CUPRESSINOXYLON FROM THE MORENO HILL FORMATION (TURONIAN-CONCIAN,CRETACEOUS) OF NEW MEXICO

Cretaceous forests of southern Laramidia commonly contained several species of gymnosperms with rare woody angiosperms. Common gymnosperm taxa in these forests include Piceoxylon, Cupressinoxylon, Circoporoxylon, and Taxodioxylon. These genera have been described from several non-marine Cretaceous sediments throughout the southwestern margin of the Western Interior Seaway. Here we investigate the fossil wood flora associated with vertebrate remains (dinosaur, turtle, crocodile, gar) in the Moreno Hill Formation of western New Mexico.

OPC2469 was collected from the upper Moreno Hill. OPC2462, OPC2464, OPC2465 were collected from the lower Moreno Hill. These samples were studied by petrographic thin section. The reported measurements and observations are based on OPC2462, the best-preserved sample, but other samples were consistent with it. Measurements are given in minimum-(average)-maximum notation.

In transverse section, tracheids are slightly rounded, pentagonal, to square. There are 1-5 tracheids found between the rays. Growth rings are distinct. The transition from earlywood growth to latewood growth is abrupt. Latewood consists of two and six cells with significant thickening of the cell walls. False growth rings are not observed.

In radial section, areolate intertracheary pitting is abietinean with only localized contiguous pits. Intertracheary pitting is uniseriate (98%), rarely biseriate (2%). Intertracheary pits are round, 14-(20)-27 mm in diameter, with an average length:width ratio of 1.05. Each crossfield contains either one or two cupressoid pits. Ray parenchyma cells are 12-(18)-31 mm wide. Ray lengths measure 117-(234)-425mm.

In tangential section, the medullary rays are 92% uniseriate though occasional partially biseriate with some instances of entirely biseriate rays. Ray height is 28-(389)-1504 mm with the number of cells per ray being 1-(18)-78. Tangential intertracheary pits are observed.

Based on these observations, all specimens can be attributed to Cupressinoxylon Göppert. With affinities to extant Cupressaceae, especially basal members (e.g., Metasequoia, Taxodium), the presence of Cupressinoxylon suggests a relatively wet temperate climate. This is supported by the proximity of the Moreno Hill Formation to the Western Interior Seaway.