Heterodon nasicus complex

We at SWCHR perceive two major problems with the taxonomy of this group: two of the former subspecies have been elevated to full species rank based upon very tenuous data (actually, only a range map in the case of one). Our inclination is to recognize only one species (H. nasicus) in this group with two subspecies (nasicus) and (kennerlyi).

Heterodon nasicus kennerlyi (Mexican Hog-nosed Snake) – Smith et al. (2003) proposed elevating this taxon to full species rank based solely on morphological characters. They found that both loreal and azygous scale counts served to separate this taxon from H. n. nasicus, but that variation in the former was clinal with respect to latitude. Azygous scale counts did not vary clinally, however, and were reliable to distinguish between these two taxa. They have, nevertheless, failed to convince us that this distinction – alone – is sufficient to warrant elevation of kennerlyi to full species status. Just as we are reluctant to accept changes based only on mtDNA, so are we with proposals based on any other single methodology. The use of multiple methods should be a minimum expectation before altering the existing taxonomic scheme. In this case, supporting evidence from mtDNA sequences – or various other methods – would be welcomed.

Heterodon nasicus nasicus (Plains Hog-nosed Snake) – Having been sunk by two previous authors – who actually studied it – (Platt 1969; Walley and Eckerman 1999), Heterodon n. gloydi, a poorly differentiated taxon, was recently elevated to full species rank (Boundy et al., 2003) using a radical interpretation of the Evolutionary Species Concept (ESC) in the fashion of Collins (1991). These authors disingenuously cite Werler and Dixon (2000) as the source of the change. Werler and Dixon (op. cit), however, expressly disavowed such taxonomic maneuvers (pp. 17-20), obviously intending to recognize gloydi as only a subspecies of Heterodon nasicus [in fact, Dixon and Werler (2005) continue to recognize gloydi as only a subspecies]. The extremely conservative criteria Werler and Dixon (op. cit.) used to formulate their range maps resulted in many apparent distribution gaps where a more liberal use of literature records and personal observations would have shown none. Additionally, it seems clear that H. nasicus has disappeared from many areas of central and eastern Texas where it was historically known, leading one to conclude that much of the distributional hiatus in this form is anthropogenic. Consequently, until authentic evidence is provided that “gloydi” is distinct from the nominate subspecies, we consider this taxon to be synonymous with H. n. nasicus.

Literature Cited

Boundy, J., Campbell, J.A. and B.I. Crother (Chair). 2003. Squamata – SNAKES in Crother, B.I., Boundy, J., Campbell, J.A., DeQuieroz, K., Frost, D., Green, D.M., Highton, R., Iverson, J.B., McDiarmid, R.W., Meylan, P.A., Reeder, T.W., Seidel, M.E., Sites, J.W., Jr., Tilley, S.G., and D.B. Blake. 2003. Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico: Update. Herp. Review 34(3): 196-203.

Collins, J.T. 1991. Viewpoint: A new taxonomic arrangement for some North American amphibians and reptiles. Herp. Review 22(2): 42-43.

Dixon, J.R. and J.E. Werler. 2005. Texas Snakes: A Field Guide. Austin: University of Texas Press.

Platt, D.R. 1969. Natural history of the Hognose snakes Heterodon platyrhinos and Heterodon nasicus. Univ. Kansas Publ. Mus. Nat. Hist. 18: 253-420.

Smith, H.M., Chiszar, D., Eckerman, C.M. and H.D. Walley. 2003. The taxonomic status of the Mexican Hognose Snake Heterodon kennerlyi Kennicott (1860). Journal of Kansas Herpetology 5: 17-20. 

Walley, H.D. and C.M. Eckerman. 1999. Heterodon nasicus. Cat. American Amph. Rept. 698: 1-10.

Werler, J.E. and J.R. Dixon. 2000. Texas Snakes. Austin: Univ. of Texas Press. xv + 437 pp.

03 Oct 2009
SWCHR Committee on Common and Scientific Names
Tom Lott, Committee Chair
Terry Cox
Riley J. Campbell
Gerald Keown (ex officio member)

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