Equicalastrobus glabratus, Rodríguez & Bodnar & Beltrán, 2024
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publication ID |
https://doi.org/10.4202/app.01130.2023 |
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persistent identifier |
https://treatment.plazi.org/id/03E45F18-FFB6-FFE8-1DB3-FA9D6EE1CE58 |
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treatment provided by |
Felipe |
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scientific name |
Equicalastrobus glabratus |
| status |
sp. nov. |
Equicalastrobus glabratus sp. nov.
Figs. 2–4 View Fig View Fig View Fig .
PFNR: urn:lsid:plantfossilnames.org:act:3302 (PFN003302).
Etymology: The specific epithet refers to the absence of trichomes on the margins of the sporangiophore discs.
Type material: Holotype, a complete closed strobilus, PBSJ 1562 ( Fig. 2A View Fig ) . Paratype, a complete open strobilus, PBSJ 1539 ( Fig. 3A View Fig ) from the type locality and horizon .
Type locality: Un Salto Creek , Barreal, San Juan Province, Argentina .
Type horizon: EF4, Don Raúl Member, Cortaderita Formation, Sorocayense Group; Ladinian, Middle Triassic.
Material.—42 impressions-compressions of closed and open strobili: PBSJ 1481, 1484, 1487, 1489, 1490, 1493–1495, 1501, 1505, 1506, 1508, 1521, 1522, 1534, 1537, 1539, 1540, 1553, 1555, 1559, 1664, 1576, 1579, 1588, 1589, 1593, 1597, 1598, 1603, 1604, 1605, 1607, 1608, 1609, 1610, 1619, 1621, 1623, 1626, 1736, 1737. All from the type locality and horizon.
Diagnosis.—Cylindrical strobili formed by a main axis on which sporangiophores are arranged in whorls. Sporangiophores consist of hexagonal peltate discs without trichomes (= glabrous). Central umbo, hexagonal, slightly elevated on the external surface of the disc. From the umbo emerges a leaf-shaped projection, with longitudinal striations, ending in a sharp tip directed towards the apex of the strobilus. Base of the strobilus with a leaf sheath protecting it. Branched axes with marked longitudinal ribs, continuous through the node. Robust first-order axes. Thinner second-order axes emerging from the nodes of the first-order axes and bearing leaf-sheaths composed of reduced leaves, fused at the base and free at the apex.
Description.—The studied material corresponds to impressions-compressions of closed and open strobili ( Figs. 2A View Fig , 3A View Fig 1 View Fig , B). The better preserved closed strobilus is cylindrical, compact, 22 mm long by 6 mm in diameter, and is formed by 18 sporangiophores with whorled arrangement, of which only the discs can be seen ( Fig. 2A View Fig ). The discs are peltate, hexagonal, smooth or glabrous, 2.0– 2.6 mm in diameter, and present on their external face the mark of a hexagonal umbo, 0.9–1.9 mm in diameter ( Fig. 2A, B View Fig ). The umbo has a leaf-shaped projection, 0.9–1.1 mm wide at its base by 3.3–3.9 mm long, pointed, with longitudinal striae ( Fig. 2C, D 2 View Fig ), and directed towards the apex of the strobilus ( Fig. 2A View Fig ). At the base of the strobilus, there are leaves 4.7 mm wide by 3.1 mm long fused forming a leaf sheath ( Figs. 2A View Fig , 4A View Fig ). The strobilus is found in organic attachment with a small axis fragment 3.2 mm wide by 8.3 mm long, with 5 longitudinal ribs ( Figs. 2A View Fig , 4A View Fig ).
The best preserved open strobilus is cylindrical, loose, 38 mm long by 11 mm wide, and is formed by 16 sporangiophore discs with regularly whorled arrangement, with a separation distance 1.7–2.2 mm between whorls. The discs are glabrous, 2.0– 3.3 mm in diameter ( Figs. 3A, B View Fig , 5C View Fig ). The umbo marks are hexagonal, 0.9–1.7 mm in diameter ( Fig. 3A View Fig ). The umbo has a leaf-shaped projection, with longitudinal striations, 1.4–7.5 mm long by 0.7–1.4 mm wide ( Fig. 3A View Fig 2 View Fig , B). Other specimens consist of scattered sporangiophore discs 2.0– 2.4 mm in diameter ( Figs. 2C, D View Fig 1 View Fig , 3C View Fig ), with a hexagonal umbo 0.9–1.4 mm in diameter, with a projection of 1.8–3 mm long by 0.9 mm wide, and sometimes showing traces of probable sporangia up to 1.5 mm long ( Fig. 2C View Fig ).
In the same slabs bearing the strobili, fragmented and entire branched axes were found ( Fig. 4C, E–G View Fig ). The first-order axes are 8–12 mm wide, with well-marked ( Fig. 4C View Fig ) or slightly marked ( Fig. 4E View Fig ) nodes. The surface of the internodes shows distinct 4–5 longitudinal ribs, separated by 0.8–1.1 mm, which are continuous as they pass through the node ( Fig. 4C, G View Fig ). No leaf sheaths were found associated with the first-order axes. The second-order axes are 2–4 mm wide, with marked nodes and internodes 9 mm long ( Fig. 4B, E View Fig ). The surface of the internodes shows four distinct longitudinal ribs, separated by 0.5–0.6 mm ( Fig. 4A, B, E View Fig ). Leaf-sheaths are 4 mm long by 4 mm wide and are preserved attached to the nodes, with eight poorly preserved leaves, fused at the base and free at the apex ( Fig. 4B View Fig ). A leaf sheath was also found attached to a 5 mm wide node, which has 15 leaves, each one 2.6 mm long by 0.7 mm wide, fused at the base and free at the apex ( Fig. 4D View Fig ).
Remarks.—The fossils here studied are assigned to Equicalastrobus because they share the main diagnostic characteristics with that taxon, i.e., cylindrical strobilus bearing peltate sporangiophores consisting of a stalk and a hexagonal disk with a single forward-directed leaf-like umbo narrow projection in its outer surface ( Grauvogel-Stamm and Ash 1999). The presence of projections on the umbo of the sporangiophores allows the specimens here studied to be differentiated from the genus Equisetostachys Halle, 1908 ( Fig. 5D View Fig 1 View Fig , D 3 View Fig , F, K), from Equisetites Sternberg, 1833 , and Neocalamostachys Kon’no, 1962, present in the Triassic of Argentina and other regions. Other genera which are characterized by projections on the umbo are Kraaiostachys Anderson & Anderson, 2018, Viridistachys Anderson & Anderson, 2018, and Neocalamites meriani ( Brongniart, 1828) Halle, 1908 , but differ from the Cortaderita fossils due to the first one presents sub-circular sporangiophore discs with an attenuated conical umbo, the second one possesses hexagonal sporangiophore discs with a wider projection that covers the entire diameter of the disc umbo ( Fig. 5H–J View Fig ), while the last one is larger with hexagonal to polygonal sporangiophores with spiny appendages. Pott et al. 2008) described the reproductive structure associated with Neocalamites meriani , but it is not found in organic connection. The strobili assigned to Neocalamites broadly correspond to the genus Neocalamostachys Kon’no, 1962, and do not present spiny appendages, so the systematic assignment of said strobili should be reconsidered. Unfortunately, there is no more information about the spiny appendages of the specimen studied by Pott et al. (2008) for comparison. Until now, two species were described within Equicalastrobus ,.e., E. chinleana ( Daugherty, 1941) Grauvogel-Stamm & Ash, 1999 , from the Upper Triassic of the USA, and E. pusillus Zhang et al., 2021 , from the Upper Triassic of China. Equicalastrobus glabratus sp. nov. is differentiated from E. chinleana ( Daugherty, 1941) Grauvogel-Stamm & Ash, 1999 , by the smaller strobili, smaller sporangiophores, and shorter and narrower umbo projections ( Fig. 5E, F View Fig ). On the other hand, the new species differs from E. pusillus by the markedly longer umbo projections ( Fig. 5D View Fig 1 View Fig , D 2 View Fig , F, G). Equicalastrobus glabratus sp. nov. also is unlike the previously mentioned species by the absence of trichomes on the margins of the discs ( Fig. 5E–G View Fig ).
Regarding the axes and leaf sheaths, Equicalastrobus glabratus sp. nov. differs from the species of Equisetites and Equisetum by the presence of longitudinal ribs passing through the node. On the other hand, the new species is distinct from Schizoneura Schimper & Mougeot, 1844 , by the leaf-sheath morphology, since in this genus they are larger and have laterally fused and flattened leaves, which are arranged in two opposite lobes ( Boureau 1964), while the leaf sheaths in Equicalastrobus glabratus sp. nov. are characterized by reduced leaves fused at the base and free at the apex, and not arranged in lobes. Finally, Neocalamites presents robust branched axes, with Asterophyllites / Annularia - type unfused leaves ( Boureau 1964), ruling out that the here studied axes can be assigned to that genus.
Stratigraphic and geographic range.—Ladinian, Middle Triassic; San Juan Province, Argentina.
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