Remarks:
This was the first species of amphibian or reptile to be documented in what we can be sure was Kansas (but in an unfortunate twist of politics that all changed) (Taggart 2021).
Thomas Say (1823) described the type specimen of the Western Ratsnake from Isle au Vache (Cow Island), Kansas (a heavily forested island on the Missouri River). His type locality stretches from NE Kansas to western Iowa. Say wrote... "It is not an uncommon species on the Missouri from the vicinity of Isle au Vache to Council Bluff.".
Cow Island was the site of Cantonment Martin, a military camp established as a supply base for Major Stephen H. Long’s engineering expedition of 1819-20 of which Say served as the naturalist. This expedition set out to survey the Rocky Mountains and the major tributaries of the Missouri River.
A flood in 1881 shifted the main channel of the Missouri River west and Cow Island became connected to the Missouri side. For several years, both Kansas and Missouri lay claim to the land that had been Cow Island and the dispute was ultimately settled in 1890 when a court ruled that a boundy would change with the gradual movement of a natural boundary (accretion) but not due to a sudden change (avulsion). Therefore, the land still belonged to Kansas and would for most of the next 60 years.
The Kansas, Missouri, and the US Congress ratified the Kansas-Missouri Boundary compact in 1949 which set the boundary at the center of the current channel of the Missouri River (which by then had been dredged, levied, and straightened so as to become effectively fixed)... and Kansas lost its first type locality.
The oldest existing specimen is in the Royal Ontario Museum (ROM 4228) and was collected in 1886 (no other associated data).
This species exhibits an ontogenetic color shift as it matures. Newborn individuals are light gray with well-defined dark blotches. In their second year, the pattern begins to be obscured as the snake transitions to an overall dark animal.
Specimens from the southwestern portion of its range in the state show a propensity for maintaining more of their blotched pattern as adults (Miller, 1986, Irwin et al., 1992).
Based on the congruence of morphological (Burbrink, 2001, Herpetol. Monogr. 15: 1–53) and mitochondrial data (Burbrink et al., 2000, Evolution 54: 2107–2118), Burbrink divided P. obsoletus into three species (P. alleghaniensis, P. obsoletus and P. spiloides) with no subspecies. Burbrink (2020) further supported the recognition of P. obsoletus as a taxon distinct from P. alleghaniensis and P. spiloides), but see Hillis and Wuster (2021). While not affecting P. obsoletus (and therefore those populations in Kansas), Burbrink (2021) noted that P. alleghaniensis should actually apply to the middle lineage (geographically; east of the Mississippi River and west of the Appalachians and Flint/Apalachicola rivers) and the oldest available name for the eastern lineage is P. quadrivittatus.
Hillis (2022) further the debated the status (specific vs. subspecific) of the Pantherophis obsoletus complex across eastern North America. He argued specifically that Burbrink et al. (2020) demonstrated a wide intergrade zone with no apparent breaks due to reproductive/genetic barriers between the their putative P. alleghaniensis, P. quadrivittatus, and P. obsoletus. There is no standard measure as to what point a hybrid/intergrade zone becomes sufficiently wide to determine if the two (or more) constituent populations are species or 'subspecies'. Nor should there be, as doing so would denigrate the delineation of real species to an arbitrary class threshold (Frost and Hillis, 1990). Hillis (2022) further argues that the reasoning (in part) invoked by Burbrink et al. (2021) for elevating P. alleghaniensis, P. quadrivittatus, and P. obsoletus; (specifically that as P. bairdi and P. obsoletus share a more recent common ancestor with each other than either does with P. alleghaniensis or P. quadrivittatus; recognizing P. bairdi and the remaining taxa as subspecies of P. obsoletus, would render P. obsoletus paraphyletic) is likely due to hybridization. However, all phylogenetic hypotheses are generated from gene data and as such are subject to being misled by xenologous/paralogous relationships of those genes with respect to the true phylogeny (which is unknowable).
Utiger et al. (2002, Russian J. Herpetol. 9: 105–124), using molecular data, divided Elaphe into eight genera. New World Elaphe are part of a clade distinct from Old World species, for which Pantherophis Fitzinger, 1843, was resurrected as the oldest available name. Further splitting of Pantherophis has been proposed (Collins and Taggart, 2008).
On the map (Carte itineraire de Prince Maximilian de Wied dans l'interieur de l'Amerique Septentrionale de Boston a Missouri superieur &c. en 1832, 33 et 34) accompanying the report of Prince Maximilian zu Weid's explorations in North America the area of Doniphan County, north and west of Wathena, is labeled "Wa-con-se-nac or Black Snake Hills".