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The Mesozoic, mid-Cretaceous (Barremian to Cenomanian) deposits of southern Croatia comprise a succession of shallow tropical-water, inner-platform deposits that formed on a Bahama-type isolated Adriatic carbonate platform in the Dinarides. This succession is dominated by benthic foraminifers and dasycladalean algae, and is exposed in a nearly continuous outcrop section on the islands and along the coast of southern Croatia. It has been studied in terms of sedimentary facies, paleoecology, and biostratigraphy. The present study documents that several species of benthic foraminifers (cuneolinids, orbitolinids, alveolinids) and dasycladalean algae (Salpingoporella) have exceptional age-diagnostic value for mid-Cretaceous biostratigraphy. These are abundant, and they have a widespread distribution and a restricted stratigraphic range. They evolved rapidly and became extinct suddenly. The mid-Cretaceous benthic associations, including a total of 106 species and 57 genera of benthic foraminifers and 48 species and 20 genera of dasycladalean algae, were analyzed to establish the principal diversity patterns at (sub)stage level of resolution. The Early Aptian marked the foraminiferal diversity maximum, whereas significant diversity drops are recorded in the Late Aptian and Early Cenomanian. The foraminiferal distribution within the oligotrophic habitats of the platform interior was controlled primarily by relative sea-level oscillations, variations in oceanic circulation rate, and nutrient availability in surface waters. There is a positive correlation between episodes of increased diversification and the regional relative sea-level rises, whereas regressive episodes resulted in reduction of oligotrophic habitats and decreased species richness. The dasycladaleans were the most diversified during the tidal-flat-dominated Barremian, and from that peak diversity decreased through the Early Aptian. A significant diversity drop occurred in the Late Aptian, and it was contemporaneous with the maximum abundance of Salpingoporella dinarica. The mid-Cretaceous dasycladaleans never fully recovered from the Early Aptian platform deepening event, and their post-Aptian diversity pattern implies dependence on factors other than relative sea level and associated changes in habitats.

Platform carbonate deposits of the Karst Dinarides area have a stratigraphic range from the Middle Triassic (or even Carboniferous in some places) to the Middle Eocene, forming a belt nearly 700 km long and, (after reduction by younger tectonics) 80–210 km wide. Besides their significant thickness (4500 to 8000 m) they are characterised by frequent lateral and vertical alternations of different facies, mostly associated with shallow marine environments. Environments ranging from peritidal through low-energy shallow subtidal–lagoons, restricted inner platform shallows, high-energy tidal bars, beach and shoreface to reefal–perireefal predominate, but there are also carbonate slope deposits and those representing temporarily drowned platform facies and intraplatform troughs.The Jurassic to Cretaceous part of this carbonate succession has been subdivided into 19 megafacies units (9 for the Jurassic and 10 for the Cretaceous), the majority of which represent an inner part ofthe ancient Adriatic Carbonate Platform. Marginal parts of the platform are mostly buried, either by the recent Adriatic Sea along theSW margin, or younger deposits along the NE margin; at some localities such Jurassic and Cretaceous deposits are represented by debrite sand/or carbonate turbidites. An additional short review of the overlying Uppermost Cretaceous and Palaeogene deposits (4 megafacies units) enabled a better insight into the post-platform evolution.The very complex vertical and lateral alternation of different megafacies units, including emerged areas which were observed throughout the studied sequence in different parts of the Karst Dinarides, indicate the significant palaeogeographic dynamics of the region. This variability resulted from interaction of the global eustatic signal and local factors, including extensive organic production on the carbonate platform and synsedimentary tectonics controlled by the specific palaeogeographic position of the platform during its geological history.

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Montegrella? gracilis n.sp. (Dasycladales) is characterized by a thick calcareous envelope and narrow central cavity. Branches display two orders of laterals with alternate arrangement between consecutive whorls. The primaries are visibly differentiated into a thin, tendril-like stalk in the proximal part and a club-shaped or ellipsoidal inflated swelling in the distal part. The secondaries are poorly visible, of unclear shape and number, with a supposedly common starting point. In the type-locality, the alga occurs within a rich, typically Upper Barremian, algal assemblage. The validity of the genus Montenegrella, being disputed by BARATTOLO (1983), is commented upon by showing the generic attribution of the same or different species either to Suppiluliumaella or to Montenegrella by different authors.

Clypeina lagustensis n. sp. has been found in the Lower Tithonian deposits of Lastovo Island (Dalmatia, Croatia). It is visually similar, obviously related and in some sections appears almost identical, to Clypeina jurassica FAVRE, from which it differs by visible swellings and thinning of the central cavity, more pronounced distance between the neighbouring whorls of fertile laterals, and in the shape and structure of the interverticillate thallus parts, characterized by having well developed, hairy, sterile laterals. These, after emerging from the exit pore, divide into several bundles which form a common tuft with a calcareous envelope in the proximal part.

According to all the main characteristics, the new species belongsto the genus Linoporella. At the species-specific level, Linoporellavesiculifera n.sp. is characterized by visibly widened distal ends ofthe secondary branches, which gives a vesiculiferous appearance tothe outer surface of the thallus. The distal widenings are sphericallyor conically shaped and open outwards in a funnel-like form. A shortreview of the taxonomic validation of some Linoporella species isalso given. The new species is derived from the Barremian deposits ofMt. Biokovo (central Dalmatia, Croatia).

An emended diagnosis of the genus Selliporella and its type-species, S. donzellii SARTONI & CRESCENTI is proposed, based on the proven existence of non-ramified laterals in the mature (basal) part of the thallus and their ramification in its higher (juvenile) parts. Given the differences in the morphological characteristics of laterals in the upper parts of the thallus, the type-species has been split into two varieties: S. donzellii var. donzellii SARTONI & CRESCENTI and S. donzellii var. galaeformis n. comb. Selliporella cornutuformis n. sp. is proposed, characterized by a distinctly articulated (segmented) and spiky thallus, with each primary lateral bearing a bundle of several trichophorous secondaries. The generic attribution of species originally described as Diplopora johnsoni PRATURLON and Triploporella neocomiensis RADOIČIĆ has been reviewed, resulting in their being unified as the same species, which, according to its newly observed morphological characters, has been ascribed to the genus Pseudoclypeina. As Diplopora johnsoni has been validly described, Triploporella neocomiensis becomes, taxonomically, the younger synonym of Pseudoclypeina johnsoni (PRATURLON) n. comb.