Abstract
Excavations in the Sand district of Bergisch Gladbach (Rhenish Massif, Germany) yielded a rich ammonoid fauna of the upper Frasnian “Archoceras” varicosum Zone (Upper Devonian I-K, interval between the two Kellwasser levels). The previously unknown assemblages include six tornoceratid genera with 20 species, including seven new species (Aulatornoceras steinhauseni sp. nov., Aul. frenklerae sp. nov., Aul. ventrosulcatum sp. nov., Crassotornoceras nudum sp. nov., Cr. hetzeneggeri sp. nov., Retrotornoceras juxi sp. nov., Tornoceras aequilobum sp. nov.) and taxa described in open nomenclature. There are five associated gephuroceratid genera with nine species. The unexpectedly high genus- and species-level diversity at Sand, supported by statistical indices, is unprecedented compared to other contemporaneous ammonoid faunas. It highlights the currently fragmentary knowledge of top-Frasnian ammonoid faunas on a global scale. Phoenixites frechi, the dominant tornoceratid of hypoxic and organic-rich Kellwasser facies of Europe and North Africa, is completely missing at Sand. The local assemblage structure is analyzed statistically and interpreted in terms of palaeoecology. The occurrence of a new type of “Housean Pits”, probably caused by parasitism, is found in nine species of five genera, mostly in tornoceratids. The Sand fauna indicates that the species origination rate in tornoceratids remained high after the Lower Kellwasser Event.
Highlights
The upper Frasnian Kellwasser Crisis was a 1st order global extinction event (e.g., Raup and Sepkoski 1982; Schindler 1990; Racki 2005; De Vleeschouwer et al 2017; Carmichael et al 2019), which was especially severe in pelagic organism groups, and notably in ammonoids (e.g., Becker 1993a, b; Becker and House 1993, 1994)
Detailed morphological comparisons can address the question of whether supposed representatives of upper Frasnian and lower Famennian taxa belonged to single species or whether there was a morphological and taxonomic change in the intervening Lazarus phases
The results of our study provide a first step towards an understanding of upper Frasnian tornoceratid diversity, extinction, and origination rates
Summary
The upper Frasnian Kellwasser Crisis was a 1st order global extinction event (e.g., Raup and Sepkoski 1982; Schindler 1990; Racki 2005; De Vleeschouwer et al 2017; Carmichael et al 2019), which was especially severe in pelagic organism groups, and notably in ammonoids (e.g., Becker 1993a, b; Becker and House 1993, 1994). Various authors claimed that the Kellwasser Crisis is better characterized by a significant reduction of speciation rates, rather than by elevated extinctions, leading indirectly to an absolute decrease in biodiversity (e.g., Bambach et al 2004; Stigall 2012) In this context, the study of upper Frasnian goniatites, and especially of tornoceratids, becomes an important topic. Even today substantial gaps of knowledge exist and require ongoing palaeontological research One of these gaps is the long neglected goniatite fauna of the upper Frasnian Sand Formation. Based on unpublished collections by KJH, HF, and HS, we present a comprehensive survey of the rich and unexpectedly diverse Sand ammonoid fauna, with a focus on the tornoceratids. Isolated specimens that cannot be placed in the new succession are listed in Table 1 in the “+” column
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