Magdy El-Hedeny’s research while affiliated with Alexandria University and other places

The palaeoenvironments of the Campanian‒lower Palaeocene composite succession in the Dakhla Oasis, Egypt, are interpreted based on the integration of sequence-stratigraphy, macrobenthic associations, and trace fossils. This succession comprises six rock units, corresponding to several transgression-regression cycles. These rock units include the Quseir Formation, the Duwi Formation, and the Mawhoob, Beris, Lower Kharga, and Upper Kharga members of the Dakhla Formation. Six unconformities delineate seven 3rd-order depositional sequences, including the lower‒middle Campanian DS-Q1, the upper Campanian DS-D1 and DS-D2, the lower Maastrichtian DS-Dk1, the upper Maastrichtian DS-Dk2 and DS-Dk3, and the lower Danian DS-Dk4. The invertebrate macrobenthic elements sporadically occurred throughout the studied succession, representing three bivalve associations: the late Campanian Nicaisolopha-Plicatula association, the late Maastrichtian Exogyra overwegi association, and an early Danian Venericardia association. At least 12 ichnotaxa have been identified, representing two ichnoassemblages: the late Campanian Thalassinoides-Psilonichnus and the latest Maastrichtian‒early Danian Rhizocorallium jenense-Tisoa siphonalis, both belonging to the Glossifungites Ichnofacies. Sequences characteristics indicate palaeoenvironments ranging from brackish, littoral, and near-shore to inner and outer neritic settings, reflecting the influence of syn-sedimentary tectonics combined with sea-level fluctuations, which resulted in varied depositional features. The distribution and the trophic structure of the body and trace fossil assemblages confirm the role of several environmental parameters, such as substrate characteristics, bathymetry, water energy, productivity level, sedimentation rates, and oxygen availability, in shaping the occurrence of different elements within these faunal assemblages.

Four new symbiotic associations between worms and tabulate corals have been described from the Hirnantian to Ludfordian of Estonia. Chaetosalpinx csp. occurs in Palaeofavosites porkuniensis from the Hirnantian of northern Estonia. Chaetosalpinx ferganensis occurs in Favosites hisingeri from the Telychian, with an infestation rate of about 18%. Chaetosalpinx siberiensis occurs in the Favosites forbesi from the Ludfordian of Estonia, with an infestation rate of about 33%. Endobiotic Cornulites sp . was discovered from the Ludfordian Favosites terrae-novae. Our data suggest that Chaetosalpinx trace makers exhibited a significantly broader parasitic behavior, infesting a wider variety of coral species during the Silurian in the Baltica. The discovery of cornulitid within the corallum of Favosites indicates that the symbiotic relationship between cornulitids and tabulates spanned a broad stratigraphic range, extending from the late Katian to the Ludfordian during the early Paleozoic in Estonia.

The present study examines the basilosaurid whale bone specimens collected from the Sandouk El-Borneta section, Wadi El-Hitan (Valley of Whales), Fayum, Egypt. These specimens are embedded in highly fossiliferous calcareous sandstones of the middle Eocene Gehannam and the upper Eocene Birket Qarun formations. These whale bones display some post-mortem alterations, representing good signs of at least three distinct stages in what is called the whale fall. The co-occurrence of shark, ray, and crocodile fossil specimens with the examined whale bones may indicate the first mobile-scavenger stage. Borings of the siboglinid polychaete genus Osedax represent the most common worm type that deeply bioeroded the whale bones, contributing to their rapid degradation, and representing the enrichment-opportunist stage. These fossil traces of the bone-eating worm Osedax represent the first record in the Eocene Epoch regionally and inter-regionally, filling the gap between the Late Cretaceous and the Oligocene occurrences. Subsequently, the studied whale bones served as hard substrates for some calcareous tube-dwelling encrusting polychaetes, balanoid barnacles, sheet‐like cheilostome bryozoans, and scleractinian corals. Furthermore, a bioerosion structure produced by polychaete annelids was also observed. The presence of these sclerobionts assemblage confirms the well-developed final reef stage with prolonged exposure and colonisation of these whale bones prior to final burial. Based on the recorded post-mortem alterations, together with other sedimentological and palaeontological data, the studied whale bones were deposited in a shallow open marine bay to sheltered gulf environments, which were characterised by low depositional energy, low to moderate rate of sedimentation, and high surface water productivity.

Bioclaustrations are extremely rare in the rugose corals from the Ordovician of Estonia. A specimen of Kenophyllum subcylindricum from the Vormsi Regional Stage (Katian) contains multiple shafts of Chaetosalpinx siberiensis?. The latter bioclaustration also occurs in the Pirgu Regional Stage (Katian). The growth lines of the host coral show a reaction to the infesting organism, suggesting that the shafts in the calyx are bioclaustrations and not post-mortem borings (Trypanites). The worm-like Chaetosalpinx tracemaker initially caused damage to the coral's soft tissues and used the coral's resources to build its domicile, resulting in a negative impact. The symbiotic worms benefited from having a domicile and protection against predators from the host's nematocysts. Chaetosalpinx siberiensis?-Kenophyllum subcylindricum association was likely parasitic. RESUMO: Bioclaustrações são extremamente raros nos corais rugosos do Ordoviciano da Estonia. Um espécime de Kenophyllum subcylindricum do estágio regional Vormsi (Katiano) contém eixos múltiplos de Chaetosalpinx siberiensis?. Essa última bioclaustração também ocorre no estágio regional de Pirgu (Katiano). As linhas de crescimento do coral hospedeiro mostram uma reação ao organismo infestante, sugerindo que os eixos no cálice são bioclaustrações e não perfurações post-mortem (Trypanites). O Chaetosalpinx tracemaker, semelhante a um verme, inicialmente causou danos aos tecidos moles do coral e usou os recursos do coral para construir seu domicílio, resultando em um impacto negativo. Os vermes simbióticos se beneficiaram do fato de terem um domicílio e proteção contra predadores dos nematocistos do hospedeiro. A associação Chaetosalpinx siberiensis?-Kenophyllum subcylindricum foi provavelmente parasitária.

Based on shell microstructure, pelagic tentaculitids have been affiliated with molluscs in the past. Species of the genus Styliolina were among the most important pelagic tentaculitids in the Devonian. The shell wall of Styliolina clavulus is single-layered and composed of thin calcareous lamellae that are parallel to the wall of the shell. The thickness of individual lamellae varies about two times but the thickness of each lamella in the shell wall is constant. The structure is clearly laminar and is similar to bryozoan, brachiopod and molluscan calcitic regularly foliated structures. Based on the structure of S. clavulus alone and the reinterpretation of published SEM images, it is impossible to rule out molluscan affinities for styliolinids, as both regularly foliated and semi-nacreous structures are known in molluscs. However, considering the whole shell structure spectrum of tentaculitoids, one should conclude that the structure of S. clavulus fits well within the group of tentaculitoids and lophophorates in general. The biomineralization of styliolinids was likely advanced and organic matrix controlled; the secreting epithelium was located within the shell and secretion likely took place lamella by lamella.

The palaeoecology and palaeoenvironment of a dense cluster of regular echinoid spines that occur in an oyster-rich limestone layer are interpreted based on detailed taphonomic study. The paucispecific macrobenthic assemblage associated with these echinoid spines have been studied in the middle Miocene Geniefa Formation, Gebel Gharra, Cairo-Suez District of Egypt. Both echinoid spines and macrobenthic assemblages are dominated by moderately to well-preserved, moderately packed, highly disarticulated, moderately to poorly sorted, re-oriented, and moderately to highly fragmented specimens, confirming parautochthonous nature of this assemblage. The spines are commonly encrusted and bored. At least four taxonomic groups of encrusters are identified, including juvenile oysters, sheet-like cheilostome bryozoans, serpulids, and balanoid barnacles. The diversity of bioerosional ichnotaxa is moderate and includes Gastrochaenolites, Entobia, Maeandropolydora, Trypanites, and Spirolites. Moreover, some echinoid spines display distinct biting traces of fish, representing the first recorded of fish tooth bite marks on remains of regular echinoid spines from the Miocene deposits of Egypt. The faunal composition and trophic structure of the studied faunal assemblage indicate fully oxygenated and euhaline shallow-marine environment with meso- to eutrophic productivity level. The controlling environmental parameters include substrate consistency, bathymetry, water energy, surface-water productivity, and rate of sedimentation. Furthermore, two scenarios for sclerobionts colonisation and development of fish bite marks have been proposed. In the first syn vivo scenario, predatory fish either focused on the encrusting organisms attached to the spines or attacked the echinoid as a food source, resulting in the separation of spines from their original test during the echinoid’s life. In the second post-mortem scenario, disarticulated spines serve as a hard substrate for the colonisation of sclerobionts. Once again, the spines became subject to attacks by fish that fed on the encrusters, resulting in additional bite marks.

The most conspicuous feature of the lower‒middle Miocene deposits of Gebel Gharra, Cairo-Suez District of Egypt, is the presence of three pectinid- and two oyster shell concentrations. They are paucispecific to polyspecific macrobenthic biotopes. Their shells were significantly colonised by abundant endobionts and common epibionts, characterising the Entobia ichnofacies, and representing successive phases of colonisation and bioerosion on stable substrates with a low sedimentation rate in high energy, shallow marine environments. Four types of shell concentrations have been distinguished. Pectinid-shell concentration of bed 2 is interpreted as a simple transgressive lag concentration that formed by reworking of previous deposited sediments in a shoal environment. Pectinid-shell concentration of bed 13 represents a coquina of high and moderately convex, sub-horizontally oriented to chaotic, and highly disarticulated and fragmented pectinid valves. It is interpreted as a remnant of previously deposited sediments that have been reworked by a single storm event without major transport of shells, and deposition in a lagoon environment. Pectinid-shell concentration of bed 14b is characterised by completely disarticulated, highly fragmented, moderately to densely packed, and re-oriented pectinid shells. It represents a composite concentration that was originated in a lagoon environment by sporadic high-energy events. Oyster-dominated concentrations of beds 9 and 22 represent “within-habitat” environmentally condensed assemblages, and formed by densely fossiliferous deposits with highly disarticulated, convex-up oysters along with articulated specimens preserved in life position, and with a moderate to high grades of bioerosion and encrustation. They were deposited by several high-energy events in supratidal and lagoonal environments, respectively.

There is a controversy involved in the models of the formation of serpulid tube microstruc-tures, which either have been formed in similar ways to molluscan structures or in an alternative, unique serpulid way. A scanning electron microscope (SEM) study of the tube microstructure of Crucigera zygophora has been performed. A new serpulid tube microstructure, an aggregative SIOP, has been discovered in C. zygophora, herein termed ASIOP. During the first phase of crystallization, the sparsely located nuclei of the ASIOP structure formed, and in the second phase of crystal growth, the nucleation of spherultic sectors took place on the surface of preformed nuclei. The ASIOP structure differs from SIOP by more sparsely located crystallisation centres (nuclei) and the slower formation (i.e., crystallisation) of basic units. The formation of the ASIOP structure cannot be fully explained by the classical carbonate slurry model. Future comparative studies should show whether molluscan crossed spindle-like structures and serpulid SIOP structures are structural analogues.