Patagoniapteris artabeae: A new species of Dipteridacean Fern from the Triassic of Argentina.

The Family Dipteridaceae today contains ten species of Ferns divided into two genera, found in tropical and subtropical areas of Asia, Australia, and the Pacific Islands. However, in the past they were much more widespread and diverse, with fossils known from all over the world. The oldest examples appear in the fossil record in the Middle Triassic, leading to speculation that they may have first evolved in the Early Triassic or even the Permian, and they reached their maximum diversity in the Late Triassic and Early Jurassic, after which they appear to have declined throughout the remainder of the Mesozoic, a pattern also seen in many other Fern groups.

The Dipteridaceae have distinctive bilobed, fan-shaped fronds, born on long stipes (leaf stems), with toothed margins and reticulate (meshed) veination. Sori (spore-bearing bodies) are scattered across the undersides of these fronds.

In a paper published in the journal Acta Palaeontologica Polonica on 29 November 2021, Silvia Cristina Gnaedinger of the Área de Paleontología at the Centro de Ecología Aplicada del Litoral of the Consejo Nacional de Investigaciones Científicas y Técnicas, and Ana María Zavattieri of the Departamento de Paleontología at the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, describe a new species of Dipteridacean Fern from the Paso Flores Formation of Neuquén Province in Argentina.

The Paso Flores Formation is found within the Neuquén Basin, a rift valley to the east of the Andes that formed in the Late Triassic and Early Cretaceous by extensional rifting on the western margin of the Gondwanan supercontinent. The formation is a sedimentary system recording a braided river system and alluvial fan. It overlies a late Palaeozoic volcanic system unconformably, and is itself overlain unconformably by Early Jurassic volcanic rocks. This formation has produced a wide range of Late Triassic fossil Plants, including three previous Dipteridacean Ferns.

 

Generalised outline of the Neuquén Basin, showing the location of the studied area of the Paso Flores Formation, Neuquén Province, Patagonia, Argentina. Gnaedinger & Zavattieri (2021).

The new species is named Patagoniapteris artabeae, where 'Patagoniapteris' means 'Patagonian Fern' and 'artabeae' honours Argentinian palaeobotanist Analia Artabe for her important contributions to the knowledge of the Triassic and Jurassic floras of Argentina. The species is described from a series of sterile and fertile frond fragment impressions. These fronds are dissected into two equal and opposite rachial arms, each one having more than 18 primary segments. The primary segments are fused together for the lower third of their length, the remaining parts are free and lance-shaped, with undulating to deeply dissected margins, The primary and secondary veins are simple, with the tertiary veins forming an irregular polygonal mesh.

 

Dipteridacean Fern Patagoniapteris artabeae from the upper Norian–Rhaetian, Upper Triassic Paso Flores Formation, Neuquén Province, Argentina. (A) MCF-PBPH 066, part of the frond showing fused and dissected portions. (A₁), (A₂) basal portion of a rachial arm with the lamina of the primary segments fused. (A₃) detail showing primary segments with the dissected portion of the lamina. (B) MCF-PBPH 415, primary segments of fertile frond; (B₁), (B₂) deeply dissected lobes. (C), (D) Primary segments of sterile frond. MCF-PBPH 067d (C) and MCF-PBPH 069 (D). (C), (D₁) deeply dissected lobes. (D₂) detail of a lobe of the primary segment, showing secondary and tertiary veins. Scale bars 10 mm. Gnaedinger & Zavattieri (2021).

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