A new species of Ashicaulis Tidwell (Osmundaceae) from Aptian strata of Livingston Island, Antarctica Ezequiel Ignacio Vera Divisio ´n Paleobota ´nica, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia’’, Av. Angel Gallardo 470, C1405DJR, Buenos Aires, Argentina Received 6 January 2006; accepted in revised form 31 July 2006 Available online 3 February 2007 Abstract A new species of Ashicaulis, A. australis sp. nov., is described in detail. The specimen, collected from the Cerro Negro Formation (Aptian) at Byers Peninsula, Livingston Island (Antarctica), increases the number of fossil representatives of the Osmundaceae in the southernmost conti- nent. The specimen shows a differential state of preservation across the stem, but is good enough to show details of most of the tissues, enabling a study of the anatomy, allowing its comparison with other Ashicaulis species, and justifying its assignment to a new species. Ashicaulis australis is characterized by the presence of parenchymatous pith, sub-exarch protoxylem clusters in the vascular ring, delayed leaf gaps and petiole bases with small patches of sclerenchyma scattered in the cortex, two groups of the same tissue lateral to the trace, and a large patch followed by 6e9 smaller aligned sclerenchymatous groups in the stipular wings. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Osmundaceae; Antarctica; Cerro Negro Formation; Cretaceous; Ashicaulis 1. Introduction The fern family Osmundaceae contains 21 extant species distributed among the genera Osmunda, Todea and Leptopteris (Hewitson, 1962) and more than 150 fossil species represented by compressed foliage, isolated spores and sporangia, and per- mineralized stems (Tidwell and Ash, 1994). Previously, 15 genera were recognized, classified in two subfamilies, Tham- nopteroidea and Osmundoidea, with the extant species in- cluded in the latter (Tidwell and Ash, 1994). Based on fossil evidence, the history of the Osmundaceae can be traced to the Early Permian, when the oldest osmundaceous fern Gram- matopteris lived (Pryer et al., 2004; Roessler and Galtier, 2002). Studies using molecular and morphological data of living species, including time constraints based on the fossil record, put back the origin of this family to the Late Carbon- iferous (Pryer et al., 2004). This group has been regarded by many authors as intermediate between the eusporangiate and leptosporangiate ferns, because they possess a mixture of spo- rangial features from both groups (Miller, 1971; Smith, 1995). Supporting this classification, the latest molecular studies place the Osmundaceae as sister group to the rest of the lepto- sporangiate ferns (Pryer et al., 2004). As pointed out by many authors (Tidwell and Ash, 1994; Stockey and Smith, 2000), Mesozoic Osmundoidea are very well represented in Gondwana, with 35 of the more than 40 species assigned to Ashicaulis, Millerocaulis and Osmunda- caulis (Rothwell et al., 2002). Nevertheless, the record of this group in Antarctica is very sparse, probably owing to the inaccessibility of the fossil sites. Previously, only three species have been described: the Triassic Ashicaulis beard- morensis (Schopf, 1978) and Ashicaulis woolfei (Rothwell et al., 2002) from the Transantarctic Mountains; and the Late Cretaceous Ashicaulis livingstonensis from Williams Point, on the eastern side of Livingston Island, South Shetland Islands (Cantrill, 1997). The Cerro Negro Formation is a succession of non-marine volcaniclastic strata on Livingston Island defined and referred E-mail address: evera@macn.gov.ar 0195-6671/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.cretres.2006.07.006 Cretaceous Research 28 (2007) 500e508 www.elsevier.com/locate/CretRes