PETRIFIED WOOD FROM THE SHORT CANYON MEMBER OF THE CEDAR MOUNTAIN FORMATION: TAXODIOXYLON

Fossil wood was found in the Short Canyon Member of the Cedar Mountain Formation. The Short Canyon Member is Albian in age and consists of conglomerate interbedded with sandstone and carbonaceous shale. The Cedar Mountain Formation contains a diverse megafauna, including dinosaurs and mammals. By studying the paleobotany of this formation, we hope to further investigate the paleoenvironment within which this megafauna lived. Measurements are given in minimum-(average)-maximum notation.

The transverse section shows rounded hexagonal tracheids with diffuse axial parenchyma. The latewood is rectangular with significantly thickened walls. Growth rings are distinct and abrupt, with latewood being 2-4 cells deep. Suspected false growth rings are present. There are 1-(4)-7 tracheids between ray cells. The rays are resiniferous, and resin is associated with intertracheary pits.

In the radial section, areolate intertracheary pits are 75% uniseriate and 25% biseriate, with both isolated pairs and larger areas of opposite biseriation. The intertracheary pits are 13-(19)-25µm in diameter and are unornamented, with an average height:width ratio of 0.96. Pitting is abietinean but can be mixed locally. Crassulae are present and frequent. Rays are 72-(137)-270µm long radially and 14-(23)-36µm in diameter. End walls are thin and smooth, with slightly thicker radial walls. Earlywood crossfields have 1 (to 3) taxodioid pits, with podocarpoid and cupressoid pitting frequently observed in earlywood.

In tangential section, rays are 1-(13)-65 cells and 56-(398)-1599µm tall. Rays are 89% uniseriate with frequent partial biseriation (10-30% of the ray height). Single biseriate pairs have an opposite arrangement, while larger areas of biseriation are alternate. Axial parenchyma is frequent and distinct. Tangential intertracheary pits are absent.

This sample is interpreted as Taxodioxylon cf. albertense (Penhallow) Shikamura. Taxodioxylon has affinities to extant Cupressaceae, especially basal members (e.g., Glyptostrobus, Metasequoia, Taxodium). Based on these affinities and the presence of false growth rings, we conclude this allochthonous fossil originated in a floodplain with a fluctuating temperate climate.