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Evaluating the Frasnian-Famennian mass extinction: Comparing brachiopod faunas

100%

Copper P.

Acta Palaeontologica Polonica

1998

tom 43

nr 2

The Frasnian-Famennian (F-F) mass extinctions saw the global loss of all genera belonging to the tropically confined order Atrypida (and Pentamerida): though Famennian forms have been reported in the literafure, none can be confirmed. Losses were more severe during the Givetian (including the extinction of the suborder Davidsoniidina, and the reduction of the suborder Lissatrypidina to a single genus), but origination rates in the remaining suborder surviving into the Frasnian kept the group alive, though much reduced in biodiversity from the late Early and Middle Devonian. In the terminal phases of the late Palmatolepis rhenana and P. linguiformis zones at the end of the Frasnian, during which the last few Atrypidae dechned, no new genera originated, and thus the Atrypida were extirpated. There is no evidence for an abrupt termination of all lineages at the F-F boundary, nor that the Atrypida were abundant at this time, since all groups were in decline and impoverished. Atypida were well established in dysaerobic, muddy substrate, reef lagoonal and off-reef deeper water settings in the late Givetian and Frasnian, alongside a range of brachiopod orders which sailed through the F-F boundary: tropical shelf anoxia or hypoxia seems implausible as a cause for atrypid extinction. Glacial-interglacial climate cycles recorded in South America for the Late Devonian, and their synchronous global cooling effect in low latitudes, as well as loss of the reef habitat and shelf area reduction, remain as the most likely combined scenarios for the mass extinction events.

Revision of latest Givetian-Frasnian Atrypida [Brachiopoda] from central North America

63%

Day J., Copper P.

Acta Palaeontologica Polonica

1998

tom 43

nr 2

The brachiopod fauna of the Middle-Late Devonian cratonic carbonate platform deposits of the Iowa Basin, central North America, contains twenty species of the order Atrypida, some of which are types for widespread genera common in Middle and Late Devonian faunas. The latest Givetian-early Frasnian deposits yield a diverse fauna consisting of ten species (two new) included in Desquamatia (Independatrypa), D. (Seratrypa), Pseudoatrypa, Radiatrypa, Spinatrypa (Spinatrypa) and Spinatrypina (Exatrypa). Many of these forms occur in, or are closely similar to species known from, coeval faunas of central and western Canada. Middle Frasnian deposits of northern Iowa contain two species included in Spinatrypa (S.) and Pseudoatrypa, both of which are new. Late Frasnian strata of the Iowa Basin yield eight species included in Costatrypa, Iowatrypa, Pseudoatrypa, and Spinatrypa (Spinatrypa), some of which are widespread in other subtropical and tropical faunas of the western US and western Canada. The taxa Pseudoatrypa witzkei sp. n., Spinatrypa (S.) bunkeri sp. n., Spinatrypa (S.) thompsoni sp. n., and Spinatrypina (Exatrypa) johnsoni sp. n. are proposed. Pseudoatrypa? sp. from the very late Frasnian of southern New Mexico is also illustrated.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Copper P.

1 Day J.

2 1998

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Evaluating the Frasnian-Famennian mass extinction: Comparing brachiopod faunas

Revision of latest Givetian-Frasnian Atrypida [Brachiopoda] from central North America