Revision of Tornoceras typus (Sandberger & Sandberger, 1851) – an iconic Devonian ammonoid of a clade with slow morphological evolution

Abstract

The ammonoid species Tornoceras types (SANDBERGER & SANDBERGER, 1851) (middle Frasnian, Late Devonian) is revised on the basis of the original material and material from the eastern margin of the Rhenish Mountains. The detailed investigation of the conch form and its ontogeny requires a more restrictive species diagnosis; a separation from morphologically similar forms from other stratigraphic units is necessary. Material from the Rhenish Mountains formerly attributed to Tornoceras typus (or "Tornoceras simplex") are newly described here as Tornoceras vretterense n. sp. (Givetian) and Tornoceras fundibulum n. sp. (early Famennian). In addition, the new tornoceratid species Domanikoceras martenbergense n. sp. (middle Frasnian) and Linguatornoceras asbeckense n. sp. (late Frasnian) are described. The morphological and stratigraphic data suggest that both Tornoceras and Linguatornoceras survived the Kellwasser crisis.