Page 97 - Land Snails of New Mexico

Pupoides albilabris (75) Vallonia cyclophorella (56)
Helicodiscus singleyanus (25) Vertigo milium (21)
Hawaiia minuscula (10) Zonitoides arboreus (10) Valloniagracilicosta(9)
Discus whitneyi (9) Ashmunella sp. (6) Pupoides hordaceus (5) Helicodiscus eigenmanni (5)
Vertigo ovata (3) Nesovitrea hammonis (3) Pupilla blandi (1)
Vallonia perspectiva (1)
Two species (Gastrocopta armifera and Vallonia
gracilicosta) in the above listings combined (Hidalgo and
Greenlee Counties) do not occur thatfar west at the present time.
Bequaert and Miller (1973:145) reported Nesovitrea hammonis
electrina as being rare in Arizona. These authors listed all three
of the above species from Pleistocene sites in Arizona including localities associated with fossil mammoths in the San Pedro
River Valley, and dated at some 10,000 to 11,000 B.P. The occurrenceofNeosovitreahammonis electrinaatthiselevation
(ca.1,100m or3,600ft)representsadepressioninelevationof some1,220m or4,000ftfromelevationswhereitoccursinthe Mogollon Mountains in New Mexico. The specimens of Ashmunella indicated were fragmentary and did not include apertural areas that might have allowed identification to species.
Intermontane Basins
There have been few reports of Pleistocene land-snail faunas
from intermontane basins. Perhaps they have not been sought for
sufficiently,orperhapsthisrelatestolessdissectionby arroyos
in these internally drained basins, where arroyo walls might
revealfossils.However, Ashbaugh and Metcalf(1986) reported
a diverse fauna including both aquatic and terrestrial snails from
theTularosaBasinintheareaofKeenSpring,ca.3.3km west
of Oscura, Lincoln Co. (Table 4). Today, K e e n Spring produces
onlyatrickleofwateratthebottom ofan entrenched arroyo,but
ancient springmounds and nature of the sediments and fauna
indicatethatitcomprisedacomplexofmuch largerspringsin the Pleistocene. Fossil snails are associated with a Pleistocene
Gastrocoptapentodon form tappaniana, Nesovitrea hammonis electrina, and the slug Deroceras laeve (slugs represented by internal shells).
Sixteen species of the Keen Spring assemblage no longer occur in the Tularosa Basin, but do occur at higher elevations in mountains flanking the basin. The presence of Ashmunella rhyssa at this elevation in the basin is noteworthy. It presently occurs only in the mountains east of the basin. However, in the past it likely colonized Salinas Peak on the west side of the b a s i n , w h e r e it p r o b a b l y w a s a n c e s t r a l t o t h e c l o s e l y r e l a t e d ( o r conspecific)A. salinasensis.
Occurrence offossilsofAshmunella rhyssa atKeen Spring supports a model of dispersal across the basin simply by locomotion of the snails themselves. Probably some other species in the Keen Spring assemblage also dispersed into the basin from nearby mountains during times of Pleistocene life zone depression. However, some of the small aquatic and hygrophilousspeciesmay havebeen dispersedby aquaticbirds,
among what were presumably marshy areas around widely scattered springs in the Tularosa Basin or larger region in the Pleistocene.
QUATERNARY FOSSILS FROM CORDILLERANNEW MEXICO
Having surveyed some Quaternary fossil faunas from lowland areas of the eastern plains, major river valleys, and intermontane basins, we now examine some records from Cordilleran areas, again chiefly from southern N e w Mexico. It hasbeenstressedabovethattheCordilleranfaunaseemstobe avenerableone,andthePleistocenerecordseemstoconformto such a model. S o m e sites are, of course, located transitionally between lowlands and mountains, in areas offoothills, as in the case of Dry Cave and of U-Bar Cave, discussed below. In this section, sites and areas in southern N e w Mexico from east to
west are discussed first,followed by remarks on a few sitesin the northern part of the state.
Dry Cave
TheDryCavelocalityisinEddyCo.,ca.24km (15mi)west of Carlsbad, in arid foothills transitional from the Pecos Valley totheGuadalupeMountainstothewest. ArthurH.Harrisand students have excavated and analyzed fossil vertebrates from Dry Cave (Harris, 1970), and Harris' locality numbers are used
mammalianfauna. belowandinTable4.Associatedwithvertebratematerialsare
TheKeen Springlocalitycomprisedfivecollectionsitesnear and downstream from the present small spring. Twenty-five speciesoflandsnailswerereportedforthelocalityandarelisted inTable4.Thisisasurprisinglylargenumberforeitherfossil ormodernland-snaillocalitiesinNew Mexico.Theoccurrence
also of 4 species of sphaeriid clams and 9 species of aquatic Snails indicates presence of permanent water presumably supplied by the former springs noted. The occurrence at one locality of 5 species of Vertigo is unusual in N e w Mexico, and indicatesexistenceofmoistconditionsprobablyassociatedwith Spring-fed marshes or d a m p areas alongside springbrooks. Also indicative of a moist environment are Carychium exiguum,
some fossilsoflandsnails(Metcalf, 1970, 1977).
Dry Cave isan extensive cave complex inPermian bedrock atanelevationof1,280m (4,200ft).Localitiesyieldingfossil mollusks are in two areas, which received fillfrom different sources:EntranceFissureandBisonSink.TheEntranceFissure
source area was at the present mouth of the cave, and, when fillingbegan,seemstohavebeenacollapsesinksome18.3m (60 ft) deep, probably with steep rocky walls. The locality designated Animal Fair (Loc. 22) lies near the bottom of this fill, and has an associated date of 15,030+210 B.P. The locality Stalag 17 (Loc. 23) lies higher and has an associated date of
11,880+250 B.P.
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