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Two new tetrapod trackways are described from the Tapinocephalus Assemblage Zone of the South African Karoo Basin. We interpret both to be traces attributable to small anamniote tetrapods. The larger footprints are tentatively referred to aff. Batrachichnus salamandroides. These imprints are distinguished from other records of Batrachichnus by a pentadactyl pes that produces only impressions of digits III–V. Digits I and II are recognized only by their drag marks. This trace occurs in association with a second set of footprints of uncertain affinities. However, these smaller imprints are not sufficiently well preserved and could represent undertracks or partially eroded footprints. None of the footprints can be attributed to the adult forms of the two temnospondyl taxa known from the Guadalupian part of the Karoo Basin: Rhinesuchus whaitsi or Rhinesuchoides tenuiceps. We interpret the aff. Batrachichnus trackway to have been produced by a small, adult temnospondyl or microsaur (Recumbirostrae), whereas the smaller set of footprints was likely made by a juvenile rhinesuchid or an unknown amphibian, either a paedomorphic form or a tiny adult form. The discovery shows that a more diverse aquatic biota existed at this time in the Karoo than osteological records currently suggest.
Conformable limestone deposits bracketing the Alamo breccia (Late Devonian, Nevada) provide a robust dataset for comparisons of depositional environments and marine communities before and after a significant meteor impact. Rank abundances of more than 3000 faunal identifications from 158 sampling localities cluster in three major faunal groups that are arranged in an onshore-offshore lithofacies gradient. Comparison of faunal clusters before and after the impact show little to no dissimilarity. The recovery of marine invertebrate communities following the Alamo impact event was geologically instantaneous. Broad geographic ranges of the fauna may have contributed to ecological resilience. From a geologic perspective, marine communities appear to rebound quickly and fully following meteor impacts, leaving impact-related extinctions as outliers that correspond only to the largest impacts.
Floral Lagerstätten deposits (i.e., fossil sites with exceptional preservation and diversity) are preserved within the Miocene brown coals of the Latrobe Group, Gippsland Basin, Australia. Three independent mechanisms are conducive to their accumulation. Throughout the coal seams the conversion of plant material into charcoal (fusain) and its accumulation in a subaqueous setting provides one means of near-perfect preservation. A second and more uncommon example occurs in the form of a 20 cm thick leaf-litter horizon that extends for over two kilometers. In this case, flooding of freshwater tributaries and lakes during the early stages of low-gradient peat development resulted in an extensive, shallow, acidic and water-filled depression that subsequently accumulated and preserved the surrounding plant material. The third and most common form results from the deposition of plant material into small, isolated pools that formed as depressions on the ombrogenous (i.e., rain-fed) and domed surface of the peatlands. In all of these settings an essential component allowing detailed floral preservation is the delivery of plant material directly to the anaerobic catotelm (i.e., below the water table), hence avoiding the physical and chemical processes of degradation that typically occur in the surficial aerobic acrotelm (i.e., above the water table). Leaf litter that falls into low-energy acidic and anoxic water-filled depressions that lie below the acrotelm will likely be well-preserved.
Durophagous (shell-crushing) fish predation is considered to have been a major force of evolutionary change in the history of marine communities. However, because fish predators are very rarely preserved in the act of predation, fossil evidence of such interactions is commonly indirect. For instance, it has been argued that shell fragments with sharp margins constitute a good proxy for durophagy. However, drawing a distinction between predation- and abiotic-induced shell damage can be challenging. Notably, experimental data on shell fragmentation by marine durophagous fishes are almost lacking. In this study, we explore whether shell breakage caused by durophagous marine fishes versus physical factors can be distinguished. Aquarium experiments involving commercially available predatory fishes (Diodon) and thin-shelled invertebrate preys (gastropods Nassarius and brachiopods Frenulina) show that the predation by some fish produces shell fragments displaying extremely low roundness and varying degree of sphericity. Importantly, these fragments typically display sharp and jagged margins, and reveal distortion of individual crystal fibers. Tumbling experiments showed that the disintegration of brachiopod shells proceeds much more rapidly than that of gastropods, which may suggest that abiotic-induced fragmentation of brachiopods may be eventually confused with predation. However, the tumbling-induced fragmentation and damage in both groups are typically characterized by the presence of spherical or discoidal and rounded shell fragments displaying smooth edges (without any microstructural distortion), and numerous abrasive scratches and wear scars on the surface. These data underscore that the shell fragments produced by a durophagous fish, if not subsequently abraded by physical factors, can be recognized in the fossil record.