Uppermost Maastrichtian Research Articles

Theropod teeth palaeodiversity from the uppermost Cretaceous of the South Pyrenean Basin (NE Iberia) and the intra-Maastrichtian faunal turnover

The South Pyrenean Basin has yielded abundant dinosaur and penecontemporaneous vertebrate fossils, becoming one of the most important areas in Europe for the study of these faunas. The studied isolated theropod teeth from the Western Tremp Syncline (NE Iberia) were recovered from the uppermost Maastrichtian (topmost Arén and Tremp formations). The studies conducted have led to the identification of eight tooth morphotypes, which are referred to cf. Paronychodon, cf. Richardoestesia, an abelisaurid, a dromaeosaurid, and a non-dromaeosaurid paravian. Together with the previously reported troodontid and ornithuromorph, this study increases the known theropod palaeobiodiversity in the area to seven taxa. The latest Maastrichtian theropod fauna of the Western Tremp Syncline is thus composed of a medium to large-sized abelisaurid as well as a high diversity of small-bodied early-branching coelurosaurians and avialans, as seen in other Ibero-Armorican localities. Revision of the literature concerning the theropods of the Ibero-Armorican domain indicates that, although similar theropod groups were present before, during, and after the intra-Maastrichtian faunal turnover (an event constrained to between the early Maastrichtian and the early late Maastrichtian; lower part of C31r to the C30r/C30n reversal), there were changes in the abelisaurid, dromaeosaurid, and large avialan assemblages, as well as in the proportions of indeterminate paravian and cf. Richardoestesia morphotypes, with the presence of troodontids only recorded in post-turnover faunas. These changes suggest that theropods might have been affected by the turnover event. Nevertheless, further studies and more complete specimens could shed more light on the effects of this faunal turnover, and on the affinities and palaeobiodiversity of the latest Cretaceous Ibero-Armorican theropods.

Elasmobranch assemblages from a bathyal environment spanning the Cretaceous-Paleogene boundary in Austria

Abstract Extensive bulk-sampling of the continuous Cretaceous-Paleogene boundary section at Gams (Styria, Austria) allows for the first time the description of the elasmobranch communities inhabiting the bathyal environment of this well-known section. The sampled succession comprises six horizons from the uppermost Maastrichtian (upper part of Nephrolites frequens Zone CC26) and five horizons from the lowermost Danian (Zone NP1), which yielded a total of 1852 elasmobranch teeth. Although the majority of the teeth are not well preserved, this study enabled the description of at least 16 taxa of the orders Hexanchiformes, Squaliformes, Orectolobiformes, Lamniformes and Carcharhiniformes, providing a rare snapshot of elasmobranch diversity of this specific environmental setting. Beside minor diversity fluctuations between the assemblages, the extensive bulk-sampling of this section did not reveal a marked diversity decline related to the end-Cretaceous mass extinction event. However, a noteworthy correlation between the deepening upward trend of the section with the appearance of frilled and goblin sharks points to changes in palaeobathymetry, which is also reflected in the increase of the total proportion of squaliform teeth in the uppermost sampled horizon. Furthermore, teeth of the extinct triakid Palaeogaleus were recovered exclusively from the Danian deeper deposits, expanding the palaeoecological range of the genus down to fairly deep marine environments. In addition, this study provides the first record of the lamniform Cretolamna ex gr. borealis from the Danian of the Tethyan Realm expanding the palaeogeographic distribution of this group.

Binkhorstiidae, a new family of crabs (Decapoda, Brachyura, Retroplumoidea) from the Upper Cretaceous of the Netherlands and Belgium

Abstract In addition to the type species, Binkhorstia ubaghsii, which is fairly common in the upper part of the Nekum Member (Maastricht Formation) in the wider vicinity of Maastricht (the Netherlands) and Binkhorstia euglypha, which appears to be restricted to the overlying Meerssen Member of the same formation (uppermost Maastrichtian), a third member, B. desaegheri nov. sp., is recorded from the upper middle Santonian of the Campine area in north-east Belgium. The history of Binkhorstia is convoluted, serving as a prime example of how attempts to unravel the higher-level taxonomic position of late Mesozoic crabs may prove difficult. Over time, the genus has been referred to various families or subfamilies, either podotreme or putative eubrachyuran; here the new family Binkhorstiidae is placed in the superfamily Retroplumoidea. Binkhorstiids appear to have been a relatively short-lived endemic group that fell victim to Cretaceous‒Paleogene (K/Pg) boundary perturbations.

Maastrichtian to Paleocene facies evolution and Cretaceous/Tertiary boundary in Middle and Southern Egypt

The sedimentary history and facies development of southern Egypt during the Latest Cretaceous and Early Paleogene is summarized. The G . eugubina Zone is reported for the first time from middle Egypt, where the conglomerate usually marking a disconformity at the Cretaceous/Tertiary boundary, is absent. The Uppermost Maastrichtian strata are attributed to the M . prinsii Zone, the Late Maastrichtian index foraminifer Abathomphalus mayaroensis (Bolli) was not recovered in the investigated samples.

Historical material of cf. Thoracosaurus from the Maastrichtian of Denmark provides new insight into the K/Pg distribution of Crocodylia

Crocodylia are one of the distinctive groups that survived the K/Pg mass extinction event. New material from Upper Cretaceous–lower Palaeogene deposits is therefore important to understanding shifts in crocodylian distribution and ecology. This paper describes a fragmentary mandible of a marine crocodylian, from the lower Maastrichtian (Upper Cretaceous) of Møns Klint (Denmark). The specimen is referred to cf. Thoracosaurus (Gavialoidea). Although the material was collected in 1968, it has not yet been formally described. However, the specimen warrants further attention, given its palaeoecological and palaeobiogeographical significance. For instance, the Møns Klint “Thoracosaurus” is an indication of increased competition between large piscivores, and of added predation pressure on fish and cephalopod communities. This gavialoid therefore provides new insight into predator-prey interactions in the Danish Chalk palaeoenvironment. Regarding crocodylian distribution, the Møns Klint specimen represents the oldest European gavialoid record, with all other material deriving from uppermost Maastrichtian and Danian deposits. This indicates that Gavialoidea were present in the European “Chalk Sea” throughout the Maastrichtian, rather than being latest Maastrichtian arrivals. Furthermore, the Møns Klint “Thoracosaurus” represents one of few lower Maastrichtian gavialoids worldwide, the other two being from Mississippi and New Jersey (USA). The specimen thus extends the palaeogeographical range of lower Maastrichtian gavialoids across the proto-Atlantic. This reveals transatlantic distribution of Gavialoidea dating back to the earliest Maastrichtian, providing further evidence for distributional communication between marine vertebrate faunas of North America and Europe. These factors make the Møns Klint “Thoracosaurus” particularly valuable to understanding the distribution of K/Pg Crocodylia.

The K-Pg boundary section at Nasiłów, Poland: stratigraphic reassessment based on foraminifers, dinoflagellate cysts and palaeomagnetism

The Nasiłów section represents the uppermost part of the Middle Vistula River section, a classical Polish extra-Carpathian Cretaceous section, and gives access to the Cretaceous–Paleogene (K-Pg) boundary interval. Despite many papers that have been published so far, our newly collected data shed new light on the completeness of biostratigraphic and sedimentary records of the K-Pg at that site. The Nasiłów section encompasses the upper Maastrichtian regional XII and XIII foraminiferal assemblage zones and the lower Danian P0?-Pα standard planktonic foraminiferal zones. The K-Pg boundary is placed at the top of a phosphatic layer. The grey marly chalk unit, never before subjected to examination of biostratigraphically important taxa, displays blooms of guembelitrids pointing to the uppermost Maastrichtian (XIII foraminiferal assemblage Zone) as well as of planktonic and benthic foraminifers of a reduced test size. Such foraminiferal dwarfism is commonly observed near the end of the Cretaceous and interpreted as a response to the Deccan volcanism (possible 2nd phase) that caused climate changes and ocean acidification. The terminal Maastrichtian age of the marly chalk unit is additionally supported by an acme of the dinoflagellate cyst Palinodinium grallator , together with Tallasiphora pelagica and Disphaerogena carposphaeropsis . The “Greensand”, a distinct glauconite-quartz sand unit, contains exclusively terminal Maastrichtian planktonic foraminifers and dinoflagellate cyst assemblages. Individual specimens of Danian age are interpreted to be either an effect of contamination or were translocated down by burrowers into the Greensand. The lowermost portion of the Siwak (informal lithostratigraphic unit) demonstrates an early Danian age based on the co-occurrence of the common planktonic foraminifers Globoconusa daubjergensis, Guembelitria cretacea, Muricohedbergella monmouthensis, M. planispira, Planoheterohelix globulosa, Parvularuglobigerina extensa and P. alabamensis . The last occurrence of Palynodinium grallator and the first occurrences of Carptella cornuta and Senoniasphaera inornata , recorded directly above the phosphatic layer, support the same age assignment. The new palaeomagnetic data cannot prove remagnetization at the boundary interval, in contrast to previous research which gave support to a hiatus in the critical interval

Cretaceous–Paleogene transition interval in the north flank of the Alborz Mountains (N Iran); Planktic foraminiferal biostratigraphy and stable isotopes evidence

A Cretaceous/Paleogene (K/Pg) boundary interval in the north flank of Alborz Mountains (Aboksar section), northern Iran, has been studied to investigate the biological and geochemical variations of this event in the eastern Tethys. Abathomphalus mayaroensis at the late Maastrichtian, Pα (Parvularugoglobigerina eugubina), P1a (Parasubbotina pseudobulloides) and P1b (Subbotina triloculinoides) at the early Danian are the recognized planktic foraminiferal biozones and subzones in the studied area. The Plummerita hantkeninoides subzone at the uppermost Maastrichtian and P0 Biozone at the base of Danian were not defined in the studied section. This proposes a short-term hiatus and sedimentary discontinuity at the base of Paleocene and probably uppermost Maastrichtian, which most likely caused by winnowing of sediments after a cooling phase and development of bottom current in the Albors Basin. The K–Pg transition in the Aboksar section is characterized by a bloom in the Guembelitria cretacea, evolution of first Danian species (Pv. eugubina, Pv. longiapertura), δ13C negative shift (about 0.5‰), and a gentle Ir anomaly (0.1 ppb). Planktic foraminifera were diverse and abundant during the late Maastrichtian of studied section in a warm (relatively lower δ18O contents) and well stratified environment. Bloom of the opportunist species, G. cretacea, and decrease of planktic foraminiferal abundance and diversity at the base of Paleocene interval propose an abnormal stressful environment in this time probably after the asteroid impact and its following temperature decline. The appearance of more complete species with more specialized shells and larger sizes, such as Globoconusa daubjergensis, Parasubbotina pseudobulloides, Eoglobigerina eobulloides and Subbotina triloculinoides in the P1a and P1b subzones and return of carbon isotope diagram into the pre-boundary values testify an environmental recovery and optimization of ecosystem conditions.

Paléoécologie des foraminifères benthiques de nouvelles coupes de basse latitude du passage Crétacé-Paléogène : Coupes de l’Oued Es Smara et de l’Oued Abiod (région de Téjerouine, NW Tunisie)

Due to an impact of a bolide at the K/Pg boundary, the planktonic foraminifera have suffered sever mass extinction. However, no small Benthic Foraminifera species have documented mass extinction at the K/Pg boundary. Nevertheless, many species showed disturbance. The Maastrichtian assemblages may be different from those of the lower Paleogene by their species content, diversity and frequencies. At Oued Es Smara and Oued Abiod sections, the small benthic foraminifera indicate lower bathyal environment, and manifest significant faunal turnover. Until the uppermost Maastrichtian, their assemblages are highly diversified, with 77 species and 76 species respectively at Oued Es Smara and Oued Abiod sections. These are dominated by endobenthic morphotypes. At the K/Pg boundary, although 33 species (42,85%) (Oued Es Smara section) and 27 species (35,52%) (Oued Abiod section) of them seem to disappear, but only few species have really extinct such as Arenobulimina obesa. Nevertheless, the majority of species persist elsewhere at the Danian (e.g., Pseudoglandulina manifesta, Cibicioides proprius, Clavulinoides amorpha, Coryphostoma plaitum, Pullenia coryelli). At the lower Danian, the survivor Maastrichtian species are of 58% (Oued Es Smara) and 65% (Oued Abiod). Throughout the Parasubbotina pseudobulloides subzone, 4 others species were progressively disappeared. They are oligotrophic and low oxygen tolerant. About the Masstrichtian species, at the two studied sections (e.g. Gaudryina inflata and Tritaxia midwayensis) they seem to be more trophic exigent. Consequently, the benthic Foraminifera did not suffer massive extinction at the K/Pg boundary, but their assemblages underwent a significant faunal turnover which reflects important environmental changes. These changes are compatible with the catastrophic scenario induced by the large asteroid impact.

Dinoflagellate cyst-based paleoenvironmental reconstructions and phytoplankton paleoecology across the Cretaceous–Paleogene (K/Pg) boundary interval, Vancouver Island, British Columbia, Canada

A conformable K/Pg boundary succession is reported for this first time in North America west of the Rocky Mountains and in the north-eastern Pacific based on biostratigraphic controls, occurring within the upper Maastrichtian–lower Selandian marine sedimentary rocks of the Oyster Bay Formation, Vancouver Island, British Columbia. Approximate placement of the boundary is made possible by a suite of temporally constrained palynological K/Pg interval indicator taxa. The low-diversity, homogenous coastal dinoflagellate cyst assemblages of the Cordosphaeridium, Glaphyrocysta, Hystrichosphaeridium and Spiniferites-dominated uppermost Maastrichtian of the Lynnwood section transition to that of a more intermixed estuarine setting dominated by Areoligera, Exochosphaeridium and Ginginodinium along with peaks of low-salinity tolerant Senegalinium into the Danian–Selandian strata of the Appian Way and Oyster River sections. A marine assemblage turnover in the middle Oyster Bay Formation under conditions of elevated primary productivity and community heterogeneity owing to nutrient-rich waters is observed. Evidence for this interpretation is reinforced by the presence of overall higher cyst concentrations, peridinioid abundance and greater species diversity in association with botanical and shallow marine invertebrate fossil assemblages. The palynological data record probable eustatic regressive and transgressive sequences which illustrate a history of fluctuation between a predominantly coastal and largely estuarine paleoenvironment punctuated by the end-Cretaceous event. The presence of heavily negative δ13Corg values in addition to facies changes throughout the succession support a neritic profile for the Oyster Bay Formation. The palynological assemblages reflect localized paleoenvironmental conditions and climatic changes across the K/Pg boundary consistent with observations from numerous localities across both hemispheres.

The Tetrapod Fossil Record from the Uppermost Maastrichtian of the Ibero-Armorican Island: An Integrative Review Based on the Outcrops of the Western Tremp Syncline (Aragón, Huesca Province, NE Spain)

The South-Pyrenean Basin (northeastern Spain) has yielded a rich and diverse record of Upper Cretaceous (uppermost Campanian−uppermost Maastrichtian) vertebrate fossils, including the remains of some of the last European dinosaurs prior to the Cretaceous-Paleogene (K-Pg) extinction event. In this work, we update and characterize the vertebrate fossil record of the Arén Sandstone and Tremp formations in the Western Tremp Syncline, which is located in the Aragonese area of the Southern Pyrenees. The transitional and continental successions of these sedimentary units are dated to the late Maastrichtian, and exploration of their outcrops has led to the discovery of numerous fossil remains (bones, eggshells, and tracks) of dinosaurs, including hadrosauroids, sauropods, and theropods, along with other tetrapods such as crocodylomorphs, testudines, pterosaurs, squamates, and amphibians. In particular, this fossil record contains some of the youngest lambeosaurine hadrosaurids (Arenysaurus and Blasisaurus) and Mesozoic crocodylomorphs (Arenysuchus and Agaresuchus subjuniperus) in Europe, complementing the lower Maastrichtian fossil sites of the Eastern Tremp Syncline. In addition, faunal comparison with the fossil record of Hațeg island reveals the great change in the dinosaur assemblages resulting from the arrival of lambeosaurine hadrosaurids on the Ibero-Armorican island, whereas those on Haţeg remained stable. In the light of its paleontological richness, its stratigraphic continuity, and its calibration within the last few hundred thousand years of the Cretaceous, the Western Tremp Syncline is one of the best places in Europe to study the latest vertebrate assemblages of the European Archipelago before the end-Cretaceous mass extinction.

Cephalopods from the Cretaceous-Paleogene (K-Pg) Boundary Interval on the Brazos River, Texas, and Extinction of the Ammonites

We report on new collections of cephalopods (ammonites and nautilids) from the Cretaceous-Paleogene (K-Pg) successions of the Corsicana and Kincaid formations exposed along the Brazos River in Falls County, Texas. An abundant fauna of eight species comprising four genera of ammonites is described from the Corsicana Formation, including Discoscaphites mullinaxorum n. sp. The presence of abundant aptychi (probably lower jaws) of Discoscaphites and Eubaculites, as well as juvenile specimens, indicates a living population that experienced little postmortem drift. The lytoceratid genus Gaudryceras is also reported for the first time from the Brazos River area. Presence of the index taxon Discoscaphites iris (Conrad, 1858) indicates that the fauna belongs to the D. iris Range Zone, the highest ammonite range zone in North America. Correlation with new and existing microfossil data indicates that the fauna represents the uppermost Maastrichtian, and comparison with published records further suggests that this is the most diverse D. iris Zone fauna yet reported from the Gulf and Atlantic Coastal Plains of North America. Three ammonite genera are recorded from the basal units of the K-Pg event deposit at Brazos, which likely represents deposition in the immediate aftermath of the Chicxulub impact event. A single specimen of the nautilid Eutrephoceras is reported from the Danian Kincaid Formation, less than 300 kyr after the K-Pg boundary. These data provide new information on the differing fate of these cephalopod groups during the K-Pg mass extinction and add to the picture of diverse and abundant Maastrichtian ammonite faunas prior to the Chicxulub impact event.

First record of a giant bird (Ornithuromorpha) from the uppermost Maastrichtian of the Southern Pyrenees, northeast Spain

ABSTRACT Throughout the evolutionary history of Avialae, several members of this clade have evolved into giant forms, in different time periods and ecological contexts. In Europe, the first birds that show this condition, the Gargantuaviidae, occur during the Late Cretaceous (late Campanian–early Maastrichtian), but it is during the Paleogene when more groups evolve large forms. However, until now, there was no record of any giant bird during the late Maastrichtian of Europe, close to the K/Pg boundary. Here we describe a cervical vertebra (MPZ 2019/264) from Beranuy (Huesca, NE Spain), which is the first fossil evidence of a giant bird from the late Maastrichtian of Europe, within Chron C29r. The vertebra displays some features, such as a well-marked heterocoelous articulation, lateral pneumatic foramina, ventral carotid processes, and a low neural spine, that support its inclusion within the clade Ornithuromorpha. This phylogenetic assignment is supported by two cladistic analyses. The vertebra is clearly different from the one assigned to Gargantuavis, meaning that it belonged to a distinct taxon. Although the kinship between these two taxa of giant birds is still unclear, this finding demonstrates that large-sized birds were part of the ecological communities of the Ibero-Armorican island from the late Campanian to the Late Maastrichtian, being present during the last hundreds of thousands of years prior to the K/Pg extinction event.

Lithostratigraphy and biostratigraphy of the uppermost Cretaceous to lowermost Palaeogene shallow-marine succession: top of the Adriatic Carbonate Platform at the Likva Cove section (island of Brač, Croatia)

The Likva Cove section on the island of Brač (Croatia) represents a rare example within the Adriatic Carbonate Platform (AdCP) succession of the basal Palaeocene limestones overlying the uppermost Maastrichtian shallow-platform limestones with evidence of only a brief stratigraphic hiatus at the Cretaceous/Palaeogene (K/Pg) contact. Detailed study of the 50-m-thick section resulted in the description of eight lithofacies arranged into six lithostratigraphic units: (A) rudist limestones, (B) deposits with coral–stromatoporoid patch reefs, (C) bindstones, and (D) fine-grained limestones with benthic and rare planktonic foraminifera in the uppermost Maastrichtian (comprising microfossil assemblage biozones I and II), and (E) limestones with benthic foraminifera (mostly discorbids), ostracods and rare planktonic foraminifera, and (F) ostracod–discorbid limestones in the lowermost Palaeocene (representing microfossil assemblage biozone III).The K/Pg contact is constrained between the last occurrence of Maastrichtian benthic and rare planktonic foraminifera, and the first occurrence of Danian planktonic and benthic foraminifera. The uppermost Cretaceous bed represents a firmground, but low biostratigraphic resolution precludes defining duration of a probable short-lasting hiatus at the K/Pg contact. Planktonic foraminifera are mixed with benthic forms in a 3.5-m-thick interval comprising the K/Pg contact as a consequence of decreased depositional rate and probable storm influence.Top of the section contains well developed coral patch reefs intensely karstified during a long-lasting regional unconformity, which in the studied part of the AdCP commenced in the early Palaeocene, i.e. later than at most parts of the platform. Therefore, the end of AdCP deposition should be locally extended into the Palaeocene in both its NW and SE parts.

Benthic Foraminifera Across the Cretaceous/Paleogene Boundary in the Eastern Tethys (Northern Alborz, Galanderud Section): Extinction Pattern and Paleoenvironmental Reconstruction

AbstractExtinction patterns, paleobathymetric inferences, and paleoenvironmental changes based on benthic foraminifera were investigated across the Cretaceous/Paleogene (K/Pg) boundary at the Galanderud section (Northern Alborz, Iran), which contains one of the most continuous and expanded K/Pg transitions in the eastern Tethys. On the basis of benthic foraminiferal taxa abundance and distribution, an outer neritic to uppermost bathyal paleo-depositional setting is inferred. In addition, benthic foraminiferal assemblages and planktic/benthic ratios do not indicate any major change in relative sea level during latest Maastrichtian-early Danian time.Changes in benthic foraminiferal assemblages, morphotypes, diversity, heterogeneity, and benthic foraminiferal oxygen index, coupled with statistical analyses, define three intervals. In the first interval (uppermost Maastrichtian Plummerita hantkeninoides Zone), benthic foraminiferal assemblages are moderately to well preserved and highly diverse, with a combination of epibenthic and endobenthic taxa indicating stable, mesotrophic to weakly eutrophic, normal marine conditions. A major change in benthic foraminiferal assemblages at the K/Pg boundary defines a second interval (basal Danian Guembelitria cretacea and lower part of Parvularugoglobigerina eugubina Zones) that is marked by a decrease in the endobenthic morphogroups as well as a decrease in diversity, heterogeneity, genus and species richness. This second interval denotes highly oligotrophic conditions and a collapse in productivity and food availability due to the extinction of some primary producers, with the exception of the three chalk beds representing short-lived blooms of calcareous dinoflagellates. Benthic foraminifera do not show significant extinction at the end of the Cretaceous at this section with only about an 8% loss of species. Additionally, the abundance of some opportunistic species, including Cibicidoides pseudoacutus and Tappanina selmensis, may reflect instability in the benthic foraminiferal assemblages. The third interval (middle-upper part of the Pv. eugubina Zone) is characterized by the dominance of epibenthic morphogroups (up to 70% of the assemblages) with a partial recovery of endobenthic groups. The characteristics of the benthic foraminiferal assemblages indicate that the flux of food to the benthos had not fully recovered during the early Danian.

Microscale trace-element distribution across the Cretaceous/Palaeogene ejecta layer at the Agost section: Constraining the recovery of pre-impact conditions

A high-resolution, sub-mm scale analysis of the distribution of major and trace elements across the ejecta layer marking the Cretaceous/Palaeogene boundary (KPgB) at the Agost section (SE Spain) was performed using Laser Ablation-Inductivity Coupled Plasma-Mass Spectrometry (LA-ICP-MS). A KPgB interval ≈17 mm thick, has been selected for this study. It includes gray calcareous marl from the uppermost Maastrichtian (Cretaceous), 2.02-mm-thick red clay (the ejecta layer), and blackish-gray clay (boundary clay layer) from the lowermost Danian (Palaeogene). The unconsolidated sediments were resin-embedded under O2-free conditions and analyzed by LA-ICP-MS line continuous scan measurements at 20 μm increments and a laser-beam of 120 μm. These micron-scale analyses show that the anomalous contents of trace and major elements in this boundary are restricted to the ejecta layer, which displays a relatively uniform distribution over its ≈2 mm thickness. Trace and major elemental ratios, such as Ca/Al, Ti/Al, Cr/Al, Fe/Al, Ni/Al, Cu/Al, Zn/Al, As/Al, Sb/Al and Pb/Al have similar values below and above the ejecta layer, consistent with similar palaeoenvironmental conditions prior to and after the impact event. Such element distribution points to anomalies exclusively restricted to the ejecta, thus a nearly instantaneous re-establishment of pre-impact conditions right after the impact event is observed.

Osteology, phylogenetic affinities and taxonomic status of the enigmatic late Maastrichtian ornithopod taxon Orthomerus dolloi (Dinosauria, Ornithischia)

Ornithopod dinosaurs were abundant inhabitants of European islands during the Late Cretaceous. The long history of dinosaur research in Europe has led to the establishment of new taxa for numerous ornithopod specimens that received considerable attention in the literature; however, many of these remain essentially unstudied. This explains why little is known of their potential phylogenetic, ecological and biogeographical importance. Here we provide a reassessment of Orthomerus dolloi, an enigmatic ornithopod taxon that was established on the basis of isolated appendicular elements, including a left tibia, a right femur, a left femur and a metatarsal. The material originates from the uppermost Maastrichtian of southern Limburg (the Netherlands) or adjacent Belgian territory. Despite the fact that they have been known for almost 140 years, none of these elements has been evaluated in detail since their original description. Here we redescribe and illustrate the syntypes of O. dolloi, and compare them to corresponding elements in other latest Cretaceous ornithopods from Europe. The character distribution in O. dolloi is further explored by means of phylogenetic analyses, using a revised ornithopod-wide dataset. The material belongs to at least two, probably conspecific, individuals that show clear hadrosauroid affinities, although the exact placement of the taxon within the clade remains contentious, because it is likely that its elements are osteologically immature. Therefore, the common assignment of O. dolloi to hadrosaurid ornithopods is questionable. Nevertheless, our revision of the material has not identified any autapomorphies, nor a combination of characters that would be indisputably unique among Hadrosauroidea.

Cretaceous-Paleogene (K/T) boundary in the North-Eastern Caucasus (Dagestan): sedimentology, geochemistry and biota

The Cretaceous/Paleogene (K/T) boundary interval was studied in the Okhli and Gubden sections, northeastern Caucasus. Two sediment successions represented in these sections were accumulated in different zones of the paleobasin and distinguished by their lithological and geochemical characteristics. The high-resolution study of nannofossils revealed very gradual changes in nannoplankton community at the Cretaceous/Paleogene transition. The nannofossil assemblage becomes poor from the level ca. 4 m below K/T boundary and it is very scarce in the last 2.5 m of uppermost Maastrichtian. The significant sea-level fall is evidenced in the beginning of the K/T event. It led to erosion and redeposition of Maastrichtian calcareous sediments within the thin layer of clay, covering erosional surface in the Okhli section. The clay mineral assemblage, starting from this surface contains palygorskite. The concentrations of coprolites (Decapoda?) and microspherulas (diagenetic microconcretions) with higher content of some trace elements were found within the small red lenses at the base of the clay layer overlying the Maastrichtian erosional surface. The reliable evidence of impact event are not recognized. The evolutional trends which are recorded within the Cretaceous/Paleogene transitional interval in the Okhli and Gubden sections are similar to trends recognized in studied sections of the K/T event on the adjacent territories of the North-Eastern Peri-Tethys (e.g., southern Turkmenistan and Mangyshlak Peninsula).

Maastrichtian-Paleocene larger Foraminifera biostratigraphy and facies of the Şahinkaya Member (NE Sakarya Zone, Turkey): Insights into the Eastern Pontides arc sedimentary cover

Maastrichtian to Paleocene shallow-water carbonate rocks are common in many parts of Turkey. The occurrence of the Şahinkaya Member limestones in the Çayırbağı-Çalköy (Düzköy/Trabzon) district of the Sakarya Zone represents the neritic expression in marginal areas of a more extensive back-arc deposition, dominated by the hemipelagic sediments of the Tonya Formation. In this contribution, the larger Foraminifera biostratigraphy of the Şahinkaya Member is revisited in order to define the presence of hiatuses associated with the Eastern Pontides arc-continent collision. The study presented here allows for the definition of an upper Maastrichtian and an overlying Paleocene sequence. They are separated from each other by an unconformity of regional meaning extending between the uppermost Maastrichtian to the lower Danian. Shallow Benthic Zones 1–3 (upper Danian to lower Thanetian) have been recognized. The stratigraphy of the Şahinkaya Member and the paleoenvironmental distribution of some larger Foraminifera suggest that, unlike other areas of the Eastern Pontides, the Paleocene deposition was ongoing but still influenced by regional tectonism.

New sections of the Cretaceous–Paleogene transition in the southwestern Tethys (Médéa, northern Algeria): planktic foraminiferal biostratigraphy and biochronology

Two sections (Sidi Ziane and Djebel Zakhamoune from Medea, northern Algeria) of the Cretaceous–Paleogene (K–Pg) transition have been found, sampled, and studied in detail for the first time in Algeria. In order to obtain a biochronological control to evaluate the potential of the Medea area for the study of the K/Pg boundary event and close paleoclimatic episodes as LMWE and Dan-C2, we have reviewed the biostratigraphical scales with planktic foraminifera from the uppermost Maastrichtian to the middle Danian and dated the main key bioevents through graphic correlations comparing the Bottaccione (Italy), Agost and Caravaca (Spain), and Kalaat Senan (Tunisia) sections. The biostratigraphic study has revealed the presence of the last biozone of the Maastrichtian in both sections (zone CF1 or Plummerita hantkeninoides zone). The thickness of this biozone (13.5 m in Sidi Ziane and 9 m in Djebel Zakhamoune) is one of the largest identified to date, suggesting that the uppermost Maastrichtian is complete and continuous in the Medea area. Based on graphic correlation, it has been determined that sedimentation rates of the Maastrichtian in Sidi Ziane and Djebel Zakhamoune are, respectively, 8.98 and 6.58 cm/kyr, only comparable with the most expanded and continuous sections worldwide, such as Ain Settara (Kalaat Senan). It has also recognized a hiatus affecting the lower Danian in both sections, estimated in 610.4 and 644.9 kyr long in Djebel Zakhamoune and Sidi Ziane, respectively. Nevertheless, the presence of reworked specimens of the index species Parvularugoglobigerina longiapertura strongly suggests that the lowermost Danian may be recorded in the Medea area.

Blooms of aberrant planktic foraminifera across the K/Pg boundary in the Western Tethys: causes and evolutionary implications

AbstractWe report a detailed study of the different categories and types of abnormal morphologies in planktic foraminifera recognizable in the lowermost Danian, mainly from the El Kef and Aïn Settara sections, Tunisia. Various types of abnormalities in the test morphology were identified, including protuberances near the proloculus, abnormal chambers, double or twinned ultimate chambers, multiple ultimate chambers, abnormal apertures, distortion in test coiling, morphologically abnormal tests, attached twins or double tests, and general monstrosities. Detailed biostratigraphic and quantitative studies of the Tunisian sections documented a major proliferation of aberrant planktic foraminifera (between approximately 5% and 18% in relative abundance) during the first 200 Kyr of the Danian, starting immediately after the Cretaceous/Paleogene (K/Pg) boundary mass extinction (spanning from theGuembelitria cretaceaZone to the lower part of theP. pseudobulloidesZone). This contrasts with the proportionately low frequency of aberrant tests (generally <2%) identified within the uppermost Maastrichtian, suggesting more stable environmental conditions during the last ~50–100 Kyr of the Cretaceous. Two main pulses with abundant aberrant tests were recognized in the earliest Danian, the one recorded in the well-known K/Pg boundary clay being the more intense of those (maxima of >18%). These main pulses of aberrants coincide approximately with relevant quantitative and evolutionary turnovers in the planktic foraminiferal assemblages. In this paper, we explore the relation of these high values of the foraminiferal abnormality index with the environmental changes induced by the meteorite impact of Chicxulub in Yucatan, Mexico, and the massive eruptions of the Deccan Traps, India.