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Among the species of mammals known from the Guiana Shield, 250 (91%) have been recorded in Venezuela (Amazonas with 209, Bolívar with 227, and Delta Amacuro with 113), 218 (79%) in Guyana, 185 (67%) in Surinam, and 183 (67%) in French Guiana. Of the political units within Venezuela, Delta Amacuro has 62% of the mammal species recorded in the next smallest and less diverse unit (French Guiana). In addition to its relatively small size (less than half the area of French Guiana), Delta Amacuro is composed of predominately semi-inundated ecosystems (mangroves, marsh forests, palm swamps, and grasslands), which are marginal habitat for many species. Delta Amacuro also represents the state of the Venezuelan Guayana Region with the lowest effort for mammal inventories.

Twenty-nine percent (81) of the species recorded in the region are considered widely distributed, because they are found in all six political units. In terms of endemism, there are 25 species (9%) of mammals confined to this region. Of these, five have been collected only in highlands (located primarily in Venezuela with smaller sectors in adjacent Guyana and Brazil, in addition to an outlying peak -Tafelberg- in central Surinam): Marmosa tyleriana, Platyrrhinus aurarius, Podoxymys roraimae, Rhipidomys macconnelli, and Rhipidomys wetzeli (Tate, 1939; Lim and Engstrom, 2000, 2001; Gardner, 1989). The distribution of the Roraima mouse (Podoxymys roraimae) is confined to the top of Mount Roraima (2,772 m), where the borders of Brazil, Guyana, and Venezuela converge. The mouse opossum Marmosa tyleriana has been recorded only on three Venezuelan tepuis: Duida, Auyantepui and Jaua (Ochoa, 1985). The climbing rat Rhipidomys wetzeli is known only from the tepuis in three Venezuelan national parks: Canaima, Duida-Marahuaca, and Neblina. We do not consider Didelphis imperfecta and Proechimys hoplomyoides highland endemics as reported by Gardner (1989) and Tate (1939), although their distributional patterns are restricted to the Guiana Shield. The former species has been found in lowland rainforests as a sympatric taxon with D. marsupialis (Ochoa 2000; Lim and Engstrom, unpublished data), and specimens listed as D. albiventris from Surinam (Genoways et al., 1981) and French Guiana (Catzeflis et al., 1997) are most likely also referable to D. imperfecta. In the case of P. hoplomyoides, this spiny rat has been found in lowlands of Amazonas and Bolívar state (Ochoa et al., 1988, unpublished data).

The lowland area of the Guiana Shield has 10 endemic species, of which five have restricted distributions. The Orinoco agouti (Dasyprocta guamara) is found only in Delta Amacuro State; the fiery squirrel (Sciurus flammifer) is restricted to northern Bolívar State; Fernandez's sword-nosed bat (Lonchorhina fernandezi) is known only in a small area from northern Amazonas State and western Bolívar State; Barnes's free-tailed bat (Molossus barnesi ) has been recorded only in French Guiana; and the Oyapock fish-eating rat (Neusticomys oyapocki) is known from French Guiana and neighboring AmapĀ  State in Brazil. In addition to these taxa, the short-tailed mouse opossum Monodelphis orinoci, although not restricted to the Guiana Shield, is considered endemic in a relatively small area of lowlands in Venezuela (Central Llanos to northern Bolívar State). The other lowland endemics of the Guiana Shield are more widely distributed and include Lasiurus atratus, Ateles paniscus, Pithecia pithecia, Neacomys dubosti, and Isothrix sinnamariensis. Nine species are endemic to, but found throughout the Guiana Shield: Didelphis imperfecta, Monodelphis brevicaudata, Lophostoma schulzi, Neacomys guianae, N. paracou, Oecomys auyantepui, O. rex, O. rutilus, and Coendou melanurus. One endemic species (Proechimys hoplomyoides) is restricted to the western Guiana Shield.

Within taxonomic order, there are five species of bats endemic to the Guiana Shield (Lonchorhina fernandezi, Platyrrhinus aurarius, Lophostoma schulzi, Lasiurus atratus, and Molossus barnesi), three endemic marsupials (Didelphis imperfecta, Marmosa tyleriana, and Monodelphis brevicaudata), and two endemic primates (Ateles paniscus and Pithecia pithecia). The majority of the other endemic species are rodents (15), which represent slightly more than one-quarter of the diversity within this order.

Excluding the estuarine dolphin and the river dolphin (both recorded at inland aquatic ecosystems), we do not include other cetaceans in this paper due to their primary association with marine environments outside the region. However, there are reports of eight species of marine cetaceans close to the northeastern boundary of the Guiana Shield (Eubalaena australis, Balaenoptera acutorostrata, B. borealis, B. physalus, Delphinus delphis, Globicephala macrorhynchus, Pseudorca crassidens, and Physeter catodon). Aside from domesticated animals, there are four introduced feral species of mammals in the Guiana Shield, which are also excluded from our checklist but are discussed briefly here. The mongoose (Herpestes javanicus) was intentionally introduced by humans to control rat populations in agricultural fields (Husson, 1978), and appears to be confined to coastal areas with records from Surinam and Guyana. Old World mice and rats (Mus musculus, Rattus norvegicus , and R. rattus) were unintentionally introduced in the region and thrive in association with human habitation along the coastal strip. Of these invasive species, only R. rattus seems to have penetrated inland, with records in southern Venezuela (Handley, 1976) and interior French Guiana (F. Catzeflis, pers. com.).

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