Lithotrochus humboldtii (von Buch, 1839 )

Ferrari, S. Mariel, 2013, New Early Jurassic gastropods from west-central Patagonia, Argentina, Acta Palaeontologica Polonica 58 (3), pp. 579-593 : 581-582

Lithotrochus humboldtii (von Buch, 1839)

Fig. 2A .

1839 Pleurotomaria humboldtii ; von Buch 1839: 9, pl. 2: 26.

non 1942 Lithotrochus humboldti (von Buch, 1839) ; Wahnish 1942: 60–61, pl. 2: 4.

2008 Lithotrochus humboldtii (von Buch, 1839) ; Damborenea and Ferrari 2008: 202, figs. 4.1–21, 7.1 (see here for complete synonymy list).

Material.—MPEF−PI 4127; fragmentary, re−crystallized teleoconch. LT 1 site from Cerro La Trampa locality, Chubut province, Argentina, Mulanguiñeu Formation, Lower Jurassic, Upper Pliensbachian, Lower Toarcian.

Dimensions.—MPEF−PI 4127: height 35 mm; spire height 27.3 mm; width 35.1 mm; spire width 24.5 mm.

Description.—Dextral, anomphalous, medium sized, high spired and conical shell. The protoconch is not preserved. The three of four earlier teleoconch whorls are trochiform, becoming slightly cyrtoconoid during the last growth. The whorls are flat and the shell is gradated in outline, and the sutures are distinctly incised. The ornament is poorly developed on the shell surface; an adapical spiral keel or carina borders the periphery of each whorl. The base is flat and bordered by a strong spiral keel. The aperture is fragmentary.

Remarks.—According to the diagnosis given by Damborenea and Ferrari (2008), the single specimen here described shows the typical characters of Lithotrochus humboldtii . However, the present material does not show the diagnostic spiral cords of the species, probably due to its poorly preserved conditions. L. humbildtii was previously reported in the Early Jurassic (Pliensbachian) of Arroyo Pescado locality from Chubut province (see Damborenea and Ferrari 2008: fig. 4.21) Stratigraphic and geographic range.—Early Sinemurian– Late Pliensbachian Fanninoceras Zone ; Andean region of South America, from northern Peru to Argentinean Patagonia.

Lithotrochus cf. rothi Damborenea and Ferrari, 2008 Fig. 2B .

Material.—MPEF−PI 3581; fragmentary, re−crystallized teleoconch. LO 29 site from Lomas Occidentales locality, Chubut province, Argentina, Mulanguiñeu Formation, Lower Jurassic, Upper Pliensbachian, Lower Toarcian.

Dimensions.—MPEF−PI 3581: height 26 mm; spire height 17.6 mm; width 20.6 mm.

Description.—Dextral, anomphalous, conical, trochiform to cyrtoconoid, and medium sized shell. The protoconch is not preserved. The teleoconch consists of six whorls; the spire whorls are flat to slightly convex. The ornament is poorly developed; it consists of a spiral keel or carina that borders the periphery of each whorl. The aperture is circular and holostomatous, with a thin and smooth columellar lip. The base is slightly convex.

Remarks.—The cyrtoconoid shell with imbricate whorls and a peripheral carina suggest an assignment to Lithotrochus . The specimen here described strongly resembles Litotrochus rothi Damborenea and Ferrari (2008: 205 , fig. 6) from the Late Pliensbachian (Early Jurassic) of Neuquén province, Argentina. However, some diagnostic features of the species, such as spiral threads on the base and prosocline collabral lamellae on the lateral flanks of the whorls are not preserved in Lithotrochus cf. rothi .

Lithotrochus cf. rothi could be the first occurrence of the species in the Early Jurassic marine deposits of Chubut province.

Lithotrochus humboldtii (von Buch 1839) from the Sinemurian–Pliensbachian (Early Jurassic) of South America is very similar to Lithotrochus cf. rothi ; however, von Buch’s species is larger than the species here described, has strong spiral keels on the whorl flank intercepted with fine and prosocline growth lines, the adult teleoconch has two strong peripheral spiral keels, and fine growth lines appear on the base ( Damborenea and Ferrari 2008: 204, fig. 4).

Trochidae ? gen. et sp. indet. 1

Fig. 2C, D .

Material.—MPEF−PI 4120 and 4121; two fragmentary, recrystalized teleoconchs. LO 29 site from Lomas Occidentales locality, Chubut province, Argentina, Mulanguiñeu Formation, Upper Pliensbachian–Lower Toarcian, Lower Jurassic.

Dimensions.—MPEF−PI 4120: height 65.5 mm; width 81. 4 mm. MPEF−PI 4121: height 67.2 mm; width 77.3 mm.

Description.—Dextral, anomphalous, trochiform, conical, large sized and low spired shell. The protoconch is not preserved. In the best preserved specimens, the teleoconch comprises three/four whorls, with flat to slightly convex outline. Sutures are weakly incised. The shell is smooth or the orna−

http://dx.doi.org/10.4202/app.2011.0090

ment is poorly developed. The base is flat and the aperture fragmentary.

Remarks.—The general shell morphology of the specimens here described suggests that they may belong to Trochidae . However, the material is very poorly preserved, so it is left in open nomenclature.

Trochidae ? gen. et sp. indet. 2

Fig. 2E .

Material.—MPEF−PI 4122; one fragmentary, re−crystallized teleoconch. LT 2 site from Cerro La Trampa locality, Chubut province, Argentina, Mulanguiñeu Formation, Upper Pliensbachian–Lower Toarcian, Lower Jurassic.

Dimensions.—MPEF−PI 4122: height 12.7 mm; width 13.5 mm.

Description.—Trochiform, conical, low spired, and small sized shell. The protoconch is not preserved. The teleoconch consist of three flat whorls. Sutures are very weakly incised. The shell is smooth or the ornament is poorly developed. The base is flat, and the apertural characters are not preserved.

Remarks.—The single specimen here described seems to be a member of Trochidae ; however, as the material shows very few diagnostic characters to be included certainly into the family, it is left in open nomenclature. Trochidae ? gen. et sp. indet. 2 differs from Trochidae ? gen. et sp. indet. 1 in having flatter whorls and in being smaller.

Figures

Fig. 2. Early Jurassic gastropods from Lomas Occidentales and Cerro La Trampa fossiliferous localities. A. Lithotrochus humboldtii (von Buch, 1839), MPEF−PI 4127; teleoconch in lateral (A1, A2), latero−apical (A3), and apertural (A4) views. B. Lithotrochus cf. rothi Damborenea and Ferrari, 2008, MPEF−PI 3581; teleoconch in lateral (B1) and apertural (B2) views; apertural detail (B3); teleoconch in basal and apertural view (B4). C, D. Trochidae gen. et sp. indet. 1. C. MPEF−PI 4120, teleoconch in lateral views (C1, C2). D. MPEF−PI 4121, teleoconch in lateral view. E. Trochidae? gen. et sp. indet. 2., MPEF−PI 4122, teleoconch in lateral view. F–I. Pseudomelania feruglioi sp. nov. F. MPEF−PI 4155, holotype, juvenile teleoconch in apertural (F1) and oblique apertural (F2) views. G. MPEF−PI 4087, paratype, juvenile teleoconch in lateral view. H. MPEF−PI 4101, adult teleoconch in lateral view. I. MPEF−PI 4098, juvenile teleoconch in lateral view. Scale bars: A–E 10 mm, F–I 3 mm.