Famory Sissoko's research while affiliated with National Center for Scientific and Technological Research and other places

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”

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.

2010. First Mesozoic record of the stingray Myliobatis wurnoensis from Mali and a phylogenetic analysis of Mylio− batidae incorporating dental characters. Acta Palaeontologica Polonica 55 (4): 655–674. New specimens, including the first record of lower dental plates, of the extinct myliobatid Myliobatis wurnoensis were re− covered from the Maastrichtian (Late Cretaceous) of the Iullemmeden Basin, Mali, and are the oldest record of the taxon. We evaluated the phylogenetic position of this taxon with reference to other myliobatids (extinct and extant) using osteology and dentition. Our results indicate that Myliobatinae and Myliobatis are each paraphyletic, and that Aetobatus and Rhinoptera are monophyletic. We also found that taxa known only from the Cretaceous, Brachyrhizodus and Igdabatis, are highly nested within Myliobatidae. The phylogenetic position of these taxa unambiguously extends the ori− gin of Myliobatidae and most of its representative taxa into the Mesozoic.

The Paleocene Teberemt Formation south of the Adrar des Iforas Mountains, between Saguirilidad and In Fargas, Mali, yielded a nearly complete skull of a new genus and species of side-necked turtle, Acleistochelys maliensis. Acleistochelys is a member of the family Bothremydidae Baur, 1891, because: 1 the fossa precolumellaris is absent, 2 the foramen stapedio-temporale faces anteriorly, 3 the eustachian tube is separated from the stapes by bone, and 4 an exoccipital-quadrate contact is present. Within the Bothremydidae, Acleistochelys belongs to the tribe Taphrosphyini because: 1 the maxilla-quadratojugal contact is absent, 2 the palate is dorsally arched, 3 there is only a small contribution of the palatine to the triturating surfaces, and 4 the septum orbitotemporale is at least partially open. Acleistochelys is most closely related to Azabbaremys because both share a narrow vomer lacking a posterior attachment to the palatines. The specimen was found in a marine limestone associated with crocodiles, echinoids, and mollusks.

We describe fragmentary new postcranial remains of a sauropod from “Continental Intercalaire” rocks of the Tilemsi Valley in northeastern Mali. Addition of this taxon to recently published cladistic analyses indicates that it is nested within Titanosauria and it is among the oldest members of this clade. “Continental Intercalaire” rocks have been poorly understood and, until now, few vertebrate fossils from these rocks have been tied to stratigraphic sections. We present a preliminary description of the dinosaurian locality and tie it to a synthetic stratigraphic section of the Tilemsi Valley. Preliminary analysis of the geology and sedimentology of the locality suggests that the bones fossilized in fluvial deposits of Early Cretaceous (pre-Cenomanian) age.

Fossils from early Tertiary phosphate deposits of northern Mali include a new diminutive proboscidean taxon intermediate in size between Daouitherium rebouli and Phosphatherium escuilliei. Although a fragmentary specimen, it has two dentary characters previously demonstrated to be diagnostic for basal proboscideans: a labially expanded mandibular corpus in the region of m2 and m3 and a mesiolabially positioned mandibular ramus. The locality that produced the fossils, Tamaguélelt, has historically been hard to date even though it has produced many vertebrates. A section is presented that includes the locality and relates it to surrounding sediments. The locality is Eocene, lies very close to the Paleocene-Eocene boundary, and is most likely early Eocene (Ypresian). The depositional environment suggests substantial reworking of older sediments, and the fossils within them, including the proboscideans, may be even older than early Eocene. The Mali proboscidean is one of the oldest members of Afrotheria that has been found in Africa and this locality is the southernmost African early Eocene locality for mammals.

We describe new dyrosaurid fossils from three localities in Mali, representing strata of Maastrichtian, Paleocene, and Eocene ages. The fossils significantly extend the temporal and geographic ranges of several known dyrosaurid taxa. Rhabdognathus keiniensis and Chenanisuchus lateroculi are identified for the first time from Maastrichtian sediments. Additional material is referred to Phosphatosaurus gavialoides and, tentatively, the genus Sokotosuchus. These discoveries represent the first occurrence of Chenanisuchus and possibly of Sokotosuchus from Mali. Previously unknown morphological character states are incorporated into existing data matrices, reducing the amount of missing data. Phylogenetic analyses largely corroborate prior hypotheses of dyrosaurid relationships, but indicate a need for new characters to resolve the relationships of certain genera and species. The occurrence of both basal (e.g., Chenanisuchus lateroculi) and highly nested (e.g., Rhabdognathus keiniensis) members of Dyrosauridae on both sides of the K/T boundary indicates that dyrosaurid diversification was well underway by the latest Cretaceous, and that most, if not all dyrosaurid species survived the extinction event. The geology of the Mali's Tilemsi Valley is clarified; some rocks previously assigned to the Iullemmeden Basin actually represent extensions of other basins: the Taoudeni Basin and Gao Trench.

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.

Bivalve borings are described for the first time in coprolites. They occur along with bored bone from Cretaceous through Eocene phosphatic conglomerates in the Taoudeni and Iullemmeden Basins of northeastern Mali. Coprolites are extensively penetrated by flask-shaped borings (Gastrochaenolites): the oldest known occurrence of the ichnospecies G. ornatus preserves mechanical scratch traces at the base of some early Eocene coprolite borings. The alleged tracemaker, a pholad bivalve of the Subfamily Martesiinae, is preserved as an external mold in one of the early Eocene coprolites. It is the first occurrence of rock-borers in this subfamily from the Paleocene of West Africa. Bored coprolites were very firm to fully lithified (paleocoprolites) when bored by the pholads, indicating early-diagenetic phosphogenesis of the clasts. The intense and repeated bioerosion of coprolites and bone by pholads suggests a long residence time in shallow-marine waters for the clasts. Therefore, the vertebrate fossil assemblages in these Mali conglomerates are considered highly time-averaged. Recognition of Gastrochaenolites borings in vertebrate remains provides useful taphonomic and paleoenvironmental information, despite their destructive impact on the fossils.

A well-preserved crocodyliform specimen from the Maastrichtian or Paleocene of Mali preserves the braincase and posterior dermatocranium. It is referred to Dyrosauridae on the basis of several derived features (a prominent anterior process of the postorbital, discrete occipital processes on the exoccipitals, significant quadratojugal contribution to jaw joint) and tentatively referred to Rhabdognathus on the basis of supratemporal fenestra shape. The lacrymal and prefrontal are relatively short compared with those published for other dyrosaurids. The palatines border the internal choanae anteriorly, and the choanae are divided by a midline septum derived from the pterygoids. The prefrontal pillars are mediolaterally broad and contact the palate ventrally. One stapes is preserved in place. The basicranial pneumatic system is very unusual, in that the anterior and posterior branches of the median eustachian canal are both separate at the palatal surface, and the pterygoids form part of the border for the anterior branch. The lateral eustachian openings lie within fossae on the lateral surface of the braincase and face laterally, with a descending process of the exoccipital nearly intersecting the opening. The braincase and surrounding dermal bones are elongate anteroposteriorly, and the postorbital's posterior ramus extends along the posterodorsal margin of the infratemporal fenestra. The quadrate ramus projects ventrally. These observations clarify character optimizations in previous phylogenetic analyses of Crocodyliformes.