Small fossils are preserved as phosphatic (carbonate fluorapatite) micro-steinkerns (~ 0.5 mm diameter) in Upper Ordovician beds of the Cincinnati area. Mollusks are common, along with bryozoan zooecia, echinoderm ossicles, and other taxa. Similar occurrences of Ordovician micromorphic mollusks have been interpreted as ecologically dwarfed and adapted to oxygen-starved conditions, an interpretation with implications for ocean anoxia. An alternative explanation for small phosphatic steinkerns is taphonomic. Stable carbonate fluorapatite selectively filled small voids, thus preserving small fossils, including larval/young mollusks. Reworking concentrated small phosphatic steinkerns from multiple generations while larger, unfilled calcareous shells were destroyed, resulting in small fossils progressively replacing larger fossils. With thin sections and insoluble residues, we document evidence that many of these steinkerns are incomplete (“teilsteinkerns”) recording small parts of larger, normal-sized animals, or juveniles, along with smaller species. This finding suggests that these fossil assemblages are taphonomically, not ecologically, size-limited. Based on the ecology of modern oxygen minimum zones in which shelled mollusks are rare, the presence of abundant shelled organisms actually argues against severe oxygen stress. Our results also imply that the process by which the “small shelly fossils” of the Cambrian were preserved continued into the Ordovician.

The Soap Wash flora contains 152 angiosperm leaf fossils from the Albian–Cenomanian boundary of central Utah. The flora exhibits many well-preserved examples of insect folivory for which the extent and type of damage on each leaf was recorded. Fewer than half of the specimens in the collection exhibit insect damage and most of the leaf damage affects less than five percent of the leaf area. Damage was distributed unevenly across the 18 leaf morphotypes described in the flora. Nineteen damage types were recognized. Most of the damage was of a generalized type, dominated by indiscriminate removal of leaf tissues (whole leaf feeding). We observed no correlation between leaf mass per area (M_A) and the degree of damage by herbivores, which contrasts with Cenozoic and modern patterns. The low rate, modest area, and low diversity of damage type is similar to patterns reported through the Late Cretaceous and is consistent with a plateau in insect folivore diversity that persisted through the end of the Mesozoic. The preponderance of generalized damage types dominated by whole leaf feeding may reflect (1) the early stage in angiosperm radiation represented by this flora, and (2) the associated lag in folivore diversification and specialization.

The southern Bouse Formation (late Miocene–early Pliocene) in Blythe basin, CA-AZ, contains a controversial record of the events that preceded the integration of the developing Colorado River with the Gulf of California. High resolution microfaunal and stable isotope (δ¹⁸O, δ¹³C; VPDB) data from a key outcrop of marl and claystone record an abrupt change in water chemistry that we interpret to be the result of a catastrophic sill breach. Basal marl contains a mix of brackish-water ostracodes and marine foraminifers. Ostracode δ¹⁸O values are slightly negative and 6‰ higher than the host sediment carbonate precipitated in the upper water column, indicating isotopically stratified hydrologic conditions during deposition. Freshwater ostracodes abruptly appear in the overlying sediments in association with marine foraminifers, in conjunction with an abrupt change in the isotopic composition of ostracode and host sediment carbonate. The δ¹⁸O values from brackish and freshwater ostracodes and the host sediment carbonate are similar (~ −10‰), indicating an isotopically well-mixed water body during deposition. Sediment δ¹³C values decrease by 4.5‰ across this transition but ostracode δ¹³C values remain unchanged. We infer that the transition from stratified to well-mixed conditions likely took less than 300 years. The abruptness of this transition is best explained by catastrophic failure of a paleodam that rapidly altered the isotopic composition and salinity of a lake in Blythe basin. A marine or estuarine environment is unlikely. Our interpretation is consistent with other evidence for catastrophic breaching of another lacustrine Bouse Formation-bearing basin to the north.

Three general types of composite ichnofabric can be distinguished based on mechanisms responsible for trace-fossil overprinting, number of ichnocoenoses present, and relative timing of ichnocoenosis emplacement. Autocomposite ichnofabrics, which comprise a single ichnocoenosis, form by gradual upward migration of vertically partitioned benthic communities in pace with sedimentation; because they are presumed to reflect paleoenvironmental stasis, they are most useful in assessing aspects of benthic paleoecology (e.g., endobenthic tiering). Heterocomposite ichnofabrics comprise two or more ichnocoenoses produced in response to short- to long-term environmental perturbations within a depositional system; they reflect depositional process (e.g., event sedimentation) and longer-term paleoenvironmental dynamics. Ultracomposite ichnofabrics form by overprinting of ichnocoenoses that are significantly temporally disjunct and reflect bioturbation in disparate depositional systems. Although the latter ichnofabrics are comparatively rare, their recognition is vital for paleoichnologic studies, particularly those that target surface exposures upon which there may be a modern biogenic overprint.

Marattialean ferns and medullosan seed ferns are two dominant groups in late Carboniferous lowland tropical floras. Differences in their foliage suggest that some seed ferns may have had a higher preservation potential when compared to marattialean ferns. Should this be accurate, it would suggest that when the two groups are found together, marattialean ferns would be better preserved and potentially better represented than seed ferns. Such taphonomic biases would have direct implications for evaluating plant diversity in deep time. To evaluate this hypothesis, we analyzed more than 880 fern and seed fern fossils encased in siderite (FeCO₃) concretions from the ~ 308 Ma Mazon Creek Lagerstätte to test if seed fern foliage is better preserved than fern foliage with respect to taxonomic information. For comparative purposes, we conducted a series of decay experiments on two modern ferns and a cycad (the last providing a seed fern analogue) for 160 days. Despite anatomical and compositional differences, fossil analyses demonstrate that ferns and seed ferns are equally well preserved in the Mazon Creek Lagerstätte with respect to venation, which represents one of the most important taxonomic characters of the flora. The decay experiments support this conclusion: despite having a more robust leaf, cycad leaves decayed at a similar rate to the thinner, more hypothetically fragile ferns. Together, our results indicate that our ability to discriminate within and between ferns and seed ferns is not biased by differential preservation in the Mazon Creek flora.