Palaeocene high-latitude leaf flora of Antarctica Part 2: Tooth-margined angiosperms

The late Palaeocene (Thanetian) Cross Valley Formation on Seymour Island is one of the few floras of this age in Antarctica. Understanding the diversity is critical for comparisons with coeval high-latitude forests and their evolution across South America and Australasia. This macroflora has few conifers and ferns but a significant diversity of angiosperms. Taxonomic assessment of previously undescribed morphotypes, based on new and existing collections, facilitated the identification of twelve new tooth-margined angiosperms of uncertain affinities. Comparisons to Gondwanan families already established in the Cross Valley Flora from pollen and wood records include Nothofagaceae, Proteaceae and Cunoniaceae. A total of 37 angiosperm taxa, including 23 tooth-margined and 14 entire-margined morphotypes, have been described from the Cross Valley Flora. They provide evidence that the most diverse Palaeocene floral assemblage recorded from this region inhabited the east side of the Antarctic Peninsula. The new morphotypes enrich the cool-temperate nature of the angiosperms that dominated over the conifers in these high-latitude forests. They indicate dynamic forests that responded to frequent disturbance as they grew on the slopes of active volcanoes; a physical divide that created a rainfall and climatic gradient from east to west across the Antarctic Peninsula. Floral elements, such as Proteaceae that indicates drier climates and Nothofagaceae that indicates cooler climates, signify that these forests were on the lee side of volcanoes on the Antarctic Peninsula. These forests represent extirpation and retraction of the Valdivian cool-temperate rainforests, which extended further south than their modern Patagonian distribution, in southern South America. Thus, the new morphotypes suggest additional floral diversity was present in the late Palaeocene and highlight the diversity contrast between the east and west Antarctic Peninsula.

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