Mesenteriophyllum serratum Sixtel, 1961

Bomfleur, Benjamin, Krings, Michael, Taylor, Edith L. & Taylor, Thomas N., 2011, Macrofossil evidence for pleuromeialean lycophytes from the Triassic of Antarctica, Acta Palaeontologica Polonica 56 (1), pp. 195-203 : 198

Mesenteriophyllum serratum Sixtel, 1961

Fig. 4 .

Material.—PCUK T5568, one block containing three larger leaf segments and abundant smaller leaf fragments.

Description.—Leaves strap−shaped, apparently sterile, exceeding 10 cm in length, up to 15 mm wide proximally ( Fig. 4A ), slightly tapering toward the tip, entire−margined, with two longitudinal rows of transversely to slightly obliquely oriented ridges and furrows alternating at regular intervals of about 1 to 2 mm ( Fig. 4A–C ); in compression fossils the margins having a serrated macroscopic appearance ( Fig. 4A, B ). Central leaf portion with rectangular elongated cells arranged longitudinally in a brick−like manner ( Fig. 4F, G ), cuticles with prominent longitudinal striae and dense pattern of small circular depressions ( Fig. 4C, E ); leaf margins with about fifteen to twenty more or less regular longitudinal rows of transversely elongated, rectangular to rounded cells with smooth cuticle ( Fig. 4C, D ).

Remarks.—The genus Mesenteriophyllum has been characterized in the original description as long, linear leaves with a single, thick, centrally positioned vein and a transversely wrinkled or folded lamina ( Sixtel 1961, 1962). The present specimens are assigned to Mesenteriophyllum serratum ( Fig. 5 ), which differs from the type species M. kotschnevii in its smaller size (100–150 mm length by 10–15 mm width), tapering outline, and by the characteristic small “teeth” along the lateral margins ( Sixtel 1961, 1962). The Antarctic specimens indicate that the margins are in fact entire, and that the serrate macroscopic appearance represents an alternating pattern of transverse ridges and depressions close to the leaf margins.

Figures

Fig. 4. Pleuromeialean lycophyte leaf Mesenteriophyllum serratum Sixtel, 1961 from the Upper Triassic of the “Alfie’s Elbow” site, central Transantarctic Mountains. A. Two overlying leaf fragments recognizable primarily by the distinct serrate appearance of the leaf margins. B. Detail of A showing serrate appearance of margins.C. Detail of leaf margin with alternating transverse ridges and furrows, and preserved cell pattern. Note longitudinal striae (s), circular holes on central leaf portion (some marked with arrows), and vertical alignment of transversely elongated epidermal cells (e) on leaf margin. D. Detail of leaf margin with cellular preservation, showing transversely elongated cells aligned in vertical rows. E. Detail of longitudinal striae on central leaf portion. F, G. Orthogonal pattern of epidermal cells in central leaf portion, visible only in places where carbonized cuticle layer is lifted off.

Fig. 5. Pleuromeialean lycophyte leaf Mesenteriophyllum serratum Sixtel, 1961 from the Triassic Madygen Formation, Kyrgyz Republic. Modified from Sixtel (1961). Leaf width up to ~12 mm.