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The Devonian Period: a time of major plant diversification: a symposium in honor of Patricia G. Gensel and her contributions to Devonian paleobotany.

Strother, Paul [1].

The cryptospore record and the origin of land plants.

The origin of land plants was not a singularity in evolutionary time. It began with the de novo origin of an amphibious archegoniate gametophyte, which was followed by the progressive evolution of the subaerial sporophyte phase during the early Paleozoic. It ended with the origin of the polysporangiates during the Wenlock. The cryptospores, spore-like microfossils found in lower Cambrian to Devonian strata, provide us with two basic character sets which can be used to document evolutionary processes involved in plant sporophyte origins: 1) spore wall ultrastructure provides a model for the plesiomorphic condition of embryophyte sporoderm, 2) topology provides direct evidence of spore developmental patterns. The late Cambrian cryptospore, Agamachates casearius, demonstrates endosporic development that is consistent with aeroterrestrial Coleochaete as a model for early spore production. The antithetic alternation hypothesis of Bower is further supported by finds of Dapingian dyad clusters organized into “vegetative” thalli. The cryptospore fossil record indicates a Darriwilian transition from sequential to simultaneous meiosis in sporogenesis; however, the persistence of in situ dyads well into the Devonian indicates that isomorphic tetrads are not necessarily tracking the origin of embryophytes. Thus, the cryptospore record can be viewed as tracking the evolution of spore development in charophyte lineages which were leading up to the Wenlockian origin of the plant embryo, not as tracking the origin of embryophytes per se. The origin of aeroterrestrial algae, their influence on the pre-embryophytic landscape, and the evolution of early sporophyte development remain key evolutionary questions which will benefit from future paleobotanical inquiry.

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1 - Boston College, Paleobotany Laboratory, Weston Observatory, 381 Concord Road, Weston, MA, 02493, USA

Keywords:
cryptospores
Cambrian
antithetic alternation
character evolution
early land plants.

Presentation Type: Symposium or Colloquium Presentation
Session: SY10
Location: Prince of Wales/Riverside Hilton
Date: Wednesday, July 31st, 2013
Time: 8:15 AM
Number: SY10002
Abstract ID:181
Candidate for Awards:None


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