J. Mark Erickson

Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications

• Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies. • Here we quantify leaf-climate correlations from 92 globally distributed, climatically diverse sites, and explore potential confounding factors. Multiple linear regression models for mean annual temperature (MAT) and mean annual precipitation (MAP) are developed and applied to nine well-studied fossil floras. • We find that leaves in cold climates typically have larger, more numerous teeth, and are more highly dissected. Leaf habit (deciduous vs evergreen), local water availability, and phylogenetic history all affect these relationships. Leaves in wet climates are larger and have fewer, smaller teeth. Our multivariate MAT and MAP models offer moderate improvements in precision over univariate approaches (± 4.0 vs 4.8°C for MAT) and strong improvements in accuracy. For example, our provisional MAT estimates for most North American fossil floras are considerably warmer and in better agreement with independent paleoclimate evidence. • Our study demonstrates that the inclusion of additional leaf traits that are functionally linked to climate improves paleoclimate reconstructions. This work also illustrates the need for better understanding of the impact of phylogeny and leaf habit on leaf-climate relationships.

Migration of a Late Cretaceous fish.

Late Cretaceous sediments from the Western Interior of North America yield exceptionally well preserved fossils that serve as proxies for the rapidly changing climate preceding the Cretaceous/Tertiary boundary (about 67–65 Myr ago). Here we reconstruct the ontogenetic history of a Maastrichtian-age fish, Vorhisia vulpes, by using the carbon, oxygen and strontium isotope ratios of four aragonite otoliths collected from the Fox Hills Formation of South Dakota. Individuals of V. vulpes spawned in brackish water (about 70–80% seawater) and during their first year migrated to open marine waters of the Western Interior Seaway, where they remained for 3 years before returning to the estuary, presumably to spawn and die. The mean δ18O from the marine growth phase of V. vulpes yields a seawater temperature of 18 °C, which is consistent with leaf physiognomy and general-circulation-model temperature estimates for the Western Interior during the latest Maastrichtian.

Diagenesis of Fossiliferous Concretions from the Upper Cretaceous Fox Hills Formation, North Dakota

ABSTRACT Three fossiliferous concretions of the Fox Hills Formation (Upper Cretaceous) of North Dakota display similar diagenetic histories. Petrographic and geochemical data from each concretion have yielded the following diagenetic sequence: 1) bioturbation by marine benthos; 2) partial phosphatization of glauconite, fecal pellets, and shell material; 3) sulfate reduction and pyrite formation; 4) siderite precipitation; 5) radial-fibrous calcite precipitation, and 6) equant calcite precipitation. Although the occurrence of open-marine faunas and glauconite indicates that concretion sediments were deposited under marine conditions, geochemical data suggest that marine pore fluids were replaced by brackish and meteoric water. As the Fox Hills Formation is part of a regressive, marginal marine equence, it is likely that the transition from marine to freshwater is recorded in concretion paragenesis. Early diagenetic minerals indicate oxidation of organic matter at shallow burial depths under normal marine conditions. Locally reducing conditions, produced initially by degradation of molluscan soft parts and later by degradation of organic material in crustacean and annelid fecal pellets, occurred at shallow burial depths. Alteration of iron silicates (glauconite) produced pore fluids enriched in Fe2+. Due to the abundance of reactive organic matter, subsequent reduction of marine sulfate yielded a small amount of disseminated pyrite. Following the removal of H2S, elevated Fe2+, pH, and bicarbonate concentrations soon exceeded siderite saturation and siderite was precipitated. Elevated Ca and Mg compositions and marine 18O values of siderite cements indicate that pore fluids were essentially reduced marine fluids. Depleted 13C values suggest that siderite precipitated in an environment dominated by the oxidation of organic matter. Isotopic compositions from the earliest and latest carbonate phases constrain intermediate phases and allow comparison of environments of precipitation. Carbon and oxygen isotopic data from skeletal aragonite provide an estimate of the isotopic composition of marine carbonate. The latest phase of equant calcite cement is characterized by invariant 18O, coupled with highly variable and light 13C. This characteristic isotopic signature and occurrence in overlying fluvial sediments suggests a meteoricphreatic origin for equant spars. Isotopic values of radial-fibrous calcite lie between those of marine (aragonite, siderite) and freshwater (equant calcite) ph ses and represent a complex mixing of marine and meteoric pore fluids. The paragenetic sequence of carbonate cements records a gradual decrease in ambient fluid Mg, Fe, and Mn content during shallow burial. Such decreases are consistent with the influx of oxidizing meteoric fluids.

Temperature and salinity of the Late Cretaceous Western Interior Seaway

The Western Interior Seaway (WIS) was a shallow and expansive body of water that covered the central United States during the Late Cretaceous. Attempts to reconstruct temperatures in the seaway using the oxygen isotopic composition of biogenic carbonates have suffered from uncertainty in the oxygen isotopic composition of seawater (δ 18 O w ) in the semi-restricted basin. We present new reconstructed temperature and δ 18 O w data from marine and estuarine environments in the WIS and freshwater environments in WIS source rivers, derived from clumped isotope analyses of bivalve and gastropod shells. We find temperatures of 5–21 °C, δ 18 O w values below contemporaneous Gulf of Mexico marine sites, and a strong correlation between δ 18 O w and environmental setting. We propose that decreasing δ 18 O w values reflect decreasing salinity driven by an increasing contribution of continental runoff. Using a two-end-member salinity-δ 18 O w mixing model, we estimate salinities of 29–35 psu (practical salinity units) for the deep marine, 20–32 psu for the shallow marine, and 11–26 psu for the estuarine environments of the WIS. New climate model simulations agree with reconstructed temperatures and salinities and suggest the presence of salinity driven stratification within the seaway.

DESCRIPTION AND INTERPRETATION OF SANCTUM LAURENTIENSIS, NEW ICHNOGENUS AND ICHNOSPECIES, A DOMICHNIUM MINED INTO LATE ORDOVICIAN (CINCINNATIAN) RAMOSE BRYOZOAN COLONIES

Abstract During the Late Ordovician, arborescent and frondose trepostome, and cystoporate Bryozoa were frequently bored in a manner distinctly different from Trypanites, Palaeosabella, and Vermiforichnus, domichnia that are commonly associated with these organisms. Maysvillian and Richmondian bryozoan taxa on the Cincinnati Arch were particularly infested by an unidentified organism that used the interior of bryozoan branches as its domicile. The domichnial trace Sanctum laurentiensis is newly described. Dwelling openings range in size from 1.1 mm to 3.2 mm and are located singly on surfaces of colony branches, commonly in a somewhat protected position. The circular opening leads through the exozone into an elongate or saccate chamber representing a variably shaped excavation of the bryozoan endozone. Traces ranging from 3.0 mm to 8.8 mm wide and 9.7 mm to 53 mm long are documented. Thin sections demonstrate that chambers were unlined and had irregular interior walls resulting from organismal mining of zooecial tubes. Cavity makers likely were multiple individuals of amphipod-like crustaceans (Arthropoda) that fed outside their domicile. Bryozoan colonies were occupied while upright, either entirely or partially live, or in some cases dead and overgrown by other bryozoans. Avoidance of predation and the ability to dwell and feed in a higher tier than that of infaunal tracemakers at the sediment-water interface were potential benefits of this domichnium. Presence of cavities reduced the strength of host branches, thus having a profound effect on colony morphology and growth over its lifetime. Unlike the many epizoans that used trepostomes as substrates with little long-term affect, Sanctum laurentiensis significantly impacted its bryozoan host.

FOSSIL LEAF SPECIES FROM THE FOX HILLS FORMATION (UPPER CRETACEOUS: NORTH DAKOTA, USA) AND THEIR PALEOGEOGRAPHIC SIGNIFICANCE

Abstract Seven fossil leaf species are described from impression fossils collected from the Upper Cretaceous (Maastrichtian) Fox Hills Formation in south-central North Dakota, USA. They are Marmarthia johnsonii n. sp., Nilssoniocladus yukonensis n. comb., Nilssoniocladus comtula n. comb., Mesocyparis borealis, Rhamnus salicifolius, Paloreodoxites plicatus, and Zingiberopsis magnifolia. These species represent some of the elements of the Fox Hills flora that have paleogeographic ranges to the northwest (N. yukonensis, N. comtula, and M. borealis) and to the southwest (M. johnsonii, R. salicifolius, P. plicatus, and Z. magnifolia) of the Fox Hills type area. The identification and reappraisal of these species represent an effort to understand the biogeographic relationships of Late Cretaceous floras across the Northern Hemisphere.

FRESHWATER UNIONID BIVALVE SHELLS AS SUBSTRATA FOR TRICHOPTERA ATTACHMENT

ABSTRACT A variety of competitive advantages accompany colonization of hard substrates in aquatic settings, and as a result, many organisms adopt this mode of life. Similarly, adverse effects may occur to organisms that have themselves been encrusted. Many marine basibiont faunas (organisms that provide a substrate for populations of attached epibiontic organisms), including bivalve mollusks, are known to employ a range of chemical and physical deterrents to minimize the incidence of epibiotic attachment, with its attendant detrimental impacts. Freshwater basibiont and epibiont associations, however, are poorly documented. We collected an assemblage of dead, empty freshwater mussel (unionid bivalve) shells from the Saint John River, New Brunswick, Canada. Some unionid specimens exhibited colonization by attached Trichoptera (caddisfly) cases, in either their final instar larval or pupal developmental stages. The trichopteran assemblage, identified from case morphology, included abundant Neophylax sp. together with common Goera sp. and rarer Helicopsyche borealis. For all genera, site-selective attachment occurred upon the shell surfaces. Crystalline aragonite and organic layers exposed within taphonomically damaged regions of molluscan shell were not colonized. Attachment was instead confined to areas of intact periostracum posterior to the umbonal region of the shell, the periostracum perhaps being selected for its rough surface texture in comparison to aragonitic layers. Trichoptera cases dislodged during handling of specimens revealed no damage to the underlying shell. Observations undertaken on the bivalve shells using scanning electron microscopy suggest that physical barriers to attachment are absent within these faunas, and evidently, any chemical barriers, if present, are largely ineffective.

Wind-oriented gastropod shells as indicators of paleowind direction

ABSTRACT The stoss face of a large parabolic dune at Dillon Beach, California, is being actively eroded by wind action. The result is formation of a lag deposit consisting largely of shells of Helminthoglypta arrosa (Gould), a heliciform, terrestrial gastropod. Wind velocities up to thirty miles per hour serve to orient many of these sand-filled shells with the aperture away from the prevailing wind direction. In addition, sandblasting by saltating grains produces a wedge-shaped abrasion or decortication pattern on the spire of the shell with the wedge pointing downwind. Wind-oriented gastropod shells and decortication wedges may be useful criteria for determination of paleowind directions in ancient dune deposits.

Ischyodus rayhaasi (Chimaeroidei; Callorhynchidae) from the Campanian-Maastrichtian Fox Hills Formation of Northeastern Colorado, USA

Modern ratfish (chimaeroids) are examples of a poorly documented lineage of cartilaginous fishes that extends back to Triassic time. Here we report on the discovery of abundant remains of the callorhynchid chimaeroid Ischyodus rayhaasi Hoganson and Erickson 2005 from a Campanian-Maastrichtian age locality in the Fox Hills Formation of northeastern Colorado. A second, distinct group of chimaeroid specimens, designated Ischyodus sp., occurs at the same locality and may represent a species separate from I. rayhaasi, an earlier ontogenetic stage, or sexual dimorphism within I. rayhaasi. The presence of chimaeroid fishes is discussed in regard to the paleoecology and paleogeography of the Late Cretaceous Western Interior Seaway.