Tannuolina pavlovi, Kouchinsky & Bengtson & Murdock, 2010

Kouchinsky, Artem, Bengtson, Stefan & Murdock, Duncan J. E., 2010, A new tannuolinid problematic from the lower Cambrian of the Sukharikha River in northern Siberia, Acta Palaeontologica Polonica 55 (2), pp. 321-331 : 322-327

publication ID	https://doi.org/ 10.4202/app.2009.1102
persistent identifier	https://treatment.plazi.org/id/783987A1-C709-DF5B-FCE0-FB2F21EFD2C2
treatment provided by	Felipe
scientific name	Tannuolina pavlovi
status	sp. nov.

Treatment

Genus Tannuolina Fonin and Smirnova, 1967 Tannuolina pavlovi sp. nov.

Figs. 2–6 View Fig View Fig View Fig View Fig View Fig .

Etymology: In honour of geophysicist Dr. Vladimir Pavlov (Institute of Physics of the Earth, Moscow, Russian Federation) for his contributions to the geology of Siberia.

Type material: Holotype: SMNH X4102 View Materials , a complete sellate sclerite ( Figs. 2A View Fig , 3 View Fig ) . Paratypes: SMNH X4103 View Materials – X4106 View Materials , nearly complete sellate sclerites ( Fig. 2B–E View Fig ) and SMNH X4107 View Materials – X4115 View Materials , partial mitral sclerites ( Figs. 4 View Fig , 5A–C View Fig ) .

Type locality: 67°12'31''N; 87°22'58''E, Sukharikha River (right tributary of the Enisej River ), Igarka region, northern Siberia ( Fig. 1 View Fig ) GoogleMaps .

Type horizon: Base of the Krasnoporog Formation (same as sample A 301 in Kouchinsky et al. 2007: fig. 5), Nochoroicyathus sunnaginicus Biozone, Tommotian Stage , Lower Cambrian .

Material.—The material investigated consists of 10 nearly complete sellate sclerites, 15 partial mitral sclerites (usually fragments with apex), and more than 50 other fragments from the same sample. All fossils are preserved as calcium phosphate.

Diagnosis.—Species of Tannuolina with bilaterally symmetrical sellate and slightly asymmetrical mitral sclerites. Sellates with gently coiled apex and transversely convex sides without pronounced sella and duplicature; the lateral doi:10.4202/app.2009.1102

edges carry prominent rows of macropores that bifurcate toward the inner wall surface. Mitrals with apex slightly overhanging a flattened decrescent side and without carina on the inner surface.

Description.—The sellate sclerites are bilaterally symmetrical and triangular in outline, ranging in size (length of the available specimens in the plane of symmetry) between 0.5 and 2.0 mm, with an apical divergence angle of 45–60° ( Fig. 2 View Fig ). The apex overhanging the duplicatural side is coiled, up to 3/4 whorls in the largest specimen (holotype; Figs. 2A View Fig , 3 View Fig ). The aperture is lens−like in apertural view (corresponding to the cross−section perpendicular to the wall) ( Fig. 2E View Fig 4 View Fig ), but is crescent−like with the opposite growing edges arched towards the apex in duplicatural view (corresponding to a section oblique to the wall; Fig. 2A View Fig 1, D, E 1 View Fig ). The sellate and duplicatural surfaces of the sclerites are transversally convex, because of the absence of a pronounced sella and duplicature as developed in other species of Tannuolina . A narrow median depressed zone may be situated at the apex, on the sellate side (arrowed in Fig. 2B View Fig 1 View Fig ). This zone, which may be homologous to the sella, can be traced through a deflection of the co−marginal folds toward the apex at later growth stages ( Fig. 2B View Fig 1 View Fig ). The co−marginal folds cover the sellate and lateral sides of the sclerites ( Fig. 2A 2, B, C 2 View Fig ). The duplicatural side has narrower co−marginal folds with irregular boundaries and a lateral curvature toward the aperture ( Fig. 2A View Fig 1 View Fig , A 3 View Fig , A 4 View Fig , D, E 1 View Fig ). Fine pores, 1–2 µm in diameter, are situated on the sellate side ( Figs. 2A 2 View Fig , C, 3B View Fig ). These penetrate to about 3–15 µm depth and usually end in a bulb−like swelling, 3–4 µm in diameter ( Fig. 3D, G View Fig ). Coarser pores are aligned along the lateral margins, increasing in diameter towards the aperture from 5 µm at the tip of the apex ( Fig. 2E View Fig 6 View Fig ) to 40 µm in larger specimens ( Figs. 2A View Fig 3 View Fig , A 4 View Fig , B 3 View Fig , B 4 View Fig , C 1 View Fig , E 2 View Fig , E 3 View Fig , E 5 View Fig , 3 View Fig ). They regularly coalesce about 30–40 µm below the wall surface from an apically and an aperturally directed basal branch, forming an angle of nearly 90° ( Fig. 3F, H View Fig ). Pores of intermediate size concentrated to the sellate side do not show such a coalescence ( Fig. 3E View Fig ).

The mitral sclerites are slightly asymmetrical, rapidly expanding cones covered with co−marginal folds ( Figs. 4 View Fig , 5 View Fig ). The asymmetry is expressed by deflection of the apical part clockwise ( Fig. 4A View Fig 5 View Fig ) or counter−clockwise ( Fig. 4C View Fig 2 View Fig ) when the sclerites are seen in apical view. These forms may be homologous to the D− and L−forms of Tannuolina mitrals, respec−

doi:10.4202/app.2009.1102

tively (Qian and Bengtson 1989). Judging from larger fragments available in the material, the apertural width reached 2 mm ( Fig. 5B, D, E View Fig ). The decrescent side is flattened and triangular in shape ( Figs. 4A View Fig 3 View Fig , D 2 View Fig , 5A View Fig 4 View Fig ). It is delimited by sharp edges, where the growth lines change direction ( Figs. 4A View Fig 1, C 1 View Fig , 5A View Fig 1 View Fig , B, C 2 View Fig , D). The opposite (accrescent) side of the sclerite is convex ( Fig. 4A View Fig 2 View Fig , B 3, C 3 View Fig ) and passes into flattened lateral sides ( Fig. 4A View Fig 1 View Fig , A 5 View Fig , B 1 View Fig , D 3 View Fig ). The apex is tapered and overhangs the decrescent side ( Figs. 4A 4 View Fig , C 3 View Fig , D 4 View Fig , 5A View Fig 1 View Fig ). The aperture is not completely preserved in any of the specimens, but it appears to be broadly oval and more or less isometric, with the growing edge at the decrescent side arched towards the apex ( Fig. 5C View Fig 1 View Fig ). Pores are present on the entire surface, including the initial part. They are, however, scarce on the decrescent side ( Fig. 4B View Fig 1 View Fig ) and numerous on the accrescent side ( Figs. 4A–C View Fig , 5A View Fig 3 View Fig , B 1, C 1 View Fig ). The pores increase in size towards the aperture and medially, from 5–10 µm ( Fig. 5B, D, E View Fig ) to 40 µm (in bigger specimens). There is no evidence of coalescence of pores such as in the lateral areas of the sellate sclerites. No internal lamination has been observed in the specimens investigated with SRXTM ( Fig. 3 View Fig and Supplementary Online Material at http://app.pan.pl/SOM/app55-Kouchinsky_etal_SOM.pdf).

Comparison.— Tannuolina Fonin and Smirnova, 1967 includes three other species, T. multifora Fonin and Smirnova, 1967 , T. zhangwentangi Qian and Bengtson, 1989 , and T. fonini Esakova in Esakova and Zhegallo, 1996. The sellate sclerites of T. pavlovi sp. nov. are different from those of the other three species in the consistent absence of a pronounced sella and duplicature on the respective sides of sclerites, as well as in having regularly distributed large pores on the lateral edges. Qian and Bengtson (1989), however, noted that in some “sellate” sclerites of T. zhangwentangi the sella is less developed or absent, and that in those cases the duplicature is tightly adpressed to the apex. One of the “non−sellate sellates” they figured (Qian and Bengtson: fig. 54B) also has a recurved apex, similar to those of T. pavlovi and T. fonini , although it lacks the distinct row of lateral pores seen in T. pavlovi . In contrast to the other three species, the asymmetry of the mitral sclerites of T. pavlovi sp. nov. is not expressed by a radial furrow on the outer surface and a corresponding internal carina. Thus, there is no clear distinction between the carinate and obcarinate (lateral) sides. The mitral sclerites of T. pavlovi are also different from those of the other species in their having a tapered and slightly overhanging apex, and from T. multifora and T. fonini in having a more flattened decrescent side. Sclerites of Tannuolina from other localities typically have an internal wall structure consisting of loose, curving lamellae (cf. Fonin and Smirnova 1967). Such structures in the tomography scans of T. pavlovi sclerites are absent.

Remarks.—A single sclerite, flattened in the direction facing the decrescent side and curved laterally ( Fig. 6 View Fig ), is interpreted as an aberrant mitral sclerite of the same species. The sclerite carries pores on the accrescent side ( Fig. 6A View Fig ).

Stratigraphic and geographic distribution.—Known only from its type locality and horizon.