Page 84 - Land Snails of New Mexico

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Families included in these reports are listed below, using the abovenumberstoindicateinclusionoffamilyin thereport:
"ancient Cordilleran fauna," a term used previously and to be used hereafter.
Helicinidae - 2, 4
Grangerellidae - 2, 4
Eocene-Oligocene Transition
Ellobiidae (Carychium) - 1, 5
Pupillidae-1,5,6 Valloniidae -6
An Eocene-Oligoceneboundaryageof36.5Ma proposedby Berggrenetal.(1985:Fig.4)hasbeencitedwidely.Morerecent analyses by Berggren et al. (1992:40-42) and McIntosh et al. (1992a:462) support, respectively, boundary ages of about 34
Subulinidae - 5
Urocoptidae - 1,2,3,4(?), 6, 8
Bulimulidae-1,2,3,8
and 33.4 Ma.
Various authors concur in the view that Laramide
Discidae (Discus) - 1, 2, 4
Oreohelicidae - 1(?), 2, 4 , 5, 6 Succineidae - 6
deformation terminated about 38-36 Ma, in the late Eocene. According toDickinson (1989:9-10), in the Late Eocene to early
Polygyridae - 2, 4, 6
Oligocene, a "steepening of slab descent beneath the continental block" led to a reversal of Laramide-type conditions, with the magmatic arc sweeping from N e w Mexico back westward to Californiafrom latestEocene through mid-Miocene time (37-15 Ma), and creating extensional rather than the compressional deformation, which had taken place earlier. Elston (1984:229) has referred to this as an "extensional orogeny," which was marked by episodes ofupliftand volcanism from latestEocene toearliestMiocene.
Zonitidae (Mesomphix) -6
Thysanophoridae (Microphysula) - 4
Camaenidae-1,7
Ammonitellidae - 5, 6
Helminthoglyptidae -5, 6, 7, 8 Humboldtianidae - 6
In addition to the above, Roth (1986) also included the following families in his compilation of regional records, citing them only from the regional compilation of Taylor (1975): Strobilopsidae (Strobilops), Clausiliidae (genus indet.), charopidae (Charopa), and Oleacinidae (genus indet). Taylor (1975:87) also listed the Vitrinidae (Vitrina) from one locality in the Powder River Basin, Wyoming. These records from Taylor (1975) are based on materials from only one or two localities, and in the case of the Oleacinidae, on a single fragmentary shell (Taylor, 1975:441).
Insomeareas,acessationoftectonismoccurredinthelate
Of the above-mentioned families, the Grangerellidae is extinct,andmaynothaveoccurredasfarsouthasNew Mexico. The Ammonitellidae probably always has been a family of the Pacific Northwest. O f the remaining 21 families, 15 (ca. 7 0 % ) stilloccurinNew Mexico,where theylikelyhavebeenlong time sojourners. These include Ellobiidae, Pupillidae,
(Dickinson, 1989:9) and in southern Colorado (Epis and Chapin, 1975, Scott, 1975; Dickinson et al., 1988: 1035). There have been some suggestions of similar erosional surfaces in cordilleran N e w Mexico (Smith et al., 1985:306, Dolliver,
Valloniidae, Urocoptidae, Bulimulidae, Charopidae (as
thatwouldhavepertainedtothepaleoflora.They derivedamean
Radiocentrum), Discidae, Succineidae, Polygyridae, Zonitidae
annual paleotemperature of ca. 10.7°C and an elevation of 2 , 4
(but not Mesomphix), Vitrinidae, Thysanophoridae,
2.7km (7,874-8,858ft),whichisnearthepresentelevationfor .
Oreohelicidae, Humboldtianidae, and Helminthoglyptidae.
Florissantof2.5km (8,202ft).From analysisofvariousstudies,
Representatives ofthe Helicinidae, Strobilopsidae, Subulinidae, andOleacinidaeoccurasnearasTexasand/ornorthernMéxico
Wolfe (1992:426) concluded that "the Rocky Mountains in centralColoradoandsouthwesternMontanawerenear...their
and there are records of fossil Strobilops and of a possible
presentaltitudesbythelatestEocene." Thismaywellapplyto lateEoceneNew Mexicoaswell.WherelateEocenesurfaces
helicinid (Solem, 1979:283--"Helix" chriacorum) from N e w Mexico.ThecamaenidsarenowknownnocloserthantheWest
attained such elevations, it would seem that they must have produced conditions inimical not only to subtropical-tropical floras,asshownatFlorissant,butalsotolandsnailsthathad flourishedinwarmerenvironmentsintheearlierEocene.
Indies and Costa Rica, although occurring as fossils in N e w Mexico and elsewhere in the western United States. Whether
members of the Clausiliidae ever occurred in the Cordilleran
region requires further investigation, given their present American distribution, far to the south, and their being reported from only a single fossil locality in Wyoming (Taylor,
Although late Eocene erosional surfaces, like the above, seemtohaveexistedinsomeplacesinNew Mexico,itappears thatinmany placesfairlyintactLaramide landscapes, ofmarked relief, continued to exist up until late Eocene volcanism commenced.AtsitesstudiedinsouthernNew Mexico,Seager and Mack (1986:672) showed that, although active Laramide upliftessentially h a d c e a s e d b y t h e t i m e o f o n s e t o f latest E o c e n e volcanism,Laramide uplifts,themselves, stillwere exposed and serving as sources of sediments deposited in adjacent basins. In a study of Datil Group volcanics in west-central N e w Mexico,
1975:138).
An overallpatternshowsthat,atthefamilylevel,many ofthe
taxa of the Cordilleran Paleocene/Eocene still exist in the generalsouthernCordilleranareaofNew Mexicoandnorthern
México. To the extent that taxa of the present southern Cordillera descend from earlier progenitors like those discussed above, they might be termed as comprising elements of an
Eocene between the termination of Laramide compressional
activity and the beginning of mid-Tertiary extensional
deformation--and uplifted areas developed graded erosion surfaces. Such surfaces have been described in Arizona
1990:73-74). At leastinthe Laramide Front Range in Colorado,
the late Eocene surface developed at a relatively high elevation
according to an analysis by Gregory and Chase (1992). These
investigatorsutilizedfoliarphysiognomy oftheFlorissantfossil
flora to calculate a mean annual temperature and an elevation