Neoliothyrina nakremi Bitner, 2019

Hryniewicz, Krzysztof, Amano, Kazutaka, Bitner, Maria Aleksandra, Hagström, Jonas, Kiel, Steffen, Klompmaker, Adiël A., Mörs, Thomas, Robins, Cristina M. & Kaim, Andrzej, 2019, A late Paleocene fauna from shallow-water chemosynthesis-based ecosystems, Spitsbergen, Svalbard, Acta Palaeontologica Polonica 64 (1), pp. 101-141 : 103-105

Neoliothyrina nakremi Bitner sp. nov.

Figs. 2 , 3 .

?1927 Terebratulina sp. ; Gripp 1927: 30, pl. 6: 13–14.

2016 Pliothyrina ? sp.; Hryniewicz et al. 2016, table 2.

ZooBank LSID: urn:lsid:zoobank.org:act:C889EAF7-1909-4819-9B0E-9709A1EBA6ED

Etymology: In honour of Norwegian palaeontologist Hans Arne Nakrem, in recognition of his studies on fossil chemosynthesis-based faunas from Spitsbergen.

Type material: Holotype: ZPAL V.48/9-1, decorticated specimen with broken beak ( Fig. 3A ) . Paratypes: ZPAL V.48/9-2–4, decorticated specimens with broken beak ( ZPAL V.48/9-2) and anterior part ( ZPAL V.48/9-2–3); a set of acetate peels ( ZPAL V.48/9-4) ( Figs. 2 , 3B, C ) .

Type locality: Fossildalen , Spitsbergen, Svalbard .

Type horizon: Cold seep carbonates from the Basilika Formation, upper Paleocene .

Material. — 13 specimens ( ZPAL V.48/9-1–13), complete specimens, apart from the holotype all with broken anterior part, all from the type locality and horizon .

Measurements.— Holotype ( ZPAL V.48/9-1): L, 25.6 mm; W, 19.9 mm; H, 12.9 mm; other specimens inappropriate for measurements.

Diagnosis. —Small Neoliothyrina with rectimarginate anterior commissure. Outer hinge plates relatively wide, ventrally concave, inner hinge plates narrow and short, not contacting each other. Crural processes short, bluntly pointed. Loop short.

Description. —Shell of medium size, subpentagonal to elongate oval in outline, biconvex with ventral valve deeper. Shell surface smooth with numerous growth lines. Lateral commissure slightly ventrally convex, anterior commissure rectimarginate. Beak suberect with rounded beak ridges. Foramen large, circular, mesothyrid. Symphytium small, only partially visible.

Internal characters investigated in transverse serial sections. Cardinal process distinct, flat, surface with numerous grooves. Inner socket ridges thick, parallel to valve margin. Dental sockets moderately deep. Outer hinge plates relatively wide, ventrally concave, separated from inner hinge plates by distinct crural bases. Inner hinge plates short, narrow, not connecting. Crural processes short, tapering, slightly inwardly curving. Loop short, transverse band not preserved.

Remarks. —Probably the first record of this species is Terebratulina sp. described and figured by Gripp (1927), but the material is missing and the precise identification from the figure alone is impossible. The material studied herein was initially questionably assigned to Pliothyrina Roy, 1980 (see Hryniewicz et al. 2016); however, the investigations of internal structures suggest attribution to Neoliothyrina . Pliothyrina is known from the Oligocene to Pliocene in northern Europe ( Cooper 1983), while Neoliothyrina is known from the Upper Cretaceous (Santonian–Maastrichtian) of Great Britain, Germany, and Poland ( Steinich 1965; Popiel-Barczyk 1968; Cooper 1983). Both genera are characterized by the presence of inner hinge plates, a feature rarely present in terebratuloids ( MacKinnon and Lee 2006). Pliothyrina differs from Neoliothyrina in having very narrow or absent outer hinge plates and its crural processes are unusually long and curved anteromedially ( Cooper 1983), whereas the outer hinge plates are well-developed and the crural processes are bluntly pointed in Neoliothyrina . These characters are all observed in the material from Svalbard.

Due to the rectimarginate anterior commissure, very narrow and short inner hinge plate, and small crural processes, Neoliothyrina nakremi Bitner sp. nov. closely resembles the Maastrichtian Neoliothyrina plana Popiel-Barczyk, 1968 , from Poland. Neoliothyrina nakremi is, however, more elongate and more pentagonal compared with N. plana . Thus, the present finding extends the stratigraphical and geographical range of this genus into the Paleocene.

The investigated specimens differ strongly from the type species, Neoliothyrina obesa Davidson, 1852 . Neoliothyrina obesa is much larger than N. nakremi , having its anterior commissure distinctly biplicate and its inner hinge plates are well developed, contacting or even overlapping each other in many specimens ( Steinich 1965; Popiel-Barczyk 1968; Cooper 1983). Also, Neoliothyrina fallax ( Lundgren, 1885) has a larger maximum size than the taxon from Svalbard ( Brünnich Nielsen 1909; Popiel-Barczyk 1968) and exhibits a more curved beak and biplicate anterior commissure. The species Neoliothyrina fittoni ( Hagenow, 1842, assigned to this genus by Steinich 1965), is similar in size to N. nakremi but differs in the character of cardinal process; in N. fittoni , the cardinal process has a distinct cardinal knob that is very poorly developed in other Neoliothyrina species ( Steinich 1965; Popiel-Barczyk 1968).

The specimens assigned by Gripp (1927) to Terebratulina d’Orbigny, 1847 , undoubtedly belong to smooth, shortlooped terebratulides and most probably represent the new species described here. However, the genus Terebratulina is characterized by a ribbed surface, not seen on Gripp’s (1927) figures, and an incomplete foramen with disjunct deltidial plates, absent in the material studied herein.

Stratigraphic and geographic range. —Upper Paleocene cold seep carbonates from the Basilika Formation, Fossildalen, Spitsbergen, Svalbard.

Figures

Fig. 2. Transverse serial sections of the sellithyrid brachiopod Neoliothyrina nakremi Bitner sp. nov. paratype (ZPAL V.48/9-4) from the upper Paleocene, Basilika Formation, Fossildalen, Spitsbergen, Svalbard. L>20.2 mm. Numbers indicate distance in mm from the tip of the ventral umbo.

Fig. 3. Sellithyrid brachiopod Neoliothyrina nakremi Bitner sp. nov. from the upper Paleocene, Basilika Formation, Fossildalen, Spitsbergen, Svalbard. A. Holotype, ZPAL V.48/9-1, decorticated shell in ventral (A1), dorsal (A2), and posterior (A4) views; left-lateral view of both valves (A3). B. Paratype, ZPAL V.48/9-2; decorticated shell in ventral (B1), dorsal (B2), and posterior (B4) views; left-lateral view of both valves (B3). C. Paratype, ZPAL V.48/9-3, decorticated shell in ventral (C1), dorsal (C2), and posterior (C4) views; left-lateral view of both valves (C3).