Abstract Detail



Paleobotany

Nibbelink, Megan [1], Tomescu, Alexandru [2].

Exploring zosterophyll diversity in the Emsian (Early Devonian) permineralized assemblages of the Battery Point Formation (Québec, Canada).

The Battery Point Formation of Québec, Canada hosts a rich Emsian (Early Devonian) flora, with plants preserved as compressions or permineralized fossils. Several of these have been assigned to the Zosterophyllopsida. Members of this group are recognized based on their laterally attached bivalvate sporangia, exarch protosteles with Gosslingia-type (G-type) tracheids, and sometimes K-branching or subaxillary tubercles. Up until now, three zosterophyll genera have been recognized in compression fossils of the Battery Point Formation (not counting Renalia): ZosterophyllumSawdonia, and Crenaticaulis. Of these, only Crenauticaulis is known also from permineralized specimens in this unit. Our survey of the Battery Point Formation flora has uncovered additional permineralized zosterophylls. All 15 or more specimens are relatively small axis segments possessing exarch protosteles with G-type tracheids. Taphonomically, these specimens range from relatively well preserved axes to fully decorticated xylem strands; a few are charcoalified. Five of the axes exhibit instances of branching and one specimen bears a circinate side-branch. At least two distinct morphotypes are present in this new material. One of them has axes c. 1.5 mm thick that display a distinct phloem layer around the xylem, as well as a layer of thicker-walled cells in the parenchymatous inner cortex, reminiscent of an endodermis. One of these axes exhibits two minor xylem strands that undulate longitudinally through the cortex along the main xylem strand, which is oval in cross section. The tissues of this axis host structures interpreted as fungal spores and hyphae. The second morphotype consists of generally smaller axes with a cylindrical xylem strand. These axes have a parenchymatous cortex preserved as a generally amorphous light-colored organic material, and a characteristic epidermis consisting of very large cells with thick, convex outer periclinal walls. Incomplete preservation of several zosterophyll axes precludes assignment to a particular morphotype, whereas other axes await detailed investigation. The minute circinate branch of one of the specimens contains fully differentiated tracheids close to its tip, which suggests a dormant branch primordium. This initial survey of anatomically-preserved zosterophylls in the Battery Point Formation reveals encouraging diversity and reiterates the importance of permineralized fossils in documenting patterns of diversity, as well as their potential to uncover unexpected details relevant to the physiology of these plants. This survey also underscores the need for developing a solid set of criteria to distinguish the different zosterophyll genera anatomically and to resolve the taxonomic placement of new fossils.


1 - Humboldt State University, Biological Sciences, 1 Harpst St, Arcata, CA, 95521, USA
2 - Humboldt State University, 1 Harpst St., Arcata, CA, 95521, United States

Keywords:
fossil
Devonian
Canada
anatomy
zosterophyll
Zosterophyllopsida.

Presentation Type: Oral Paper
Number: 0003
Abstract ID:944
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award


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