Erdei, Boglarka , Manchester, Steven .
Dioonopsis leaves from the Eocene of Western North America--a cycad shared with the Paleogene of Japan.
Reexamination of western North American Cenozoic cycad leaves, with attention to epidermal anatomy as well as morphology and venation, indicates that species formerly assigned to extant genera Ceratozamia, Dioon and Zamia from the Eocene of California and Alaska do not actually represent these modern cycad genera. Reinvestigation of cycad leaf and leaflet remains from the Eocene floras of Hamilton Bay, Alaska and La Porte, California leads to the recognition that they belong to Dioonopsis, an extinct genus first recognized in the Paleogene of Japan. The leaves are simply pinnate. The pinnae that vary from entire margined to minutely spinose are inserted suboppositely on the rachis with broad bases, similar to species of Dioon. Venation is parallel, with common dichotomies and occasional anatomoses. Leaves are hypostomatic with haplocheilic stomata scattered, and randomly arranged in intercostal areas. Guard cells are sunken and overarched by subsidiaries (4-7) forming a strongly cutinized coronal rim. Ordinary epidermal cells are isodiametric and slightly elongated over veins. The epidermal features distinguish these fossils from extant genera but coincide well with the extinct genus Dioonopsis. Confirmation of Dioonopsis in the Eocene of western North America as well as Japan, combined with its apparent absence in the European Tertiary, indicates that it probably spread via the Beringial phytogeographic pathway. This contrasts with our current knowledge of another extinct cycad, Eostangeria, shared between the Paleogene of North America and Europe which suggests linkage across the North Atlantic connection. The presence of Dioonopsis in southern Alaska during the Eocene, along with current understanding that these fossiliferous strata were nearly in their modern latitudinal position by the Eocene, leads to the conclusion that these cycads were able to occupy high latitude environments. This, however, implies that Alaskan Dioonopsis was exposed to light stress contrary to the present-day environment of modern cycads where light is not a limiting factor. This investigation was supported by a Fulbright award to the first author.
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1 - Hungarian Natural History Museum, Botanical Department, ,Budapest, , H-1476, POB222, Hungary
2 - University of Florida, Florida Museum of Natural History, PO Box 117800, Gainesville, FL, 32611, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Forsyth Room/Chase Park Plaza
Date: Wednesday, July 13th, 2011
Time: 11:15 AM