Stratigraphic Appearance Research Articles

The Ediacaran–Cambrian Chapel Island Formation of Newfoundland, Canada: evaluating the impact of outcrop quality on trace-fossil data sets at the Cambrian GSSP and less-explored sections

In 1992, the Chapel Island Formation at Fortune Head was selected as the Cambrian GSSP, which was placed at the first appearance of the ichnotaxon Treptichnus pedum. Although the transition from the Ediacaran to the Cambrian was well studied in Fortune Head and Grand Bank Head, it is also exposed at Lewin’s Cove and Point May. Here, we report new ichnologic and sedimentologic data sets from the four localities. Ichnologic data sets consist of bioturbation intensities, burrow width and depth, ichnotaxonomic composition, and stratigraphic appearances. Sedimentologic data sets include sediment grain size, bed thickness and architecture, sandstone/mudstone ratio, and physical sedimentary structures. In addition, the quality of each outcrop is evaluated (i.e., accessibility, lateral and vertical continuity, stratigraphic completeness, and type of exposure). At the four localities, the base of the Cambrian can be placed at the first appearance of Treptichnus pedum or of vertical trace fossils of the T. pedum Ichno-Assemblage Zone. In addition, Fortune Head, Grand Bank Head, and Lewin’s Cove display increases in ichnodiversity and bioturbation intensities that are concomitant with the first appearance of penetrative trace fossils. Point May stands out as a section with low ichnodiversity and an inconsistent data set on bioturbation intensities. Its limited data set is a consequence of poor bed surface exposures, which impact negatively on the preservation and visibility of horizontal trace fossils. This study demonstrates that evaluation of outcrop quality should be an essential procedure to any research addressing evolutionary trends that took place at this critical time of the history of life.

Topology, divergence dates, and macroevolutionary inferences vary between different tip-dating approaches applied to fossil theropods (Dinosauria).

Dated phylogenies of fossil taxa allow palaeobiologists to estimate the timing of major divergences and placement of extinct lineages, and to test macroevolutionary hypotheses. Recently developed Bayesian 'tip-dating' methods simultaneously infer and date the branching relationships among fossil taxa, and infer putative ancestral relationships. Using a previously published dataset for extinct theropod dinosaurs, we contrast the dated relationships inferred by several tip-dating approaches and evaluate potential downstream effects on phylogenetic comparative methods. We also compare tip-dating analyses to maximum-parsimony trees time-scaled via alternative a posteriori approaches including via the probabilistic cal3 method. Among tip-dating analyses, we find opposing but strongly supported relationships, despite similarity in inferred ancestors. Overall, tip-dating methods infer divergence dates often millions (or tens of millions) of years older than the earliest stratigraphic appearance of that clade. Model-comparison analyses of the pattern of body-size evolution found that the support for evolutionary mode can vary across and between tree samples from cal3 and tip-dating approaches. These differences suggest that model and software choice in dating analyses can have a substantial impact on the dated phylogenies obtained and broader evolutionary inferences.

New Notoungulates (Notostylopidae and Basal Toxodontians) from the Early Oligocene Tinguiririca Fauna of the Andean Main Range, Central Chile

ABSTRACT Here we describe two new notoungulate taxa from early Oligocene deposits of the Abanico Formation in the eastern Tinguiririca valley of the Andes of central Chile, including a notostylopid (gen. et sp. nov.) and three basal toxodontians, cf. Homalodotheriidae, one of which is formally named a new species. The valley's eponymous fossil mammal fauna became the basis for recognizing a new South American Land Mammal “Age” intervening between the Mustersan and Deseadan of the classical SALMA sequence, the Tinguirirican. As a temporal intermediate between the bracketing SALMAs (Deseadan and Mustersan), the Tinguirirican is characterized by a unique cooccurrence of taxa otherwise known either from demonstrably younger or more ancient deposits, as well as some taxa with temporal ranges restricted to this SALMA. In this regard, two of the notoungulates described here make their last known stratigraphic appearances in the Tinguiririca Fauna, Chilestylops davidsoni (gen. et sp. nov.), the youngest notostylo...

Oldest known marine turtle? A new protostegid from the Lower Cretaceous of Colombia

Recent studies suggested that many fossil marine turtles might not be closely related to extant marine turtles (Chelonioidea). The uncertainty surrounding the origin and phylogenetic position of fossil marine turtles impacts our understanding of turtle evolution and complicates our attempts to develop and justify fossil calibrations for molecular divergence dating. Here we present the description and phylogenetic analysis of a new fossil marine turtle from the Lower Cretaceous (upper Barremian-lower Aptian, >120 Ma) of Colombia that has a minimum age that is >25 million years older than the minimum age of the previously recognized oldest chelonioid. This new fossil taxon, Desmatochelys padillai sp. nov., is represented by a nearly complete skeleton, four additional skulls with articulated lower jaws, and two partial shells. The description of this new taxon provides an excellent opportunity to explore unresolved questions about the antiquity and content of Chelonioidea. We present an updated global character-taxon matrix that includes D. padillai and marine turtles known from relatively complete specimens. Our analysis supports D. padillai as sister taxon of D. lowi within Protostegidae, and places protostegids as the sister to Pan-Dermochelys within Chelonioidea. However, this hypothesis is complicated by discrepancies in the stratigraphic appearance of lineages as well as necessarily complicated biogeographic scenarios, so we consider the phylogeny of fossil marine turtles to be unresolved and do not recommend using D. padillai as a fossil calibration for Chelonioidea. We also explore the definition of “marine turtle,” as applied to fossil taxa, in light of many littoral or partially marine-adapted fossil and extant lineages. We conclude that whereas the term “oldest marine turtle” depends very much on the concept of the term being applied, we can confidently say that D. padillai is the oldest, definitive, fully marine turtle known to date.

Late Triassic (Carnian– Rhaetian) palynology of Hopen, Svalbard

Triassic strata crop out extensively on the Svalbard Archipelago and subcrop under much of the Barents Sea. However, due to the remoteness of the region, relatively few palynostratigraphic studies of the Upper Triassic succession have been conducted. Consequently, existing palynological zonations for the Late Triassic in the region are of relatively low temporal resolution. In this study, 154 palynological samples from eight outcrop localities on the island of Hopen, Svalbard Archipelago, were analysed. Hopen offers unique insights into the subsea geology of the Barents Sea due to its position as the most southeasterly island of the archipelago. Samples spanning the De Geerdalen, Flatsalen and Svenskøya formations (Kapp Toscana Group) yielded well preserved palynofloras. The dense vertical and lateral distribution of samples makes this the most detailed palynological investigation of LateTriassic strata conducted thus far in the region. Six palynological assemblages were recognised using relative abundance and first stratigraphic appearance data; in ascending stratigraphic order these are the: (1)Leschikisporis aduncus assemblage (late Carnian), (2)Protodiploxypinus spp. assemblage (late Carnian– ? early Norian), (3)Classopollis torosus assemblage (early Norian), (4)Rhaetogonyaulax rhaetica assemblage (early Norian), (5)Limbosporites lundbladii– Quadraeculina anellaeformis assemblage (? late Norian–? Rhaetian) and the (6)Rogalskaisporites ambientis assemblage (? late Rhaetian). The palynological assemblages are compared to previous palynological studies on the island and to existing palynozonations for the region. A revised age interpretation for Hopen is provided based on the integration of palynology and independent chrono- and biostratigraphic evidence. The youngest strata are interpreted to be of Rhaetian age and yielded palynomorph assemblages remarkably similar to contemporaneous assemblages previously described from China, Australia and New Zealand. The study contributes important empirical data concerning the Late Triassic palynofloras along the northern shores of Pangaea.

New Paleomagnetic and Stable‐Isotope Results from the Nanxiong Basin, China: Implications for the K/T Boundary and the Timing of Paleocene Mammalian Turnover

The Nanxiong Basin (Guangdong Province, China) preserves the most complete Asian stratigraphic record of the Cretaceous‐Paleogene (K/Pg) boundary extinction and the subsequent Paleocene mammalian radiation. Despite extensive study, the precise placement of the K/Pg boundary in the Nanxiong Basin sequence has been controversial, and the timing of subsequent mammalian turnover is poorly constrained. We present new paleomagnetic and geochemical data from the Late Cretaceous Pingling Formation (Nanxiong Group) and the overlying Paleocene Shanghu, Nongshan, and Guchengcun formations (Luofozhai Group). Our samples are directly correlated with previous geochemical and paleontological sampling localities, allowing for easy comparison with other local proxy records. Results indicate that the traditional placement of the K/Pg boundary at the base of a chaotic channel sandstone bed marking the highest stratigraphic appearance of dinosaur eggshell fragments and lowest stratigraphic appearance of Paleocene mammalian fossils lies about two‐thirds of the way up Chron C29R, consistent with the placement of the boundary in all other well‐documented sections. The average carbon isotope composition of paleosol carbonates decreases by >2‰ in the Early Paleocene, consistent with a major disruption to global carbon cycling after the K/Pg boundary. Constraints on the age of the first major Cenozoic mammalian turnover event in Asia (the Shanghuan‐Nongshanian Asian Land Mammal Age boundary) support its placement near the top of Chron C27N, which coincides with a similar turnover in North America and geochemical changes recorded in several deep sea cores.

Bone histology of the Middle Jurassic turtle shell remains from Kirtlington, Oxfordshire, England

The Middle Jurassic (Bathonian) turtle material from the Mammal Bed at Kirtlington, Oxfordshire, England, has recently been tentatively referred to the Pleurosternidae, although the known synapomorphies of this clade were absent from the specimens. Here we present new evidence from shell bone histology that corroborates reports of pleurosternids at Kirtlington and further reveal that two different histomorphs (= two different taxa) are present in this locality. The first histomorph presents the distinctive histological structure of pleurosternids, which is described herein for the first time: the external cortical bone layers are differentiated into an inner zone of coarse, irregularly interwoven structural fibre bundles and an outer fine-fibred zone. The second histomorph has a more plesiomorphic structure and can only be assigned to Cryptodira indet. A morphological reassessment of the Kirtlington material fails to recognize two different taxa and shows that only sparse evidence supports the presence of pleurosternids in this locality. Shell bone histology thus appears as a powerful tool to study poorly preserved specimens and may in some case (like with pleurosternids) help resolve phylogenetic relationships. According to our results, the stratigraphic appearance of the Pleurosternidae is adjusted from the Kimmeridgian (Late Jurassic) to the Bathonian (Middle Jurassic), which significantly reduces the ghost lineage of Paracryptodira. Bone histology, turtles, Paracryptodira, Pleurosternidae, Middle Jurassic, Kirtlington.

Radio‐echo layering in West Antarctica: a spreadsheet dataset

AbstractOf the various information recovered from radio‐echo sounding (RES) of polar ice sheets, internal layering is currently under‐utilized by glaciologists, due in part to a lack of available data. Here, RES layering of the West Antarctic Ice Sheet, from the 1970s RES survey of approximately 70 per cent of this ice mass, is made available in a series of spreadsheets. Three types of internal layers are evident in the dataset. The first is continuous layers that have a stratigraphic appearance and can often be traced easily for hundreds of kilometres. The second is buckled layering, which also resembles stratigraphy and can sometimes be traced over tens of kilometres (although layer identification can often be difficult). The roughness of these layers is often greater than the bed at the same wavelength. The third is highly distorted or absent layering, which is not possible to trace laterally. Despite debate concerning the origin of RES layers, they are thought by most glaciologists to represent isochronous surfaces. The pattern of internal layering is potentially of importance to glaciologists for three reasons. (1) The position of undeformed layers below the ice surface is a function of accumulation rate, ice flow and basal melting conditions. Numerical modelling (including new ‘data assimilation’ techniques) could be used to discriminate between these processes, so revealing important information about the ice sheet and its environment. (2) Buckled layers are deformed by ice flow process, and so their occurrence can be related to the flow dynamics of the ice sheet. (3) Very buckled layers are often associated with ice stream flow, which allows their location to mark the positions of past and present fast‐flowing ice. Copyright © 2005 John Wiley & Sons, Ltd.

Cycles in fossil diversity

It is well known that the diversity of life appears to fluctuate during the course of the Phanerozoic, the eon during which hard shells and skeletons left abundant fossils (0-542 million years ago). Here we show, using Sepkoski's compendium of the first and last stratigraphic appearances of 36,380 marine genera, a strong 62 +/- 3-million-year cycle, which is particularly evident in the shorter-lived genera. The five great extinctions enumerated by Raup and Sepkoski may be an aspect of this cycle. Because of the high statistical significance we also consider the contributions of environmental factors, and possible causes.

BIOMODULE: a Java program to help model and interpret the stratigraphic record

A combination of a stratigraphic simulation package (STRATA) and an evolutionary-ecological model (BIOSTRAT) can be used to simulate the distribution of species within a sequence stratigraphic framework. BIOMODULE is an extension of this model approach in that it facilitates the visualization and interpretation of those simulations and their input data. Environmental factors (e.g., sea-level changes or sedimentation rates) and ecological factors (preferred water depth, depth tolerance, abundance) that determine the spatial and temporal distribution of species are easily and quickly investigated. In addition, BIOMODULE can be used to compile the stratigraphic first and last appearances of those species and export them into available graphic correlation software packages (Conop9 and GraphCor). This can be used to test the graphic correlation technique and investigate its accuracy and precision under a range of different conditions (e.g., different stratigraphic architectures and sampling densities) since the true correlation of the different sections is already known.

Chitinozoan biostratigraphy of the Late Devonian formations in well Caima PH-2, Tapajós River area, Amazonas Basin, northern Brazil

The chitinozoan biostratigraphy of the Barreirinha Formation in its type area (Tapajós River near Itaituba town, Pará State, Amazonas Basin, north Brazil), and of the lower part of the overlying Curiri Formation, is calibrated against the local miospore succession, which in turn can be readily correlated with standard miospore biozonations of Euramerica. The present study is based on 375 samples from a ca. 137-m-thick section in the Caima PH-2 shallow borehole. The 26 chitinozoan species encountered are used to recognize eight biozones in the studied well. The applicability of this zonation is yet to be tested elsewhere in the Amazonas Basin. The zones in ascending stratigraphic order are: the total range zone of Angochitina katzeri n. sp., total range subzone of Ramochitina derbyi n. sp, total range subzone of Lagenochitina avelinoi, interval zone of Urochitina bastosi, total range zone of Angochitina carvalhoi n. sp., interval zone of Angochitina rathbuni n. sp. and Ramochitina praeritae n. sp., total range zone of Ramochitina ritae n. sp., and total range zone of Ramochitina cf. R. ritae. Eleven species are newly described; in order of stratigraphic appearance: Ramochitina derbyi, Angochitina katzeri, Ramochitina hartti, Angochitina carvalhoi, Angochitina rathbuni, Ramochitina praeritae, Ramochitina clarkei, Ramochitina ritae, Angochitina loboziaki, Ramochitina oliveirai, and Ramochitina famennense.

How good is the fossil record of arthropods? An assessment using the stratigraphic congruence of cladograms

AbstractA total of 179 published cladograms of arthropods was tested for their congruence with the palaeontological record. Congruence for data sets including 510 tetrapod and 157 fish trees was also calculated for comparison. Results provide support for the hypothesis that the fossil record of arthropods is less complete (at levels of stratigraphic and taxonomic resolution pertinent to most macroevolutionary studies) than the records of several other taxa. Differences in tree size, shape, balance and the distribution of first stratigraphic appearances (potential sources of bias) were controlled for by various randomization procedures. Most measures of congruence for arthropods were statistically poorer than those for other groups, even when the sample was divided into broad temporal bins. Many of the most robust and widely reproduced sister groupings of arthropods are attended by ghost ranges of many tens or hundreds of millions of years. Fossils of a number of presently very diverse and abundant arthropod groups are conspicuously absent from the record, despite many spectacular examples of the detailed preservation of others. There is probably no single reason for the apparently poor record of arthropods. Low preservation potential, small size of individuals, small numbers of individuals, and restricted palaeobiogeography almost certainly play a role in particular cases. Copyright © 2001 John Wiley & Sons, Ltd.

Correlation of the Type Bashkirian Stage (Middle Carboniferous, South Urals) with the Morrowan and Atokan series of the midcontinental and western United States

The graphic correlation technique has been used to directly relate the stratigraphic appearances of key species in the Bashkirian Stage stratotype to those in a North American composite section. The type Bashkirian is separated from the underlying Serpukhovian Stage by an erosional unconformity and associated lacuna of undetermined, but probably minor duration. Accordingly, the base of the type Bashkirian (base of Bogdanovkian Horizon) is only slightly younger than the international mid-Carboniferous boundary. A level within the upper part of the Tashastian Horizon (Upper Bashkirian Substage) most likely correlates with the Morrowan-Atokan boundary. This level roughly coincides with a sequence boundary at the Bashkirian stratotype and with a regional unconformity in the North American midcontinent. The top of the Bashkirian Stage (top of Asatauian Horizon) is lower Atokan in North American terms. On the basis of recent 40Ar/39Ar and SHRIMP zircon geochronology studies, the age of the mid-Carboniferous boundary is estimated at 314 Ma and a horizon of early Atokan age is dated at 310.8 Ma. Accepting the present biostratigraphic correlations, these values suggest a duration for the Bashkirian Stage of slightly more than 3.2 m.y. and a duration of the Morrowan Series of slightly less than 3.2 m.y.

Noyon Uul syncline, southern Mongolia: Lower Mesozoic sedimentary record of the tectonic amalgamation of central Asia

To explore the hypothesis that a regionally extensive early Mesozoic collisional foreland basin existed on strike to the east of documented Mesozoic foreland basins in western China, we conducted a reconnaissance study of a >5 km section of Upper Permian-Lower Jurassic(?) nonmarine strata exposed in the Noyon Uul syncline in southern Mongolia. This paper documents the depositional settings of these poorly known strata, their provenance, and their regional tectonic significance in the context of the Mesozoic amalgamation of central Asia. We interpret Noyon Uul strata to be composed of (1) a coarse-grained, braided fluvial facies, (2) a meandering fluvial facies, and (3) a poorly oxygenated lacustrine facies that represent three principal depositional environments. Sandstone compositions are dominantly volcanic (mean compositions = Qm 20 F 23 Lt 57 ; Qp 13 Lv 82 Ls+Lm 5 ), likely reflecting derivation from Carboniferous and older volcanic-arc sequences. Increased proportions of alkalic granite pebbles and cobbles above the first coarse-grained, braided fluvial unit and the first stratigraphic appearance of detrital K-feldspar in basal coarse-grained, braided fluvial strata suggest unroofing of Permian alkalic granites. The Noyon Uul deposits likely are syntectonic, as suggested by their thickness, environments of deposition, coarse-grained character, and accumulation rates. Overlap of the Noyon Uul syncline by relatively undeformed Upper Jurassic and Lower Cretaceous strata, together with the presence of a regional unconformity between Middle and Upper Jurassic rocks, requires a phase of Middle-Late Jurassic deformation. The erosional remnants of a Middle-Upper Jurassic north-verging thrust belt have been documented just 100 km south of Noyon Uul, suggesting that the Noyon Uul deposits may be foreland in origin. Specifically Triassic thrusting has not been recognized in southern Mongolia, but Permian-Jurassic contractile deformation associated with the collisional amalgamation of Asia is documented or reasonably inferred for extensive areas of China to the south and west. Although sedimentary attributes of the Noyon strata are most compatible with a foreland interpretation, it is possible that the Noyon deposits and their deformation may be related to strike-slip faulting. Neither the attributes of the Noyon deposits nor their ages are compatible with widespread Late Jurassic-Early Cretaceous rifting that occurred across southeastern Mongolia.

Late Ordovician extinctions of bryozoans

An analysis of the final stratigraphic appearances of byrozoan species and genera, compiled in a world-wide bryozoan data base, revealed three discrete Late Ordovician extinctions. A Late Carddoc (Onnian) extinction was most pronounced on the plates of Baltica and Siberia. Endemic species and genera, confined to one plate and one lithotope were most affected and the extinction was coincident with increased migrations of bryozoan genera to Baltica and Siberia. The Late Caradoc extinction may be related to decreasing provinciality and competition between migrant and stenotopic taxa. Two major extinctions occurred in the Late Ashgill. The greatest of the two is recognized at the end of the Rawtheyan. and affected primarily taxa on the North American plate. The extinction at the end of the Hirnantian affected primarily Baltic taxa. The exact timing of the end-Rawtheyan extinction in North America cannot be established owing to incompleteness of the stratigraphic record. The Rawtheyan extinction occurred during a major glaciation centered in North Africa and a regression of epeiric seas. The large majority of North American survivors of the extinction are represented by Faunas preserved on Anticosti Island. which remained submerged during the regression. This evidence supports regression as a cause of the Rawtheyan extinctions in North America. The end-Hirnantian extinctions may be related to the ensuing transgression or to a wave of faunal migrations associated with the transgression. *Bryozoa, extinctions, Ordovician, Rawtheyan, Hirnantian, North America, Baltica.

The Recognition of Stratigraphic Anomalies Through Improved Acquisition and Processing Technology in the Hugoton Embayment

Oil has recently been discovered in the Hugoton Embayment, Kansas, through the use of stratigraphic interpretation of seismic data. This oil is located in traps of channel sands in the Morrow and Chester Formations. Current seismic data, from which producing well locations were selected, were 'deprocessed' to simulate older data. Field acquisition and seismic processing parameters were duplicated for six of the prior twenty-four years. This simulated data shows the logical progression of field acquisition and processing technology. This method also demonstrates the stratigraphic appearance of the anomaly on the data during those years. Both field acquisition and processing parameters and techniques are reviewed on each of two lines. The resulting impact of the changes on each of the sections and its anomaly is noted as we progress through time. In addition to showing full sections for each of the six years, blowups of the actual anomaly location on each of the simulations are shown with the original data for easy comparison.

Recognition of Stratigraphic Anomalies Through Improved Acquisition and Processing Technology, Hugoton Embayment: ABSTRACT

Oil has recently been discovered in the Hugoton embayment, Kansas, through the use of stratigraphic interpretation of seismic data. This oil is located in traps of channel sands in the Morrow and Chester formations. Current seismic data, from which producing well locations were selected, were deprocessed to simulate older data. Field acquisition and seismic processing parameters were duplicated for six of the prior 24 years. This simulated data shows the logical progression of field acquisition and processing technology. This method also demonstrates the stratigraphic appearance of the anomaly on the data during those years. Both field acquisition and processing parameters and techniques are reviewed on each of two lines. The resulting impact of the changes on each of the sections and its anomaly is noted as they progress through time. In addition to showing full sections for each of the six years, blowups of the actual anomaly location on each of the simulations are shown with the original data for easy comparison.

A basal cretaceous dinoflagellate suite from northeastern Australia

Abstract A palynological sequence is described from the Neocomian of the Carpentaria Basin in Northern Queensland. Emphasis is given to the dinoflagellate biostratigraphy in the oldest marine Cretaceous sequence known from eastern Australia. The phytoplankton documentation includes 72 species (and 2 lower categories) assigned to 38 genera. Three informal intervals are described in chronological succession as zones DK1, DK2, and DK3, and their lower limits are marked by the oldest stratigraphic appearances of certain widely known dinoflagellate species; namely Chlamydo‐phorella nyei, Dingodinium cerviculum, Muderongia tetracantha, M. staurota, Odontochitina operculata, and Canningia colliveri. Restricted stratigraphic occurrences of certain dinoflagellate species in Australia, Europe, and North America are taken as evidence for tentatively dating zone DK1 as latest Jurassic‐Berria‐sian, zone DK2 as Valanginian, and zone DK3 as Hauterivian. Contemporaneous spore and pollen subzones of the Murospora florida Zone in Queensland are dated by direct association with the dinoflagellate record. Geological age and paleoenvironments of the associated Gilbert River Formation, Helby Beds, and basal part of the Rolling Downs Group are briefly summarized. Palynology indicates that the base of the Rolling Downs Group becomes progressively younger to the south, reflecting diachronous facies boundaries as a Neocomian sea gradually transgressed in that direction.

A review of certain non-tabulate Cretaceous hystrichospherid dinocysts

Species assignable to three Cretaceous non-tabulate hystrichospherid dinocysts genera, Kleithriasphaeridium, Florentinia and Silicisphaera gen. nov. are reviewed and five new species proposed: K. loffrensis, F. resex, S. buspina, S. tenera and S? torulosa. Members of these genera are basically spherical in shape, possess either a precingular (3″) or combination precingular (3″)-apical archaeopyle and a variable number of differently shaped intratabular processes. Specific differentiation is based mainly on variation in process number and size. Much of the new information given in this paper is derived from the study of material from (1) the Ryazanian and Valanginian of eastern England, and (2) the Late Albian to Senonian of the Loffre Borehole, northern France. The stratigraphic ranges of all the species are discussed; since a succession of stratigraphic appearances and extinctions occurs in the Cretaceous and the ranges of individual species are fairly limited, careful identification of species will give fine stratigraphic control. The new genus, Silicisphaera, first appears in the mid-Turonian and apparently becomes extinct by the close of the Senonian. Florentinia and Silicisphaera are considered to be ancestral to the Tertiary Diphyes and Hystrichokolpoma.