RARE LEAF FOSSILS OF MONIMIACEAE AND ATHEROSPERMATACEAE (LAURALES) FROM EOCENE PATAGONIAN RAINFORESTS AND THEIR BIOGEOGRAPHIC SIGNIFICANCE

Two Eocene fossil sites in Patagonia, Argentina, Laguna del Hunco (LH, ca. 52.2 Ma) and Río Pichileufú (RP, ca. 47.7 Ma), 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. We focus on rare, toothed fossil leaves that show affinities to Laurales, a magnoliid order in the basal angiosperms. These fossils represent the families Atherospermataceae and Monimiaceae, which currently exhibit broad, often disjunct southern distributions and thus hold much interest for Gondwanan biogeography. However, the fossil records of these families are exceptionally scarce. For Laurelia guinazui Berry 1935 (Atherospermataceae), we report 16 new fossil specimens from LH and RP that have greater detail preserved than in the two syntypes (RP). Morphological character evaluation suggests an extinct genus with closest affinity (in decreasing order) to the extant genera Daphnandra, Doryphora (both Australia), Laureliopsis (Chile and Argentina), and Laurelia (New Zealand and Chile). Laurelia guinazui was long considered a probable Patagonian element of the RP flora, but this study suggests stronger modern affinity to Australia. Monimiaceae is represented by a single fossil specimen from LH. Among extant genera, the greatest morphological similarity is to Wilkiea (Australia), apparently in contrast with molecular analyses that place the divergence of the clade containing Wilkiea in Australasia between 16 and 38 Ma (Renner et al., 2010. J. Biogeography 37:1227). This result implies that the lineage may be much older and have a much broader biogeographic history across Gondwana. Our results significantly improve the fossil record of two families in Laurales by establishing occurrences in Eocene Patagonia. The fossils were found at great modern distance from many of their closest living relatives, increasing the links of the LH and RP fossil floras to Australasia and further weakening their signal in extant South American forests.