340 research outputs found

    A critical revision of the fossil record, stratigraphy and diversity of the Neogene seal genus Monotherium (Carnivora, Phocidae)

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    Historically, Monotherium had been one of the few genera of extinct Phocidae (true seals) that served as a wastebin taxon. Consequently, it did neither aid in understanding phylogenetic relationships of extinct Phocidae, nor in understanding seal diversity in deep time. This urged the reassessment of the genus. Before our review, Monotherium included five different species: Monotherium aberratum, Monotherium affine, and Monotherium delognii from Belgium; Monotherium gaudini from Italy; and Monotherium? wymani from the east coast USA. In this work we redescribe the fossil record of the genus, retaining the type species M. delognii. Monotherium aberratum and M. affine are reassigned to the new phocine genus Frisiphoca. Monotherium gaudini is renamed and considered a stem-monachine (Noriphoca gaudini). The holotype of the monachine M.? wymani requires further study pending the discovery of new fossil material that could be attributed to the same taxon. Reinvestigating the stratigraphic context reveals that N. gaudini most likely represents one of the two oldest named phocid seals, or even the oldest, dated to the late Oligocene-earliest Miocene. Our results allow questioning the widespread idea that Phocidae originated in the western Atlantic and better appreciate their palaeobiogeography during the late Oligocene-Miocene interval in the North Atlantic realm

    On Prophoca and Leptophoca (Pinnipedia, Phocidae) from the Miocene of the North Atlantic realm : redescription, phylogenetic affinities and paleobiogeographic implications

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    Background: Prophoca and Leptophoca represent the oldest known genera of phocine seals, dating from the latest early to middle Miocene. Originally, Prophoca rousseaui and Prophoca proxima were described based on fragmentary remains from the Miocene of Belgium. However, several researchers contested the union of Prophoca rousseaui and Prophoca proxima into one genus, without providing evidence. The stratigraphic context of Prophoca remained poorly constrained due to the lack of precise data associated with the original specimens collected in the area of Antwerp (north of Belgium). Methods: Prophoca and Leptophoca are redescribed and their phylogenetic position among Phocidae is reassessed using PAUP. Dinoflagellate biostratigraphy has been carried out on sediment samples associated with specimens from Prophoca and Leptophoca to elucidate their approximate ages. Results: Whereas the species Prophoca rousseaui is redescribed, Prophoca proxima is considered synonymous to Leptophoca lenis, with the proposal of a new combination Leptophoca proxima (Van Beneden, 1877). Sediment samples from specimens of both taxa have been dated to the late Langhian-early Serravallian (middle Miocene). Following a reinvestigation of Leptophoca amphiatlantica, characters from the original diagnosis are questioned and the specimens of Leptophoca amphiatlantica are considered Leptophoca cf. L. proxima. In a phylogenetic analysis, Prophoca rousseaui and Leptophoca proxima constitute early branching stem-phocines. Discussion: Leptophoca proxima from the North Sea Basin is younger than the oldest known find of Leptophoca proxima from North America, which does not contradict the hypothesis that Phocinae originated along the east coast of North America during the late early Miocene, followed by dispersal to Europe shortly after. Morphological features of the appendicular skeleton indicate that Prophoca rousseaui and Leptophoca proxima have archaic locomotory modes, retaining a more prominent use of the fore flipper for aquatic propulsion than extant Phocidae

    Dinoflagellate cysts and acritarchs from the Miocene Zonderschot sands, Northern Belgium: stratigraphic significance and correlation with contiguous areas

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    A palynological investigation of the Miocene Zonderschot Sands (Berchem Formation) from the type locality Zonderschot (northern Belgium) has revealed the presence of a diverse dinoflagellate cyst and acritarch association. The dinoflagellates reflect a shallow marine environment, although the oceanic species Nematosphaeropsis and Impagidinium are prominent in the association and indicate the presence of an oceanic influence. This can be explained only by the depositional area being located at the very southern margin of the relatively isolated North Sea Basin during a period of maximum landward extent of the marine realm. A precise biostratigraphical correlation of the Zonderschot Sands with the Antwerpen Sands (Berchem Formation) from the Antwerp area is established. Biostratigraphical evaluation of key dinoflagellate cyst species indicates a latest Burdigalian (latest Early Miocene) -(earliest?) Langhian (early Middle Miocene) age for the Zonderschot Sands.Sedimentological and biostrati-graphical arguments are proposed that may indicate that the Génicot Formation was deposited just before, during and just after the Hirnantian (latest Ordovician) glaciation. This means the first indication of the presence of the latter in Belgium

    Dinoflagellate cyst stratigraphy of the upper cretaceous of western Belgium

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    A detailed micropalaeontological analysis with dinoflagellate cysts of the Cretaceous sections intercepted by five wells in western Belgium allows a biostratigraphical correlation and a chronostratigraphical interpretation of the sediments concerned. The transgression of the Cretaceous sediments on the southern part of the Palaeozoic Brabant Massif appears to be strongly diachronous. In the Nieuwkerke and Oostduinkerke wells, situated south of the present day topographic crest of the Brabant Massif (Nieuwpoort-Oudenaarde), the transgression is dated as Late or latest Cenomanian and close to the crest in the Keiem well as Late Turonian. North of the crest, in the De Haan and Knokke wells, it is dated as Late Santonian. The Late Cenomanian strata are present only in the Nieuwkerke and tbe Oostduinkerke wens, at some distance south of the crest. Sediments dated as Turonian are found only south of the crest, with a decreasing thickness towards the crest, from the Nieuwkerke to the Keiem well. The Coniacian also occurs only south of the crest, with a similar thickness in the two latter wells. The Santonian bas a similar thickness in the same two wells south of the crest and is present only with a reduced thickness of Late Santonian age in the De Haan and Knokke wells. Campanian sediments occur only north of the crest, in both latter wells. Only Lower Campanian is present in the De Haan well, while a more complete Campanian section, followed by Maastrichtian, is observed more to the north, in the Knokke well. A post-Cretaceous erosion is thought to be responsible for the observed thickness variations in the Campanian north of the cres

    Diversity of late Neogene Monachinae (Carnivora, Phocidae) from the North Atlantic, with the description of two new species

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    While the diversity of 'southern seals', or Monachinae, in the North Atlantic realm is currently limited to the Mediterranean monk seal, Monachus monachus, their diversity was much higher during the late Miocene and Pliocene. Although the fossil record of Monachinae from the North Atlantic is mainly composed of isolated specimens, many taxa have been erected on the basis of fragmentary and incomparable specimens. The humerus is commonly considered the most diagnostic postcranial bone. The research presented in this study limits the selection of type specimens for different fossil Monachinae to humeri and questions fossil taxa that have other types of bones as type specimens, such as for Terranectes parvus. In addition, it is essential that the humeri selected as type specimens are (almost) complete. This questions the validity of partial humeri selected as type specimens, such as for Terranectes magnus. This study revises Callophom obscure, Homiphoce capensis and Phophoca etrusca, all purportedly known from the Lee Creek Mine, Aurora, North Carolina, in addition to their respective type localities in Belgium, South Africa and Italy, respectively. C. obscure is retained as a mona chine seal taxon that lived both on the east coast of North America and in the North Sea Basin. However, FL capensis from North America cannot be identified beyond the genus level, and specimens previously assigned to Pl. etrusca from North America clearly belong to different taxa. Indeed, we also present new material and describe two new genera of late Miocene and Pliocene Monachinae from the east coast of North America: Auroraphoca atlantica nov. gen. et nov. sp., and Virginiaphoca magurai nov. gen. et nov. sp. This suggests less faunal interchange of late Neogene Monachinae between the east and west coasts of the North Atlantic than previously expected

    A reappraisal of the stratigraphy of the upper Miocene unit X in the Maaseik core, eastern Campine area (northern Belgium)

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    The stratigraphy of the Tortonian-Messinian sequence from the Maaseik core, located on the shoulder of the Roer Valley Graben (RVG) in the eastern Campine area in northern Belgium, was improved. The analysis of the marine palynomorphs (dinoflagellate cysts and acritarchs) from the uppermost part of the Breda Fonnation, the unnamed unit X and the basal part of the Lower Waubach Member led to the recognition of the mid to upper Tortonian Hystricho.sphaeropsis ohseum hiozone. Therefore deposition of this entire analyzed sequence took place sometime between 8.8 to 7.6 Ma. Paleoenvironmental interpretation of the palynomorphs points to shallow marine conditions and most probably a stressed environment during the deposition of unit X. A comparison with the time equivalent stratigraphy in the nearby Belgian Campine, the Dutch RVG and the German Lower Rhine Basin allowed the identification of the Inden Fonnation and required a shift in the base of the Kieseloolite Formation compared to the earlier lithostratigraphic interpretation of the Maaseik core. The regional stratigraphic scheme shows the progressive northwestward extension of the river facies from the Lower Rhine during the late Tortonian

    The architecture of the Kattendijk Formation and the implications on the early Pliocene depositional evolution of the southern margin of the North Sea Basin

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    An east-west correlation profile through the upper Neogene succession north of Antwerp, based on cone penetration tests, reveals the architecture of the lower Pliocene Kattendijk Formation. It shows a basal incision of the Kattendijk Formation down to 20 m in Miocene sands and locally even Lower Oligocene clays. The incision is part of a much larger gully system in the region at the base of the Kattendijk Formation. The strongest gully incision is observed along the western profile, and coincides with increases in the thickness of the Kattendijk Formation from its typical four to six meters thickness in the east towards a maximum of 15 m in the west. Correlations show that this additional thickness represents a separate sequence of the Kattendijk Formation that first filled the deepest part of the gully prior to being transgressed and covered by the second sequence deposited in a larger gully system. Both sequences of the Kattendijk Formation have basal transgressive layers, and are lithologically identical. Initial, deep incision at the base of the Kattendijk Formation might have been the result of the constriction of early Pliocene tidal currents that invaded and expanded fluvial or estuarine gullies that had developed during the latest Miocene sea-level low. A similar mechanism had been proposed for the development of late Miocene gully system at the base of the Diest Formation further southeast in northern Belgium. As the wider area was transgressed and covered by the second sequence of the Kattendijk Formation, flow constriction ended, currents weakened and gully incisions were reduced in size
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