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El-Abdallah, Samar [1], Bippus, Alexander [2], Tomescu, Alexandru [3].

Characterizing an Early Devonian zosterophyll from the Beartooth Butte Formation of Wyoming.

Western North America marks a significant blank spot in Early Devonian plant biogeography. Here, the Beartooth Butte Formation (Wyoming) hosts the only abundant Early Devonian plant fossil assemblages, dated to the Lochkovian-Pragian (c. 415-409 Ma ago). Because of their age and geographic position, these assemblages are key to revealing the picture of Early Devonian vegetation and global comparisons across geologic time and space, and can contribute new taxa for studies of early tracheophyte phylogeny and morphological evolution. However, few of the plant types present in the Beartooth Butte Formation have been characterized in detail, to date. One abundant previously uncharacterized plant types is represented by numerous (>400) compression specimens, some bearing cuticle. Axes of this plant are smooth, 2.7-6.2 mm wide. At the base of the plant, multiple axes radiate from a central point. At branching points, spaced 5-57 mm apart, axes diverge at acute angles running more-or-less parallel to each other; we observed specimens including up to four orders of axes. Axes terminate in circinate tips, which consist of several coils or may be simpler and hook-like. The reniform sporangia, attached laterally, are sparse and were probably spaced far apart along the axes; occasionally, several sporangia may be borne in a file directly below apical croziers, along their ‘adaxial’ side. The axes also bear bumpy lateral structures with rounded or slightly coiled apices. These structures consist of darker material than the subtending axes and probably represent dormant branch meristems. The laterally attached sporangia and circinate apices are indicative of zosterophyll affinities. Among zosterophylls, this plant is similar to Gosslingia and Oricilla due to the size range of its smooth axes, crozier morphology, and the distinctive parallel branching. The paucity of sporangia fits a pattern that characterizes the Beartooth Butte Formation flora, more generally, suggesting that clonality was the main mode of propagation in these plant populations. The dormant branch meristems are consistent with a clonal growth strategy. Taphonomic evidence (plant fragment size and grouping, low frequency of aquatic invertebrate encrusters) suggests that populations of this plant were growing a short distance up-slope from the floodplain areas wherein their fossils were preserved in flood deposits. We are currently performing morphometric analyses of the rich material representing this plant type. These analyses will result in a whole-plant concept, which will enable more precise taxonomic placement and empirically-informed inferences on the life history of this plant.

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1 - Humboldt State University, Department of Biological Science, Arcata, CA, 95521, USA
2 - Oregon State University, Department of Botany and Plant Pathology, 2701 SW Campus Way, Corvallis, 97331, USA
3 - Humboldt State University, Department Of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, United States

early tracheophyte.

Presentation Type: Oral Paper
Session: PL3, Paleobotany: Honoring Fran Hueber - Session 1
Location: /
Date: Tuesday, July 20th, 2021
Time: 11:30 AM(EDT)
Number: PL3004
Abstract ID:448
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award

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