Abstract

AXSMITH, Brian J.; TAYLOR, Edith L.  and  TAYLOR, Thomas N.. The "New Approach to Corystospermales" and the Antarctic Fossil Record: A Critique. Ameghiniana [online]. 2007, vol.44, n.1, pp.223-230. ISSN 1851-8044.

Much is now known about the Mesozoic pteridosperm order Corystospermales based on over seventy years of research. However, several concepts of corystosperm evolution have been proposed that avoid well-established phylogenetic methodology and arbitrarily discount evidence of the group from Antarctica. Here, we focus on the "New approach to Corystospermales" published by Artabe and Brea, which establishes a phylogeny for corystosperms based mainly on a restricted concept of anomalous wood anatomy in this group, and assumed relationships with cycads and medullosan pteridosperms. These authors also question evidence regarding attached corystospermalean organs from Antarctica. Based on a reconsideration of the Antarctic record, we reaffirm the evidence for a Dicroidium leaf in attachment to branches that also bear distinctive short shoots. Umkomasia cupulate organs occur on identical attached short shoots. We also emphasize that wood morphotaxa attributed to the corystosperms from Antarctica, including Jeffersonioxylon and Kykloxylon, indicate that anomalous secondary growth is not necessarily basic to the corystosperms. We conclude that a greater understanding of the corystosperms will require a consideration of all relevant evidence, and will not be advanced by single organ phylogenies based on fossils from one region.

Keywords : Antarctica; Corystospermales; Dicroidium; Gondwana; Phylogeny; South America; Triassic; Seed ferns.