Cretaceous seeds from Austral Basin, Argentina: their context in the angiosperm dispersal and evolution

A. IGLESIAS, A. ZAMUNER, D. POIRÉ, A. VARELA, A. CARIGNANO, S. RICHIANO, M. LUENGO, AND R. IRIBARREN

La Plata, Bs. As., Argentina

Congreso; VII Congreso Latinoamericano de Paleontología- X Cong. Arg. de Paleo. y Bioestrat.; 2010

With angiosperm radiation and diversification during Upper Cretaceous, deep floristic changes occur that drive to modern ecosystems. Little is known about plant ecology and seed dispersal during the Cretaceous. Rich compression floras founded in Piedra Clavada (Albian), Mata Amarilla (Cenomanian), and La Anita (Conicacian?-Campanian?) formations in the northern Austral Basin, allow the recognition of diversified angiosperm floras of leaves, flowers, fruits, and seeds. Up to now there was identified seven seed types all with very small size (0.4-5 mm); coincident with global Cretaceous records. Some seeds preserve woody envelope with regulate ornamentation and two lateral wings, similar to Albian records from USA. Spherical seeds with pedunculate hilum show a pair of wing and others three longitudinal keels. Some of these, with exceptional preservation, confirm endosperm cells. The biggest seeds were found inside small dry fruits. Presence of winged seeds and the general small seed size in these floras indicate both anemochory like the most common seed dispersal mechanism and fast growing seedling. The Cretaceous is important in the evolution of seed disperser like mammals and birds. Several interaction theories have been proposed base on cretaceous seeds shape and size for the North Hemisphere. The Austral Basin fossil record plus several others Upper Cretaceous and Paleogene Patagonian macrofloras under study, could give light in the understanding of the plant-disperser evolution in southern South America with a fairly continuous fossil record.