Systematics of Modern Benthic Foraminiferal Assemblages From the Deltaic Mangrove Ecosystem of Sundarbans

The contemporary intertidal foraminifera and estuarine environment information were collected from the four sites adjoining the deltaic mangrove environment in the Sundarbans. The marsh zones of the south-western coastal region of Bangladesh were examined for modern benthic foraminifera and to expound on the relationship of the foraminiferal assemblages with the environment. Due to high inaccessibility and remoteness, the taxonomic study of foraminifera and its depositional environment remains largely overlooked in the Sundarbans of Bangladesh. This study includes a detailed survey of depositional environment of these fluvio-deltaic to shallow marine sediments. The seventeen species belonging to fourteen genera representing nine families were recorded from surficial sediment of supratidal, intertidal, and dune environment of Kotka, Jamtala, Kochikhali, and Dimer char area. In the present study, these foraminiferal assemblages are characterized calcareous and agglutinated foraminifera. The Kotka beach is recognized as Nonionina assemblage zone, Jamtala beach designated as Ammonia assemblage zone, Kochikhali as Nonionina assemblage zone and Dimer char as Rosalina-Nonionina-Nonionella assemblage zone. The deposition of foraminifera is restricted to Sundarbans’ low to high marsh zone. J. Asiat. Soc. Bangladesh, Sci. 47(2): 121-136, December 2021

Biostratigraphy and Facies Analysis of Upper Valanginian-Upper Hauterivian (Sarmord Formation) in Maten Anticline, Northern Iraq

Biostratigraphical and sedimentological study of the Sarmord Formation (Upper Valanginian - Upper Hauterivian) at the southern limb of Maten anticline is conducted within a well-exposed section. The formation is composed of marl, marly limestone, limestone, and dolostone, which yielded moderately diversified benthonic foraminiferal fauna, green algae, echinoderms, gastropods and some bioclast. The stratigraphic distribution of the benthonic species permits the recognition of two well-defined biozones. These are Everticyclammina kelleri Assemblage Zone, which represents the Late Valanginian age and Pseudocyclammina lituus Assemblage Zone, indicating Hauterivian age. These larger benthonic foraminiferal biozones are correlated with other zonal schemes inside and outside of Iraq, which indicates that the age of the Sarmord Formation in Maten anticline extends from Late Valanginian to Late Hauterivian age. The Sarmord Formation in the studied section is composed of limestone, dolomite, marl and conglomerate lithofacies types. Limestone lithofacies is represented by lime wackestone microfacies. According to the characteristic features of these facies, the depositional environments extend from tidal flat to shallow open marine environments.

Palinostratigraphy of glaciomarine and marine sedimentsof the Barents Sea

By combining the palynologic, lithologic and published geophysical data a stratigraphic division into three main sedimentary units representing major stages in the development of post-glacial sedimentary environments in the southeastern and central parts of the Barents Sea has been substantiated. Unit 3 presumably characterizes proglacial environments of the early deglaciation (tentatively older than 15 ka) and is represented by relatively fine-grained, dark grey sediment matrix with numerous coarse terrigenous clasts. The unit contains low in diversity and concentration pollen assemblage, which is dominated by reworked, mostly Mesozoic pollen and sparse dinocysts of a cryophylic species Islandinium var. minutum. Unit 2 represents later deglacial conditions (estimated ca 12-15 ka) and is composed of finely laminated, grey to brownish sandy/silty muds with coarse clasts interpreted as iceberg-rafted debris. It is characterized by pollen assemblage zone with a low concentration of plant remains, a significant proportion of reworked pre-Cenozoic microfossils and club mosses among spores as well as a high percentage of dwarfBetula, Poaceae and Artemisia Islandinium var. minutum dominates among the aquatic palynomorphs. Unit 1, younger than ca 12 ka, is composed of soft, olive-grey mud with traces of bioturbations and spots of hydrotroilite at the top or sandy-silty mud within the South-Novozemelskii Trough and sand with inclusions of pebbles and broken shells within the Kanin Plateau. Three pollen assemblage zones correspond to it. They are marked by a high percentage of birch and pine pollen, an increased share of pollen of spruce and alder, as well as Sphagnum mosses and ferns. Constant presence of sparse pollen of broad-leaved plants in combination with peak values of Operculodinium centrocarpum and Spiniferites sp. testify the enhancement of Atlantic water influence upon the studied regions.

Late Cretaceous Palynostratigraphy of Subsurface Sediments of Southern Bornu Basin, Nigeria: Implications For Depositional Environments And Palaeoclimate.

Presented in this study are the findings of a cross-examination of the subsurface stratigraphic successions (1500-4600 m) penetrated by the Gaibu-1 well, Bornu Basin, NE Nigeria to understand the palaeoenvironmental settings and the palaeoclimatic conditions of the sediments. Sedimentological/textural description, lithological identification and palynological analysis were carried out using standard laboratory procedures and wireline (gamma-ray and SP) logs. The sediments consist predominantly of sandstone, siltstone, sandy shale, and shale. The sandstones range from fine-coarse, angular to sub-rounded, moderate to poorly sorted, and are texturally immature. Five (5) stratigraphic sub-divisions; the Bima, the Yolde, the Gongila, the Fika (Upper, Middle and Lower members) and the Gombe formations were identified. The palynozonation enabled four distinctive zones: (i) A (1) Triorites africaensis Assemblage Zone, (ii) A (2) Cretacaeiporites scabratus / Odontochitina costata Assemblage Zone, (iii) A (3) Droseridites senonicus Assemblage Zone, A (4) Syncolporites/Milfordia spp. Assemblage Zone. These suggest the well penetrated Cenomanian – Maastrichtian (younger) successions, interpreted to have been deposited in a series of continental to marginal marine environments. The sediments are characterised by palynofloral assemblages that are indicative of a tropical to subtropical climate condition that is warm and humid, which correspond to the late Cretaceous Palmae Province of Africa – Southern America.

Inter-element variation in the bone histology of Anteosaurus (Dinocephalia, Anteosauridae) from the Tapinocephalus Assemblage Zone of the Karoo Basin of South Africa

Despite its abundance in the Permian fossil record of South Africa, little is known about the life history of Anteosaurus. Here we examine the bone microstructure of multiple skeletal elements of Anteosaurus from the Tapinocephalus Assemblage Zone of the Karoo Basin. The bone histology of Anteosaurus magnificus reveals that the cortex is composed of highly vascularized, uninterrupted fibrolamellar bone tissue surrounding the inner spongy medullary region. However, the histology of two ribs and a previously described femur of another Anteosaurus taxon revealed an interrupted growth pattern with lines of arrested growth and peripheral rest lines occurring in the compacta, indicating periodic pauses in growth possibly linked to the slowing down of growth during maturity. Given that the fibula of the same individual has well-vascularised fibrolamellar bone tissue without any growth marks in the cortex; this suggests variation in skeletal growth. Based on our histological results, three growth dynamic stages are deduced for the genus Anteosaurus: (i) the earliest growth stage is represented by the predominance of highly vascularized, uninterrupted fibrolamellar bone tissue in the inner cortex, which suggests rapid periosteal bone deposition during early ontogeny; (ii) the next stage of growth shows periodic interruptions in the bone deposition as indicated by the deposition of lines of arrested growth; (iii) the third stage shows the development of lamellar bone tissue with rest lines in the peripheral part of the cortex suggesting a slowing down of growth prior to death. Most of the skeletal elements are characterized by thick bone walls, extensive secondary reconstruction and the complete infilling of the medullary cavity. However, the radius and a previously studied femur have open medullary cavities with struts of bony trabeculae. Based on histologic structures and comparisons with extant taxa, it is likely that Anteosaurus may have been more terrestrial as its osteology point towards terrestriality, but it may have occasionally inhabited ephemeral pools like modern semi-aquatic Hippopotamus.

A New Late Permian Burnetiamorph From Zambia Confirms Exceptional Levels of Endemism in Burnetiamorpha (Therapsida: Biarmosuchia) and an Updated Paleoenvironmental Interpretation of the Upper Madumabisa Mudstone Formation

A new burnetiamorph therapsid, Isengops luangwensis, gen. et sp. nov., is described on the basis of a partial skull from the upper Madumabisa Mudstone Formation of the Luangwa Basin of northeastern Zambia. Isengops is diagnosed by reduced palatal dentition, a ridge-like palatine-pterygoid boss, a palatal exposure of the jugal that extends far anteriorly, a tall trigonal pyramid-shaped supraorbital boss, and a recess along the dorsal margin of the lateral temporal fenestra. The upper Madumabisa Mudstone Formation was deposited in a rift basin with lithofacies characterized by unchannelized flow, periods of subaerial desiccation and non-deposition, and pedogenesis, and can be biostratigraphically tied to the upper Cistecephalus Assemblage Zone of South Africa, suggesting a Wuchiapingian age. Isengops is the second burnetiamorph recognized from Zambia and is part of a tetrapod assemblage remarkably similar to others across southern Pangea during the Wuchiapingian. A revised cladistic analysis of Biarmosuchia yielded over 500 most parsimonious trees that generally reaffirm the results of previous analyses for burnetiamorphs: Lemurosaurus is basal, Lobalopex and Isengops are proximate burnetiid outgroups, and Bullacephalus, Burnetia, Mobaceras, Niuksenitia, and Pachydectes are burnetiines. Furthermore, Russian biarmosuchians are scattered throughout the tree and do not form sister taxon relationships with each other. Burnetiamorphs display a wide disparity of cranial adornments and are relatively speciose (13 species), especially when compared to the number of specimens discovered to date (∼16 specimens). As has been suggested in some other tetrapod clades (e.g., ceratopsian dinosaurs), the burnetiamorph fossil record supports an inferred macroevolutionary relationship between cranial adornment and increased speciation rate.

Cranial anatomy of Bolotridon frerensis, an enigmatic cynodont from the Middle Triassic of South Africa, and its phylogenetic significance

The cynodont fauna of the Trirachodon-Kannemeyeria Subzone of the Middle Triassic Cynognathus Assemblage Zone (AZ) is almost exclusively represented by taxa belonging to the clade Eucynodontia. However, there is one basal (non-eucynodont) cynodont known to have survived into this assemblage: the enigmatic Bolotridon frerensis. BSPG 1934-VIII-7 represents by far the most extensive specimen of B. frerensis, consisting of a partial skull with occluded lower jaw. The specimen was initially described by Broili & Schröder (1934), but their description was limited to surface details of the skull and the dental morphology. Here, by using a computed tomographic (CT) reconstruction, we redescribe this specimen, providing novel information on its palatal and internal anatomy. New endocranial characters recognized for this taxon include ridges in the nasal cavity indicating the presence of cartilaginous respiratory turbinals. New data obtained from the CT scan were incorporated into the most recently published data matrix of early non-mammalian cynodonts to test the previously unstable phylogenetic position of Bolotridon. Our phylogenetic analyses recovered Bolotridon as the sister-taxon of Eucynodontia, a more crownward position than previously hypothesized.

New Specimen of the Enigmatic Dicynodont Lanthanostegus mohoii (Therapsida, Anomodontia) from the Southwestern Karoo Basin of South Africa, and its Implications for Middle Permian Biostratigraphy

Lanthanostegus is an unusual dicynodont known from only two partial skulls from a single locality near Jansenville in the Eastern Cape Province of South Africa. Although these specimens can be constrained to near the base of the late middle Permian (Guadalupian) Abrahamskraal Formation, their precise age is uncertain as a result of diachroneity of the base of the Formation and the absence, in the Jansenville area, of index taxa to correlate this horizon with the biostratigraphy established in the Western Cape Province. Here, we describe a third skull that we identify as Lanthanostegus, which we recently discovered from a locality north of Laingsburg, on the western side of the main Karoo Basin. This skull reveals morphological details of the palate, occiput, and lower jaw that are not preserved in the described specimens of Lanthanostegus mohoii and will advance understanding of this poorly known dicynodont. This discovery provides the first direct correlation between the lower Abrahamskraal Formation at Jansenville on the eastern side of the basin and the southwestern part of the basin, and suggests that Lanthanostegus occurs in the lowest Tapinocephalus Assemblage Zone (AZ), or possibly to a new assemblage transitional between the Eodicynodon and Tapinocephalus AZs. This supports earlier work proposing that the Eodicynodon AZ is present only on the western side of the Karoo Basin and that the transition from a marine to continental depositional environment occurred later toward the East.

The late Pliensbachian (Early Jurassic) ammonoid Amaltheus in Japan: systematics and biostratigraphic and paleobiogeographic significance

The genus Amaltheus, one of the representative late Pliensbachian ammonoids, has biostratigraphic and paleobiogeographic significance in Japan. Four species, Amaltheus stokesi (Sowerby, 1818), A. margaritatus de Montfort, 1808, A. repressus Dagis, 1976, and A. orientalis new species, have been found in the Kuruma Group in central Japan; A. stokesi and A. margaritatus are also from the Toyora Group in southwest Japan. On the basis of taxonomic analysis of the genus Amaltheus, we distinguish two successive ammonoid biozones in the lower part of the Teradani Formation of the Kuruma Group: the Amaltheus stokesi–Amaltheus repressus and the Amaltheus margaritatus assemblage zones, in stratigraphic ascending order. This study also establishes the presence of the Amaltheus stokesi Assemblage Zone in the Higashinagano Formation of the Toyora Group. The stokesi–repressus and the stokesi assemblage zones correspond biostratigraphically to the Amaltheus stokesi Standard Subzone of the margaritatus Zone. The margaritatus Assemblage Zone is correlated with the Amaltheus subnodosus and Amaltheus gibbosus standard subzones. The Japanese early–middle late Pliensbachian ammonoid faunas are composed almost entirely of pan-Boreal and Arctic species of the genus Amaltheus. This faunal composition has an affinity with that of the Northeast Russian region, and thus suggests a strong paleobiogeographic relationship between East Asian and Northeast Russian faunas throughout this time interval. UUID: http://zoobank.org/5F08121F-1DAF-4B24-BCBE-B08F7101CF29

Evidence from South Africa for a protracted end-Permian extinction on land

Earth’s largest biotic crisis occurred during the Permo–Triassic Transition (PTT). On land, this event witnessed a turnover from synapsid- to archosauromorph-dominated assemblages and a restructuring of terrestrial ecosystems. However, understanding extinction patterns has been limited by a lack of high-precision fossil occurrence data to resolve events on submillion-year timescales. We analyzed a unique database of 588 fossil tetrapod specimens from South Africa’s Karoo Basin, spanning ∼4 My, and 13 stratigraphic bin intervals averaging 300,000 y each. Using sample-standardized methods, we characterized faunal assemblage dynamics during the PTT. High regional extinction rates occurred through a protracted interval of ∼1 Ma, initially co-occurring with low origination rates. This resulted in declining diversity up to the acme of extinction near the Daptocephalus–Lystrosaurus declivis Assemblage Zone boundary. Regional origination rates increased abruptly above this boundary, co-occurring with high extinction rates to drive rapid turnover and an assemblage of short-lived species symptomatic of ecosystem instability. The “disaster taxon” Lystrosaurus shows a long-term trend of increasing abundance initiated in the latest Permian. Lystrosaurus comprised 54% of all specimens by the onset of mass extinction and 70% in the extinction aftermath. This early Lystrosaurus abundance suggests its expansion was facilitated by environmental changes rather than by ecological opportunity following the extinctions of other species as commonly assumed for disaster taxa. Our findings conservatively place the Karoo extinction interval closer in time, but not coeval with, the more rapid marine event and reveal key differences between the PTT extinctions on land and in the oceans.