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Laboratory experiments conducted with larvae and adults of the northern or southern masked chafer beetle (Scarabaeidae: Cyclocephala lurida or C. borealis) tested hypotheses that beetle larvae construct meniscate, backfilled burrows and that they are distinct from backfilled burrows constructed by marine organisms. Beetle larvae were placed in narrow enclosures with laminated moist, fine-to-medium-grained sand and allowed to burrow for several weeks. Beetle larvae did not create open burrow systems but instead excavated single open cells approximately twice their body width and roughly equal to their body length. Burrowing was accomplished by scraping sediment with the head and mandibles, consolidating excavated sediment into a ball, rotating 180° with the ball to the back of the cell, and packing the ball onto the posterior end of the cell. The beetle larvae produced vertical-to-horizontal traces that were straight to tortuous and composed of discrete packets of meniscate backfill. Adult chafer beetles moved through the media using a sand-swimming motion, that is, by passing sand around their bodies with the legs. Traces produced by adults are characterized by straighter axes and mixed passive and active fill resulting from sediment collapse and sediment transported backward. When vertical, adult burrows contain chevron-shaped fill. Traces produced by these beetles are similar to adhesive meniscate burrows found in many ancient continental deposits as old as the Permian and can be assigned to Naktodemasis isp. We propose that Naktodemasis with this kind of burrow morphology were soil-dwelling insect larvae that used burrowing mechanisms similar to chafer beetle larvae. These experiments demonstrate that this kind of burrow morphology is terrestrial in origin, suggesting that previous interpretations that the burrows are subaqueous in origin need to be reevaluated.
Shallow-water Sporolithon rhodoliths from New Zealand are described here on the basis of shape, size, composition, internal structure, and major taphonomic attributes, with the aim of discussing their significance in the framework of current ecological and paleoecological models of rhodolith formation and accumulation. The very shallow water environment (<2 m) of the Whangaparaoa Peninsula undergoes daily tidal currents and seasonal storm conditions. These factors, along with the availability of cobbles and pebbles as suitable substrate, lead to the accumulation of spherical, fruticose, monospecific, nucleated, and internally compact rhodoliths. The observed taphonomic features include apical abrasion, intercalary growth of protuberances after mechanical breakage, and multiple growth stages with distinctive bioerosion (by bivalves, annelids, and cyanobacteria), which are identified by internal abrasion surfaces and dark layers. A review of the pattern of global distribution of the coralline genera comprising very shallow-water rhodoliths (<2 m) identifies five major categories: (A) unattached protuberances, commonly monospecific, made up of one or more genera (Phymatolithon, Lithothamnion, Lithophyllum) in cool to cold waters at middle to high latitudes; (B) rhodoliths composed of dominant Hydrolithon and other mastophoroids (Neogoniolithon or Spongites) with subordinate Lithophyllum in the tropics; (C) unattached protuberances of Neogoniolithon associated with seagrass meadows, from middle latitudes, in warm to warm-temperate waters; (D) mainly fruticose, monospecific, rhodoliths composed of Mesophyllum, Lithothamnion, Hydrolithon, and Neogoniolithon under tidal currents in cool waters in the Southern Hemisphere; and (E) Sporolithon rhodoliths of cool waters in the Southern Hemisphere, which suggest an austral polar emergence of the genus.
The Late Miocene Libros biota is a lacustrine-hosted, Konservat-Lagerstätte from Libros, near Teruel in northeast Spain. Adult frogs are characterized by the preservation of their soft tissues, some in histological detail. The soft tissues of the body outline are preserved as a layered structure, which comprises a central carbonaceous bacterial biofilm enveloped by the phosphatized remains of the mid-dermal Eberth-Katschenko layer, external to which is a second, thinner, carbonaceous bacterial biofilm. Bacterial autolithification is restricted to limited phosphatization of the cell margins of bacteria adjacent to phosphatized dermis. Phosphatization occurred during the late stages of decay; phosphate was sourced primarily from the dermis itself. Other tissues and organs are also defined in authigenic minerals: nervous tissue (aragonite), the stomach (calcium phosphate), and collagen fibers of the dermal stratum compactum (calcium sulphate); bone marrow is organically preserved. The disparate modes of soft-tissue preservation within individual specimens reflects development of several highly localized, chemically distinct microenvironments within the frog carcasses during decay. These microenvironments correspond to individual organs and tissues, were established at different times during decay, and varied in their duration. The preservation of soft tissues via multiple taphonomic pathways was controlled ultimately by anatomical and physiological factors.
Most research regarding ecological response to extinction in the fossil record focuses on qualitative, taxonomically based analyses. Shifting to quantitative analyses that incorporate paleocommunity-level data offers a richer ecological perspective on how paleocommunities respond to extinction. During the Late Ordovician (Mohawkian), a regional extinction occurred among marine taxa in the Appalachian Basin of eastern North America. To examine community-level paleoecological change across this extinction boundary, field censusing of macroinvertebrate genera was completed for the Nashville Dome of Tennessee, the Jessamine Dome of central Kentucky, and the Valley and Ridge area of western Virginia. In each region, shallow and deep subtidal environments were sampled in four stratigraphic sequences representing preextinction and postextinction intervals (M3 and M4 sequences and M5 and M6 sequences, respectively). Diversity metrics calculated from subsampled field data generally decrease across the extinction boundary and into the M6 sequence, with more significant declines in the deep subtidal facies and Virginia samples. These facies and regional differences in diversity reflect environmental and geographic variability not only in the effects of the extinction but also in the extent of immigration of new taxa to different areas of the basin. Despite diversity declines, evenness varies little among sequences, facies, and regions across the extinction boundary, suggesting no major change to the relative abundance structure of paleocommunities. Analyses of shifts in ecospace use (particularly tiering and motility of taxa) and multivariate ordination, however, also reveal strong environmental and geographic differences in ecological response due to changes in rank abundance of common taxa.
Lower Triassic carbonate sedimentary rocks exhibit fabrics and facies indicative of reduced bioturbation and reduced abundance of skeletal animals and algae relative to their Permian counterparts. Widespread microbial mounds are one widely cited example. Micritic spheroids of probable microbial origin occur at a few horizons in the Spathian (uppermost Lower Triassic) Virgin Limestone Member of the Moenkopi Formation, exposed in southern Nevada. These spheroids (3–12 mm) consist of an irregular framework of micrite clots up to 100 μm in diameter and micrite-walled filaments ∼10 μm wide and <500 μm long. Based upon their microstructure, we suggest that these microbial spheroids formed through the rapid microbial precipitation of calcium carbonate from seawater. As such, they probably represent unattached analogues of Early Triassic microbial mounds. The microbial spheroids formed and lithified rapidly in shallow-water, high-energy settings. Their presence, in concert with other carbonate microbialites from the Moenkopi, is consistent with the observation that microbially mediated precipitation was an important carbonate depositional mode in the aftermath of the end-Permian mass extinction.