Page 107 - Land Snails of New Mexico

Colorado Plateau Province
Datil–Mogollon Section
High Plains
Molluscan Province
I-,
Figure2.A,Physiographicprovinces,sections,andsubsectionsinNew MexicoproposedbyJohnW. Hawley(1986;p.24,bypermissionofthe UniversityofNew MexicoPress), B,MolluscanprovincesandsubprovincesinNew Mexicoproposedherein.BoundariesofsomeofHawley's provinces, etc.,(left)are employed, and scale isthe same.
included in the Province. They would, however, conform well with the Rocky Mountain Molluscan Province, as they encompass populations of Oreohelix (not including Radiocentrum), the definitive large land-snail genus of the Rocky Mountain Province. The Rocky Mountain Province is vast, as mapped by Henderson (1931:Fig. 1--see Fig. 1A, herein) and defined by Bequaert and Miller (1973:7). Itcould well be divided into subprovinces, in which case a Colorado Plateausubprovincemightcompriseanaturaldivision.The New Mexico part of the Colorado Plateau is so mapped here in Fig.
2B. The fauna of this subprovince in New Mexico is
depauperate in comparison with that of the Southwestern
Molluscan Province, as mapped to the east and south. These and
other molluscan provinces in New Mexico show a close
correspondence to some of the physiographic provinces and
sections mapped for New Mexico by Hawley (1986:24),
indicated in Fig. 2A. In Fig. 2B, a Colorado Plateau Subprovince
has been drawn using boundaries of Hawley's Colorado Plateau
Physiographic Province, and the Southwestern Molluscan
Province has been drawn after his combined Basin and Range
Province and Datil-Mogollon Section. The Rocky Mountain
Molluscan Province, proper, uses the boundaries of Hawley's
Southern Rocky Mountain Physiographic Province in N e w Mexico.
The problem of how to treat the faunally depauperate northwesternpartofNew Mexicoisechoedinturningtothe e a s t e r n o n e - t h i r d o f t h e state, w h i c h a l s o h a s a d e p a u p e r a t e l a n d
snail fauna. In addition, ithas a complex interrelationship with the Rocky Mountain Molluscan Province. This area in eastern N e w Mexico was allocated simply to an "Eastern Division" by Henderson (1931:Fig. 1), a division comprising a vast region extending from the Atlantic Coast to the R o c k y Mountains. This allocation might be justifiable ifthe western part of the region were thought of as being simply a zone in which the Eastern Division fauna becomes progressively depauperate westward. However, as discussed above, the Pleistocene history of the fauna ofthe High Plains indicatesmore complexity than a simple east-west gradient. Derivation of the Pleistocene High Plains molluscan fauna from western, northern, and eastern sources was suggested by Wells and Stewart (1987), and influences from these directions were discussed, above, in terms of an arch configuration, with the top of the arch pointed north.
Bequaert and Miller (1973:9) briefly discussed a High Plains molluscan fauna, noting that a region occupied by such a fauna would approximate that comprised in the Kansan Biotic Province of Dice (1943:26). In N e w Mexico, the area in questionapproximatesapartoftheareamappedbyHawley (1986:24) as pertaining to the Great Plains Physiographic Province. Herein, a High Plains Molluscan Province is indicated in Fig. 2B, using the boundaries employed by Hawley (1986:24) for the Pecos Valley and Llano Estacado Sections of his Great Plains Physiographic Province.
In terms of both physiography and molluscan faunas, the northernpartoftheHighPlainsregioninNew Mexicois
Colorado Plateau Sub-Province
Southwestern Molluscan Province
*
101
Southern
Rocky Mountain Province
Basin and Range Province
Great Basin Province (Raton Section)
Great Basin
Province
(PecosValley & Llano Estacado
Sections)
i -\
RockyMountainMolluscanProvince Raton
(*Sub-Province *