Mesozoic Pteridosperms: Moving Back in Time

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Mesozoic Pteridosperms: Moving Back in Time

Lucas, S.G. and Zeigler, K.E., eds., 2005, The Nonmarine Permian, New Mexico Museum of Natural History and Science Bulletin No. 30. 150 MESOZOIC PTERIDOSPERMS: MOVING BACK IN TIME HANS KERP Forschungsstelle für Paläobotanik, Westfälische Wilhelms-Universität, Hindenburgplatz 57, 48143 Münster, Germany Many paleobotany textbooks, even rather recent ones, make a clear distinction between late Palaeozoic and Mesozoic pteridosperms. Typical Palaeozoic pteridosperms include the Lyginopteridales, Medullosales and Callistophytales, whereas Peltaspermales, Corystospermales and Caytoniales are traditionally considered to be typical Mesozoic groups. The Lyginopteridales became extinct during the Westphalian, whereas the youngest representatives of the Medullosales and Callistophytales are known from the Lower Permian. The peltasperms were originally described from the Lower Triassic of South Africa and the Rhaetian of Greenland. The recognition of peltaspermaceous fructifications in the Rotliegend of Germany and the Autunian of France demonstrates that peltasperms had developed much earlier. The earliest representatives had lax strobilii with bilaterally symmetrical megasporophylls. These can be correlated with the foliage traditionally known as Callipteris conferta. Because the correlation with ovuliferous and polliniferous organs is well established, the whole plant has been described as Autunia conferta. Autunia conferta foliage is known from the latest Carbon- iferous, e.g., from the Stephanian of the St. Étienne Basin (stratotype!) and the Autun Basin (France). More advanced forms with radially symmetrical megasporophylls are known from the Lower Rotliegend of Germany and the Lower Permian of Morocco. Several other peltasperms have now been reported from Permian rocks in the Northern Hemisphere. The corystosperms are traditionally regarded as typical of the Triassic of Gondwana. The earliest representatives of the genus Dicroidium have been described from the Induan of eastern Autralia. The discovery of several species of Dicroidium, showing the typical leaf morphology and with excellently preserved cuticles, in the Upper Permian of the Dead Sea region (Jordan,) demonstrates that this group also originated earlier than previously thought. The earliest representatives of the peltasperms and the corystosperms evolved in the palaeotropics. They were not part of the typical tropical wetland vegetation, but they grew in (temporarily) drier - most probably better drained - tropical lowland areas. In such environments other groups of gymnosperms, i.e. Ginkgophytes and Cycadophytes, also evolved. All these groups survived the end-Permian biotic crisis and they further ex- panded during the Early and Middle Triassic..

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