Monday, May 28, 2012

Mixcoatlus, A New Genus for Some Montane Mexican Pitvipers

Mixcoatlus browni, UTA
The numbers of known New World pitvipers have increased greatly from the 90 species in nine genera recognized only two decades to almost 120 species in 15 genera today. Mexico is well known for its diverse pitvipers with at least 56 species and nine genera. And, our knowledge of pitviper diversity and relationships is constantly being refined as independent geographical lineages are distinguished and new species are discovered.

In a relatively recent article Jadin et al. (2011) sort out some taxonomic confusion surrounding Cerrophidion barbouri Dunn 1919 a pitviper restricted to the Sierra Madre del Sur in southern Mexico at elevations above 2000 m. Agkistrodon browni Shreve, 1938, has been considered a junior synonym of C. barbouri, until now. Cerrophidion barbouri is rarely collected and prior to recent decades it was known from only a few specimens. A careful re-examination of nearly all known specimens of C. barbouri and the type series of A. browni reveals that both names represent valid species and they resurrect A. browni. Both species are extremely variable with respect to head scalation and colour pattern, which has previously confounded efforts to identify them. Jadin et al. provide phylogenetic analyses using both Bayesian and maximum parsimony criteria of New World pitvipers to investigate the phylogenetic position of A. browni and C. barbouri. Their phylogenetic tree, based on 2235 bp of mitochondrial data [12S, 16S, cytochrome b, NADH, ND4)], strongly supports a clade consisting of A. browni, C. barbouri, and Ophryacus melanurus, which has a distant sister relationship to Ophryacus undulatus. Based on the deep phylogenetic divergences amongst these species and distinctive morphology they establish the new genus Mixcoatlus which now contains Mixcoatlus barbouri, Mixcoatlus browni, and Mixcoatlus melanurus. Similar to Ophryacus, Mixcoatlus are pitvipers endemic to the highlands of southern Mexico.

Mixcoatlus barbouri and M. browni are restricted to highland humid pine-oak and cloud forest habitats of the Sierra Madre del Sur in Guerrero, Mexico, while M. melanurus occurs in highland arid tropical scrub, high deciduous forest, and seasonally dry pine-oak forest in southern Puebla and northern Oaxaca. This limited distribution of southern Mexico makes this genus the most restricted of New World pitvipers.

Citation
Jadin, R. C., E. N. Smith, and J.Campbell. 2011. Unravelling a tangle of Mexican serpents: a systematic revision of highland pitvipers. Zoological Journal of the Linnean Society, 163, 943–958.





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