Exploring the limits of morphospace: Ontogeny and ecology of late Viséan ammonoids from the Tafilalt, Morocco Author Klug, Christian Author Baets, Kenneth De Author Korn, Dieter text Acta Palaeontologica Polonica 2016 2016-01-18 61 1 1 14 http://dx.doi.org/10.4202/app.00220.2015 journal article 10.4202/app.00220.2015 1732-2421 10626349 Calygirtyoceras darkaouaense Korn, Klug, and Mapes, 1999 Fig. 5 . Holotype : GPIT 1851-87 ; Korn et al. 1999 : pl. 1: 7. Type locality : 12 km southeast of Dar Kaoua, southeast of Erfoud, eastern Anti-Atlas, Morocco . Type horizon : Early late Viséan ( Entogonites assemblage). Material .— 6 specimens : three juvenile conchs in PIMUZ 31509 , PIMUZ 31516 , PIMUZ 31519 ; two additional juveniles in PIMUZ 31508 ; an incomplete adult specimen with septal crowding in PIMUZ 31513 . Emended diagnosis (modified after Korn et al. 1999 ).— Calygirtyoceras with a juvenile cadiconic conch (dm 5–10 mm ; ww/dm 0.60–0.71), a transitional discoidal, platyconic preadult conch shape and a large, thinly discoidal, oxyconic adult conch (dm 100–150 cm ; ww/dm 0.30–0.40). Umbilicus very wide in juvenile growth stages (uw/dm 0.08; dm 5–10 mm ) and very narrow near adulthood (uw/ dm 0.10–0.15; dm> 50 mm ). Whorl expansion rate very low in juvenile whorls (dm < 10 mm ) and increasing to almost 3 at> 50 mm diameter. Adult ornamentation with fine, crenulated growth lines with biconvex and slightly rursiradiate course. Suture line with low median saddle (median saddle width/height ratio 0.30), broadly rounded ventrolateral saddle, and narrow external lobe (external lobe width/height ratio 0.55). Description .—PIMUZ 31516 ( Fig. 5B ) is a cadiconic juvenile with a thinly to thickly globular, very evolute conch. The whorl cross section is strongly depressed with a hardly vaulted venter; at the thickest part of the flanks, 12–15 small nodes are developed at a diameter below 10 mm per half whorl. In the subsequent ontogenetic stage, the venter becomes more and more vaulted and rounded. At a whorl height of about 30 mm (PIMUZ 31513), the cross section becomes subtriangular with gently rounded flanks. PIMUZ 31513 is a fragment of an adult conch (septal crowding at dm ca. 110 mm ). At this stage, the conch is extremely discoidal and involute ( Table 3 ). In this specimen, the external lobe is incompletely visible but V-shaped with a high ventrolateral saddle as present in the type-material. The V-shaped adventive lobe is inclined dorsally with a convex ventral flank. Remarks .—In the original species diagnosis by Korn et al. (1999) , the ontogenetic changes were described in a somewhat misleading way: in the same article, we ( Korn et al. 1999 : p. 354) had stated that the “Umbilicus [is] very narrow in early growth stages (uw/dm = 0.08 at 20–30 mm dm) and slightly opening during ontogeny (stages (uw/dm = 0.10 to 0.12 at 40–60 mm dm).” When measuring the umbilical width throughout the entire post-hatching ontogeny, a rather constant reduction of the uw/dm ratio from 0.62 to 0.14 was measured. Also, the latest growth stage was unknown previously. Stratigraphic and geographic range .—Early late Viséan, so far only known from the Tafilalt ( Morocco ).