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During a study of macroflora from the Astartekløft locality in Jameson Land, East Greenland, endophytic insect ovipositions (egg traces) belonging to ichnogenus Paleoovoidus were recorded for the first time in ginkgoalean (Ginkgoites, Sphenobaiera, and Baiera) fossil leaves across the Triassic–Jurassic (Tr–J) transition (ca. 200 Ma). The ovipositions may have been produced by insects in the order Odonata (dragonflies and damselflies) and are relatively more abundant before than after the Tr–J transition, possibly reflecting changes in plant-insect association. Fossil clitellate annelid (leech) cocoons were also discovered in a macerated sample from a single bed within the Tr–J transition. The cocoons belong to two species: Dictyothylakos pesslerae and Pilothylakos pilosus, extending the range of the latter genus from the Early Cretaceous to the Early Jurassic. This new evidence suggests that the ecosystem and food webs were profoundly affected by the environmental degradation surrounding the end-Triassic event (ETE), which was marked by faunal mass extinctions and floral turnover. Invertebrate ichno- and body fossils may add significantly to paleoenvironmental information provided by plant fossil assemblages, and therefore a protocol for recording evidence of invertebrate activity in paleobotanical research is suggested, including analyzing a standardized number of specimens for fossil traces and bulk maceration for discovery of invertebrate body fossils. More well-designed studies on Mesozoic plant-invertebrate associations are needed and will provide deeper knowledge about the structure and evolution of complex ecosystems.
Sediment permeability is hypothesized to affect soft tissue fossilization within concretions through its effects on organic decay and concretion growth. The role of permeability was tested in a series of experiments in which cod tissue was decayed in glass beads of varying permeabilities. Decay was measured using infrared gas analysis (IRGA), and mineral precipitation within the beads (a proxy for concretion growth) was measured using micro CT scanning. The interactions of the three variables—sediment permeability, decay, and mineralization—were assessed with MANOVA and with linear regressions of decay and precipitation per unit decay on permeability. These two linear regressions were combined into a more general, nonlinear expression of the relationship between permeability and total mineral precipitation. The results show that sediment permeability has two competing effects on precipitation, the strength of each varying dynamically depending on permeability. Low permeability environments inhibit decay, thus enhancing fossilization but inhibiting overall precipitation because a build-up of decay products is necessary to promote mineral formation (the “decay effect”). However, low permeability environments can also increase precipitation per unit decay by inhibiting the diffusion of decay products away from the carcass, allowing for a faster build-up of decay products (the “mineralization effect”). At low permeabilities, the decay effect dominates (decay controlled), and precipitation is positively correlated with permeability. At higher permeabilities, the mineralization effect dominates (permeability controlled), and precipitation is negatively correlated with permeability. The experiments show that fossilization within concretions is promoted by decay inhibition (at low permeabilities) and rapid concretion growth (at intermediate permeabilities). Thus, the effects of permeability on fossilization are complex, and influence the mechanism of fossilization.
The genus Botrychiopsis consists of leaves with substantial heteromorphism, present in late Paleozoic Gondwanan floras. The genus is recorded in paleofloras from Australia, India, South Africa, Brazil, and Argentina, and occurs from the latest Mississippian to the early Permian. Here, we report and analyze the first record of plant-insect interactions found in the Botrychiopsis-type leaves from the basinal deposits of Permian Argentina and Brazil. The samples are from three different Permian deposits: Arroyo Totoral, Bajo de Véliz (Argentina), and Morro do Papaléo (Brazil). Evidence of insect-plant interactions was present in only eight of 154 specimens analyzed. We found evidence of margin and hole feeding damage made by insects. This represents the first evidence of plant-insect interactions in Botrychiopsis leaves from Permian Gondwanan deposits. The occurrence of herbivory only on the Permian species B. plantiana may indicate that consumption of these leaves began during this interval, not in the Carboniferous, as occurred with Cordaites leaves.
Silicification is an important mode of fossil preservation but the extent to which silicified material represents an unbiased sampling of the total fossil assemblage within a given rock sample remains poorly quantified. Here, we use paired analyses of thin sections and acid-extracted silicified specimens from the same samples to examine the biases introduced during silicification of Lower Triassic Virgin Limestone carbonates preserved in the Muddy Mountains of southern Nevada. Bivalves dominate most thin sections in the point count data, but rarely silicify completely enough to be recognized in residue. Echinoderms and gastropods are less abundant in thin section but dominate the residues. The abundances of these groups in thin section and residue are only weakly correlated. These findings suggest that although silicification generally captures relative trends in proportional abundance of higher taxa among samples, the silicification process can be taxonomically biased. Given the biases that can occur during silicification, it should not be assumed that silicified collections present a pristine picture of taxonomic or paleoecologic composition. Petrographic analysis has the potential to illuminate the reliability of paleontological data based on silicified collections.
The use of rocky intertidal assemblages in paleoecology and conservation paleobiology studies is limited because these environments have low preservation potential. Here, we evaluate the fidelity between living intertidal mussel bed communities (life assemblages or LAs) and mollusk shell accumulations (death assemblages or DAs) from the environmentally harsh Patagonian Atlantic Coast. LAs were sampled from rocky mid-intertidal and mussel-dominated habitats while DAs were collected from the high water mark at beaches in close proximity to the living intertidal community to assess live-dead mismatch at regional scales. DAs were restricted to the subset of species in the DAs that inhabit rocky intertidal habitats. A total of 37,193 mollusk specimens from 15 intertidal species were included in the analysis. Ten species were present in LAs, 14 in DAs, and nine were shared by LAs and DAs. DAs showed higher diversity, less dominance, and more rare species than LAs. Despite finding good agreement in species composition between DAs and LAs within the same region, smaller species are underrepresented, as shown by differences in size-frequency distributions. Our findings indicate that the composition of DAs is a result of the combined effects of spatial and temporal averaging, size-related biases, and biases related to low detectability of boring and vagile species in LAs. Thus, DAs do not accurately detect within-provincial latitudinal gradients in composition. However, DAs clearly capture differences between the Argentine–Magellanic Transition Zone and the Magellanic Province, indicating that DAs are informative tools at regional scales despite the environmental harshness to which they are subjected.