186-2 Ecophysiological Traits of Late Mesozoic Cycadeoids

Session: New Approaches to Old Fossil Collections (Posters)

Poster Booth No.: 66

Presenting Author:

Wray Jones

Authors:

Jones, Wray D.¹, Wilson, Jonathan², Matthaeus, William J.³, White, Joseph Daniel⁴, Hametz-Berner, Rebecca⁵, Mattison, Wyatt⁶, Peppe, Daniel J.⁷

(1) Department of Geosciences, Baylor University, Waco, TX, USA, (2) Department of Environmental Studies, Haverford College, Haverford, PA, USA, (3) Trinity College Dublin, Discipline of Botany, Dublin, Ireland, (4) Department of Biology, Baylor University, Waco, TX, USA, (5) Department of Environmental Sciences, Haverford College, Haverford, PA, USA, (6) Department of Environmental Science, Haverford College, Haverford, PA, USA, (7) Department of Geosciences, Baylor University, Waco, TX, USA,

Abstract:

The enigmatic Bennettitaleans, also known as cycadeoids, were key components of late Paleozoic and Mesozoic plant communities. The unique reproductive organs of the group have received considerable scientific attention for their possible connections to the rise of angiosperms; however, little is understood about the rest of cycadeoid functional morphology. Furthermore, the broad morphological resemblance between Bennettitalean plants and extant cycads has led to the assumption that these two groups shared similar ecophysiological traits and strategies. However, the lack of attention to cycadeoid vegetative biology has meant that very little is known about cycadeoid physiology despite their common occurrence in the fossil record. Analysis of secondary xylem characteristics of Cycadeoidea provides insight into how the plants grew, interacted with their environments, and the stressors that caused them to ultimately go extinct at the end of the Mesozoic. This study focuses on bennettitalean taxa in the Wieland Type Collection housed at the Yale Peabody Museum, and focuses on four cycadeoid species: Cycadeoidea wielandii, Cycadeoidea dacotensis, Cycadeoidea nana, and Cycadeoidea paynei. We analyzed slides originally prepared by Lester F. Ward and George R. Wieland in the late 19th and early 20th centuries which still preserve measurable vascular tissue. We measured xylem characteristics, including pit density, area and tracheid length, which inform plant survival via their ability to effectively transport water from roots to shoots. Typical tracheid length within the genus Cycadeoidea ranged in size from 39–72 microns and have an average length of 2.3 millimeters. Older tracheids nearest to the pith generally are larger in diameter compared to those closest to the vascular cambium. Furthermore, tracheid and pit measurements from the early Cretaceous bennettitaleans reveal nearly indistinguishable stress resistance (P₅₀) values between all four Cycadeoidea species measured. This investigation into the variation of Bennettitalean vulnerability between species further demonstrates the necessity of understanding these unique and extinct plants’ role throughout deep time as dominant organisms and will better constrain ecosystem dynamics, including water and carbon cycling, in the Mesozoic Era.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6115

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