K/T Palms in Patagonia, Argentina

ZAMUNER ALBA B.; IGLESIAS ARI

Mendoza

Congreso; Gonwana 12; 2005

Centro de Investigaciones Geológicas UNLP-CONICET

Palms constitute a conspicuous group of angiosperms characteristic in worldwide extant tropical and subtropical biomes. This family is an old one because appeared as early as early late Cretaceous of the northern hemisphere with their major radiation apparently taking place during the Paleogene. They Show a gradual increase in diversity through time across northern and southern latitudes of the world. In southern Gonwana the record of palms begins in the late Cretaceous from Chile and Argentina. In tertiary gondwanic sequences they have a conspicuous record in Brazil, Peru, Colombia, Argentina, Chile, India and New Zealand. In Argentina, palms have had a continuously presence since the late Cretaceous. Fossil studies were mainly focused in the Cretaceous-Tertiary boundary (K/T) of Patagonia, Although palm remains are also frequently presented in northern Argentina from Paleocene to upper Pleistocene. Regional Studies of fossil palms started 30 years ago and have since diversified to include the analyses of permineralizations belong to stem that appear during the late Cretaceous of northern Patagonia and constitute the oldest records of the family, particularly of Sabaloide, Coccoide and Phoenicoide groups; these remains surpass the K/T boundary and continue into the early Paleocene of Central Patagonia with primitive taxa belonging to Sabaloide, Coccoide and Bactrioide groups. Edited and inedited remains of permineralized fruits are recorded from late Cretaceous and early Paleocene sequences showing the presence of Coryphoid group. Morpho-architectural features of leaves are very diagnostic in extant palms. The presence of foliar impression remains recently foun in the early lower Paleocene of central Patagonia point out that Coryphoid and Iriartoid groups grew in argentinean paleofloras. Pollen and  phytoliths are also conspicuously present but, in general, they do not seem to be so diagnostic for systematic approaches. All these fossil and their affinities let us conclude that Argentinean Patagonian palms arose in the late Cretaceous northern Patagonian region including groups with primitive features belonging to Coryphoideae and Arecoideae subfamilies - late Cretaceous palms from central Chile enlarge the distribution of Coryphoid near the Pacific sea-.  During the early Paleocene, the record of both subfamilies continued, the Nyphoideae emerging at that time. These fact show that around K/T boundary, this clade was moderately diversified with five living groups growing at middle high latitudes in northern and central Patagonia.