Helicoplacoids are Early Cambrian echinoderms with triradiate ambulacra that are covered by helically-arranged columns of calcite plates. They are abundant only in shales of the Middle Member of the Lower Cambrian Poleta Formation (Atdabanian) at Westgard Pass in the White-Inyo Mountains of California. To identify and understand the unique taphonomic conditions that led to their preservation, 146 helicoplacoid specimens were examined along with the rocks in which they are preserved. Considering their loosely articulated skeletal construction, together with their common occurrence at the base of cm-scale graded beds, helicoplacoids most likely were preserved during obrution events. A majority (69%) of helicoplacoid specimens are partially disarticulated, probably indicating that most helicoplacoids underwent some combination of pre-burial and post-burial decay. Because most (73%) helicoplacoid specimens are preserved on the same bedding plane as at least one other individual, and many (39%) are preserved on bedding planes containing at least 10 individuals, it appears that helicoplacoids were gregarious and frequently were preserved in mass mortality obrution deposits. Low levels of bioturbation, possible microbial stabilization of the sediment, a shallow redox boundary, and a normally calm depositional environment capable of preserving obrution deposits are all factors that aided in the preservation of helicoplacoids. Additionally, the presence of helicoplacoids in several facies of the Middle Member of the Poleta Formation indicates that they lived in a wider range of paleoenvironments than those represented by the shales, where they are found most commonly. The exceptional preservation of helicoplacoids, therefore, is most likely narrowly restricted stratigraphically and geographically because the proper balance of energy regimes, together with the factors mentioned above, was achieved only rarely during the Early Cambrian, not because helicoplacoids were restricted to living in one paleoenvironment.

Environmental controls on the distribution of fossils most commonly are found by recognizing that certain distinctive fossil assemblages are associated with particular lithofacies. Lack of change in lithofacies commonly is used as indicating a lack of significant environmental effects on the stratigraphic distribution of fossils. The results presented here challenge that view. The Upper Ordovician Kope Formation of the Cincinnati, Ohio, area has long been considered a single unit, both lithostratigraphically and in terms of depositional environment. Gradient analysis of over 1000 fossil assemblages reveals subtle environmental control on the distribution of fossils, in the absence of obvious lithologic change. This gradient analysis is used to construct an ecological model of the Kope fauna, with values of preferred depth, depth tolerance, and peak abundance estimated for the most common fossils. This method, conducted within a single lithofacies, offers the potential for reconstructing sequence architecture because faunas can be more sensitive recorders of environment than lithofacies. In addition, the presence of subtle facies control as in the Kope raises the prospect that environmental controls on paleobiologic and biostratigraphic patterns may be more pervasive than generally acknowledged.

Two types of large diameter burrows, recognized by non-overlapping size distributions, occur in high paleolatitude floodplain deposits of the Lower Triassic Fremouw Formation, Shackleton Glacier area, Antarctica. Type G (giant) burrows are gently dipping tunnels 8 to 19 cm in diameter. Type L (large) burrows are 2 to 6.5 cm in diameter, curved or subhorizontal tunnels that rarely branch; scratch markings on both burrow types generally are parallel or tangential to the long axis of the burrows.

Type G burrows are interpreted as produced by tetrapods based on similarity in size, architecture, and surface markings to Permian burrows from South Africa that contain complete skeletons of therapsids. These are the first tetrapod burrows described from Antarctica. Type L burrows have characteristics of both fossil tetrapod and crayfish burrows, precluding identification of an unique producer.

Triassic tetrapods, including therapsids, that lived in high southern latitudes probably burrowed to dampen the effects of seasonal environmental fluctuations, just as do many of their mammalian counterparts living today in high latitudes. The paleolatitudinal and paleooclimatic distributions of burrowing therapsids and their mammalian descendents can be assessed by focusing search efforts on very large burrows, and by identifying producers using criteria delineated herein; this will clarify the extent to which the burrowing habit originated and persisted in high latitudes.

Two previously unknown rare Middle Jurassic dinosaur megatracksites are reported from the Bighorn Basin of northern Wyoming in the Western Interior of the United States. These trace fossils occur in carbonate units once thought to be totally marine in origin, and constitute the two most extensive Middle Jurassic dinosaur tracksites currently known in North America. The youngest of these occurs primarily along a single horizon at or near the top of the “basal member” of the “lower” Sundance Formation, is mid-Bathonian in age, and dates to ∼167 ma. This discovery necessitates a major change in the paleogeographic reconstructions for Wyoming for this period. The older tracksites occur at multiple horizons within a 1 m interval in the middle part of the Gypsum Spring Formation. This interval is uppermost Bajocian in age and dates to ∼170 ma.

Terrestrial tracks found, to date, have been all bipedal tridactyl dinosaur prints. At least some of these prints can be attributed to theropods. Possible swim tracks of bipedal dinosaurs are also present in the Gypsum Spring Formation. Digitigrade prints dominate the Sundance trackways, with both plantigrade and digitigrade prints being preserved in the Gypsum Spring trackways. The Sundance track-bearing surface locally covers 7.5 square kilometers in the vicinity of Shell, Wyoming. Other tracks occur apparently on the same horizon approximately 25 kilometers to the west, north of the town of Greybull. The Gypsum Spring megatracksite is locally preserved across the same 25 kilometer east-west expanse, with the Gypsum Spring megatracksite more extensive in a north-south direction with tracks occurring locally across a 100 kilometer extent. Conservative estimates for the trackway density based on regional mapping in the Sundance tracksite discovery area near Shell suggests that over 150,000 in situ tracks may be preserved per square kilometer in the Sundance Formation in this area. Comparable estimates have not been made for other areas.

Similarities between the two megatracksites include their formation and preservation in upper intertidal to supratidal sediments deposited under at least seasonally arid conditions. Microbial mat growth on the ancient tidal flats apparently initiated the preservation of these prints.

Rare Earth Element (REE) signatures have been used to test whether mosasaur bones in a basal Hornerstown Formation bonebed (the Main Fossiliferous Layer, or MFL) in New Jersey were reworked from the underlying Maastrichtian beds or deposited synchronously with the bones of other taxa in the Hornerstown Formation. The interpreted age of the bonebed (Maastrichtian vs. Danian) and the position of the K-T boundary in New Jersey are affected by the possible reworking. Statistical techniques, such as ANOVA and Discriminant Analysis, show that signatures of REE in MFL bones are different from those of bones in either the underlying Navesink Formation or the upper part of the Hornerstown Formation, suggesting a unique depositional setting for this bonebed. REE signatures of the MFL mosasaur bones conform with signatures in bones from other taxa within the MFL, suggesting that their deposition was contemporaneous with that of the other taxa. Thus, the MFL bonebed appears to be Cretaceous in age and the K-T boundary must be in or above the MFL, within the Hornerstown Formation.

The Paleocene/Eocene boundary (c. 55.2 ma) represents transient greenhouse warming of <220 ky duration that had a critical impact upon North American mammals but an apparently limited impact upon subtropical plants. The effect of enhanced warming on biomes already tolerant of paratropical/tropical climate conditions is essentially unknown at the Paleocene/Eocene boundary because most research has centered on high latitude changes in plant turnover. Fossil pollen and spores from the US Gulf Coast allow an assessment of the impact that Paleocene/Eocene climate events had on a Paleo—paratropical/tropical vegetation type. Pollen data from two marginal marine sections either side of the boundary in Alabama, USA, demonstrate secular but subdued changes in composition that are manifest primarily as a restructuring of the vegetation type. Taxa found in the Paleocene remain dominant in the early Eocene (≥89% of taxonomic groups), and both extinction and immigration rates are moderate. Immigrants probably came from at least two different continents, Europe and South America, which implies a highly individualistic response of plant species from different Paleocene biomes to greenhouse warming. Diversity changes are not pronounced across the boundary, but within-sample diversity changes reflect a more heterogeneous, or possibly more successional, early Eocene vegetation type than the late Paleocene. This does not lead to greater between-sample diversity because the Paleocene palynofloras are moderately more diverse, if less heterogeneous at the within-sample level. Results imply that on time-scales of 10⁵ years, Paleocene/Eocene warming is correlative with only minor compositional and diversity changes in paratropical vegetation types.

The stable carbon and oxygen isotope compositions of serial samples of enamel from tusks of Gomphotherium productus (Mammalia, Proboscidea) from Port of Entry Pit, Oklahoma (early Hemphillian North American Land Mammal Age, ca. 7.5 Ma), were measured to examine intra-annual and interannual variation. Sample series from each of six tusks spanned approximately one year of tusk growth. Carbon isotope compositions range from −11.3 to −9.2‰ (VPDB) and exhibit no pattern of seasonal variation, indicating the diet of gomphotheres at Port of Entry Pit was dominated by C₃ vegetation throughout the year. Phosphate oxygen isotope composition (δ¹⁸O_p) ranges from 18.9 to 22.2‰ (VSMOW); carbonate oxygen isotope composition (δ¹⁸O_c) ranges from 26.1 to 30.1‰ (VSMOW). None of the tusks exhibit seasonal variation in δ¹⁸O, and the average within-tusk range in δ¹⁸O_p is 1.7‰. Neither the fluorine composition of the specimens nor the relationship between δ¹⁸O_p and δ¹⁸O_c values from splits of the same samples suggest significant post-depositional alteration. The oxygen isotope data imply that Hemphillian meteoric water had δ¹⁸O values that are indistinguishable from modern values in the region today. However, because polar ice sheets were smaller and mean ocean water δ¹⁸O lower than present, the estimates of meteoric water composition from gomphothere tusk δ¹⁸O_p are consistent with warmer mean annual temperatures during the Hemphillian. The within-tusk variations in δ¹⁸O_p are consistent with similar or much reduced patterns of seasonal temperature variation in comparison to today, depending on air mass flow during the late Miocene. Alternative explanations include seasonal migratory behavior and reliance by the gomphotheres at Port of Entry Pit on sources of drinking water with relatively constant δ¹⁸O values.

Sixteen erosional surfaces are recognized in a 144-m-thick condensed package of Tertiary (Eocene-Pliocene) clinoform-toe sediments recovered at ODP Site 1073 on the New Jersey slope. Most of these surfaces are associated with significant hiatuses or extremely condensed intervals defined by Sr isotopes or biostratigraphic data, and many can be linked to sequence boundaries defined in onshore and shelf seismic studies. All surfaces define the bases of fining upward sequences; they separate clay or biogenic muds below from authigenic glauconitic sandy muds or sands above. The entire Tertiary package is thoroughly bioturbated and dominated by ichnotaxa representing softground conditions. Burrow densities, burrow preservation, and the relative importance of certain ichnotaxa vary through the Tertiary package, reflecting changes in water depth, relative degree of condensation, and associated glaucony authigenesis, all related to margin progradation. Nonetheless, when individual sequences are considered, little or no change in softground ichnofossil assemblages is recognized across bounding surfaces. However, most surfaces are marked clearly by firmground Thalassinoides, burrow systems that penetrate deeply (up to 2 m) into subjacent clays and are characterized by extremely sharp walls and coarser glauconitic fills. In shallower shelf sequences, firmground ichnofabrics develop at sequence boundaries in response to subaerial exposure and transgressive ravinement. In contrast, the Tertiary firmgrounds on the New Jersey margin formed in deep water in response to phases of rapid transgression and net erosion; consolidated mud substrates were exhumed as a result of sediment starvation and bottom-current winnowing, facilitated by bioerosion, at or near the bases of slope clinoforms. These observations extend the previously established sequence stratigraphic utility of the substrate-controlled Glossifungites ichnofacies to deeper water facies.