Palaeobiogeography of late cretaceous belemnites of Europe

A North Temperate Realm, characterized by Belemnitellidae Pavlov, and a South Temperate Realm, characterized by Dimitobelidae WHITEHOUSE, existed throughout the Late Cretaceous, while Tethyan belemnites belonging to Belemnopseidae Naef existed only in the Cenomanian and disappeared afterwards. The North Temperate Realm may be subdivided into North European and North American Provinces. The latter province includes Greenland, Canada, the Western Interior Region of North America, and the Atlantic and Gulf coasts of North America. The belemnites from the North American Province, consisting of populations of the generaActinocamax Miller andBelemnitella d’Orbigny, are closely related to the belemnites of the North European Province and appear to have migrated from this province to North America via Greenland and Arctic Canada. The North European Province extends from Ireland to the Ural Mountains. Belemnites from this province belong to the following genera:Neohibolites Stolley,Parahibolites Stolley,Belemnocamax Crick,Actinocamax Miller,Belemnellocamax Naidin,Gonioteuthis Bayle,Belemnitella d’Orbigny,Belemnella Nowak, andFusiteuthis Kongiel. Two subprovinces within the North European Province have been recognized: the Central European and Central Russian Subprovinces. These subprovinces are well-defined in the late Coniacian-Early Campanian and are characterized by theGonioteuthis stock andBelemnitella stock, respectively. The two subprovinces are less distinct in other periods of the Late Cretaceous and may disappear completely.     

Annalepis, a pioneering lycopsid genus in the recovery of the Triassic land flora in South China

Fossil plants are scarce in the Earliest Triassic marine deposits of western Guizhou and eastern Yunnan. Only Annularia shirakii, Lobatannularia sp., Paracalamites stenocostatus, Gigantopteris sp., Pecopteris sp. were reported from the base of the Kayitou Formation dated as Early Induan by marine fauna. Recently, we discovered numerous representatives of the genus Annalepis in the same Lowermost Triassic beds: A. latiloba, A. brevicystis, A. angusta, Annalepis spp. occur associated with a basal Triassic marine fauna. This discovery fills the biostratigraphic gap between the Late Permian “Gigantonoclea guizhouensis-Ullmannia cf. bronnii-Annularia pingloensis” and the late Lower Triassic “Neuropteridium–Albertia–Voltzia” assemblages reported from South China. It represents an important datum dealing with the very beginning of a new terrestrial flora installation after the Permian flora disappearance following the Permian–Triassic boundary mass extinction. This “starting point” of a new vegetal cover in South China is to be taken into account in reconstructing through space and time the settlement process of the Mesozoic floristic provinces.     

Concepts of macro- and microevolution as related to the problem of origin and global expansion of the plague pathogen Yersinia pestis

The relationship between macro- and microevolutionary processes is considered with reference to the ecological scenario of the origin of the plague pathogen and its subsequent natural and anthropogenic global expansion. The macroevolutionary transformation of the ancestral pseudotuberculosis microbe clone into the initial plague microbe Yersinia pestis tarbagani occurred in Central Asia at the end of the Late Pleistocene by a “vertical” Darwinian way in an inadaptive heterothermal continual intermediate environment—the Mongolian marmot Marmota sibirica—flea Oropsylla silantiewi system—via a sequence of unstable and currently extinct intermediate forms. Its natural geographic expansion on the “oil spot” principle in the postglacial time led to the microevolutionary formation of 20–30 hostal subspecies circulating in populations of the background species of burrowing rodents and pikas in arid areas of Eurasia. The intercontinental spread of the “marmot” and “rat” pathogen subspecies in the past few centuries has been exclusively anthropogenic, with the involvement of synanthropic (ship) rats.     

New discoveries on the giant hedgehog Deinogalerix from the Miocene of Gargano (Apulia,Italy)

During the Miocene, the Abruzzo/Apulia region (Italy), isolated from the continent, was the theatre of the evolution of a vertebrate ecosystem in insular context. During the Late Miocene, the protagonists of this ecosystem called “Mikrotia fauna” show a high endemic speciation level, presenting spectacular giant and dwarf species of mammals and birds. Deinogalerix is one of the most uncommon forms of this peculiar fauna. It is the largest Galericinae that ever lived. From Gargano (Apulia, Italy) deposits (also called “Terre Rosse”), Deinogalerix has been, since its discovery in the 1970s’, the subject of two publications in which various morphotypes were described. Its presence is also attested at Scontrone (Abruzzo, Italy). In 2005, the new Miocene fissure “Mikrotia 013” (M013) was found in the Gargano area at Cava Dell’Erba by a team of the Università degli studi di Torino. The study of the micromammals, and in particular the presence of an archaic form of Mikrotia, attests that M013 is the oldest fissure known to date. All the Deinogalerix remains come from the smallest morphotype ever found. The morphological features (other than size) allow us to describe the new species Deinogalerix masinii. It presents a large variability of dental and mandibular features expressed in mosaic patterns within the material: the robustness of the upper and lower P3 and P4, and the characteristic trigonid of m1 of the genus; the archaic morphology of the maxilla and the mandible; the abrading pattern of the teeth are unique for Deinogalerix. These new remains allow us to update the knowledge of Deinogalerix. The suit of characters testified that D. masinii nov. sp. is an archaic form on the evolutionary trend toward the most derived representatives of the genus. The affinities of Deinogalerix with the Parasorex group are confirmed, but the time of immigration in Gargano remains debated.     

Anthocyanin content of Tulipa species and cultivars and its impact on tepal colours

Flowers of tulips (17 species and 25 cultivars) were subjected to qualitative and relative quantitative examination for anthocyanins. Altogether five anthocyanins were identified as the 3-O-(6″-O-α-rhamnopyranosyl-β-glucopyranoside) of delphinidin (1), cyanidin (2) and pelargonidin (3), and the 3-O-[6″-O-(2‴-O-acetyl-α-rhamnopyranosyl)-β-glucopyranoside] of cyanidin (4) and pelargonidin (5). The pigments 1–5 represented 7%, 43%, 12%, 2% and 31%, respectively, of the total anthocyanin amount in the tepals of the Tulipa species, and 20%, 37%, 30%, 6% and 4%, respectively, in the cultivar tepals. Nearly 50% of the samples contained acetylated anthocyanins. The colours of the freeze-dried tepals described by the CIELab coordinates, hue angle (h_ab), saturation (C*), and lightness (L*) together with the anthocyanin content were subjected to multivariate analysis. All tepals classified with hue angles described as “blue nuances” were from cultivars. They contained 1 as the major anthocyanin, and no or just traces of pelargonidin derivatives. The species and cultivars having “magenta nuances” showed similar anthocyanin content with increased relative proportions of 2 at the expense of 1. Orange coloured tepals were to a large extent correlated with high relative proportions of the pelargonidin derivatives, 3 and 5. Acetylation of anthocyanins furnished a weak colour effect opposite to the bluing effect previously reported for anthocyanins with aromatic acyl groups. All six species belonging to the section Eichleres (subgenus Tulipa) were after principal component analysis grouped closely together. They were characterized by high concentrations of the pelargonidin derivatives 3 and 5, and orange petal nuances. However, within section Tulipa (subgenus Tulipa), considerable anthocyanin variation was observed. Species in the subgenus Eriostemones were generally characterized by the two anthocyanins 1 and 2, and no pelargonidin derivatives.     

Ecological aspects of the origin of Yersinia pestis,causative agent of the plague: Concept of intermediate environment

Modern phylogenies of Yersinia pestis (Logh.), causative agent of the plague, constructed using molecular-genetic methods, do not receive a satisfactory functional and adaptive interpretation and are far from being ecologically valid. We have presented an ecological scenario of the origin of the causative agent of the plague through the transition of the initial pseudotuberculosis microbe Yersinia pseudotuberculosis O:1b to a free hostal ecological niche (and a new adaptive zone) under ultracontinental climatic conditions of the Late Pleistocene (Sartan time, 22000–15000 years ago) in southern Siberia and Central Asia. An intermediate environment, i.e., the “Mongolian marmot Marmota sibirica-flea Oropsylla silatiewi” parasitic system, where the process of adaptation development of the plague microbe took place, has been characterized. A scenario based on the major principles of the modern synthetic theory of evolution opens the way to an ecological-genetic synthesis of the problem of plague origin and is an appropriate model for developing a theory of molecular evolution of pathogenic (plaguelike) microorganisms.     

Taxonomy of subgenus Temnoclemmys Bergounioux, 1958 (Testudines: Geoemydidae: Ptychogasterinae) based on new material from the Vallès-Penedès Basin (NE Iberian Peninsula)

The taxonomy of the freshwater turtle subgenus Ptychogaster (Temnoclemmys) (Testudines, Geoemydidae, Ptychogasterinae) is revised based on new and previously-published material from the Vallès-Penedès Basin (NE Iberian Peninsula). Additional remains of subgenus Ptychogaster, first reported from this basin, are also described. Although the oldest remains of Temnoclemmys are left unassigned, most of the available remains are attributed to its type species, Ptychogaster (Temnoclemmys) batalleri, originally described from the Late Miocene (MN9 and MN10) of this basin. The new material expands the chronostratigraphic range of P. batalleri in the Vallès-Penedès Basin back to the MN7 + 8 and shows that “Testudo” celonica is its junior synonym. Emended diagnoses for Ptychogaster and Temnoclemmys are also provided.     

Late Miocene Proboscidea (Mammalia) from Macedonia and Samos Island, Greece: preliminary results

The abundant Late Miocene proboscidean remains of Greece have never been studied in detail and compared with those of Eurasia in order to determine their taxonomy and their biostratigraphical and palaeoecological significance. The first results of such study are given in this article. During the past decades, several new proboscidean specimens have been added to the old collections, significantly enriching the available material. The Axios Valley (Macedonia, Greece) proboscidean fossils belong mainly to two species of Choerolophodon: C. anatolicus of early Vallesian age and C. pentelici of late Vallesian–Turolian age. Deinotherium giganteum is rare and recognized only in the late Vallesian locality Ravin de la Pluie of Axios Valley. A zygodont form has also been identified in the Turolian of Axios Valley, attributed to “Mammut” sp. The Late Miocene localities of Nikiti (Macedonia, Greece) revealed several remains of C. pentelici, which are similar to the Turolian ones of Axios Valley. The Samos proboscidean collection includes C. pentelici, “Tetralophodon” atticus, “Mammut” sp. and Deinotherium gigantissimum. The taxonomy of the Late Miocene peri-Mediterranean Choerolophodon is given, and the biostratigraphy and palaeoecology of the Greek Late Miocene proboscideans are discussed.     

Evolution and phylogenetic relationships in subterranean rodents of the Ctenomys mendocinus species complex: Effects of Late Quaternary landscape changes of Central Argentina

We conducted a thorough survey of populations of Ctenomys within the distributional ranges of all species that currently represent the Ctenomys mendocinus species complex in Central Argentina. From the Atlantic Southeastern coast to the heights of the Los Andes mountain range we sampled individuals for all the previously recognized species within this species complex (C. australis, C. azarae, C. porteousi, C. “chasiquensis” and C. mendocinus). Sequences of different fragments of mitochondrial DNA were used to assess the phylogenetic relationships between individuals and to understand the processes responsible for the observed geographic distribution of genetic variation. The genetic differentiation among most of the sequences was moderated, although highly divergent haplotypes were recorded in some localities in the West of our study area, suggestive of the occurrence of a new so far undescribed species. The phylogenetic reconstructions suggested the presence of three major clades into C. mendocinus complex species that do not agree with the currently proposed taxonomy. Phylogeographic and demographic estimates indicated that the C. mendocinus species complex experienced a strong and recent process of population expansion. We propose that the pattern of distribution of haplotype diversity in the C. mendocinus species complex corresponds to a scenario of mild local differentiation with subsequent expansion to the current distribution ranges. Demographic changes through time suggest that glacial-interglacial cycles of Late Quaternary, and the consequent variation in the aridity of Central plains in Argentina, had strong effects on the evolution and cladogenesis of the C. mendocinus species complex.     

The timing and the mode of evolution of wild grapes (Vitis)

Wild grapes are woody climbers, found mostly in temperate regions of the northern hemisphere, comprising the genus Vitis. Despite its importance, the evolutionary history of Vitis is still contentious. Past studies have led to conflicting hypotheses about the phylogeny, speciation events, and biogeographic history of the genus. Here we investigate the evolutionary history of Vitis using data from four chloroplast spacers (trnH-psbA, trnK-rps16, trnF-nahJ, and rpl32-trnL) and the nuclear gene RPB2-I, and we explore mechanisms that could have shaped the observed distribution of current species. Maximum likelihood and Bayesian analyses provided similar results, strongly supporting the presence of two subgenera and suggesting a species clustering within subgenus Vitis that mainly mirrors the disjunction between the Old and New World. Vitis vinifera subsp. sylvestris was found to be sister to the Asian species while three major clades were found in the American species. A network approach confirmed the main geographic groups and highlighted different chloroplast haplotype patterns between Asian and American species. Molecular dating analysis provided the time boundaries to discuss our results. Our study shows wild grape diversification to be a continuous and complex process that concerned the Tertiary as well as the Quaternary, most likely involving both geographical and climatic forces. Local variations in extent and timing of these forces were discussed based on observed differences between groups. In the context of the Tertiary–Quaternary debate, we provide evidence in favor of the “continuous hypothesis” to explain present diversity. Finally, two directions for future research are highlighted: (i) was the earliest grape American or Asian? and (ii) are all modern grape species real?     

Sylvienodus,a new replacement genus for the Cretaceous pycnodontiform fish “Pycnodus” laveirensis

Sylvienodus nov. gen. is erected as replacement for “Pycnodus” laveirensis, from the marine Cenomanian, Late Cretaceous, of Laveiras, Portugal. Significant differences between Sylvienodus and Pycnodus include: absence of dermocranial fenestra, a single premaxillary tooth, simple contact of arcocentra, extremely falcate dorsal and anal fins, lesser enlargement of hypochordal elements on caudal endoskeleton, simpler dorsal ridge scales, oval notch between 1st and 2nd dorsal ridge scales, and a single post-cloacal ventral keel scale. After the removal of the species laveirensis, the genus Pycnodus is considered restricted to the Eocene; its type species, P. apodus, is the only one known from complete specimens. Sylvienodus laveirensis is provisionally assigned to the Pycnodontinae, pending revision of this subfamily.     

Leaf flavonoid glycosides as chemosystematic characters in Ocimum

Thirty-one accessions of nine species belonging to three subgenera of Ocimum (basil, family Lamiaceae) were surveyed for flavonoid glycosides. Substantial infraspecific differences in flavonoid profiles of the leaves were found only in O. americanum, where var. pilosum accumulated the flavone C-glycoside, vicenin-2, which only occurred in trace amounts in var. americanum and was not detected in cv. Sacred. The major flavonoids in var. americanum and cv. Sacred, and also in all other species investigated for subgenus Ocimum, were flavonol 3-O-glucosides and 3-O-rutinosides. Many species in subgenus Ocimum also produced the more unusual compound, quercetin 3-O-(6″-O-malonyl)glucoside, and small amounts of flavone O-glycosides. The level of flavonol glycosides produced was reduced significantly in glasshouse-grown plants, but levels of flavone glycosides were unaffected. A single species investigated from subgenus Nautochilus, O. lamiifolium, had a different flavonoid glycoside profile, although the major compound was also a flavonol O-glycoside. This was identified as quercetin 3-O-xylosyl(1‴→2″)galactoside, using NMR spectroscopy. The species investigated from subgenus Gymnocimum, O. tenuiflorum (=O. sanctum), was characterised by the accumulation of flavone O-glycosides. These were isolated, and identified as the 7-O-glucuronides of luteolin and apigenin. Luteolin 5-O-glucoside was found in all nine species of Ocimum studied, and is considered to be a key character for the genus.     

Allozyme characterisation of four Mediterranean evergreen oak species

Polymorphism at 11 enzyme loci was used to compare the four evergreen oak species of the Mediterranean Basin and to establish their taxonomical relationships. As a comparison, two evergreen oak species from Tibet, located in the primary distribution area of evergreen oaks, were analysed at the same loci. Cladistic analyses led to the separation of a cluster of four species, namely the three Mediterranean Q. ilex, Q. coccifera and Q. alnifolia and the Tibetan Q. aquifolioides. The other Tibetan species, Q. semicarpifolia, and Q. suber, from the Western Mediterranean Basin, were very distinct genetically from the four other species. These results were not consistent with previous taxonomical treatment, based on morphology alone, which classified Q. ilex and Q. coccifera in “ilex group” (=subgenus Sclerophyllodrys O. Schwartz), and the other four species in “cerris group” (subgenus Cerris, according to Schwartz). Allozyme variation has thus provided useful information to clarify the taxonomy of evergreen oaks.     

Late devonian facies inter-relationships in bordering areas of the North Atlantic and their palaeogeographic implications

Late Devonian faunal and facies relationships are examined in seven around the North Atlantic — in eastern North America, Greenland, western Europe and northwest Africa. A shallow marine (“littoral”) environment, characterized by the genus Cyrtospirifer, is distinguished from a deeper water (“bathyal”) goniatite-conodont milieu on the one hand, and from the “Old Red Sandstone” terrestial facies bearing plant an d fresh-water fish remains on the other.Current or source directions indicate that an “Acadian Divide” existed, separating west-flowing drainage systems in North America from those flowing to the east on the Afro-European side. All species of the osteolepid Latvius, and the majority of species of Glyptopomus are found on the eastern flank. Conversely, the earliest amphibian, Ichthyostega, may have been confined to the western side of the divide.Palaeogeographic reconstruction places northwest Africa fairly close to the Catskill Delta in the Late Devonian, thus accounting for the presence of an “American fauna” in the former. North—south migration of littoral faunas along the Afro-European shores was, however, apparently inhibited.     

Pollen morphology of the genus Iris L. (Iridaceae) from Croatia and surrounding area: taxonomic and phylogenetic implications

In Croatia and the surrounding area, the genus Iris is represented with about 20 Alpine-Dinaric, Mediterranean and Pannonian taxa from the subgenera Iris and Limniris. We researched pollen morphology of all taxa by using scanning electron microscopy. All pollen grains are sulcate with few palynological features, which could have taxonomic importance on different classification levels: shape of dry pollen grains; shape, outline and approximate size of hydrated pollen grains, approximate size of the sulcus, and ornamentation of the sulcus membrane and of the exine. At least four pollen types were recognised and taxonomically delimited to the series level: two characterise the subgenus Iris, section Iris (series Elatae and Pumilae), and two the subgenus Limniris, section Limniris (series Laevigatae, Sibiricae and Spuriae). Taxonomic implications of pollen morphology of their critical groups and taxa have been evaluated. Possible phylogenetic implications of pollen morphology of the genus Iris on the Southern European area were suggested: the subgenus Iris is more advanced than the subgenus Limniris; I. graminea seems to be the most primitive member of the subgenus Limniris on the Southern European territory; and pollen morphology of the population of the subspecies I. sibirica subsp. erirrhiza from the Mountain Bjelolasica could represent a link between the subgenera Limniris and Iris in the territory of Southern Europe. The possible pathway of evolution of the genus Iris on the territory of Southern Europe was suggested: from the subgenus Limniris, through the “linked taxon” I. sibirica subsp. erirrhiza from the Bjelolasica Mountain, to the subgenus Iris, series Pumilae, and finally to the series Elatae.     

Taxonomic position of Afghan vole (Subgenus <Emphasis Type="Italic">Blanfordimys</Emphasis>) by the sequence of the mitochondrial <Emphasis Type="Italic">cytb</Emphasis> gene

It is rather difficult to construct a system of gray voles of the tribe Microtini by a set of morphological and karyological characters because form generation is mosaic at these organization levels. The sequence of the mitochondrial cytochrome b gene was used to study the phylogenetic relationships and taxonomic position of the Central Asian subgenus Blanfordimys. Afghan vole Microtus (Blanfordimys) afghanus and Bucharian vole M. (Blanfordimys) bucharensis clustered with Pamir vole M. (Neodon) juldaschi, which is conventionally assigned to another subgenus. The last two species proved to be significantly closer to each other than either of them was to M. (Blanfordimys) afghanus, which disagrees with the monophyletic origin accepted for Blanfordimys. The genetic distances between the species of the subgenus Blanfordmys and M. juldaschi were comparable with the distances between the sister subgenera Microtus s. str. and Sumeriomys or Pallasiinus and Alexandromys and with the basal divergence of supraspecific clades in the subgenus Terricola. It was assumed that a special Central Asian group of species exists within the tribe Microtini and includes species of the subgenus Blanfordimys and M. juldaschi and that the subgenera Neodon and Blanfordimys should be revised.     

Taxonomy and systematics of the genus Pinus based on morphological, biogeographical and biochemical characters

For a long time, systematists have subdivided the genus Pinus into Diploxylon and Haploxylon according to morpho-anatomy and the number of needles. Nevertheless, divergent views remain regarding the structure of these two subgenera, mainly at the section and subsection levels. We propose to clarify some of these uncertainties by studying 45 Pinus taxa of different origins. Our results, based on morphometric and biochemical (flavonoids) parameters, complement those obtained from classical anatomical and morphological studies, and also modern macro-molecular markers (proteins, DNA). We confirm the subdivision of the genus into Pinus = Diploxylon versus Strobus = Haploxylon and the further sectioning of the first subgenus into sections Pinus and Trifoliae. Moreover, we specify the different subsections, whereby the contents of the methylated flavonol isorhamnetin coupled with needle morphometry play a significant role (subsections Pinus vs. Pinaster in section Pinus, Australes + Ponderosae vs. Contortae in section Trifoliae). Given that isorhamnetin proceeds from quercetin by the irreversible action of an O-methyl-transferase, this methylated flavonol becomes a dynamic marker in such way that the taxa rich in isorhamnetin can be considered as more “derived = evolved”. In addition, there exists a highly significant negative correlation between methylation index and number of needles. Consequently, the pines from the Holarctic Strobus group (with five needles and low isorhamnetin contents) can be considered as “ancestral”, in reference to a Laurasian origin of the genus. In the subgenus Pinus, the Nearctic group (=section Trifoliae) remains near the ancestral base. On the other hand, the Holarctic subset “densiflorae” is connected to the other members (mainly European) of the polyphyletic subsection Pinus, in particular with series “sylvestres”. Because of their very high contents of isorhamnetin, the Mediterranean pines result from an accentuation of this evolutionary trend (=subsection Pinaster). In fact, the pines growing under hot and dry climates (Mediterranean region) are highly evolved compared to those from cold and/or wet regions (Eurasia and North America but also, to a lesser extent, the south-eastern USA and East Asia). Our dynamic propositions based on plant phenolics data complete those from more modern macromolecular (DNA, proteins) studies.     

Physiological,Biochemical, and Molecular Characters for the Taxonomy of the Subgenera of Scenedesmus (Chlorococcales,Chlorophyta)

Biochemical and physiological properties of 16 Scenedesmus species representing the three subgenera Scenedesmus, Acutodesmus, and Desmodesmus are not suitable for species differentiation. All Scenedesmus species studied thus far produce secondary carotenoids, e.g. astaxanthin and canthaxanthin, under nitrogen-deficient conditions. In addition, with the exception of one strain, hydrogenase activity under anaerobic conditions is generally present. Sequence analyses of ribosomal 18S RNAs indicate that the subgenus Desmodesmus is phylogenetically well separated from the other subgenera, whereas the separation of Scenedesmus and Acutodesmus appears less convincing and is dismissed in favour of a single subgenus, Scenedesmus. Three taxa formerly assigned to the genus Chlorella are shown to be unicellular species of the genus Scenedesmus. “Chlorella” fusca var. vacuolata and “C.” fusca var. rubescens, which is closely related to S. obliquus, belong to the Scenedesmus/‘Acutodesmus group. “C.” fusca var. fusca is closely related to S. communis and thus belongs to the subgenus Desmodesmus. Inclusion of Kermatia pupukensis into the genus Scenedesmus is also strongly supported by the RNA data which furthermore indicate a relationship with the subgenus Desmodesmus.     

New data on the Cricetidae from the Miocene “Terre Rosse” of Gargano (Apulia,Italy)

The Gargano “Terre Rosse” deposits are paleokarst fissure fillings found in the Mesozoic limestone of the Apricena-Poggio Imperiale area. They are an important source of information for evolutionary and paleobiogeographic studies. The Late Miocene-Early Pliocene assemblages found in the Terre Rosse attest the complex history of endemic faunal distribution in a paleoarchipelago. Based on the cricetid samples from six distinct fissures (F15, F21a, F21b, F21c, F1, F9, NBS) stored in the Department of Earth Sciences of the University of Florence, three species of endemic cricetids are described: the small-sized Hattomys beetsi, the middle-sized Hattomys nazarii, and the large-sized Hattomys gargantua. The specimens from fissure F15 are attributed to H. beetsi, those from F21a-b to the transitional form Hattomys beetsi-nazarii, those belonging to NBS are ascribed to H. nazarii, whereas those from F1 and F9 are classified as H. gargantua. F21c is considered contaminated with material from different fissures. In line with previously published results, the analysis confirms that the endemic cricetids underwent a remarkable increase in size through time. The morphological variations show a marked trend towards increasing enamel thickness, but also the tendency of the cusps to assume a carved-in aspect. The variations of the morphological characters confirm that the three species likely belong to the same lineage.     

Fossil microphytoplankton dynamics across the Ordovician–Silurian boundary

A critical review of all available data on acritarch biostratigraphy and diversity dynamics across the Late Ordovician through the early Silurian, permits a better appreciation of the potential of acritarchs for the recognition of the systemic boundary. This analysis also reveals the response of marine microphytoplankton populations to the Late Ordovician palaeoenvironmental crisis (Hirnantian glaciation). Previous zonal schemes are improved, and an updated acritarch biostratigraphic chart is proposed, plotted against the most recent chronostratigraphic subdivisions. Sections from Anticosti Island (Québec, Canada), Algeria, Morocco, and Estonia preserve the best palynological record for the investigated interval. The present analysis shows that no true mass-extinction event occurred in latest Ordovician times in connection with the well known glacial event. “Pre-glacial” Ashgill acritarch suites are dominated by species of Baltisphaeridium, Multiplicisphaeridium, Ordovicidium, Orthosphaeridium, and netromorph acritarchs. An important proportion of these taxa (excluding Ordovicidium and Orthosphaeridium) survive the onset of glacial conditions in Hirnantian (latest Ordovician) times and continues through the early Silurian. The development of morphological polymorphism appears as a response (a survival strategy?) to the establishment of glacial conditions.In glacial-related sediments of Hirnantian age in North Africa, acritarch assemblages display a burst of relative abundance and intra-specific morphological variability (polymorphism) of long-ranging taxa such as Veryhachium, Multiplicisphaeridium, Dactylofusa, Poikilofusa, and Evittia. The extinction of several species characteristic of Upper to uppermost Ordovician strata occurs near the boundary, in “post-glacial” Ashgill (uppermost Hirnantian). This extinction event is counterbalanced by the almost contemporaneous (within the limits of stratigraphic resolution) appearance of several new taxa showing already a clear “Silurian affinity”, e.g., Tylotopalla, Cymbosphaeridium, and Visbysphaera. This origination event is observable in, and correlatable between the North African, the Bohemian and the Anticosti sections, making it global in extent.The completion of the palynological turnover and the establishment of a diverse Silurian acritarch suite occurs well above the base of the Silurian, during Aeronian times. The strong survival capability of the oceanic plankton through periods of palaeoenvironmental crisis in latest Ordovician times (but also throughout the Phanerozoic) could have played an important role in the post-extinction rebounds of metazoan clades, by assuring the continuity of marine trophic resources to consumers and avoiding irreversible disruptions of the trophic chains.