INSIGHTS INTO THE LEAF CUTICLE FINE STRUCTURE OF GINKGOITES SKOTTSBERGII LUNDBLAD FROM THE ALBIAN OF PATAGONIA AND ITS RELATIONSHIP WITHIN GINKGOALES

DEL FUEYO, G.; GUIGNARD, G.; VILLAR DE SEOANE, L.; CARRIZO, M.; LAFUENTE DÍAZ, M.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

IANIGLIA Mendoza - CONICET

During the Mesozoic, the Ginkgophytes were one of the most diversified and worldwide spread groups of gymnosperms that began radically to decline in the Cenozoic and nowadays are restricted to East Asia. In Argentina, the fossil record of the group can be traced back to the Carboniferous, represented by a few taxa although during the Mesozoic its diversity becomes higher. This richness is observed particularly in the Cretaceous of Patagonia where several vegetative and reproductive remains have been found. Among the first records, leaves of Ginkgoites Seward are remarkably abundant in number of species, having most of them well preserved cuticular features. In this contribution the leaf cuticle fine structure of Ginkgoites skottsbergii Lundblad recovered from the Kachaike Formation (Albian) at Bajo Comisión locality in Santa Cruz Province, Argentina, is described in order to compare it with those of other Ginkgoites and Ginkgo-like species and also, to find out its correct family affinity within Ginkgoales. The cuticle of G. skottsbergii was observed using both electron (SEM and TEM) microscopic techniques. G. skottsbergii has a simple, petiolate and amphistomatic leaf with deeply incised lamina up to 12 lanceolate-lineal lobes. Epidermal cells in both adaxial and abaxial surfaces vary from rectangular to isodiametric in shape; their anticlinal walls are pitted. Stomatal apparatuses are irregularly disposed; monocyclics to dicyclics with 6-8 papillate subsidiary cells overarching the pit while the guard cells are sunken. As several Ginkgo and Gingkoites taxa already studied at ultrastructural level, the cuticle of G. skottsbergii consists of a cuticle proper (divided in polylamellate A1 upper and lower zones, then granular A2 layer) and a cuticular layer (fibrilous B1 layer), however proportions of the layers are significantly distinct and therefore specific for this taxon. These results show that the leaf gross morphology and the cuticle fine structure of G. skottsbergii, are clearly different from those seen in other studied fossil species of Ginkgoites, Ginkgo and the living G. biloba. In addition, very well preserved cuticle in G. skottsbergii confirms the importance that this type of study has for the correct specific identification of this taxon. In Patagonia, during the Early Cretaceous two ginkgoalean lineages were already well established; the Karkeniaceae and the Ginkgoaceae represented by Ginkgoites tigrensis Archangelsky and G. ticoensis Archangelsky, respectively. In this contribution a new Patagonian member, G. skottsbergii, is added to the Ginkgoaceae, highlighting Patagonia as a key area for the development of the Ginkgoales.