Trans-Saharan Seaway Research Articles

Phylogenomic and anatomical evidence for the Late Cretaceous diversification of African characiform fishes, including a new family, under the influence of the Trans-Saharan Seaway

Abstract Geological evidence supports the occurrence of an epicontinental Trans-Saharan Seaway bisecting the African continent during the Late Cretaceous to early Paleogene. The seaway formed a wide saltwater channel connecting the Neotethys with the South Atlantic, yet no previous study has investigated its impact on freshwater fish diversification. Phylogenomic data and time-calibrated trees indicate a Late Cretaceous signature for the appearance of three modern lineages of characiform fishes. Phylogenetic analyses using ultraconserved elements of 83 characiforms reveals that Alestidae, Hepsetus, and Lepidarchidae fam. nov. originated during the Santonian-Campanian of the Late Cretaceous (84–77.5 million years ago; Ma). Lepidarchidae consists of two monotypic taxa not previously recognized as sister species: the Niger tetra Arnoldichthys endemic to the lower Niger and Ogun rivers of Nigeria, and the dwarf jellybean tetra Lepidarchus from coastal rivers of Ghana, Côte d'Ivoire, Liberia, Sierra Leone, and Guinea. Microcomputed tomography scans (µCT) of 117 characiforms provide three novel morphological characters supporting Hepsetus and Lepidarchidae, four characters for monophyly of Lepidarchidae and five for a restricted Alestidae. The Santonian-Campanian divergence indicates allopatric speciation processes influenced by the Trans-Saharan Seaway, partitioning the African ichthyofauna in a west-east orientation. The timing for African characiform cladogenesis aligns with the Cenomanian fossil record and is circa 16–23 Ma younger than the earliest characiform-like fossils from Late Cretaceous outcrops of Morocco and Sudan. This study highlights the magnitude of Cretaceous transgression events shaping the freshwater biota and gaps in our understanding of the evolutionary history and paleobiogeography of ray-finned fishes across the African continent.

Taxonomy, paleoecology, and paleobiogeographical significance of the middle-late Eocene molluscs from the Garet Gehannem section in the Fayoum depression, Egypt

The studied middle-upper Eocene Garet Gehannam section exhibits moderate macrofossil diversity and notably high macrofossil abundance. Eleven molluscan species were identified and described, including five bivalves and six gastropods. Three macrobenthic assemblages were recognized: The turritelline-dominated assemblage, Carolia placunoides assemblage and Turkostrea multicostata assemblage. The Turritelline-dominated assemblage indicates high-nutrient environments, which typically exhibit normal to slightly below normal marine salinities, low sedimentation rates, and high-energy environments. Carolia placunoides assemblage indicates brackish water environment during times of sea level regression. Turkostrea multicostata assemblage provides compelling evidence of a prevailing hot climate and an environment rich in calcium, characterized by nutrient-rich water and low to moderate energy levels and high light availability. The investigation of the articulation of Carolia placunoides Cantraine1838 and Turkostrea multicostata (Deshayes, 1818) shells strongly suggests a parautochthonous assemblage. In terms of paleobiogeography, Turkostrea multicostata (Deshayes, 1818) first appeared during the Paleocene in the southern Tethys, specifically in Tunisia and Algeria, as well as in the Trans-Saharan Seaway in Mali. Consequently, its paleobiogeographic distribution can be allied to current circulation along the Tethys Ocean, firstly from its original area in the southern Tethys regions and Trans-Saharan Seaway to neighboring regions of the southern and northern Tethys, as well as the West Africa provinces. The paleobiogeographic map of the identified species shows that the identified species were prevailing in two bioprovinces during the middle – late Eocene epochs: i) the North-West, North, and South Tethyan Margins Province, ii) and the West Africa Province.

The Ornamented Shell of a New Bothremydid Turtle from the Uppermost Cretaceous of Niger

A new pleurodiran turtle is described here. It is identified as attributable to Bothremydidae. The new taxon comes from an upper Maastrichtian (Upper Cretaceous) outcrop located in Southwestern Niger (in the Indamane Mount area, belonging to the Abalak Department of the Tahoua Region). Abalakemys chapmanae gen. et sp. nov. is identified by an almost complete large shell of about 65 cm in length. The new bothremydid turtle is recognized as a member of Bothremydodda, showing several autapomorphies (an exclusive ornamental pattern on the plate’s outer surface, covered by small depressions; small fourth pleural scutes, only anteromedially reaching the sixth pair of costal plates; and noticeably wedged posterior plastral lobe toward the posterior region), as well as a unique combination of characters for this clade. This turtle could belong to Nigeremydini, a poorly understood Maastrichtian to Paleocene lineage of Bothremydodda, which integrates large coastal taxa that inhabited the African Trans-Saharan seaway, and for which shell information is currently extremely limited.

Sedimentary and stratigraphic characteristics of the Maastrichtian Dukamaje formation of southern Iullemmeden Basin: Implications for the paleogeography of the Upper Cretaceous trans-Saharan seaway

The Maastrichtian Dukamaje Formation is a fossiliferous, shale- and marl-dominated unit, albeit with contentious paleodepositional environment, of the Rima Group, southern Iullemmeden Basin (northwestern Nigeria). The Basin holds records of the global sea-level highs of the Late Cretaceous - Paleocene. Hence, an improved understanding of the associated sedimentary infill will provide opportunity for an improved reconstruction of paleogeography and ancient stratigraphic sequences. Two different models (a low-energy, hypersaline lagoon and marsh based on predominance of fine grains with gypsum and preserved vertebrate fossils, or high energy/inshore, shallow marine environment supported with Libycoceras ammonite fossil) have been proposed by different workers who studied the same outcrop sections. The discrepancy in these previous models is partly due to inherent depositional complexities and the need to invoke deductive interpretations for epicontinental basins. Here, we used a systematic facies analysis (for the first time and with particular attention to stratigraphic relationships and correlation of some of the outcrop sections) integrated with previous biostratigraphic data in order to reconstruct the paleogeography of the Dukamaje Formation. The objectives are to describe the facies characteristics and provide a well-constrained interpretation for the depositional setting of the Dukamaje Formation. Results: two alternating, low-energy facies associations (marsh and lagoonal and restricted?/nearshore marine) were identified. The marsh and lagoonal facies association is characterised by fossiliferous and gypsiferous shale enriched in arenaceous foraminifera. The restricted marine facies association comprises highly fossiliferous nodular marls. The facies associations form a coastal sabkha facies succession, deposited in a marginal marine environment with likely brackish influence, under a warm tropical climate. The coastal sabkha facies succession is interpreted as a retrogradational system, which suggests that the Dukamaje Formation is a product of marine transgression of a low-lying, embayed, partially restricted, stable coast. By implication, the hypothesised Upper Cretaceous epicontinental sea (“trans-Saharan seaway”) across the North to West Africa was, rather than fully open, restricted in some places. Restrictions were related to presence of embayments in which hypersaline conditions developed due to low circulation. This model is largely consistent with the view of a partially restricted shallow marine for the Upper Cretaceous of the southern Iullemmeden Basin.

Paleoecological and paleobiogeographical inferences of the Paleocene ostracods from Sinai, Egypt

The present study aims to detect the paleoecology and paleobiogeography of the Paleocene ostracods from Sinai, Egypt. In order to reach our goals, the Paleocene rocks were examined in four outcrops (El Dokh, El Qussaima, Matulla, and Ekma sections) from Sinai, Egypt. The recognized rock units include Dakhla Formation (at the base) and Tarawan Formation (at the top). The investigation of the ostracod fauna yielded 49 species and subspecies, which enabled the recognition of one Paleocene biozone, Mauritsina teiskotensis - Ordoniya ordoniya Zone. The Early and Middle Paleocene have diverse assemblages, while the Late Paleocene showed a rarity of ostracods. Based on the shape of the carapaces and the surface ornamentation, four ostracod morphogroups were recognized. Morphogroup 4 is the most common group in all the studied sections. The structure of ostracod assemblages (abundance, richness and the morphogroups) besides the lithology pointed out to middle - outer neritic depositional environment for the studied Paleocene sections. The identified species have a wide geographic range, extending from West Africa, North africa to the Middle East. The paleobiogeographic framework is carried out with the aid of multivariate analyses. The suggested matrix consists of 25 ostracod species from 10 countries, including Egypt, Libya, Tunisia, Algeria, Jordan, Israel, Senegal, Ivory Coast, Niger and Mali. The outcomes of the Q-mode cluster analysis indicate that the selected countries may be categorized into three provinces, North Africa (Libya, Algeria, Tunisia and Egypt), West Africa (Senegal, Mali, Ivory Coast and Niger), and Middle East (Israel and Jordan). The similarity of ostracod assemblages between North Africa, including Egypt, with that of Jordan and Israel, suggests the migration and exchange through the southern Tethyan coast. The common deep marine species between North and West Africa may be migrated along the West African coast on the Atlantic Ocean, while shallow species migrated through the trans-Saharan seaway.

Sedimentary environment of the Upper Cretaceous Yogou Formation in Termit Basin and its significance for high-quality source rocks and Trans-Saharan Seaway

The Yogou Formation of the Upper Cretaceous is a potential source rock in the Termit Basin of Niger, and the TOC content of the upper member is 1.8–9 times that of the lower member. However, the influence of the sedimentary environment evolution on its organic matter heterogeneity is still unclear. In this paper, the evolution of the sedimentary environment of the Yogou Formation profile was studied from the aspects of micropaleontology, element geochemistry and biomarkers. A total of three third-order sequences (YSQ1, YSQ2 and YSQ3, from bottom to top) were identified in the Yogou Formation. The distribution of micropaleontology in different sequences indicates that YSQ1 mainly deposited in the marine environment, while, the YSQ2 and YSQ3 mainly deposited in the marine-continental transitional environment. The elemental geochemical analysis shows that the water salinity of YSQ1 was higher than that of YSQ2 and YSQ3. From YSQ1 to YSQ3, the terrestrial input increased, the climate became warmer and wetter, and the reducibility of water generally weakened. The biomarker characteristics and organic geochemical parameters indicate that the YSQ1 generally deposited in a sub-anoxic to anoxic environment, while the YSQ3 deposited in the environment frequently alternating from reduction to oxidation, and the reducing environment may provide a good preservation condition for the enrichment organic matters. The abundant terrigenous materials input and good preservation conditions may be the basic reason to form the mudstone with high TOC content in the upper member of the Yogou Formation. The same micropaleontological species found in the Termit Basin, Benue Trough and Bornu Basin provide evidence for the hypothesis that there was a trans-Saharan seaway between the Tethys Sea and the South Atlantic during the Cenomanian and Turonian transgressions. This study not only helps to clarify the enrichment and distribution regularity of high-quality source rocks in the Yogou Formation, but also provides some evidence for the existence of trans-Saharan seaway.

Sedimentary Environment of the Upper Cretaceous Yogou Formation in Termit Basin and its Significance for High-Quality Source Rocks and Trans-Saharan Seaway

Sedimentary Environment of the Upper Cretaceous Yogou Formation in Termit Basin and its Significance for High-Quality Source Rocks and Trans-Saharan Seaway

Migration routes of the genus Buntonia Howe, 1935 (Ostracoda, Crustacea) during the Late Cretaceous–Paleogene in Africa

Buntonia is a common genus in the Maastrichtian to Late Eocene basins of Africa. Analysis of similarity (ANOSIM), hierarchical clustering (HC), and non-metric multidimensional scaling (nMDS) were used to analyze the geographic pattern of Buntonia species based on the presence/absence matrix of 42 species. The Jaccard-based HC shows that the African countries can be subdivided into three main bioregions: North Africa (Algeria, Libya, Tunisia, Morocco, and Sudan), West Africa (Mali, Togo, Benin, Cote d’Ivoire, Senegal, Ghana, Gambia, Nigeria, Cameron, and Mauritania), and South Africa (Namibia and South Africa). ANOSIM indicated a non-significant difference between North and West African countries and between West and Southern Africa. However, a significant difference was found between North and Southern Africa (sequential Bonferroni corrected p < 0.01). These patterns are well-characterized also by both of HC and nMDS. Moreover, analyses of the stratigraphic ranges of the Buntonia species revealed a distinct range shift within the regions of the Guinean Gulf (Togo, Benin, and Cote d’Ivoire) through Senegal towards North Africa. The latter indicates two possible migration routes from West Africa to North Africa through the Trans-Saharan seaway and from the Atlantic to the Tethyan Sea. Migration from region to region played an important role in the distribution of the studied Buntonia species rather than origination of new species and/or extinction of existing species.

Nature of dispersed organic matter and paleoxygenation of the Campano-Maastrichtian dark mudstone unit, Benin flank, western Anambra Basin: Implications for Maastrichtian Trans-Saharan seaway paleoceanographic conditions

The Campano-Maastrichtian age is an important time in the geological evolution of Nigeria as it marked the re-establishment of the Trans-Saharan seaway that was broken due to Santonian inversion tectonics. In this paper, we conducted a high-resolution investigation of the dark mudstone unit of the Campano-Maastrichtian Mamu Formation exposed in 4-outcrops in the western segment of the Anambra basin, Nigeria, using multidisciplinary tools involving geochemistry, palynofacies, and microfabric analyses. Our objectives were to determine the nature of organic matter preserved in the sediments and the paleo-oxygenation conditions of the Trans-Saharan seaway. Our findings reveal that the Trans-Saharan seaway was of low salinity, characterized by the dominance of terrestrial organic matter in the more proximal marsh and bay sub-environments (organic facies C and CD) and mixed terrestrial – marine organic matter (organic facies BC and C) in the more distal central basin. Bottom water paleo-oxygenation was predominantly oxic. However, palynofacies and microfabric evidences as well as inferences from Fe-TS-TOC relationship suggests pyrite formation occurred in at least two phases. The first phase of syngenetic to early diagenetic pyrite formation, which was due to bacterial sulphate reduction that occurred in the anoxic zone below the sediment water interface, whereas secondary (late diagenetic) pyrite growth which formed the bulk of pyrite preserved occurred at the base of the bottom water. Furthermore, we hypothesize that pyrite formation occurred faster, and was better preserved in the central basin than in the other sub-environments. This is attributed to the presence of more reactive organic matter (marine palynomorphs), higher salinity (more sulphate), mineralogy (higher clay content), and microfabric (thinner lamination with low degree of bioturbation).

Stratigraphy and Paleobiology of the Upper Cretaceous-Lower Paleogene Sediments from the Trans-Saharan Seaway in Mali

An epicontinental sea bisected West Africa periodically from the Late Cretaceous to the early Eocene, in dramatic contrast to the current Sahara Desert that dominates the same region today. Known as the Trans-Saharan Seaway, this warm and shallow ocean was a manifestation of globally elevated sea level associated with the rapid break-up of the supercontinent Gondwana in the late Mesozoic. Although it varied in size through time, the Trans-Saharan Seaway is estimated to have covered as much as 3000 km2 of the African continent and was approximately 50 m deep. The edges of the sea were defined in part by the high topography of the Precambrian cratons and mobile belts of West Africa. Over its approximately 50 million year episodic existence, through six major periods of transgression and regression, the Trans-Saharan Seaway left behind extensive nearshore marine sedimentary strata with abundant fossils. The waters that yielded these deposits supported and preserved the remains of numerous vertebrate, invertebrate, plant, and microbial species that are now extinct. These species document a regional picture of ancient tropical life that spanned two major Earth events: the Cretaceous-Paleogene (K-Pg) boundary and the Paleocene-Eocene Thermal Maximum (PETM). Whereas extensive epeiric seas flooded the interior portions of most continents during these intervals, the emerging multicontinental narrative has often overlooked the Trans-Saharan Seaway, in part because fundamental research, including the naming of geological formations and the primary description and analysis of fossil species, remained to be done. We provide such synthesis here based on two decades of fieldwork and analyses of sedimentary deposits in the Republic of Mali. Northern parts of the Republic of Mali today include some of the farthest inland reaches of the ancient sea.We bring together and expand on our prior geological and paleontological publications and provide new information on ancient sedimentary rocks and fossils that document paleoequatorial life of the past. Ours is the first formal description of and nomenclature for the Upper Cretaceous and lower Paleogene geological formations of this region and we tie these names to regional correlations over multiple modern territorial boundaries. The ancient seaway left intriguing and previously unclassified phosphate deposits that, quite possibly, represent the most extensive vertebrate macrofossil bone beds known from anywhere on Earth. These bone beds, and the paper shales and carbonates associated with them, have preserved a diverse assemblage of fossils, including a variety of new species of invertebrates and vertebrates, rare mammals, and trace fossils. The shallow marine waters included a wide range of paleoenvironments from delta systems, to hypersaline embayments, protected lagoons, and carbonate shoals.Our overarching goal has been to collect vertebrate fossils tied to a K-Pg stratigraphic section in Africa. We provide such a section and, consistent with prior ideas, indicate that there is a gap in sedimentation in Malian rocks in the earliest Paleocene, an unconformity also proposed elsewhere in West Africa. Our phylogenetic analyses of several vertebrate clades across the K-Pg boundary have clarified clade-by-clade species-level survivorship and range extensions for multiple taxa. Few macrofossil species from the Trans-Saharan Seaway show conspicuous change at either the K-Pg boundary or the PETM based on current evidence, although results are very preliminary. Building on our earlier report of the first record of rock-boring bivalves from the Paleocene of West Africa, we further describe here a Cretaceous and Paleogene mollusk fauna dominated by taxa characteristic of the modern tropics. “This abstract has been truncated. To view the complete abstract please download the PDF”

PALEOGEOGRAPHIC NORTHEASTERN LIMITS OF APHRODINA DUTRUGEI (COCQUAND, 1862) (HETERODONTA, BIVALVIA) FROM THE CENOMANIAN OF THE ARABIAN PLATFORM

The finding of Aphrodina dutrugei (Cocquand, 1862) in a rich collection of non-rudist bivalve fauna from the famous Cenomanian-Turonian carbonates of the Afro-Arabian Plate has permitted the reevaluation of venerid bivalves during an important period of their evolution. The genus Aphrodina Conrad, 1869, Family Veneridae Rafinesque, 1815, embraces several Tethyan Cretaceous species that range from Cenomanian to Santonian. During the late Albian-Maastrichtian ‘Aphrodiniid’ venerids, were distributed along the western margin of the Atlantic (North and South America), the Afro-Arabian Plate (Jordan, SE Turkey, Morocco, Algeria and Egypt), the eastern Tethys, and the Southern Ocean (India, Japan, western Australia and New Zealand). They are also known in the Turonian-Santonian Trans-Saharan Seaway (Gabon). Until now these fossils have been unknown in any Upper Cretaceous localities of southeastern Turkey. In this paper, we report the first record of one of the most common and widespread shallow infaunal species, Aphrodina dutrugei, in the Cenomanian Derdere Formation in the Mardin-Mazidagi area, SE Turkey, which is in the extreme northeastern part of its known range.

Large palaeophiid and nigerophiid snakes from Paleogene Trans-Saharan Seaway deposits of Mali

The Paleogene was a time of high diversity for snakes, and was characterized by some of the largest species known to have existed. Among these snakes were pan-Tethyan marine species of Nigerophiidae and Palaeophiidae. The latter family included the largest sea snake, Palaeophis colossaeus, known from the Trans-Saharan Seaway of Mali during the Eocene. This paper describes new material collected from Malian Trans-Saharan Seaway deposits, including additional material of Palaeophis colossaeus, a new, large species of nigerophiid, Amananulam sanogoi gen. et sp. nov., and a medium-sized snake of indeterminate affinities. The material provides new information on the intracolumnar variation of the vertebral column in Palaeophis colossaeus. We estimate the total length of each species by regression of vertebral measurements on body size. Both Palaeophis colossaeus and Amananulam sanogoi gen. et sp. nov. are the largest or among the largest members of their respective clades. The large size of Tethyan snakes may be indicative of higher temperatures in the tropics than are present today.

Dinosaur trackways from the early Late Cretaceous of western Cameroon

Dinosaur trackways have rarely been reported in Cretaceous strata across the African continent. To the exception of ichnological occurrences in Morocco, Tunisia, Niger and Cameroon, our knowledge on the composition of Cretaceous dinosaur faunas mostly relies on skeletal evidence. For the first time, we document several dinosaur trackways from the Cretaceous of the Mamfe Basin in western Cameroon. Small and medium-size tridactyl footprints as well as numerous large circular footprints are present on a single horizon showing mudcracks and ripple marks. The age of the locality is considered Cenomanian-Turonian and if confirmed, this ichnological assemblage could be younger than the dinosaur footprints reported from northern Cameroon, and coeval with or younger than skeletal remains reported from the Saharan region. These trackways were left in an adjacent subsiding basin along the southern shore of the Benue Trough during a time of high-sea stand when the Trans-Saharan Seaway was already disconnecting West Africa from the rest of the continent. We predict that other similar track sites may be occurring along the margin of the Benue Trough and may eventually permit to test hypotheses related to provincialism among African dinosaur faunas.

MULTISPECIES SHARK FEEDING IN THE TRANS-SAHARAN SEAWAY: EVIDENCE FROM LATE CRETACEOUS DYROSAURID (CROCODYLIFORMES) FOSSILS FROM NORTHEASTERN MALI

Feeding traces help to characterize trophic interactions of ancient ecosystems. In rare cases, they may also provide information that is not otherwise represented by body fossils in a particular paleoenvironment. Here, we describe a diverse suite of surficial bone modifications preserved on dyrosaurid crocodyliform bones. These new fossils come from extensive Upper Cretaceous (Maastrichtian) bone and coprolite-dominated phosphate conglomerates from deposits of the Trans-Saharan Seaway in northern Mali. Five specimens have bite traces indicative of feeding by at least two species of neoselachian sharks. Features of some traces suggest they were not made in a fatal attack, but after the dyrosaurids had died, and therefore represent instances of scavenging. Other traces may be attributed to predation or early scavenging. In addition to the shark bite traces, one specimen bears minute, crescent-shaped traces that we tentatively attribute to invertebrate activity. Importantly, the traces described here document the presence of species for which body fossils have not yet been discovered.

Cenomanian–Coniacian (Upper Cretaceous) bivalves of the Sergipe Basin, Brazil: Order Pholadomyida

Twenty-two species of the bivalve order Pholadomyida, belonging to six genera and seven subgenera of the families Pholadomyidae, Pleuromyidae and Poromyidae are described from the Cenomanian–Coniacian Cotinguiba Formation of the Sergipe Basin, north-eastern Brazil. Eleven species, Pholadomya (Ph.) cf. agrioensis Weaver, Ph. (Ph.) kasimiri Pusch, Ph. (Ph.) nodulifera Munster, Ph. (Ph.) occidentalis Morton, Ph. (Procardia) vignesi Lartet, Pleuromya ligeriensis (d’Orbigny), Pl. servesensis Choffat, Liopistha (L.) aequivalvis (Goldfuss), L. (Psilomya) elongata Stanton, L. (P.) globulosa (Forbes) and L. (Sergipemya) gigantea (J. Sowerby) are recorded from the Sergipe Basin for the fi rst time. The new subgenus Sergipemya of the genus Liopistha, family Poromyidae, is erected on the basis of morphological characters such as numerous commarginal ribs, large and highly infl ated valves, a well-developed rounded umbonal anterior ridge bordering a deep depression on the anterior part, and the presence of two unequal cardinal teeth with a cardinal tear-shaped socket in the left valve. The pholadomyid fauna of Sergipe closely resembles that of other Tethyan regions in western and southern Europe, northern and western Africa and the Middle East. The distribution patterns of the taxa were probably influenced by east–west-directed currents. Southern Tethyan pholadomyids reached western Africa and north-eastern South America via the Trans-Saharan Seaway.

Additions to the sauropod dinosaur fauna of the Cenomanian (early Late Cretaceous) Kem Kem beds of Morocco: Palaeobiogeographical implications of the mid-Cretaceous African sauropod fossil record

Determining the relationships of mid-Late Cretaceous African taxa is central to understanding the timing and resultant palaeobiogeographical patterns of Gondwanan fragmentation. The early Late Cretaceous (Cenomanian) Kem Kem beds of southeastern Morocco preserve a diverse vertebrate fauna, including sauropod dinosaurs. Sauropod material includes the holotype of the rebbachisaurid diplodocoid Rebbachisaurus garasbae and fragmentary remains representing indeterminate titanosauriforms and rebbachisaurids. Here, we describe two new specimens from the Kem Kem beds. A dorsal neural arch with complex internal pneumaticity is tentatively attributed to a somphospondylan titanosauriform. A caudal vertebra possessing several rebbachisaurid synapomorphies is excavated by a large and pervasive lateral pneumatic foramen, a feature undocumented in other rebbachisaurids. However, caudal vertebrae are currently unknown for the sympatric R. garasbae, so this element could be referable to that taxon or a second, previously unknown, rebbachisaurid species. Interestingly, this new caudal vertebra displays a mosaic of features otherwise restricted to limaysaurine or nigersaurine rebbachisaurids, suggesting a placement basal to these clades, which is the position usually recovered for R. garasbae in phylogenetic analyses. A review of the mid-Cretaceous African sauropod fossil record removes the Cretaceous record of dicraeosaurids from Africa, restricting this clade to a single post-Jurassic occurrence in Argentina. All diagnostic sauropod remains can be attributed to titanosauriforms or rebbachisaurids. Whereas rebbachisaurids were seemingly restricted to northwestern Africa and disappeared post-Cenomanian, titanosauriforms were widespread across the African continent and survived until the latest Cretaceous. The development of the mid-Cretaceous Trans-Saharan Seaway might have acted as a dispersal barrier for rebbachisaurids and other vertebrate groups. In contrast, titanosauriforms might have been able to cross this barrier, but it is possible that they were also unable to disperse, and that northwestern African titanosauriforms were not closely related to taxa from the rest of the African continent. New materials and a better understanding of titanosaur interrelationships will be crucial in teasing these scenarios apart.

Cenomanian–Early Turonian Ostracoda of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography

The Cenomanian–Lower Turonian succession exposed in west central Sinai is carefully studied for their ostracode content. The Raha and Abu Qada Formations were studied in 4 sections. Their ostracode content includes the recognition of 70 species belonging to 34 genera. One species is considered as new (Spinoleberis grosdidieri n. sp.). The vertical distribution of the ostracodes in the sections enables the detection of four local biostratigraphic zones with a Barren Interzone in between. In terms of paleobathymetry, each studied sequence reveals deposition on a shallow reefal carbonate platform of less than 100m depth. The flourishing of cytherellids in repeated intervals refers to kenoxic events within the Cenomanian section. These events are enhanced just below the Cenomanian–Turonian boundary referring to the Oceanic Anoxic Event 2. The wide paleobiogeographic distribution of the recorded Cenomanian ostracodes reveals that there was a direct connection throughout the Southern Tethyan Realm countries. Also, there was a migration path between the Southern Tethyan bioprovince and the West African bioprovince during the Cenomanian via the Trans-Saharan Seaway and along the Atlantic coast of West Africa.

Late Cenomanian–Early Turonian ammonites of the southern Tethys margin from Morocco to Oman: Biostratigraphy, paleobiogeography and morphology

The Cenomanian–Turonian ammonite biostratigraphical framework for the southern Tethys margin (North Africa, Middle East and the Arabian Peninsula) is becoming better understood. A first attempt at a synthetic range chart is presented, with 85 taxa and precise correlations for ammonites along a west–east transect from Morocco to Oman, inclusive of the Trans-Saharan Seaway as far south as northern Nigeria. On the basis of a critical review of ammonite taxonomy, 13 bioevents can be identified in the interval from the Late Cenomanian to the Early Turonian (c. 3.5 myr) with each bioevent corresponding to a time interval of approximately 270,000 years, on average. They are consistent throughout several regions along the southern Tethys margin, though some gaps remain, at least at the stage boundary. These bioevents are correlated with the zonation defined for the stratotype (GSSP) of the base of the Turonian in the Western Interior (USA). The paleobiogeographic distribution of ammonites reveals some endemism but the predominant picture is that of a homogeneous fauna throughout the area, even though distinct Boreal and Western Tethys (Atlantic domain) marine influences are evident. An interpretation of the evolution of conch morphology and ornamentation through the zones of the Late Cenomanian–Early Turonian is proposed.

Late Cenomanian–Turonian (Cretaceous) ammonites from Wadi Qena, central Eastern Desert, Egypt: taxonomy, biostratigraphy and palaeobiogeographic implications

ABSTRACT Nagm, E. and Wilmsen, M. 2012. Late Cenomanian-Turonian (Cretaceous) ammonites from Wadi Qena, central Eastern Desert, Egypt: taxonomy, biostratigraphy and palaeobiogeographic implications. Acta Geologica Polonica, 62 (1), 63-89. Warszawa. In Egypt, marine Upper Cenomanian-Turonian strata are well exposed in the Eastern Desert. The southernmost outcrops are located in the central part of Wadi Qena, where the lower Upper Cretaceous is represented by the fossiliferous Galala and Umm Omeiyid formations. From these strata, numerous ammonites have been collected bed-by-bed and 13 taxa have been identified, which are systematically described herein. Four of them (Euomphalocerascostatum, Vascoceras globosum globosum, Thomasites gongilensis and Pseudotissotia nigeriensis) are recorded from Egypt for the first time. The ammonite ranges are used for a biostratigraphic zonation of the lower Upper Cretaceous succession in the northern and central part of Wadi Qena: the Upper Cenomanian-Lower Turonian has been subdivided into five biozones (including a new upper Lower Turonian biozone based on the occurrence of Pseudotissotia nigeriensis), and one biozone has been recognized in the Upper Turonian. Palaeobiogeographically, the ammonite assemblage has a Tethyan character. During the Early Turonian, influences of the Vascoceratid Province were predominant with strong affinities to typical Nigerian faunas. This shows the significance of faunal exchange between Egypt and Central and West Africa via the Trans-Saharan Seaway. Compared to contemporaneous ammonoid faunas from the northern part of the Eastern Desert, Boreal influences are much less obvious in Wadi Qena. Thus, the present study greatly enhances the knowledge of the Late Cretaceous palaeobiogeography and biostratigraphy of Egypt and adjacent areas.

Phosphate Taphonomy of Bone and Coprolite Conglomerates: A Case Study from the Eocene of Mali, NW Africa

Repeated sequences of carbonate and shale are punctuated by condensed sections of phosphatic conglomerate in the epeiric deposits of the Trans-Saharan Seaway in northeastern Mali. To characterize the taphonomic and depositional setting of these phosphates, a thick Eocene conglomerate from the area of Tamaguelelt was targeted for quantitative analysis. Systematic grid sampling demonstrates that nearly all of the clasts are derived from vertebrate sources (bones = 27%, coprolites = 20%, probable coprolites = 53%), and invertebrate body fossils are nearly absent. Bony and cartilaginous fish dominate the bone assemblage, which also includes minor reptilian elements from sea turtles, sea snakes, and dyrosaurid crocodilians. Coprolites are of five distinct varieties, including three spiral forms probably produced by separate fish taxa. Repeated episodes of abrasion and minor bioerosion with modest levels of sorting characterize the taphonomy of the phosphate conglomerate and are consistent with a shallow-marine-to-brackish-water depositional environment between fair-weather and storm-wave base. Early phosphogenesis strongly favored the preservation and lithification of phosphate-rich bones and coprolites, probably during periods of marine transgression and sediment starvation. Combined with evidence from sedimentology, these vertebrate-dominated fossil assemblages appear extensively reworked and highly time averaged as a result of amalgamation and concentration by storm activity during periods of marine transgression.