Abstract
The Late Oxfordian ammonite faunas of the semimammatum and semiarmatum biohorizons are described, mostly based on material from the Impressamergel Formation of the Plettenberg Quarry near Dotternhausen (western Swabian Alb). 21 ammonite are recorded, including some previously undescribed from the Upper Jurassic of SW Germany. Previously, the semimammatum Biohorizon has been studied in Franconia, Western France and central Poland and the semiarmatum Biohorizon only in Western France, respectively. Compared to the semimammatum Biohorizon, the semiarmatum Biohorizon is characterized by a significant increase of Submediterranean and Tethyan taxa and a total decline of Subboreal ones. This phenomenon is interpreted as the result of a seawater warming trend towards the above following bimammatum Biohorizon, which correlates with the recently suggested Oxfordian/Kimmeridgian stage boundary. This article summarizes the current state of knowledge of the Hypselum Zone in SW Germany. A lectotype is designated for Richeiceras lochense (Oppel, 1863).
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