Gattenpleura pfeifferi Weyer 1976

Gattenpleura pfeifferi Weyer, 1976 Fig. 26; Table 17 Gattenpleura pfeifferi Weyer, 1976: 848, pl. 3 figs 1–7, text-figs 6–8. Gattenpleura pfeifferi – Weyer 1979: pl. 5 fig. 12. — Bartzsch & Weyer 1988: 44, text-fig. 3, photo 5. Diagnosis Species of Gattenpleura with thinly discoidal and involute conch at 30 mm dm (ww/dm ~ 0.40; uw/dm ~ 0.03). Whorl profile weakly depressed (ww/wh ~ 0.75); coiling rate low (WER ~ 1.60). Shallow lateral spiral groove, weak ribs with rursiradiate direction and convex course on the flank. Material examined Holotype GERMANY • Thuringia, Saalfeld-Obernitz, Pfaffenberg; bed 2 (“ Gattendorfia Limestone ”); Bartzsch Coll.; illustrated by Weyer (1976: pl. 3 figs 1–7); MB.C.764.1. Additional material GERMANY • 1 specimen; Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Denckmann 1912 Coll.; MB.C.765 • 1 specimen; Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1934 Coll.; BGRB X13404. Description Specimen MB.C.765 is a somewhat deformed but otherwise relatively well-preserved conch with a diameter of 32 mm (Fig. 26A). It is thinly discoidal with an almost closed umbilicus (ww/dm =0.39; uw/ dm =0.03) and has a low coiling rate (WER =1.61). The whorl profile shows an evenly rounded venter and almost parallel flanks with a shallow depression on the inner flank near the umbilicus caused by a shallow longitudinal groove. The umbilical margin is slightly raised. The ornament shows a change on the last whorl. Initially, only sharp growth lines are visible, but at about 24 mm conch diameter, flat, rounded plications appear, which become coarser on the second half of the last whorl. Their course is first radial from the umbilicus and they bend strongly backwards on the inner flank to form a rather narrow ventral sinus. On the venter the ribs are weaker than on the outer flank. Between the ribs and on the ribs stand sharp, dense growth lines. The smaller specimen BGRB X13404 (Fig. 26B) is 20 mm in diameter and is stouter with a slightly wider umbilicus (ww/dm =0.52; uw/dm=0.07) than in specimen MB.C.765; however, this can be explained by ontogenetic changes. It also shows incipient radial plications and a weaker dorsolateral depression. Remarks Gattenpleura pfeifferi differs from G. bartzschi in the much narrower umbilicus (uw/dm ~ 0.25) and less pronounced dorsolateral depression. The other similar species is Weyerella concava, which has a very similar conch form; however, this species has no ribs.Published as part of Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Gattendorf (Devonian-Carboniferous boundary; Upper Franconia, Germany), pp. 1-61 in European Journal of Taxonomy 883 on pages 52-53, DOI: 10.5852/ejt.2023.883.2179, http://zenodo.org/record/817786