Abstract Detail



Paleobotany

Bonacorsi, Nikole [1], Gensel, Patricia [2], Hueber, Francis [3], Leslie, Andrew [4].

An Early Devonian (Emsian) plant with implications for the evolution of heterospory.

Heterospory, or the production of different spore size classes, is integral to derived vascular plant reproductive strategies. Heterospory has evolved multiple times and is widespread across extinct and living lineages, but early stages in its evolution have rarely been observed. We describe a Devonian plant with an unusual distribution of spore sizes, Omniastrobus dawsonii gen. nov., which may show an intermediate step in the emergence of heterospory. We examined Early Devonian (early Emsian) material from the Campbellton Formation of New Brunswick consisting of fragmentary strobili containing numerous (more than 80 in total) carbonized spore masses. We macerated these spore masses using standard techniques and characterized spore size distributions within and across sporangia and strobili. The vegetative parent axes and the exact arrangement of strobili in Omniastrobus are unknown, but strobili are morphologically similar to those of the Devonian order Barinophytales and consist of two rows of large lateral sporangia. Unlike other Barinophytales, however, sporangia within strobili show a continuous gradient in average spore size, from those producing smaller spores (~70-150 μm) to those producing larger spores (>200 μm). Sporangia with larger spores appear to be produced towards, but not at, the strobilus tip, while more basal sporangia produced smaller spores. Sporangia from the only preserved strobilus apex produced a bimodal mix of spore sizes, a form of heterospory otherwise known only from Barinophytales among vascular plants. Although preservation of Omniastrobus is fragmentary, strobilus morphology and the presence of lateral sporangia suggest placement within lycophytes, either in Barinophytales or zosterophylls more broadly. Omniastrobus is coeval with the earliest previously known heterosporous plant (the early euphyllophyte Chaleuria) and it represents the oldest non-homosporous lycophyte. The highly variable spore size distribution of Omniastrobus is unusual among known plants, although similar patterns are present in a few unrelated Paleozoic taxa, suggesting that this may be a common early step in the evolution of heterospory.


1 - Hamilton College, Biology Department, 198 College Hill Rd, Clinton, NY, 13323, USA
2 - University Of North Carolina, Department Of Biology, CB# 3280, Coker Hall, Chapel Hill, NC, 27599, United States
3 - 529 School Lane, Rehoboth Beach, DE, 19971, United States
4 - Stanford University, Geological Sciences, 450 Jane Stanford Way, Building 320, Room 118, Stanford, CA, 94305, United States

Keywords:
heterospory
Lycophyte
reproductive biology
reproductive strategy.

Presentation Type: Oral Paper
Number:
Abstract ID:414
Candidate for Awards:None


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