Sigillariostrobus saltwellensis, Thomas & Seyfullah, 2016

Thomas, B. A. & Seyfullah, L. J., 2016, Two new species of megasporangiate Sigillariostrobus Schimper (Sigillariostrobaceae) fructifications from the British Coal Measures, Fossil Record 19 (1), pp. 1-9 : 3-4

Sigillariostrobus saltwellensis sp. nov.

( Figures 2–3 )

Holotype: Specimen Pb. 53- C.203, stored in the Hunterian Museum , Glasgow.

Type locality: Saltwells Pit, near Cradley Heath, Staffordshire, Great Britain.

Type stratum: Alluvial coal-bearing facies – upper Langsettian–Duckmantian.

Etymology: Named after the locality of the specimen that we designate as the type.

Diagnosis: Cone at least 86 mm long, ca. 17–20 mm in diameter, axis 1.2 mm, pedicel ca. 8 mm long, sporangia 7 mm long, sporophyll laminae 12 broad at base, 6.3 mm long spreading outwards from the cone. Sporangia 7 mm long, 2.5 mm high. Megaspores trilete, probably originally plano-convex, average diameter 2000 µm in their equatorial planes, smooth walls with a thickened area between the arms of the trilete mark. Lesurae approximately half the spore radius, ca. 15 µm broad at the centre of the spore.

Description: Both cones are preserved as dark compression ( Figs. 2a–b , 3a–b ), although they are broken somewhere above their bases ( Figs. 2a, c , 3a, c ), so their complete length is unknown. The megasporophylls have free tips approximately 6.3 mm long ( Fig. 3d ), only slightly diverging from the sides of the cone. The megasporophylls are not well preserved ( Figs. 2b–c , 3d ) and the compression material is very brittle, so the cuticle could not be prepared. Numerous obvious large red-brown megaspores are visible to the naked eye ( Figs. 2d , 3e ). They all measure approximately 2000 µm in diameter in their equatorial plane, with lesurae 50 µm long. The entire surfaces of the spores are smooth ( Figs. 2e , 3f ).

Comments: A second specimen, Pb. 707, also stored in the Hunterian Museum, Glasgow, is referred to this species, but the locality and horizon information for this specimen is not known.

Discussion: The megaspores clearly fit within the parameters of the dispersed spore genus Laevigatisporites and are closest to the species L. glabratus (Zerndt) Potonié and Kremp, 1956 . We agree with Karczewska (1967) that the spores described by Zerndt (1930) as Types 9 and 10 should be referred to Laevigatisporites glabratus as a result of Bochenski’s (1936) description of the spores from his Sigillariostrobus czarnockii . Bochenski (1936) described the spores as 440 to 2700 µm in diameter, and underdeveloped spores which were triangular, thicker than the normal ones and with strongly marked lesurae. Zerndt (1932) agreed that Bochenski’s finding of his megaspores of Types 9 and 10 ( Zerndt, 1930) in the same cone was considerably important to the understanding of Triletes glabratus (now Laevigatisporites glabratus ).

We also agree that there are no reliable grounds to distinguish such species as Laevigatisporites primus Wicher and Laevigatisporites reinschi Ibrahim , as has been done by Potonié and Kremp (1955). Erecting the species Sporites primus, Wicher (1934) assigned only the specific name to the spores, described by Bennie and Kidston (1886) and Zerndt (1930) as Triletes Type I Kidston. Wicher (1934) interpreted the species Sporonites reinschi Ibrahim to be identical to Sporites primus ; he erected himself and – contrary to the law of priority – included Sporonites reinschi Ibrahim in the synonymy of S. primus Wicher. After the publication of Bochenski’s work, it became clear that the spores of Triletes Type I Kidston (= Sporonites reinschi = Sporites primus ) and Triletes glabratus Zerndt belong to the same species. Triletes glabratus Zerndt, 1930 , is the oldest specific name and, therefore, has specific priority.

In situ spores identified as being identical to Laevigatisporites glabratus (Zerndt) Potonié and Kremp have been also described from four species of Sigillariostrobus . They are S. tieghemi Zeiller, 1884 ( Schenk 1885, Zeiller 1888), S. quadrangularis (Lesquereux) White, 1903 ( Wood, 1957), S. czarnockii Bochenski, 1936 , and S. leiosporous Abbott, 1963 . The features of these cones together with those of the British cones are summarised in Table 1 .

Both S. czarnockii and S. leiosporous have sporophyll laminae with ciliate edges, which is a feature not observed in the cones from localities in Britain. S. quadrangularis has its sporophylls in whorls, which is a most unusual character for Sigillariostrobus . This again is different from the helical arrangement in the cones from localities in Britain. S. tieghemi is described as having downward-projecting heels at the distal end of the pedicel, a feature which is again not shown by the cones from localities in Britain. Although all these cones contain megaspores that would be included in the same dispersed spore species, Laevigatisporites glabratus , there are characters of the cones which lead us to the conclusion that they are all different in some respects. For that reason we accept them all as distinct species and therefore refer the British specimens to a new species.

The anatomically preserved monosporangiate Mazocarpon Benson, 1918 includes two species that contain spores referable to Laevigatisporites glabratus . They are M. oedipterum Schopf , from the McLeansboro Group, in Illinois ( Schopf, 1941, late Pennsylvanian (Stephanian A)), and M. bensonii Pigg , from the Duquesne Coal, Conemaugh Group, Ohio (late Pennsylvanian (Stephanian B)). Pigg (1983) showed the two species to have sufficiently different anatomical features to be separated. Although it is almost certain that Sigillariostrobus and Mazocarpon represent the same type of sigillarian cone but are merely preserved differently, we hesitate to include our S. saltwellensis within either of these two species because of the lack of anatomical evidence and their rather different ages.

Figures

Figure 2. Type specimen of Sigillariostrobus saltwellensis sp. nov. Specimen Pb. 53-C.203, Hunterian Museum, Glasgow. Alluvial coalbearing facies – upper Langsettian–Duckmantian. (a) Cone (scale bar 10 mm). (b) Detail of apical portion of the cone (scale bar 5 mm). (c) Detail of basal portion of the cone (scale bar 5 mm). (d) In situ glabrous megaspores (scale bar 2 mm).(e) Spore referable to Laevigatisporites glabratus macerated from the cone (scale bar 1000µm).

Figure 3. Second cone of Sigillariostrobus saltwellensis sp. nov. Specimen Pb. 707, Hunterian Museum, Glasgow. (a) The cone (scale bar 20 mm). (b) Detail of the upper part of the cone (scale bar 5 mm). (c) Detail of the mid-region of the cone, showing the megasporophyll impressions at the edge of the cone, often without the cuticle preserved (scale bar 5 mm). (d) Detail of (c), showing the megasporophylls with fissile compression and scattered megaspores (scale bar 5 mm). (e) Detail of (d), showing details of megaspores within the cone (scale bar 2 mm). (f) Megaspore referable to Laevigatisporites glabratus macerated from the spore mass shown in (e) (scale bar 2000 µm).