Resumo

BODNAR, Josefina  e  ARTABE, Analía E.. Systematic and palaeodendrological study of a Triassic Cupressaceae wood from the Ischigualasto Formation, San Juan Province, Argentina. Ameghiniana [online]. 2007, vol.44, n.2, pp.303-319. ISSN 1851-8044.

A silicified wood collected from the Ischigualasto Formation, San Juan Province, Argentina and assigned to Protojuniperoxylon ischigualastense Bonetti emend. is revised. This conifer wood was previously assigned either to Cupressaceae or "Protopinaceae". The presence of axial parenchyma with resin contents found in P. ischigualastense plus the occurrence of cupressoid cross-fields, bead-like thickenings in the ray cells and ray tracheids allow the convalidation of Cupressaceae assignation. Consequently, P. ischigualastense represents the earliest record of the family in Argentina. Quantitative growth ring anatomy analysis leads to the conclusion that the trees were evergreen gymnosperms. The cumulative algebraic sum of each cell's deviation from the mean of the radial diameters was calculated for each growth ring increment and plotted as a zero-trending curve (CS-DM curve). This Cupressaceae species exhibits right-skewed CSDM curves as typical of evergreen conifers. Furthermore, latewood percentage, cellular diminution percentage and ring markedness index were calculated. P. ischigualastense quantitative growth ring parameters are similar to those of extant conifers with moderate-to-high leaf longevity.

Palavras-chave : Fossil wood; Argentina; Triassic; Ischigualasto Formation; Cupressaceae; Growth rings.