Page 102 - Land Snails of New Mexico

96
Range,alltheseseem tobepartofaninterrelatedgroup,which also m a y include Oreohelix caballoensis, mentioned above.
floridaoccurinhillslopecolluvialdeposits,apparentlyliving thereatatimewheneventhesearidhillswerewoodedtosome
In the Cuchillo Mountains, only a few fossil shells, mainly of Oreohelix metcalfei cuchillensis, have been collected. The richestfossiliferous deposits in the Black Range area have been foundinthecalcareouseasternfoothillsoftherange.Deposits containinglargenumbersofAshmunellamendaxandOreohelix subrudisoccuronasouth-facinghillslopeabout3.7km (2.3mi) north-northeast of Kingston and the latter species also occurs in hillslope colluvium in road cuts on the northwestern side of ApacheHillalongNewMexicoHighway27,ca.1.6km(1.0 mi) north of the ghost town of Lake Valley. The present habitat
extent.
Still farther southwest, distinctive fossil and living faunas
atthislocalityisdesertgrassland,butitseems thattheremust
have been found in the Big Hatchet Mountains and in calcareous outlying mountains to their northwest and south. The Big Hatchet Mountains are dominated by Big Hatchet Peak (=Hacheta Grande), which reaches 2,550 m (8,366 ft) in elevation. T h e y retain a f a u n a o f a s o m e w h a t relict nature, w h i c h includesanumberofspeciesthathavebecome extinctinnearby, lower mountains. Table 6 indicates 16 living species recorded for the Big Hatchet Mountains, several of which also have been taken as fossils in slope colluvium in the range. Howells Ridge, a northern calcareous outlier of the Little Hatchet Mountains, liessome27km(17mi)tothenorthoftheBigHatchet Mountains.MetcalfandSmartt(1974)reportedeightfossil species from cave deposits and hillslope colluvium there (Table 6).Fourofthese,plusoneadditionalspecies,(Table6)still inhabit Howells Ridge. This led the above authors to suggest thatthepresentfaunawas "intheprocessofextinction." Most o f t h e e x t i n c t s p e c i e s o f H o w e l l s R i d g e still o c c u r o n t h e h i g h e r peaks of the Big Hatchet Mountains to the southeast.
have been a woodland with some nonconifers (oaks?) on the
northslopeofApacheHillatthetimewhenOreohelixsubrudis wasabundantthere.
A faunacomprisingonlyafewspecieshasbeenfoundin colluviuminanareaofcalcareousbedrockinthenorthwestern
foothills of Cooke Peak (the main peak is of igneous rocks), at the ghost town of Cooke's (or Cook's). These include Helicodiscus eigenmanni, Glyphyalinia indentata, Ashmunella macromphala, and Oreohelix florida.
CalcareousrocksoccurintheFloridaMountains,from Baldy Peak in the central part of the range, southward. In this area, a few fossils of Oreohelix florida have been found in slope colluvium.More productiveoffossilshavebeensedimentsina
Southward from Big Hatchet Peak, H. A. Pilsbry and L. E. Daniels (Pilsbry, 1915) collected on Teocalli Butte and other low, aridmountains, and Icollected living specimens (Table 6) still farther south on a mountain called, herein, "U-Bar Cave Mountain."Themountainislocatedwestofthenorthernendof
cave located on the northwestern side of Baldy Peak, which has
beenexcavatedbyA.H.Harris,R.A.Smartt,andR.D. the(igneous)AlamoHuecoMountainsinsecs.25,26,35,and
Worthington. The fossils they took from the cave deposits are listedon theleft,below. For comparison, livingspeciesfrom the FloridaMountains, reportedby Pilsbry(1915) and collectedby m e in the 1970s, are indicated to the right:
36,T32S,R 16W.Thisnameisappliedinformallyherein reference to U-Bar Cave, located in the southwestern part of the mountain.U-BarCaveliesatanelevationof1,570m (5,150ft) in an area of massive Cretaceous limestone. Over a period of several years, Arthur H. Harris and associates have excavated vertebrateandmolluscanfossilsfrom guano-richdepositsinU
Cave Deposits Living
Valloniagracilicosta Gastrocoptaashmuni BarCave.Thecaveanditsvertebratefaunahavebeendiscussed
Vallonia perspectiva
Gastrocopta pilsbryana
by Harris (1985, 1987).
Table 6 shows that the fossil land-snail fauna of late
Helicodiscus eigenmanni
Gastrocopta pellucida
Discus whitneyi Hawaiia minuscula
Vallonia perspectiva Hawaiia minuscula
Pleistocene age from U-Bar Cave is considerably richer (12 species) than the livingfauna taken on U-Bar Cave Mountain (five species). T h e fossil fauna resembles the living fauna of the Big Hatchet Mountains to the north, with nine species in
Oreohelix florida Sonorellahachitanaflora
Glyphyalinia indentata Ashmunella walkeri
s h e l l s o f O r e o h e l i x f l o r i d a f r o m t h e r a n g e , a n d it m a y w e l l b e extinct there.
Thysanophorahornii common.Thus,theU-BarCavefossilfaunashowsevidenceof
Sonorellahachitanaflora life-zone depression when compared to the Big Hatchet Peak Vallonia gracilicosta and Discus whitneyi seem to be extinct fauna of today. In general, the area and fauna treated here seem intheFloridaMountainsandothersouthwesternmostmountains toprovideasimplifiedexampleoftheeffectofPleistocenelife
ofNewMexico,althoughValloniasonoranaofBigHatchet
zonedepressionsonmontanelandsnails.Presumably,Big Hatchet Peak acts and acted as a refugium during interglaciations, and provided propagules for dispersal to nearby,lowermountainsduringglacial-equivalenttimes.
Peak actually may be conspecific with V gracilicosta or be
d e s c e n d e d f r o m it. T o m y k n o w l e d g e , n o o n e h a s t a k e n l i v i n g
Radiocentrum ferrissi seems to be an especially good example of a Big Hatchet Mountains relict, as it formerly havebeenfoundsouthoftheFloridaMountains,nearColumbus occurrednotonlyonHowellsRidgeandonU-BarCave
Fossils of Oreohelix florida and of Sonorella hachitana ssp
inthe Tres Hermanas Mountains. Living specimens of the latter species recently (1992) have been discovered in the range by Richard D. Worthington.
Mountain, but also in the Franklin Mountains of El Paso Co., Texas.
No livingspeciesoflandsnailswerefoundwestoftheTres Hermanas Mountains in the Sierra Rica (a low, arid range along the U.S.-Mexican boundary). However, fossils of Oreohelix
numbers of specimens of Thysanophora hornii recovered
The U-Bar Cave fossil fauna is noteworthy for the large
(Table 6). This is a species of the Lower and Upper Sonoran Life Zones.