Abstract Unique remains of Mesozoic phyllosphere fungi found by the late M. Reymanówna on gymnosperm cuticles from Middle Jurassic (Bathonian) deposits in southern Poland are described. The cuticles with fungal remains belong to various groups of gymnosperms such as seed ferns, cycads, bennettitaleans, ginkgophytes and conifers. Two new fossil genera ( Insolitomyces G. Worobiec and Reymanomyces G. Worobiec) and four new fossil species ( Entopeltacites grojecensis G. Worobiec, Insolitomyces ctenidis G. Worobiec, Reymanomyces ctenidis G. Worobiec, and Trichopeltinites zabierzowiensis G. Worobiec) of phyllosphere fungi are described. The phyllosphere fungi and their associated Mesozoic plants point to a warm and humid palaeoclimate in the Małopolska land during the Bathonian. Insolitomyces ctenidis and Reymanomyces ctenidis show clear host‐specificity to the genus Ctenis . The thalli of Insolitomyces ctenidis and Reymanomyces ctenidis can often be observed attached together, which may indicate the earliest known fungicolous association of phyllosphere fungi. In view of the relative paucity of data on fossil phyllosphere fungi from the Jurassic, our results significantly expand knowledge of this group of fungi in the Middle Mesozoic.

Abstract A fundamental assumption of hypothesis‐driven decay experiments is that, during decay, the loss of anatomy follows a sequence broadly controlled by the intrinsic compositional properties of tissues. Recent work investigating the succession of postmortem endogenous microbial communities (thanatomicrobiome) challenges this assumption in that the internal thanatomicrobiome exhibits a predictable succession in response to physical and chemical environmental changes that occur within a carcass. Thus, reproducible sequences of character loss during decay could be controlled by thanatomicrobiome succession dynamics. If so, exceptionally preserved fossil anatomy would reflect a succession of ancient contemporaneous microbial communities, about which we know nothing, rendering decay experiments uninformative. Here, we investigate two questions: (1) what is the role of exogenous and endogenous bacteria during formation of the thanatomicrobiome; and (2) do thanatomicrobiome successions control the sequence of anatomical character loss within a decaying carcass? Our analysis shows that the internal thanatomicrobiome is dominated by endogenous bacteria and that, even in the presence of inoculum, exogenous bacteria do not invade the carcass and replace native bacteria (while the carcass remains intact). This confirms that the use of environmental inoculum in decay experiments introduces a confounding variable. Our analysis also finds no correlation between thanatomicrobiome successions and the sequence of anatomical character loss, supporting the hypothesis that fossil non‐biomineralized characters correlate with their propensity to decay in extant relatives. These findings indicate that the inability to model ancient bacteria does not invalidate decay experiments. We present a synthesis of the role of bacteria in non‐biomineralized fossilization.

Abstract Taphonomic studies of Cenozoic mammals are scarce. We report a study of the taphonomy of the Corralito site (Middle Pleistocene to Holocene), Córdoba Province, Argentina, which documents the last population of the South American native ungulate typotherid Mesotherium cristatum. We discovered two specimens of M. cristatum (a hemimandible and postcranial remains) with numerous traces, along with one indeterminate camelid metapodial. Extensive and detailed analysis of these traces using macroscopic and confocal laser scanning microscopy has allowed us to identify various taphonomic agents: carnivoran bite traces, rodent gnawing, trampling, and root etching. We document the ichnotaxa Machichnus and Nihilichus and describe Corralitoichnus conicetensis gen. et sp. nov., which are attributed to Ctenomys incisors, along with Katagmichnus myelus gen. et sp. nov., associated with deep transverse traces on long bones diaphysis linked to bone breakage and marrow consumption by a medium–large carnivoran. This represents the first evidence of such behaviour in South America during the Cenozoic. Furthermore, the taphonomic time sequence of each recognized biological agent was reconstructed using a comprehensive understanding of the different biological processes that affected the specimens from post‐mortem to post‐burial. This study offers direct evidence of distinct biological agents from the Middle Pleistocene, particularly in the western Pampean region, focusing on one of South America's most iconic mammals (M. cristatum). It establishes a solid foundation for future taphonomic research on fossil bones, especially on predation or scavenging traces (Family Machichnidae), a relatively understudied area in South American native ungulates and the continent as a whole.

Abstract The characteristic cardinal spines of Isoxys, a cosmopolitan bivalved arthropod, have been focal to understanding its role in Cambrian ecosystems. It has been proposed that the spines had either a hydrodynamic function, to aid buoyancy, or a defensive function, to protect against predators. Here, we demonstrate that the unusually elongated cardinal spines in Isoxys volucris (by far the most abundant taxon in the lower Cambrian Sirius Passet Lagerstätte, North Greenland) had a primary defensive function. Spine measurements of 85 specimens show a negative allometry during ontogeny, with the ratio of cardinal spine length to carapace length decreasing from >3.2 to 0.9. Negative allometric growth is inconsistent with a hydrodynamic function since larger carapaces would require spines which are proportionally at least as long (isometry or positive allometry). Instead, the negative allometry provides evidence for a defensive adaptation comparable to that seen in modern lower‐trophic organisms, in which elongated spines increase the overall size of juveniles to deter predators. Isoxys volucris was the dominant food source for higher‐trophic benthic and pelagic predators in the Sirius Passet biota, as revealed by the gut contents of arthropods, lobopods, palaeoscolecids and stem‐chaetognaths. Its long spines therefore indicate similar adaptive responses to extremely high predation pressures in both modern and early Cambrian ecosystems.

Abstract A nearly complete and relatively well‐preserved skeleton of the giant ground sloth Megatherium sp. in the hyperarid core of the Atacama Desert reveals how climate related taphonomic processes drastically transformed these remains over time. The individual, semi‐exposed in situ by wind erosion, was found in late Pleistocene palaeowetland sediments that formed during the Central Andean Pluvial Event. Several radiocarbon dates on bone bioapatite and carbonate tufas date the specimen to c. 16 500 cal yr BP. Physical, organic, and inorganic traces were identified using histotaphonomic, mineralogical, and microscopic analyses (optical, scanning electron and petrographic microscopy, x‐ray diffraction and FTIR‐ATR). Surficial bones with rounded, polished surfaces due to wind erosion are well preserved, while buried bones are poorly preserved and structurally weak due to an early phase of bioerosion, which was followed by desiccation revealed by micro‐cracks. Iron and manganese were deposited under anoxic conditions, followed by carbonates such as sparite and micrites, which formed due to a drier context, resulting in the encrustation of these bones by halite and calcium sulfates in hyperarid conditions that continue to this day. These observations imply that the ground sloth lived in a much wetter environment compared to today and its remains were subsequently affected by anaerobic wet cycles, an oxidizing sedimentary environment, and later an oxidizing hyperarid climate. In summary, the unravelled histotaphonomy is written in small fractions of bones which emerge as new proxies for understanding the complex palaeoclimatic history of the Atacama Desert.

Abstract Decay experiments are ever increasing in complexity to better understand taphonomic processes. However, adding new variables, such as sediment, can create methodological biases, such as artificial anatomical character loss during exhumation. Non‐invasive in situ imaging techniques such as x‐ray computed tomography (XCT scanning) could mitigate this, but the consequences of exposing carcasses to x‐rays are not fully understood, and evidence regarding the impact of x‐rays on internal microbial faunas that drive decay is conflicting. Here, we test whether XCT scanning impacts the decay of Danio rerio carcasses within a substrate. Our control experiments show that quartz sand sediment physically stabilizes the carcass throughout decay and the sequence of anatomical character loss remains constant, however, sand initially accelerates the onset and rate of decay of soft tissues. Our XCT data show that exposure to x‐rays does not cause a deviation from the normal sequence of decay, validating XCT as a non‐destructive visualization method for decay experiments. Furthermore, when accompanied with traditional exhumation and dissection, XCT provides decay data with higher accuracy of character analysis than traditional methods, and allows novel quantitative techniques to monitor physical changes in the decaying carcass (e.g. total volume, build‐up of gases, collapse of the body cavity etc.) We underline limitations with the technique, but our experiment acts as an important ‘stepping stone’ for progression toward non‐invasive designs of decay experiments.