New record of mollusks from the El Molino mammoth site, Parras, Coahuila, Mexico

Abstract

We present new Late Pleistocene and
Holocene records of a land and freshwater malacofauna assemblage from
the mammoth bearing site El Molino in
Parras, Coahuila, northern Mexico. We
identified 19 mollusk taxa, 14 species
were found within the Late Pleistocene
sediments and 10 species in the different
strata belonging to the Holocene. The
gastropods Gastrocopta tappaniana, Pupilla
hebes and Habroconus sp. are new Late
Pleistocene records for Mexico, the first
two being previously recorded for United
States Pleistocene deposits. New Mexican
Holocene fossil records include Euglesa
casertana, Galba humilis, Gastrocopta cristata,
Zonitoides arboreus, Hawaiia minuscula, and
Deroceras laeve. The habitat requirements
of the El Molino site malacofauna assemblage provides additional information on
the environmental changes that occurred
during the Pleistocene-Holocene transition. Woodland associated, hygrophilic
and hydrophilic malacofauna suggest a
humid forested and grassland habitat
during the Late Pleistocene, which subsequently changed to xeric conditions with
the colonization of xerophytic and aridity-tolerant aquatic species during and
after the Pleistocene-Holocene transition
at the study area.

Full text

New record of mollusk fossils from northern Mexico
1Boletín de la Sociedad Geológica Mexicana
/ 74 (1) / A051021/ 2022 /
How to cite this article:
Butrón Xancopinca, P.G., Czaja, A., Carolina
Aguillón, M., Gómez Núñez, R., Vallejo
González, I., Estrada Rodríguez, J.L., 2022,
New record of mollusks from the El Molino
mammoth site, Parras, Coahuila, Mexico:
Boletín de la Sociedad Geológica Mexicana,
74 (1), A051021. http://dx.doi.org/10.18268/
BSGM2022v74n1a051021
Peer Reviewing under the responsibility of
Universidad Nacional Autónoma de México.
This is an open access article under the CC BY-NC-SA
license(https://creativecommons.org/licenses/by-nc-sa/4.0/)
RESUMEN
Se presentan nuevos registros de un ensamblaje de
moluscos terrestres y de agua dulce perteneciente
al Pleistoceno tardío y el Holoceno del yacimiento
de mamuts El Molino en Parras, Coahuila,
ubicado en el norte de México. Se identificaron 19
taxones de moluscos, entre los cuáles 14 especies
se distribuyen dentro del Pleistoceno tardío y 10
especies en los distintos estratos del Holoceno. Los
nuevos registros de moluscos del Pleistoceno tardío
para México incluyen a las especies Gastrocopta
tappaniana, Pupilla hebes y Habroconus sp. de
las cuáles, las primeras dos habían sido registra-
das anteriormente en depósitos Pleistocénicos de
los Estados Unidos. En el Holoceno de México,
se presentan por primera vez los registros fósiles
de las especies Euglesa casertana, Galba humi-
lis, Gastrocopta cristata, Zonitoides arboreus,
Hawaiia minuscula y Deroceras laeve. Los
requisitos de hábitat del conjunto de malacofauna
hallada en el sitio El Molino proponen informa-
ción adicional sobre los cambios ambientales suce-
didos durante la transición Pleistoceno-Holoceno.
La presencia de malacofauna higrófila e hidrófila
asociada a bosques sugiere un hábitat boscoso
húmedo con pastizales durante el Pleistoceno
tardío, el cual cambió posteriomente a condiciones
xéricas con la colonización de especies xerófitas y
acuáticas tolerantes a la aridez durante y después
de la transición Pleistoceno-Holoceno en el área.
Palabras clave: Pleistoceno
tardío, Holoceno, moluscos de
agua dulce, moluscos terres-
tres, paleoreconstrucción.
ABSTRACT
We present new Late Pleistocene and
Holocene records of a land and fresh-
water malacofauna assemblage from
the mammoth bearing site El Molino in
Parras, Coahuila, northern Mexico. We
identified 19 mollusk taxa, 14 species
were found within the Late Pleistocene
sediments and 10 species in the different
strata belonging to the Holocene. The
gastropods Gastrocopta tappaniana, Pupilla
hebes and Habroconus sp. are new Late
Pleistocene records for Mexico, the first
two being previously recorded for United
States Pleistocene deposits. New Mexican
Holocene fossil records include Euglesa
casertana, Galba humilis, Gastrocopta cristata,
Zonitoides arboreus, Hawaiia minuscula, and
Deroceras laeve. The habitat requirements
of the El Molino site malacofauna assem-
blage provides additional information on
the environmental changes that occurred
during the Pleistocene-Holocene transi-
tion. Woodland associated, hygrophilic
and hydrophilic malacofauna suggest a
humid forested and grassland habitat
during the Late Pleistocene, which subse-
quently changed to xeric conditions with
the colonization of xerophytic and arid-
ity-tolerant aquatic species during and
after the Pleistocene-Holocene transition
at the study area.
Keywords: Late Pleistocene,
Holocene, freshwater mol-
lusks, terrestrial mollusks,
paleoreconstruction.
1 Universidad Michoacana de San Nicolás de
Hidalgo, Instituto de Investigaciones en Cien-
cias de la Tierra, Ciudad Universitaria, 58030,
Morelia, Michoacán, Mexico.
2 Facultad de Ciencias Biológicas, Universidad
Juárez del Estado de Durango, 35010, Gómez
Palacio, Durango, Mexico.
3 Laboratorio de Paleontología, Museo del
Desierto, Boulevard Carlos Abedrop Dávila
#3745, 25022, Saltillo, Coahuila, Mexico.
* Corresponding author: (P.G. Butrón Xanco-
pinca) perlab2010@hotmail.com
ABSTRACT
Perla Guadalupe Butrón Xancopinca1,*, Alexander Czaja2, Martha Carolina Aguillón3,
Rosario Gómez Núñez3, Ignacio Vallejo González3, José Luis Estrada Rodríguez2,
New record of mollusks from the El Molino mammoth site, Parras, Coahuila,
Mexico
Nuevo registro de moluscos del yacimiento mamuts El Molino, Parras, Coahuila, México
Manuscript received: April 4, 2021
Corrected manuscript received: June 26, 2021
Manuscript accepted:October 5,2021

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INTRODUCTION
1. Introduction
Although Northern Mexico presents extensive
areas with sediments of numerous paleolakes that
covered the region during the late Quaternary,
only a few sites have been studied for their fossil
remains. Nevertheless, more studies have been
carried out recently, especially from the paleolakes
of the Chihuahuan and Sonoran Deserts with
species-rich molluscan assemblages (Catto and
Bachhuber, 2000; Czaja et al., 2014a, 2014b).
We present a new assemblage of terrestrial
and freshwater malacofauna located at the south-
ern portion of the state of Coahuila in northern
Mexico. The study area is located among farm-
lands at Rancho Buena Fe, called the El Molino
Mammoth site, approximately 4 km east of the
city of Parras de la Fuente (Figure 1). The locality
was described in detail by Miller et al. (2008) and
consists of an abandoned well site approximately
eight meters deep by 6 meters wide, excavated in
the year 2000 (25° 25’54.8” N, 102° 08’56.52”
W; Elevation 1,530 m) (Figures 2a and 2b). The
same authors carried out a Carbon14 dating of
the basal sediments of the cross section which
yielded an age of 11,740 ± 50 years B.P. (Late
Pleistocene). The macrofauna remains found at
the site included mammoth (Mammuthus columbi),
horse (Equus ssp.), camels (Camelops cf. hesternus)
and several small mammal remains (Miller et al.,
2008). During the last few years, partial collapses
within the well have buried the Late Pleistocene
sediments, making them inaccessible for sampling.
This paper focuses on reporting new Late
Pleistocene and Holocene records of a continen-
tal malacofauna assemblage from the El Molino
Mammoth site in Rancho Buena Fe, Parras, Coa-
huila, as well as to propose additional information
on the environmental changes during the Pleisto-
cene-Holocene transition.
2. Materials and methods
Because of the collapsed basal part of the geolog-
ical strata, Late Pleistocene sediments could not
be sampled for this study. However, we used the
sediments remaining from the mammoth excava-
Figure 1 Location of the abandoned well at the El Molino Mammoth site in Rancho Buena Fe, Parras, Coahuila, Mexico.

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MATERIALS AND METHODS
tion in 2000, which were stored at the laboratory of
Paleontology of the Museo del Desierto in Saltillo,
Coahuila, Mexico.
 Atthesite,ve1kgsedimentsampleswerecol-
lected from the 3.30 m Holocene strata currently
exposed within the abandoned well (Figure 2c).
Samples from the C and D strata correspond to
the Late Pleistocene-Holocene transition, while the
remaining B1, B2 and A samples belong to the Holo-
cene (Miller et al., 2008). The samples were screened
through two sieves with 0.5 mm and 0.3 mm mesh
sizes. The selection of mollusks was carried out
under a stereoscopic microscope, and subsequently
washed with 3% hydrogen peroxide in order to
remove mud or any other organic residue. All shells
were photographed with a Zeiss AxioCam ERc 5s
camera attached to a Zeiss Stemi 2000-C micro-
scope.MolluskidenticationsarebasedonPilsbry
(1946, 1948), Leonard (1950, 1952), Metcalf and
Smartt (1997), Nekola (2004), Wethington et al.
(2009), Nekola and Coles (2010), and Walther et al.
(2010). The revision was based mainly on biodiver-
sity websites including WoRMS (World Register of
Marine Species), and MolluscaBase (MolluscaBase,
2021). The material is part of the University Juárez
Malacological Collection (UJMC) and is housed
at the Faculty of Biological Science of the Juarez
State University of Durango (UJED).
Figure 2 a. The El Molino Mammoth sites abandoned well in present-day Rancho Buena Fe; b. Image of the abandoned well from the
year 2000 excavation; c. Geological profile of the Holocene strata sampling points. Black dash lines represent the start of the D strata.
Image b is modified from Miller et al. (2008).

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MATERIALS AND METHODS/
RESULTS
3. Results
The studied material comprises a total of 19 mol-
lusk taxa belonging to 15 families and 17 genera.
Mollusks found within the Late Pleistocene strata
include 14 species belonging to 12 families and
14 genera, while the Holocene strata includes 10
species (8 families and 9 genera) (Table 1).
3.1. SYSTEMATIC DESCRIPTIONS
Bivalvia Linnaeus, 1758
Family Sphaeriidae Deshayes, 1855
Genus Euglesa Jenyns, 1832
Euglesa casertana (Poli, 1791)
(Figure 3j)
Ecology: Perennial and ephemeral swamp ponds,
streams, rivers and lakes (Herrington, 1962).
Current distribution: United States, Mex-
ico, Cuba, Puerto Rico and from Honduras to
Patagonia (Herrington, 1962).
Stratigraphic remarks: The stratigraphic
distribution of E. casertana at the El Molino
Mammoth site is limited to the A strata belong-
ing to the Holocene. This species has also been
found in a Late Pleistocene site of San Luis
Potosí, Mexico (Arroyo-Cabrales et al., 2008).
Referred material: UJMC 600, 18
specimens.
Measurements: Length: 2.2 mm; diameter:
3 mm.
Euglesa compressa (Prime, 1852)
(Figure 3i)
Family Genus Species
Late
Pleistocene Holocene
Bivalves
Sphaeriidae Euglesa E. compressa x
E. casertana x
Aquatic
Lymnaeidae Galba G. humilis x
G. obrussa x x
Physidae Physella P. acuta x
Planorbidae Gyraulus G. parvus x
Ferrissia F. californica x
Terrestrial
Ellobiidae Carychium C. exiguum x
Succineidae Succinea Succinea sp. x x
Cochlicopidae Cochlicopa C. lubrica x
Gastrocoptidae Gastrocopta G. cristata x
G. tappaniana x
Pupillidae Pupilla P. hebes x
Valloniidae Vallonia V. gracilicosta x
Gastrodontidae Zonitoides Z. arboreus x x
Glyphyalinia G. indentata x x
Euconulidae Habroconus Habroconus
sp. x
Pristilomatidae Hawaiia H. minuscula x
Agriolimacidae Deroceras D. laeve x x
Table 1. Taxonomic list of Late Pleistocene and Holocene malacofauna from the El Molino Mammoth site in Rancho Buena Fe, Parras,
Coahuila.

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RESULTS
Ecology: E. compressa is restricted to areas of per-
manent water, preferring shallow sandy bottoms
and rooted vegetation (Czaja et al., 2014b).
Current distribution: Canada and United
States. In Mexico it can be found in Chihuahua,
Coahuila and Tamaulipas (Burch, 1972; Bequaert
and Miller, 1973).
Stratigraphic remarks: The stratigraphic
distribution of E. compressa at the El Molino Mam-
moth site is limited to Late Pleistocene strata. The
rstPleistocenerecordfor this species in Mexico
was reported by Czaja et al. (2014b) from paleolake
Irritila, Coahuila, northern Mexico.
Referred material: UJMC 601, 44 specimens.
Measurements: Length: 4 mm; diameter: 5
mm.
Gastropoda Cuvier, 1795
FamilyLymnaeidaeRanesque,1815
Genus Galba Schranck, 1803
Galba humilis (Say, 1822)
(Figure 3b)
Ecology: This semi-aquatic species preferers
muddy areas along the edges of creeks, lakes,
ponds, and swamps (Clarke, 1981; Stewart and
Dillon, 2004).
Current distribution: North America. Mex-
ican states of Chihuahua, Coahuila, Hidalgo,
Nuevo León, Sonora and Tamaulipas (Mazzotti,
1956; Landeros et al., 1981; Thompson, 1999;
Thorp and Rogers, 2016).
Stratigraphic remarks: At the El Molino
Figure 3 a. Deroceras laeve; b. Galba humilis; c. Ferrissia californica; d. Physella acuta; e. Gyraulus parvus; f. Galba obrussa; g. Carychium
exiguum; h. Hawaiia minuscula; i. Euglesa compressa; j. Euglesa casertana. Scale bars = 2 mm.

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RESULTS
Mammoth site, the stratigraphic distribution of G.
humilis is limited to the Holocene A strata. Galba
humilis is widely known with its synonymous name,
Lymnaea humilis.
Referred material: UJMC 602, 14
specimens.
Measurements: Height: 8.5 mm; aperture
length: 4 mm.
Galba obrussa (Say, 1825)
(Figure 3f)
Ecology: Galba obrussa is common along the edges
of small bodies of water such as streams and
ponds, preferring areas along river banks or under
protected spots (Baker, 1928; Miller, 1966).
Current distribution: From the Atlantic
to the Pacic. From Canada to the
southern state of Arizona and into
northern Mexico, including the states
of Durango and Coahuila (Baker, 1928;
Mazzotti, 1955; Naranjo-Garcia, 2010).
Stratigraphic remarks: The stratigraphic
distribution of G. obrussa at the El Molino Mam-
moth site ranged from the Late Pleistocene up to
the Holocene D strata. This species was formerly
known and described as Fossaria obrussa. This is the
rstPleistocenerecordof thisspeciesinCoahuila,
previously known only from a Late Pleistocene
locality within the Valsequillo basin of central
Mexico (Stevens et al., 2012).
Referred material: UJMC 603-604, 11
specimens (Late Pleistocene: 7; Holo-
cene: 4).
Measurements: Height: 4 mm; aperture length:
1.90 mm.
Family Physidae Fitzinger, 1833
Genus Physella Haldeman, 1842
Physella acuta (Draparnaud, 1805)
(Figure 3d)
Ecology: Physella acuta populations can be found
in ponds, reservoirs, and the margins of rivers
and streams, especially in disturbed sediments or
disturbed areas rich in organic material environ-
ments (Wethington et al., 2009).
Current distribution: Cosmopolitan, can
be found across six continents due to their high
expansiveness by natural processes and acciden-
tal dispersal mediated by humans during the
transport of exotic plants to Europe. In Mexico,
the species is reported from Coahuila, Durango,
Puebla, Aguascalientes, Veracruz and Michoacán
(Arroyo-Cabrales et al., 2008; Wethington et al.,
2009; Vinarski, 2017; Spyra et al., 2019; Czaja et
al., 2020).
Stratigraphic remarks: The stratigraphic dis-
tribution of P. acuta at the El Molino Mammoth
site is limited to the A strata (Holocene). Holocene
and Pleistocene records for this species are known
from Coahuila and Mexico City (Arroyo-Cabrales
et al., 2008; Czaja et al., 2014a, 2014b).
Referred material: UJMC 605, 14
specimens.
Measurements: Height: 5.1 mm; aperture
length: 3.85 mm.
FamilyPlanorbidaeRanesque,1815
Genus Gyraulus Charpentier, 1837
Gyraulus parvus (Say, 1817)
(Figure 3e)
Ecology: Gyraulus parvus is usually associated with
abundant vegetation in shallow water (Tuthill et al.,
1964).
Current distribution: North America. The
species distribution in Mexico includes Durango,
Morelos, Puebla and Sonora (Arroyo-Cabrales et
al., 2008; Thompson, 2011; Czaja et al., 2020).
Stratigraphic remarks: At the El Molino
Mammoth site, the stratigraphic distribution of G.
parvus is limited to Late Pleistocene strata. This
is therst record of G. parvus for the Pleistocene
of Coahuila. This species has also been reported
from other Late Pleistocene localities of central
Mexico (Arroyo-Cabrales et al., 2008) and south-
ern Mexico (Guerrero-Arenas et al., 2013).
Referred material: UJMC 606, 33
specimens.

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RESULTS
Measurements: Diameter: 4.8 mm.
Genus Ferrissia Walker, 1903
Ferrissia californica (Rowell, 1863)
(Figure 3c)
Ecology: Ferrissia californica can be found in small
bodies of water, often capable of surviving dry
conditions (Walther et al., 2010).
Current distribution: Members of the gas-
tropod genus Ferrissia have a near-cosmopolitan
distribution (Walther et al., 2010).
Stratigraphic remarks: The stratigraphic
distribution of F. californica at the El Molino Mam-
moth site is limited to Late Pleistocene strata. F.
californica has also been found in Pleistocene and
Holocene localities within the state of Coahuila
(Czaja et al., 2014 a, b).
Referred material: UJMC 607, 5
specimens.
Measurements: Height: 1.2 mm; length: 2.8
mm.
FamilyEllobiidaePfeier,1854
Genus Carychium Müller, 1773
Carychium exiguum (Say, 1822)
(Figure 3g)
Ecology: Carychium exiguum inhabits humid
environments such as swampy areas, is strongly
hygrophilous and usually found under fallen leaves
rocks and logs not far from water (Branson, 1961).
Current distribution: Canada, Colorado,
New Mexico and Alabama, and Nuevo
León in Mexico (Hubricht, 1985; Con-
treras-Arquieta, 1995).
Stratigraphic remarks: At the El Molino
Mammoth site, the stratigraphic distribution of C.
exiguum is limited to Late Pleistocene strata. This
istherst Pleistocenerecord of this speciesfrom
Coahuila. Arroyo-Cabrales et al. (2008) recorded
C. exiguum from a Late Pleistocene locality of San
Luis Potosí.
Referred material: UJMC 608, +100
specimens.
Measurements: Height: 2 mm.
Family Succineidae Beck, 1837
Genus Succinea Draparnaud, 1801
Succinea sp.
(Figure 4c)
Ecology: Members of the Family Succineidae can
be found in disturbed areas but prefers freshwater
habitats with humid conditions among rocks, logs
or leaf litter (Forsyth, 2005).
Current distribution: The Succineidae Family
in Mexico is found distributed in Baja Califor-
nia, Central Mexico, Tamaulipas and Veracruz
(Naranjo-García and Fahy, 2010).
Stratigraphic remarks: Late Pleistocene and
the Holocene A, B1 and D strata. Late Pleistocene
records in Mexico include Villa Acuña, Coahuila
and Rancho La Amapola, San Luis Potosí (Arroyo-
Cabrales et al., 2008).
Referred material: UJMC 609-610, 62
specimens (Late Pleistocene: 18; Holo-
cene: 44).
Measurements: Height: 5.5 mm; aperture
length: 3 mm.
Family Cochlicopidae Pilsbry, 1900
Genus Cochlicopa Férussac, 1821
Cochlicopa lubrica (O.F. Müller, 1774)
(Figure 4a)
Ecology: Cochlicopa lubrica is considered a wood-
land mollusk and is usually found in forested mon-
tane habitats among damp under leaves (Judd,
1963; Kolb et al., 1975; Metcalf and Smartt, 1997).
Current distribution: The genus Cochlicopa
contains a single Mexican species, C. lubrica, which
inhabits northwest Chihuahua, southern Nuevo
León and Durango (Pilsbry, 1953; Bequaert and
Miller, 1973; Contreras-Arquieta, 1995; Cor-
rea-Sandoval, 2003; Naranjo-García and Fahy,
2010).
Stratigraphic remarks: The stratigraphic dis-
tribution of C. lubrica at the El Molino Mammoth
site is limited to Late Pleistocene strata. Fossil

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RESULTS
records include sites in Coahuila and the Grava
Valsequillo Formation of Puebla (Arroyo-Cabrales
et al., 2008).
Referred material: UJMC 611, 12
specimens.
Measurements: Height: 6.5 mm; aperture
length: 2.1 mm.
Family Gastrocoptidae Pilsbry, 1918
Genus Gastrocopta Wollaston, 1878
Gastrocopta cristata (Pilsbry and
Vanatta, 1900)
(Figure 4d)
Ecology: Gastrocopta cristata is found in wooded
slopes near streams and under fallen logs, as well
as in grass where moisture conditions are favorable
and stable (Leonard, 1950).
Current distribution: Kansas, Oklahoma
and Texas to western New Mexico and
Arizona. In Mexico it is reported from
Sonora (Leonard, 1950; Bequaert and
Miller, 1973).
Stratigraphic remarks: At the El Molino
Mammoth site, the stratigraphic distribution of
G. cristata includes the entire Holocene strata. This
species has only been recorded in Late Pleistocene
Figure 4 a. Cochlicopa lubrica; b. Glyphyalinia indentata; c. Succinea sp.; d. Gastrocopta cristata; e. Zonitoides arboreus; f. Habroconus
sp.; g. Pupilla hebes; h. Gastrocopta tappaniana; i. Vallonia gracilicosta. Scale bars = 2 mm.

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RESULTS
deposits from Rancho La Amapola, San Luis
Potosí (Arroyo-Cabrales et al., 2008).
Referred material: UJMC 612, +100
specimens.
Measurements: Height: 3 mm.
Gastrocopta tappaniana (C.B. Adams,
1841)
(Figure 4h)
Ecology: G. tappaniana is a hydrophilic species
observed in grasslands, lowland forests, wooded
slopesandoodplainswithpoordrainage,usually
among leaf litter and below logs and stones (Leon-
ard, 1950; Branson, 1961; Nekola, 2004).
Current distribution: Arizona, New Mex-
ico, Kansas, South Dakota in the United
States and Alberta and Manitoba in
Canada (Pilsbry, 1948). Not reported
from Mexico.
Stratigraphic remarks: The stratigraphic dis-
tribution of G. tappaniana at the El Molino Mam-
moth site is limited to Late Pleistocene strata. This
istherstfossilrecordof thisspeciesinMexico.
Referred material: UJMC 613, 23
specimens.
Measurements: Height: 2.8 mm.
Family Pupillidae Turton, 1831
Genus Pupilla Fleming, 1828
Pupilla hebes (Ancey, 1881)
(Figure 4g)
Ecology: Pupilla hebes can be found in forested
mountain habitats consisting of wet meadows
(Metcalf and Smartt, 1997).
Current distribution: The species has been
reported in the United States from
various localities of the western moun-
tains, except in California. In Mexico,
it has been found in Chihuahua and
Baja California (Metcalf and Smartt,
1997; Miller, 1981).
Stratigraphic remarks: At the El Molino
Mammoth site, the stratigraphic distribution of P.
hebes is limited to Late Pleistocene strata. This is
therstfossilrecordof thisspeciesinMexico.
Referred material: UJMC 614, 9
specimens.
Measurements: Height: 3.1 mm.
Family Valloniidae Morse, 1864
Genus Vallonia Risso 1826
Vallonia gracilicosta Reinhardt, 1883
(Figure 4i)
Ecology: Common under bushes protected spots
such as under litter, rocks and dead grass. It is not
restricted to a wooded habitat and can tolerate dry
conditions (Kolb et al., 1975; Metcalf and Smartt,
1997).
Current distribution: Oklahoma, New
Mexico and adjacent states. In Mexico,
it is recorded only in Nuevo León (Met-
calf and Smartt, 1997; Correa-Sando-
val, 2003).
Stratigraphic remarks: The stratigraphic
distribution of V. gracilicosta at the El Molino
Mammoth site is limited to Late Pleistocene strata.
Arroyo-Cabrales et al. (2008), recorded V. gracilicosta
in two Pleistocene localities in Mexico, one near
the municipality of Villa Acuna in Coahuila and
the other at Rancho La Amapola, San Luis Potosí.
Referred material: UJMC 615, 62
specimens.
Measurements: Diameter: 2.5 mm.
Family Gastrodontidae Tryon, 1866
Genus Zonitoides Lehmann, 1862
Zonitoides arboreus (Say, 1817)
(Figure 4e)
Ecology: Zonitoides arboreus occurs in woodlands
and is associated with trees as well as living under
shaded areas such as bark, leaves and stones
(Leonard, 1950; Metcalf and Smartt, 1997).
Current distribution: From Canada
through the southern United States,
Mexico and Central America. The distri-
bution in Mexico includes Chihuahua,

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RESULTS
Nuevo León, San Luis Potosí, Puebla,
and Veracruz (Metcalf and Smartt,
1997; Naranjo-García and Fahy, 2010).
Stratigraphic remarks: At the El Molino
Mammoth site, the stratigraphic distribution of Z.
arboreus includes both Late Pleistocene and Holo-
cene strata. The rst Pleistocene record for this
species was made by Arroyo-Cabrales et al. (2008)
near the municipality of Villa Acuna in Coahuila.
Referred material: UJMC 616-617, +100
specimens (Late Pleistocene: +100;
Holocene: 14).
Measurements: Diameter: 5 mm.
Genus Glyphyalinia von Martens, 1892
Glyphyalinia indentata (Say, 1822)
(Figure 4b)
Ecology: This species can be usually
found in leaf litter in forests, open
meadows, and anthropogenic impacted
habitats (Nekola, 2010).
Current distribution: Arizona, New Mex-
ico, Texas, Mexico and Guatemala. In
Mexico, it has been reported from Baja
California, Durango, Jalisco, Micho-
acán, Mexico City, Morelos and Puebla
(Thompson, 2011).
Stratigraphic remarks: The stratigraphic
distribution of G. indentata at the El Molino Mam-
moth site includes Late Pleistocene and Holocene
Astrata.TherstPleistocenerecordforthisspe-
cies in Coahuila was made by Arroyo-Cabrales et
al. (2008) near the municipality of Villa Acuna.
Referred material: UJMC 618-619, 53 speci-
mens (Late Pleistocene: 40; Holocene: 13). Mea-
surements: Diameter: 3.5 mm.
Family Euconulidae Baker, 1928
Genus Habroconus Cross & P. Fischer, 1872
Habroconus sp.
(Figure 4f)
Ecology: Members of the genus Habroconus can
be found in wooded and forested habitats, under
rocks, leaf litter, shrubs and trees (Baker, 1930;
Veitenheimer-Mendes and Aguiar-Nunes, 2001;
Veitenheimer-Mendes and Postal, 2003).
Current distribution: Habroconus specimens
in Mexico can be found in the states of Jalisco,
Quintana Roo, Mexico, Michoacán, Nuevo Leon,
Puebla, San Luis Potosí, Sonora, Tamaulipas,
Veracruz and Yucatan (Pilsbry, 1919b; Baker,
1930; Thompson, 1967b; Correa-Sandoval, 1997;
Araiza y Naranjo-Garcia, 2013; Naranjo-García
and Fahy, 2010; Van Devender et al., 2012)
Stratigraphic remarks: The stratigraphic dis-
tribution of Habroconus sp. at the El Molino Mam-
moth site is limited to Late Pleistocene strata. This
istherstfossilrecordof thisspeciesinMexico.
Referred material: UJMC 620, 35
specimens.
Measurements: Diameter: 2.8 mm.
Family Pristilomatidae Cockerell,
1891
Genus Hawaiia Gude, 1911
Hawaiia minuscula (A. Binney, 1841)
(Figure 3h)
Ecology: Hawaiia minuscula is an inhabitant of
humid environments, living on leaf mold, beneath
the bark of trees and among mosses. It is capable
of withstanding long periods of drought and high
temperatures (Leonard, 1950).
Current distribution: Canada and United
States. In Mexico, the species has been reported
from Baja California, Sonora, Tamaulipas,
San Luis Potosí, Veracruz, Puebla, Nayarit and
Yucatán (Bequaert and Miller, 1973; Metcalf and
Smartt, 1997).
Stratigraphic remarks: At the El Molino
Mammoth site, the stratigraphic distribution
includes the Holocene A, B2, C and D strata.
Arroyo-Cabrales et al. (2008) reported H. minuscula
from the Late Pleistocene locality of Rancho La
Amapola near the city of San Luis Potosí.
Referred material: UJMC 621, +100
specimens.
Measurements: Diameter: 2 mm.

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RESULTS/DISCUSSION
Family Agriolimacidae Wagner, 1935
Genus DerocerasRanesque,1820
Deroceras laeve (O.F. Müller, 1774)
(Figure 3 a)
Ecology: Deroceras laeve has a circumpolar distri-
bution and is considered a hygrophilous species. It
can be found at low elevations among cultivated,
urban and marshy areas. In mountains, it occurs
along springs, streams and other bodies of water
(Bequaert and Miller, 1973; Metcalf and Smartt,
1997; Rowson et al., 2014).
Current distribution: Originally, this species
was found native to North America but can be
found today on other continents as well. In Mex-
ico, it has been recorded in Mexico City, Puebla
and Veracruz (Bequaert and Miller, 1973; Metcalf
and Smartt, 1997).
Stratigraphic remarks: The stratigraphic dis-
tribution of D. laeve at the El Molino Mammoth
site includes the Late Pleistocene and Holocene A
andCstrata.TherstLatePleistocenerecordfor
D. laeve was reported from Rancho La Amapola
near San Luis Potosí by Arroyo-Cabrales et al.
(2008).
Referred material: UJMC 622-623, 17
specimens (Late Pleistocene: 11; Holo-
cene: 6).
Measurements: Height: 4 mm; width: 2
mm.
Table 2. The habitat requirements of the El Molino Mammoth Site Late Pleistocene and Holocene malacofauna (modified from Miller,
1966).
Species Habitat requirements
C. exiguum Hygrophilic: moist situations in shaded areas not far
from water.
G. tappaniana
D. laeve
E. compressa Perennial water: stream or lake with slow to moderate
current and shallow spots not affected by seasonal
drying.
G. parvus Shallow quiet water: small body of water with no current
or areas of rooted vegetation with little current, both not
subjected to significant seasonal drying.
Habroconus sp. Woodland: moist areas under leaf litter, down timber,
among tall marsh grass.
C. lubrica
Z. arboreus
G. indentata
G. obrussa Marginal situations: Wet mud, sticks, stones or any other
debris along water's edge, also in shallow ponds and
protected spots.
V. gracilicosta Sheltered situations: these species are not restricted to a
woodland habitat and can tolerate drier conditions.
P. hebes
G. cristata
H. minuscula
F. californica Shallow quiet water: small body of water that may
become dry during part of the year.
E. casertana
P. acuta
G. humilis
Succinea sp. From relatively dry to humid conditions, preferring the
later.

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DISCUSSION
4. Discussion
4.1. NEW MOLLUSCAN RECORDS
From the 14 mollusk taxa reported for the Late
Pleistocene of the El Molino Mammoth site, all
but three species were found distributed around
Mexico and the United States Quaternary depos-
its.Forthersttime,wereportthespeciesGastro-
copta tappaniana, Pupilla hebes and Habroconus sp. for
thePleistocene of Mexico, of whichtherst two
were previously known from Pleistocene deposits
within the United States. Today, these species
are extinct in the area, with G. tappaniana being
mostly distributed outside of Mexico, usually from
western to north eastern United States. In the
case of P. hebes, recent distribution includes only
the northern Mexican states of Chihuahua and
Baja California, whereas specimens of the genus
Habroconus can be found from the northern state
of Nuevo Leon to the southern state of Yucatan.
For the state of Coahuila, new Pleistocene records
include G. tappaniana, G. obrussa, C. exiguum, G. par-
vus, P. hebes, D. laeve and Habroconus sp. The remain-
ing species (E. compressa, F. californica, Succinea sp.,
C. lubrica, V. gracilicosta, Z. arboreus and G. indentata)
have previously been reported from other Pleisto-
cene sites around the state.
Of the 10 Holocene mollusk taxa reported
from the El Molino Mammoth site, three species
have been previously recorded from Holocene
fossil localities in Mexico. These include G. obrussa
and P. acuta from Coahuila (Czaja et al., 2019) and
Succinea sp. from Sonora (Copeland, 2011). The
Figure 5 Generalized sediment sequence and malacofauna distribution from the abandoned well at the El Molino Mammoth site.

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DISCUSSION
remaining seven species, E. casertana, G. humilis, G.
cristata, G. indentata Z. arboreus, H. minuscula, and D.
laeve, are new fossil records for the Holocene of
Mexico.
4.2. PALEOECOLOGICAL INTERPRETATIONS
Most of the El Molino Mammoth site mollusk taxa
were also present during the early Quaternary in
various sites of North America, making possible
detailed paleoenvironmental interpretations
through the available data associated with their
environmental preferences and requirements (Car-
obene et al., 2018). Generally, species composition
and abundance of certain taxa in each assemblage
depend on climatic conditions and local ecological
factors, especially vegetation cover (Sümegi and
Krolopp, 2002; Carobene et al., 2018).
The large amount of terrestrial mollusks from
the Late Pleistocene strata of the El Molino Mam-
moth site is noteworthy (Table 2). Miller (1966)
associated the same species (C. lubrica, Z. arboreus
and G. indentata) with those from the Great Plains
to be woodland associated and commonly found
in forested areas among shallow bodies of water.
Additionally, thending of numerousfragmental
remains of fossil wood among the Late Pleisto-
cenesedimentsconrmthepresenceof arboreous
vegetation at the site. In addition, the area must
have also supported grassland patches due to the
numerous shells found of V. gracilicosta, a species
commonly recorded from humid permanent bod-
ies of water with grassland vegetation (McMullen
and Zakrzewski, 1972). These habitat require-
ments well conrm the previous environmental
interpretation given by Miller et al. (2008) for
the site based on the vertebrate fauna. The fossil
remains of horses, camels and other mammals
found infer woodland and grassland habitats, thus
supporting a community of species representing
localized woodland interrupted by grassland habi-
tats near a permanent body of water at the site.
In the Late Pleistocene and Early Holocene, the
climatic conditions of the deserts in northern
Mexico were much cooler than at the present
(Metcalf et al., 2000). Most of the Late Pleistocene
malacofauna of the El Molino Mammoth site
did not survive the rapid environmental changes
during the Pleistocene-Holocene transition. Nota-
blein theElMolinoMammothsite proleisthe
Figure 6 Comparison of the habitat association percentage between Late Pleistocene and Holocene mollusks from the El Molino
Mammoth site.

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DISCUSSION/CONCLUSION
sudden appearance of numerous species typically
associated with grasslands such as, G. cristata and
H. minuscula, and the simultaneous disappearance
of wetland species (Figure 5). Both presumably
reect the striking change of  climate conditions
during and after the transition.
The early mid-Holocene was probably warmer
and wetter than today, and true desert conditions
did not set in until about 4000 yr B.P. (Metcalf et
al., 2000). It is likely that the B horizon with its
gypsum and calcium carbonate crystals represent
these desert condition with dry climates and peri-
ods of evaporation and drought, and would likely
explain the rapid colonization of the xerophytic
elementsintheprolethatoverallrepresent60%
of the malacofauna during this period (Figure 6).
Duringthenalphaseof thebodyof water,there
was an increase in the aquatic species P. acuta and
G. humilis, accompanied by the aridity tolerant
freshwater bivalve E. casertana. Agenbroad and
Mead (1994) point to the abundance of Phy-
sella as indicative of warm waters. On the other
hand, G. humilis is an excellent colonizer of new
habitats and known for invading ponds devoid of
vegetation and other species of gastropods (Joki-
nen, 2005). The ten species of the malacofauna
that survived the transition into the Holocene are
known for their tolerance of high temperatures
(Miller, 1966). During this time, the site consisted
of an ephemeral pond with predominant vegeta-
tion consisting mainly of short grasses and shrubs.
5. Conclusion
Our ndings expand the mollusk data record
known for Mexico with the entry of the three new
Late Pleistocene gastropods, Gastrocopta tappaniana,
Pupilla hebes and Habroconus sp. as well as seven new
Holocene mollusk fossils, E. casertana, G. humilis,
G. cristata, G. indentata, Z. arboreus, H. minuscula,
and D. laeve, from the El Molino Mammoth site
of Northern Mexico. The Late Pleistocene and
Holocene molluscan fauna from the site provide a
broader view of the paleoenvironmental changes
that occurred in northern Mexico during this time
period.Therecordedspeciesconrmthepresence
of a humid forested and grassland habitat capable
of supporting the hygrophilic and hydrophilic
malacofauna along with the fossil remains of
horses, camels and other mammals. Many mollusk
species were not able to survive the strong shift to
the more xeric conditions after and during the
Pleistocene-Holocene transition. The surviving
freshwater mollusks relied on the ephemeral body
of water until the long periods of drought resulted
in the total evaporation of water from the El
Molino Mammoth site.
Contributions of authors
The authors of this research are: Perla Guadalupe
Butrón Xancopinca (PGBX), Alexander Cza-
ja(AC), Martha Carolina Aguillón (MCA), Rosario
Gómez Núñez (RGN), Ignacio Vallejo González
(IVG) and José Luis Estrada Rodríguez (JLER).
Inaddition,itsspeciccontributionis:1.Concep-
tualization: PGBX and AC; 2.Data acquisition:
PGBX and AC; 3.Methodologic/technical devel-
opment: PGBX and AC; 4.Writing of the original
manuscript: PGBX and AC; 5.Writing of the cor-
rected and edited manuscript: PGBX, AC, RGN,
MCA, IVG and JLER; 6.Graphic design: PGBX;
7.Fieldwork: PGBX, AC, RGN, MCA, IVG and
JLER; 8.Interpretation: PGBX and AC; 9.Financ-
ing: Universidad Juárez del Estado de Durando,
Campus Gómez Palacio, Mexico.
Financing
Universidad Juárez del Estado de Durando, Cam-
pus Gómez Palacio, Mexico.
Acknowledgements
We thank Jorge Banda, owner of Rancho Buena
Fe, for allowing us to access the abandoned well

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ACKNOWLEDGEMENTS/
CONTRIBUTIONS OF AUTHORS
site. A special thanks to the Paleontologists Rosario
Gómez Núñez and Martha Carolina Aguillón as
well as Ignacio Vallejo González for their support
during the visit to the Laboratory of Paleontology
of the Museo del Desierto in Saltillo, Coahuila
and for generously providing the Late Pleistocene
material utilized in this study. We express our
gratitude to Dr. Wade E. Miller and Dr. Jim I.
Mead for their comments and suggestions towards
the improvement of this manuscript. Transport
funding was provided by the authorities of the
Universidad Juarez del Estado de Durango.
Conflicts of interest
The authors declare that there is no conict of 
interest with other authors, institutions or other
third parties about the content of this article.
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