Climate's role in the distribution of the Cretaceous terrestrial Crocodyliformes throughout Gondwana

A high diversity of terrestrial crocodyliform species has been found in the continental Cretaceous deposits of Gondwana. They are widespread in the sedimentary basins of Brazil, Uruguay, Argentina, Bolivia, Morocco, Cameroon, Niger, Malawi, Madagascar and Pakistan, from alluvial, fluvial and lacustrine deposits. A peculiar aspect of these terrestrial crocodyliforms is that only some of them are cosmopolitan. They comprise distinct groups as the basal Notosuchia, baurusuchids, sphagesaurids and Sebecian peirosaurids. There is a distribution pattern of the terrestrial Crocodyliformes faunas throughout the Cretaceous. The oldest are composed of the small and probably omnivorous Notosuchia and Araripesuchus, found in Early Cretaceous deposits. In the Late Cretaceous this fauna was enriched by the medium-sized to large-size baurusuchids, sphagesaurids, peirosaurids and larger Araripesuchus which present specializations as active terrestrial predators. The distribution analysis of the terrestrial Crocodyliformes from Early and Late Cretaceous palaeogeographic and palaeoclimatic maps indicates that temperature was the principal influence on their Gondwanan distribution. Although expressed seasonality, aridity is a limiting factor for the distribution of extant crocodilians. The Cretaceous basal Notosuchia, baurusuchids, sphagesaurids, Araripesuchus, Sebecian peirosaurids, are found in arid climatic belts during Early and Late Cretaceous. To live in a hot and arid climate they have presumably developed ecological strategies that allowed such habits. The aridity or seasonal warm and cyclic dry and wet climate periods plays a role, that have not yet been analyzed, that may explain the domain of bizarre Crocodyliformes in Gondwana during the Cretaceous.     

New xylological data and the biogeography of the Iberian Peninsula during the Early Cretaceous

The position of the Iberian Peninsula during the Early Cretaceous, sandwiched between Laurasia and Gondwana, makes it an important area for the biogeography study of terrestrial ecosystems. Relevant data are, however, scarce. The discovery of silicified wood in the west of the Cameros Basin, in the village Hacinas (Spain), is the first record of the genus Protopodocarpoxylon in Spain and the seventh of Agathoxylon. A new species, Protopodocarpoxylon haciniensis sp. nov., is described. The anatomy of the samples studied shows that paleoclimatic conditions during the Early Cretaceous in the western part of the Cameros Basin were favorable to tree growth, with good water supply during the growth season. Although much impoverished in comparison with Western Europe, the Iberian Early Cretaceous wood floras are clearly Laurasian in affinity.     

Hardly a relict: freezing and the evolution of vesselless wood in Winteraceae

The Winteraceae are traditionally regarded as the least-specialized descendents of the first flowering plants, based largely on their lack of xylem vessels. Since vessels have been viewed as a key innovation for angiosperm diversification, Winteraceae have been portrayed as declining relicts, limited to wet forest habitats where their tracheid-based wood does not impose a significant hydraulic constraints. In contrast, phylogenetic analyses place Winteraceae among angiosperm clades with vessels, indicating that their vesselless wood is derived rather than primitive, whereas extension of the Winteraceae fossil record into the Early Cretaceous suggests a more complex ecological history than has been deduced from their current distribution. However, the selective regime and ecological events underlying the possible loss of vessels in Winteraceae have remained enigmatic. Here we examine the hypothesis that vessels were lost as an adaptation to freezing-prone environments in Winteraceae by measuring the responses of xylem water transport to freezing for a diverse group of Winteraceae taxa as compared to Canella winterana (Canellaceae, a close relative with vessels) and sympatric conifer taxa. We found that mean percent loss of xylem water transport capacity following freeze-thaw varied from 0% to 6% for Winteraceae species from freezing-prone temperate climates and approximately 20% in those taxa from tropical (nonfreezing) climates. Similarly, conifers exhibit almost no decrease in xylem hydraulic conductivity following freezing. In contrast, water transport in Canella stems is nearly 85% blocked after freeze-thaw. Although vessel-bearing wood of Canella possesses considerably greaterhydraulic capacity than Winteraceae, nearly 20% of xylem hydraulic conductance remains, a value that is comparable to the hydraulic capacity of vesselless Winteraceae xylem, if the proportion of hydraulic flow through vessels (modeled as ideal capillaries) is removed. Thus, the evolutionary removal of vessels may not necessarily require a deleterious shift to an ineffective vascular system. By integrating Winteraceae's phylogenetic relationships and fossil history with physiological and ecological observations, we suggest that, as ancestors of modern Winteraceae passed through temperate conditions present in Southern Gondwana during the Early Cretaceous, they were exposed to selective pressures against vessel-possession and returned to a vascular system relying on tracheids. These results suggest that the vesselless condition is advantageous in freezing-prone areas, which is supported by the strong bias in the ecological abundance of Winteraceae to wet temperate and tropical alpine habitats, rather than a retained feature from the first vesselless angiosperms. We believe that vesselless wood plays an important role in the ecological abundance of Winteraceae in Southern Hemisphere temperate environments by enabling the retention of leaves and photosynthesis in the face of frequent freeze-thaw events.     

Structure and diversity of the Mesozoic wood genus Xenoxylon in Far East Asia: implications for terrestrial palaeoclimates

Although the faunal elements of Far East Asian Mesozoic terrestrial biota have attracted much attention in recent years, their palaeoecology remains poorly known. In particular, features of the palaeoclimate are highly controversial. To address this point we used the Mesozoic fossil wood Xenoxylon , a genus recognized as an indicator of wet temperate biotopes and which is common in the area during the Carnian–Maastrichtian interval. We re-appraised bibliographic data and gathered new data for Xenoxylon in the Mesozoic of Far East Asia. This demonstrated that previous taxonomic approaches to the genus have been so far idiosyncratic. We examined the anatomical diversity of morphogenus Xenoxylon in Far East Asia and compared it to that of samples from Europe. This indicates that in an area centred on north-eastern China, Xenoxylon reached a level of anatomical diversity unmatched elsewhere in the world. We hypothesize that this diversity witnesses the persistence of palaeoecological conditions particularly suitable for Xenoxylon and that a wet temperate climate prevailed over most of the area throughout the Carnian–Maastrichtian interval. It is in this setting that the famous Jehol Biota probably evolved.     

The palaeoxylological record of Metapodocarpoxylon libanoticum (Edwards) Dupéron-Laudoueneix et Pons and the Gondwana Late Jurassic–Early Cretaceous continental biogeography

Aim Vertebrates, palynomorphs and leaf floras each give a different picture of continental biogeography of Northern Gondwana during the Middle Jurassic–Early Cretaceous interval. A new biogeographical marker is required to get a clearer picture. Location Northern part of the Gondwana during the Middle Jurassic–Early Cretaceous interval. Methods Comparisons and correlations of wood data from the literature and new material. Results We have selected Metapodocarpoxylon Dupéron‐Laudoueneix et Pons because it has a restricted distribution, temporally and geographically; it is a well‐defined Mesozoic fossil wood monospecific genus, and there are wide‐ranging data on its distribution. Conclusions Metapodocarpoxylon distribution draws a clear latitudinal belt extending from Lebanon westward to Peru. Climate being the main factor of plant distribution at a global scale, the Metapodocarpoxylon area probably underlines a climatic belt. This has several implications, for example, choosing among different Global Circulation Models or discussing dinosaur distribution.     

Considerations on the age of the Tiouaren Formation (Iullemmeden Basin,Niger, Africa): Implications for Gondwanan Mesozoic terrestrial vertebrate faunas

Pre-Aptian mid-Mesozoic terrestrial vertebrates from the African continent are still very poorly known. In Niger, the Tiouaren Formation in the Iullemmeden Basin has yielded dinosaur and other vertebrate remains, and this unit has been dated as Early Cretaceous, most probably pre-Aptian, on the basis of its fish fauna and geological relations to other units in the basin. A review of the fish fauna and invertebrates from this formation does not provide any evidence for such an age, and the geological relations only help to constrain the upper limit for the age of the formation (Aptian). In contrast, the described dinosaur taxa are phylogenetically nested with late Middle Jurassic to Early Late Jurassic taxa from other localities, and thus indicate a pre-Kimmeridgian, probably late Middle Jurassic age for the Tiouaren Formation. Under the assumption of such an age, the dinosaur fauna of this formation provides new insights into dinosaur faunal provincialism during the latest Middle Jurassic. Northern Gondwanan faunas of that time seem to have been different from southern Gondwanan faunas, and show closer affinities to Eurasian faunas than to the latter. A possible explanation for this might be a climatically controlled geographic barrier due to pronounced arid conditions and thus desert environments in central Gondwana during this time.     

Crocodyliform biogeography during the Cretaceous: evidence of Gondwanan vicariance from biogeographical analysis

Explanations of the distributions of terrestrial vertebrates during the Mesozoic are currently vigorously contested and debated in palaeobiogeography. Recent studies focusing on dinosaurs yield conflicting hypotheses. Dispersal, coupled with regional extinction or vicariance driven by continental break-up, have been cited as the main causal factors behind dinosaur distributions in the Mesozoic. To expand the scope of the debate and test for vicariance within another terrestrial group, I herein apply a cladistic biogeographical method to a large sample of Cretaceous crocodyliform taxa. A time-slicing methodology is employed and a refinement made to account for the divergence times of the analysed clades. The results provide statistically significant evidence that Gondwana fragmentation affected crocodyliform diversification during the Mid-Late Cretaceous. Detection of a vicariant pattern within crocodyliforms is important as it helps corroborate vicariance hypotheses in other fossil and extant groups as well as furthers the move towards more taxonomically diverse approaches to palaeobiogeographical research.     

Fossil Woods from Late Cretaceous of Heilongjiang Province,Northeast China,and Their Palaeoenviromental Implications

Three species of fossil coniferous woods, Cupressinoxylon jiayinense Wang R. F., Wang Y. F. et Chen Y. Z., Taxodioxylon cryptomeria Schonfeld and Protopiceoxylon amurense Du N. Z. from late Cretaceous of Heilongjiang Province,Northeast China, were described. Their wood structural characters showed their affinities to the extant Cupressus, Cryptomeria and Keteleeria respectively. The data from fossil woods, fossil foliage and pollen assemblage of late Cretaceous in the same region showed that the flora consists of conifers and broad-leaved trees and most elements were subtropic or warm-temperate, only a few of them were temperate vegetation. At the same time, the occurrence of fungi filaments in the wood of Cupressinoxylon fiayinense might suggest a type of humid and warm environment. All of these evidences indicated that a humid warm temperate or subtropic paleoclimate had existed in Heilongjiang Province during Late Cretaceous.     

黑龙江晚白垩世化石木及其古环境研究

描述了3种出自黑龙江省嘉荫县晚自垩世的化石木:嘉荫柏型木(Cupressinoxylon jiayinense WangR.F.,Wang Y.F.et Chen Y.Z.)、柳杉型木(Taxodioxylon cryptomeria Schonfeld)和黑龙江原始云杉型木(Protopiceoxylon amurense DU N.Z.)。它们分别与现存的柏木属(Cupressus)、柳杉属(Cryptomeria)和油杉属(Keteleeria)有较近的亲缘关系。综合化石本研究与其现存近缘3属的地理分布区的环境分析和已有的植物叶大化石及孢粉的研究成果,黑龙江嘉荫地区晚自垩世的植被类型为针阔叶混交林,植物群由松柏类和阔叶树种组成,大多数是亚热带-暖温带分子,少量是温带分子。同时,嘉荫柏型木中真菌菌丝的侵入生长指示湿热生境的存在。上述证据表明黑龙江省嘉荫县晚自垩世为温暖、湿润的亚热带-暖温带气候。     

Illicioxylon, an Element of Gondwanan Polar Forests? Late Cretaceous and Early Tertiary Woods of Antarctica

The Late Cretaceous and early Tertiary sediments from the northernPeninsula region of Antarctica yield a rich assemblage of fossilwood with well preserved anatomy. Wood specimens of a previouslyrecognized morphotype are described. The woods are characterizedby diffuse porous wood, mainly solitary vessels with long scalariformperforation plates, scalariform and opposite vessel-ray pitting,generally uniseriate and biseriate heterogeneous rays, and tracheidswith obvious uniseriate, circulate, bordered pits. These fossilspecimens show greatest anatomical similarity to the organ genusIllicioxylon Gottwald and extant members of the Illiciaceae.The occurrence of illiciaceous-like wood in Gondwana suggeststhat the distribution of this family may have been more widespreadin the geological past and that a relatively warm temperateclimate prevailed over the northern Peninsula region of Antarcticaduring the Late Cretaceous and early Cenozoic. Copyright 2000Annals of Botany Company Fossil, wood, Illiciaceae, Illicioxylon, Illicium, Cretaceous, Tertiary, Gondwana, Antarctica     

Early Carboniferous radiolarians from north-west Thailand: palaeogeographical implications

Moderately well-preserved radiolarian assemblages are described from bedded cherts south of Mae Hong Son, north-west Thailand. Twenty species and subspecies are identified, including one new species ( Archocyrtium sashidai Feng sp. nov.). The assemblages belong to the middle Early Carboniferous Albaillella indensis and Eostylodictya rota zones. The new data suggest that there was a pelagic basin between the Shan-Thai terrane and Gondwana during the Early Carboniferous. This implies, contrary to previous interpretations, that the Shan-Thai terrane had already rifted apart from Gondwana during the Early Carboniferous.     

Comparative patterns in taxonomic and functional spider diversities between tropical vs. temperate forests

High diversity in tropical compared to temperate regions has long intrigued ecologists, especially for highly speciose taxa like terrestrial arthropods in tropical rainforests. Previous studies showed that arthropod herbivores account for much tropical diversity, yet differences in the diversity of predatory arthropods between tropical and temperate systems have not been properly quantified. Here, we present the first standardized tropical–temperate forest quantification of spider diversities, a dominant and mega‐diverse taxon of generalist predators. Spider assemblages were collected using a spatially replicated protocol including two standardized sampling methods (vegetation sweep netting and beating). Fieldwork took place between 2010 and 2015 in metropolitan (Brittany) and overseas (French Guiana) French territories. We found no significant difference in functional diversity based on hunting guilds between temperate and tropical forests, while species richness was 13–82 times higher in tropical versus temperate forests. Evenness was also higher, with tropical assemblages up to 55 times more even than assemblages in temperate forests. These differences in diversity far surpass previous estimates and exceed tropical–temperate ratios for herbivorous taxa.     

Ginkgoalean woods from the Jurassic of Argentina: Taxonomic considerations and palaeogeographical distribution

A specimen of Baieroxylon rocablanquense nov. sp. from the Roca Blanca Formation (Early Jurassic), and a specimen of Ginkgomyeloxylon tanzanii Giraud and Hankel from the La Matilde Formation (Middle Jurassic), both located in the Santa Cruz province, Argentina, are described in detail. Identification of the morphogenus Baieroxylon is based upon secondary xylem characteristics (cross-field tracheid pitting, cross-fields and ray characters), while identification of Ginkgomyeloxylon is based upon pith, primary xylem and secondary xylem features. A synthesis of Ginkgoalean woods is presented, which combines diagnostic anatomical evidence with data related to stratigraphic and paleogeographical distributions. Based on the results of this analysis, a key for genus-level identification is provided and a new genus, Ginkgopitys, is proposed. These results are used to elucidate global patterns of historical distribution over the course of geological time. In Gondwana, a great diversity of “mixed-type” woods was present during the Mesozoic, especially during the Late Triassic. In contrast, in Laurasia a lower diversity of the mixed-type is recorded for the Paleozoic and Mesozoic, with increases in “abietinoid-type” wood – similar to extant Ginkgo – taking place at the beginning of the Cretaceous. During the Jurassic and Early Cretaceous in both Laurasia and Gondwana, mixed-type and abietinoid-type woods co-existed, illustrating that important evolutionary changes in wood anatomy occurred during the Mesozoic (Jurassic-Cretaceous).     

Paleobiogeography of Africa: How distinct from Gondwana and Laurasia?

Although Africa was south of the Tethys Sea and originally belonged to the Gondwana, its paleobiogeographical history appears to have been distinct from those of both Gondwana and Laurasia as early as the earliest Cretaceous, perhaps the Late Jurassic. This history has been more complex than the classical one reconstructed in the context of a dual world (Gondwana vs. Laurasia). Geological and paleobiogeographical data show that Africa was isolated from the Mid-Cretaceous (Albian-Aptian) to Early Miocene, i.e., for ca. 75 million years. The isolation of Africa was broken intermittently by discontinuous filter routes that linked it to some other Gondwanan continents (Madagascar, South America, and perhaps India), but mainly to Laurasia. Interchanges with Gondwana were rare and mainly “out-of-Africa” dispersals, whereas interchanges with Laurasia were numerous and bidirectional, although mainly from Laurasia to Africa. Despite these intermittent connections, isolation resulted in remarkable absences, poor diversity, and emergence of endemic taxa in Africa. Mammals suggest that an African faunal province might have appeared by Late Jurassic or earliest Cretaceous times, i.e., before the opening of the South Atlantic. During isolation, Africa was inhabited by vicariant West Gondwanan taxa (i.e., taxa inherited from the former South American-African block) that represent the African autochthonous forms, and by immigrants that entered Africa owing to filter routes. Nearly all, or all immigrants were of Laurasian origin. Trans-Tethyan dispersals between Africa and Laurasia were relatively frequent during the Cretaceous and Paleogene and are documented as early as the earliest Cretaceous or perhaps Late Jurassic, i.e., perhaps by the time of completion of the Tethys between Gondwana and Laurasia. They were permitted by the Mediterranean Tethyan Sill, a discontinuous route that connected Africa to Laurasia and was controlled by sea-level changes. Interchanges first took place between southwestern Europe and Africa, but by the Middle Eocene a second, eastern route — the Iranian route — involved southeastern Europe and southwestern Asia. The Iranian route was apparently the filtering precursor of the definitive connection between Africa and Eurasia. The relationships and successive immigrations of mammal (mostly placental) clades in Africa allow the recognition of five to seven phases of trans-Tethyan dispersals between Africa and Laurasia that range from the Late Cretaceous to the Eocene-Oligocene transition. These Dispersal Phases involve dispersals toward Laurasia and/or toward Africa (immigrations). The immigrations in Africa gave rise to faunal assemblages, the African Faunal Strata (AFSs). All successful and typical African radiations have arisen from these AFSs. We recognize four to six AFSs, each characterized by a faunal association. Even major, old African clades such as Paenungulata or the still controversial Afrotheria, which belong to the oldest known AFS involving placentals, ultimately originated from a Laurasian stem group. Africa was an important center of origin of various placental clades. Their success in Africa is probably related to peculiar African conditions (endemicity, weak competition). Although strongly marked by endemicity, the African placental fauna did not suffer extinctions of major clades when Africa contacted Eurasia. The present geographic configuration began to take shape as early as the Mid-Cretaceous. At that time, the last connections between Africa and other Gondwanan continents began to disappear, whereas Africa was already connected to Eurasia by a comparatively effective route of interchange.     

The Role of Substrate Type on Benthic Diatom Assemblages in the Daly and Roper Rivers of the Australian Wet/Dry Tropics

The selection of one or more river substrata for the collection of benthic diatoms is fundamental to any monitoring or research programme because it can potentially bias the diatom data set. In the wet/dry tropics of Australia, where the use of benthic diatoms for river health assessment is in its infancy, the comparability of diatom assemblages on river substrata has been assessed. Benthic diatoms were sampled from seven river sites, with a range of ionic chemistries (conductivities 27–6500 μS cm⁻¹) but low nutrient concentrations. At each site, triplicate samples were collected from 3 to 6 substrata. The diatom assemblages sampled were: epilithon (assemblages on rock), epiphytes on macroalgae and macrophytes, epidendron (assemblages on wood), epipsammon (assemblages on sand), epipelon (assemblages on mud) and bacterial slime. The variability between substrate assemblages, at each site, were assessed according to the following: (1) a multivariate analysis of diatom assemblages, (2) ANOVA tests of species richness, (3) ANOVA tests of the relative abundance of common species (defined by an abundance of at least 10% in any one sample), and (4) a comparison of the number of species unique to a substrate. A total of 198 taxa were identified, with some taxa common to temperate Australia. Common species were found on all substrata, with sometimes statistically significantly different relative abundances. Taxa unique to a substrate had low relative abundances (0.1–2%), were most often found on only one replicate, and are unlikely to be substrate specific because many are known to occur on other substrata. The assemblages on hard substrata, epilithon and epidendron, were found to be most similar. Diatom assemblages on macroalgal and macrophyte substrata, compared to other substrata, were highly variable. This is attributed to the loss of diatoms from grazing and sloughing, followed by recolonisation of newly exposed substrate. Other assemblages, notably epipsammon, were similar to epilithon and epidendron but sometimes differed in their relative abundance of common species. The principal finding of the study was the similarity of the epilithon and epidendron, which are considered to be indistinguishable. Rock and wood hard substrata can be substituted for one another during field surveys, thereby increasing the number of potential sample sites available for monitoring activities that standardise to a hard substrate.     

A Middle Jurassic abelisaurid from Patagonia and the early diversification of theropod dinosaurs

Abelisaurids are a clade of large, bizarre predatory dinosaurs, most notable for their high, short skulls and extremely reduced forelimbs. They were common in Gondwana during the Cretaceous, but exceedingly rare in the Northern Hemisphere. The oldest definitive abelisaurids so far come from the late Early Cretaceous of South America and Africa, and the early evolutionary history of the clade is still poorly known. Here, we report a new abelisaurid from the Middle Jurassic of Patagonia, Eoabelisaurus mefi gen. et sp. nov., which predates the so far oldest known secure member of this lineage by more than 40 Myr. The almost complete skeleton reveals the earliest evolutionary stages of the distinctive features of abelisaurids, such as the modification of the forelimb, which started with a reduction of the distal elements. The find underlines the explosive radiation of theropod dinosaurs in the Middle Jurassic and indicates an unexpected diversity of ceratosaurs at that time. The apparent endemism of abelisauroids to southern Gondwana during Pangean times might be due to the presence of a large, central Gondwanan desert. This indicates that, apart from continent-scale geography, aspects such as regional geography and climate are important to reconstruct the biogeographical history of Mesozoic vertebrates.     

Interplate dispersal paths for megathermal angiosperms

The dispersal of megathermal angiosperms between tectonic plates is reviewed on the basis of fossil evidence for the Cretaceous and Tertiary periods, since the radiation of the angiosperms, and the period of break-up of Gondwana. The combination of tectonic plate disassembly and redistribution, coupled with phases of global warming followed by pronounced cooling, has resulted in the formation of intermittent dispersal opportunities for frost-intolerant plants, and has been a major factor in determining the direction of angiosperm diversification. The Early Cretaceous radiation of angiosperms seems to show little relationship to the formation of Tethys. However, for the Late Cretaceous and Tertiary nine relevant dispersal routes can be differentiated that can be divided into two distinct categories: routes which formed following the break-up of Gondwana during the Late Cretaceous and Earlier Tertiary, when warm climates encouraged dispersal of megathermal elements globally, and routes which formed since the Middle Eocene, following phases of plate collision, as global climates were cooling down, inhibiting such dispersal. Most inter-plate dispersal of megathermal angiosperms took place in the Late Cretaceous and Early Tertiary at a time when global climates were markedly different from those of today, and the global area of megathermal vegetation several times greater than at present. Under such a scenario, it is likely than opportunities for speciation were much higher than for present-day megathermal plants.     

Phylogeny and biogeography of the sharpshooters (Hemiptera: Cicadellidae: Cicadellinae)

Sharpshooters (Cicadellinae), a large subfamily of the Cicadellidae, exhibit a global distribution and a broad array of ecological preferences. To explore the phylogenetic relationships and roles of global historical, biotic and biogeographic processes in the diversification of sharpshooters, we analysed DNA sequence data from three mitochondrial and two nuclear genes for 243 taxa representing all Cicadellinae tribes, generic groups, regional faunas and data of geographic distributions of sharpshooter species compiled from online databases and available literature. The maximum likelihood (ML) and Bayesian inference (BI) analyses strongly support the monophyletic clade including Cicadellinae and Phereurininae. Divergence time estimates and biogeographic analyses suggest that sharpshooters originated in the Neotropical region or were more widespread in Gondwana during the Early Cretaceous and diversified through a combination of ancient vicariance and dispersal following the evolution of angiosperm-dominated habitats. The earliest divergence during the Cretaceous gave rise to Oriental and New World lineages, the latter of which subsequently dispersed into the Old World and gave rise to the diverse endemic fauna of Madagascar. The Oriental lineage shows high diversity and endemism in tropical Asia and the Pacific, with striking distributional discontinuities in Wallacea. These results suggest that a combination of environmental and evolutionary factors including continental-scale vicariance, long-distance dispersal and diversification of terrestrial microhabitats and host plants may explain the diversity of the modern sharpshooter fauna.     

Microfloristic provincialism in the Upper Triassic Circum-Mediterranean area and palaeogeographic implication

This study represents a contribution to the developing knowledge about the microfloristic provincialism affecting Upper Triassic palynoflora. The compositional differences existing between the Onslow and the Ipswich microfloras are mainly based on the presence, in the Onslow microflora, of a diverse and more varied group of gymnosperm pollen grains, including typical European elements. In this study, the palynological assemblages recovered from Carnian successions of the western Tethyan margin (Sicily, Tunisia, Albany, Libya and Israel) are compared with those of West Timor microfloral assemblages, which have been referred to the Onslow microflora of southern hemisphere. They contain several common taxa, mainly consisting of conifer miospores widely recorded in Carnian European successions and less frequently recovered in the Carnian of western and eastern Australia. The number of Circum-Mediterranean sporomorphs in the Onslow microflora assemblages is wider than previously thought, providing new evidences to extend the distribution of the Onslow microflora to include Carnian associations formerly assigned to the Circum-Mediterranean assemblages. These broad microfloral affinities seem to indicate the existence of a homogeneous microflora that maintains, with minor variations, its composition from western Tethys coasts to the northern Australian margin (West Timor). The parent plant community grew in a coastal environment, along the continental margins; the establishment of an equable climatic regime influenced by warm equatorial currents and suitable humid conditions probably conditioned its diffusion. It has long been recognised that the strong floral provinciality which characterised the Late Triassic world gave way to a more homogeneous flora in the Early Jurassic. The decrease in macrofloral diversity is associated with a less pronounced microfloristic provincialism, which in turn coincides with the rise, to strong dominance, of cheirolepidiaceous conifers (Circumpolles producers). This important microfloristic event occurs in the southern hemisphere during the Early Jurassic, however this study reveals their incipient diffusion during the Norian.     

Bryophyte evolution and geography

The three extant Divisions comprising the bryophytes extend, as fossils, well back into Palaeozoic time. Bryophyte origin is part of the rise of terrestrial, vascularized, plants with sporopollenin-walled spores in the Silurian. Before the end of Carboniferous time, bryophyte lines were widely present. Separation of Gondwana and Laurasia by the Permian Tethys Sea and subsequent widespread desert episodes fragmented an already diversified bryoflora subjecting it to intense selective pressure. The cool, mesic climate of southern Gondwana provided a refugium for austral bryophytes. Warmer and drier climates of the Permo-Triassic Laurentian-Laurasia favoured drought-adapted or niche-specific groups creating marked systematic discontinuities. The Angaran wet, probably cool, temperate region provided refuge for basic stock for much of today's rich holarctic and wet ‘tropical’ bryofloras. Climatic changes, correlated with tectonic events and the rise of angiosperms, opened habitats favourable for a diversity explosion. Despite demonstrated potential for long-distance dispersal, modern distributions are mostly linked with total floras or establishment on islands prior to niche saturation. Remnants of Gondwanan bryoflora persist in high southern latitudes as disjunctions with the possibility that the folded ranges of the African Cape have been an insular fragment at higher latitudes becoming attached shortly after angiosperm diversification. Floras of southern India and east Africa have common features but the Himalayan flora shows evidence that the Gondwanan flora of the Indian plate was lost during the movement through desert and tropical latitudes; neotropical and palaeotropical floras are distinctive. Much of the northern Australian bryoflora is recently Malesian-derived while the southeast shows strong austral influence and commonality with New Zealand. Tropical Pacific island floras are mostly Malesian-derived but with both holarctic and austral elements present as in Hawaii and the Society Islands. Holarctic bryoflora is circum-polar with temperate areas of Euro-American and far eastern elements floristically bound by disjunct and vicariad species. Kroeber Coefficients of Correlation differ as Pacific island floras are compared and Guttman-Lingoes Smallest Space Coordinates indicates floristic subgroups within Polynesia. Although these and other mathematical treatments yield potentially promising results, the methods are yet unrefined and there is some uncertainty whether characteristics of numbers or of organisms are implicit in the summations.