The microfossil record of early land plants

Dispersed microfossils (spores and phytodebris) provide the earliest evidence for land plants. They are first reported from the Llanvirn (Mid-Ordovician). More or less identical assemblages occur from the Llanvirn (Mid-Ordovician) to the late Llandovery (Early Silurian), suggesting a period of relative stasis some 40 Myr in duration. Various lines of evidence suggest that these early dispersed microfossils derive from parent plants that were bryophyte-like if not in fact bryophytes. In the late Llandovery (late Early Silurian) there was a major change in the nature of dispersed spore assemblages as the separated products of dyads (hilate monads) and tetrads (trilete spores) became relatively abundant. The inception of trilete spores probably represents the appearance of vascular plants or their immediate progenitors. A little later in time, in the Wenlock (early Late Silurian), the earliest unequivocal land plant megafossils occur. They are represented by rhyniophytoids. It is only from the Late Silurian onwards that the microfossil/ megafossil record can be integrated and utilized in interpretation of the flora. Dispersed microfossils are preserved in vast numbers, in a variety of environments, and have a reasonable spatial and temporal fossil record. The fossil record of plant megafossils by comparison is poor and biased, with only a dozen or so known pre-Devonian assemblages. In this paper, the early land plant microfossil record, and its interpretation, are reviewed. New discoveries, novel techniques and fresh lines of inquiry are outlined and discussed.     

Pliocene coastal palaeomorphology and ostracod faunas of the Bass Strait hinterland,southeast Australia

Early to late Pliocene sedimentary strata present across the northern Bass Strait hinterland, southeastern Australia yield extensive fossil proxy data relevant to the interpretation of high sea level coastal palaeomorphology. Within the Pliocene Whalers Bluff Formation exposed in coastal cliffs near the township of Portland, Victoria, marine microfossil faunas delineate two broad cycles of deposition. Both these sedimentary cycles are bound below by unconformity surfaces. Within the lower sedimentary cycle, a basal stress-tolerant (low diversity) marginal marine microfossil fauna devoid of ostracods and suggestive of bottom-water hypoxia, is succeeded by a diverse shallow marine ostracod fauna dominated by stenohaline species indicative of a sheltered (but open) oceanic embayment. This lower sedimentary cycle has an early Pliocene (Zanclean) age. Equivalent shallow marine (e.g. coastal embayment) deposits occur broadly across the coastal hinterland of southeastern Australia—reflecting the generally higher global sea levels of this time. The upper cycle in the cliff exposures at Portland is late Pliocene (Piacenzian) in age. Equivalent deposits across the Bass Strait hinterland are restricted to former incised river valley settings. Euryhaline estuarine/coastal lagoon Ostracoda are present throughout the upper cycle in the Portland cliffs. These are associated with a low diversity microfauna at the base of the upper cycle and a high diversity microfauna towards the top of the cycle. Early Pliocene coastal marine deposits can be distinguished from late Pliocene coastal marine deposits across the northern Bass Strait hinterland on the basis of the presence or absence of certain open marine (‘stenohaline’) ostracod species.     

Comparison of contemporary and fossil diatom assemblages from the western Antarctic Peninsula shelf

During the past ten years, the Antarctic Peninsula has been identified as the most rapidly warming region of the Southern Hemisphere and it is important to place this warming in the context of the natural climate and oceanographic variability of the recent geological past. Many biological proxies, such as marine diatom assemblages, have been used to determine Southern Ocean palaeoceanographic conditions during the Late Quaternary, however, few investigations have attempted to link observations of modern floras with the fossil record. In this study we examine a suite of modern austral spring (December 2003) and summer (February 2002) surface water samples from along the western Antarctic Peninsula (WAP) continental shelf and compare these to core-top, surface sediment samples. Using detrended correspondence analysis (DCA) and principal component analysis (PCA) of diatom abundance data we investigate the relationship of contemporary diatom floras with the fossil record. This multivariate analysis reveals that our modern assemblages can be divided into three groups: summer southern WAP sites, summer northern WAP sites, and spring WAP sites. Sea surface temperature (SST) is an important environmental variable for explaining seasonal differences in diatom assemblages between spring and summer, but sea surface salinity (SSS) is more important for understanding temporally-equivalent regional variations in assemblage. Our summer diatom samples are more reminiscent of early season assemblages, reflecting the unusually late sea ice retreat from the region that year. When the modern assemblages are compared to the fossil record, it is clear that most of the important diatoms from the summer assemblage are not preserved into the sediments, and that the fossil record more closely reflects spring assemblages. This observation is important for any future attempts to quantitatively reconstruct palaeoceanographic conditions along the WAP during the Late Quaternary and highlights the need for many more such studies in order to address longer timescales, such as interannual variability, in the context of the fossil record.     

Ostracod range charts as a chronoecologic tool

Using a linear time scale and equating the durations of species with those of their ecologic niches, range charts of ostracods show ecologic events. As a non-marine example, the Upper Miocene record of the genusCyprideis shows asymptotic freshening of the Central Paratethys. Duration charts of British Jurassic and Cretaceous shallow marine species reflect shore-line movements which generally do, but sometimes do not correlate with global sea-level changes.Charts of all (marine and non-marine) ostracod species distinguish regressions due to progradation during a sea-level rise or highstand from those caused by falling sea-level.Global sea-level changes not only directly induce large-scale creation and destruction of shallow-water benthic niches, but also will drastically affect pelagic and terrestrial environments. The ostracod record discussed in this paper suggests that eustacy is an important driving force behind macroevolution.     

Modern planktic foraminifera

Planktic foraminifers are marine protozoans with calcareous Shells and chambered tests. They first appeared in the mid-Jurassic and spread since the mid-Cretaceous over all the world’s oceans. Modern planktic foraminifers evolved since the early Tertiary, when the first spinose species occurred. Most species live in the surface to sub-thermocline layer of the open ocean, and in marginal seas like the Mediterranean, Caribbean, South China Sea, and Red Sea. Planktic foraminifers are absent in shallow marginal seas, for example, the North Sea. Planktic foraminifers respond to food, temperature and chemistry of the ambient seawater. Species abundance varies according to seasons, water masses, and water depths. Symbiont-bearing species depend on light and are restricted to the euphotic zone. Planktic foraminifers constitute a minor portion of total Zooplankton, but are major producers of marine calcareous particles (shells) deposited on the ocean floor where they form the so-called foraminiferal ooze. Planktic foraminifers contribute substantially to the fossil record of marine Sediments and are of high ecologic, paleoceanographic, and stratigraphic significance since the mid-Cretaceous. Radiocarbon (¹⁴C) gives an absolute age of shell formation within late Pleistocene and Holocene Sediments. Factors that determine the modern faunal composition are applied to Interpretation of the fossil assemblages, for example, by multiple regression techniques (transfer functions) to yield an estimate on ancient environmental parameters. The chemical composition of the calcareous shell (stable isotopes and trace elements) holds clues to the chemical and physical State of the ambient seawater and is useful in the reconstruction of temperature, chemical State, and biological productivity of the ancient marine environment.      

Spatio‐temporal transitions in Paleozoic Bivalvia: A field comparison of upper Ordovician and upper Paleozoic bivalve‐dominated fossil assemblages

Because of the uncertain relationship between relative abundance and taxonomic richness, abundance data are potentially critical components in any analysis of faunal dominance within fossil assemblages. However, such data are often not available in the literature. In this paper, relative abundance data collected during field work at 25 Upper Ordovician and 22 Upper Pennsylvanian to mid‐Permian localities are used to evaluate Paleozoic transitions in the environmental distributions of bivalve molluscs. On the basis of multivariate analyses of these data, it is shown that even early in their history, during the Ordovician, bivalves were generally not restricted in abundance to just marginal environments. They apparently thrived in terrigenous—dominated regions, both nearshore and offshore, but were less abundant in carbonate settings. However, by the late Paleozoic, bivalve abundances had increased in some carbonate environments, in part because of the growing abundances of free‐burrowing suspension‐feeders, which had been substantially less abundant even in terrigenous environments earlier in the Paleozoic. The results of this study corroborate those of a companion analysis, using literature‐derived data, of paleoenvironmental diversity transitions exhibited by Paleozoic Bivalvia.     

Brood care in a Silurian ostracod

An exceptionally preserved new ostracod crustacean from the Silurian of Herefordshire, England, preserves eggs and possible juveniles within its carapace, providing an unequivocal and unique view of parental brood care in the invertebrate fossil record. The female fossil is assigned to a new family and superfamily of myodocopids based on its soft-part anatomy. It demonstrates a remarkably conserved egg-brooding reproductive strategy within these ostracods over 425 Myr. The soft-tissue anatomy urges extreme caution in classifying 'straight-hinged' Palaeozoic ostracods based on the carapace alone and fundamentally questions the nature of the shell-based Palaeozoic ostracod record.     

COMPARISONS BETWEEN PALAEOCENE–EOCENE PARATROPICAL SWAMP AND MARGINAL MARINE POLLEN FLORAS FROM ALABAMA AND MISSISSIPPI, USA

Abstract:  Climate warming at the Palaeocene/Eocene boundary ( c . 55.8 Ma) had significant permanent affects on paratropical and warm-adapted vegetation types. Pollen and spore records which document vegetation turnover from the eastern US Gulf Coast have all been taken from sediments of marginal marine depositional environments. Pollen and spores (sporomorphs) are preserved excellently in these marginal marine depositional environments but these assemblages contain grains transported from many different vegetation types and over huge geographic distances. Currently it is unclear whether the turnover from important paratropical areas like the US Gulf Coast is a reflection on actual vegetation change in the local region or from source areas far away in the continental interior. Sporomorph data from 20 former swamps (lignites) from the Nanafalia, Tuscahoma and Hatchetigbee formations in Mississippi and Alabama, USA, are used to test the fidelity of the marine sporomorph record across the Palaeocene–Eocene transition. Data show that extinction is noted in the swamp record (≥7 per cent of Palaeocene taxa) and that swamps were susceptible to immigration in the Early Eocene with the first occurrences of Brosipollis spp. (Burseraceae), Dicolpopollis spp. (Palmae), Nuxpollenites psilatus (Loranthaceae) and Platycarya spp. (Juglandaceae). Swamps have higher within-sample diversity in the Eocene but higher among-sample diversity in latest Palaeocene–earliest Eocene samples, which parallels exactly diversity trends estimated from marine sporomorph assemblages. Palms also increase in abundance in the Eocene. The swamp data demonstrate that the flora growing in these ancient paratropical forests was diverse ( c. 120 taxonomic groups) but incorporated an unusual admixture of plants with modern tropical affinities together with those that now live in modern temperate to subtropical North America.     

Paleoecology,biostratigraphy and biogeography of late Silurian to early Devonian acritarchs and prasinophycean phycomata in well A161, Western Libya,North Africa

Diverse and well preserved acritarch and prasinophycean phycomata assemblages were recovered from the late Silurian to Lower Devonian strata of well A161 in western Libya, and four distinct acritarch biozones are recognized, based on the stratigraphic distribution of 156 species. The palynoflora is independently dated by means of chitinozoans, and allows discussion of the evolution of acritarchs and prasinophyte phycomata across the Ludlow–Přı́dolı́ boundary in relation to probable major climatic change, as well as in the early and middle Přı́dolı́, and the lower Lochkovian. Correlations are proposed with the British Isles, Baltica, and Algerian Sahara. Sedimentation occurred in shallow high-energy conditions throughout, but with periodic rise of sea level. The changes in marine to terrestrial palynomorph ratios through the section document the relationship between marine palynomorph assemblages and sea surface conditions in these marginal marine environments. The major drift of Gondwana towards low latitudes during the Ludlow–Přı́dolı́ transition seems to have been the driving force behind homogenization of assemblages on the two sides of the Rheic ocean, and explains the similarities between phytoplanktonic assemblages of the north Gondwanan margin and the South of Baltica. The data suggest that the Rheic ocean was almost closed by the late Silurian, and had become restricted to a moderately deep sea. In the Lochkovian the microflora are strongly facies-dependent and delineate more restricted provinces such as the Ibarmaghian domain in the sense of Plusquellec (1987) including the Maghreb and Ibero–Armorican areas.Nine new species are described: Arkonia nova, Arkonia paulumstriata, ?Cymatiosphaera florida, Cymatiosphaera nimia, Dactylofusa hispidusa, Disparifusa quasibernesgae, Evittia areolata, Multiplicisphaeridium verticisum, and ?Villosacapsula steemansii. In addition, three new combinations are suggested: Visbysphaera bonita (Cramer) comb. nov., Visbysphaera jardinei (Cramer) comb. nov. and Visbysphaera albanega (Cramer et al.) comb. nov.     

Paleoenvironmental reconstruction of an Albian plant community from the Ariño bonebed layer (Iberian Chain,NE Spain)

The AR-1 layer, corresponding to the Escucha Formation (Lower Cretaceous) in the Santa Maria Mine of Ariño, has supplied rich and well-preserved macrofloral and palynological assemblages showing interesting data about both taphonomic and environmental conditions. This single layer is located in the Oliete Sub-Basin from the Maestrazgo Basin in northeastern Spain, and it represents one of the most outstanding single layer fossil sites in the world. This site shows abundant and diverse fauna containing exquisitely preserved vertebrate and invertebrate fossils (dinosaur bones, turtles, crocodiles, fishes, molluscs and ostracods) and also plant remains of Albian age. The assemblage is especially significant for dinosaur phylogenetic analysis. The sedimentary environment corresponds to a freshwater swamp plain with sporadic marine inputs within a deltaic–estuarine system under subtropical–tropical climate.     

Shifting ecological baselines and the demise of Acropora cervicornis in the western North Atlantic and Caribbean Province: a Pleistocene perspective

 In recent years, marine scientists have become increasingly alarmed over the decline of live coral cover throughout the Caribbean and tropical western Atlantic region. The Holocene and Pleistocene fossil record of coral reefs from this region potentially provides a wealth of long-term ecologic information with which to assess the historical record of changes in shallow water coral reef communities. Before fossil data can be applied to the modern reef system, critical problems involving fossil preservation must be addressed. Moreover, it must be demonstrated that the classic reef coral zonation patterns described in the early days of coral reef ecology, and upon which “healthy” versus “unhealthy” reefs are determined, are themselves representative of reefs that existed prior to any human influence. To address these issues, we have conducted systematic censuses of life and death assemblages on modern “healthy” patch reefs in the Florida reef tract that conform to the classic Caribbean model of reef coral zonation, and a patch reef in the Bahamas that is currently undergoing a transition in coral dominance that is part of a greater Caribbean-wide phenomenon. Results were compared to censuses of ancient reef assemblages preserved in Pleistocene limestones in close proximity to each modern reef. We have determined that the Pleistocene fossil record of coral reefs may be used to calibrate an ecological baseline with which to compare modern reef assemblages, and suggest that the current and rapid decline of Acropora cervicornis observed on a Bahamian patch reef may be a unique event that contrasts with the long-term persistence of this taxon during Pleistocene and Holocene time. Accepted: 19 May 1998     

Ancient DNA sheds new light on the Svalbard foraminiferal fossil record of the last millennium

Recent palaeogenetic studies have demonstrated the occurrence of preserved ancient DNA (aDNA) in various types of fossilised material. Environmental aDNA sequences assigned to modern species have been recovered from marine sediments dating to the Pleistocene. However, the match between the aDNA and the fossil record still needs to be evaluated for the environmental DNA approaches to be fully exploited. Here, we focus on foraminifera in sediments up to one thousand years old retrieved from the Hornsund fjord (Svalbard). We compared the diversity of foraminiferal microfossil assemblages with the diversity of aDNA sequenced from subsurface sediment samples using both cloning and high‐throughput sequencing (HTS). Our study shows that 57% of the species archived in the fossil record were also detected in the aDNA data. However, the relative abundance of aDNA sequence reads and fossil specimens differed considerably. We also found a limited match between the stratigraphic occurrence of some fossil species and their aDNA sequences, especially in the case of rare taxa. The aDNA data comprised a high proportion of non‐fossilised monothalamous species, which are known to dominate in modern foraminiferal communities of the Svalbard region. Our results confirm the relevance of HTS for studying past micro‐eukaryotic diversity and provide insight into its ability to reflect fossil assemblages. Palaeogenetic studies including aDNA analyses of non‐fossilised groups expand the range of palaeoceanographical proxies and therefore may increase the accuracy of palaeoenvironmental reconstructions.     

Evolution of the sebkha Dreîaa (South-Eastern Tunisia,Gulf of Gabes) during the Late Holocene: Response of ostracod assemblages

The quantitative and qualitative study of the ostracod assemblages supported by the correspondence analysis (CA) allowed the reconstruction of the palaeoenvironnemental change during the Holocene in the sebkha Dreîaa of Skhira (Gulf of Gabes, SE Tunisia). Five phases were distinguished: the first phase (> cal. 6471–6874 yr BP) coincides with the first Holocene marine transgression following the deposition of the continental Holocene series. It induces the setting of an open lagoon where numerous Bivalvia, Gastropoda and marine ostracods lived. The second one (cal. 6471–6874 yr BP) is characterized by the development of brackish ostracods, high diversity index values and comparable percentages of the brackish, lagoonal and coastal assemblages. It corresponds to an open lagoon subjected to estuarine influences. During the third phase (cal. 3350–3752 yr BP), a marine environment, marked by the enrichment of marine ostracods, is evolving toward the closing. The settlement of the restricted lagoonal environments is linked to the building-up of sandy spit. At cal. 2839–3057 yr BP, the dominance of coastal ostracods, associated with coarse sands, show an open lagoon and probably a marine transgression evidenced by the progressive modification in the ostracods assemblages. After this transgression, the southern part of Sebkha of Dreîaa emerged and evolved towards the present state. The last phase, cal. 515–777 yr BP, is marked by a strong marine influence, in the northern part of the sebkha, with transport of marine Bivalvia, Gastropoda and ostracods towards the inner lagoon by means of storms. The rupture of sandy spits induced the introduction of marine macrofauna and microfauna which were accumulated and associated with charcoals and coarse sands.     

Fossils as keys to evolution in fungi.

Both flagellated and nonflagellated fungi have an extensive fossil record, which is, however, unevenly documented and often difficult to interpret. Recent work on Silurian, Devonian and Carboniferous terrestrial assemblages has provided plausible evidence for all major groups of extant fungi in the Paleozoic. Key events in fungal macroevolution thus probably took place in the early Paleozoic or the late Precambrian, and the likelihood of finding definitive fossil evidence for them is small. The fossil record also provides evidence for morphological conservatism and early establishment of a spectrum of intimate associations between fungi and vascular plants. A model for the origin of terrestrial fungi involving two distinct lines of biotrophs in lichen-like symbioses with algae is proposed.     

Evidence that Early Carboniferous ostracods colonised coastal flood plain brackish water environments

A study of the stable isotope composition (δ¹⁸O, δ¹³C) of biogenic (ostracod, mollusc) and authigenic carbonates in the Ballagan Formation, Lower Carboniferous of Scotland, coupled with evidence from sedimentology and associated fossil fauna and flora, supports the argument that this formation was deposited in a coastal flood plain setting, in brackish (0.5 < 30‰ NaCl) and hypersaline (> 40‰ NaCl) waters, but in the absence of persistent normal marine conditions. The oxygen isotope data from the Ballagan Formation divide into three clusters: a diagenetic field defined by low δ¹⁸O (< − 11‰ VPDB); an intermediary field (δ¹⁸O − 11‰ to − 9‰) composed of a mixture of known primary and secondary (diagenetic) carbonates; and samples within the range of − 9‰ to − 4‰ which, as far as we can ascertain, are largely unaltered. No samples give typical Early Carboniferous δ¹⁸O marine values. Average marine carbonates from Europe have δ¹⁸O between − 4‰ to − 3‰. The Ballagan Formation carbonates were probably deposited in evaporated freshwater and/or brackish water. This conclusion is supported by the presence of evaporites (gypsum, anhydrite, halite pseudomorphs) and common desiccation-cracked mudstone surfaces throughout the Ballagan Formation, suggesting conditions of fluctuating salinity in ephemeral bodies of water. The stable isotope data support the notion that the ostracod assemblages of the Ballagan Formation were colonising brackish water and hypersaline ecologies on a coastal flood plain during the Early Carboniferous, a stage of development that may have encouraged their colonisation of fully non-marine (limnetic) environments during the later Carboniferous. The ostracods include cytherellacean and kloedenellacean species known from marginal marine sites elsewhere, but probably tolerant of brackish water, podocopid species such as ‘Bythocypris’ aequalis that may have been adapted for brackish water settings on coastal flood plains (ephemeral lakes and lagoons), and paraparchitacean-dominated assemblages that may signal harsh (hypersaline or desiccating) environments.     

High diversity Pleistocene rainforest Dasyurid assemblages with implications for the radiation of the dasyuridae

It is commonly accepted that dasyurids (Marsupialia: Dasyuridae) radiated in the late Miocene or early Pliocene in response to a drying trend in Australia's climate as evidenced from the high diversity of dasyurids from modern arid environments compared with Miocene rainforest assemblages. However, mid‐Pleistocene dasyurid assemblages from cave deposits at Mt Etna, Queensland are more diverse than any previously known from rainforest habitats. New taxa will be described elsewhere, but include three new genera as well as new species of Dasyurus, Antechinus and Phascogale. Comparison of dasyurids from Mt Etna sites that are interpreted as rainforest palaeoenvironments with fossil and extant assemblages indicate that they are at least as diverse as those from modern arid environments. Thus Neogene diversification of dasyurids occurred in both arid and rainforest habitats, but only the former survived continuing aridification. Hence, aridification cannot be invoked for the diversification of all dasyurid lineages.     

Magnesium and strontium in non-marine ostracod shells as indicators of palaeosalinity and palaeotemperature

Measurements of the Ca, Sr, and Mg contents of individual calcitic shells of non-marine ostracods and their host waters, both in lakes and controlled aquaria, permit the calculation of the distribution coefficients of Sr/Ca and Mg/Ca partitioning in ostracod shells. We report new K_D[Sr] for seven genera of non-marine ostracods and K_D[Mg] for Cyprideis at 25°C.Strontium partitioning is virtually temperature-independent, and is related to the Sr/Ca of the host water, and in Ca²⁺-saturated waters, to the salinity of the water. Magnesium partitioning is dependent on both temperature and Mg/Ca of the host water.For simple closed-basin lakes (crater lakes are ideal), the Sr content of ostracods is a sensitive indicator of salinity and thus evaporation/precipitation changes, which in turn, indicate variations in continental climate. A 10000-year continuous palaeosalinity record established by Sr and Mg contents of fossil ostracods for Lake Keilambete, southeastern Australia, is in close agreement with an independent palaeosalinity estimate based on sediment textures.We suggest rules that allow Sr and Mg analyses of suites of individual fossil ostracod shells from lacustrine sediments to be interpreted in terms of palaeosalinity and palaeotemperature variations.     

Did the Mediterranean marine reflooding precede the Mio–Pliocene boundary? Paleontological and geochemical evidence from upper Messinian sequences of Tuscany,Italy

The events related to the Messinian salinity crisis are among the most deeply investigated of Earth's history. According to the current hypothesis of Neogene paleogeographic evolution, approximately 5.5 Ma ago, after evaporitic sedimentation and before the Mio–Pliocene boundary, the Mediterranean was characterized by the widespread development of non-marine environments inhabited by molluscs and ostracods of brackish affinity. The Messinian post-evaporitic deposits that testify such a dramatic environmental change are commonly referred to as ‘Lago-mare’ and have been reported from several outcrops and boreholes throughout the entire Mediterranean basin. The origin of ‘Lago-mare’ conditions is commonly interpreted as the result of the synergistic effect of both the humid climatic conditions and change of the drainage patterns at the Mediterranean scale, with the capture of Paratethyan brackish waters. A few recent studies, however, suggest that such a scenario probably represents an oversimplification of the original context, from both a paleogeographical and paleoenvironmental point of view. Unfortunately, the results of these studies have never been commonly accepted and the proposed evidences have been considered questionable. In this paper we describe the fish assemblages from the ‘Lago-mare’ deposits of two localities, Cava Serredi and Podere Torricella, located in the Neogene hinterland basins of Tuscany, central Italy. These assemblages consists of a mixture of marine euryhaline and stenohaline taxa suggesting that the depositional environments were characterized by permanently open connections with a marine basin filled with normal marine waters. In order to better define the paleontological significance of these upper Messinian fish assemblages, the oxygen, carbon and strontium isotopic composition of fish otoliths and other fossils has been measured. These isotopic compositions are strongly indicative of the presence of normal marine conditions close to the depositional environments testified by the sedimentary sequences, thereby implying that the interpretation of the geochemical results are consistent with those derived from the paleoecological analyses of the fish assemblages. Based on the integrated paleoichthyological–geochemical approach discussed in this paper it is possible to unambiguously demonstrate that normal marine rather than fresh- or brackish waters were present in the Mediterranean at least during the upper part of the ‘Lago-mare’ event, providing an unquestionable evidence that the marine refilling of the basin preceded the Mio–Pliocene boundary.     

Were all trilobites fully marine? Trilobite expansion into brackish water during the early Palaeozoic

Trilobites, key components of early Palaeozoic communities, are considered to have been invariably fully marine. Through the integration of ichnological, palaeobiological, and sedimentological datasets within a sequence-stratigraphical framework, we challenge this assumption. Here, we report uncontroversial trace and body fossil evidence of their presence in brackish-water settings. Our approach allows tracking of some trilobite groups foraying into tide-dominated estuaries. These trilobites were tolerant to salinity stress and able to make use of the ecological advantages offered by marginal-marine environments migrating up-estuary, following salt wedges either reflecting amphidromy or as euryhaline marine wanderers. Our data indicate two attempts of landward exploration via brackish water: phase 1 in which the outer portion of estuaries were colonized by olenids (Furongian–early late Tremadocian) and phase 2 involving exploration of the inner to middle estuarine zones by asaphids (Dapingian–Darriwilian). This study indicates that tolerance to salinity stress arose independently among different trilobite groups.     

Euryhalinity of Palaeozoic articulate brachiopods

OMonotypic and very low diversity virgianid shell beds from the Upper Ordovician to Lower Silurian dolomites of North Greenland were formed in marginal marine quiet-water hypersaline environments. In the light of this evidence the salinity tolerances of other Palaeozoic articulate brachiopods is evaluated. There are only a small number of species apparently invading hypersaline or brackish environments, but it is significant considering that previously all articulate brachiopods were thought to be fully marine. Two types of occurrence are noted, those species specifically related to marginally marine environments, disappearing with the introduction of fully marine faunas, and the majority of species which extend their normal marine range into marginal conditions. No brachiopod species appears to have invaded very hypersaline or truly brackish conditions. No single group of articulate brachiopods specifically specialised in colonising marginal marine environments, apart from possibly the virgianid pentamerids. Palaeozoic, Upper Ordovician, Lower Silurian, Brachiopoda. Pentamerida, Virgianidae, Greenland, palaeoecology. hypersaline environments, brackish environments .