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This study documents the traces and burrowing behaviors of nymphs of the prairie cicada Cicadetta calliope (Hemiptera: Cicadidae), as observed in neoichnological experiments. Cicada nymphs were collected from the C horizons of sandy Fluvents along the Kansas River east of Lawrence, Kansas. The nymphs appeared to be fifth instars, 13–17 mm long and 6–7 mm wide. Nymphs were placed in plastic enclosures containing layers of colored, moist, very fine-grained sand. They burrowed immediately, excavating air-filled, sediment-enclosed cells between 20 mm and 40 mm long and averaging 9 mm wide. Burrowing was completed in three stages: (1) sediment in the forward portion of the cell was excavated and rolled into a ball with the forelimbs; (2) the nymph turned 180° using a forward roll, and moved to the back of the cell; and (3) the sediment ball was pushed up against the back wall of the cell and kneaded with the forelimbs into a thin layer. Resulting burrow traces are sinuous and distinctly meniscate and demonstrate that insect larvae construct meniscate, backfilled burrows in well-drained terrestrial settings. Cicadetta calliope nymphs and their traces are excellent analogs for meniscate trace fossils commonly found in late Paleozoic–Cenozoic alluvial deposits and paleosols. Such meniscate trace fossils are useful for interpreting the paleoenvironment and paleohydrogeology of the units in which they are found. In addition, such backfilled burrows can be used to supplement the fossil record of cicada-like hemipterans, currently known only from the latest Permian to the Early Triassic.
Most paleoecological and paleobiologic studies of the postextinction interval following the end-Permian crisis have been focused on rocks deposited in shallow shelf, open marine settings. Lower Triassic marginal marine environments have not been examined closely but represent a crucial piece of the postextinction puzzle since they provide an end member to which studies of open marine environments can be compared. The Lower Member of the Lower Triassic (Smithian-Spathian) Union Wash Formation is a mixed carbonate-siliciclastic succession deposited in environments ranging from intertidal to lagoonal and provides a glimpse into Early Triassic marginal marine settings and faunas. Fossil components of the member are dominated by echinoid spines and debris, which are interpreted to represent a parautochthonous fossil assemblage concentrated primarily in tidal-dominated distributary channels and as grain-rich mouth bars. This Early Triassic echinoid assemblage affords an opportunity to examine the paleoecology of echinoids during the postextinction interval and to speculate about how the extinction and recovery relate to long-term paleobiological trends. Echinoids of the Lower Member of the Union Wash Formation inhabited environments very proximal to the intertidal zone, and this distribution may have provided a survival mechanism in the wake of the end-Permian mass extinction by allowing echinoids to avoid shelfal stresses such as shallow-water anoxia and euxinia. These shallow-water echinoid forms would likely seed the diversification of all later echinoid taxa, and indeed, all later shelfal and deep-sea echinoids can be traced back to post-Paleozoic shallow-water forebears.
The seventh largest mass extinction of the Phanerozoic Era occurred in the Late Mississippian and coincided with the onset of the late Paleozoic ice age. Analyses of brachiopod genera from Mississippian strata of the Central Appalachian Basin reveal that the regional expression of the mass extinction occurred after the development of high-amplitude glacioeustasy by several million years and occurred instead during low-latitude cooling and the expansion of glaciation near the Mississippian-Pennsylvanian boundary. The Late Mississippian mass extinction was even more severe for genera in the Central Appalachian Basin than global metrics would predict; in addition to the genera of this basin that disappeared globally, many others disappeared regionally but survived elsewhere. The Late Mississippian mass extinction did not select against genera because of their environmental breadth, number of regional occurrences (a proxy for relative abundance), species diversity, or body size. Nearshore genera suffered very slightly higher rates of extinction. The mass extinction did, however, strongly select against genera with narrow global latitudinal ranges. These patterns of selectivity closely resemble those reported for the five largest Phanerozoic mass extinctions (Late Ordovician, Late Devonian, end-Permian, end-Triassic, and end-Cretaceous). This selective regime also underpinned the whole of the late Paleozoic ice age because genera that survived the Late Mississippian mass extinction dominated the global brachiopod fauna until the ice age ended in the middle Permian.
The Triassic Ischigualasto-Villa Unión Basin is an extensional basin located in central-western Argentina. It includes the Los Rastros Formation, a lacustrine-deltaic sequence comprising several coarsening-upward cycles of black shale, siltstone, and sandstone. We performed a taphonomic analysis of the floral and faunal fossils of the Los Rastros succession and have defined five plant taphofacies, four invertebrate taphofacies, and four vertebrate taphofacies. Our taphonomic model characterizes four subenvironments within the lacustrine-deltaic environment of Los Rastros Formation. These include 1) offshore lacustrine, 2) prodelta, 3) deltaic mouth bar, and 4) deltaic plain subenvironment. Our analysis of fossil assemblages allows us to reconstruct the structure of the original ecosystem. The lake margins were vegetated with small ginkgophytes, corystosperms, and sphenophytes. River margins were characterized by riparian thickets of sphenophytes, while the proximal floodplains supported closed woodlands of corystosperms, cycadophytes, and pteridophytes. More distal floodplains were covered with open conifer forests. The invertebrate fauna included insects (Blattoptera, Hemiptera, Coleoptera) associated with lakeshore vegetation and conchostracans that inhabited both the lake shoreline and smaller ponds in the floodplains. Fish and temnospondyl amphibians probably inhabited the delta plain and incoming fluvial systems. The activity of nonmammalian therapsids, crurotarsal archosaurs, and putative dinosaurs is recorded by trackway surfaces in the lake shoreline subenvironment.
The Kimmeridgian shallow-water carbonates of the Swiss Jura Mountains display stratigraphic levels containing mass accumulations of nerineoidean gastropods. The macro- and microfacies of the rocks with these nerineoidean assemblages suggest that their occurrence was related to water depth, physical energy within the habitat, sedimentation rate, substrate stability, and food supply. Typical nerineoidean shells are high spired and exhibit unique spiral laminae (folds) on the internal walls. Mass accumulations consisting of large, heavy individuals are believed to represent a semisessile, suspension-feeding community that utilized an external food source. During times of enhanced precipitation and run-off from the hinterland, terrestrial organic matter may have been supplied into the shallow sea, thus forming a source of food for the nerineoids. Alternatively, relative sea-level change during transgression may have led to large-scale coastal erosion and flooding of the platform, also potentially leading to a mobilization of organic matter. Size and morphology of the high-spired shells seem to indicate a trend toward maximal external volume. Development of folds within the shell is interpreted as a modification to maintain a small internal volume. The faunal and floral composition of the strata indicates a suspension-rich, high-energy environment with a low-sedimentation rate and a stable substrate. This allowed mass colonization by epifaunal nerineoids, which, in turn, formed a frameworklike structure. The heavy shells acted as a grid, trapping the sediment in between. In this way, a reinforced carbonate accumulation formed.
Isotopic variation in northern and southern hard clam (quahog) shells is used in studies including paleoecology, paleoclimatology, and archaeology. It is unknown, however, whether species-specific isotopic differences exist. Three genotypes—Mercenaria mercenaria, M. campechiensis, and their natural hybrid form—are found in coastal Florida waters and differentiation of genotypes can be difficult to determine morphologically. This issue may be problematic when using archaeological shells as paleoclimate archives, because genetic analysis cannot be done on such specimens. Their co-occurrence in coastal Florida waters provides a unique opportunity to study whether all three genotypes of modern individuals record the same environmental information preserved as variation in oxygen and stable carbon isotope ratios. A random sample of 49 individuals collected alive at the same time and from the same locality in Pine Island Sound were classified to genotype using allozyme electrophoresis. Three juveniles from each genotype were selected for isotopic analysis to control for ontogenetic effects. Timing of growth increment formation inferred from oxygen isotope ratios reveals similar overall patterns wherein dark (slow growth) increments formed in mid- to late spring and light (fast growth) increments formed in late fall. Results of the mixed model ANOVA (analysis of variance) indicate that no significant species-related differences exist in the variation of oxygen and carbon isotope ratios, although the Kolmogorov-Smirnov goodness-of-fit test detected a systematic difference among δ13C values of M. mercenaria and M. campechiensis comparison and M. mercenaria and the hybrid shell comparison. Any genotype or combination thereof is, thus, suitable for environmental and climate reconstruction using oxygen isotope ratios. The utility of carbon isotope ratios as an environmental proxy, however, remains questionable.
Analysis of the saber-tooth morphology within the Felidae indicates that canines of various saber-toothed species grow differently. Stable oxygen isotopes analyzed from tooth enamel reveal that the scimitar-toothed Homotherium serum, which possessed short, broad sabers, had tooth crown growth rates similar to modern lions. This contrasts with the longer and thinner, dirk-toothed saber species in the genus Smilodon, S. gracilis and S. fatalis, which had much faster growth rates. With a more rapid growth rate, Smilodon reduced the total duration of crown growth to a period of time similar to that observed in modern lions, even though its tooth crown was twice as large. While comparable in overall morphology, developmental differences may reflect ecological differences among taxa bearing saber-toothed canines.