Abstract Detail

Paleobotany

Torres, Sirena A. [1], Stockey, Ruth [2], Rothwell, Gar [3], Tomescu, Alexandru [4].

A third tricostate moss from the Lower Cretaceous of Vancouver Island (British Columbia, Canada).

The Early Cretaceous (Valanginian, 136 Ma) fossil assemblages at Apple Bay on Vancouver Island host abundant fossil bryophytes preserved by permineralization in near-shore marine concretions. Notable within this assemblage are mosses characterized by tricostate leaves, two of which have been formally described. A third type of tricostate moss is characterized by relatively large gametophytes with stems 600 µm in diameter possessing small (15 µm), thick-walled epidermal cells and cortical cells that are increasingly larger and thinner-walled toward the center. The incompletely preserved central tissues of the stem probably consisted of large thin-walled cells. Branch primordia occur at close intervals (every 1.5-2 mm) above leaf axils, in three different positions around the stem. Leaves are densely arranged, arising every 200-400 µm in 1/3 helical phyllotaxis. They are ovate (at least 3.5 mm long and 2.4 mm wide), with a 1.2 mm wide base. Leaves bear three strong costae (310 µm wide, 120 µm thick): one central and two symmetric lateral costae. The costae are abaxially convex and flat adaxially, diverge separately from the stem, and fuse close to the leaf apex. Between the two differentiated epidermal layers, costae have homogeneous anatomy with long, narrow (up to 10 µm), thin-walled cells, and irregular elongate air spaces. The lamina is unistratose (narrow bistratose portions adjacent to costae), up to 480 µm wide between costae and 240 µm laterally, to the leaf margin. Laminal cells are isodiametric, polygonal-rectangular, up to 18 µm in diameter, like the cells that form the abaxial epidermis of the costae. Three-dimensional branching architecture, indicating upright growth habit, and the isodiametric laminal cells are consistent with acrocarpy, a condition also seen in three other Apple Bay mosses: Meantoinea, Tricarinella, and an unnamed leucobryacean. In contrast, the two other tricostate mosses described from Apple Bay (Tricosta and Krassiloviella) are pleurocarps. Aside from Apple Bay, tricostate mosses are known only as compressions assigned to genus Tricostium in Mesozoic rocks of Russia and Mongolia. Species of Tricostium differ from the Apple Bay moss in having a central costa more pronounced than the lateral costae, and lanceolate leaves, but further comparisons with Tricostium are hindered by differences in mode of preservation. Characterization of this new moss continues ongoing efforts to document patterns of diversity in the rich Apple Bay bryoflora. The unique combination of characters of this moss reiterates the importance of the fossil record in revealing hidden diversity relevant to bryophyte evolution.

1 - Humboldt State University, 1 Harpst St., Arcata, CA, 95521, USA
2 - Oregon State University, Department Of Botany And Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331.0, United States
3 - Ohio University, and Oregon State University, Environmental and Plant Biology, and Botany and Plant Pathology, 308 Porter Hall, Ohio University, Athens, OH, 45701, USA
4 - Humboldt State University, 1 Harpst St., Arcata, CA, 95521, United States

Keywords:
bryophytes
moss
fossil
anatomy
acrocarpous
Cretaceous
Canada
British Columbia.

Presentation Type: Oral Paper
Session: CK2, Cookson Award Session II
Location: Tucson G/Starr Pass
Date: Monday, July 29th, 2019
Time: 10:30 AM
Number: CK2002
Abstract ID:620
Candidate for Awards:Isabel Cookson Award