BOLETÍN DE LA SOCIEDAD GEOLÓGICA MEXICANA Vol 65, Núm. 3, 2013, P. 631-643 http://dx.doi.org/10.18268/BSGM2013v65n3a14

Eocene Bursera (Burseraceaea) in La Carroza Formation, Mexico:
a dry tropical flora member

Laura Calvillo-Canadell^1,*, Oris J. Rodríguez-Reyes², Rosalinda Medina-Lemos³,
Sergio R.S. Cevallos-Ferriz¹

¹Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Circuito de la Investigación Científica, Del. Coyoacán, 04510 México D.F., Mexico.

²Department of Earth Sciences, Royal Holloway, University of London.
³Departamento de Biología, Instituto de Biología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Circuito Exterior, Del. Coyoacán, 04510 México D.F., México.

* This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

History of plant diversity in Mexico might be sought in detailed descriptions and comparisons of fossil taxa. Fossil plants allow the recognition of plant communities and their history, especially if they include key elements. In Mexico, Bursera is correlated with dry tropical habitats, and its presence in the fossil record certainly helps to trace the history of both the taxon and the habitat. Eocene material from the La Carroza Formation, La Popa basin, in Nuevo León, Mexico contains a diverse leaf assemblage among which certain leaves resemble two morphotypes, both members of Bursera. A brief description of the leaf architecture of Burseraceae is presented in order to unify criteria and establish comparative parameters that allow identification of fossil leaflet compressions and impressions. Burseraceae has variable leaf architecture, and a single character can change in a single leaf and/or leaflet. For example, the characteristic brochidodromous condition of the family may change to craspedodromous, semi-craspedodromous or even eucamptodromous, in a single leaf. Both Eocene species that are recognized here suggest that the sections Bursera and Bullockia, were differentiated around Middle Eocene; however, previous studies suggest an earlier differentiation of these sections. The two new fossil species in La Popa basin support the presence of members of the extant dry tropical forest in northwestern Mexico, but not necessarily the presence of a dry community. This community developed at a time of geologic/physiographic changes in the area, promoting drought and the establishment of a dry flora.

Keywords: Burseraceae leaves; Eocene; La Carroza Formation; leaf architecture; Nuevo León, Mexico.