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The earliest Petroxestes borings were excavated in large trepostome bryozoans in the Sandbian (earliest Late Ordovician) of Estonia. The Estonian specimens are morphologically similar to the type material from the later Katian of North America. Petroxestes pera is rare in the Sandbian of Estonia and occurs only in biogenic hard substrates. Petroxestes borings occur in muddy environments that were preferred by macroborers in the Hirnantian and early Silurian of North America. It is possible that muddy environments supported higher bioerosion intensities and higher diversity of bioerosional traces in the shallow epicontinental seas of the Late Ordovician. The discovery of Petroxestes in the Sandbian of Estonia supports the idea that there was an earliest Late Ordovician peak in the diversification of borings in Baltica. It is possible that there was a migration of bioerosional trace makers from Baltica to Laurentia in the Late Ordovician.
Coprolites are traditionally analyzed from a morphological perspective. Few studies exist from an organic geochemical perspective, and most of these consider recent specimens. This study represents an analysis of coprolites from deep time, using both traditional one-dimensional and also two-dimensional gas chromatography-mass spectrometry. We find organic molecules preserved in coprolites from the Triassic, and that both dietary habits of the defecators and paleoenvironment can be interpreted using comparative distributions of biomarker abundances in the coprolites. Steranes having 27 carbon atoms are known to be derived from animal steroids whereas those with 29 carbon atoms are known to be derived from plant steroids. The predominance of steranes with 27 carbon atoms over those with 29 carbon atoms in a non-marine environment was interpreted as evidence for the defecator(s) being predominantly carnivorous or possibly omnivorous. A series of tricyclic terpanes ranging from C19 to C28 was examined to determine the environment. The present study suggests that one or possibly all of the defecators may have been small-medium carnivores that lived in an aquatic or near aquatic setting.
Centipedes extend to the Silurian yet have a relatively poor fossil record. Many species of extant centipedes are semi-fossorial to fossorial and contribute to soil processes, suggesting that their trace fossils should be common in paleosols. The goal of this project was to document the types of biogenic structures produced by two species of large, semi-fossorial centipedes, Hemiscolopendra marginata and Scolopendra polymorpha, to aid in the recognition of fossil centipede burrows. Ten specimens of each species were placed in large, sediment-filled terrariums and observed over periods of 14 days. The centipedes burrowed via intrusion, compression, and excavation, moving throughout the enclosure both near the surface and deep within the sediment. Open burrows produced by the centipedes were cast with plaster and the ichnofabric produced was observed through the enclosure walls. The centipedes primarily produced J-, U-, and Y-shaped burrows as well as complexes of linked burrows. The burrows were elliptical in cross section and possessed thin, intermittent, compressional linings. The centipede burrows were compared to burrows of other extant soil arthropods including millipedes, spiders, and scorpions as well as Pennsylvanian to Permian ichnofossils. The centipede burrows were distinct from those of other soil arthropods and many aspects of the ichnofossils were similar to those produced by the centipedes. Description of burrows produced by centipedes can aid in the interpretation of continental ichnofossils and improve our understanding of the composition of ancient soil ecosystems. This knowledge is especially important given the poor preservation potential of centipedes in the environments they inhabit.
Extensive areas covered by semi-permanent water bodies were common during the Miocene in the Neotropics. These floods are noteworthy because of their possible role in promoting the high biological diversity observed today in the Amazonia. In particular, a relatively good understanding of the floods has been achieved for the Llanos basin of Colombia and western Amazonia. In these two basins the evidence suggests episodes of marine incursions and development of lacustrine systems at different times during the Miocene. Other intra-montane basins in Colombia, like the Middle and Upper Magdalena basins, also show clear evidence that water bodies covered them during that time. However, the chronostratigraphy and paleoecology of these deposits are still unclear. In this study, we use the palynological record of the Middle and Upper Magdalena valleys to establish the age of the deposits of the Barzalosa Formation, a unit that preserves a detailed record of a lacustrine system deposited during the late early Miocene in the Upper Magdalena Valley. The results indicate that the Barzalosa Formation is correlative with the lacustrine deposits of the La Cira fossiliferous horizon in the Middle Magdalena Valley. This indicates that extensive lacustrine systems covered the intramontane basins of the northern Andes during the early Miocene. Paleoecologically, the Barzalosa Formation is the result of the evolution of a lacustrine system in three phases, which show marked differences in the proportion of algae, palynological composition and sedimentary depositional sequence. Climate and tectonic processes were the most probable mechanisms controlling the evolution of the Barzalosa system.
A new teichichnoid trace fossil, Syringomorpha cyprensis from the Miocene of Cyprus, is proposed as a vertical burrow composed of an arcuate-like tube with horizontal parts to subhorizontal distally and vertical to subvertical parts proximally and triangular spreiten in the inner corner of the tube. Previously, this ichnogenus was represented only by the lower Paleozoic, shallow marine S. nilssoni, which disappeared after the Cambrian. Syringomorpha cyprensis marks the reappearance of similar behavior, in a deep-sea environment with pelagic, contouritic, and turbiditic sedimentation, influenced by frequent turbiditic and bottom current flows. Both ichnospecies of Syringomorpha could be produced by the same taxonomic group of probable worm like organisms (polychaetes?). Energy conditions were a stronger influence on the distribution of S. cyprensis tracemaker rather depth.
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