MartŪnez, Camila , Cuneo, Nestor , Gandolfo, Maria A. .
Angiosperm fossil leaves with preserved cuticles from the Lefipan Formation, Late Cretaceous, Patagonia, Argentina.
The Maastrichtian, the last stage of the Cretaceous (70.6 to 65.5 million years ago), was a period of time characterized by two major thermic events, the first episode started at the end of the Campanian and extended to the beginning of the Maastrichtian (71- 69.5 Ma) while the second began approximately 68 Ma and terminated at about 65.5 Ma, at the K/T boundary. It was during the second episode that the temperatures decreased in surface and intermediate waters in the southern high latitudes, affecting the continental temperatures. The temperatures were cooler than those in other basins. Herein, we report on a study focused on venation patterns, leaf venation density values, cuticle analyses, and leaf insect damage of impression/compressions of angiosperm leaves from the Maastrichtian Lefip√É¬°n Formation of Patagonia, Argentina that support the decrease in temperature during the K/T boundary for the southern high latitudes. Based on their leaf architecture six angiosperm morphotypes are described. Interestingly, one of these morphotypes is characterized by the presence of strong intramarginal secondary veins, and major secondary polygonal reticulodromous vein pattern with decurrent attachment, and for its very well-preserved cuticle in which trichomes, polycytic stomatal type and papillae cuticular surface ornamentation are clearly observable. Altogether, these characters are indicative of Lauraceae affinities. Additionally, six leaf insect-damages are described for this morphotype (galling, surface, hole and margin feeding). We also calculate the leaf venation density with the goal of inferring the type of ecosystem in which these plants grew. The obtained values are much lower than the values from previously described Maastrichtian tropical areas that show peak values that are comparable with modern megathermal rainforest angiosperm trees. The low value of leaf venation density of the Lefip√É¬°n paleoflora shows a different pattern more associated to temperate zones with low productivity. Because the presence of this particular Lauracean morphotype was also described for the Danian (Paleocene) Salamanca Formation, it provides an example of plants that survived the K/T boundary. The new fossil locality described for the Lefip√É¬°n formation provides evidence to understand the diversity and dynamics of Cretaceous South American angiosperms.
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1 - Universidad de los Andes, BotŠnica y SistemŠtica, Cra. 1 #18A-10, BogotŠ, BogotŠ, Colombia
2 - MEF AV. FONTANA 140, TRELEW-CHUBUT, N/A, 9100, Argentina
3 - Cornell University, L. H. BAILEY HORTORIUM, 410 Mann Library Building, ITHACA, NY, 14853-4301, USA
Leaf venation density.
Presentation Type: Oral Paper:Papers for Sections
Location: Union A/Hyatt
Date: Monday, July 9th, 2012
Time: 2:45 PM