Cryptaulax nulloi, Ferrari, 2009

Ferrari, S. Mariel, 2009, Cosmopolitan Early Jurassic marine gastropods from west-central Patagonia, Argentina, Acta Palaeontologica Polonica 54 (3), pp. 449-461 : 457-459

Cryptaulax nulloi sp. nov.

Fig. 3F–H .

Etymology: Dedicated to Francisco E. Nullo.

Type material: Holotype, MPEF−PI 1870 , well preserved teleoconch; paratype, MPEF−PI 1861 , poorly preserved teleoconch.

Type horizon: Osta Arena Formation, Lower Toarcian, Jurassic .

Type locality: PA 06 site, “ El Córdoba ” fossiliferous locality .

Other material.—MPEF−PI 1862, MPEF−PI 1866, MPEF−PI 1873, MPEF−PI 1881, MPEF−PI 1869, MPEF−PI 1871, and MPEF−PI 1885, poorly preserved teleoconch fragments.

Diagnosis.—Anomphalous and turriculate shell. Juvenile teleoconch characterized by predominance of axial ornament and presence of weak nodes. Adult teleoconch with spiral ornament predominant, consisting of two strong ribs near the suture both in adapical and abapical parts of the flank, and weaker ribs between. On adult teleoconch whorls conspicuous nodes are present. Subcircular holostomatous aperture.

Description.—Dextral, small−sized, and high−spired shell, anomphalous, slender and turriculate. Protoconch is not preserved. Teleoconch comprises eight whorls which are straight in outline. Sutures are well delimited and bordered by two spiral ribs. Teleoconch ornament consists of spiral and axial ribs with nodose intersections. The early teleoconch whorls (juvenile stage) differ from the adult stage in having a strongly axial ornament pattern, with orthocline ribs intersecting two weak spiral ribs near the sutures. At the intersections of axial and spiral ribs, eight weak nodes are developed. The mature ornament of the teleoconch stabilizes on the fifth whorl; a strong spiral ornament appears and the axial ribs become weaker. The spiral elements comprise two strong ribs near the sutures; additionally, a number of much weaker ribs appears. The presence of strong spiral ribs near the suture gives the whorl face a concave appearance. Base is convex and ornamented with four spiral ribs. The aperture is holostomatous and subcircular.

Dimensions.—See Table 1.

Discussion.—The presence of strong axial and weak spiral ribs on juvenile teleoconch whorls allow this material to be identified as Cryptaulax . The adult teleoconch whorl with strong spiral ribs and conspicuous nodes separate C. nulloi sp. nov. from other species of the genus. Cryptaulax nulloi sp. nov., C. damboreneae sp. nov., and C. cf. damboreneae are the first cryptaulacins recorded from the Early Jurassic of Argentina. C. nulloi sp. nov. and C. damboreneae sp. nov. are similar in having a small−sized high−spired shell and axial and spiral ribs with nodose intersections. C. nulloi nov. sp., however, has weakly developed axial ribs and much better developed spiral ribs during ontogeny. C. damboreneae sp. nov. is slightly smaller than C. nulloi sp. nov., has fewer nodes and strong axial ornament pattern on all growth stages. C. cf. damboreneae differs from C. nulloi sp. nov. in having better developed axial ribs and more spiral ribs.

Stratigraphic and geographic range.— PA−06 site, from “El Córdoba ” fossiliferous locality, Chubut province, Argentina. Osta Arena Formation, Lower Toarcian , Lower Jurassic .

Figures

Fig. 3. Early Jurassic gastropods from Argentina A. Zygopleuridae? gen. et sp. indet., “El Córdoba” fossiliferous locality, Chubut Province. MPEF−PI 1886, latex cast of external mold in lateral view. B–D. Cryptaulax damborenae sp. nov., “El Córdoba” fossiliferous locality, Chubut Province. B. MPEF−PI 1878b, holotype, latex cast of external mold in lateral (B1, B2) and basal (B3) views, ornament detail (B4). C. MPEF−PI 1877, paratype, latex cast of external mold of incomplete teleoconch in apertural view. D. MPEF−PI 1872b, paratype, latex cast of external mold of incomplete teleoconch in lateral view. E. Cryptaulax cf. damboreneae sp. nov., Cerro Puchenque locality, Mendoza Province. MLP 18742, latex cast of external mold of incomplete teleoconch; adult teleoconch in lateral view. F–H. Cryptaulax nulloi sp. nov., “El Córdoba” fossiliferous locality, Chubut Province. F. MPEF−PI 1870, holotype, latex cast of external mold. Adult teleoconch in lateral view (F1), juvenile teleoconch in lateral view (F2). G. MPEF−PI 1861, paratype, latex cast of external mold in lateral and apertural view. H. MPEF−PI 1871, latex cast of external mold of incomplete teleoconch in lateral view (H1), and its ornament detail (H2). Scale bars 1 mm.