Format: ORAL

Vivi Vajda1, SylvainSylvain G. Razafimandimbison2, Nicolas Rakotosolofo3 andHery L. Ranarijaona3

1 Department of Paleobiology, Swedish Museum of Natural History, Svante Arrhenius v. 9, Stockholm, Sweden. 2 Department of Botany, Swedish Museum of Natural History, Svante Arrhenius v. 7, Stockholm, Sweden. 3 École Doctorale sur les Ecosystèmes Naturels, Faculté des Sciences, Université de Mahajanga, Mahajanga, Madagascar.

Here we present results originating from a collaborative project involving paleontologists, geologists, and botanists from the Swedish Museum of Natural History and Mahajanga University, Madagascar. Madagascars geological history is central to interpreting the origins of its flora and fauna as the island separated from continental Africa in the Jurassic c. 165 million years ago, leaving Madagascar and its biota to develop in isolation from other continental landmasses. Paleobotanical studies are few, most dating back to the 1960sand 1970s by Appert, who described Upper Jurassic (Oxfordian) assemblages from the Manamana massif (southwestern Madagascar). Dipteridaceous ferns, conifers belonging to the genera Brachyphyllum, Elatocladus, Cupressinocladus., Cyparissidium, and Araucarites, as well as minor amounts of seed ferns, make up the majority of these impression floras. Our palynological results from two outcrop sections within the Mahajanga Basin, reveal well-preserved palynological assemblages of entirely continental aspect. While the older assemblage is highly dominated by fern- and lycophyte spores, including Cyathidites, Baculatisporites, Dictyophyllidites, Ceratosporites and Retritiletes, the younger assemblage is dominated by gymnosperm pollen, which constitutes c. 70%. Within the gymnospermsClassopollis, Araucariacites, Perinopollenites, and Callialasporites are the most abundant spore genera. Based on these taxa, we assign the studied assemblage to the Early Jurassic (Pliensbachianearly Toarcian) Corollina torosa Zone of Helby et al. (1987). The floras are very similar to the coeval floras of, e.g., Sweden and Australia, revealing a highly homogenous global vegetation pattern at the time growing in a stable ecosystem for many million years, as similar floras are present in the Late Jurassic, as outlined by Appert.