Paleoceanography of the Late Cretaceous (Maastrichtian) Western Interior Seaway of North America: evidence from Sr and O isotopes

Well-preserved fossils of the Late Cretaceous Western Interior Seaway (WIS) of North America have been analyzed for Sr concentration and Sr and O isotopes in order to decipher paleosalinities and paleotemperatures. The samples are from four biofacies within the Seaway (late Maastrichtian): offshore Interior (Pierre Shale), nearshore Interior (Fox Hills Formation), brackish (reduced salinity; Fox Hills Formation) and freshwater (Hell Creek Formation). Samples were also obtained from the Severn Formation of Maryland (considered to be representative of the open ocean). All biofacies (except the freshwater) are demonstrably within the Jeletzkytes nebrascensis ammonite zone (<1 Ma duration). The ⁸⁷Sr/⁸⁶Sr ratios show significant and systematic decreases from marine (mean±1 S.D.=0.707839±0.000024) to brackish facies (mean±1 S.D.=0.707677±0.000036), consistent with dilution by freshwater with a lower ⁸⁷Sr/⁸⁶Sr ratio than seawater. Such variation disallows using the ⁸⁷Sr/⁸⁶Sr ratios of fossil shell material to assign ages to fossils from the Late Cretaceous WIS without knowledge of the salinity in which the organism grew. The Sr isotope ratios for scaphitid ammonites within a single biofacies are similar to each other and different from those for scaphites in other biofacies, implying that these organisms are restricted in their distribution during life. The ⁸⁷Sr/⁸⁶Sr values of freshwater unionid mussels range widely and are not compatible with the freshwater endmember ⁸⁷Sr/⁸⁶Sr ratio required by the trend in ⁸⁷Sr/⁸⁶Sr vs. biofacies established from the other samples. Paleosalinities for the biofacies are estimated to range from 35‰ in the open marine to a minimum of 20‰ in the brackish, based on the presence of cephalopods in all four facies and the known salinity tolerance of modern cephalopods. Producing reasonable ⁸⁷Sr/⁸⁶Sr values for the freshwater endmember of a ⁸⁷Sr/⁸⁶Sr vs. 1/[Sr] plot requires a Sr concentration 0.2-0.5 that of seawater for the dominant freshwater input to the WIS. Such high Sr concentrations (relative to seawater) are not observed in modern rivers, and we suggest that the brackish environment in the WIS arose through the mixing of freshwater and seawater in a nearshore aquifer system. Reactions of the solution with aquifer solids in this ‘subterranean estuary’ [Moore, Mar. Chem. 65 (1999) 111-125] produced brackish water with the Sr concentration and isotopic composition recorded in the brackish biofacies. δ¹⁸O values of the fossils show decreases from the marine to brackish biofacies consistent with increasing temperatures (from ∼13 to 23°C) or, if temperatures were relatively constant, to a decrease in the δ¹⁸O of the water in which the shell formed. The latter interpretation is consistent with less-than-fully marine salinities in the nearshore biofacies, but both changes in temperature and the isotopic composition of the water may have occurred in this environment.     

Durophagous predation on scaphitid ammonoids in the Late Cretaceous Western Interior Seaway of North America

This study is the first to report a trend of predation intensity on scaphitid ammonoids from the Turonian to the Maastrichtian (Late Cretaceous) on the basis of analysis of ventral shell breakage in large samples from the US Western Interior Province. Analysis of 835 adult specimens revealed ventral shell breakage in 50 specimens. In most of the damaged specimens, the breakage occurred in a preferred position at the rear part of the body chamber. Ventral breakage is rare in the Turonian specimens, whereas it is common in the Campanian and Maastrichtian specimens. The shell diameter of adult scaphitid ammonoids tends to increase with time. The position of the breakage and the absence of repairs indicate that the ventral breakage resulted from lethal predation. Based on the incidence of breakage and the size and shape of the breaks, possible predators include fish, reptiles and cephalopods such as Placenticeras, Eutrephoceras and coleoids. Our statistical analysis of ventral shell breakage indicates that the incidence of lethal predation increased in conjunction with an increase in adult shell size, suggesting that the body size of the prey was an important factor in predator–prey interactions. In addition, the predatory damage is more extensive in larger adults.     

Sharks that pass in the night: using Geographical Information Systems to investigate competition in the Cretaceous Western Interior Seaway

One way the effects of both ecology and environment on species can be observed in the fossil record is as changes in geographical distribution and range size. The prevalence of competitive interactions and species replacements in the fossil record has long been investigated and many evolutionary perspectives, including those of Darwin, have emphasized the importance of competitive interactions that ultimately lead one species to replace another. However, evidence for such phenomena in the fossil record is not always manifest. Here we use new quantitative analytical techniques based on Geographical Information Systems and PaleoGIS tectonic reconstructions to consider this issue in greater detail. The abundant, well-preserved fossil marine vertebrates of the Late Cretaceous Western Interior Seaway of North America provide the component data for this study. Statistical analysis of distributional and range size changes in taxa confirms earlier ideas that the relative frequency of competitive replacement in the fossil record is limited to non-existent. It appears that typically, environmental gradients played the primary role in determining species distributions, with competitive interactions playing a more minor role.     

Late Cretaceous (Cenomanian to Campanian) paleoenvironmental history of the Eastern Canadian margin of the Western Interior Seaway: bonebeds and anoxic events

Upper Cretaceous strata in the Pasquia Hills of the northern Manitoba Escarpment, eastern Saskatchewan, Canada provide a detailed paleoenvironmental and sea-level record of the eastern margin of the Western Interior Seaway. Sediments deposited during the Cenomanian/Turonian Greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column, with bottom-water anoxia recurrently reaching into the photic zone. A middle Cenomanian sea-level lowstand event followed by transgression left a series of bonebeds within the Belle Fourche Member of the Ashville Formation, indicating a sedimentary environment starved of coarse siliciclastics. Maximum sea level resulted in the formation of limestone beds within the Favel Formation, further favoured by reduced terrigenous sediment input compared to the western margin. Limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions, and reducing zoo- and phytoplankton diversities. During final Greenhorn regression, eastern Saskatchewan probably turned into a restricted basin severely limiting marine circulation. Poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the Cenomanian/Turonian transgressive/regressive cycle. This was caused either by a freshwater lid, stratification of Boreal and Tethyan-derived watermasses, or both, to various intensities affected by changing sea level. Basin oxygenation during Niobrara time varies between localities along the eastern margin as documented by presence/absence of benthic and planktic foraminifera.     

Anaerobic and Aerobic Oxidation of Methane at Late Cretaceous Seeps in the Western Interior Seaway,USA

The Late Cretaceous (Campanian) Tepee Buttes represent a series of conical, fossiliferous limestone deposits embedded in marine shales that deposited in the Western Interior Seaway. The previously suggested origin of the Tepee Buttes at methane-seeps was confirmed by this study. δ¹³C values as low as ?50‰ of early diagenetic carbonate phases of two Tepee Buttes near Pueblo (Colorado) reveal that methane was the major carbon source. Molecular fossils released from a methane-seep limestone contain abundant ¹³C-depleted archaeal lipids (PMI, biphytane; δ ¹³C: ?118 and ?102‰), derived from anaerobic methanotrophs. A suite of ¹³C-depleted bacterial biomarkers (branched fatty acids; ?73 to ?51‰) reflects the former presence of sulfate-reducing bacteria, corroborating that a syntrophic consortium of archaea and bacteria mediating anaerobic oxidation of methane already existed in Cretaceous times. Molecular fossils also suggest that methane was not exclusively oxidized in an anaerobic process. A series of unusual C₃₄/C₃₅-8,14-secohexahydrobenzohopanes with low δ¹³C values (?110 and ?107‰) points to the presence of aerobic methanotrophic bacteria at the ancient seep site.     

Nautilid nurseries: hatchlings and juveniles of Eutrephoceras dekayi from the lower Maastrichtian (Upper Cretaceous) Pierre Shale of east‐central Montana

The nautilid Eutrephoceras dekayi (Morton 1834) is relatively abundant in the lower Maastrichtian (Upper Cretaceous) Pierre Shale of east‐central Montana. We analysed the morphology, size frequency distribution, and isotope composition of a large collection of 220 well‐preserved specimens including hatchlings, juveniles and adults. The newly hatched shell is approximately 14 mm in diameter with a body chamber one‐third whorl in angular length terminating in the nepionic constriction. Internally, the embryonic shell contains five septa. Juveniles are abundant and comprise two‐thirds of the sample whereas sub‐adults, defined by the incipient flattening of the venter, are rare. Adults comprise approximately one‐third of the sample and average 100 mm in diameter. The co‐occurrence of newly hatched shells, small juveniles and adults suggests that the eggs were laid in the same area in which the hatchlings developed. Based on the excellent preservation of the juveniles, we conclude that they did not float into the area after death, but lived in the region, implying that this area served as a nursery for young animals. The calculated temperatures of the embryonic shells are similar to those of the post‐embryonic shells and generally range from 16 to 18 °C. Upon hatching, the nautilids probably followed a demersal mode of life and lived in well‐oxygenated water ≤50 m deep. An examination of lethal injuries (puncture holes) suggests that all ontogenetic stages were equally vulnerable to predation. The proximity of the site to the Sheridan Delta suggests that the specimens were smothered by sudden pulses of sediment transported into the area by major storms.     

Late Albian Dinosaur Tracks from the Cratonic (Eastern) Margin of the Western Interior Seaway,Nebraska, USA

At least 22 tridactyl dinosaur tracks, poorly preserved in various degrees of expression, have recently been found at an exposure in the Dakota Formation (Lower Cretaceous, Albian) in Jefferson County, Nebraska. These tracks generally have broad, blunt digits and a broad posterior margin. The largest of the tracks measures 57 cm in length and 58 cm in width. All of the tracks lie within a stratigraphic horizon of 40 cm or less, but they do not form a single trackway. We interpret the trackmakers to have been ornithopods.

The Jefferson County tracks are in a well-cemented sandstone with oscillation ripples, at a stratigraphic level between two well-established sequence boundaries. Channel forms and lateral accretion units are common in the stratigraphic interval enclosing the tracks, and the site is interpreted as a bar or sand flat in a tidally influenced river.

The Jefferson County tracks are only the second known occurrence of large Mesozoic tetrapod tracks east of the Rocky Mountain Front-High Plains Margin, including the Black Hills of South Dakota, west of the Atlantic Coastal Plain, and north of the Gulf Coastal Plain. Further, this paper is the first documentation of in situdinosaur fossils from the Nebraska-Iowa area.     

Taxonomy, biostratigraphy and paleoecology of Cenomanian and Turonian ostracodes from the Western Interior Basin, Southwest Utah, USA

Cenomanian-Turonian ostracodes are reported from the western Colorado Plateau (Western Interior Basin) in the United States. Fifteen genera and twenty species are illustrated, six of which are new: Cytheromorphaperornata nov. sp., Looneyellaleckiei nov. sp., Asciocythereposterangulata nov. sp., Asciocytherearizonensis nov. sp., Cytheropteronclavifragilis nov. sp. and Hourcqiadakotaensis nov. sp. Three ostracode interval zones are proposed that broadly correspond to the existing late Cenomanian through to Middle Turonian Ammonite-zones of Kauffman et al. (1993). Paleoenvironments range from estuarine to coastal plain.     

The radula of the Late Cretaceous scaphitid ammonite Rhaeboceras halli (Meek and Hayden, 1856)

Abstract: Radular teeth occur between the jaws in two specimens of the Late Cretaceous scaphitid ammonite Rhaeboceras halli (Meek and Hayden, 1856) from the Western Interior of the United States. The detailed morphology of the teeth has been revealed by propagation phase contrast X‐ray synchrotron microtomography. Each row of the radula of R. halli consists of a total of seven teeth (a central rachidian, two pairs of lateral and one pair of marginal teeth), as in other known ammonoid radulae, although the central tooth could not be confirmed in the specimens examined. The lateral teeth are multicuspid and robust, and the marginal teeth are long (4.6 mm) and slender. In overall morphology, the heterodont and ctenoglossan radula of R. halli is similar that of Jurassic and Cretaceous ammonites with the same aptychus‐type lower jaw, that is, the Aptychophora. This discovery reveals the range of variation in radular morphology, which could be related to ecological or phylogenetic factors. It also invalidates the hypothesis that the hook‐like structures in R. halli previously described are radular elements.     

Mass mortality of an asteriid starfish (Forcipulatida,Asteroidea, Echinodermata) from the late Maastrichtian (Late Cretaceous) of Morocco

Abstract: A mass occurrence, numbering tens of thousands of individuals in a single lens, belonging to a single species of asteroid, is described from the late Maastrichtian (Late Cetaceous) of Morocco. The lens of partially silicified asteroidal limestone is made up largely of fully articulated specimens of similar size and probably represents the mass mortality of a single recruitment. By comparison with mass strandings of the present‐day species Asterias rubens (Linnaeus), it can be inferred that a feeding swarm of individuals was swept into a submarine channel by either a storm or an exceptionally strong tidal current, and permanently buried. The genus and species are herein described as Cretasterias reticulatus gen. et sp. nov. The exceptional preservation of the material enables the identification of wreath organs (clusters of crossed pedicellariae set in a dermal pad around spines) for the first time in the fossil record. Comparison between extant Asteriidae, putative fossil asteriids and C. reticulatus provides ambiguous evidence of its affinities; it appears to display a combination of plesiomorphic and derived characters. It is shown that all Mesozoic forcipulatid asteroids described so far share a very simple arm construction (single row of adradial ossicles) unknown in adult extant Forcipulatida.     

Sporophytes and gametophytes of Dicranaceae from the Santonian (Late Cretaceous) of Georgia, USA

A new species (Campylopodium allonense) of the moss family Dicranaceae is described for fossil sporophyte capsules and associated gametophytes from the late Santonian (Late Cretaceous) Buffalo Creek Member of the Gaillard Formation in central Georgia, USA. The sporophyte capsules are most comparable to those of the living genus Campylopodium. Sporangia are curved, cylindrical, and strumose, with an obliquely rostrate operculum, cucullate calyptra, and compound annulus. The peristome is haplolepidous with 16 dicranoid, apically bifid teeth that are vertically striate on the outer surface and asymmetrically trabeculate on the inner surface. Spores are spherical, alete, and finely rugose, and thus differ from the finely papillose spores of extant Campylopodium. Associated fossil gametophytes are consistent with the morphology of extant Campylopodium and have leaves with a broad sheathing base and a narrow blade. Spores identical to those in the sporangium occur on the leaf surfaces of one of the gametophyte specimens, providing circumstantial evidence that both sporophyte and gametophyte belong to the same species. Inadequacies of the moss fossil record have led to contrasting interpretations of the timing of evolutionary change in this lineage since the Paleozoic. Campylopodium allonense unequivocally provides the earliest evidence of Dicranaceae in the fossil record. This material, along with other fossil mosses from this late Santonian locality, indicates the presence of modern families of mosses in the Cretaceous. In a phylogenetic context, these fossils from two different subclasses imply that mosses were already diverse by the Late Cretaceous.     

Cladistic Analysis of A Problematic Ammonite Group: the Hamitidae (Cretaceous, Albian–turonian) and Proposals for New Cladistic Terms

The Hamitidae are a family of mid–Cretaceous heteromorph ammonites including lineages leading to four other families. Problems are outlined in trying to describe the phylogeny of completely extinct groups such as these heteromorph ammonites using the existing cladistic terminology, which is largely concerned with extant taxa and their ancestors. To solve these problems, two new terms are proposed: †crown groups and †stem groups, which are equivalent to crown and stem groups in terms of the evolutionary history of a clade, but are not defined on the basis of extant taxa. Instead they are defined by the topology of the phylogenetic tree, the †crown group being a clade defined by synapomorphies but which gave rise to no descendants. A †stem group is a branch of a phylogenetic tree which comprises the immediate sister groups of a given †crown group but is not itself a clade. Examples of these terms are described here with reference to the phylogeny of the Hamitidae and their descendants. The Hamitidae are paraphyletic and form †stem groups to a number of †crown groups, namely the Anisoceratidae, Baculitidae, Scaphitidae, and Turrilitidae. The definitions of the genera and subgenera are refined with respect to the type species and the clades within which they occur, and four new genera are described: Eohamites , Helicohamites , Sziveshamites , and Planohamites .     

Mesofossils with platanaceous affinity from the Dakota Formation (Cretaceous) in Kansas, USA

The Platanaceae holds a basal position in the phylogeny of eudicots and therefore is of great interest to angiosperm systematists. The fossil record of the family is found in strata ranging from the Cretaceous to Recent in America, Europe and Asia. The research on the Platanaceae in the Dakota Formation can be traced back to 19th century; however, mesofossils of reproductive organs of the Platanaceae were never reported in the Midwest of North America before. This paper reports several specimens of Friisicarpus (Platanaceae) from the Dakota Formation in Kansas, USA. It complements the existing fossil records, and provides more information on reproductive biology of the family. The comparison with similar fossils from eastern North America and Europe provides some hints on biostratigraphy of the Cretaceous.     

Glandulocalyx upatoiensis, a fossil flower of Ericales (Actinidiaceae/Clethraceae) from the Late Cretaceous (Santonian) of Georgia, USA

Background and Aims

Ericales are a major group of extant asterid angiosperms that are well represented in the Late Cretaceous fossil record, mainly by flowers, fruits and seeds. Exceptionally well preserved fossil flowers, here described as Glandulocalyx upatoiensis gen. & sp. nov., from the Santonian of Georgia, USA, yield new detailed evidence of floral structure in one of these early members of Ericales and provide a secure basis for comparison with extant taxa.

Methods

The floral structure of several fossil specimens was studied by scanning electron microscopy (SEM), light microscopy of microtome thin sections and synchrotron-radiation X-ray tomographic microscopy (SRXTM). For direct comparisons with flowers of extant Ericales, selected floral features of Actinidiaceae and Clethraceae were studied with SEM.

Key Results

Flowers of G. upatoiensis have five sepals with quincuncial aestivation, five free petals with quincuncial aestivation, 20–28 stamens arranged in a single series, extrorse anther orientation in the bud, ventral anther attachment and a tricarpellate, syncarpous ovary with three free styles and numerous small ovules on axile, protruding-diffuse and pendant placentae. The calyx is characterized by a conspicuous indumentum of large, densely arranged, multicellular and possibly glandular trichomes.

Conclusions

Comparison with extant taxa provides clear evidence for a relationship with core Ericales comprised of the extant families Actinidiaceae, Roridulaceae, Sarraceniaceae, Clethraceae, Cyrillaceae and Ericaceae. Within this group, the most marked similarities are with extant Actinidiaceae and, to a lesser degree, with Clethraceae. More detailed analyses of the relationships of Glandulocalyx and other Ericales from the Late Cretaceous will require an improved understanding of the morphological features that diagnose particular extant groups defined on the basis of molecular data.     

Oichnus Bromley Borings in the Irregular Echinoid Hemipneustes Agassiz from the Type Maastrichtian (Upper Cretaceous,The Netherlands and Belgium)

Three ichnospecies of Oichnus Bromley occur in tests of the large holasteroid echinoid Hemipneustes striatoradiatus (Leske) in the type area of the Maastrichtian (Upper Cretaceous) in The Netherlands and Belgium; Oichnus simplex Bromley (penetrative), Oichnus paraboloides Bromley (nonpenetrative and showing two distinct morphologies), and Oichnus excavatus isp. nov. (nonpenetrative). The two distinct morphologies of O. paraboloides (both shallow, one with a central boss) are gregarious, but do not occur together on the same specimens, suggesting they were generated by different taxa. Oichnus paraboloides with a central boss occurs on H. striatoradiatus from the upper Nekum Member, Maastricht Formation (Maastrichtian, Upper Cretaceous). Tests of the host echinoid are smaller in the overlying Meerssen Member, Maastricht Formation, where they are infested by O. excavatus, the largest borings considered herein, which have concave walls and a large central boss. Blisters inside tests from the Meerssen Member show that this infestation occurred when the echinoid was alive. It is postulated that producers of these borings in H. striatoradiatus may have been genetically related and increased in size during the Maastrichtian even as the host echinoids showed a size decrease. This size increase in H. striatoradiatus was genetic and cannot be related to increase in size of borings.     

A new Late Cretaceous (Maastrichtian) serial planktic foraminifer (Family Heterohelicidae) with early planispiral coil and revision of Spiroplecta Ehrenberg, 1844

A new planktic foraminifer, Hartella harti nov. gen., nov. sp. is described from the Maastrichtian sediments of the Atlantic Ocean. H. harti likely evolved from Fleisherites glabrans (Cushman). Spiroplecta Ehrenberg is reviewed and considered monospecific. The only species assigned to this genus is Spiroplecta americana Ehrenberg, which evolved from Heterohelix globulosa (Ehrenberg). It is demonstrated that the early planispiral coil developed in at least three separate lineages of serial planktic foraminifera in the Late Cretaceous (late Campanian-early Maastrichtian).     

The ammonite genera Fagesia and Neoptychites (family Vascoceratidae) in the Iberian Trough, Spain

The ammonites assigned to the genera Fagesia Pervinquière, and Neoptychites Kossmat, of the Wiedmann (Tübingen, Germany) and Goy, Carretero and Meléndez (Madrid, Spain) collections obtained from the Iberian Trough have been revised. New mainly lower Turonian specimens of the species Fagesia catinus (Mantell), F. tevesthensis (Peron), F. rudra (Stoliczka), F. superstes (Kossmat), F. pachydiscoides Spath, and Neoptychites cephalotus (Courtiller) have also been presented. In addition we have described one new species: F. mortzestus. Studies of the morphologies and the geographical and stratigraphical distributions of all these species have led to the identification of several phylogenetic relationships between them, and to distinguishing one main phase in the evolution of the family Vascoceratidae Douvillé, characterised by the dominance of Fagesia with Neoptychites.     

Evolutionary patterns–tested with cladistics–and processes in relation to palaeoenvironments of the Upper Barremian genus Gassendiceras (Ammonitina,Lower Cretaceous)

Abstract: Phylogenetic reconstruction of the Upper Barremian ammonite genus Gassendiceras (Gassendiceratinae) was performed using a cladistic analysis incorporating continuous data. Some morphological features were found to vary identically among all the analysed species and therefore carry no phylogenetic information (= symplesiomorphic). The single obtained cladogram allows interpreting the evolution of the Gassendiceras as an anagenetic succession of eight species, in stratigraphic order of appearance, Gassendiceras multicostatum, G. alpinum, G. hoheneggeri, G. rebouleti, G. bosellii, G. quelquejeui, G. coulletae and G. enayi. The clade Pseudoshasticrioceras/Imerites is derived from G. enayi, so the genus Gassendiceras appears to be paraphyletic. But here, we accept this fact as the best evolutive classification. The evolution over time of Gassendiceras is modulated by some processes, which could have constrained the inferred phylogenetic pattern with the drift of the global variability towards the most gracile forms over time. It is tempting to interpret this evolution as a constant selection over time of the Gassendiceras modulated by environmental control due to eustatic variation across a transgressive sequence. Thus, the most peramorphic (gracile) individuals seemed favoured at the expense of those most robust (paedomorphic).