Neorotomaria obertraunensis, Szabó, 2017

Szabó, János, 2017, Gastropods of the Lower Jurassic Hierlatz Limestone Formation, part 3. New pleurotomarioideans from the fauna of Hierlatz Alpe (Hallstatt, Austria), Fragmenta Palaeontologica Hungarica 34, pp. 9-48 : 37-38

Neorotomaria obertraunensis n. sp.

( Figs 116–119, 130 )

pars 1861 Pleurotomaria princeps Koch et Dunker – STOLICZKA, p. 189, pl. 4, figs 7 a-c.

pars 2009 Pyrgotrochus ? cf. precatoria (J. A. Eudes-Deslongchamps, 1849) – SZABÓ, p. 47, Figure 39: D-E.

Type specimen – Holotype: GBA 2008/69/43/2/2.

Type locality – Hierlatz Alpe (Hallstatt, Austria) .

Type strata – Hierlatz Limestone within the Lower Sinemurian to lowermost Pliensbachian (Lower Jurassic) interval .

Derivation of name – Obertraun is a nearby village NE from the type locality.

Diagnosis – Conoidal shell consisting of convex early teleoconch whorls, separated by impressed suture; latest whorl(s) not preserved. Base feebly concave as whole with flat wall and broad umbilicus; abaxial rim of base angular. Selenizone position little below midwhorl. Early whorls with dense, sharp, collabral riblets crossed by few, marked spiral threads; granules subsuturally at crossings, strengthening subsequently as collabrally elongated elevations, weakening towards selenizone and making shell wavy. Early riblets gradually vanishing but new ones appearing along abapical suture together with new granules. Selenizone having midline thread with sparse and coarse lunulae on early teleoconch whorls then changing into smooth cord/carina.

Material – Single multi-damaged specimen without protoconch and latest whorls. On base of the latest whorl, trace of lost further whorl(s) is recognisable.

Measurements – Height of remnant: 20 mm, maximal diameter of shelly parts: 18 mm.

Description – Outline of the shell is conoidal, the remnants of the earliest and latest shell parts suggest trochiform undamaged shape. The whorls are convex without angulation, and rather low; they are about three times wider than their height (= distance of nearest sutures). A slightly impressed suture separates them while follows the outermost spiral cord of the base, running next to the angular periphery of the whorls. The position of the selenizone is little below the midwhorl; its submedian elevation provides the highest spiral line of the shell surface. The base is feebly concave with flat wall and a broadly open umbilicus, having a rounded angular basal rim. No part of the peristome is preserved but the remnants of a damaged whorl on the apparent base of the available specimen indicate a parietal lip, appearing as thin shell enamel that does not hide fully the coarse elements of the basal ornament (spiral cords).

The early teleoconch whorls are ornamented by dense, sharp, collabral riblets above and below the selenizone that are crossed by single marked spiral threads in the middle of both belts, resulting in a kind of network. Another strong spiral thread is just above the suture. Granules developed in the subsutural belt at the crossings. Subsequently these granules become sparser and strengthen as collabrally elongated, nod-like elevations, which are strongest at the suture and vanish before reaching the selenizone. The elevations are internally empty so making not only the shell but also the inner mould wavy. The early riblets gradually weaken then disappear but new, dense ones appear along the abapical suture together with rows of new granules. A few new spiral lines also appear during the growth, the earliest one below the adapical suture, subsequently one above the selenizone and one between the two strong treads above the suture. The earliest visible part of the median elevation on the selenizone is a thread with dense, granule-like lunulae that gradually become subaxially more elongated and thinner while the thread strengthens as cord. On the latest available whorl, the lunulae are fully absent and the elevation is a cord with smooth surface. The base is ornamented by 7–8 sparse, differently strong spiral ribbons that are crossed by dense, very thin collabral threads.

Remarks – In the available Neorotomaria obertraunensis specimen, angulation and ramp on the whorl surface do not appear at all. However, this statement is true only for the earliest whorls in N. subgradata n. sp, then an obscure angulation and ramp gradually develop for the latest whorls. Since the shape and ornament of the latest whorls of N. obertraunensis show clear divergences from the whorls of the same growth stages of N. subgradata , the unknown latest whorls of N. obertraunensis must be also different from the corresponding parts of the other species (see also Figs 129–130 ). Though the early teleoconch whorls have similar pattern of the ornament in both species, on the measurements and arrangement of its elements they are also distinguishable.

Distribution – Within Sinemurian to lowermost Pliensbachian (Lower Jurassic) part of the Hierlatz Limestone Formation in Hierlatz Alpe, Hallstatt, Austria.

Figures

Figs 116–130. Neorotomaria obertraunensis n. sp. and Neorotomaria subgradata n. sp. – 116–119. Neorotomaria obertraunensis n. sp., holotype (GBA 2008/69/43/2/2). – 116–117. Lateral view (×1 and ×3). – 118. Apertural view (×1). – 119. Basal view (×1). – 120–128. Neorotomaria subgradata n. sp. – 120–124. Holotype (GBA 2018/002/0014/01). – 120–121. Lateral view to show the outline of the shell (×2 and ×1). – 122. Apical view (×2). – 123. Lateral view with the largest surface of preserved ornament (×2). – 124.Basal view to document the presenceof a broad umbilicus (×1). – 125–128. Paratype (GBA 2018/002/0014/02) representing early shell parts of the species. – 125–126. Lateral view (×4 and ×1). – 127–128. Apical view (×4 and ×1). 129–130. Comparative images of two Neorotomaria species to follow the similarities and divergences in the development of the shells. – 129. Neorotomaria subgradata n. sp. (×3). – 130. Neorotomaria obertraunensis (×3)