INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
The cycadalean seed Cycas umphii as a model for the larger carboniferous medullosalean ovules
ZODROW, E L; D`ANGELO, J A
Congreso; 4th International Palaeontological Congress; 2014
Much has been written about the larger Carboniferous petrified/coalified medullosalean ovules/seeds, and separately about the genus Cycas Linnaeus. It has been commonly conjectured, however tenuous the evidence, that the cycads ascended from a stock of Carboniferous seed ferns. However, the question of occurrence of fossil cycadaleans in rocks of late Pennsylvanian/Late Triassic age is still controversial, and thus the hypothesis of evolutionary pteridosperm/cycadalean lineage is at a stalemate at best. Our continuing studies of coalified medullosalean ovules prompted us to search the literature for morphological/analytical comparisons between extant larger cycadalean and extinct medullosalean ovules, however without success. On request, Dr. D. Stevenson (The New York Botanical Garden) kindly supplied particularly seed specimens of Cycas rumphii Miquel which we propose as a biological model for the larger Permo/Carboniferous trigonocarpalean/pachytestal ovules. For the methodological modeling approach, two evidential lines are appropriated, one of which involves direct observation and measurement, and the other inferences. The first includes physical aspects of the seeds/ovules and the endosperm (=female gametophyte), attachments of the former to stalks, and comparisons of microstructure and micromorphology (nucellii and their epidermises). Particularly emphasized is the similarity in numbers of resistant tissues the fossil and extant ovules share, i.e., seven. Also considered are pollen and pollination characteristics. Inferences are based on comparing oxidative reactions, the spectrochemistry, including atomic mass units, and elemental analyses with published results of the medullosalean ovules. On balance, the sum-total evidence favors C. rumphii as a suitable model as stipulated, which does not imply exclusivity. Details to this effect, and implications thereof, will be published at a future date.