Late Cretaceous Sea Research Articles

Hot carbonates deep within the Chicxulub impact structure.

Constraining the thermodynamic conditions within an impact structure during and after hypervelocity impacts is extremely challenging due to the transient thermal regimes. This work uses carbonate clumped-isotope thermometry to reconstruct absolute temperatures of impact lithologies within and close to the ∼66 Myr old Chicxulub crater (Yucatán, México). We present stable oxygen (δ18O), carbon (δ13C), and clumped-isotope (Δ47) data for carbonate-bearing impact breccias, impact melt rock, and target lithologies from four drill cores on a transect through the Chicxulub structure from the northern peak ring to the southern proximal ejecta blanket. Clumped isotope-derived temperatures (T(Δ47)) are consistently higher than maximum Late Cretaceous sea surface temperatures (35.5°C), except in the case of Paleogene limestones and melt-poor impact breccias outside of the crater, confirming the influence of burial diagenesis and a widespread and long-lived hydrothermal system. The melt-poor breccia unit outside the crater is overlain by melt-rich impact breccia yielding a much higher T(Δ47) of 111 ± 10°C (1 standard error [SE]), which likely traces the thermal processing of carbonate material during ejection. Finally, T(Δ47) up to 327 ± 33°C (1 SE) is determined for the lower suevite and impact melt rock intervals within the crater. The highest temperatures are related to distinct petrological features associated with decarbonation and rapid back-reaction, in which highly reactive CaO recombines with impact-released CO2 to form secondary CaCO3 phases. These observations have important climatic implications for the Cretaceous-Paleogene mass extinction event, as current numerical models likely overestimate the release of CO2 from the Chicxulub impact event.

The Late Cretaceous marine basin of platform Ukraine (morphometry, stages of development, lithology and stratigraphy of sedimentary formations)

Formulation of the problem. The relevance of the research is related to the formation of a holistic view of the Late Cretaceous Sea basin of the study area: its boundaries, area, the existence of probable land areas, conditions of sediment accumulation and historical development. The purpose of the article. Based on the results of exploratory, structural-exploratory and parametric drilling conducted during the State Geological Survey on scales of 1:50,000, 1:100,000 and 1:200,000 and own field research, we supplemented the information on the geohistorical chronicle of the Late Cretaceous of the southwestern part of the SEE. Methods. The material for writing the article was the results of drilling more than 10,000 exploration, structural and parametric drilling wells conducted during the State Geological Survey at scales of 1:50,000, 1:100,000 and 1:200,000, which are stored in the State Information Geological Fund of Ukraine. Also, the results of own field research of 47 most complete open sections of the Upper Cretaceous of Platform Ukraine were taken into account and a significant literature on the geological structure of the studied area was processed. Research methods: facies and formation analysis, lithological, petrographic, paleontological, litho-biostratigraphic, geophysical, etc. At the final stage of the mapping of the Upper Cretaceous sediments of Platform Ukraine, the methodology of sedimentary basin monitoring and modeling of formation units was used with the help of the domestic software package "Geomapping" with further conversion to the ArcView grid format. Results. To find out the spatio-temporal distribution of the Upper Cretaceous deposits of the study area, their composition, stratigraphic position and parameters of the Late Cretaceous sea basin, we analyzed the materials of mapping, structural search, exploratory and parametric drilling over the past 50 years were analyzed, our own studies of open sections of the Upper Cretaceous were taken into account, and significant stock material on the geological structure of the studied area was also processed. The most informative wells were selected as reference wells. Their number varied from 1179 for Early-Middle Cenomanian deposits to 1103 for Turonian deposits. The maximum density of the studied sections of support wells was recorded for the territory of Volyn-Podillia and individual blocks of the Ukrainian Shield (USH) and is 23.1 wells per 1000 km2, the minimum - in the water areas of the Ukrainian part of the Black and Azov Seas - about eight per 1000 km2. The absence of Upper Cretaceous deposits on a significant territory of platform Ukraine was established. Early-Middle Cenomanian and Turonian deposits have the largest distribution area, and Maastrichtian deposits have the smallest. In our opinion, areas with continental conditions of existence in certain ages or during the entire Late Cretaceous period have been identified. This made it possible to calculate the areas of land areas and areas covered by the sea with the help of software, with a certain percentage of error (up to 10%). The area of the sea basin was up to 80% of the territory of platform Ukraine. In the historical development of the Late Cretaceous Sea basin of the study area, two stages are distinguished: early-Middle Cenomanian and late Cenomanian-Maastrichtian, which differed significantly from each other in terms of hydrological, hydrochemical, temperature regimes and the nature of sedimentation. The lithological characteristics of the deposits according to the modern stratigraphic division of the Upper Cretaceous rock complex are given.

Rapid growth in Late Cretaceous sea turtles reveals life history strategies similar to extant leatherbacks.

Modern sea turtle long bone osteohistology has been surprisingly well-studied, as it is used to understand sea turtle growth and the timing of life history events, thus informing conservation decisions. Previous histologic studies reveal two distinct bone growth patterns in extant sea turtle taxa, with Dermochelys (leatherbacks) growing faster than the cheloniids (all other living sea turtles). Dermochelys also has a unique life history compared to other sea turtles (large size, elevated metabolism, broad biogeographic distribution, etc.) that is likely linked to bone growth strategies. Despite the abundance of data on modern sea turtle bone growth, extinct sea turtle osteohistology is virtually unstudied. Here, long bone microstructure of the large, Cretaceous sea turtle Protostega gigas is examined to better understand its life history. Humeral and femoral analysis reveals bone microstructure patterns similar to Dermochelys with variable but sustained rapid growth through early ontogeny. Similarities between Progostegea and Dermochelys osteohistology suggest similar life history strategies like elevated metabolic rates with rapid growth to large body size and sexual maturity. Comparison to the more basal protostegid Desmatochelys indicates elevated growth rates are not present throughout the entire Protostegidae, but evolved in larger and more derived taxa, possibly in response to Late Cretaceous ecological changes. Given the uncertainties in the phylogenetic placement of the Protostegidae, these results either support convergent evolution towards rapid growth and elevated metabolism in both derived protostegids and dermochelyids, or a close evolutionary relationship between the two taxa. Better understanding the evolution and diversity of sea turtle life history strategies during the Late Cretaceous greenhouse climate can also impact current sea turtle conservation decisions.

Taxonomy and paleobiogeography of rudist bivalves from Upper Cretaceous strata, Gulf Coastal Plain and Puerto Rico, USA

AbstractThis study provides the first focused investigation of rudist bivalves from the Upper Cretaceous of the Gulf Coastal Plain (GCP) in the southern US and previously undescribed specimens from the Flor de Alba Limestone Member of the Pozas Formation in Puerto Rico. Identified rudists from the GCP comprise the Monopleuridae, including Gyropleura, as well as Radiolitidae, including Biradiolites cardenasensi, Durania maxima, Guanacastea jamaicensis, Radiolites acutocostata, and Sauvagesia. Integrating rudist occurrences within well-established GCP biostratigraphy allows for extension of upper ranges of D. maxima and R. acutocostata into the late Campanian, and extension of the lower ranges of B. cardenasensis and G. jamaicensis into the early Campanian. Identified rudists from Puerto Rico comprise the Hippuritidae and include Barrettia monilifera, which supports the age of the Flor de Alba Limestone Member of the Pozas Formation as middle Campanian. Combined taxonomic, biostratigraphic, and paleobiogeographic analyses indicate there is no rudist fauna endemic to the GCP, and the region marks the northeastern range of the Caribbean genera Biradiolites, Durania, Guanacastea, Gyropleura, Radiolites, and Sauvagesia during the Campanian and Maastrichtian. The new occurrences help inform future updates of Late Cretaceous sea surface-current reconstructions for the Caribbean and Western Interior Seaway, USA.

The first report of Chelonioidea cf. Ctenochelys from the Late Cretaceous of the Maastrichtian type area

Abstract A mandible of a Late Cretaceous sea turtle with affinities to Ctenochelys is reported from the Maastrichtian type area of the Netherlands. The triangular mandible has a well-developed symphyseal ridge surrounded on both sides by large, concave areas on the triturating surface. It represents the first potential occurrence of Ctenochelys from the Maastrichtian type area. This finding increases the diversity of the turtle fauna known from the Maastrichtian type area.

Early Cretaceous sea surface temperature evolution in subtropical shallow seas

Late Cretaceous sea surface temperatures (SST) are, amongst others, traditionally reconstructed by compiling oxygen isotope records of planktonic foraminifera obtained from globally distributed pelagic IODP drill cores. In contrast, the evolution of Early Cretaceous SSTs is essentially based on the organic TEX86 palaeothermometer, as oxygen-isotope data derived from well-preserved ‘glassy’ foraminifer calcite are currently lacking. In order to evaluate the extraordinary warm TEX86-derived SSTs of the Barremian to Aptian (130–123 Ma) subtropics, we present highly resolved sclerochemical profiles of pristine rudist bivalve shells from Tethyan and proto-North Atlantic shallow water carbonate platforms. An inverse correlation of seasonal ontogenetic variations in δ18Orudist and Mg/Ca ratios demonstrates the fidelity of oxygen isotopes as palaeotemperature proxy. The new data shows moderate mean annual SSTs (22–26 °C) for large parts of the Barremian and Aptian and transient warm pulses for the so-called Mid-Barremian Event and Oceanic Anoxic Event 1a (reaching mean annual SSTs of 28 to 30 °C). A positive shift in mean annual oxygen-isotope values (δ18O: ≤ − 0.3‰) coupled with invariant Mg/Ca ratios at the Barremian–Aptian boundary points to a significant net loss of 16O in Tethyan shallow-marine settings. As the positive oxygen-isotope rudist shell values are recorded immediately beneath a major superregional hiatal surface, they are interpreted to be related to a major cooling phase and potential glacio-eustatic sea-level lowering. Our new sclerochemical findings are in clear contrast to open ocean SST records based on TEX86, which indicate exceptionally warm Barremian to earliest Aptian subtropical oceans and weak meridional SST gradients.

Late Cretaceous (Turonian-Coniacian) sequence stratigraphy, sea level, and deltaic facies, Magothy Formation, U. S. Middle Atlantic Coastal Plain

ABSTRACT: The peak "hothouse" interval of the Turonian-Coniacian (93-87 Ma) is represented on the U.S. middle Atlantic Coastal Plain by sequences of the Raritan/Bass River, Magothy, and Cheesequake Formations deposited on a passive continental margin as mixed wave-, tide-, and river dominated deltas. We apply sequence stratigraphy integrated with biostratigraphy to identify and map two major sequence boundaries separating the Raritan/Bass River, Magothy, and Cheesequake Formations and four to five (Mg1, Mg2, Mg3, ?Mg4, Mg5) Magothy sequences using continuous cores, outcrops, and geophysical logs in New Jersey. We extend correlations into New York and Delaware using well logs. The Magothy sequences disconformably overlie the well-dated (>93 Ma) lower Turonian to Cenomanian marine Raritan/Bass River sequences and are disconformably overlain by the marine Cheesequake Formation, which straddles the Coniacian/Santonian boundary. A "mid-Turonian" hiatus (ca. 93-90 Ma) associated with this major disconformity is a global sequence boundary (K-Tu4) reflecting a ~ 25 m sea-level lowering based on published NJ and Russian Platform backstripping records that indicate this was a major lowering of Global Mean Sea Level (GMSL).Higher-order (~1 Myr scale) sequence boundaries bracketing Mg1-Mg5 apparently correlate with global sequences but are only associated with low-amplitude (<25 m) sea-level falls.Mapping of sequences within the Magothy Formation shows the influence of 2 to 3 moderate-sized river sources, with thickening northeastward toward Long Island, New York, and thinning southwestward toward Delaware. Thick northern depocenters contrast with the preceding Potomac Formation (Barremian-early Cenomanian) with thick southern depocenters. This seesawing of basins on the 100-300 km and 2-10+ Myr scales is due to tectonism likely from changes inmantle dynamic topography. The remarkably widespread distribution of Magothy sequences and facies indicates stability of this deltaic depositional system over ~ 4Myr despite low-amplitude (less than 25m) sea-level variations.Widespread facies correlation provides a predictable distribution of aquifer sands and confining-unit clays tied to sea-level changes on complex deltaic facies.

Estimating the evolutionary rates in mosasauroids and plesiosaurs: discussion of niche occupation in Late Cretaceous seas.

Observations of temporal overlap of niche occupation among Late Cretaceous marine amniotes suggest that the rise and diversification of mosasauroid squamates might have been influenced by competition with or disappearance of some plesiosaur taxa. We discuss that hypothesis through comparisons of the rates of morphological evolution of mosasauroids throughout their evolutionary history with those inferred for contemporary plesiosaur clades. We used expanded versions of two species-level phylogenetic datasets of both these groups, updated them with stratigraphic information, and analyzed using the Bayesian inference to estimate the rates of divergence for each clade. The oscillations in evolutionary rates of the mosasauroid and plesiosaur lineages that overlapped in time and space were then used as a baseline for discussion and comparisons of traits that can affect the shape of the niche structures of aquatic amniotes, such as tooth morphologies, body size, swimming abilities, metabolism, and reproduction. Only two groups of plesiosaurs are considered to be possible niche competitors of mosasauroids: the brachauchenine pliosaurids and the polycotylid leptocleidians. However, direct evidence for interactions between mosasauroids and plesiosaurs is scarce and limited only to large mosasauroids as the predators/scavengers and polycotylids as their prey. The first mosasauroids differed from contemporary plesiosaurs in certain aspects of all discussed traits and no evidence suggests that early representatives of Mosasauroidea diversified after competitions with plesiosaurs. Nevertheless, some mosasauroids, such as tylosaurines, might have seized the opportunity and occupied the niche previously inhabited by brachauchenines, around or immediately after they became extinct, and by polycotylids that decreased their phylogenetic diversity and disparity around the time the large-sized tylosaurines started to flourish.

Quantifying the paleogeographic driver of Cretaceous carbonate platform development using paleoecological niche modeling

Platform carbonates are a major component of the Earth System but their spatial extent through geological time is difficult to reconstruct, due to the incompleteness of the geological record, sampling heterogeneity and their intrinsic complexity. Here we use coupled ecological niche modeling and deep-time general circulation models to predict the occurrence of platform carbonates at the global scale during the Cretaceous. Specifically, niche modeling uses fuzzy logic to predict probable occurrence of platform carbonates as a function of sea-surface temperature, sea-surface salinity, primary productivity and water depth. The first three parameters derive from Cretaceous global paleoclimatic simulations using a coupled ocean-atmosphere general circulation model, while bathymetry is based on paleogeographical reconstructions. Model predictions are validated with the well-documented and abundant geological data from the Aptian. The methodologies developed for the Aptian are subsequently extended to other Cretaceous time intervals. The results of the niche model accurately predict the geographic distribution of Aptian carbonate platforms if a preference for low open-marine productivity levels is assumed for the rudist-dominated carbonate factories. However, if a preference for high productivity levels is assumed, the modeling results do not match the reported global distribution of Aptian carbonate platforms. From the Early Cretaceous into the Late Cretaceous sea level rose and the continents, on average, moved into lower latitudes. The model predicts a corresponding increase in the extent of the carbonate platforms, mainly due to the increasing extent of shallow-water environments available to carbonate development. These results indicate that long-term sea-level rise may have been a major factor responsible for the increase in the area of platform carbonates during the Cretaceous.

Mixed siliceous-carbonate sedimentation in a Late Cretaceous epeiric sea: New evidence from the eastern Russian Platform

Mixed siliceous-carbonate sedimentation in a Late Cretaceous epeiric sea: New evidence from the eastern Russian Platform

Geological evolution of the Chalk Group in the northern Dutch North Sea: inversion, sedimentation and redeposition

AbstractIn contrast to the Norwegian and Danish sectors, where significant hydrocarbon reserves were found in chalk reservoirs, limited studies exist analysing the chalk evolution in the Dutch part of the North Sea. To provide a better understanding of this evolution, a tectono-sedimentary study of the Late Cretaceous to Early Palaeogene Chalk Group in the northern Dutch North Sea was performed, facilitated by a relatively new 3D seismic survey. Integrating seismic and biostratigraphic well data, seven chronostratigraphic units were mapped, allowing a reconstruction of intra-chalk geological events.The southwestward thickening of the Turonian sequence is interpreted to result from tilting, and the absence of Coniacian and Santonian sediments in the western part of the study area is probably the result of non-deposition. Seismic truncations show evidence of a widespread inversion phase, the timing of which differs between the structural elements. It started at the end of the Campanian followed by a second pulse during the Maastrichtian, a new finding not reported before. After subsidence during the Maastrichtian and Danian, renewed inversion and erosion occurred at the end of the Danian. Halokinesis processes resulted in thickness variations of chalk units of different ages.In summary, variations in sedimentation patterns in the northern Dutch North Sea relate to the Sub-Hercynian inversion phase during the Campanian and Maastrichtian, the Laramide inversion phase at the end of the Danian, and halokinesis processes. Additionally, the Late Cretaceous sea floor was characterized by erosion through contour bottom currents at different scales and resedimentation by slope failures.

Big oyster, robust echinoid: an unusual association from the Maastrichtian type area (province of Limburg, southern Netherlands)

Large, denuded tests of holasteroid echinoids were robust benthic islands in the Late Cretaceous seas of northwest Europe. A test of Hemipneustes striatoradiatus (Leske) from the Nekum Member (Maastricht Formation; upper Maastrichtian) of southern Limburg, the Netherlands, is encrusted by a large oyster, Pycnodonte (Phygraea) vesiculare (Lamarck). This specimen is a palaeoecological conundrum, at least in part. No other members of the same oyster spatfall attached to this test and survived. Indeed, only two other, much smaller bivalve shells, assignable to the same species, attached either then or somewhat later. The oyster, although large, could have grown to this size in a single season. The larval oyster cemented high on the test and this would have been advantageous initially, the young shell being elevated above sediment-laden bottom waters. However, as the oyster grew, the incurrent margin of the commissure would have grown closer to the sediment surface. Thus, the quality of the incurrent water probably deteriorated with time.

Echinoid Bite Traces on Late Cretaceous (Early Maastrichtian) Sea Lilies from Southern Poland

Abstract. Echinoid bite traces on Late Cretaceous (early Maastrichtian) bourgueticrinids and isocrinids of southern Poland (Miechow Trough) were documented. The bitten sea lilies co-occurred with Goniopygus, a regular echinoid possessing an Aristotle's lantern. This is the first record of Goniopygus in the lower Maastrichtian of Poland. Considering former studies, as well as direct in situ observations of extant sea lilies and sea urchin behavior, the traces at hand could be most likely linked with predatory actions of the Goniopygus echinoid. Such studies on predatory phenomena are crucial and could provide baseline data concerning the evolutionary trends among organisms engaged in the “arms race”.

Late Cretaceous Sea Lilies (Crinoids, Crinoidea) from the Miechów Trough, Southern Poland

Late Cretaceous Sea Lilies (Crinoids, Crinoidea) from the Miechów Trough, Southern Poland

Redox conditions in the Late Cretaceous Chalk Sea: the possible use of cerium anomalies as palaeoredox indicators in the Cenomanian and Turonian Chalk of England

AbstractThe cerium anomalies preserved in the Chalk have been investigated as possible palaeoredox indicators of the Late Cretaceous Sea and its sediment. This has been based upon over a hundred new rare earth element analyses of selected samples and grain size fractions from the Chalk. Particular attention has been given to the methodology of differentiating between the cerium anomalies preserved in the bioclastic calcite and those in carbonate-fluorapatite preserved in the acetic acid insoluble residues of chalks. Variations in the cerium anomaly of different particle size fractions of uncemented chalks suggest that fractionation of rare earth elements between the Chalk’s seawater and the various organisms that contributed skeletal material to the bioclastic calcite of the Chalk may have occurred. Post-depositional processes of calcite cementation and late diagenetic sulphidisation have had no apparent effect on the cerium anomaly of the acetic acid insoluble residues. The cerium anomalies associated with the acetic acid insoluble residues from (1) an alternating sequence of chalks and marls from Ballard Cliff (Dorset, UK) typical of Milankovitch cyclicity show a marked diagenetic pattern, whereas those from (2) non-volcanic and volcanic marls display a pattern that is best explained by the variations in the availability of phosphorus and the timing of argillisation of volcanic glass during diagenesis. The general conclusion is drawn that the cerium anomalies preserved in the Chalk can provide an insight into the changing palaeoredox conditions in the Late Cretaceous Sea as well as in the pore fluids of its sediments.

Cretaceous-Tertiary (K-T) boundary evaporites in the Malatya Basin, eastern Turkey

The Malatya basin is situated on the Anatolid-Torid plate of the Neo-Tethys Sea. Evaporites were deposited in the northwestern part of the Malatya basin, which is referred to as the Hekimhan sub-basin. Although the Gunduzbey sub-basin in the southeastern Malatya basin has coeval deposits, it contains no evaporate deposits. The evaporite is most likely the result of the last transgressive–regressive cycle of the Late Cretaceous Sea. The pre-evaporitic unit is represented by the carbonate platform deposit of the Loftusia banks, which partly underwent dolomitization and overlies the deep marine sediments. Celestite-bearing algal limestone was deposited directly below the gypsum-dominated evaporate unit in association with the organic-rich mudstone. Evaporite sedimentation took place in various types of environments, such as marginal shallow subaqueous with the association of sabkha–coastal lagoon and deeper subaqueous. It is assumed that the tectonic evolution of the basin margin, which occurred during the latest stage of the Cretaceous regression, was responsible for the environmental restriction leading to evaporate sedimentation under arid/semiarid climatic conditions. The 87Sr/86Sr ratios obtained from 38 samples of the gypsum and celestite-bearing limestones (11 samples) range between 0.707817 and 0.707980 and between 0.707783 and 0.707864, respectively. The δ34S values range from +19.5 to +22.4 ‰, and the δ18O values range from +9.6 to +12.7 ‰. These isotopic signatures correspond to that of Late Cretaceous/Early Paleocene (Cretaceous-Tertiary boundary) marine water. However, celestite exhibit(s) relatively higher δ34S and 87Sr/86Sr values than expected marine values, which could be a result of contribution of diagenetic fluid into the celestite-precipitated environment.

Sea surface temperature record of a Late Cretaceous tropical Southern Tethys upwelling system

Late Cretaceous sea surface temperatures (SSTs) were reconstructed based on TEX86 data from the unique high productivity upwelling system in the Southern Tethys margin, Israel. SSTs were determined from two oil shale sequences of the Santonian–early Maastrichtian (~85 to 68Ma) in southern (Efe Syncline) and central (Shefela basin) Israel (paleo latitude 8–15°N). These two sampling sites represent the inner and outer belts of the upwelling system. Our TEX86 data indicate a significant long-term SST cooling trend from 36.0 to 29.3°C during the late Santonian and the early Campanian in the Southern Tethys margin consistent with the opening of the Equatorial Atlantic Gateway (EAG).Based on our data from the equatorial region and literature data from the polar region we reassessed the equator to pole SST gradient to 22°C. This value is closer to the modern ocean equator-to-pole SST gradient (30°C) than suggested from previous studies.Furthermore, the SST data suggests the presence of cooler surface water in the inner belt (27.7°C) caused by the upwelling system and warmer surface water (29.2°C) further seaward in the outer belt.

Late Cretaceous (Santonian-Campanian) sea lilies (Echinodermata, Crinoidea) from the glacial rafts of northwestern Poland

Seven Santonian (Isocrinus? minutus, Tetracrinus jagti, Cyathidium senessei, Bourgueticrinidae indet., Notocrinidae indet., Glenotremites paradoxus, Marsupitestestudinarius) and seven Campanian (Nielsenicrinus carinatus, Austinocrinus sp., Bourgueticrinidae indet., Bourgueticrinus cf. constrictus, B. ellipticus, B.? suedicus, Roveacrinina gen. et sp. indet.) crinoid taxa from the Cretaceous glacial rafts of northwestern Poland (near Wolin Island) are described for the first time. The taphonomy and palaeogeographic implications are discussed. The present assemblage differs taxonomically from the crinoid faunules recently described from the glacial rafts of eastern Poland. However, these faunules are similar to crinoids from the autochthonous Upper Cretaceous sediments of southern and eastern Poland (Miechow Trough, Krakow-Czestochowa Upland, Middle Vistula River valley). An update of Late Cretaceous crinoids from the Miechow Trough and Krakow-Czestochowa Upland is also given.

First evidence of a Late Cretaceous sea turtle from Australia

The isolated scapula of a chelonioid sea turtle is described from the Upper Cretaceous (upper Maastrichtian) Miria Formation of the Giralia Ranges in Western Australia. Character states including the wide angle of divergence between the scapular processes (possibly reaching 140°), projection of the glenoid on a constricted scapular neck, and highly vascular glenoid articular surfaces suggest affinity with dermochelyoids—the most diverse and geographically widespread clade of Mesozoic chelonioids. The Miria Formation chelonioid scapula constitutes the first definitive record of a Late Cretaceous sea turtle from Australia and is one of the few occurrences thus far documented from Upper Cretaceous–Paleogene deposits in the Southern Hemisphere.

Charting the Late Cretaceous seas: mosasaur richness and morphological diversification

ABSTRACT Abundant, readily identifiable, and biostratigraphically resolved specimens make mosasaurs ideal candidates to test fluxes in generic richness and morphological trends among marine vertebrates during the late Cretaceous. More than 1800 globally distributed mosasaur specimens are allocated to fifteen substage-level stratigraphically correlated assemblages. These data are quantitatively analyzed to illuminate trends within the group. Following their first appearance in the Cenomanian, mosasaurs experienced a significant radiation in the Coniacian and Santonian. Richness levels continued increasing into the Maastrichtian while mosasaurs incrementally exploited new predatory niches recognized via accumulation of novel dental morphologies. Their extinction at the end of the Cretaceous occurred at the zenith of mosasaur morphological and ecological diversity.