Introduction

Intraspecific variation of conch shape has been documented for many Mesozoic ammonoids (e.g., Aguirre-Urreta, 1998; Bhaumik et al., 1993; Dagys and Weitschat, 1993a, b; Mitta, 1990; Tanabe, 1993), while Paleozoic ammonoids are commonly regarded as expressing much less variability. Traditionally, species concepts which

N. H. Landman et al. (eds.), CephalopodsPresentandRst:NewInsightsandFreshPerspectives, 57-85. © 2007 Springer.

were applied on Devonian ammonoids were strictly typological and based on the holotype and few paratypes. The investigation of larger populations was only rarely achieved (cf. Dzik, 1985 for Mesozoic ammonoids). However, it is urgently required to apply new methods such as population studies for a better understanding of phylogenetic relationships, intraspecific variability, and spatial biodiversity.

During the last 20 years, the Montagne Noire emerged as one of the most important regions in which Devonian sedimentary rocks are exposed. Detailed studies of the fossiliferous sections of pelagic sediments documented the completeness of the successions. This resulted in the designation of three global stratotypes, for the Givetian-Frasnian boundary at Col du Puech de la Suque (Klapper et al., 1987), for the Frasnian-Famennian boundary at Coumiac (Klapper et al., 1993), and for the Devonian-Carboniferous boundary at La Serre (Paproth et al., 1991).

The composition of ammonoid assemblages from immediately below and above the Frasnian-Famennian boundary in the abandoned quarries at Coumiac (Fig. 3.1) was already documented by House et al. (1985) and Becker and House (1993). They showed that ammonoid diversity decreased dramatically at the global Kellwasser event at the end of the Frasnian stage (Fig. 3.2).

The entire suborder Gephuroceratina, whose species dominated the Frasnian assemblages, disappeared at the top of the upper Kellwasser Horizon. After an earliest Famennian interval with an extremely sparse ammonoid fauna, the Tornoceratina experienced a rapid diversification.

Ammonoids from lower in the section, i.e., from intensely red-colored nodular limestones of Frasnian age, which have been commercially exploited in the

Fig. 3.1 Map of the Montagne Noire (southern France) with outcrops of Devonian rocks and the ammonoid-bearing locality at Coumiac.

Upper Kellwasser Horizon

Lower Kellwasser Horizon ^(sample of Manticoceras

Fig. 3.2 Ammonoid stratigraphy and regional conodont stratigraphy of the Frasnian (Late Devonian). The asterisk marks the age of the Manticoceras-bearing horizon in Coumiac.

Upper Kellwasser Horizon

Lower Kellwasser Horizon ^(sample of Manticoceras

Fig. 3.2 Ammonoid stratigraphy and regional conodont stratigraphy of the Frasnian (Late Devonian). The asterisk marks the age of the Manticoceras-bearing horizon in Coumiac.

Coumiac quarry, are known since the end of the 19th century. Böhm (1935) figured a few specimens of Manticoceras and Beloceras, all of which are stored under the catalogue number UMDK in the Institut des Sciences de l'Evolution Montpellier (ISEM). In addition to these specimens, a suite of more than 100 specimens, assembled by the private collector J. Albeille, is available for study. Most likely, these specimens came from a single horizon. This collection is of considerably high value due to the current inability to extract such large numbers of specimens from the abandoned quarry.

The specimens belonging to Manticoceras display a remarkable variability in the unfolding of conch parameters in their ontogenetic development, and hence assignment to distinct species is extremely difficult or even impossible. This study is thus mainly focused on the range of morphological variability, rather than on taxonomic descriptions.

Intraspecific coiling variability among manticoceratid ammonoids has been known for a long time. It was explicitly noticed by Clarke (1899), but subsequent authors paid relatively little attention to this phenomenon when they described assemblages from various regions in a kind of parataxonomy. Perhaps this is one reason for the immense number of species which were attributed to Manticoceras. Until now, at least 85 species names are available for ammonoids that belong to Manticoceras and closely related genera, all of which are assembled in the family Gephuroceratidae (for an overview, see Korn and Klug, 2002). These were described in numerous monographs, of which those by Bogoslovsky (1958, 1969), Clarke (1899), Clausen (1969), Glenister (1958), Miller (1938), Petter (1959), and Wedekind (1913, 1918) provide an overview of the diversity of the Gephuroceratidae.

If one reduces the morphological range of the genus Manticoceras s. str., i.e., by separation of the oxyconic forms as Carinoceras, the more globose as Sphaeromanticoceras, etc. (as done by Becker and House, 1993), there still remain more than 40 species names. Considering that the ornament of all these species is very similar and that all have similar suture lines, species discrimination is mainly possible by using conch parameters. As we will show, these parameters are very plastic and uncover major problems in manticoceratid systematics. This can not only be demonstrated for the material from Coumiac, but also for supplementary samples of manticoceratids from the Rhenish Mountains, the Eifel Mountains, etc.

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