The Tertiary history of the northern temperate element in the northern Latin American biota

Abstract

The time of origin of cool-to-cold-temperate plants of northern affinities in the Latin American biota is unsettled. Two models have been proposed-a Paleogene origin from a once widespread temperate rain forest, and a Neogene origin by introductions from the north which is best supported by new evidence. Fourteen palynofloras of Tertiary age are now available from Mexico and Central America, in addition to numerous others from the southeastern United States and northern South America. Pollen of cool-temperate plants occurs in the Eocene of southeastern United States, but not in northern Mexico, central Panama, or northern South America. In the Miocene this pollen is sparse in deposits from Mexico and Guatemala, rare in Panama, and absent from northern South America. In the Pliocene pollen representing a diverse northern temperate element of ten genera is present in the Pliocene of southeastern Veracruz, Mexico, five in northeastern Guatemala, and two (Myrica, Salix) first appear in northern South America; Alnus and Quercus are added in the Pleistocene. This north-to-south and early-to-late pattern is consistent with the appearance of highlands in southern Central America and northern South America in the Neogene, closure of the isthmian marine portal between 3.5 and 2.5 Ma (million years ago), and the late Cenozoic cooling trend evident in the O/O-based paleotemperature curve.

Allopatric genetic origins for sympatric host-plant shifts and race formation in Rhagoletis

“…Under the introgression hypothesis, we estimate that Mexican and U.S. flies initially separated Ϸ1.57 Mya. This date is consistent with the biogeography of many temperate plants having disjunct eastern U.S.͞Mexican distributions, including the Rhagoletis hosts Crataegus and Cornus (29,30). The timeframe and concordance of multiple taxa suggest a possible role for climatic and biotic changes associated with Pleistocene glaciation in the isolation of U.S. and Mexican flies.…”

Genetic Variation in Two Rare Endemic Mexican Trees, Magnolia sharpii and Magnolia schiedeana

“…al.·Silvae Genetica (2008) 57-6, 333-340 had a major impact on forest distribution and composition (HEINE and OHNGEMACH, 1976), and may have led to the fragmentation and restriction of the cloud forests in which Magnolia currently occurs. Mexican cloud forests, which are today fragmented throughout their range, are remnants of a 'temperate rain forest' that extended to the eastern United States during the early Tertiary (GRAHAM, 1973;1976). Those populations characterised by different cpDNA haplotypes may have been isolated for a substantial period of time .…”

Análisis florístico de un bosque de Abies y el bosque mesófilo de montaña adyacente en Juanacatlán, Mascota, Jalisco, México

“…Para este estrato, en el área de estudio es notable la dominancia que ejercen los elementos holárticos del periodo Terciario, Mioceno tardío-Plioceno temprano, hace 5 m.a. (Graham, 1999), como Abies, Cornus, Fraxinus, Ilex, Juglans, Ostrya, Prunus y Tilia, sobre el elemento Neotropical y del este de Asia. Incluso, este último tiene algunas afi nidades holárticas.…”