178-9 Changes in Average Miospore Size Through the Silurian and Devonian

Session: Paleontology, Diversity, Extinction, Origination

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Authors:

Abstract:

An increase in spore size is a well-known feature of the Devonian plant fossil record. Early land plant spores were generally small (<50 microns in diameter), but maximum sizes had increased dramatically by the end of the Middle Devonian. This increase has often been linked with the initial evolution of heterospory and large megaspores, but it also encompasses many apparently homosporous taxa with intermediate spore size ranges (100-200 microns in diameter) which are rare outside of the Devonian. The late Early through Middle Devonian then represents one of the most unusual intervals in the plant palynological record, but the exact nature, timing, and geographic extent of the trend towards larger spores is unclear. We compiled spore corpus diameter measurements in published Silurian and Devonian palynofloras from modern North America, Europe, South America, Africa, the Middle East, Australia, and China to explore when this spore size increase occurs and whether it occurs globally or regionally. We find that large spores are generally characteristic of the Middle Devonian with increases in spore size beginning in the Pragian seen in areas with complete data sets (North America, Europe, South America, Africa and the Middle East). Across regions, shifts in spore size are associated with taxic turnover, where late Early to Middle Devonian increases reflect the appearance of larger spore genera combined with the loss of smaller ones. Though the turnover varies between regions with different regions showing turnover of different genera. Consistent with this, increasing spore size appears to be an active trend in regions with appropriate sampling, reflecting a shift in the mean and distribution of spore sizes rather than simply an increase in maximum size. Our data then suggests that the larger spores characteristic of the late Early to Middle Devonian are a globally synchronous phenomenon that likely reflects changes in plant ecology towards the end of the Early Devonian that favored the evolution of larger spores.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9509

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