Goniatites lazarus Korn, Klug, and Mapes 2005
Creators: name: Klug, Christian
name: Baets, Kenneth De
name: Korn, Dieter
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Ammonoidea
Goniatitidae
Goniatites
Goniatites lazarus

description: Goniatites lazarus Korn, Klug, and Mapes, 2005
Fig. 2−4.
Type material: Holotype GPIT 1851–97 (Korn et al. 2005: figs. 8.1, 8.2); paratypes MB.C. 5307 and MB.C. 5308.
Type locality: 12 km southeast of Dar Kaoua, southeast of Erfoud, eastern Anti –Atlas, Morocco.
Type horizon: Early late Viséan (Entogonites assemblage).
Material.— 25 juveniles: 6 in PIMUZ 31508, 1 in PIMUZ 31509, 6 in PIMUZ 31510, 2 in PIMUZ 31512, 1 in PIMUZ 31520, 2 in PIMUZ 31518, 7 in PIMUZ 31519. 4; adults: MB.C. 25130, PIMUZ 31514–16.
Emended diagnosis (modified after Korn et al. 2005).— Goniatites with an extremely broad spindle-shaped juvenile conch (dm 1.1–6 mm; ww/dm up to 1.76), later with a pachyconic conch up to 40 mm dm (ww/dm 0.70) and thickly discoidal conch at 70–100 mm diameter (ww/dm 0.6–1.00). Umbilicus almost closed (uw/dm 0.01–0.03) in all growth stages. Low aperture, moderate whorl expansion rate (1.7 in juvenile whorls, and nearly 2 near adulthood). The spindle-shaped juvenile whorls carry an umbilical ridge that vanishes at a diameter of about 7 mm. Suture line with V-shaped external lobe with slightly sinuous flanks, moderately high median saddle (one-third of the symmetric, narrowly rounded ventrolateral saddle). Shell ornament with crenulated growth lines with convex course in juvenile to adult whorls.
Description.—At diameters of 2–7 mm, the whorl width/diameter ratio ranges between 1.4 and almost 1.8 (e.g., PIMUZ 31512; Figs. 2–4; Table 2). This ratio lies between 1.4 and 1 in later ontogeny (dm <70 mm) and further decreases to 0.6 in the still pachyconic adults (PIMUZ 31514, dm 97 mm; Table 2). The umbilicus is very narrow throughout the post-hatching ontogeny. Until a diameter of about 7 mm, the spindle-shaped shell carries an umbilical ridge (PIMUZ 31512; Fig. 2A 3). Adult conchs are globose with rounded venter and very involute (PIMUZ 31514; Fig. 3). Ornamentation is limited to fine growth lines, which are rather straight in small juveniles (e.g., PIMUZ 31520; Fig. 2C 2) and can be slightly crenulated in adults (PIMUZ 31514). In PIMUZ 31515, the crenulation consists of 2 minute waves on the growth lines or lirae, which are spaced at 0.5–0.8 mm at a diameter of 85 mm. The juvenile suture is poorly visible in PIMUZ 31512; its overall course corresponds to the adult suture, but details are not visible in all juvenile specimens. The adult suture (PIMUZ 31514; Fig. 3) was examined at ca. 77 mm diameter. At this size, the V-shaped external lobe is almost twice as high as wide at the mid of its height. The median saddle measures 0.36 of the E-lobe height. The ventrolateral saddle has a nearly isosceles triangle-shape with shallow bulges near the bases and tops of both flanks and gentle concavity in the middle. Its adapertural tip is slightly asymmetrical and narrowly rounded. The adventive lobe is similar in size and shape, except that it is somewhat lower and broader.
Remarks.—The inner whorls of G. lazarus strongly resemble those of Kornia citrus Bockwinkel and Ebbighausen, 2006. We cut and polished two subadult G. lazarus from the same locality (Fig. 4A), which confirmed that the spindle-shaped juveniles indeed belong to this species and not to Kornia. With a conch width index (ww/dm) of up to 1.8, juveniles of this species belong to the ammonoids with the most extreme whorl width/diameter ratio. Similar changes in conch ontogeny have been documented from several goniatitids including, e.g., G. fimbriatus (Fig. 4B) and K. citrus (Fig. 4C).
Stratigraphic and geographic range.—Early late Viséan, so far only known from the Tafilalt (Morocco).
description: Published as part of Klug, Christian, Baets, Kenneth De & Korn, Dieter, 2016, Exploring the limits of morphospace: Ontogeny and ecology of late Viséan ammonoids from the Tafilalt, Morocco, pp. 1-14 in Acta Palaeontologica Polonica 61 (1) on pages 3-6, DOI: 10.4202/app.00220.2015, http://zenodo.org/record/10626349