Crazy Mountains Research Articles

Lost in the New West: Performing Western Identity in Thomas McGuane’s Deadrock Novels

Lost in the New WestPerforming Western Identity in Thomas McGuane’s Deadrock Novels Mark Asquith (bio) Getting lost in the New West is easy because nobody seems to know where or even what it is. Even after years of scholarly study, western historian Donald Worster confided in his ironically titled “New West, True West” that “I could not put my finger on the map and say, ‘There is the West’” (143). Perhaps a map is not the best place to start. The Center of the American West’s promisingly titled Atlas of the New West (1997) is full of colorful maps that codify everything from dams, roads, and Native American reservations— but remains elusive in defining what binds them together into a cohesive whole (18). For Frederick Jackson Turner the West was less a place than a process of nation-building, but for the New Historians of the eighties it was the echo chamber of marginalized voices left out by Turner’s Anglo imperialism (Native Americans, African Americans, women in general). Much recent settler colonial criticism has accepted this pluralist vision while simultaneously seeking to replace its tendency toward American exceptionalism with a transnational comparative model that places the West within the context of other colonial projects. Conversely, the approach of post-structuralists has been to reject geography in favor of the West conceived as a signifier endlessly repeated and reinterpreted globally. Neil Campbell coins the term the “rhizomatic West,” which rejects the linearity of Turner (associated with the rootedness of a tree) in favor of the complex underground horizontal root system of the rhizome (which erupts everywhere) (Rhizomatic West 35). Whether a region defined by aridity, an idealistic direction of travel, a political paradigm endorsed through the ideology of “the Frontier,” a romantic “wilderness” promising self-identification (another Anglo-Imperial construct), or a free-floating cultural signifier comprised of kitsch symbols—how could we not get lost! [End Page 1] Thomas McGuane has spent a lifetime exploring the porous texture of the West. He writes in his foreword to William Allard’s photographic collection Vanishing Breed, Photographs of the Cowboy and the West: The West, whatever that is, is still there, believe it or not, in its entirety. It is the leading chimera of our geography. The dead windmills lost behind the high wire of the missile range, the stove-up cowboy at the unemployment office, the interstate that plunges through the homesteads, all bring aches to an American race memory. . . . The West vanished for the Indian and the drover; it vanished for the cowboy. Simultaneously it reappeared in all the same places, and in movies and rodeos. It’s like fire. Hollywood, calf tables, and depreciation schedules can’t kill it. (6–7) This is typical McGuane—the mockery lubricates the dryly serious and adds nuance while the scripted diffidence (“whatever that is”) is both flippant and demanding critical scrutiny. Campbell’s rhizomatic West is replaced with a set of combustible cultural signifiers—landscapes, homesteads, and vanishing Indians (McGuane’s preferred term)—making up a hopeful if misguided race memory. It lives in a set of landscapes, symbols (Stetsons and windmills), archetypes, and ritualistic tropes independent of both geography and history that help to produce a particular identity. The West becomes a “thirdspace” that flattens the distinction between new and old, fake and real in favor of competing narratives and dialogues (a form of Bakhtinian polyphony), the most important being the region’s conversation with its own past.1 McGuane’s West is symbolized by the town of Deadrock (a play on McGuane’s Livingston home), a cliché of a western town nestling beneath the aptly named Crazy Mountains. The mountains should act as a site of spiritual regeneration but are emblematic of Deadrock men struggling for self-definition in the shadow of hypermasculine mythology. It is a riposte to what he denounces in an interview with Gregory Morris as “the pompous backward-looking revisionist West of Wallace Stegner, Vardis Fisher, and even A. B. Guthrie” (McGuane, “Thomas McGuane” 210) and, as he makes [End Page 2] clear in the essay “Roping from A–B,” the southern nostalgia of Faulkner, whose Yoknapatawpha is a “morbid Cloud-Cuckoo...

Diagenesis of the Sappington Formation in the Bridger Range, Montana: Implications for the burial and thermal history of the Western Crazy Mountain Basin

The Devonian-Mississippian Sappington Formation in the Bridger Range, Montana was investigated for its paragenetic sequence and thermal history. These results were used to establish a burial history for the area and compared to data from nearby oil and gas wells. The paragenetic evolution of the Sappington includes early diagenetic feldspar dissolution, formation of quartz overgrowths, and illite precipitation during early diagenesis at temperatures < 50 °C. Subsequent burial diagenesis resulted in the precipitation of non-ferroan and ferroan dolomite, followed by calcite cementation and replacement, pyrite replacement, and hydrocarbon generation and expulsion at temperatures > 130 °C. Devonian formations were the source of the non-ferroan dolomite cement and began precipitating in the latest Mississippian. Subsequent growth of ferroan dolomite resulted from clay transformation reactions in the Upper and Lower Sappington Members and was initiated during rapid burial in the late Cretaceous. The Bridger Range and the adjacent Western Crazy Mountain Basin underwent similar Paleozoic and Mesozoic burial histories. Vastly different Cenozoic burial histories resulted from movement along the Cross Range and Pass thrusts that caused the Bridger Range to begin uplift prior to the cessation of deposition of the Livingston Group in the early Paleocene. The discrepancies in burial history caused the Sappington Formation to reach a maximum temperature of ~135 °C in the Bridger Range and ~230 °C in the western Crazy Mountain Basin.

Magnetostratigraphy of Upper Cretaceous (Lancian) to Middle Paleocene (Tiffanian) strata in the northeastern Crazy Mountains Basin, Montana, U.S.A.

Magnetostratigraphy of Upper Cretaceous (Lancian) to Middle Paleocene (Tiffanian) strata in the northeastern Crazy Mountains Basin, Montana, U.S.A.

Theoretical Investigations on Mapping Mean Distributions of Particulate Matter, Inert, Reactive, and Secondary Pollutants from Wildfires by Unmanned Air Vehicles (UAVs)

Evaluated Weather Research and Forecasting model inline with chemistry (WRF/Chem) simulations of the 2009 Crazy Mountain Complex wildfire in Interior Alaska served as a testbed for typical Alaska wildfire-smoke conditions. A virtual unmanned air vehicle (UAV) sampled temperatures, dewpoint temperatures, primary inert and reactive gases and particular matter of different sizes as well as secondary pollutants from the WRF/Chem results using different sampling patterns, altitudes and speeds to investigate the impact of the sampling design on obtained mean distributions. In this experimental design, the WRF/Chem data served as the “grand truth” to assess the mean distributions from sampling. During frontal passage, the obtained mean distributions were sensitive to the flight patterns, speeds and heights. For inert constituents mean distributions from sampling agreed with the “grand truth” within a factor of two at 1000 m. Mean distributions of gases involved in photochemistry differed among flight patterns except for ozone. The diurnal cycle of these gases’ concentrations led to overestimation (underestimation) of 20 h means in areas of high (low) concentrations as compared to the “grand truth.” The mean ozone distribution was sensitive to the speed of the virtual UAV. Particulate matter showed the strongest sensitivity to the flight patterns, especially during precipitation.

Widespread basement erosion during the late Paleocene-early Eocene in the Laramide Rocky Mountains inferred from 87Sr/86Sr ratios of freshwater bivalve fossils

Reconstruction of the timing and pattern of exhumation of basement-involved uplifts during the Laramide is essential to the understanding of the mechanisms of crustal shortening and thickening in the region. We use reconstructions of the 87 Sr/ 86 Sr ratios of Late Cretaceous–early Cenozoic river water from fossil shells in six basins of the Rocky Mountains contextualized by modern river-water Sr chemistry studies to trace the erosion of Precambrian basement cores in the Laramide ranges. The 87 Sr/ 86 Sr ratios and Sr concentration of modern river water in the Rocky Mountains are controlled by river bedrock lithology. Weathering of Precambrian silicate rocks in the cores of Laramide ranges produces high 87 Sr/ 86 Sr ratios in highland rivers. Weathering of Paleozoic and Mesozoic carbonates along the basin margins reduces the 87 Sr/ 86 Sr ratios and increases Sr concentration of rivers as they flow basinward. Lowland rivers that have headwaters in Precambrian basement mostly have 87 Sr/ 86 Sr ratios >0.711, whereas rivers confined to or with very long reaches in basins have 87 Sr/ 86 Sr ratios between 0.709 and 0.711. River-water δ 18 O values do not change in response to changes in catchment elevation. Our results from fossil shells show that carbonate weathering dominated the river-water Sr chemistry in the Alberta Foreland, Williston, and Crazy Mountains Basins, and that Proterozoic low-grade metamorphic carbonates in the Belt-Purcell Supergroup were not exposed in the Canadian Rocky Mountains during Late Cretaceous–early Paleocene time. Silicate weathering influenced the Sr chemistry of surface waters in the Powder River Basin during the late Paleocene and the Washakie Basin during the early Eocene, suggesting Precambrian silicate basement rock was extensively exhumed and eroded. The observation that Precambrian basement was eroded earlier around the Powder River Basin than around the Washakie Basin is consistent with a previous study that suggests Laramide ranges in northeast Wyoming reached high elevation earlier than the ranges adjacent to the Sevier thrust belt. Widespread basement erosion in late Paleocene–early Eocene time was controlled by tectonic exhumation, and may have been intensified by the wet and warm global climate.

Late Paleocene high Laramide ranges in northeast Wyoming: Oxygen isotope study of ancient river water

The distribution and initial timing of the establishment of high surface elevations in the Rocky Mountains during the Early Cenozoic remain controversial despite the importance of these data in testing tectonic models for this region. We track the timing and distribution of high elevation in the Rocky Mountains during the Late Cretaceous–Early Eocene by examining annual and seasonal δ 18O values of the ancient river water, which are calculated from the δ 18O values of well-preserved freshwater bivalve shells. In the Powder River basin of the eastern Laramide province, the δ 18O values of the ancient river water vary between − 23.0‰ and − 8.0‰ SMOW in both seasonal and annual records in the Late Paleocene–Early Eocene. The large variation suggests that the ancient rivers were fed yearly or seasonally by snowmelt from highlands of 4.5 ± 1.3 km. This can be explained by the existence of the Bighorn Mountains and Black Hills with a drainage pattern similar to the present in northeast Wyoming. The δ 18O values of ancient river water along the front of the Sevier thrust belt generally follow a trend from lower values in north, − 14.2 ± 1.4‰ in the Early Paleocene Crazy Mountains basin, to higher values in south, − 11.1 ± 0.8‰ in the Late Paleocene Bighorn basin, and − 7.1 ± 1.6‰ in the Early Eocene Washakie basin. The variations within each basin are relatively small. These rivers most likely rise in the Sevier thrust belt, and may reflect highland elevation of 1–2 km. The δ 18O values in the Alberta foreland and Williston basin are very low (− 20.5‰) in the Late Cretaceous, indicating the rivers were fed by snowmelt from the Canadian Rocky Mountains of 4.3 ± 1.0 km high. The attainment of high elevation in the eastern Laramide province prior to the western province could be explained by southwestward progression of back-thrusts soled into an earlier east-directed master detachment, which may be formed by the westward rollback of subducted shallow slab.

40Ar/39Ar dates from alkaline intrusions in the northern Crazy Mountains, Montana: Implications for the timing and duration of alkaline magmatism in the central Montana alkalic province

Intrusive rocks in the Crazy Mountains, Montana, consist of numerous stocks, dike swarms, laccoliths and/or sills of strongly alkaline to subalkaline affinity that have intruded and metamorphosed Tertiary sedimentary strata of the Crazy Mountains Basin. The subalkaline rocks form stocks, sills, and radiating dikes and are located primarily in the southern Crazy Mountains (e.g., Big Timber stock, Loco Mountain stock). With the exception of the Ibex Mountain sill (?), the alkaline rocks are restricted to the northern Crazy Mountains. New 40 Ar/ 39 Ar dates are reported for alkaline rocks of the northern Crazy Mountains, with results ranging between 50.61 Ma and 50.03 Ma. Five dates from the strongly alkaline nepheline and mafic nepheline syenites of the Ibex Mountain sill (?), Robinson anticline intrusive complex, and Comb Creek stock (?) and dike swarm give tightly clustered dates suggesting that they were emplaced during a restricted time interval at ∼50.1 Ma. The dates from the alkaline rocks of the northern Crazy Mountains are slightly older than those previously reported from the subalkaline Big Timber stock in the southern Crazy Mountains (i.e., 49.3–49.2 Ma, biotite 40 Ar/ 39 Ar) (du Bray and Harlan, 1996). However, the limited span of dates (i.e., 50.6–49.2 Ma) and the geographic proximity between the alkaline and subalkaline rocks indicate that the magmas represented by these different geochemical groups were closely associated in both time and space. Furthermore, all the igneous rocks in the Crazy Mountains were emplaced in a narrow time interval of 1–2 m.y. On a regional scale, the 51–49-Ma age span from the Crazy Mountains is similar to that of most of the igneous centers of the central Montana alkalic province and is coeval with the peak of widespread volcanism in the Absaroka-Gallatin volcanic field immediately to the south of the Crazy Mountains Basin.

Chapter 25

Mimotricentes tedfordi, new species, is a small arctocyonid mammal whose type specimen is from the Tiffanian (late Paleocene) Laudate local fauna, found at the base of informal member 4b of the Goler Formation, southwesternmost Great Basin, Kern County, California. The type specimen is a fragmentary maxilla with P4–M3. Smaller than morphologically similar taxa based on upper teeth, M. tedfordi is characterized by a large, projecting parastyle on M1 and M2, by a proliferation of mesostyle-like cusps on the molars, by lack of complete cingula around the lingual bases of the molar protocones, and by somewhat crenulated enamel surfaces on the posterior slope of P4 and possibly the molars when unworn. M. tedfordi is most similar to, but 20% smaller than, certain specimens formerly identified as Chriacus sp. from the earliest Tiffanian of Douglass Quarry, eastern Crazy Mountain Basin, Montana. Also, newly collected specimens from the Goler Formation of other mammalian taxa show strong Tiffanian affinities. As a whole, these data support a Tiffanian age for the Laudate local fauna, but require that an unnamed anisonchine periptychid similar to Conacodon be considered a Tiffanian relict.

The mineralogy of Ba- and Zr-rich alkaline pegmatites from Gordon Butte, Crazy Mountains (Montana, USA): comparisons between potassic and sodic agpaitic pegmatites

At Gordon Butte (Crazy Mountains, Montana), agpaitic nepheline–syenite pegmatites intrude potassic alkaline rocks (principally, malignites and nepheline microsyenites). All pegmatite veins are composed predominantly of potassium feldspar, nepheline, prismatic aegirine, barytolamprophyllite, wadeite, eudialyte, loparite-(Ce) and altered rinkite ("vudyavrite") embedded in spherulitic and fibrous aegirine. Well-differentiated veins contain "pockets" filled with calcite, fluorapatite, mangan-neptunite, Mn–Ti-enriched prismatic aegirine, calcium catapleiite, and an unidentified Ca–Ti silicate. The potassium feldspar corresponds to Ba-rich sanidine with relatively low Na contents. The nepheline contains low levels of SiO2 and elevated Fe contents. The compositions of nepheline cluster in the lower portion of the Morozewicz–Buerger convergence field, indicating low-temperature crystallization and/or chemical re-equilibration of this mineral. The association of sanidine with nearly stoichiometric nepheline is unusual for agpaitic rocks and probably reflects inhibition of Al/Si ordering in the feldspar by Ba. At least four types of clinopyroxene can be distinguished on the basis of their morphology and composition. All these types correspond to Al- and Ca-poor aegirine (typically <0.6 and 2.6 wt% Al2O3 and CaO, respectively). The overall evolutionary trend of clinopyroxene in the Gordon Butte rocks is from Fe-poor diopside to aegirine–augite in the malignites and nepheline microsyenites, and culminates with the pegmatitic aegirine. This trend is characteristic for potassic alkaline complexes and results from preferential partitioning of Fe2+ into biotite during the magmatic crystallization. Barytolamprophyllite in the pegmatites is primary (as opposed to deuteric); only a few crystals contain a core composed of lamprophyllite. The evolutionary history of the Gordon Butte pegmatites can be subdivided into primary, agpaitic, and deuteric stages. The earliest paragenesis to crystallize included accessory zircon and thorite. Sr-rich loparite also precipitated relatively early serving as a major repository for Sr, REE, and Nb. During the agpaitic stage, diverse titano- and zircono-silicates (barytolamprophyllite, eudialyte, wadeite, and rinkite, among others) consumed most of the Ba, Sr, Ti, Zr, and Nb still remaining in the melt. The final stage in the evolution of the pegmatites involved interaction of the earlier-formed mineral assemblages with deuteric fluids. In common with the Rocky Boy pegmatites, Sr–REE–Na-rich fluorapatite, Ba–Fe titanates and REE-bearing carbonates (ancylite, calcio-ancylite, and bastnasite–parisite series) are chief products of the deuteric stage. The alteration of the primary mineral assemblages by deuteric fluids also produced muscovite–zeolite pseudomorphs after nepheline, replacement of wadeite and eudialyte by catapleiite-group minerals, re-deposition of Ba in the form of hyalophane, baotite, and benitoite, and cation leaching from rinkite, eudialyte, and loparite. The mineralogy of the pegmatites from Gordon Butte, other potassic complexes, and sodic agpaitic occurrences is compared in detail.

New specimens of Elphidotarsius russelli (Mammalia, ?Primates, Carpolestidae) and a revision of Plesiadapoid relationships

ABSTRACT Significant new material of the plesiadapiform Elphidotarsius russelli is described from Montana and Alberta. Previously the most poorly documented carpolestid, this species is now known from numerous isolated teeth and many jaw fragments. New material from the Crazy Mountains Basin, Montana substantially extends its known geographic range and shows that E. russelli is the most derived species of Elphidotarsius, with many features that foreshadow characteristics of Carpodaptes; consequently, emending the diagnosis of Elphidotarsius has been necessary. A phylogenetic analysis based on 73 characters scored for all species of Elphidotarsius, Pronothodectes, and Saxonella, as well as Purgatorius unio, Purgatorius janisae, Pandemonium dis, Chronolestes simul, and Carpodaptes hazelae, indicates that Elphidotarsius is a paraphyletic stem taxon at the base of Carpolestidae. Numerous crossing synapomorphies among these taxa show that a single anagenetic lineage can no longer represent the evolution of early carpolestids. This analysis also clarifies basal plesiadapoid relationships. Carpolestidae is the sister taxon to Plesiadapidae, and Saxonellidae is sister group to the carpolestid/plesiadapid clade. Contrary to previous hypotheses, Chronolestes and Pandemonium are found to lie outside of a clade including the other members of Carpolestidae, Saxonellidae, and Plesiadapidae, implying that they are basal plesiadapoids that diverged before the evolution of the common ancestor to the three main plesiadapoid families.

First Report of Dothistroma septospora on Native Limber and Whitebark Pine in Montana.

Dothistroma septospora (Doroguine) Morelet (= Dothistroma pini Hulbary), the anamorph of Mycosphaerella pini Rostr. in Munk, has been reported to cause needle blight in 29 Pinus species and hybrids in North America, including limber pine (P. flexilis James) in plantings in Kansas, Nebraska, and Ohio. We are unaware of any reports of D. septospora on limber or whitebark pine (P. albicaulis Engelm.) growing within their native ranges in the western United States. In June 1997, limber and whitebark pine in Montana were observed with severe defoliation and symptoms typical of those caused by D. septospora: affected second- and third-year needles were green at the base with brown tips or reddish-brown spots or bands, and black fruiting bodies in discolored portions of needles. Symptomatic needles were collected in natural stands of limber pine at 22 locations representing 15 counties in central, south-central, and southwestern Montana, and whitebark pine at three locations representing two counties in the Crazy Mountains in south-central Montana. Approximately 20 needles and five stromata from each location were examined with dissecting and compound microscopes to observe morphological features. Stromata were black, linear, 150 to 1450 μm (average 650 μm) by 65 to 450 μm (average 190 μm), subepidermal, and erumpent. Conidiophores were hyaline and unbranched. Conidia were 16.0 to 23.5 μm (average 18.5 μm) by 3.0 to 4.1 μm (average 3.4 μm), hyaline, 3 to 5 septate, blunt at the ends, and slightly falcate. The fungus described above was found at all sample locations. The teleomorph, M. pini, was not observed. Symptom expression and mycological characteristics were consistent with Hulbary's lectotype (1) of D. pini (= D. septospora). This is the first report of D. septospora on limber and whitebark pine within the hosts' native ranges. Reference: (1) R. L. Hulbary. Ill. Nat. Hist. Surv. Bull. 21:231, 1941.

Crazy Mountains

Crazy Mountains

Abstract: Thermal Maturity of Cretaceous and Tertiary strata, Crazy Mountains Basin, South-Central Montana&nbsp;

Abstract: Thermal Maturity of Cretaceous and Tertiary strata, Crazy Mountains Basin, South-Central Montana&nbsp;

A new species of Purgatorius (Mammalia; Primatomorpha) from the Lower Paleocene Bear Formation, Crazy Mountains Basin, south-central Montana

Purgatorius titusi, represented by 51 teeth and jaw fragments, is described from the lower Paleocene Bear Formation of the Crazy Mountains Basin in south-central Montana. Several synapomorphies, including a weak postprotocingulum and mesial inflection of molar trigonids, are indicative of the taxon's “plesiadapiform” affinities. Other features, such as wider stylar shelf and a less squared lingual outline on upper molars, are more primitive than those of Purgatorius unio, heretofore the earliest occurring species of well-represented primatomorphs.

A spatial and temporal continuous surface‐subsurface hydrologic model

A hydrologic model integrating surface‐subsurface processes was developed based on spatial and temporal continuity theory. The raster‐based mass balance hydrologic model consists of several submodels which determine spatial and temporal patterns in precipitation, surface flow, infiltration, subsurface flow, and the linkages between these submodels. Model parameters and variables are derived directly or indirectly from satellite remote sensing data, topographic maps, soil maps, literature, and weather station data and are stored in a Geographic Information System (GIS) database used for visualization. Surface resolution of cells in the model is 20 m by 20 m (pixel resolution of the Systeme Probatoire d'Observation de la Terre (SPOT) satellite image) over a 2511 km2 study area around the Crazy Mountains, Alaska, a watershed on the Arctic Circle draining into the Yukon River. The outputs from this model illustrate the interaction of physical and biologic factors on the partitioning of hydrologic components in a complex landscape.

Crazy mountains: learning from wilderness to weigh technology

Crazy mountains: learning from wilderness to weigh technology

The Eocene Big Timber stock, south-central Montana: Development of extensive compositional variation in an arc-related intrusion by side-wall crystallization and cumulate glomerocryst remixing

The Eocene Big Timber stock in the Crazy Mountains of south-central Montana is an elliptical, 8 by 13 km, compositionally and texturally diverse composite intrusion with a well-developed radial dike swarm. A sharp intrusive contact separates its two phases: the core of the intrusion is fine-grained quartz monzodiorite, and the volumetrically dominant remainder is composed of medium-grained diorite and gabbro. Differentiation-related major oxide variation within the stock is extensive and spatially nonsystematic. However, abundances of most trace elements were not strongly influenced by differentiation; late zircon and apatite fractionation caused moderate heavy and slight light rare earth element abundance depletions, respectively. Mineral compositions and assemblages indicate crystallization between ≈950 and 700 °C at a pressure of ≈0.8 kbar (3 km). Mixing models indicate that fractionation of varying amounts of plagioclase, orthopyroxene, clinopyroxene, magnesio-hastingsite, hornblende, biotite, titanite, apatite, and magnetite (the stock9s principal constituents, with quartz and potassium feldspar) and remixing of these minerals and residual liquids controlled compositional evolution in the reservoir. Crystals apparently nucleated at the reservoir wall while residual silicate liquid was displaced inward and remixed. Some crystals were plucked from the solidification front, as indicated by glomerocrysts present throughout the stock, and also remixed with residual liquid. Solidification of the reservoir represented by the stock involved heat loss to enclosing wall rock, side-wall crystallization, and subsequent, variably effective, crystal-liquid remixing. This process is an important variant of conventionally invoked models pertaining to solidification of intrusions and explains extensive, relatively nonsystematic compositional variation. The genesis of compositional evolution in other intrusions characterized by extensive, spatially nonsystematic variation may result from the important process documented herein. Compositional and geologic relationships are consistent with magma genesis related to subduction and magmatic-arc processes inboard from the western edge of the early Cenozoic North American plate. Arc magmatism in south-central Montana during Eocene time is consistent with models pertaining to early Cenozoic southward sweep and westward retreat of magmatism. Magmatism represented by the Big Timber stock provides significant new support for steepening subduction, westward retreat of the subduction hinge line, and development of an asthenospheric mantle wedge that fueled renewed magmatism beneath the western edge of the North American continent following early Cenozoic shallow subduction.

Comparative paleoecology of Paleogene and Neogene mammalian faunas: body-size structure

Abstract Species size is correlated with many aspects of life history, ecology, and behavior, which means that size changes within species, lineages, and faunas represent an important component of evolutionary paleoecology. Comparison of Paleogene mammalian faunas from the Bighorn, Clarks Fork, and Crazy Mountains basins of Wyoming and Montana with Neogene mammalian faunas from the Siwalik Group of northern Pakistan reveals similarities and differences in patterns of size change through intervals of 10 m.y. Two approaches to size change are presented. The first is to evaluate changes in the size distribution of faunas over three time intervals in each sequence. Rank-ordered size distributions, or cenograms, are used to depict faunal size structure for non-carnivorous species. The slopes and gaps in different regions of the size spectrum reflect conditions of vegetation and climate, by analogy with modern mammalian faunas (Legendre, 1986, 1989). For the Paleogene and Neogene faunas, subtle changes over time in size structure reflect changes in local vegetation and climate. The Paleogene cenograms suggest a habitat shift from mesic to humid forest, and the Neogene cenograms suggest a shift from open woodland to savannah scrub. These interpretations are supported by concurrent changes in trophic structure, faunal turnover, and in floral and geologic indicators. The second approach focuses on size change within species and lineages in several families of predominantly herbivorous species. For 60 Paleogene species and 39 Neogene species, change in average species size over successive biostratigraphic intervals is assessed by a criterion of doubling or halving of body mass relative to the preceding interval. New occurrences are compared to established species of the same genus and of the same family. In both records, size increases occur slightly more often than size decreases. The size distribution of groups changes more often through appearances of species of more than double or less than half the size of established species of the same group or by disappearances, rather than through rapid change of size within species. The pattern of change in median size and size range of contemporaneous species varies among families in both records. Three causes of evolutionary size change—climatic change, competition, and predation—are evaluated. In both records, climatic change and interspecific competition are considered the principle mechanisms for the observed changes.

Mammalian generic diversity and turnover in the late Paleocene and early Eocene of the Bighorn and Crazy Mountains Basins, Wyoming and Montana (USA)

Abstract Patterns of mammalian generic turnover, richness, and faunal composition were investigated for faunas from 17 biostratigraphic zones in middle Paleocene through early Eocene deposits of the Bighorn and Clarks Fork basins of northern Wyoming and the Crazy Mountains Basin of south-central Montana. Significance of turnover was evaluated (1) by comparison of observed turnover to expected turnover (calculated from the multiple regression of turnover on zone duration and generic richness), and (2) by comparison of observed turnover to a bootstrapped turnover distribution. Patterns of turnover and richness also were assessed in light of relative sampling quality of each faunal zone. The analysis identified four intervals of significant faunal change: the Torrejonian Tiffanian transition, the late Tiffanian, the earliest Wasatchian, and the middle-to-late Wasatchian. The first interval was characterized by a high number of last occurrences in the latest Torrejonian, resulting in a decrease in standing generic richness in the earliest Tiffanian, but no major changes in ordinal composition. During the next interval of significant turnover, the late Tiffanian, higher-than-expected first occurrences resulted in an increase in standing richness and a change in faunal composition, most probably reflecting the immigration of taxa from outside North America. The third, and most dramatic, interval of significant generic turnover took place in the earliest Wasatchian and was distinguished by a high number of first occurrences, but relatively few last occurrences. This led to a marked increase in generic richness, a pattern similar to that for the early Wasatchian of North America as a whole. The major change in faunal composition, as in the late Tiffanian, was largely composed of immigrants from other continents. The pattern of faunal change during the early Wasatchian of the Bighorn Basin, along with evidence for global warming at the Paleocene-Eocene boundary, supports previous interpretations associating this episode in mammalian evolution with the opening of high latitude intercontinental dispersal routes. During the fourth interval of interest, the middle to late Wasatchian, the Bighorn Basin fossil record shows a drop in generic richness. This differs from the overall North American pattern, and may be, in part, an artifact of still inadequate sampling for the latest part of the stratigraphic sequence in the Bighorn Basin.

Biochronology of uppermost Cretaceous and Lower Tertiary nonmarine Mollusca of the northern Great Plains, U.S.A. and Canada

The biochronologic use of nonmarine mollusks commenced in the northern Great Plains with the pioneering studies of F.B. Meek and F.V. Hayden in the 1850s and ‘60s. Their research focused on the chronostratigraphic organization of nonmarine and marine strata and included the naming of the Fort Union Group, which represents the Paleocene throughout the northern plains. Current research has focused on ascertaining the biostratigraphic distribution of nonmarine taxa throughout the post-Fox Hills Formation sections in the northern Great Plains, specifically in the Williston (WB: North Dakota, Montana, Saskatchewan), Powder River (PRB: Montana, Wyoming), and Crazy Mountains (CMB: Montana) Basins. The strata represented include the uppermost Cretaceous Lance (PRB) and Hell Creek (WB, PRB, CMB) Formations; Paleocene Fort Union Group, including (in ascending order) the Ludlow (WB)—Tullock (WB, PRB)—Bear (CMB), Slope (WB)—Lebo (PRB, CMB), Bullion Creek (WB)-Tongue River (WB, PRB)-Melville (CMB), and Sentinel Butte (WB)—lower “Wasatch” (PRB) Formations, and the Bear Den Member of the Golden Valley (WB) Formation; and the Lower Eocene Camels Butte Member of the Golden Valley Formation (WB) and main body of the “Wasatch” (PRB) Formation. About 2000 nonmarine molluscan localities have been collected from these strata and correlated with all of the approximately 200 relevant mammalian local faunas. The geologic section represented by each study area has a segment of the section that is biostratigraphically and biochronologically relatively well controlled by either molluscan or mammalian occurrences or both. These segments overlap sufficiently well to provide a nearly continuous composite section for the uppermost Cretaceous, Paleocene, and Lower Eocene. In the Montana portion of the Williston Basin, the uppermost Cretaceous (Lancian) taxon ranges of nonmarine mollusks and mammals are stratigraphically well controlled. Less abundant or less well-controlled occurrences elsewhere support the view that a diverse, molluscan assemblage, largely composed of highly sculptured unionid bivalves, is extinguished, relatively suddenly, near but before the end of the Cretaceous. The lower and lower middle Paleocene (Puercan and Torrejonian) section, as evidenced in isolated fossil occurrences, is a time of a substantially reduced number of low-diversity molluscan faunules consisting of a small mesogastropod-dominated snail fauna, a few taxa of which cross the Cretaceous-Tertiary boundary, and a small, unornamented (except for the umbonal region) fauna of unionids. The upper middle Paleocene (Torrejonian) and lower upper Paleocene (Tiffanian) contain a record indicating a resurgence in the molluscan fauna, particularly in the upland Paleocene terrains preserved in the upper Lebo and lower Melville Formations of the Crazy Mountains Basin. A relatively large number of localities contain a diversifying mesogastropod-dominated snail fauna, an increasing number of terrestrial taxa, and an increasingly diversified, but unsculptured, unionid fauna. The middle upper Paleocene (Tiffanian 3–4) faunal record, representing the “classic” Fort Union molluscan fauna of Meek and Hayden, was comparatively diverse, abundant, and dominated by freshwater snail taxa. Although known from substantially fewer localities, this interval also contains an increase in diversity and novelty of aquatic and terrestrial pulmonates. Unionids are locally abundant, but remain relatively undiverse. The uppermost Paleocene (presumed Clarkforkian) record in the Powder River Basin documents a continued increase in pulmonate taxa and a sustained, but compositionally different, diversity of mesogastropods. The unionid fauna is relatively unchanged. The Paleocene-Eocene (Wasatchian) boundary, based on mammalian, palynomorph, and plant criteria, is clearly shown by a widespread change in the composition of the molluscan assemblage. The overall faunal diversity is somewhat reduced, with a noted reduction in the diversity of certain freshwater mesogastropods, a few unionid taxa, and a continued increase in the representation of pulmonate taxa. In summary, uppermost Cretaceous and lower Tertiary strata in the northern Great Plains contain a sequence of nonmarine molluscan faunas that are sufficiently diverse and changing so as to permit the construction of a substantially more resolved biochronology than previously considered possible.