Two new species of Ginkgoales from the Middle Jurassic of Mexico M. Patricia Velasco-de Leo ´n a *, Diego E. Lozano-Carmona a , Miguel A. Flores Barragan a , O. Daniel Martı ´nez Paniagua a and A. Silva Pineda b a Facultad de Estudios Superiores Zaragoza, Universidad Nacional Auto ´noma de Me ´xico, Av. Guelatao 66, Col. Eje ´rcito de Oriente, Iztapalapa C.P. 09230, Me ´xico D.F.; b Instituto de Geologı ´a, UNAM, Circuito Exterior, Ciudad Universitaria, Mexico City 04510, Mexico D.F. (Received 21 October 2013; accepted 9 December 2013; first published online 25 February 2014) This paper reports two new species of Ginkgoales collected from the Can ˜ada Alejandro and Rı ´o N ˜ umi (Zorrillo and Zorrillo – Taberna Undifferentiated Formations, Middle Jurassic). Thirty-one fossils were selected and compared with 14 species from different localities. A numerical taxonomy analysis was performed through a data matrix formed by 15 characters. Results indicate an important speciation process of the Ginkgoales during the Jurassic in the southeast of Mexico. New evidence suggests the existence of eight species from the Ginkgoidium Yokoyama, 1889 and Sphenobaiera (Florin) Harris and Millington, 1974 genera and two new species Ginkgoidium nundichii Velasco-de Leo ´ n, Lozano-Carmona, Flores, Martı ´nez and Silva and Sphenobaiera mixteca Velasco-de Leo ´n, Lozano-Carmona, Flores, Martı ´nez and Silva Keywords: gymnosperms; Middle Jurassic; Ginkgoidium; Sphenobaiera; North America Introduction The Ginkgoales is a group of gymnosperms with an affinity for a controversial taxonomic position. A lot of different classifications have been proposed based on morphological characters, cuticles characteristics and reproductive structures (Florin 1936; Anderson and Anderson 2003; Naugolnykh 2007); the last classification made by Zhou (2009) considers six families and nine genera based on the whole plant reconstruction. As a result of the lack of cuticles and reproductive structures, there are other classifications based on the morphology of the leaf; for example, Gnaedinger and Herbst (1999) considered the variability of current and fossil leaves from this order. The stratigraphic range of the Ginkgophytes goes back to the Permian (present in six localities from Laurasia and only two from Gondwana) having its climax on the Triassic and Jurassic Period [increasing on a total record of 29 localities around the world, actually one species (Ginkgo biloba) is present in China (Sims 2002; Zhou and Wu 2006; Zhou 2009)]. In North America, the records are just a few; for the Triassic, the majority corresponds to specimens found in the Newark Supergroup in the eastern USA with a greater number of Sphenobaiera striata Bock, S. spectabilis Nathorst and Ginkgoites milfordensis Bock, and for this region, Ash (2010) proposed a new species Ginkgoites watsoniae Ash. In the North of Mexico (Santa Clara Formation), Weber et al. in 1980 described Sphenobaiera sp. They mentioned the presence of two completely peculiar samples from Baiera radiata Newberry that due to the lack of material cannot be defined by species; however, Ash (2010) transfers this species to B. radiata. The most common basic types of leaves mention in the literature are Ginkgoites Seward, Ginkgoidium Yokoyama, 1889, Baiera (Braun) Florin and Sphenobaiera (Florin) Harris and Millington (Figure 1). For the Jurassic Period in the south-central region of Mexico, this group has not been registered yet; Person and Delevoryas (2002) thoroughly studied the flora in Oaxaca and explain that the lack of this order is due to a tropical paleoclimate. The purpose of this paper is to make known the presence of new species of Ginkgoales during the Jurassic Period in Mexico. Geological setting Zorrillo Formation The Zorrillo Formation was proposed by Erben (1956); the lithology was formed by a fine-to-medium-grained sandstone and silstone; sometimes with a thin cross- stratification, it also shows fine grey-yellowish limolite that has a large number of plants, carbonic shale and mantles of carbon; the thickness of this formation varies between 20 and 80 m based on the stratigraphic position, and the age was determined to be Bajocian. In the Can ˜ada Alejandro (CA) locality, the work was done on 13.30- m-thick silstone strata, the flora is mainly formed by Bennettitales and lacks Filicales (Figure 2). q 2014 Taylor & Francis *Corresponding author. Email: pativel@correo.unam Historical Biology , 2015 Vol. 27, Nos. 3–4, 366–373, http://dx.doi.org/10.1080/08912963.2013.874423