A new cycad stem from the Cretaceous in Argentina and its phylogenetic relationships with other Cycadales

Abstract

The cycads are an ancient group of seed plants. Fossil stems assigned to the Cycadales are, however, rare and few descriptions of them exist. Here, a new genus of cycad stem, Wintucycas gen. nov., is described on the basis of specimens found in the Allen Formation (Upper Cretaceous) at the Salitral Ojo de Agua locality, Río Negro Province, Argentina. The most remarkable features of Wintucyas are: a columnar stem with persistent leaf bases, absence of cataphylls, a wide pith, medullary vascular bundles, mucilage canals and idioblasts; a polyxylic vascular cylinder; inverted xylem; and manoxylic wood. The new genus was included in a phylogenetic analysis and its relationships with fossil and extant genera of Cycadales were examined. In the resulting phylogenetic hypothesis, Wintucycas is circumscribed to subfamily Encephalartoideae, supporting the existence of a greater diversity of this group in South America during the Cretaceous. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 436–458.

Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia?

“…The MP analysis of the modified morphological matrix of Martinez et al [48] resulted in 242 equally parsimonious trees of 196 steps. In the strict consensus tree, Bowenia and Eobowenia are in a polytomy with most of the other fossil taxa.…”

“…In the bootstrap analysis, a sister group including Eobowenia and Bowenia does not receive support, being retrieved in only 50% of the bootstrap replicates. Forcing the molecular backbone constraint from Salas-Leiva et al [7] on the modified morphological matrix of Martinez et al [48] results in 594 trees of 222 steps. In the consensus tree, only a few relationships are resolved, but Bowenia and Eobowenia result sister taxa.…”

“…5Phylogenetic placement of Eobowenia . a Number of steps necessary to place Eobowenia on a tree based on Salas-Leiva et al [7] using the modified Martinez et al [48] matrix. Placement as sister to Bowenia results in the shortest trees, but other placements are only marginally less parsimonious.…”

“…To test the placement of Eobowenia in the phylogeny of the Cycadales, we coded Eobowenia and Almargemia by incorporating the new data from our investigation in a modified version of the morphological matrix from Martinez et al [48]. We removed the taxa that had no character overlap with our foliage taxa from the matrix.…”

The last Patagonian cycad,Austrozamiastockeyigen. et sp. nov., early Eocene of Laguna del Hunco, Chubut, Argentina

“…There are numerous Patagonian records of Late Cretaceous to possibly early Paleocene petrified-stem genera allied with Encephalarteae, including Menucoa, Neochamberlainia, Wintucycas, and Worsdellia (Petriella 1969;Artabe and Stevenson 1999;Artabe et al 2004Artabe et al , 2005Cúneo et al 2010;Martínez et al 2012). If it is Paleocene, Menucoa is also the heretofore "youngest Patagonian cycad."…”