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Despite the rise of marine diatoms in the world's oceans throughout the Cretaceous, only a handful of fossil localities worldwide detail invasion of freshwater habitats by diatoms commencing in the Late Cretaceous. We report on the occurrence of numerous freshwater diatom specimens and species from the Battle Formation, an extensive freshwater locality in western Canada that formed in the Late Cretaceous approximately 66.5 million years ago (Ma). The formation represents one of the oldest known localities worldwide harboring definitive remains of freshwater diatoms, contains the oldest known freshwater specimens of the centric diatom genus Aulacoseira, and confirms that these early Aulacoseira colonizers formed filaments linked together with interdigitating spines. We further document a high diversity of araphid pennate diatoms belonging to the order Fragilariales. Seven pennate morphotypes were uncovered, six of which definitively lacked a raphe and whose closest modern relatives are in the genera Fragilariforma, Fragilaria, and Stauroforma. Given the extensive coverage of the Battle Formation, it is possible that it represents a network of numerous smaller shallow waterbodies that collectively offered a diversity of environments for colonization, making it a unique deposit for examination of early freshwater diatoms.
In the Central Anti-Atlas (Morocco), the lower part of the Fezouata Shale has yielded locally abundant remains of soft-bodied to lightly sclerotized taxa, occurring in low diversity assemblages characterized by strong spatial and taxonomic heterogeneities, and frequently, by the occurrence of small-sized individuals. Size frequency analyses of Celdobolus sp., Wosekella sp. (both linguliformean brachiopods) and Babinka prima (babinkid bivalve) collected in deposits of the Fezouata Shale and associated with distinct paleoenvironmental conditions show that short-lived communities of epifaunal and shallow infaunal taxa were regularly smothered and killed by distal storm deposits. Small-sized individuals more likely represent juveniles, rather than ‘dwarfed' adults (Lilliput Effect). Consequently, unstable environmental conditions (regular storms, and possibly low oxygenation of the water column) probably explain the unusual community dynamics of late Tremadocian assemblages of the Fezouata Biota (high density of individuals, low α-diversity, and high γ-diversity), interpreted as short-lived, opportunistic populations. This process has wider implications for the understanding of occurrences of small individuals elsewhere in the fossil record.
The volume of literature on taphonomic modifications to faunal remains created by a particular animal species in an actualistic neotaphonomic (ANT) context has grown rapidly since the 1960s. A sample of 454 investigations on the taphonomic traces created by bone modifying animal species published starting in 1911 and through mid-2018 includes studies of 115 species of mammal and 78 species of bird. The most frequently studied bone modifying mammal species is spotted hyaena (Crocuta crocuta) and the most studied bird is barn owl (Tyto alba). One-hundred seventy two of 609 individuals (28.2%) have authored more than one investigation. One-hundred eight of 417 texts (25.9%) compare faunal remains accumulated and modified by ≥ 2 species in an effort to establish signature criteria—modifications to carcasses and bones diagnostic of a particular bone modifying species. Two hundred and four texts (of 417 [48.9%]) document how one or more animal species modify bones, many with the unelaborated warrant that such documentation has paleozoological implications. Commonly reported variables include the kinds of modifications to bones (238 of 417 [57.1%] texts) and skeletal part frequencies (217 of 417 [52.0%] texts). Thoughtful consideration of taphonomic variables chosen for measurement and construction of interpretive models having dynamic sufficiency (the model includes the correct processes and variables to account for the field of inquiry), empirical sufficiency (included variables can be measured in the real world), and agreed upon tolerance limits (the model matches the empirical record sufficiently closely to be analytical useful) will enhance the value of ANT research.
Exposures of Upper Cretaceous and lower Paleocene strata at the Moscow Landing site in western Alabama, U.S. Gulf Coastal Plain, include a series of isolated, thin coarse-grained clastic bodies referred to as the Clayton sands. Positioned at the K–Pg transition and below a regional transgressive surface, these sand bodies previously have been interpreted as lowstand incised valley fills or as catastrophic megawave deposits associated with the end-Cretaceous bolide impact on the Yucatan peninsula. The sedimentology and ichnology of the Moscow Landing exposure were revisited in attempt to elucidate the mechanisms responsible for Clayton sand deposition. Stratigraphic relations and character of sand bodies strongly suggest that impact-generated faulting and deformation of the underlying Maastrichtian Prairie Bluff Chalk created Clayton sand depocenters, that the bulk of Clayton sands was emplaced, possibly from the south, by runup and backwash of oscillating impact-generated megawaves, and that transgressive ravinement followed shortly after catastrophic deposition. Several Clayton sand bodies contain in their upper parts internal bioturbated horizons characterized by Thalassinoides, for which there are two viable explanations. These horizons may record short-term colonization by allochthonous crustaceans that were transported and transplanted by waning megawave currents. Alternatively, associated sand bodies may be composites; Thalassinoides horizons may reflect colonization of sands that accumulated under normal marine conditions in remaining accommodation space atop megawave deposits in response to ensuing transgression. Careful systematic biostratigraphic sampling and analyses will be necessary to test the relative virtues of these two scenarios.