SIMILARITIES AND DIFFERENCES IN DICOTYLEDONOUS WOODS OF THE CRETACEOUS AND PALEOCENE - SAN-JUAN BASIN, NEW-MEXICO, USA

Fossil wood is common in the Late Cretaceous and Early Paleocene of th e San Juan Basin, New Mexico. Six types of dicotyledonous wood are rec ognized: Paraphyllanthoxylon arizonense Bailey, Paraphyllanthoxylon an asazi sp. nov., Plataninium piercei sp. nov., Metcalfeoxylon kirtlande nse gen. et sp. nov., Chalkoxylon cretaceum gen. et sp. nov., Carlquis toxylon nacimientense gen, et sp. nov. Woods with the characteristics of Paraphyllanthoxylon arizonense Bailey are the most common and occur in the Cretaceous Kirtland Shale and the Paleocene Ojo Alamo Sandston e and Nacimiento Formation. This wood type's characteristics are stabl e from the Cretaceous to the Paleocene. There were no significant diff erences in the vessel diameters, vessel densities, ray sizes, or estim ated specific gravities of the P. arizonense woods from the Late Creta ceous (Kirtland Shale) and Early Paleocene (Nacimiento Formation and O jo Alamo Sandstone). Based on the samples examined for this study, dic otyledonous woods were more diverse in the Cretaceous (five types) tha n in the Paleocene (two types) of the San Juan Basin. Diameters of the Cretaceous woods examined ranged from 14-40 cm indicating they were t rees rather than shrubs; diameters of the Paleocene woods examined ran ged from 10-80 cm. All the woods have generalized structure with combi nations of features seen in more than one extant family, order, or sub class. Information from databases for fossil and extant woods indicate s that some combinations of features (e. g., solitary narrow vessels, low vessel density and scalariform perforation plates, as seen in Metc alfeoxylon kirtlandense and Chalkoxylon cretaceum), while relatively c ommon in the Cretaceous, represent strategies of the hydraulic system that are extremely rare in the Tertiary and at present. None of the di cotyledonous woods have distinct growth rings, although some samples o f Paraphyllanthoxylon arizonense from the Paleocene show variations in vessel density and vessel diameter that may correspond to seasonal va riations in water availability.