Dena M. Smith

OSSE Mapping of Galactic 511 keV Positron Annihilation Line Emission

The Oriented Scintillation Spectrometer Experiment (OSSE) observations of the Galactic plane and Galactic center region have been combined with scanning observations by the Transient Gamma-Ray Spectrometer (TGRS) and Solar Maximum Mission (SMM) instruments to produce maps of the Galactic narrow 511 keV positron annihilation line radiation. Two different mapping methods, singular value decomposition and maximum entropy, have been applied to the data. In both cases, the resulting maps show evidence for three distinct features: (1) a central bulge, (2) emission in the Galactic plane, and (3) an enhancement or extension of emission at positive latitudes above the Galactic center. Modeling of the data confirmed the existence of these features. The derived distribution is found to be in good qualitative agreement with nearly all of the historical observations of narrow 511 keV line emission from the Galactic center region. No evidence of time variability is found. Various possible production mechanisms for the observed positrons, including the positive-latitude enhancement, are presented. It is found that supernovae are capable of producing positrons at the required rate to account for the intensity and morphology of the observed 511 keV line emission.

The fossil record and macroevolutionary history of the beetles

Coleoptera (beetles) is the most species-rich metazoan order, with approximately 380 000 species. To understand how they came to be such a diverse group, we compile a database of global fossil beetle occurrences to study their macroevolutionary history. Our database includes 5553 beetle occurrences from 221 fossil localities. Amber and lacustrine deposits preserve most of the beetle diversity and abundance. All four extant suborders are found in the fossil record, with 69% of all beetle families and 63% of extant beetle families preserved. Considerable focus has been placed on beetle diversification overall, however, for much of their evolutionary history it is the clade Polyphaga that is most responsible for their taxonomic richness. Polyphaga had an increase in diversification rate in the Early Cretaceous, but instead of being due to the radiation of the angiosperms, this was probably due to the first occurrences of beetle-bearing amber deposits in the record. Perhaps, most significant is that polyphagan beetles had a family-level extinction rate of zero for most of their evolutionary history, including across the Cretaceous–Palaeogene boundary. Therefore, focusing on the factors that have inhibited beetle extinction, as opposed to solely studying mechanisms that may promote speciation, should be examined as important determinants of their great diversity today.

How Physical Characteristics of Beetles Affect their Fossil Preservation

Abstract Although insect size and robustness often have been hypothesized to be factors that lead to taphonomic bias in the insect fossil record, no studies have examined how these factors directly affect an insects preservation potential. In this study, laboratory experiments were performed on modern Coleoptera (beetles) to examine the importance of insect morphology on preservation potential. A rotary tumbling barrel was used to determine how insect size and robustness would influence sinking and disarticulation rates. Although size and robustness were not correlated directly, beetles that were larger and more robust were more resistant to disarticulation than smaller, less-robust beetles. Waterlogged specimens gained increased flexibility in their exoskeletons, and were difficult to puncture. Sinking and disarticulation rates were correlated, although it took fewer days for beetles to sink than it took to begin disarticulating. A white-colored film was apparent on all specimens within a few days of their introduction to the tumbling barrel; however, major disarticulation did not occur until the specimens sank to the bottom. An examination of the fossil-beetle literature also suggests the importance of hardness in preservation potential. Although often considered fragile, given the right physical characteristics and environmental conditions, insects can be resistant to disarticulation and decay.

GENERATING EMPIRICALLY DETERMINED, CONTINUOUS MEASURES OF LEAF SHAPE FOR PALEOCLIMATE RECONSTRUCTION

Abstract Paleobotanists have developed numerous methods for quantifying correlations between leaf form and climate, so that fossil leaves can be used to estimate past terrestrial climate. Approaches currently used can be broken into two classes: those using categorical, primarily qualitative shape characters (such as round base) and those describing shape as ratios or other abstract mathematical descriptors (such as perimeter-to-area ratio). Both classes of approach have limitations and are hard to compare to one another. We show how eigenshape analysis provides both interpretable characters and measures of continuous variation, thus potentially overcoming the limitations of both current approaches. We applied eigenshape analysis to a sample of 394 nonlobed leaves from extant assemblages to empirically identify independent leaf shape characters. This resulted in the identification of 20 shape characters. Of these, 13 reflected variation due to broad-scale asymmetry as well as asymmetry localized to the tip, base, and lamina-petiole junction. The remaining seven characters, in order of variance explained, corresponded roughly to base shape, tip angle, location of widest portion of the leaf (ovate to obovate variation), extent of widest portion of the leaf (elliptic to oblong variation), tip shape (blunt to drip tip), ovate to obovate variation localized to the middle of the leaf, and extension of the lamina along the petiole at the lamina-petiole junction. All 7 of these characters and only 1 of the 13 asymmetry characters had an association with climate. These characters corresponded to five of the seven broad categories of Wolfes Climate-Leaf Analysis Multivariate Program shape descriptors, excluding only tooth shape and lobing. The results of this study indicate that eigenshape-generated measures of leaf shape merit further exploration.

EXCEPTIONAL PRESERVATION OF INSECTS IN LACUSTRINE ENVIRONMENTS

Abstract Insects are diverse and abundant components of most terrestrial ecosystems today and are well represented in the fossil record with first occurrences in the Early Devonian. Fossil deposits that include exceptionally preserved insect assemblages are found in several different types of Lagerstätten, with their preservation in amber and in lake sediments being of greatest importance. Researchers have used a variety of approaches to study the taphonomy of insects preserved in lacustrine environments and have identified several important variables that contribute to the preservation potential of insects. A combination of insect ecology, morphology, and the depositional setting in which an insect specimen rests influence the preservation potential of insects and ultimately affect the spatial, temporal, and compositional resolution of fossil assemblages. In general, lacustrine insect assemblages experience very little spatial and temporal averaging. Compositional fidelity of assemblages tends to be low, with an overabundance of allochthonous taxa from smaller size classes. In addition, the composition of fossil insect assemblages will be biased depending on the specimens position within a lake, dependent on both water depth and distance from shore. Focus areas for future research are outlined, as are recommendations for improving field collecting methods and statistical approaches. Finally, the benefits of conducting synthetic studies using global databases and the importance of studying unexceptional deposits are discussed.

TAPHONOMY OF DIPTERA IN LACUSTRINE ENVIRONMENTS: A CASE STUDY FROM FLORISSANT FOSSIL BEDS, COLORADO

Abstract The purpose of this paper is to study the taphonomy of fossil flies (Diptera) preserved in the lacustrine deposits of the Florissant Fossil Beds (late Eocene), Colorado, United States. Three hundred and twenty-six fossil Diptera were examined, collected from a nearshore (n = 215) and an offshore (n = 111) site. The degree to which a specimens preservation quality correlated with the ability to identify the specimen to various taxonomic levels and whether specimen size, orientation, or disarticulation had an effect on a preservation quality were evaluated. Also examined was the influence of depositional environment on these variables. Preservation quality was found to be important for identification to species level, but specimens of low preservation quality were still identifiable to the family and genus levels. Specimen size, orientation, and disarticulation were not correlated with the identifiability of a specimen. There was no significant difference in the orientation, disarticulation, or preservation quality of specimens found in the nearshore and offshore sites. There was a significant difference in the size of specimens preserved at each site, with larger specimens being found offshore. More specimens were found in the offshore site, but species richness did not differ between the two sites. Composition of taxa did differ depending on the site. These results demonstrate the importance of collecting all specimens, as even poor quality and disarticulated specimens are identifiable and useful in studies of insect ecology and evolution. In addition, depositional environments should be documented, as size sorting can bias the taxonomic composition of assemblages.

Exceptionally Preserved Fossil Insect Ears from the Eocene Green River Formation of Colorado

Abstract Tympanal ears in insects are important for both intraspecific communication and for the detection of nocturnal predators. Ears are thought, based on modern forms, to have originated independently multiple times within insects and can be found on multiple regions of the body. Here we describe and document the exceptionally well preserved tympanal ears found in crickets and katydids from the Eocene Green River Formation of Colorado, which are virtually identical to those seen in modern representatives of these groups. These specimens are among the best preserved insect ears in the fossil record and establish the presence of ears in two major clades of Orthoptera 50 million years ago. Also discussed and evaluated are previously described insect ears from the Mesozoic and the implications of the findings of the present study for studying the evolution of ears within insects.

Depositional Setting and Fossil Insect Preservation: A Study of the Late Eocene Florissant Formation, Colorado

Abstract To study how lacustrine depositional environments influence the preservation of insects, the abundance, size, and quality of insect specimens were compared across shale, mudstone, and siltstone within the Florissant Formation of Colorado. These lithologies were chosen because they reflect differences in associated energy, grain size, and presence of diatom layers. Eight hundred and twenty-three fossil insects were collected from a single stratigraphic section within the lacustrine deposits of the Florissant Formation (late Eocene). Sampling across these lithologies was associated with low specimen collection rates (3.7–5.6 insects collected per collector-day) that did not differ across the sedimentary environments. In addition, the relative abundance of insect orders did not differ across the sedimentary environments. Specimens were significantly smaller and less variable in size within the siltstone than they were within the shale and mudstone, likely due to differences in temporal and spatial averaging. Overall, 56% of insect specimens were disarticulated and 66% were considered of low quality. Insect disarticulation levels, preservation quality, and specimen orientation did not differ across all lithologies in general and for the other three insect orders, despite differences in coleopteran (beetles) preservation in siltstone where they were less disarticulated and more commonly preserved in a lateral position. This indicates that insect specimens of the quality typically associated with shale deposition also can be found in mudstone and siltstone, which increases the areas within lakes that can be sampled and compared for paleoecological studies.

Host fidelity over geologic time: restricted use of oaks by oak gallwasps

Abstract. Oaks and their associated gallwasps are often cited as a classic example of coevolution in a plant-insect system. Therefore, it is expected that these gallwasps should demonstrate a high degree of host fidelity over their evolutionary history. To test this, we studied 25 fossil floras from the Oligocene through Pliocene of the western United States. Galls were found on the leaves of Quercus simulata-type Knowlton, 1898 and Q. pollardiana-type (Knowlton) Axelrod, 1940, and match previously reported galls of the form genus Antronoides Waggoner and Poteet, 1996. These fossil leaf-galls are similar to those made on oaks by modern Cynipini wasps, and were restricted to two oak species. Galls are present on these oaks in western floras for a span of 30 million years, indicative of remarkable host fidelity through time. The distribution of galled leaves from across the western United States indicates that the radiation of this group of gallwasps occurred more or less simultaneously across a wide geographic area.

FIRST FOSSIL ORTHOPTERA FROM THE JURASSIC OF NORTH AMERICA

Abstract A new species of Orthoptera, Parapleurites morrisonensis, is described from the upper Jurassic Morrison Formation of Colorado, USA. This is the first insect described from the Morrison Formation and the first orthopteran described from the Jurassic of North America. No other members of the family Locustopsidae have been described in North America previously, and the other species of Parapleurites are only known from Siberia. The lack of Jurassic Orthoptera in North America is likely due to a combination of taphonomic variables and collector bias. The discovery of Parapleurites morrisonensis and the potential for finding other Jurassic Orthoptera are important to understanding the evolution of this diverse and widely distributed group.