During the past five years, renewed prospecting and collecting of mammalian fossils in the Florissant Formation within Florissant Fossil Beds National Monument in central Colorado has nearly tripled the known diversity of fossil mammals from this rock unit. Taxa first recorded here from the Florissant Formation include the eomyid rodent Paradjidaumo trilophus , the lagomorph Palaeolagus , and the rare artiodactyl Pseudoprotoceras longinaris . We also describe an isolated deciduous premolar of a protoceratid. We update the mammalian faunal list of the Florissant Formation, which includes some 16 species in 13 families and 6 orders. The mammalian fauna corroborates the Chadronian (latest Eocene) age determined by others. Geographic ranges of Pelycomys , Palaeolagus , and Paradjidaumo trilophus are extended slightly southwest from northeastern Colorado, and the range of Pseudoprotoceras longinaris is extended southwest from Wyoming and Nebraska. Based upon comparison with nearest living relatives and plausible analogs, the mammalian taxa represented in the Florissant Formation seem to be consistent with the moist, warm temperate, relatively high elevation wetland and woodland habitats that have been inferred by others for the area in and around late Eocene Lake Florissant.

The fossil plants found in the Eocene Florissant Formation and Green River Formation are preserved with a level of detail that allows one to closely examine traces of insect feeding damage. Levels (amounts) and patterns (abundance of various types) of fossilized insect feeding damage from Florissant and the middle Eocene Green River Formation were compared. This allowed for a detailed examination of feeding damage and provided an opportunity to examine long-term patterns of change in insect herbivory during a period of climate fluctuation. Samples including 624 fossil leaves from Florissant and 584 fossil leaves from the Green River Formation were examined to document overall damage levels, the presence/absence of specific feeding guilds (i.e., hole-feeding, skeletonization, leaf-mining), and host-specific damage types. Florissant insects show host specificity in their feeding preferences as evidenced through the distribution of feeding damage on plants and through the presence of identifiable host-specific interactions. Some of these interactions appear to be long lasting as they are also apparent on the same, or closely related, leaf species found in the Green River Formation. Insect damage levels declined from the middle to late Eocene. This decline is correlated with a cooling event during this time interval and is in concurrence with the findings of other authors who have examined fossilized herbivory and climate change patterns. There is also an increase in the abundance of galls during this same interval, which also may be related to climate change.

Scanning electron microscopy (SEM) of insect and plant fossils in the lacustrine shales of the Eocene Florissant Formation of Florissant, Colorado, was used to investigate the mechanisms of fossil preservation. The fossiliferous Florissant “paper shales” are composed of thin laminae of diatomite that form couplets with alternating smectitic clay laminae. The millimeter-scale sedimentary couplets may preserve an episodic record of sedimentation and are interbedded with less frequent, coarser volcaniclastic layers. The insect and plant fossils are associated with biofilms of extracellular polymeric substances (EPS) secreted by diatoms. The preserved organisms are entangled in the diatom aggregates coated with the EPS biofilm. We suggest that decomposition of the organisms was arrested during sedimentation and burial by the protective nature of the mucus covering, the properties of which limited the actions of bacteria and grazers and may have enhanced fossilization. A novel contribution of the study is a demonstration that this mechanism of exceptional preservation is also common at other similar lacustrine fossil sites, as supported by a further SEM analysis of insect and plant fossils from other Cenozoic lake deposits formed in environments comparable to the Floris-sant Formation. The deposits include the Oligocene shale at Canyon Ferry, Montana; the Miocene Savage Canyon Formation, Stewart Valley, Nevada; and the Miocene Shanwang Beds of Shandong Province in northeast China. In addition, cultures of diatomaceous biofilms, grown in the laboratory display morphological features identical to those of the fossil diatomaceous biofilms. Our contribution indicates the significance of biofilms in fossil preservation at Florissant and other deposits.

Using available shape characters we conducted an outline morphometric analysis to make family-level identifications of fossil spiders from the Florissant Formation in Colorado. In this analysis we used carapace shape because it is a character that can be observed on most fossil spiders, and we also used linear leg characters. All measurements were first made on 202 modern spiders from eight families found in localities similar to the fossil lake environment. A multiple discriminant analysis (MDA) of the eigenshape axes was used to predict family placement among the modern data set to test the accuracy of the predictions. The modern spider families that were predicted correctly most often were the Salticidae (91.2%), Linyphiidae (80%), Dictynidae (76.5%), Tetragnathidae (68.2%), Clubionidae (66.7%), and Araneidae (65.5%). Families that produced less successful results were the Agelenidae (46.7%) and the Lycosidae (39.1%). Forty-three fossil spiders from Florissant were then added to the model to determine their family placement. All fossils were placed into modern families with varying degrees of accuracy. Only 42% of our identifications agree with those made by previous authors, but it is likely that these specimens were originally misidentified. With the addition of more taxa and characters, we believe that an outline morphometric approach shows great promise for helping to identify fossil taxa that are lacking traditional taxonomic characters.

Abstract The purpose of this paper is to briefly review the upper Eocene and Oligocene lacustrine deposits in the southwestern part of the United States and to discuss how they have been used to understand the paleoclimate, tectonic history, and volcanic environment in this region. Two well-studied lacustrine deposits(upper Eocene Florissant and Oligocene Creede Formations)will be a primary focus because they represent two major types of lake basins that formed in the region during this time. The Florissant Formation was deposited in a lake basin formed by a blocked stream drainage (McElroy and Anderson, 1966). The Creede Formation was deposited in a lake basin formed by caldera collapse (Steven and Ratte, 1965; Larsen and Crossey, 1996). Other examples of these two types of lake basins and other lake deposits in the region area lso discussed (see Figure 1 and Table 1). Much of the southwestern part of the United States(Arizona, Utah, Colorado, and New Mexico) was elevate drelative to surrounding regions during the latest Eocene through Oligocene (Figure 1) (Christiansen and Yeats, 1992; Elston and Young, 1991; Gregory and Chase, 1992; Chapin and Cather, 1994; Wolfe et al.,1998). This was largely the result of Laramide-style high-angle faulting and filling of adjacent Laramide style basins (Miller et al., 1992; Dickinson et al., 1988).Prominent erosional surfaces existed adjacent to tectonichighlands in the Rocky Mountains (Evanoff, 1990;Chapinand Cather, 1994) and northern Arizona-southern Utaharea (Elston and Young, 1991). Voluminous volcani sminitially produced intermediate-composition compositevolcanoes in numerous areas. This was followed in the Sawatch Range, San Juan, Marysvale, Latir, and Mogollon-Datil volcanic fields by silicic calderas (seelocations on Figure 1) (Steven, 1975; Elston, 1984;Christiansen and Yeats, 1992). Latest Eocene and early Oligocene sedimentation occurred largely in a fewbroad, low-relief Laramide basins (Claron: southwestern Utah, Gold strand, 1994; Baca, central New Mexico,Cather and Johnson, 1986; Uinta: northeastern Utah,Andersen and Picard, 1972) and in volcaniclasticaprons and proto-rift basins adjacent to the volcanicregions (Anderson et al., 1975; Ingersoll et al., 1990).Few other late Eocene-Oligocene deposits are presentin the region, and most of those are associated within itial extension in the southern Rio Grande rift (Macket al., 1994) and southern Basin and Range (Grover,1984; Eberly and Stanley, 1978; Christiansen and Yeats,1992). Small, localized accumulations of fluvial and lacustrine deposits in volcanic depressions and blocked stream drainages (see Figure 1 and Table 1)preserve the only sedimentary records for understanding the tectonic, climatic, and paleoenvironmental history of this region during this time.

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.