Paleogene imbricate-leaved podocarps from King George Island (Antarctica): assessing the geological context and botanical affinities

Abstract

Imbricate-leaved podocarps (Dacrydium s.l.) are the dominant conifer remains in the Upper Cretaceous and Cenozoic successions of King George Island, increasing its abundance in the post-Late Paleocene strata and maintained until the Early Oligocene times, with poor taphoflora registered in the last. However, a more precise taxonomic relationship of their remains was ever difficult given the fragmentary nature of the fossils and most known from ex situ material. In new field works and collections looking for the original levels, the recent phylogenetic approaches proposed and comparisons with extant floras have been applied to these fossils, and have helped to clarify their taxonomic status and their preferable association with the Upper Paleocene-Lower Eocene levels. The two kinds of foliage discussed here initiated the taxonomic revision of the Podocarpaceae related fossils on the island and attest to a modern affinity with Dacrydium vel Halocarpus and Dacrycarpus, which was in part proposed by previous works. Those genera comprise today an important component of the eastern Southern Hemisphere forests, and their occurrence in the Antarctic Peninsula areas during the Paleogene supports a broader distribution in the past and attests to the importance of the ancient Antarctic coastal areas in the modern distribution of the Podocarpaceae.RESUMO -As Podocarpaceae são o principal grupo de coníferas nas floras do Cretáceo-Paleógeno da ilha King George, Península Antártica e, após o final do Paleoceno, tipos dotados de folhas pequenas e imbricadas, inicialmente agrupados em Dacrydium s.l., passam a ser dominantes nas assembléias. O caráter incompleto dos fósseis, que dificulta uma atribuição taxonômica mais precisa, fez também com que este epíteto genérico, sem afinidades filogenéticas bem estabelecidas, fosse muito utilizado nos primeiros estudos feitos. Novas análises e a ampliação das coletas, embora não tenham solucionado de todo este problema, mostraram ser úteis para tornar mais precisos os tipos de Podocarpaceae presentes. Neste trabalho, dois morfotipos são revistos e sugerida sua afinidade preferencial com Dacrydium vel Halocarpus e Dacrycarpus, hoje importantes componentes dos biomas do setor oriental do Hemisfério Sul. São igualmente localizados de modo mais preciso e a partir de novos trabalhos de campo, os níveis com plantas do Monte Wawel (= Pontal Hennequin), na baía do Almirantado, previamente conhecidos a partir de material ex situ, o que permitiu propor uma idade Eoceno Inferior para estes depósitos. A presença destes gêneros de Podocarpaceae em áreas da Península Antártica durante o Cenofítico, não apenas confirma sua ocorrência mais ampla no passado, como o importante papel exercido pelas áreas costeiras da Antártica na moderna distribuição da família.

Eocene sedimentary facies in a volcanogenic succession on King George Island, South Shetland Islands: a record of pre-ice sheet terrestrial environments in West Antarctica

“…A Mid dle Eocene to Late Oligocene age for the Point Hennequin Group has been sug gested by many au thors (Pankhurst and Smellie, 1983;Smellie et al, 1984;Zastawniak et al, 1985;Birkenmajer, 1989aBirkenmajer, , 2003Dutra, 2004;Fontes and Dutra, 2010), how ever, a new se ries of K-Ar datings of the Mount Wawel For ma tion points to its Eocene age (Z. Pécskay, pers.…”

“…A Mid dle Eocene age for the Mount Wawel For ma tion was pro posed by Nawrocki et al (2011) as a re sult of U-Pb and 40 Ar-39 Ar anal y ses. Tak ing into ac count that sim i lar plant beds were found in the Fildes For ma tion on Fildes Pen insula and dated to be Eocene in age (Poole et al, 2001;Fontes and Dutra, 2010), a sim i lar age of the Point Thomas For ma tion in Ezcurra In let is highly prob a ble (Mozer, 2012). A Mid dle Eocene age was sug gested for the Lions Cove For ma tion (Z. Pécskay, pers.…”

“…Ge nus Dacry carpus (co ni fers be long ing to the Podocarp fam ily) oc curs in moun tain for ests up to 3600 m a.s.l. in south-east Asia, is lands of Mel a ne sia and New Zea land, and only one New Zea land spe cies Dacrycarpus dacrydioides grows in mixed swamp for ests (Zastawniak, 1981), whereas Nothofagus for ests grow to day usu ally in very hu mid hab i tats, mainly in tem per ate and tem per ate-cool cli mates (Zastawniak, 1981;Fontes and Dutra, 2010). The pres ence of leaves from Arau ca ria and Nothofagus trees in sed i ments of Point Thomas For ma tion sug gest that the palaeoenvironmental con di tions were not so ex treme.…”

“…Macroflora de pos its that had orig i nated from an in di vid ual lo cal ity named Dragon Gla cier Mo raine, were known and had been de scribed (Zastawniak, 1981;Zastawniak et al, 1985;Fontes and Dutra, 2010). Leaf im prints are the pre dom i nant plant re mains vis i ble in tuffaceous rocks.…”

“…Rich ter res trial flo ras pre served in Eocene sed i ments of this re gion pro vide sig nif i cant clues about Ce no zoic cli mate change. Several au thors have used var i ous bi otic com po nents to re construct depositional and cli ma tic con di tions dur ing the ac cu mu lation of the sed i men tary se quences: wood (Lucas and Lacey, 1981;Fran cis and Poole, 2002), leaves im print (Zastawniak, 1981(Zastawniak, , 1990(Zastawniak, , 1998Zasta wniak et al, 1985;Zastawniak, 1986, 1989a, b;Li, 1992;Dutra, 2001Dutra, , 2004Hunt and Poole, 2003;Kellner et al, 2007;Fontes and Dutra, 2010), plant and fish as sem blage (Doktor et al, 1996), wood, tree-ring and palynomorph set to gether (Askin and Spicer, 1995;Duan and Cao, 1998;Fran cis et al, 2008;Panti et al, 2012). The terres trial flo ras con firmed a warm (i.e., frost-free) Eocene cli mate with a gen eral cool ing trend up the suc ces sion, cul mi nat ing in a sig nif i cant cool ing dur ing the Late Eocene.…”