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- W2078652362 abstract "A major mid-Devonian floral event is the incoming and proliferation of the archaeopteridalean progymnosperms. They are generally accepted to have originated from the aneurophytalean progymnosperms. The spores from both groups (the microspore Geminospora lemurata and its megaspore Contagisporites optivus—Archaeopteridales; Rhabdosporites langii—Aneurophytales) are well represented in the Orcadian Basin, Scotland. Study of a long section in southern Orkney shows that G. lemurata first occurs not by progressive size reduction of R. langii but as a small thick-walled spore (“early form”) which is presumed to originate by heterochrony directly from an immature Rhabdosporites. It then progressively increases in size. This early stage of evolution can be timed using the lacustrine cyclicity. Subsequently a rapid increase in abundance occurs with G. lemurata replacing R. langii as the dominant element of the palynofloras. Originating after the first appearance of G. lemurata are spores transitional in morphology between R. langii and C. optivus indicating the progressive development of the megaspore. These changes together with the presence of a three-walled species of Rhabdosporites (Rhabdosporites streelii Marshall, sp. nov.) give a hint of the complex changes occurring within the sporangia of the archaeopteridalean group at this time. These changes show how detailed investigation of related spore taxa can reveal the pattern of the development of heterospory in the Progymnosperms. This permits for the first time a test of the theoretical models for the development of heterospory. The recognition that an “early form” of G. lemurata exists indicates that some caution should be exercised in using the first occurrence of this species as a stratigraphic marker. Rhabdosporites parvulus is confirmed as a small R. langii but the bulk of specimens formerly attributed to this species are G. lemurata. The means that the Eday Group sediments of Orkney are contemporaneous with the Devonian deposits of southeast Shetland and Fair Isle." @default.
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- W2078652362 title "Rhabdosporites langii, Geminospora lemurata and Contagisporites optivus: an origin for heterospory within the progymnosperms" @default.
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- W2078652362 doi "https://doi.org/10.1016/0034-6667(95)00125-5" @default.
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