Australian analogs for an Eocene Patagonian Paleorainforest
Open Access
- Author:
- Merkhofer, Lisa Marie
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 02, 2014
- Committee Members:
- Peter Daniel Wilf, Thesis Advisor/Co-Advisor
- Keywords:
- leaf size
paleoecology
Laguna del Hunco
paleorainforest - Abstract:
- The diverse Laguna del Hunco (LH) paleoflora from early Eocene Patagonia, Argentina, has striking similarities to subtropical and tropical Australian rainforests. Previous research recognized the Simple Notophyll Vine Forests (SNVFs) of montane New South Wales, Australia, as potential analogs for the paleoflora in terms of diversity, floristic composition, leaf size, and environment. In this study, I test this hypothesis by: (1) inferring the Laguna del Hunco rainforest type; (2) quantitatively comparing the paleoflora to 596 Australian rainforest plots; and (3) comparing these results to non-Australian regions in Australasia and Southeast Asia where Laguna del Hunco’s nearest living relatives also occur. First, I inferred rainforest type using paleofloristics and fossil dicot leaf area. Fossil leaf area was measured directly or estimated with the Cain and Castro formula, the Raunkiaer-Webb size classes, or vein scaling, a new method that has not yet been applied to fossils and uses a scaling relationship between leaf area and secondary vein density. By testing all three methods on 159 fossil leaves with intact areas, I found that vein scaling was as accurate at predicting leaf area as the Raunkiaer-Webb size classes, but more applicable to fragmentary leaves. When I used vein scaling to reconstruct the areas of 94 fragmented specimens from LH, the paleoflora’s grand mean leaf area increased by ~360 mm2, recovering large leaf areas that were previously undetected. Across 1152 fossil leaves representing 154 dicot species, Laguna del Hunco’s mean leaf size was 1755 mm2, or large microphyll. The paleoflora’s leaf size index and floristic composition were found to support its similarity to an SNVF. Secondly, I found that subtropical rainforests with moderate, but not montane elevations, were the closest Australian analogs for LH both in terms of leaf size, family composition, and the generic occurrences of Laguna del Hunco’s nearest living relatives (NLRs). Lastly, I found that Laguna del Hunco’s NLRs occurred in three non-overlapping climate regions: cool-dry areas in subtropical Australia, hot-wet areas in tropical Australia, and cool-wet areas not found in Australia, but in montane Australasia and Southeast Asia. These results suggest that Australia no longer has the cool, wet montane environment needed to support some of the lineages from the paleoflora. This study uses a novel, quantitative method of fossil-modern comparison that can be applied to other paleofloras, allowing paleoecological interpretations to be more precisely based on both taxon-free and taxon-informed data.