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Abstract Detail

Paleobotanical Section

Shelton, Glenn W.K. [1], Rothwell, Gar [2], Stockey, Ruth [2], Tomescu, Alexandru M.F. [1].

A second tricostate moss from the Early Cretaceous of Vancouver Island, British Columbia.

The Early Cretaceous (Valanginian, ca. 136 Ma) fossil flora of Apple Bay (Vancouver Island) is emerging as a hotspot of fossil bryophyte diversity: up to 18 or more distinct moss and leafy liverwort gametophyte morphotypes, and several types of thalloid gametophytes, are preserved by calcium carbonate permineralization in near-shore marine carbonate concretions. Among the mosses, at least four types exhibit tricostate leaves. The gametophytes of these tricostate mosses range from robust to diminutive, with sparse to profuse branching, a heterogeneity not uncommon among extant moss groups. They share helical phyllotaxy, unistratose, tricostate leaves with costae extending close to the leaf tips. One of the four morphotypes consists of highly branched gametophytes bearing numerous antheridia on lateral branches and likely belongs in the pleurocarpous clade. The second tricostate morphotype is represented by at least six gametophyte shoots up to 1 cm long, which bear infrequent branches. Stems are 230-370 µm in diameter and typically preserve only ca. ten of the outermost cell layers; cell diameters are 8-12 µm and the epidermis consists of smaller, thicker-walled cells. Foliage density is moderate (4-6 leaf bases/mm). The leaves are narrow and probably lanceolate. They are up to 4 mm long, 0.6 mm wide at the base, up to 0.9 mm wide mid-leaf, and tapering abruptly to ca. 0.5 mm in their distal half. Laminae are unistratose throughout and thin (12-14 µm), with three weak plications. Laminal cells are small (4.5-25 µm) with thin walls and typically quadrate. Cell morphology does not appear to change with position along the leaf and juxtacostal cells are not differentiated from laminal cells. Alar regions consist of patches of ca. 10 x 10 round or irregularly shaped cells 16-27 µm in diameter. The costae are strong (ca. 0.9 of the leaf length) and ca. 7 cells wide; the cells are long (36-66 µm) and narrow (4.5-12 µm diameter). Median costae are up to 145 µm wide and 45 µm thick, while lateral costae are up to 88 µm wide and 45 µm thick. Aside from the Early Cretaceous of Apple Bay, tricostate mosses (with three independent costae) are known only from Mesozoic rocks in Russia and Mongolia. Together with the Apple Bay tricostate mosses, these fossils may represent a unique group of extinct mosses which had radiated throughout Laurasia by the Early Cretaceous.

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1 - Humboldt State University, Department of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA
2 - Oregon State University, Department of Botany and Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331, USA

tricostate moss

Presentation Type: Oral Paper:Papers for Sections
Session: 3
Location: Melrose/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 9:15 AM
Number: 3005
Abstract ID:916
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award

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