Schubertellidae Skinner, 1931

Davydov, Vladimir I., 2011, Taxonomy, nomenclature, and evolution of the early schubertellid fusulinids, Acta Palaeontologica Polonica 56 (1), pp. 181-194 : 182-184

Family Schubertellidae Skinner, 1931 Genus Schubertella Staff and Wedekind, 1910

1910 Schubertella gen. nov.; Staff and Wedekind 1910: 121, pl. 4: 8. 1937 Schubertella Staff and Wedekind ; Thompson 1937: 120–121. 1937 Eoschubertella Thompson ; Thompson 1937: 123–124.

Type species: Schubertella transitoria Staff and Wedekind, 1910 , the exact location unknown (see discussion below), Spitsbergen, Carboniferous–Permian boundary transition.

Description.—Test small, usually less than 1–1.5 mm in length, ovoid to elongate fusiform with convex lateral slopes and sharply to bluntly pointed poles. The initial one−two volutions are nautiloid in outline with form ratio less than 1.0. They are coiled in one plane, but always skewed at large, but variable angles in regards to the following planispiral volutions. Mature forms consist of four−six volutions, 0.5 to 1.5 mm in length and 0.3 to 0.9 mm in width. Form ratio typically is 1.5–2.0 sometimes up to 3.0. The ratio of diameter of proloculus vs diameter of final volution of the test is 1:10 to 1:20 (proloculus/test ratio). The wall is composed of a primatheca (dark tectum and lighter lower layer), lighter upper layer on the chamber floors (upper tectorium). On well preserved specimens, small and straight (mural) pores penetrating entire wall can be seen ( Fig. 1C, H, I). Septa are numerous (up to 20 at maturity) and straight throughout the length of the test, except at the axial ends where they are sometimes slightly wavy. Chomata developed weakly to moderately and outlined the tunnel.

Remarks.—There is a puzzling story associated with the type−species of Schubertella , Schubertella transitoria Staff and Wedekind, 1910 . The authors originally presented drawings of two specimens (see Fig. 1A, B herein) that were regarded by them as dimorphic representatives of the species. Nevertheless, Thompson (1937: pl. 8: 4) designated only one of them ( Fig. 1A herein) “… as typical of S. transitoria ” ( Thompson 1937: 122) designating that way the lectotype of the type−species of Schubertella . The second specimen as noted by Thompson (1937), which has a very large proloculus, planispiral coiling and symmetrical volutions does not even belong to the genus. In my opinion this specimen probably is a juvenile form of Schellwienia that co−occurs with Schubertella in the original sample.

The “microspherical” specimen possesses an endothyroid juvenarium, but on the drawing it appears planispiral. Although, Hans von Staff generally photographed fusulinids, in the case of S. transitoria only a drawing was provided ( Staff and Wedekind 1910: pl. 4: 7, 8). Probably a magnification of over 100 times could not be technically accomplished by Hans von Staff at that time. Also, it might be that in the thin−section of the lectotype, the axis of the initial nautiloid volution was in the same plane as the thin−section and thus all volutions looked planispiral on the drawing. Staff and Wedekind (1910) mentioned two localities, Tempel Bay and Klas Billen Bay from which the samples they studied came, but they did not specify the exact location.

Although Thompson (1937) designated the lectotype from Staff and Wedekind’s (1910) publication, he found that the original material was lost. Thus, Thompson (1937) studied samples from several localities in Spitsbergen from which the collections obtained by Alfred G. Nathorst in 1882 and studied by Staff and Wedekind (1910) came. One collection came from Tempel Bay which Thompson thought could be from where one of the topotypes of S. transitoria came. He found there a specimen ( Thompson 1937, refigured herein as Fig. 1C) that since has been used as an illustrative reference to S. transitoria in many publications (Miklukho−Maklay et al. 1959; Thompson 1964; Loeblich and Tappan 1988). In the same paper in which he described the topotype of S. transitoria, Thompson (1937) erected the new subgenus Eoschubertella Thompson, 1937 with Schubertella lata Lee and Chen in volution of this specimen. D, E. Schubertella lata Lee and Chen in Lee at al., 1930. D. The Huanglungshan, Lungtan, S. China, Huanglung Limestone, Moscovian, repository unknown, axial section of holotype (as designated by Thompson 1937), from Lee et al. (1930: pl. 6: 9). E. Lower part of the Huanglung Limestone, the Huanglungshan, Lungtan, S. China, repository unknown, axial section of paratype, from Lee et al. (1930: pl. 6: 10). I. Mesoschubertella thompsoni Sakagami in Kanuma and Sakagami, 1957; limestone pebbles of the Tamanouchi limestone conglomerate from Hinode−mura, Nishitama−gun, Tokyo−to, Kwanto massif, Japan. 23918−A holotype (I 1); 23918−A (I 2) enlarged internal volutions of holotype showing the structure of the wall (arrow pointed to diaphanotheca) from Kanuma and Sakagami (1957: pl. 8: 6, 7). J. Mesoschubertella mullerriedi (Thompson and Miller, 1944) ; Secret Canyon section, 270.1 meters above the base of the section, Artinskian, Nevada. SUI 114209, sample WS8973; axial section (J 1), enlarged internal volutions (J 2) showing the structure of the wall with diaphanotheca. Scale bars A–G, I 2 and J 2 0.1 mm; H and J 1 0.5 mm.

doi:10.4202/app.2010.0026

Lee et al. (1930) as the type species (refigured herein Fig. 1D, E). The concept of this genus was somewhat loose at the beginning. Eoschubertella as described possesses many features of Schubertella except, as stated by Thompson (1937), it lacks a four−layered wall with diaphanotheca. However, later Thompson (1964) and more recently Groves (1991) recognized that Schubertella has a three−layered wall. The other major difference between Eoschubertella and Schubertella according to the original description is the minute size and ellipsoidal to subglobular outline in the former as opposed to the fusiform and generally larger size in the latter ( Thompson 1937; Groves 1991). Furthermore, Thompson (1937) specifically mentioned that Eoschubertella is early Pennsylvanian in age. Since that time fusulinid workers have reffered early– middle Pennsylvanian minute ellipsoidal to subglobular forms to Eoschubertella . I agree with the concept of considering minute globose to ellipsoidal forms as a separate genus. The irony, however, is that the type species of Eoschubertella , Schubertella lata Lee and Chen, 1930 is substantially larger than either the lectotype of Schubertella transitoria in Staff and Wedekind (1910) or specimens from Spitsbergen in Thompson (1937) ( Fig. 1A–E, herein). Schubertella lata , however, was printed with × 30 magnification, whereas specimens of Thompson (1937) from Spitsbergen were printed nearly three times larger, with × 84 magnification making S. lata appear as a “miniature” form. In the original description of S. lata ( Lee et al. 1930: 111) the authors mentioned the elliptical outline of the loosely coiled test with a total length 0.6–0.75 mm and form ratios 1.5–1.75, coiling of the first volution at nearly 90 ° in regards to outer volutions, small but distinct chomata and slightly wavy septa at the polar ends; the thin wall (20 µm) is three−layered, with a tectum and two tectoria. As stated by the authors (Lee and Chen in Lee et al. 1930: 111): “The absence of the light, transparent layer or diaphanotheca is, however, a fact beyond doubt”. All features of S. lata suggest its close resemblance to Schubertella transitoria at the generic level. Thus, in my opinion Eoschubertella is a junior synonym of Schubertella .

The genus Schubertina Marshall, 1969 , although not known widely, has always been placed in synonymy with Eoschubertella ( Loeblich and Tappan 1988; Groves 1991; Ueno in Fohrer et al. 2007), because it best fits the concept proposed by Thompson for Eoschubertella . However, since the type−species of the latter genus is a junior synonym of Schubertella , Schubertina becomes a valid taxon.

Another new genus Pseudoschubertella also has been erected by Marshall (1969: 124–125) with type−species Pseudoschubertella fusiforma Marshall, 1969 . The author agrees with Groves (1991) and Ueno in Fohrer et al. (2007) that Schubertina and Pseudoschubertella are very similar and belong to the same genus, and thus the latter is a synonym of the former.

Thompson (1948: 19) specifically pointed out that advanced Schubertella have a spirotheca composed of a tectum and relatively thick lower clear layer that he sometimes called the diaphanotheca. This group of schubertellids is also characterized by a relatively large test that usually exceeds 1–1.5 mm in length, has large chomata and septa strongly fluted in the polar ends. This group best fits the concept of Mesoschubertella Sakagami in Kanuma and Sakagami, 1957

(see below). Stratigraphic and geographic range.— Schubertella is distributed globally within the tropics−subtropics and known from Moscovian to Wordian ( Rauser−Chernousova et al. 1951; Skinner and Wilde 1966; Leven 1998a, b).