Asterotheca merianii ( Brongniart, 1828a ) Stur, 1885

Pott, Christian, 2014, The Upper Triassic flora of Svalbard, Acta Palaeontologica Polonica 59 (3), pp. 709-740 : 716

Asterotheca merianii ( Brongniart, 1828a) Stur, 1885

Fig. 3A–J.

1828 Pecopteris merianii ; Brongniart 1828a: 57, 194.

1834 Pecopteris merianii ; Brongniart 1834: 289, pl. 91: 5.

1885 Asterotheca merianii Bgt. ; Stur 1885: 5.

1972 Asterotheca merianii (Brongn.) Stur ; Vasilevskaya 1972: 36, pls. 2: 4–9; 3: 1–17; 9: 6b; 17: 3b.

2011 Asterotheca merianii (Brongniart) Stur 1885 ; Kustatscher and Van Konijnenburg-van Cittert 2011: 210, pl. 1: A–I, text-fig. 12A.

Material.— Spitsbergen: Bertilryggen ( NRM S080247); Fleur de Lyshamna ( NRM S080072, S080076, S080078, S080089, S080090, S080111); Wimanfjellet ( VSEGEI 10979-08, 10979-12–10979-14); Trehøgdene ( NRM S151681); Wichebukta ( VSEGEI 10979-15, 10979-82, 10979-83). Barentsøya: Vossebukta ( VSEGEI 10979-18–10979-21, 10979-80, 10979- 81). Edgeøya: Kapp Lee ( NRM S080188, S080189, S080191, S080193, S080197, S080204, S080205, S080209, S080211– S080215, S080221, S080223, S080240; VSEGEI 10979-16, 10979-17, 10979-24, 10979-25, 10979-44, 10979-53, 10979- 84–10979-86); Kvalpynten ( NRM S080241); Negerpynten VSEGEI 10979-22, 10979-23, 10979-79). Carnian (Upper Triassic).

Description.— Asterotheca merianii is typically preserved as sterile (Fig. 3A–C, G, I) and fertile (Fig. 3D–F, H, J) isolated pinnae in the Svalbard assemblages. The longest fragment measures 108 mm. Pinnules are densely spaced, 8–14 mm long (decreasing in length apically), and inserted by their whole base lateral to the rachis. The basal width of pinnules is consistently 3–4 mm. Pinnules are inserted at 75° and have relatively parallel margins ending in bluntly rounded apices. The pinnae vascular bundle gives off first order veins at 75°, the latter giving off 4–6 pairs of secondary veins that usually bifurcate once close to the base. Additional bifurcations are not found in the preserved specimens. Fertile pinnules bear regularly arranged sori (on the abaxial side) that are arranged parallel to the midline of the pinnule; 4–8 pairs of sori are present on a pinnule (e.g., Fig. 3J), each consisting of four sporangia.

Remarks.— Asterotheca merianii is one of the most common ferns in Upper Triassic floras of Europe and Asia and it may represent a useful stratigraphic index fossil. The size of several A. merianii fossils argues for these plants having been quite tall tree-like ferns similar to modern Dicksonia species. Fertile and sterile pinnules were produced on different pinnae, and most likely on separate fronds. Asterotheca merianii is also one of the dominant elements of the Carnian flora of Lunz. This species is readily identified, but it is not strongly palaeoecologically informative. Vasilevskaya

1972) was able to isolate spores from the A. merianii specimens from Svalbard and these match perfectly with the spores published by Bhardwaj and Singh (1957) from A. merianii specimens from the Lunz flora and by Kustatscher and Van Konijnenburg-van Cittert (2011) from A. merianii specimens from the Thale flora. These authors also provide a thorough discussion of this species, its history and a comparison with other species. Asterotheca merianii occurs widely among the fossil localities in Svalbard, and where it is one of the dominant taxa. At some localities, it is the only taxon found.

Geographic and stratigraphic range.— Europe, Asia; Ladinian–Carnian.