GNAEDINGER silvia cristina
congresos y reuniones científicas
First record of Hamshawvia Anderson & Anderson and Stachiopitys Schenk in the Triassic if Rio Grande do Sul, South Brazil
Congreso; GONDWANA 15 North meets South; 2014
The Triassic fossil levels containing Dicroidium and other Corystospermales from South Brazil are also rich in leaves and reproductive structures of Ginkgophyta, representing 17% of the studied paleocommunity. Leaves of Taeniopteris and Equisetales are also common and the last ones indicates a near water growing to the original flora. In the lacustrine succession from Brazil, new and well-preserved forms were found in the last years. The laminated shales, lenticular in geometry, represents a restricted part in the dominant fluvial deposits, composed by trough and planar cross-bedded sandstones and intraformational conglomerates, assigned to the Passo das Tropas Member, the basal unit of Santa Maria Formation. In association with diversified leaves of Baiera and Sphenobaiera, at least three isolate and distinct forms of Hamshawvia (ovulate structure), and one of Stachiopitys (male fructification), were identified. One of the Hamshawvia type specimens exhibit a next relation with H. longipedunculata Anderson & Anderson (Anderson & Anderson, 2003) by the elongated, slender, once-forked axis, bearing a pair of fleshy and round megasporophylls. The other forms are still insert in its specific affinities. Stachiopitys is represented by numerous pendant microsporangia disposed in rosettes around an axis (not preserved), and suggests an affinity both with S. mazarinus Anderson & Anderson and S. lacrisporangia Anderson & Anderson from the Molteno beds. The Hamshawia and Stachiopitys fossil record spans from the Ladinian (Nymboida Coal Measures from Australia) to the Carnian of South Africa (Molteno Formation) and Ladinian-Carnian from Argentina (Potrerillos and Cacheuta formations, Kogogian et al., 1993, Barredo et al., 2012). The presence of reproductive and vegetative organs (even without organic connections), associated to leaves of Sphenobaiera shenkii sensu Anderson & Anderson and Baiera spp. approximates this deposits to other Gondwanaland occurrences, especially those from South Africa, and extends the fossil record of the Ginkgophyta in Brazil. Support: CNPq/CAPES/FAPERGS (Brazil)/CONICET (Argentina).