González-Ramírez, Ixchel , Calvillo-Canadell, Laura , Silva-Pineda, Alicia , Cevallos-Ferriz, Sergio .
Cupressaceae conifers from the Cretaceous of Chiapas.
In recent years work in a quarry located in the Southwestern Mexico, near Ocozocuautla Espinoza, Chiapas, yielded a new interesting biota The new locality forms part of the Sierra Madre Formation (Aptian-Cenomanian), in which thin laminar layers of limestone have been interpreted as marine and transitional depositional environments, like coastal lagoons/ estuaries and continental platform, containing flora and fauna.The plant association found on this site is characterized by a high dominance of gymnosperms morphospecies, particularly three conifers. Branches of second or third orders of these morphospecies have been assigned to Cupressaceae based on the presence of mature acicular or thickened at the base scale leaves, with a single central vein, spiral or alternate in crisscross phyllotaxy, and opposite juvenile needle-like leaves, that become more intertwined as they approach the apical region. Based on their architecture and phyllotaxis fossil morphotypes have been compared with the extant genera Cryptomeria (hard leaves, concave, with enlarged base and spiral arrangement), Glyptostrobus (soft leaves, slightly wider at the base, opposite in pairs on the same axis and very regular monopodial branching), and Chamaecyparis/ Athrotaxis (facial and lateral leaves of the same size, scale-shaped, opposite in pairs in crisscross and overlapping towards the apex of the branch; the distal region of the scales is conspicuous). Today all these genera have are stricted distribution in Asia, but the disjunct distribution suggested bythis identification is supported by previous reports of fossil Glyptostrobus in America, and by the close phylogenetic relationship of Cryptomeria with Taxodium, a genus widely distribuited in North America. These plants represent new records for the Cretaceous of Mexico, and increase the reported abundance of conifers in the area during the Mesozoic,which contrasts with their low presence in the Paleogene and complement the biogeographic history of conifers in the country, which appears to be complex.
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1 - Facultad de Ciencias, UNAM, Biología, Manuel Álvarez 111, Mod 1, Dpto A-103, Col. Juan Escutia, Iztapalapa, Mexico, N/A, 09100, Mexico
2 - Instituto De Geología, UNAM, Circuito De La Investigación, Ciudad Universitaria, Coyoacan, N/A, 04510, Mexico
3 - Instituto De Geología, UNAM, Circuito De La Investigación, Ciudad Universitaria, Coyoacan, N/A, 04510, Mexico
4 - Instituto De Geología, UNAM, Department Of Palentology, Ciudad Univwersitaria, Coyoacan, MEXICO D.F., N/A, 01900, Mexico
Presentation Type: Oral Paper:Papers for Sections
Location: Union A/Hyatt
Date: Monday, July 9th, 2012
Time: 1:45 PM