Dictyophyllum tenuifolium Stipanicic and Menéndez, 1949 emend. Bonetti and Herbst, 1964 (Stipanicic and Menendez, 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 : 403-405

Dictyophyllum tenuifolium Stipanicic and Menéndez, 1949 emend. Bonetti and Herbst, 1964

Fig. 6A, D–F .

1949 Dictyophyllum tenuifolium sp. nov.; Stipanicic and Menéndez 1949: 11–12, pl. 4: 1–3, pl. 5: 1–2, pl. 6: 1, 2, 4.

1964 Dictyophyllum tenuifolium Stipanicic and Menéndez, 1949 emend.; Bonetti and Herbst 1964: 275, pl. 1: 1–5, text-figs. a, b.

1992 Dictyophyllum (Dictyophyllum) tenuifolium ( Stipanicic and Menéndez, 1949) emend. Bonetti and Herbst, 1964 ; Herbst 1992a: 27–28.

Neotype: BAPb 8174 , here designated, fragments of four pinnae, with the lamina margin preserved and distinct venation.

Type locality: Paso Flores Depocenter, Neuquén Province, Argentina.

Type horizon: Paso Flores Formation, late Norian–Rhaetian (Upper

Triassic).

Material.— PBSJ 412 a, b, c, EF4, lower member of Cortaderita Formation , early Ladinian (Middle Triassic), Cortaderita Creek, Barreal-Calingasta Depocenter, San Juan Province, Argentina , and PBSJ 1051 , EF7, lower member of Cortaderita Formation , early Ladinian (Middle Triassic), La Tinta Creek, Barreal-Calingasta Depocenter, San Juan Province, Argentina .

Description.—Fragments of up to 6.5 cm long and 3 cm wide of once-pinnate, bilaterally symmetrical, and fan-shaped fronds. The precise maximum size is unknown, but is probably 8 cm in diameter. Petiole is not preserved. The lamina is divided, forming at least 8 linear-lanceolate pinnae. A basal web of lamina unites adjacent pinnae for a length of up to 1.5 cm ( Fig. 6A ). The free part of pinnae reaches 5 cm in length and 1.5 cm in width, in the most complete specimens. The lamina of the pinnae is glabrous and their margin is lobate to serrate with deep irregular lobes, of triangular shape and acute apex.

The rachis gives rise to a series catadromous to isodromous primary veins; each one represents the main vein of the pinnae. Primary veins are longitudinally striate and straight, 0.3–0.5 mm wide. Secondary veins are smooth and alternate to sub-alternate, departing from the primary veins at an angle between 45° and 60° and extending up to the lobule apex. In the basal part of the pinna, secondary veins are sinuous and weakly marked; while they are straight to falcate and conspicuous in the free part of the pinna. Tertiary veins are alternate to sub-alternate and depart from secondary veins at 45–60°. They are straight near the primary vein and sinuous near the lobule apex. They dichotomize three times to form a fine reticulate mesh of polygonal areoles. First order areoles are elongated, 0.8–2 mm wide and 0.9–4.1 mm long, decreasing their size towards the pinna margin. Second order areoles are isodiametric, 0.6–0.9 mm of diameter. Sori and sporangia are not observed.

Remarks.— Dictyophyllum tenuifolium has been erected by Stipanicic and Menéndez (1949) based on fossils coming from the Barreal Formation, but they did no designate a holotype, and, unfortunately, the original specimens on which the diagnosis was established are lost. According to a recent revision of the fossil levels and localities studied by Stipanicic and Menéndez (1949), the type horizon is actually located within the Cortaderita Formation and not the Barreal Formation ( Bodnar 2010; Bodnar et al. in press). Bonetti and Herbst (1964) emended the specific diagnosis after studying new fossils from the Paso Flores Formation (also Triassic of Argentina), but they have not designated a neotype. From the material published by Bonetti and Herbst (1964), we only found three specimens in the National Palaeobotanical Collection of the Museo Argentino de Ciencias Naturales ( BAPb 8169, BAPb 8175, BAPb 8174). Among them, we selected the specimen BAPb 8174 as the neotype of the species, since it is the most complete one and presents all the characters included in the emended diagnosis of Bonetti and Herbst (1964). D. tenuifolium is characterized by once pinnate lamina, with 5–7 oblanceolate pinnae per rachial arm, pinna margin dentate to pinnatifid, polygonal areoles and circular sori. Even though the samples studied here do not show reproductive characters, the remaining traits coincide with the characterization of the species. Stipanicic and Menéndez (1949) and Bonetti (1963) mentioned the presence of this species in the Upper Triassic of Sweden, based on the transfer of the samples determined as Dictyophyllum sp. cf. D. exile by Johansson (1922). However, these specimens have been recently assigned to D. exile by Pott and McLoughlin (2011). Thus, D. tenuifolium has, until now, been only recorded in the Middle and Upper Triassic of Argentina.

Stratigraphic and geographic range.—Early Ladinian of the the lower member of Cortaderita Formation, Sorocayense Group, San Juan Province, Argentina; and late Norian– Rhaetian of the Paso Flores Formation, Neuquén Province, Argentina.

Figures

Fig. 6. Dipterid ferns from Barreal-Calingasta, San Juan Province, Argentina. A, D–F. Dictyophyllum tenuifolium Stipanicic and Menéndez, 1949 emend. Bonetti and Herbst, 1964; Cortaderita Formation (Ladinian, Middle Triassic). A. PBSJ 412a. D. PBSJ 1051. E. PBSJ 412b. F. PBSJ 412c. B, C. Hausmannia faltisiana Stipanicic and Menéndez, 1949 emend. herein; Barreal Formation (Anisian, Middle Triassic). B. BAPb 6248. C. BAPb 6254. Scale bars: A, C, D, 10 mm; B, 20 mm; E, F, 5 mm.