Thaumatopteris barrealensis Stipanicic and Menéndez, 1949

Bodnar, Josefina, Drovandi, Juan Martín, Morel, Eduardo Manuel & Ganuza, Daniel Gustavo, 2018, Middle Triassic dipterid ferns from west-central Argentina and their relationship to palaeoclimatic changes, Acta Palaeontologica Polonica 63 (2), pp. 397-416 : 408-409

Thaumatopteris barrealensis Stipanicic and Menéndez, 1949

Fig. 7 .

1949 Thaumatopteris barrealensis sp. nov.; Stipanicic and Menéndez 1949: 16–17, pl. 8: 2, pl. 9: 1–4, text-fig. 4.

1949 Thaumatopteris pusilla (Nathorst) Ôishi and Yamasita, 1936 ; Stipanicic and Menéndez 1949: 12–14, pl. 7: 2; pl. 7: 1, 3, text-fig. 3.

1949 Thaumatopteris cf. pusilla (Nathorst) Ôishi and Yamasita, 1936 ; Stipanicic and Menéndez 1949: 14–15, pl. 8: 4.

1992 Dictyophyllum (Thaumatopteris) barrealensis ( Stipanicic and Menéndez, 1949) ; Herbst 1992a: 31–32.

Material. — BAPb 6263, PBSJ 844–850, PBSJ 1043–1050; EF3, Barreal Formation, Anisian (Middle Triassic), Cortaderita Creek, Barreal-Calingasta Depocenter, San Juan Province, Argentina.

Description. —Fragments of up to 3.5 cm long and up to 3 cm wide of once pinnate, bilaterally symmetrical, and fan-shaped fronds. In the base of the frond where the petiole is inserted, the lamina acquires a funnel shape. The precise maximum size is unknown, but it probably reaches up to 5 cm in diameter. The lamina is divided, forming at least 8–10 lanceolate pinnae, 0.5–0.9 cm wide and 1.3–3 cm long. The lamina of the pinnae is glabrous, and their margin is pinnatisect, forming linear lanceolate to falcate pinnulae. Pinnulae are alternate to sub-opposite, and slightly decurrent, generating a winged rachis. They have entire margin and rounded to acute apex. Pinnulae measure 0.22–0.68 cm in length, 0.11–0.19 cm in width, being longer in the middle part of the pinnae than in the base and the apex. The apical pinnula is unique and deltoid to ovate.

The rachis divides into two equal opposite arms. Each arm gives rise to a series 4–5 catadromous to isodromous primary veins. They are longitudinally striated and straight to sinuous, with the width decreasing near the apex and the base, 0.2–0.3 mm wide. Secondary veins represent the midrib of the pinnulae and depart from primary veins at an angle between 40° and 50°, extending up to the pinnulae apex. They are smooth and straight to sinuous. Tertiary veins are sinuous, and alternate to sub-alternate, departing from the secondary veins at 45–50°. They dichotomize three times to form a fine reticulate mesh of polygonal (hexagonal?) areoles that are hardly discernible in most of the samples. Sori and sporangia are not observed.

Remarks. — Stipanicic and Menéndez (1949) described fronds of three species of the genus Thaumatopteris in the Barreal strata: T. pusilla ( Nathorst, 1878) Ôishi and Yamasita, 1936 , T. dunkeri ( Nathorst, 1878) Ôishi and Yamasita, 1936 , and the new species T. barrealensis ; and other specimens assigned with doubt to T. pusilla . The species T. barrealensis , as defined by Stipanicic and Menéndez (1949), is characterized by petiolate fronds, with a lamina divided into at least 5 lanceolate pinnae, 6–8 cm long and 1.9–2 cm wide, primary veins striate, pinnae dissected in alternate to sub-alternate pinnulae inserted to the rachis at an angle of 50°, pinnulae linear-lanceolate with rounded apex and coalescent base, 1.1× 3 cm in size, pinnula midrib from base to top, polygonal (hexagonal) elongated areoles, 0.7 mm in size, second order areoles pentagonal or rhomboidal. The new samples described in this work coincide with this diagnosis. The materials referred to T. pusilla and T. sp. cf. T. pusilla are very similar to T. barrealensis and only display minor differences in size. On the other hand, they differ from T. pusilla ( Table 3) from the Upper Triassic of Sweden and Japan, as the Laurasian species has pinnulae that are more spaced on the rachis, their angle of insertion is wider than 70°, and their apex is obtusely rounded apex. For all this, we transfer the materials originally determined as T. pusilla and T. sp. cf. T. pusilla to T. barrealensis . We agree with Herbst (1992a) that the specimen determined as T. dunkeri is very fragmentary, and that preserved characters are insufficient to make a specific determination. However, the original specimen is lost, and we cannot revise it in more conclusive way.

Stratigraphic and geographic range. —Anisian of the Barreal Formation, Sorocayense Group, San Juan Province, Argentina.

Figures

Fig. 7. Dipterid fern Thaumatopteris barrealensis Stipanicic and Menéndez, 1949 from Barreal Formation (Anisian, Middle Triassic) of Barreal-Calingasta, San Juan Province, Argentina. A. BAPb 6263. B. PBSJ 844; general view of the leaf (B1), detail of the pinnulae (B2), detail of the pinnula venation (B3). C. PBSJ 849. Scale bars: A, B1, 10 mm; C, 5 mm; B2, 3 mm; B3, 1 mm.