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Abstract Detail


Paleobotanical Section

Gensel, Patricia G. [1], Fetter, Karl C. [2].

Assessing morphological variation and taxonomy from a collection of Early Devonian Psilophyton, Gaspê.

A large collection (>:70 specimens) of extensively preserved Psilophyton from the Emsian of Gaspê, Canada provides an opportunity to assess morphological variation within an Early Devonian plant and the role of taphonomy in producing some of the variation. While initially identified as P. forbesii, these specimens exhibit features not included in the species diagnoses. Branching varies among individuals in frequency and pattern. Two patterns occur: 1) irregular, nearly isotomous branching with long internodes and slender axes, some terminating in sporangia; and 2) branching at regular intervals, initial division pseudomopodial, with isotomous laterals bifurcating up to 7 times, shorter internodes, many fertile. While some branching resembles that demonstrated in other Psilophyton species, the first type is novel. Some stems exhibit irregular ribbing, others appear smooth. Most exhibit tiny epidermal papillae or papilla scars. Some of the variation in stem surface features may be explained by taphonomically induced features and some by how and at which level the matrix fractured across the plant. Stems covered with papillae differ in appearance on impression and compression remains. The presence on some, but not all fossils, of false papillae scars (seen on collapsed impressions), irregularly ribbed stems, and minute striations on the stem impressions are morphological characters that would not have been observable on the living plant, resulting from stem collapse during/after decay and compaction or the level where the specimen fractured. The majority of specimens thus differ from known P. forbesii in having epidermal papillae and in lacking regular ribbing caused by the presence of cortical sclerenchyma strands as in P. forbesii. The possibility that they extend the range of variation of P. forbesii was considered. Given the inconstancy and probable cause of ribbing and the presence of undoubted papillae, these specimens may represent a new species of Psilophyton.


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1 - University of North Carolina, Department of Biology, Cb#3280, Chapel Hill, North Carolina, 27599-3280, USA
2 - Biology, University of North Carolina, Chapel Hill, NC, 27599-3280, USA

Keywords:
Psilophyton
Early Devonian
Canada
morphological variation.

Presentation Type: Oral Paper:Papers for Sections
Session: 25
Location: 169/Law
Date: Monday, July 28th, 2008
Time: 2:45 PM
Number: 25001
Abstract ID:456


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