Autopsy of a biological extinction example: the Frasnian-Famennian boundary crisis (364 Ma)

Without studying the causes of the F/F boundary mass extinction, the precise analysis of ostracod species shows evolutionary process only discernable it the global scale. About 75 % of ail species disappeared in the Uppermost Frasnian in all studied regions of the world. Others survived, with some geographic changes, owing to littoral refuges (Lazarus effect). Deep benthic ostracods seem almost untouched by this event. We show that new post-event species resulted front allopatric speciations by migration between neritic provinces or along continental slopes towards deeper environments. During the event, surviving lineages show a continuous gradation from unscathed species to chronocline species, to phyletic subspeciations or speciations (=pseudo-extinctions) and even to new genera. The durability of lineages is controlled by the migration of populations. (C) 1999 Academie des sciences

New ophthalmosaurid ichthyosaurs from the European lower cretaceous demonstrate extensive ichthyosaur survival across the Jurassic–Cretaceous boundary

Background Ichthyosauria is a diverse clade of marine amniotes that spanned most of the Mesozoic. Until recently, most authors interpreted the fossil record as showing that three major extinction events affected this group during its history: one during the latest Triassic, one at the Jurassic–Cretaceous boundary (JCB), and one (resulting in total extinction) at the Cenomanian-Turonian boundary. The JCB was believed to eradicate most of the peculiar morphotypes found in the Late Jurassic, in favor of apparently less specialized forms in the Cretaceous. However, the record of ichthyosaurs from the Berriasian–Barremian interval is extremely limited, and the effects of the end-Jurassic extinction event on ichthyosaurs remains poorly understood. Methodology/Principal Findings Based on new material from the Hauterivian of England and Germany and on abundant material from the Cambridge Greensand Formation, we name a new ophthalmosaurid, Acamptonectes densus gen. et sp. nov. This taxon shares numerous features with Ophthalmosaurus, a genus now restricted to the Callovian–Berriasian interval. Our phylogenetic analysis indicates that Ophthalmosauridae diverged early in its history into two markedly distinct clades, Ophthalmosaurinae and Platypterygiinae, both of which cross the JCB and persist to the late Albian at least. To evaluate the effect of the JCB extinction event on ichthyosaurs, we calculated cladogenesis, extinction, and survival rates for each stage of the Oxfordian–Barremian interval, under different scenarios. The extinction rate during the JCB never surpasses the background extinction rate for the Oxfordian–Barremian interval and the JCB records one of the highest survival rates of the interval. Conclusions/Significance There is currently no evidence that ichthyosaurs were affected by the JCB extinction event, in contrast to many other marine groups. Ophthalmosaurid ichthyosaurs remained diverse from their rapid radiation in the Middle Jurassic to their total extinction at the beginning of the Late Cretaceous

Ostracods and sedimentology of the La Serre Devonian/Carboniferous stratotype section (La Serre, Montagne Noire, France)

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Les ostracodes pendant l’événement Hangenberg au passage Dévonien/Carbonifère, en Montagne Noire.

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Ostracods and rock facies associated with the Devonian-Carboniferous boundary series in the Puech de la Suque section, Montagne Noire, France.

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Ostracods and sedimentology of the Frasnian-Famennian boundary beds in the Kostomloty section (Holy Cross Mountains, Poland)

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Les ostracodes au passage Frasnien/Famennien dans les Monts Sainte-Croix de Pologne.

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Ostracods and fore-reef sedimentology of the Frasnian-Famennian boundary beds in Kielce [Holy Cross Mountains, Poland]

Four major microfacies have been recognized in the Psie Górki section and the bioclastic content indicates an open marine environment in the photic zone close to an algal shole. Sedimentological studies point to a regressive episode starting close to the Frasnian–Famennian boundary. The regressive microfacies pattern is revealed by the presence of semirestricted algal microbreccias that compose all of the lower part of the Famennian. The regression was accompanied by meteoric water invasion as the sea level fell. Seventy−six ostracod species are recorded. The ostracod assemblage, dominated by podocopids, belongs to the Eifelian ecotype and is indicative of a well−oxygenated marine environment below fair−weather wave base in the Frasnian part of the section, and of shallower environments in the base of the Famennian. No ostracod assemblage characteristic of hypoxic or semi−restricted water conditions has been recorded. The rate of extinction of ostracod species (>70%) close to the Frasnian–Famennian boundary is comparable with that known on the same level in several other sections investigated in the world. Five new ostracod species are proposed by J.−G. Casier and F. Lethiers: Selebratina vellicata, Samarella? minuta, Bairdiocypris ventrorecta, Acratia pentagona, and “Bairdia” psiegorkiensis

Ostracods and fore-reef sedimentology of the Frasnian-Famennian boundary beds in Kielce (Holy Cross Mountains, Poland)

info:eu-repo/semantics/publishe