Early Cretaceous riparian vegetation in Patagonia, Argentina

Abstract

Early Cretaceous riparian vegetation in Patagonia, Argentina. An autochthonous plant as-semblage found at the Bajo Grande locality, Anfiteatro de Ticó Formation, Baqueró Group, Early Aptian of Santa Cruz province, Argentina, is described. Sedimentological data show an alternation of sandstone and lime-stone, with recurrent fossil levels associated to a fluvial system. The frequent flood in areas close to the levee had an influence on the vegetation growing along the banks of the channels. A plant assemblage composed of Ricciopsis grandensis nov. sp. (bryophyte), Adiantopteris tripinnata nov. sp., Schizaeaceae pinnules (ferns), and the gnetalean fructification Ephedra verticillata nov. sp. was found in this paleoenvironment. The taphonomical studies suggest that the plant assemblage was autochthonous, and it grew and was buried in an area near a levee. This result is congruent with environmental data provided by living representative of the fossil taxa analyzed.

Parallel evolution of leaf morphology in gnetophytes

“…A few macrofossils were described as having affinities with the group, but these were demonstrated to be unlike their modern counterparts (Crane 1996). After 1996, a number of macrofossil taxa were reported having affinities to the Gnetales, in northeastern China in particular (Cao et al 1998;Duan 1998;Sun et al 2001;Akhmetiev and Krassilov 2002;Yang et al 2005Tao and Yang 2003;Wang 2004;Rydin et al 2003Rydin et al , 2004Rydin et al , 2006aCladera et al 2007;Liu et al 2008;Krassilov 2009;Zheng 2009, 2010;Rydin and Friis 2010;Yang 2010;Han et al 2013;. Some of them were described as 'angiosperms', but actually belong to the gnetophytes (e.g.…”

“…Macro-and meso-fossils from the Early Cretaceous of Asia, Europe, N America and S America clearly indicate that the genus Ephedra originated in the Early Cretaceous (118-125 mya, Guo and Wu 2000;Sun et al 2001;Yang et al 2005;Rydin et al 2006a, b;Cladera et al 2007;Liu et al 2008;Wang and Zheng 2010;Rydin and Friis 2010;. Fossils related to Gnetum and Welwitschia were reported from the Early Cretaceous of China, e.g.…”

“…Modern Ephedra has linear leaves that are more or less connate into a thin sheath with two or three triangular teeth, rarely free from each other, each leaf usually possesses two (rarely three) brown parallel veins (Foster 1971;Gifford and Foster 1989). Fossil species from Europe and North America are only represented by seeds (Rydin et al 2006a), while macrofossils from Australia and South America bear no leaves (Krassilov et al 1998;Cladera et al 2007;Mendes et al 2011), so it is impossible to compare leaf characters of these species with the new species. Those fossil species from the Early Cretaceous of western Liaoning in China and Mongolia are frequently preserved with leaves (Guo and Wu 2000;Rydin et al 2006b;Liu et al 2008;Rydin and Friis 2010;Krassilov and Bugdaeva 1999;.…”

Itajuba yansanae Gen and SP NOV of Gnetales, Araripe Basin (Albian-Aptian) in Northeast Brazil

“…Wu [27], Ephedra hongtaoi Wang et Zheng [28] and Siphonospermum simplex Rydin et Friis [29], all species found in Barremian the Yixian Formation of Lianoning province in northeastern China. Moreover, I. yansanae was compared with fossil species related to the order Gnetales and Ephedra in the Lower Cretaceous found in the Southern Hemisphere: Cearania heterophylla Kunzmann et al [4], Cariria orbiculiconiformis Kunzmann et al [12], and a specimen possibly related to Ephedra [14], all collected in the same basin in Ceará in layers of the Crato Member of the Santana Formation (Aptian) in the Northeast of Brazil, as well as Ephedra verticillata Cladera et al [30], found in the Ticó Formation of the Baqueró Group (Aptian) in Santa Cruz province in the south of Argentina.…”

“…Both species do have a longitudinally striated stem. E. verticillata was described for an impression/compression stems [30] has sessile seed-bearing structures either singly or in clusters of the three to five, whereas those of I. yansanae are uniformly singular.…”