Western Rat Snake Scotophis obsoletus  (Say, 1823)
An adult specimen from Crawford County, Kansas, just prior to shedding its skin. Image © Suzanne L. Collins, 2005
Taxonomic Comments:
Burbrink, Lawson & Slowinski (2000 Evolution 54(6): 2107-2118), using mtDNA, convincingly demonstrated that recognition of subspecies of Elaphe obsoleta is unwarranted and is taxonomically misleading. They showed that E. obsoleta actually consists of three distinct species (see the consensus tree on page 2113), which will be formally named and defined in a future paper. Their map (page 2115) shows a distinct lineage found east of the Apalachicola River and Appalachian Mountains (= Eastern Rat Snake), a distinct lineage found between the Apalachicola River and the Mississippi River (= Midland Rat Snake), and a distinct lineage found west of the Mississippi River (= Western Rat Snake, which will retain the name Elaphe obsoleta since the type locality is Cow Island, Kansas). At the northern limits of the range of these three re-defined species, individual snakes are generally dark brown or black, evidence that such dark coloration may have evolved multiple times to select for enhanced thermoregulation in cooler environments, or that such a dark color pattern may have initially been found in the ancestor of all three species (which are each others closest relatives). Burbrink (2001 Herpetological Monographs 15: 1-53), using external morphology, convincingly demonstrated that recognition of subspecies of Elaphe obsoleta is unwarranted and is taxonomically misleading. He showed that E. obsoleta actually consists of three distinct species, which are formally recognized and defined in this paper. The name Elaphe obsoleta is restricted to those populations west of the Mississippi River. The standard common name is Western Rat Snake. Collins & Taggart (2002 Standard Common and Current Scientific Names for North American Amphibians, Turtles, Reptiles, and Crocodilians. Fifth Edition) submitted for consideration the proposals by Burbrink, Lawson, & Slowinski (2000 op. cit.) and Burbrink (2001 op. cit.) to a snake systematist group composed of Frank T. Burbrink, Jeff Camper, Harry W. Greene, L. Lee Grismer, Robin Lawson, James R. McCranie, Andrew H. Price, Javier Rodriguez-Robles, and Samuel S. Sweet, and they agreed. CNAH: The previously recognized race Elaphe obsoleta lindheimerii was placed in the synonymy of this species. Utiger, Helfenberger, Schatti, Schmidt, Ruf & Ziswiler (2002 Russian Journal of Herpetology 9(2): 105-124), using mtDNA, presented evidence that North American Rat Snakes of the genus Elaphe are a monophyletic lineage different from Old World members of the genus, and resurrected the available name Pantherophis Fitzinger for all North American (north of Mexico) taxa. Those adopting this generic name for the Western Rat Snake should be aware that spelling of the specific name changes to obsoletus. Burbrink & Lawson (2007 Molecular Phylogenetics and Evolution 43: 173-189), using DNA evidence, placed this species in the genus Pituophis. Collins, Joseph T. & Travis W. Taggart (2008. An alternative classification of the New World Rat Snakes (genus Pantherophis [Reptilia: Squamata: Colubridae]). Journal of Kansas Herpetology 26: 16-18) resurrected the generic name Scotophis for this species. Standard common name remains Western Rat Snake