Cymaclymenia lambidia, Klein & Korn, 2014

Klein, C. & Korn, D., 2014, A morphometric approach to conch ontogeny of Cymaclymenia and related genera (Ammonoidea, Late Devonian), Fossil Record 17 (1), pp. 1-32 : 16-22

Cymaclymenia lambidia n. sp.

Figures 20 and 21

1960 Cymaclymenia involvens . – Petter, p. 47, pl. 7, fig. 20, 21, 23, pl. 8, fig. 6, 8–10.

1999 Cymaclymenia involvens . – Korn, p. 170, pl. 4, fig. 3, 4.

2002 Cymaclymenia involvens . – Becker et al., p. 165, 173.

Derivation of name: After the geographic region Lambidia in the Ma’der Basin.

Holotype: Specimen MB.C.22632.1 (Korn 1998 Coll.); illustrated here in Fig. 20a .

Type locality and horizon: Madène el Mrakib; 0–5 m below Hangenberg Black Shale, probably Parawocklumeria paradoxa Assemblage (late Famennian).

Material: 128 specimens with a maximum conch diameter of 65 mm.

Diagnosis: Species of Cymaclymenia with thinly discoidal conch in the adult stage (ww / dm = 0.35–0.40); whorl cross section weakly compressed (ww / wh = 0.80–1.00). Conch shape in the intermediate stage (10 mm dm) thickly discoidal and subevolute (ww / dm = 0.50; uw / dm = 0.30–0.35). Umbilical wall steep in the adult stage, flanks moderately converging, venter broadly rounded. Ornament with fine biconvex growth lines, without riblets.

Discussion: Cymaclymenia lambidia belongs to the stouter species of the genus and is by this character separated from most of the other species such as the co-occurring C. lambidia . Only few of the described species reach the adult ww / dm ratio of 0.35.

Specimens belonging to this new species have usually been assigned to Cymaclymenia involvens Lange, 1929 . Indeed this species is very similar in conch shape ( Fig. 22 ), and differences are mainly expressed in shell ornament. Two specimens from Wocklum are available from the type material of C. involvens : (1) the smaller holotype MB.C.3695 (27 mm dm), which is fairly well preserved with a rather coarse shell ornament, and (2) the larger paratype MB.C.3695 (42 mm dm), which is a poorly preserved, rather strongly corroded internal mould providing insight into the adult conch morphology. It is not certain that the two specimens belong to only one species. However the stratigraphic restriction of the type locality, in which almost exclusively the topmost Wocklum Limestone ( Wocklumeria denckmanni Zone ) yields ammonoids, suggests that the material is conspecific. The most probable stratigraphic position of the topotypes allows for the designation of time-equivalent specimens for a more precise characterisation of the species .

C. involvens differs from the other central European species of the genus in the stouter conch, which only in C. nephroides Korn, 1981 is even wider. Like the other two very common species C. striata ( Münster, 1832) and C. costellata ( Münster, 1832) , it possesses a rather coarse shell ornament with bundled growth lines and weak riblets around the umbilicus.

C. lambidia differs from the European and Uralian species in the much weaker ornament, which particularly in subadult specimens (about 20 mm conch diameter) appears to be absent and thus suggesting a smooth shell surface. Another difference of the new species from C. involvens is the slightly stouter conch in the juvenile stage of 8 mm conch diameter (ww / dm = 0.45–0.50 in C. lambidia ; ww / dm = 0.53 in C. involvens ) ( Fig. 23 ). This criterion, however, probably does not allow for a clear separation of the two species.

Becker et al. (2002, p. 165, 173) introduced a “ Cymaclymenia involvens Zone ” for specimens of this species. This zone should occur between two sandstone members near the top of the Late Devonian succession at Lambidia (Aguelmous, Ma’der Basin); the zone was placed above the “Hangenberg Black Shale event”. However, the authors did not recognise a major fault in the outcrop, which causes duplication of the higher beds; the so-called Cymaclymenia involvens Zone is thus not justified. The beds assigned to this zone (unit R in figure 4 of Becker et al., 2002) are a repetition of unit J1 (i.e. a rock unit below the “Hangenberg Black Shale event”).

Figures

Figure 20. Cymaclymenia lambidia n. sp. from the Anti-Atlas of Morocco; all × 1.0. (A) Holotype MB.C.22632.1 (Korn 1998 Coll.) from Madène el Mrakib. (B) Paratype MB.C.22632.2 (Korn 1998 Coll.) from Madène el Mrakib. (C) Paratype MB.C.22604.1 (Korn 1995 Coll.) from Erfoud. (D) Paratype MB.C.22604.2 (Korn 1995 Coll.) from Erfoud. (E) Paratype MB.C.22604.3 (Korn 1995 Coll.) from Erfoud. (F) Paratype MB.C.22677 (Wendt Coll.) from Aguelmous.

Figure 21. Cross sections (A–I; all × 1.5) and ontogenetic trajectories (J–M) of Cymaclymenia lambidia n. sp. from the Anti-Atlas of Morocco. (A) Paratype MB.C.22632.3 (Korn 1998 Coll.) from Madène el Mrakib. (B) Paratype MB.C.22652.1 (Kullmann Coll.) from Aguelmous. (C) Paratype MB.C.22648.1 (Korn 2009 Coll.) from Lambidia (Aguelmous). (D) Paratype MB.C.22652.2 (Kullmann Coll.) from Aguelmous. (E) Paratype MB.C.22652.3 (Kullmann Coll.) from Aguelmous.(F) Paratype MB.C.22652.4 (Kullmann Coll.) from Aguelmous. (G) Paratype MB.C.22652.5 (Kullmann Coll.) from Aguelmous. (H) Paratype MB.C.22667.1 (Wendt Coll.) from Tizi Ibaouane. (I) Paratype MB.C.22626.1 (Feist 1990 Coll.) from Madène el Mrakib. (J) Conch width index (ww/ dm). (K) Umbilical width index (ww /wh). (L) Whorl width index (uw / dm). (M) Whorl expansion rate (WER).

Figure 22. Cymaclymenia involvens Lange, 1929 from the Rhenish Mountains (Germany); all × 1.0. (A) Holotype MB.C.3695 (Lange 1923 Coll.) from Wocklum. (B) Paratype MB.C.3696 (Lange 1923 Coll.) from Wocklum. (C) Specimen MB.C.22698 (Korn 1975 Coll.) from Dasberg. (D) Specimen MB.C.22699 (Korn 1990 Coll.) from Dasberg.

Figure 23. Cross section (A; × 1.5) and ontogenetic trajectories (B–E) of Cymaclymenia involvens Lange, 1929 from the Rhenish Mountains of Germany. (A) Specimen MB.C.22696 (Korn 1977 Coll.) from Becke-Oese. (B) Conch width index (ww / dm). (C) Umbilical width index (ww/ wh). (D) Whorl width index (uw /dm). (E) Whorl expansion rate (WER).