomic diversity, physical conservation, and public exhibition of collections vary with provenance. Dispersal of fossils among museums, including separation of type specimen parts and counterparts, has led to a variety of challenges for research on Florissant fossils. First, an exploratory, quantitative analysis of taxonomic diversity in four collections of fossil insects from Florissant uncovers a pattern of identification bias. Some taxonomists preferentially identify common taxa or consistently misidentify rare taxa, for instance. In light of this result, it is recommended that researchers vet any set of identifications made by multiple researchers or, ideally, identify specimens anew. Second, observations of Florissant specimens at different museums show that a large number of fossils have been lost, damaged, or destroyed due to actions such as travel on loan, display in exhibits, or application of non-archival conservation techniques. Through the digitization process, including cataloging and imaging specimens, curatorial staffs have discovered the extent of uncatalogued or missing material. Digitization has mitigated some of the challenges associated with dispersion of specimens. Collaborative projects across museums have led to rediscovery of lost specimens or discovery for the first time of parts and counterparts that correspond to the same fossil but are housed at different institutions. Online databases that serve specimen images allow researchers to assign new taxonomic determinations, controlling for bias from earlier researchers, or to examine fossils remotely from photographs, reducing the need to handle and ship fragile material for loans. Moreover, providing public access to museum specimen records through collaborative digitization projects expands the opportunities to exhibit and develop specimen-based educational curricula.

ABSTRACT The Green River Formation illustrates the expression of sequence-stratigraphic surfaces and units in lacustrine and alluvial strata. These settings are distinctly different from those of most of the mudstone units considered in this book. Our study shows how applying the sequence-stratigraphic method and approach from first principles in continental settings can provide insights into the accumulation of mudstones enriched in organic matter and biogenic material. These settings also have substantial hydrocarbon source, reservoir, and seal potential. Indeed, lacustrine settings host many of the largest oil discoveries of this century. This setting offers an opportunity to examine the expression of parasequences, depositional sequences, and key surfaces in a setting that is significantly different from the more commonly studied marine settings. Although lakes may seem completely different from oceans, they have enough similarities with oceans that their differences tell us much about what is really essential about sequence stratigraphy—and what is an accident of the depositional setting. The sequence-stratigraphic approach of recognizing a hierarchy of rock packages bounded by various surfaces works very well in lake strata. In studying lacustrine strata, we recognize the same types of sequence-stratigraphic surfaces as in marine settings along with similar stratal stacking patterns. The expressions of parasequences and sequences differ between marine and lacustrine settings, however, because of significant differences among the dynamics and responses of these systems. Despite these differences, we see that the sequence-stratigraphic approach works well for lakes. Separate models, however, are needed for each of three lake-basin types to summarize the lacustrine sequence expression—just as shallow-marine carbonate sequences look different from shallow-marine siliciclastic sequences and require separate models. Contrasts among lake and marine systems make it inappropriate to directly apply one unmodified marine sequence-stratigraphic model to all lake systems. Indeed, one lacustrine model is not applicable to all lake-basin types. …thinly laminated chalky shales, which I have called the Green River shales, …, present a peculiarly banded appearance. When carefully studied these shales will form one of the most interesting groups in the West. Hayden, 1869

The fossil record of wetlands documents unique and long-persistent floras and faunas with wetland habitats spawning or at least preserving novel evolutionary characteristics and, at other times, acting as refugia. In addition, there has been an evolution of wetland types since their appearance in the Paleozoic. The first land plants, beginning in the Late Ordovician or Early Silurian, were obligate dwellers of wet substrates. As land plants evolved and diversified, different wetland types began to appear. The first marshes developed in the mid-Devonian, and forest swamps originated in the Late Devonian. Adaptations to low-oxygen, low-nutrient conditions allowed for the evolution of fens (peat marshes) and forest mires (peat forests) in the Late Devonian. The differentiation of wetland habitats created varied niches that influenced the terrestrialization of arthropods in the Silurian and the terrestrialization of tetrapods in the Devonian (and later), and dramatically altered the way sedimentological, hydrological, and various biogeochemical cycles operated globally. Widespread peatlands evolved in the Carboniferous, with the earliest ombrotrophic tropical mires arising by the early Late Carboniferous. Carboniferous wetland-plant communities were complex, and although the taxonomic composition of these wetlands was vastly different from those of the Mesozoic and Cenozoic, these communities were essentially structurally, and probably dynamically, modern. By the Late Permian, the spread of the Glossopteris flora and its adaptations to more temperate or cooler climates allowed the development of mires at higher latitudes, where peats are most common today. Although widespread at the end of the Paleozoic, peat-forming wetlands virtually disappeared following the end-Permian extinction. The initial associations of crocodylomorphs, mammals, and birds with wetlands are well recorded in the Mesozoic. The radiation of Isoetales in the Early Triassic may have included a submerged lifestyle and hence, the expansion of aquatic wetlands. The evolution of heterosporous ferns introduced a floating vascular habit to aquatic wetlands. The evolution of angiosperms in the Cretaceous led to further expansion of aquatic species and the first true mangroves. Increasing diversification of angiosperms in the Tertiary led to increased floral partitioning in wetlands and a wide variety of specialized wetland subcommunities. During the Tertiary, the spread of grasses, rushes, and sedges into wetlands allowed for the evolution of freshwater and salt-water reed marshes. Additionally, the spread of Sphagnum sp. in the Cenozoic allowed bryophytes, an ancient wetland clade, to dominate high-latitude mires, creating some of the most widespread mires of all time. Recognition of the evolution of wetland types and inherent framework positions and niches of both the flora and fauna is critical to understanding both the evolution of wetland functions and food webs and the paleoecology of surrounding ecotones, and is necessary if meaningful analogues are to be made with extant wetland habitats.