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The hognosed pit viper snakes (Porthidium) make up one of the more basal of the 11 New World pit vipers genera (subfamily Crotalinae), and are part of an assemblage described as the “Porthidium group” found primarily in Middle America, between Mexico and Ecuador.  The genus contains nine small terrestrial species, ranging in size from 55-75 cm (22-30 inches) long, with mottled brown cryptic coloration (Lemonte et al. 2012 and references cited within).  In about half the species, the snout is slightly to strongly up turned, giving the genus its common name hognosed (Lamar and Sasa 2003). Like all viperids (family Viperidae) they are ambush predators with a pair of long, hollow fangs at the front of their mouth used for injecting toxin into their prey.  The small number of identified bites of humans by hognosed pit vipers report as these as usually causing only local pain and bruising (although some systemic cases have been reported), and less severe than bites from larger central American pit vipers such as the fer-de-lance (Bothrops asper), which have a similar venom profile but deliver a much smaller dose (Lomonte et al. 2012). 

Originally all species in the Porthidium group were contained in genus Porthidium, however much phylogenetic and taxonomic work has since separated this group into three genera (Porthidium, Cerrophidion, and Atrapoides).  Analysis of toxicological properties of the venom further distinguishes Porthidium species from Cerrophidion (Lomonte et al. 2012).  The nine currently accepted Porthidium species are: P. arcosae, P. dunni, P. hespere, P. hyoprora, P. lansbergii, P. nasutum, P. ophryomegas, P. porrasi, P. yucatanicum, P. volcanicum.  Taxa are still in flux; the rare P. volcanicum was recently discovered in Costa Rica and others have been newly recognized as species in their own right (P. arcosae, P. porrasi) rather than subspecies (Lamar and Sasa 2003; Valencia et al. 2010).  Porthidium arcosae is sometimes considered a subspecies of P. lansbergii, and the future promises further taxonomic redefinitions of this genus since many researchers recognize that P. nasutum and P. lansbergii may not be distinctly individual species but rather species complexes in need of further taxonomic attention (Campbell and Lamar 2004; Castoe et al. 2005).  Recent molecular phylogenetic analyses find two discrete lineages within the genus: an “arid-adapted” lineage including P. ophryomegas, P. dunni, and P. hespere separate from the other species which form a lineage of moist and lowland forest-dwellers (Bryson et al. 2008; Jadin et al. 2011; Valencia et al. 2010; Castoe et al. 2005). Molecular analyses show a pattern of species dispersal back and forth between South and Central America.  Molecular clock estimates of divergences suggest Porthidium initially colonized South America after the emergence of the Panamanian isthmus, unlike the pitviper genus Bothrops, which occupied South America before the isthmus arose, and may have prevented further colonization and radiation by later arriving Porthidium (Castoe et al. 2005 and references cited therein; Wüster et al. 2002). 

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