Oral Paper

         Paleobotany

A fossil moss from the Late Cretaceous (Campanian) James Ross Island, Antarctica

Presenting Author
Gar Rothwell
Description
Several specimens of an anatomically preserved moss gametophyte have been discovered in a calcium carbonate concretion from the “Baculites Hill” locality, James Ross Island, Antarctica.  The concretion is derived from the Late Cretaceous, Beta Member of the Santa Marta Formation, dated as early to middle Campanian (ca. 80 Ma).  These specimens have actinomorphic stems with alternate branching, spiral, patent leaf arrangement and large numbers of attached rhizoids. Stems are 210 µm in diameter with the largest branch measuring up to 3.7 mm long and 90-100 µm wide.  Most stems and branches appear to lack a distinct conducting strand and cell walls are thinner toward the center of the axis; but one specimen shows a central strand in several consecutive peels.  Cross sections show that the leaves are plicate with a simple D-shaped costal anatomy and unistratose intercostal area with a bistratose border. Stem leaves range from 650-700 µm wide and more than 700 µm long. The costa is percurrent, 90 µm wide and 55 µm thick. Intercostal cells are elongate, rhomboidal, L/W= 5:1.  No ornamentation or papillae have been observed on the upper medial cells of the leaf. These fossils show morphological similarities to several taxa of acrocarpus mosses, including rheophytic species of the Pottiales and some Orthotrichiales with respect to costal anatomy. Cretaceous bryophytes are underreported from Gondwana; thus, this fossil contributes meaningful data on moss diversity in Antarctic forests during late Cretaceous.