Abstract Detail

Paleobotany

Lopez, Madeleine [1], Tomescu, Alexandru [2].

An early moniliformopsid from the Lower Devonian (Emsian) of Quebec, Canada.

The Battery Point formation of the Gaspé Peninsula in Quebec hosts one of the most diverse assemblages of Emsian (Early Devonian) permineralized plant fossils worldwide, which continue to reveal new plant types from this period. One of these new plants is a previously unidentified euphyllophyte represented by axes c. 1 mm in diameter with five-lobed actinostelic primary xylem. While several specimens are heavily distorted taphonomically, well-preserved axes reveal an outline indicative of longitudinal ridges and grooves, and branch bases that protrude markedly. The epidermis, 25-50 µm thick, consists of cells with thickened walls, many with dark content and radially elongated. The relatively thin cortex has parenchymatous cells 24-28 µm in diameter. A thin phloem layer with narrow, thin-walled cells is preserved discontinuously around the xylem. The xylem strand consists of a central area of variable size (200-400 µm diameter) and lobes that protrude as far as 200 µm. Mesarch protoxylem strands are conspicuous close to the tip of each xylem lobe, but are absent from the central area. Metaxylem tracheids, up to 30-43 µm in diameter, display oval-scalariform to circular bordered pits and a pattern of decreasing size toward the xylem periphery. Vascular traces to laterals diverge radially from the xylem lobes, which become shorter immediately distal to the trace divergence. Along their trajectory through the cortex, traces become widened tangentially to 150-190 µm, elliptical to hourglass-shaped, with two conspicuous protoxylem strands. Suboptimal preservation of laterals, due to severe taphonomic processes, precludes characterization of their anatomy, but their trajectories reveal relatively extensive dichotomous branching. The protoxylem architecture of this new plant places it firmly among the moniliformopsids. This plant differs in protoxylem architecture and anatomy of trace divergence from the only other plant with bordered pits known in the Battery Point Formation, a much larger, unnamed pseudosporochnalean cladoxylopsid. Several features of this plant – undissected actinostele, with protoxylem only in the lobe tips and tracheid size decreasing toward the xylem periphery, and laterals supplied by a single trace originating from one xylem lobe – are consistent with iridopteridalean affinities, as traditionally circumscribed. However, except for the last one, all these features have been deemed homoplastic within the broader cladoxylopsid plexus. Anatomically-preserved fossils that push the origin of cladoxylopsids deeper in time and exhibit novel combinations of characters, such as this new Gaspé plant, when more fully understood, will help solve the systematic puzzles in this important Devonian plant group.

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

Keywords:
fossil
Devonian
Canada
euphyllophyte
cladoxylopsid
Cladoxylopsida
Iridopteridales
Moniliformopses.

Presentation Type: Oral Paper
Session: CK1, Cookson Award Session I
Location: Tucson G/Starr Pass
Date: Monday, July 29th, 2019
Time: 9:15 AM
Number: CK1006
Abstract ID:970
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award