[EN] THIS COMMENTARY STRESSES THE POTENTIAL SIGNIFICANCE OF THE GUAYANA HIGHLANDS, in northern South America, to provide evidence for relevant biogeographical and evolutionary theories that are being intensively discussed. Some regions of the world seem to be especially well suited for this purpose, as is for example the case of the Galapagos Islands, the Panama Isthmus, Beringia, or the Amazon basin. Singular features of these areas include a key emplacement with respect to Earth’s biogeographical regions, unique and specialized life forms, amazing biodiversity and endemism levels, or highly pristine ecosystems, among others. The remote and mysterious Guayana Highlands—the A. C. Doyle’s (1912) “Lost World,” at the top of characteristic sandstone table mountains (tepuis) of the Neotropical Guayana region, could have a place among these privileged areas (Fig. 1). The Guayana Highlands (GH), also known as Pantepui, constitute a singular biogeographical province of about 5000 km2, split into numerous topographical islands between about 1500 and 3000 m altitude (Huber 1994). Pantepui lies on the Precambrian Guayana Shield, which had been separated from the African Shield by continental drift, leading to the formation of the Atlantic Ocean, around 80–100 million years ago (Edmond et al. 1995). The tepuis are remnants of ancient erosion surfaces that have been isolated by denudation due to the Gondwana breakup and the formation of the extensiveOrinoco and Amazon river basins (Brice˜no & Schubert 1990). The uniqueness of the GH biota, as well as its striking degree of biodiversity and endemism, are well known and have been recognized for long time (Huber 2005). This is especially manifest in vascular plants, the better known organisms of the region (Berry et al. 1995), with ca 630 genera and 2500 species, of which 42 percent are endemic to the GH and 25 percent are endemic to a single tepui (Berry & Riina 2005). As a consequence, the GH have been traditionally considered an important speciation center of the Neotropics (e.g., Funk & Brooks 1990). Furthermore, the GH lie in a strategic geographical location, among key Neotropical areas such as the Amazon basin, the Caribbean region, and the Atlantic domain (Huber 1995). In addition, the almost pristine nature of the tepui summits make them unique environments to record natural environmental variability, and hence to test hypotheses about climatic or nonclimatic forcing, and the corresponding ecosystem responses.Here, themain biogeo- Received 22 December 2005; revision accepted 4 April 2006. 1 Corresponding author; e-mail: valenti.rull@uab.es graphical and evolutionary results obtained so far are presented. At this stage, the aim is not to favor one or another hypothesis, but to emphasize the suitability of the GH to address these questions.

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4 p.