RARE LEAF FOSSILS OF MONIMIACEAE AND ATHEROSPERMATACEAE (LAURALES) FROM EOCENE PATAGONIA: BIOGEOGRAPHY OF ANCIENT SOUTHERN RAINFOREST LINEAGES

Two Eocene fossil localities, Laguna del Hunco (LH, 51.9 Ma) and Río Pichileufú (RP, 47.5 Ma), from Patagonia, Argentina have some of the most diverse fossil floras known. They represent angiosperm-dominated Gondwanan rainforests and have been the focus of many paleontological and geological studies. Here, we focus on a portion of the flora that has received little attention: rare, toothed fossil leaves with affinities to the magnoliid order Laurales, representing the families Atherospermataceae and Monimiaceae. These are ancient lineages that currently exhibit broad, often disjunct southern distributions and thus hold much interest for Gondwanan biogeography. However, few fossils of these families exist to resolve their history. Our purposes are to: 1) formally describe two fossil species from new material and evaluate the presence of the families in Eocene Patagonia; 2) determine modern genera showing the closest affinities; and 3) use the results to improve current understanding of Laurales biogeography. The first fossil species, Laurelia guiñazui Berry 1938, was originally described from RP and placed in Monimiaceae. Subsequently, Laurelia (South America and New Zealand) was assigned to Atherospermataceae. We report 19 new fossil specimens of L. guiñazui from LH and RP with greater detail of venation and teeth preserved than in the holotype. From this material, we support placement of L. guiñazui in Atherospermataceae (not necessarily in any living genus) based on several typical characters: low leaf rank and vein density, acute basal secondaries, brochidodromous secondaries, and large, glandular, highly irregular, compound teeth. The second fossil species is represented by a single specimen from LH and is undescribed. It exhibits distinct ‘Monimioid’ teeth and other features allowing confident placement in Monimiaceae. Among extant genera, we note strongest similarity to Wilkiea and Austromatthaea (both Australia) based on: low leaf rank, basally thickened midvein, strongly brochidodromous secondaries with basal pair acute, and small, closely spaced glandular teeth. These preliminary results from Eocene Patagonia appear to contrast with molecular analyses, which place the divergence of the clade containing these two genera in Australasia ~29 Ma (Renner et al., 2010. J. Biogeography 37:1227).