Biogeographic analysis of jurassic-early cretaceous wood assemblages from Gondwana

The terrestrial biogeography of Gondwana during Jurassic-Early Cretaceous times is poorly resolved, and the flora is usually considered to have been rather uniform. This is surprising given the size of Gondwana, which extended from the equator to the South Pole. Documenting Gondwanan terrestrial floristic provincialism in the Jurassic-Early Cretaceous times is important because it provides a historical biogeographic context in which to understand the tremendous evolutionary radiations that occurred during the mid-Cretaceous. In this paper, the distribution of Jurassic-Early Cretaceous fossil wood is analysed at generic level across the entire supercontinent. Specifically, wood assemblages are analyzed in terms of five climatic zones (summer wet, desert, winter wet, warm temperate, cool temperate) established on the basis of independent data. Results demonstrate that araucarian-like conifer wood was a dominant, cosmopolitan element, whereas other taxa showed a greater degree of provincialism. Indeed, several narrowly endemic morphogenera are recognizable from the data. Finally, comparisons with Laurasian wood assemblages indicate strong parallelism between the vegetation of both hemispheres. (C) 2004 Elsevier B.V. All rights reserved.

The origin of modern crocodyliforms: new evidence from the Cretaceous of Australia

While the crocodyliform. lineage extends back over 200 million years (Myr) to the Late Triassic, modern forms - members of Eusuchia - do not appear until the Cretaceous. Eusuchia includes the crown group Crocodylia, which comprises Crocodyloidea, Alligatoroidea and Gavialoidea. Fossils of non-crocodylian eusuchians are currently rare and, in most instances, fragmentary. Consequently, the transition from Neosuchia to Crocodylia has been one of the most poorly understood areas of crocodyliform evolution. Here we describe a new crocodyliform from the mid-Cretaceous (98-95 Myr ago; Albian-Cenomanian) Winton Formation of Queensland, Australia, as the most primitive member of Eusuchia. The anatomical changes associated with the emergence of this taxon indicate a pivotal shift in the feeding and locomotor behaviour of crocodyliforms - a shift that may be linked to the subsequent rapid diversification of Eusuchia 20 Myr later during the Late Cretaceous and Early Tertiary. While Laurasia (in particular North America) is the most likely ancestral area for Crocodylia, the biogeographic events associated with the origin of Eusuchia are more complex. Although the fossil evidence is limited, it now seems likely that at least part of the early history of Eusuchia transpired in Gondwana.

(Table 1) Stable isotope record of Middle Cretaceous benthic foraminifera

Preservation of planktic foraminiferal calcite has received widespread attention in recent years, but the taphonomy of benthic foraminiferal calcite and its influence on the deep-sea palaeotemperature record have gone comparatively unreported. Numerical modeling indicates that the carbonate recrystallization histories of deep-sea sections are dominated by events in their early burial history, meaning that the degree of exchange between sediments and pore fluids during the early postburial phase holds the key to determining the palaeotemperature significance of diagenetic alteration of benthic foraminifera. Postburial sedimentation rate and lithology are likely to be important determinants of the paleoceanographic significance of this sediment-pore fluid interaction. Here we report an investigation of the impact of extreme change in sedimentation rate (a prolonged and widespread Upper Cretaceous hiatus in the North Atlantic Ocean) on the preservation and d18O of benthic foraminifera of Middle Cretaceous age (nannofossil zone NC10, uppermost Albian/lowermost Cenomanian, ~99 Ma ago) from multiple drill sites. At sites where this hiatus immediately overlies NC10, benthic foraminifera appear to display at least moderate preservation of the whole test. However, on closer inspection, these tests are shown to be extremely poorly preserved internally and yield d18O values substantially higher than those from contemporaneous better preserved benthic foraminifera at sites without an immediately overlying hiatus. These high d18O values are interpreted to indicate alteration close to the seafloor in cooler waters during the Late Cretaceous hiatus. Intersite differences in lithology modulate the diagenetic impact of this extreme change in sedimentation rate. Our results highlight the importance of thorough examination of benthic foraminiferal wall structures and lend support to the view that sedimentation rate and lithology are key factors controlling the paleoceanographic significance of diagenetic alteration of biogenic carbonates.

Revisiting the Late Jurassic-Early Cretaceous of the NW South Iberian Basin: new ages and sedimentary environments

The study of the Upper Jurassic-Lower Cretaceous deposits (Higueruelas, Villar del Arzobispo and Aldea de Cortés Formations) of the South Iberian Basin (NW Valencia, Spain) reveals new stratigraphic and sedimentological data, which have significant implications on the stratigraphic framework, depositional environments and age of these units. The Higueruelas Fm was deposited in a mid-inner carbonate platform where oncolitic bars migrated by the action of storms and where oncoid production progressively decreased towards the uppermost part of the unit. The overlying Villar del Arzobispo Fm has been traditionally interpreted as an inner platform-lagoon evolving into a tidal-flat. Here it is interpreted as an inner-carbonate platform affected by storms, where oolitic shoals protected a lagoon, which had siliciclastic inputs from the continent. The Aldea de Cortés Fm has been previously interpreted as a lagoon surrounded by tidal-flats and fluvial-deltaic plains. Here it is reinterpreted as a coastal wetland where siliciclastic muddy deposits interacted with shallow fresh to marine water bodies, aeolian dunes and continental siliciclastic inputs. The contact between the Higueruelas and Villar del Arzobispo Fms, classically defined as gradual, is also interpreted here as rapid. More importantly, the contact between the Villar del Arzobispo and Aldea de Cortés Fms, previously considered as unconformable, is here interpreted as gradual. The presence of Alveosepta in the Villar del Arzobispo Fm suggests that at least part of this unit is Kimmeridgian, unlike the previously assigned Late Tithonian-Middle Berriasian age. Consequently, the underlying Higueruelas Fm, previously considered Tithonian, should not be younger than Kimmeridgian. Accordingly, sedimentation of the Aldea de Cortés Fm, previously considered Valangian-Hauterivian, probably started during the Tithonian and it may be considered part of the regressive trend of the Late Jurassic-Early Cretaceous cycle. This is consistent with the dinosaur faunas, typically Jurassic, described in the Villar del Arzobispo and Aldea de Cortés Fms.

Evolution of neodymium isotopic signature of seawater during the Late Cretaceous: Implications for intermediate and deep circulation

Neodymium isotopic compositions (εNd) have been largely used for the last fifty years as a tracer of past ocean circulation, and more intensively during the last decade to investigate ocean circulation during the Cretaceous period. Despite a growing set of data, circulation patterns still remain unclear during this period. In particular, the identification of the deep-water masses and their spatial extension within the different oceanic basins are poorly constrained. In this study we present new deep-water εNd data inferred from the Nd isotope composition of fish remains and Fe-Mn oxyhydroxide coatings on foraminifera tests, along with new εNd data of residual (partly detrital) fraction recovered from DSDP sites 152 (Nicaraguan Rise), 258 (Naturaliste Plateau), 323 (Bellinghausen Abyssal Plain), and ODP sites 690 (Maud Rise) and 700 (East Georgia Basin, South Atlantic). The presence of abundant authigenic minerals in the sediments at sites 152 and 690 detected by XRD analyses may explain both middle rare earth element enrichments in the spectra of the residual fraction and the evolution of residual fraction εNd that mirror that of the bottom waters at the two sites. The results point towards a close correspondence between the bottom water εNd values of sites 258 and 700 from the late Turonian to the Santonian. Since the deep-water Nd isotope values at these two sites are also similar to those at other proto-Indian sites, we propose the existence of a common intermediate to deep-water water mass as early as the mid-Cretaceous. The water mass would have extended from the central part of the South Atlantic to the eastern part of proto-Indian ocean sites, beyond the Kerguelen Plateau. Furthermore, data from south and north of the Rio Grande Rise-Walvis Ridge complex (sites 700 and 530) are indistinguishable from the Turonian to Campanian, suggesting a common water mass since the Turonian at least. This view is supported by a reconstruction of the Rio Grande Rise-Walvis Ridge complex during the Turonian, highlighting the likely existence of a deep breach between the Rio Grande Rise and the proto-Walvis Ridge at that time. Thus deep-water circulation may have been possible between the different austral basins as early as the Turonian, despite the presence of potential oceanic barriers. Comparison of new seawater and residue εNd data on Nicaraguan Rise suggest a westward circulation of intermediate waters through the Caribbean Seaway during the Maastrichtian and Paleocene from the North Atlantic to the Pacific. This westward circulation reduced the Pacific water influence in the Atlantic, and was likely responsible for more uniform, less radiogenic εNd values in the North Atlantic after 80 Ma. Additionally, our data document an increasing trend observed in several oceanic basins during the Maastrichtian and the Paleocene, which is more pronounced in the North Pacific. Although the origin of this increase still remains unclear, it might be explained by an increase in the contribution of radiogenic material to upper ocean waters in the northern Pacific. By sinking to depth, these waters may have redistributed to some extent more radiogenic signatures to other ocean basins through deep-water exchanges.

Evolutionary biology : mass survivals

The conclusion that the primary divergences of the modern groups of mammals occurred in the mid-Cretaceous requires fresh thinking about this facet of evolutionary history — especially in ecological terms.

A molecular phylogeny for the Tribe Dacini (Diptera: Tephritidae) : systematic and biogeographic implications

With well over 700 species, the Tribe Dacini is one of the most species-rich clades within the dipteran family Tephritidae, the true fruit flies. Nearly all Dacini belong to one of two very large genera, Dacus Fabricius and Bactrocera Macquart. The distribution of the genera overlap in or around the Indian subcontinent, but the greatest diversity of Dacus is in Africa and the greatest diversity of Bactrocera is in south-east Asia and the Pacific. The monophyly of these two genera has not been rigorously established, with previous phylogenies only including a small number of species and always heavily biased to one genus over the other. Moreover, the subgeneric taxonomy within both genera is complex and the monophyly of many subgenera has not been explicitly tested. Previous hypotheses about the biogeography of the Dacini based on morphological reviews and current distributions of taxa have invoked an out-of-India hypothesis; however this has not been tested in a phylogenetic framework. We attempted to resolve these issues with a dated, molecular phylogeny of 125 Dacini species generated using 16S, COI, COII and white eye genes. The phylogeny shows that Bactrocera is not monophyletic, but rather consists of two major clades: Bactrocera s.s. and the ‘Zeugodacus group of subgenera’ (a recognised, but informal taxonomic grouping of 15 Bactrocera subgenera). This ‘Zeugodacus’ clade is the sister group to Dacus, not Bactrocera and, based on current distributions, split from Dacus before that genus moved into Africa. We recommend that taxonomic consideration be given to raising Zeugodacus to genus level. Supportive of predictions following from the out-of-India hypothesis, the first common ancestor of the Dacini arose in the mid-Cretaceous approximately 80 mya. Major divergence events occurred during the Indian rafting period and diversification of Bactrocera apparently did not begin until after India docked with Eurasia (50–35 mya). In contrast, diversification in Dacus, at approximately 65 mya, apparently began much earlier than predicted by the out-of-India hypothesis, suggesting that, if the Dacini arose on the Indian plate, then ancestral Dacus may have left the plate in the mid to late Cretaceous via the well documented India–Madagascar–Africa migration route. We conclude that the phylogeny does not disprove the predictions of an out-of-India hypothesis for the Dacini, although modification of the original hypothesis is required.

西南极南设得兰群岛中新生代火山岩基底沉积学及其大地构造制约

Livingston Island, the second island of South Shetland Island, constains Mesozoic-Cenozoic basement, Mesozoic-Cenozoic volcanic sequences, plutonic intrusions and post-subduction volcanic rocks, which document the history and evolution of an important part of the South Shetland Islands magmatic arc. The sedimentary sequence is named the Miers Bluff Formation (MBF) and is interpreted as turbidite since the first geological study on South Shetland Islands, and is interpreted as turbidite. It base and top are not exposed, but a thickness of more than 3000m has been suggested and seems plausible. The turbidite is overlain by Mid - Cretaceous volcanic rocks and intruded by Eocene tonalites. The age of the Miers Bluff Formation is poorly constrained Late Carboniferous -Early Triassic. Sedimentary Environment, tectonic setting and forming age of sedimentary rocks of the Miers Bluff Formation were discussed by means of the methods of sedimentology, petrography and geochemistry, combinig with the study of trace fossils and microfossil plants. The following conclusions are obstained. A sedimentary geological section of Johnsons Dock is made by outside measuring and watching, and then according the section, the geological map near the Spanish Antarctic station was mapped. Four pebbly mudstone layers are first distinguished, which thickness is about 10m. The pebbly mudstone is the typical rock of debris flow, and the depostional environment of pebbly mudstone may be the channel of mid fan of submarine fan. The sedimentsry structural characteristics and size analysis of sandstones show the typical sedimentary feature of turbidity flow and the Miers Bluff Formation is a deep-water turbidite (include some gravity-flow sediments). The materials of palaeocurrents suggest the continental slope dip to southeast, and indicate the provenance of turbidity sediment in the northwest area. By facies analysis, six main facies which include seven subfacies were recognized, which are formed in mid-fan and lower-fan of submarine, meanwhile, the sedimentary features of each facies and subfacies are summarized. The study of clastic composition, major elements, trace elements and rare earth elements indicates the forming setting of the Miers Bluff Formaton is active continental margin and continental island arc and the provenance is dissected magmatic arc which main composition is felsic gneiss. Many trace fossils of the whole succession were found in the turbidites of the Miers Bluff Formation. All these trace fossils are deep sea ichnofossils. There are fifteen ichnogenus, sixteen ichnospecies. Moreover, a new trace fossil was found and a new ichnogenus and new ichnospecies was proposed - Paleaichnus antarctics ichnogen, et ichnosp, nov.. Except the new ichnogenus and ichnospecies, others had been found in deep-sea flysch turbidites. Some are in mudstone and are preserved in the cast convex of overlying sandstone sole, they formed before turbidity flows occurred and belong to the high-different Graphoglyptida of fiysch mudstone. Others as Fucusopsis and Neonereites are preserved in sandstones and stand for trace assemblages after turbidity sedimentation. These trace fossils are typical members of abyssal "Nereites" ichnofacies, and provide for the depositional environment of the Miers Bluff Formation. Fairly diverse microfossil plants have been recovered from the Miers Bluff Formation, Livingston Island, including spores, pollen, acritarchs, wood fragments and cuticles. Containing a total of about 45 species (forms) of miospores, the palynofiora is quantitatively characterized by the dominance of non-striate bisaccate pollen, but spores of pteridophytes and pollen of gymnosperms are proportionate in diversity. It is somewhat comparable to the subzone C+D of the Alisporites zone of Antarctica, and the upper Craterisporites rotundus zone and the lower Polycingulatisporites crenulatus zone of Australia, suggesting a Late Triassic (possibly Norian-Rhaetian) age, as also evidenced by the sporadic occurrence of Aratrisporites and probable Classopollis as well as the complete absence of bisaccate Striatiti. The parent vegetation and paleoclimate are preliminarily deduced. At last, the paper prooses the provenance of sedimentary rocks of the Miers Bluff Formation locates in the east part to the southern Chile(or Southern South American). In the Triassic period, contrasting with New Zealand, Australia and South American of the Pacific margin of Gondwanaland, the Miers Bluff Formation is deposited in the fore-arc basin or back-arc basin of magmatic arc.

Palaeomagnetism, rock magnetism and AMS of the Cabo Magmatic Province, NE Brazil, and the opening of South Atlantic

P>Reconstruction of the South Atlantic opening has long been a matter of debate and several models have been proposed. One problem in tracing properly the Atlantic history arises from the existence of a long interval without geomagnetic reversals, the Cretaceous Normal Superchron, for which ages are difficult to assign. Palaeomagnetism may help in addressing this issue if high-quality palaeomagnetic poles are available for the two drifting continental blocks, and if precise absolute ages are available. In this work we have investigated the Cabo Magmatic Province, northeastern Brazil, recently dated at 102 +/- 1 Ma (zircon fission tracks, Ar39/Ar40). All volcanic and plutonic rocks showed stable thermal and AF demagnetization patterns, and exhibit primary magnetic signatures. AMS data also support a primary origin for the magnetic fabric and is interpreted to be contemporaneous of the rock formation. The obtained pole is located at 335.9 degrees E/87.9 degrees S (N = 24; A(95) = 2.5; K = 138) and satisfies modern quality criteria, resulting in a reference pole for South America at similar to 100 Ma. This new pole also gives an insight to test and discuss the kinematic models currently proposed for the South Atlantic opening during mid-Cretaceous.

Unique marine Permian-Triassic boundary section from Western Australia

A unique marine Permian-Triassic boundary section containing rich oil source rocks has been continuously cored in a petroleum borehole from the Perth Basin of Western Australia. Such sequences, which provide a biostratigraphic and environmental record at the time of the largest extinction event of the past 500 million years, are globally rare, and this is the first to be documented in Australia. Throughout geological history there have been periods of global marine anoxia that commonly resulted in the widespread deposition of petroleum source rocks, most notably in the mid-Cretaceous and Late Jurassic. An apparent paradox is that, previously, source rocks have not been recognised in association with the Permian-Triassic boundary, despite widespread marine anoxia at this time. The Perth Basin source rocks contain abundant and unusual biomarkers, apparently related to the highly specialised and limited biota that flourished in the aftermath of the end-Permian extinction event. Local conditions may have favoured source-rock development, either due to higher productivity resulting from coastal upwelling or through enhanced preservation under strongly anoxic conditions.

Biogeography on the early distribution of cuckoos (Aves: Cuculiformes)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Traços florais e filogenia em espécies lenhosas do cerrado

Pós-graduação em Ciências Biológicas (Botânica) - IBB

Sedimentary rocks of the Internal Hellenides, Greece: age, source, and depositional setting

Ziel der vorliegenden Dissertation war die Untersuchung der Liefergebiete und Ablagerungsräume sedimentärer Gesteine aus ausgewählten Gebieten der inneren Helleniden Griechenlands. Die untersuchten Sedimente Nordgriechenlands gehören zu den Pirgadikia und Vertiskos Einheiten des Serbo-Makedonische Massifs, zu den Examili, Melissochori und Prinochori Formationen der östlichen Vardar Zone und zur Makri Einheit und Melia Formation des östlichen Zirkum-Rhodope-Gürtels in Thrakien. In der östlichen Ägäis lag der Schwerpunkt bei den Sedimenten der Insel Chios. Der Metamorphosegrad der untersuchten Gesteine variiert von der untersten Grünschieferfazies bis hin zur Amphibolitfazies. Das stratigraphische Alter reicht vom Ordovizium bis zur Kreide. Zur Charakterisierung der Gesteine und ihrer Liefgebiete wurden Haupt- und Spurenelementgehalte der Gesamtgesteine bestimmt, mineralchemische Analysen durchgeführt und detritische Zirkone mit U–Pb datiert. An ausgewählten Proben wurden außerdem biostratigraphische Untersuchungen zur Bestimmung des Sedimentationsalters durchgeführt. Die Untersuchungsergebnisse dieser Arbeit sind von großer Bedeutung für paläogeographische Rekonstruktionen der Tethys. Die wichtigsten Ergebnisse lassen sich wie folgt zusammenfassen: Die ältesten Sedimente Nordgriechenlands gehören zur Pirgadikia Einheit des Serbo-Makedonischen Massifs. Es sind sehr reife, quarzreiche, siliziklastische Metasedimente, die auf Grund ihrer Maturität und ihrer detritischen Zirkone mit ordovizischen overlap-Sequenzen vom Nordrand Gondwanas korreliert werden können. Die Metasedimente der Vertiskos Einheit besitzen ein ähnliches stratigraphisches Alter, haben aber einen anderen Ablagerungsraum. Das Altersspektrum detritischer Zirkone lässt auf ein Liefergebiet im Raum NW Afrikas (Hun Superterrane) schließen. Die Gesteinsassoziation der Vertiskos Einheit wird als Teil einer aktiven Kontinentalrandabfolge gesehen. Die ältesten biostratigraphisch datierten Sedimente Griechenlands sind silurische bis karbonische Olistolithe aus einer spätpaläozoischen Turbidit-Olistostrom Einheit auf der Insel Chios. Die Alter detritischer Zirkone und die Liefergebietsanalyse der fossilführenden Olistolithe lassen den Schluss zu, dass die klastischen Sedimente von Chios Material vom Sakarya Mikrokontinent in der West-Türkei und faziellen Äquivalenten zu paläozoischen Gesteinen der Istanbul Zone in der Nord-Türkei und der Balkan Region erhalten haben. Während der Permotrias wurde die Examili Formation der östlichen Vardar Zone in einem intrakontinentalen, sedimentären Becken, nahe der Vertiskos Einheit abgelagert. Untergeordnet wurde auch karbonisches Grundgebirgsmaterial eingetragen. Im frühen bis mittleren Jura wurde die Melissochori Formation der östlichen Vardar Zone am Abhang eines karbonatführenden Kontinentalrandes abgelagert. Der Großteil des detritischen Materials kam von permokarbonischem Grundgebirge vulkanischen Ursprungs, vermutlich von der Pelagonischen Zone und/oder der unteren tektonischen Einheit des Rhodope Massifs. Die Makri Einheit in Thrakien besitzt vermutlich ein ähnliches Alter wie die Melissochori Formation. Beide sedimentären Abfolgen ähneln sich sehr. Der Großteil des detritischen Materials für die Makri Einheit kam vom Grundgebirge der Pelagonischen Zone oder äquivalenten Gesteinen. Während der frühen Kreide wurde die Prinochori Formation der östlichen Vardar Zone im Vorfeld eines heterogenen Deckenstapels abgelagert, der ophiolitisches Material sowie Grundgebirge ähnlich zu dem der Vertiskos Einheit enthielt. Ebenfalls während der Kreidezeit wurde in Thrakien, vermutlich im Vorfeld eines metamorphen Deckenstapels mit Affinitäten zum Grundgebirge der Rhodopen die Melia Formation abgelagert. Zusammenfassend kann festgehalten werden, dass die Subduktion eines Teiles der Paläotethys und die anschließende Akkretion vom Nordrand Gondwanas stammender Mikrokontinente (Terranes) nahe dem südlichen aktiven Kontinentalrand Eurasiens den geodynamischen Rahmen für die Schüttung des detritischen Materials der Sedimente der inneren Helleniden im späten Paläozoikum bildeten. Die darauf folgenden frühmesozoischen Riftprozesse leiteten die Bildung von Ozeanbecken der Neotethys ein. Intraozeanische Subduktion und die Obduzierung von Ophioliten prägten die Zeit des Jura. Die spätjurassische und frühkretazische tektonische Phase wurde durch die Ablagerung von mittelkretazischen Kalksteinen besiegelt. Die endgültige Schließung von Ozeanbecken der Neotethys im Bereich der inneren Helleniden erfolgte schließlich in der späten Kreide und im Tertiär.

Phylogenie und Biogeographie der Linoideae (Linaceae) - Evolution von Heterostylie, Homostylie in Linum

Die Linaceae-Linoideae, vor allem die Gattung Linum, wurden unter Verwendung von zwei molekularen Markern (rbcL und ITS) bzgl. ihrer Phylogenie und Biogeographie untersucht. Die Linaceae entstanden während der mittleren Kreide in den frühen tropischen Regenwäldern, von wo aus sich die monophyletischen Linoideae vor etwa 51-46 Mill. Jahren über die temperaten Gebiete der Nordhemisphäre ausbreiteten. Während die drei basal abspaltenden Gattungen Anisadenia, Reinwardtia und Tirpitzia bzgl. ihrer Verbreitung auf Südostasien beschränkt sind, ist die Gattung Linum heute auf allen Kontinenten vertreten. Der Ursprung von Linum liegt wahrscheinlich in Südwestasien bzw. dem östlichen Mediterraneum, wo es im Oligozän zur Aufspaltung in zwei Entwicklungslinien kam ('Blaue Gruppe' und 'Gelbe Gruppe'). Während die überwiegend blaublühenden Linum-Arten ('Blaue Gruppe') vor allem in Europa und Südwestasien vorkommen, weisen die Vertreter der 'Gelben Gruppe' ein wesentlich größeres Verbreitungsgebiet auf. Gelbblühende Linum Arten findet man auf allen Kontinenten mit Diversitätszentren in Nordostamerika und Südwestasien. Interessanterweise wurde Amerika zweimal unabhängig voneinander besiedelt. Während die gelbblühenden Arten vor etwa 22-20 Mill. Jahren von Westeuropa über den Atlantik den amerikanischen Kontinent erreichten, wanderten Vertreter der 'Blauen Gruppe' im Pliozän (vor 3.78-3.33 Mill Jahren) über die Bering-Landbrücke in die Neue Welt ein. Auch in Südafrika sind einige gelbblühende Linum-Arten zu verzeichnen, die nicht über Nordafrika (wo einige Arten der 'Gelben Gruppe' beheimatet sind) die südliche Spitze des Kontinents erreichten, sondern von Amerika aus. Die molekularphylogenetischen Ergebnisse legen eine Eingliederung der Gattungen Cliococca, Hesperolinon, Radiola und Sclerolinon in Linum nahe, die durch morphologische Merkmale gestützt wird. Linopsis, die artenreichste Sektion der Gattung Linum, bedarf einiger Umstrukturierungen auf der Basis der molekularen und morphologischen Daten. Ein interessantes Phänomen innerhalb der Linaceae ist das Vorkommen von heterostylen und homostylen Arten innerhalb der Familie. Die Kombination der molekular-phylogenetischen Ergebnisse mit morphologischen Beobachtungen des Reproduktionssystems lassen darauf schließen, dass sich Homostylie innerhalb von Linum mehrfach unabhängig voneinander entwickelt hat. Das Modell von Primula wurde als Grundlage verwendet, um Aufschluss über die Entstehung der Homostylie innerhalb von Linum zu erlangen. Aus Primula ist bekannt, dass eine Kopplungsgruppe aus mindestens drei Genen an der Vererbung von Heterostylie beteiligt ist: G/g kodiert hierbei die Griffellänge und die Selbstinkompatibilitäts-reaktion der Narbe, A/a die Länge der Filamente und P/p die Selbst-inkompatibilitätsreaktion des Pollens. Umfangreiche Kreuzungs-experimente einer homostylen und einer heterostylen Linum-Art deuten darauf hin, dass die Genotypen der beiden Blütenformen in heterostylen Linum-Arten denen in Primula entsprechen. Langgriffel sind hiernach homozygot rezessiv (gpa/gpa), während die Kurzgriffel heterozygot sind (GPA/gpa). Selbstkompatible, homostyle Arten können theoretisch durch verschiedene Rekombinations-ereignisse entstehen. Erste Ergebnisse der rasterelektronen-mikroskopischen Betrachtung der Pollenkornoberflächen und Narbenpapillen deuten darauf hin, dass innerhalb von Linum Homostylie durch unterschiedliche Rekombinations-ereignisse mehrfach aus heterostylen Arten entstanden ist. So besitzt die homostyle Linum leonii den Genotyp gPA/gPA, während für die homostylen L. tenuifolium und L. nodiflorum der Genotyp Gpa/Gpa wahrscheinlich ist.