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Prokaryota in natural environments form biofilms, which are benthic assemblages of a variety of microorganisms embedded within their extracellular mucilage. Biofilms are firmly attached to surfaces such as aquatic sediments. Quorum sensing by the many microbes in a biofilm is collective decision making and cooperation for responding to internal and external parameters affecting the community. This communication is based on chemical signaling affecting gene expression of the microorganisms. Microorganisms situated in a biofilm change behaviors and metabolic activities to comply with the requirements of the entire biofilm cooperative. Consequently, reconstruction of the evolution of prokaryotes in Earth history must consider the biofilm way of microbial life. Biogenic sedimentary structures might not represent certain microbial groups, but in fact may be relics of modified cooperative microbial activities. Future research should focus on detectable biosignatures caused by biofilm consortia as a whole instead of on the appearance or extinction of individual microbial groups. Such sedimentary structures as stromatolites and microbially induced sedimentary structures (MISS) are intrinsically controlled by biofilms, but also affected by extrinsic (environmental) conditions.
A vertebral centrum belonging to a dyrosaurid, a marine crocodilian recovered from the late Paleocene of Niger, bears a large ovoid and deep puncture on its lateral flank. This mark is identified as a wound inflicted by the bite of another crocodilian. Although the wound shows evidence of healing, the vertebral centrum has been severely damaged and deformed. It provides a rare direct evidence of the aggressive interactions taking place between these now extinct marine reptiles, the largest known marine predators of their time before the rise of the archeocetes.
During the early Turonian, Pseudaspidoceras flexuosum was a common ammonite in low and intermediate latitudes. At Vallecillo section, northeastern Mexico, 160 specimens were recovered from the section, allowing for quantitative analysis. The combination of quantitative data with sedimentology and geochemistry allow for erection of a differentiated model for the mode of life of P. flexuosum. This model provides insight into the paleobiology and paleoecology of this ammonite, and ammonites in general. The Vallecillo section contains the longest record of this species worldwide. Changes in abundance and diameter of this ammonite appear to be related to changes of oxygen content in the water column. P. flexuosum dwelled in the well-oxygenated upper surface water and formed part of the open marine pelagic ecosystem; a demersal mode of life is excluded here. Dimorphism is expressed in size and less in ornamentation, but both dimorphs bear long spines, first recorded for this species. The spines were likely used for stabilization in the water column and protection against suction-feeding fishes and comparable predators, but not against pycnodont sharks. A sensory function is also plausible for the last one to three pairs of spines. This differentiated model of the mode of life of P. flexuosum contrasts with the paleoecology reconstructed for other ammonites. Ammonites covered a wide range of ecological niches, and their complex paleoecology will only be solved with more species-based analyses.
Graphoglyptids are a group of deep-sea trace fossils that exhibit ornate burrow geometries. Feeding patterns represented by these burrows have been interpreted as fodinichnial (mining), pascichnial (grazing), and/or agrichnial (farming). In this study, several different graphoglyptid trace fossils were analyzed quantitatively using fractal analysis to determine which of these three feeding modes is most appropriate as an interpretation. Graphoglyptid burrows lend themselves to fractal geometric analysis, because they commonly exhibit the essential fractal characteristics of scale invariance and self similarity. Fractal analysis is presented as a tool for analyzing geometric configurations by combining shape complexity and space usage into one number, the fractal dimension. Fractal dimensions of such graphoglyptid burrows as Paleodictyon and Spirorhaphe were compared with those of known fodinichnial burrows, such as Zoophycos, and pascichnial trails, such as Scolicia, all from Zumaia, Spain. Results indicate that the deposit-feeding burrows (fodinichnia and pascichnia) illustrate a high fractal dimension, as would be expected for a deposit-feeding–optimal foraging strategy. Graphoglyptids illustrate a consistently lower fractal dimension than the deposit-feeding burrows, thus providing evidence against the suggestion that they represent fodinichnial or pascichnial behaviors. This observation supports the hypothesis that graphoglyptids represent agrichnial activity rather than mining or grazing activities.
Drilling predation is frequently studied in the fossil record. Less information is available from recent environments, however. Previous studies have indicated that drilling predation is usually higher in the tropics but little research has been undertaken in high latitudes. To address this hypothesis, we examine muricid-drilling predation along a 1,000 km transect in southern South America. Drilling frequencies ranged between 3% and 36%, and they were not correlated with the abundance of the predator (Trophon geversianus) or the abundance of its preferred prey. The only locality with exceptionally high predation (36%) was a heavily anthropogenically impacted site. Trophon exhibited different drilling strategies on different prey, and edge drilling represented 27%–56% of the drill holes in mytilids. Drilling frequencies were not correlated with latitude or water temperature. Our results, however, show that drilling frequencies are indeed lower at high latitudes compared to the tropics, and these data provide a recent baseline to compare and interpret spatial variability in muricid drilling predation from past environments. The fact that dead-shell assemblages seem to be recording human-related impacts in this system strengthens their relevance as potentially valuable conservation tools.
Corals are important marine archives for high-resolution reconstructions of low-latitude climate variability in preinstrumental and historical periods. Herein, we present monthly-resolved records of δ18O and Sr/Ca for the 20th century (1917–2007) from a Porites lutea colony from the Maldives (northwestern Indian Ocean). Previous studies of annual mean extension rates of this coral revealed a distinct dependency of coral growth on variations of sea surface temperature (SST) and hydraulic energy, driven by El Niño-Southern Oscillation (ENSO) and southwestern Indian monsoon forcing. This enables the investigation of coral δ18O and Sr/Ca ratios from the Maldives as archives of historical ENSO and Indian monsoon variability. Unlike other locations in the Indian Ocean, correlation of δ18O and SST is weak (r = −0.42; p < 0.001), suggesting interferences of SST and seawater δ18O at the location. These interferences probably caused significantly weaker interannual ENSO signatures in δ18O as evident in the extension rates of our coral and in geochemical proxies measured at other sites in the northwestern Indian Ocean. Sr/Ca ratios show bias by nontemperature effects, and were not used to estimate seawater δ18O and salinity. Strong decadal variability (10–14 years) in δ18O, indicative of a Pacific ENSO signal, is not found in instrumental SST, and could be explained by variations in salinity. Interannual and decadal monsoon variability (6–7 yrs and 18–19 yrs), found in the extension rates, was not found in δ18O, suggesting, in agreement with other studies, that geochemical coral proxy records from the northwestern Indian Ocean do not capture temporal variations of the Indian monsoon strength.
Microbial mats have been implicated in exceptional fossil preservation. Few analyses have addressed how these complex-multilayered biofilms promote fossil preservation. The sequence of changes during decay of neon tetra fish were tracked up to 27 months, and their decomposition in mats was compared against nonmat sediments (control fish). Statistically significant differences in quantitative variables (length, width, and thickness) are provided (ANOVA test, in all cases, P < 0.001). Changes in the qualitative features (body-head, fins, scale connection, and eye and body coloration) were phenetically analyzed resulting in two clusters and highlighting that notable differences in decay began at day 15. Mat fish show a delayed decomposition maintaining the external and internal body integrity, in which soft organs were preserved after 27 months as shown by Magnetic Resonance Imaging. We discuss how the organization, structure, and activity of this community are interrelated, favoring exceptional preservation. Microbial mats entomb the fish from the earliest stages, forming a Ca-rich coat over the carcass while embedding it in an anoxic condition. This quick entombment provides important protection against abiotic and/or biotic agents.