Query: classification: "38.21"
|Authors||C.R. Hill, R.H. Wagner, A. A. El-Khayal|
|Title||Qasimia gen. nov., an early Marattia-like fern from the Permian of Saudi Arabia|
|Abstract||The marattialean fern Qasimia schyfsmae (Lemoigne) gen. et comb. nov. is described from the Late Permian plant bed at Unayzah in central Saudi Arabia. Although no organic matter is preserved, impregnation of the compressions by iron minerals at an early stage of diagenesis has partly mineralised the synangia and spores. The impressions in a fine-grained shale preserve epidermal cell outlines, including those of the stomata. Qasimia resembles Marattia closely in its bivalved synangia and in its monolaesurate spores with a warty or spiny ornament. It differs in the rounded rather than pointed apices of the pinnules and the greater density of veins, particularly in the vegetative pinnules. Unlike Marattia, its synangia characteristically extend across the full halfwidth of the pinnules, their sporangial compartments are longer, and the cells of the dorsal walls of the compartments are mainly elongate rather than rounded. Venuli recurrentes occur in the fertile pinnules only (which show less than half the vein density of the vegetative pinnules). They are interpreted as vestigial vein branches that were surplus to the number needed to supply the synangia of the fertile pinnules. Such fibre bundles are common in Mesozoic Marattia but are absent from extant species. Marattia anglica (Thomas) Harris, one of the better known Mesozoic species, is compared both with Qasimia and with extant Marattia, and is shown to have a synangial structure like that of the extant species. Similar ferns occur in the Permian of China, the Soviet Far East and Southeast Asia and attention is drawn to Lophotheca panxianensis Zhao, from the Permian of Guizhou, which may be a preservational state of Qasimia. A new combination, Q. tobaensis comb. nov., is proposed for material previously assigned to Taeniopteris tobaensis by Li, Yao & Deng, 1982. Many ferns from the East Asian Cathaysian Province have been wrongly determined as Taeniopteris and Neuropteridium. Qasimia is the earliest known Marattia-like fern having taeniopteroid foliage, and is linked by Mesozoic species of Marattia to the extant ones. Its origin is discussed with reference to the Carboniferous pecopterid Danaeites saraepontanus Stur. Fusion of the separate sporangia of D. saraepontanus would produce bivalved synangia of the Qasimia type, and condensation of a pecopterid frond would produce taeniopteroid pinnules with rounded apices.|
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