Fossil woods from the late Campanian–early Maastrichtian Olmos Formation, Coahuila, Mexico

Three fossil wood types are described from the Olmos Formation, Coahuila, Mexico. The anatomical characters of two of them enable identification to Malvaceae and Fagaceae, while the affiliation of the third type is uncertain (Fagaceae?). The wood of the Malvaceae fossil plant is characterised by the presence of vessel-ray and vessel-parenchyma pits with reduced borders, larger than the intervascular pits, scanty paratracheal parenchyma, septate fibres and storied structure. This wood type, Javelinoxylon, has been also found in the Maastrichtian Javelina Formation, Texas. Aggregate and uniseriate homocellular rays, apotracheal diffuse and diffuse in aggregates parenchyma, simple perforation plates, vessel-ray pits variable with reduced borders and vasicentric tracheids relate the wood of a second plant to Quercinium. The third wood type, Sabinoxylon pasac Estrada-Ruiz, Martínez-Cabrera et Cevallos-Ferriz, is very similar to some species of Quercinium; however, the presence of heterocellular rays and the almost exclusive presence of scalariform perforation plates make unlikely its relationship with this genus. Since observation of vessel parenchyma and vessel ray pits was not possible, its inclusion in Fagaceae cannot be confirmed. Nevertheless, S. pasac and Quercinium centenoae Estrada-Ruiz, Martínez-Cabrera et Cevallos-Ferriz represent the earliest record of fagaceous plants in Mexico, while the presence of Javelinoxylon weberi Estrada-Ruiz, Martínez-Cabrera et Cevallos-Ferriz extends the geographic distribution of the genus in North America.