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1. Introduction
The fossil record of the Parras and La Popa basins (Difunta Group) includes a diversity of plants, invertebrates and vertebrates, distributed in diverse facies of a deltaic system that prevailed in northeastern Mexico from late Campanian to Paleocene (e.g., McBride et al., 1974; Wolleben, 1977; Vega and Perrilliat, 1989; Lawton et al., 2009). McBride et al. (1974) subdivided the Difunta Group into two sedimentary basins, the Parras and La Popa basins. Vega and Perrilliat (1992)first report continental gastropods from the Paleogene deposits of the La Popa Basin (Nuevo León). Later, Perrilliat et al. (2008) reported eleven species of freshwater gastropods from three localities of the Cerro del Pueblo Formation (Parras Basin, Coahuila). The abundance and diversity of continental gastropods, as found in lithostratigraphic units of the Difunta Group is unique in Mexico.
Although the systematics of continental gastropods are mostly based on soft-body features and molecular data, it is important to know the occurrence of these organisms, whose shell morphology resembles living species distributed around the world. The data could also be helpful for detailed paleogeographic reconstructions of the late Campanian and middle Paleocene sea shore in NE Mexico. This is because the habitats of these gastropods correspond to ponds, marshes, and swamps found near the ancient coast of NE Mexico. Continental molluscs represent the most abundant and diverse fossils of the Difunta Group, being one of the most important for facies interpretation, since nearly all of these gastropods and bivalves are found with little or no transport from their original habitats.
Salt tectonics played an important role in facies distribution and occurrence, mainly at La Popa Basin (Giles and Lawton, 1999, 2002; Lawton et al., 2001, 2009). This halokinetic control was important, especially during Paleocene times, in the formation of small, closed shallow basins. In these zones, organic matter accumulated in estuarine to freshwater environments, and aquatic continental gastropod populations developed.
On the other hand, late Campanian sequences of the Parras Basin also had significant changes in facies, but with deposition in low-gradient lower coastal plain and shallow marine environments, influenced by high-frequency changes in relative sea level, and coastal storm events (Eberth et al., 2004). This difference may explain the complete absence of terrestrialpulmonate snails in the Paleocene units of La Popa Basin.Figure 1.1 and 1.2 illustrate inferred paleogeography for NE Mexico during Late Cretaceous and Paleocene.
2. Stratigraphy and localities
2.1 Late campanian, Cerro del Pueblo formation
The Cerro del Pueblo Formation is the oldest (late Campanian) lithostratigraphic unit of the Parras Basin (McBride et al., 1974, Eberth et al., 2004) and includes shallow sedimentary environments, represented by delta plains, lagoons, and marshes, located in the ancient northeast coast of Mexico (Figure 1.1). Relatively similar environments were found during the Paleocene in this region (Figure 1.2). A diversity of marine, freshwater, and terrestrial animals has been described from several localities in NE Mexico (Figure 1.3).Perrilliat et al. (2008) reported important fossiliferous outcrops of the Cerro del Pueblo Formation. Its lithology and fossiliferous content is similar to the locality here described as Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila (25°31ʹ03ʺN, 101°40ʹ30ʺW) (Figure 1.4), also from the Cerro del Pueblo Formation. In the latter, light-brown, fine-grained sandstone beds yield hematizedgastropods, bivalves, tortoise bones, crocodile teeth, coprolites, wood fragments, and fruits, preserved under anoxic, stagnant freshwater deposits. Estuarine, non-hematized gastropods are also found a few meters above level with hematized remains. The freshwater strata are relatively thin and interbedded in cyclic sequences with shallow marine sediments that include the ostreoidFlemingostrea subspatulataForbes, 1845 and the ammoniteSphenodiscus sp.
Figure 1 1, Late Cretaceous paleogeographic map, with approximate position of Las Águilas/Porvenir de Jalpa locality. 2, Paleocene paleogeographic map, with approximate position of La Leona locality. 3, Geologic map with position of study area in NE Mexico. 4, Map of study localities in Coahuila, NE Mexico. Paleogeographic maps courtesy of Ron Blakeley (modified). Figure 1.3 modified from Barton et al. (2003). Figure 1.4 from Google Earth.
Here we report seventeen species of continental gastropods for the upper Campanian Cerro del Pueblo Formation. Five of them are new and three species were previously reported byPerrilliatet al., 2008 for the Cerro del Pueblo Formation, but from different localities (Figure 2). Pulmonate gastropods are here reported for the first time for the Difunta Group. A total of 30 continental gastropods are now known from the Cerro del Pueblo Formation (Figure 3), and a significant number of bivalves are to be reported in future studies.
2.2 Paleocene, Las Encinas formation
Four species of freshwater gastropods were reported byPerrilliat et al. (2008) from red beds (delta plain) of the Las Encinas Formation (Parras Basin). The Paleocene Adjuntas, Viento and Carroza formations in La Popa Basin also contain continental gastropods. These specimens were found in delta-plain deposits, with some species in common with those from the Paleocene of Las Encinas Formation (Figure 2).
Figure 2 Distribution of continental gastropods in Campanian and Paleocene lithostratigraphic units of the Difunta Group, Parras and La Popa basins.
Two species of continental gastropods are here reported from fluvial deposits of the Paleocene Las Encinas Formation at La Leona locality, Ramos Arizpe, Coahuila, (25°58ʹ47ʺN, 101°06ʹ23ʺW) (Figure 1.4). A total of 12 Paleocene continental gastropod species are now known from the Paleocene Las Encinas, Adjuntas, and Carroza formations (Figure 3).
Figure 2 illustrates the Upper Cretaceous and Paleocene lithostratigraphic units of the Difunta Group (Parras and La Popa basins), indicating those that yield continental gastropods, for a total of 42 species now known from the Campanian-Paleocene deposits of the Difunta Group (Figure 3). Acronym used: CPC which stands for the Colección de Paleontología, Museo del Desierto, Saltillo, Coahuila.The order of families is based onBouchet et al. (2017).
3. Systematic paleontology
Class GastropodaCuvier, 1797
Subclass CaenogastropodaCox, 1959
Order SorbeoconchaPonder and Lindberg, 1997
Superfamily CerithioideaFleming, 1822
Family Hemisinidae Fischer and Crosse, 1891
GenusPyrguliferaMeek, 1877
Pyrgulifera humerosa(Meek, 1860)
Description. Elongate shell, with concave shoulder and transversal ribs that finish as tubercles. Fine spiral lines and fine growth lines over the ribs, which give the shell reticulate appearance. Suture well marked. Apex not well preserved and aperture absent.
Material examined. Four specimens, CPC- 1034, height = 26.3 mm, width = 17.1 mm, whorls = 6; CPC-1035, height = 21.7 mm, width = 12.6 mm, whorls = 5; CPC-1036, height = 18.7 mm, width = 14.4 mm, whorls = 6 remaining; CPC-1037, height = 19.6 mm, width = 14.0 mm, whorls = 4 remaining.
Figure 3 List of continental gastropod species reported for the Cerro del Pueblo (Campanian), the Las Encinas (Paleocene), theAdjuntas and Carroza formations, Parras and La Popa basins, Difunta Group, Coahuila and Nuevo León, NE Mexico.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian. Wyoming, Bear River Formation, Eocene; Sulphur Creek, Utah, Upper Kanab.
Discussion. The specimens studied here have the characteristics seen inPyrgulifera humerosa(Meek, 1860) from the Cenomanian Bear River Formation, Wyoming. Yen (1958) reached the conclusion that the genus became extinct in the Maastrichtian.
Pyrguliferahas been found in limestone and calcareous shales, together with fresh water genera, However, there is evidence that it was in associations of alternating fresh to brackish water,nonetheless of low salinity (estuary) (Yen, 1958).PyrguliferaMeek, 1877is a fossil mollusk inhabiting brackish and freshwater environments, althoughBandel and Riedel (1994) suggested that the habitat for the genus was more of brackish water, with certain tolerance of fresh water. Its distribution was greatest during the Late Cretaceous and also during the late Cenomanian (Yen, 1958). Its distribution includes the Sulphur Creek, near Bear River, southwest Wyoming (Yen, 1958). In Europe, it has been found in southern France in lignite beds in the Rhone River basin. Yen (1958) consideredHantkenia munieriRepelin, 1902 from the upper Cenomanian Gardonian Formation of southeast France, a truePyrgulifera. Various species ofPyrguliferawere described from the coal beds of the Gosau Formation close to Brandenberg, Austria. In addition, in western Hungary other set of species was described from the coal seams of the Ajka Formation (Yen, 1958). Stilwell (1997) recordedPyrgulifera kahuitaraStilwell, 1997 from the Campanian? -Maastrichtian Kahuitara Tuff of Pitt Island, New Zealand. To Stilwell (1997),Pyrguliferadistribution includes Cenomanian to Danian fossiliferus beds of Europe, North America, Asia, India, New Caledonia, and Chatman Islands. However, differing from Yen (1958) who believed thatPyrgyliferawas a brackish and freshwater inhabitant, Stilwell (1997), at least forPyrgulifera kahuitara, considered it from a marine environment.
Family PachychilidaeFischer and Crosse, 1892
GenusMoniquiaPacaud and Harzhauser, 2012
Moniquia ypresiana(Vega and Perrilliat, 1992) new combination
Description. Shell medium-sized, turreted; protoconch unknown; teleoconch of four whorls, convex; sculpture of curved axials of moderate strength that extends from suture below almost to suture above; spiral sculpture of threads of subequal strength; aperture not preserved.
Material examined. Two specimens, CPC- 2145, height = 62.3 mm, width = 19.2 mm, whorls = 6; CPC-2146, height = 9.2 mm, width = 6.2 mm, whorls = 5.
Occurrence. La Leona, Ramos Arizpe, Coahuila, Las Encinas Formation, Paleocene.
Discussion.Pacaud and Harzhauser (2012) made a review of Cretaceous and Paleogene species of relatively similar genera, includingMelanatriaBowdich, 1822. Most of the morphological features used by these authors to erect the genusMoniquiaare found in the numerous specimens ofM. ypresiana, first reported from the Paleocene Adjuntas Formation of La Popa Basin, Difunta Group, Nuevo León (Vega and Perrilliat, 1992). Although an early Eocene age (Ypresian) age was originally interpreted for the Adjuntas Formation, more recent data suggest a middle Paleocene age for this lithostratigraphic unit (Lawton et al., 2009).
Figure 4 1 - 3,Pyrgulifera humerosa; 1a, 1,034, ad.; 1b, ap.; 2a, 1,035, ad.;2b, ap.; 3a, 1036, ad.; 3b, ap. 4 - 6,Goniobasis unilirataNaranjo- Garcíaand Aguillón, n. sp.; 4a, ho. 1042, ad.; 4b, ap.; 5a, pa. 1,043, ad.; 5b, ap.; 6a,pa. 1,044, ad.; 6b, ap. 7 - 9,Pleurocera giganticaNaranjo- García and Aguillón, n. sp.; 7a, ho. 1047, ad.; 7b, ap.; 7c, po.; 8a, pa. 1048, ad.; 8b, ap.; 8c, po.; 9a, pa. 1,049, ad.; 9b, ap.; 9c, po. 10, 11,Moniquia ypresiana;10a, 2145, ad.; 10b, ap.; 11a, 2146, ad.; 11b, ap. 12,Acirsa cf. A. gravida;12a, 2160, ad.; 12b, ap. 13 - 15,Melanoides (Melanoides) yolandae; 13a, 1,038, ad.; 13b, ap.; 14a, 1,039, ad.; 14b, ap.; 15a, 1,040, ad.; 15b, ap. 16,M. (M.) wollebeni; 16a, XXXX, ad.; 16b, ap. 17,Pachymelaniawyomingensis; 17a, 2147, ad.; 17b, ap. 1 - 6, 12 - 17, Coahuila, Cerro delPueblo Formation, Campanian; 7 - 11, Coahuila, Las Encinas Formation,Paleocene. Ad = adapertural, ap = apertural, ho = holotype, pa = paratype,po = posterior.
Specimens are abundant in green mudstone of delta plain facies in the Adjuntas and Las Encinas formations.
Family PleuroceridaeFischer, 1885
GenusGoniobasisLea, 1862
Goniobasis unilirataNaranjo-García and Aguillón, new species
Diagnosis. Medium sized elongate conic shell, 5 to 7 whorls; smooth surface, with carinate periphery, aperture elongated, bent columella.
Description. Medium sized shell, elongate conic, whorls flattened, well-marked suture, 5 to 7 whorls. Smooth surface, with carinate periphery over the body whorl, apex unknown, aperture elongated, bent columella to the outside with a lamella over it.
Material examined. Five specimens, holotype CPC-1042, height = 14.9 mm, width = 6.0 mm, whorls = 6; paratype CPC-1043, height = 13.5 mm, width = 5.9 mm, whorls = 5; paratype CPC- 1044, height = 10.6 mm, width = 4.8 mm, whorls unmeasurable; paratype CPC-1045, height = 9.9 mm, width = 5.2 mm, whorls = 5 remaining; paratype CPC-1046, height = 9.6 mm, width = 4.8 mm, whorls = 7.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. Goniobasis unilirata n. sp. resemblesG. macilentaWhite, 1895 of the Bear River Formation of Wyoming and Utah, in the flattened whorls and smooth surface (Grabau and Shimer, 1909). However,G. macilentahas no carina over the body whorl, being taller and more slender thanG. uniliratan. sp. The family Pleuroceridae has an ample distribution. It is found in North and South America, Africa, and Asia. However, the family has had its maximum development in North America (Burch, 1989).
Etymology. The name “unilirata” is given due to the presence of a ridge over the shoulder of the body whorl of the specimens.
GenusPleuroceraRafinesque, 1818
Pleurocera giganticaNaranjo-García and Aguillón, new species
Diagnosis. Shell conic elongated, imperforated, over 10 whorls; whorls with well-marked wave shaped growth lines, with basal cord over the suture; suture strongly indented; base of body whorl with three to six spiral cords; periphery of shell angular at body whorl; parietal callus ample, extending to columellar base.
Description. Shell conic elongated, imperforated, all the specimens lack the apex. The species has over 10 whorls. Sculpture: whorls remaining with well-marked wave shaped growth lines (retracted in the middle: »). Whorls have a basal cord over the suture. Suture strongly indented, whorls round and swollen below the cord of previous whorl. Base of body whorl with three to six spiral cords (three in juvenile specimens and six in mature ones). One cord at the edge of the whorl, the most voluminous (prominent), and the other immediately below (less developed), then 4 spiral incised lines after the cords. At body whorl the periphery of shell is angular. Parietal callus ample, which extends to columellar base; rest of aperture unknown.
Material examined. Twelve specimens, see Table 1.
Occurrence. La Leona, Ramos Arizpe, Coahuila, Las Encinas Formation, Paleocene.
Discussion. Pleurocera gigantica n. sp. ResemblesP. unciale hastatum(Anthony, 1854) of the Recent, from North and South Fork of the Holston River, Sullivan County Tennessee (Burch, 1988) in the general outline of the shell; its body whorl is also angular, with two cords at the base close to the uture. Also, the new species reached over 100 mm, whileP. unciale hastatumhas a height of 23.5 mm; other differences are thatP. gigantican. sp. has a deeper suture and the base of the bodywhorl has 4 spiral incised lines after the cords. It should be noted that the known Pleuroceridae of the Recent from the United States are small (about 22 mm; Burch, 1989), and in South America can reach 50 mm (Simone, 2006). The specimens examined here are three to five times taller.
Table 1 Measurements of Pleurocera gigantica Naranjo-García and Aguillón new species, from the Paleocene Las Encinas Formation, Parras Basin.
| Catalog number | Type | Height mm | Width mm | Whorls number |
|---|---|---|---|---|
| CPC-1,047 | Holotype | 74.5 | 43 | 7 |
| CPC-1,048 | Paratype | 80.6 | 45 | 7 |
| CPC-1,049 | Paratype | 74.7 | ̴ 39.9 (incomplete aperture) | 7 |
| CPC-1,050 | Paratype | 61.8 | 42.6 (incomplete aperture) | 5 |
| CPC-1,051 | Paratype | 71 | 50.8 | 4 |
| CPC-1,052 | Paratype | 67 | 38.9 | 8 |
| CPC-1,053 | Paratype | 66.3 | 38.6 | 8 |
| CPC-1,054 | Paratype | 80.8 | 43.2 | 8 |
| CPC-1,055 | Paratype | 61.5 | 43.5 | 5 |
| CPC-1,056 | Paratype | 95.2 | 47.3 | 5 |
| CPC-1,057 | Paratype | 84.7 | 51.9 | |
| CPC-1,058 | Paratype | 61.5 | Sectioned specimen in the middle | 4 |
The family Pleuroceridae is distributed in North and South America, Africa and Asia; nonetheless, its maximum diversity is seen in North America (Burch, 1989). It is of interest to note that Mesozoic and Paleogene records were very different to the faunas seen in later times (Pliocene),Taylor (1985) alludes to a remarkable situation, pointing out that among other freshwater molluscan families the Pleuroceridae was of a massive size. Such is the case of thePleurocera giganticadescribed herein. In the Recent,GoniobasisandPleurocerahave a large number ofNorth American species (Thiele, 1931-1935).
Etymology. It is named because of the unusual big size for aPleuroceraspecies.
Family ThiaridaeGill, 1871
GenusMelanoidesOliver, 1804
Melanoides (Melanoides) yolandaePerrilliat, Vega,
Espinosa and Naranjo-García, 2008
Description. Shell small, slender, turreted; protoconch unknown; teleoconch of eight whorls; whorls profile straight; suture impressed; the first three whorls with two beaded spirals, subsequent whorls with three beaded spirals, the anterior whorl less prominent; last whorl with eight spirals, only the upper three remain beaded, the others becoming nearly smooth; axial sculpture not preserved; aperture ovate.
Material examined. Three specimens, CPC- 1038, height = 10.3 mm, width = 2.2 mm, whorls = 6; CPC-1039, height = 9.8 mm, width = 2.3 mm, whorls = 5; CPC-1040, height = 10.7 mm, width = 2.4 mm, whorls = 6.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. More than 200 specimens of this species were reported byPerrilliat et al. (2008) from outcrops of the upper Campanian Cerro del Pueblo Formation near RincónColorado, 7 km NE of General Cepeda, Coahuila, being one of the most abundant continental species of the Difunta Group.
Melanoides (Melanoides) wollebeniPerrilliat, Vega,
Espinosa and Naranjo-García, 2008
Description. Shell small, narrowly conic or turriform; whorls flattened on the periphery, with two spiral cords that become three over the body whorl. The upper cord wider, the middle lessdeveloped and the third cord underdeveloped. Chain of spiral papillae over shoulder. Body whorl with 6 to 7 spiral ribs. Aperture with thick callus over columella. Apex and aperture not well preserved.
Material examined. Four specimens, CPC- 1038, height = 9.9 mm, width = 3.2 mm, whorls = 7; CPC-1039, height = 10.3 mm, width = 3.9 mm, whorls = 4; CPC-1040, height = 10.3 mm, width = 3.2 mm, 8 whorls; CPC-1041, height = 5.4 mm, width = 2.5 mm, whorls = 6.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. The specimens differ fromMelanoides (Melanoides) yolandaePerrilliat, Vega, Espinosa and Naranjo-García, 2008, being wider, with weaker tubercles on last whorl spirals.M. (M.) yolandaehas two chains of nodules over the entire shell, and the observed specimens ofM. (M.) wollebenihave only one chain of nodules over the shoulder. The Family Thiaridae is known from Africa, Asia and the Americas. Their closer relatives are the Planaxidae (Morrison, 1954). Thiarids use partenogenetic reproduction and inhabit fresh water (Burch, 1989). The familyThiaridae represents the tropical assemblage of the fauna (Taylor, 1985).Melanoidesis also found in Quaternary deposits in northeast Africa and Asia (Williamson, 1981;Leng, et al., 1999). In the Recent, is distributed in southeast Asia, India and South Africa (with 30 species) (De Kock and Wolmarans 2009). Morrison (1954) stated that all species of the genus are ovoviviparous and parthenogenetic. They live in lentic or lotic waters and might be intermediate host of human or animal parasites (Pointier, 1999). In addition, the speciesMelanoides tuberculata(Müller, 1774) had become an invasive species in new habitats where it is introduced (Gutiérrez-Amador et al., 1995). Nowadays, it is widely spread around the world (Abbott, 1973; Pointier et al., 1993; Contreras-Arquieta and Contreras-Balderas, 2000;Guimarães et al., 2001;Facon et al., 2003).M. tuberculatahas a rapid growth and it has numerous offspring. It withstands desiccation andlives in diverse habitats and has a life span of 2 years (Dudgeon, 1989).
GenusPachymelaniaSmith, 1893
Pachymelania wyomingensis(Meek, 1873)
Description. Shell medium-sized, moderately convex; teleoconch of seven whorls; suture linear; sculpture in last whorls with a prominent, strong spiral rib, outward projecting with tubercles;upper whorls with crenulated longitudinal ribs, crossed by five spiral lines.
Material examined. Eight specimens, see Table 2.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. This is by far the most abundant continental gastropod from the upper Campanian
Table 2 Measurements of Pachymelania womingensis (Meek, 1873), from the upper Campanian Cerro del Pueblo Formation, Parras Basin.
| Catalog number | Height mm | Width mm | Whorls number |
|---|---|---|---|
| CPC-2147 | 41.5 | 8.7 | 8 |
| CPC-2148 | 38.6 | 6.9 | 7 |
| CPC-2149 | 37.7 | 8.2 | 9 |
| CPC-2150 | 28.1 | 6.6 | 8 |
| CPC-2151 | 27.2 | 8.8 | 7 |
| CPC-2152 | 30.1 | 7.9 | 7 |
| CPC-2153 | 32.3 | 8.9 | 7 |
| CPC-2154 | 22.8 | 10.2 | 5 |
| CPC-2155 | 30.1 | 6.2 | 7 |
| CPC-2156 | 35.4 | 5.8 | 8 |
| CPC-2157 | 20.8 | 9.5 | 5 |
| CPC-2158 | 33.3 | 8.1 | 7 |
| CPC-2159 | 25.5 | 7.8 | 7 |
Figure 5 1 - 12,Pachymelania wyomingensis; 1a, 2148, ad.; 1b, ap.; 2a, 2149, ad.; 2b, ap.; 3a, 2150, ad.; 3b, ap.; 4a, 2151, ad.; 4b, ap.; 5a, 2152, ad.; 5b, ap.; 6a, 2153, ad.; 6b, ap.; 7a, 2154, ad.; 7b, ap.; 8, 2155, spi.; 9, 2156, spi.; 10, 2157, spi.; 11, 2158, ap.; 12a, 2159, ad.; 12b, ap. 13, Littorinidae; 13a, 2161, ad.; 13b, ap. 14, 15,Birgella burchiNaranjo-García and Aguillón, n. sp.; 14a, ho. 1032, ad.; 14b, ap.; 15a, pa. 1033, ad.;15b, ap. 16, 17,Cylichnasp.; 16a, 2162, ad.; 16b, ap.; 16c, an.; 17a, 2163,ad.; 17b, ap.; 17c, an. 18,Physasp.; 18a, 1059, ad.; 18b, ap. Coahuila,Cerro del Pueblo Formation, Campanian. Ad = adapertural, an = anterior, ap= apertural, ho = holotype, pa = paratype, spi = spire.
Cerro del Pueblo Formation. Some specimens have attached serpulid worms and ostreoids, suggesting an estuarine habitat. This species was also reported from the Maastrichtian Laramie Formation of Colorado (Hartman, 1998) and Wyoming (Taylor, 1975).
Superfamily Epitonioidea Berry, 1910
Family Epitoniidae Berry, 1910
GenusAcirsaMørch, 1857
Acirsacf.A. gravidaSohl, 1964
Description. Shell medium-sized, moderately convex; teleoconch of five whorls; suture linear; sculpture in last whorls with a prominent, strong spiral rib, outward projecting with tubercles;upper whorls with crenulated longitudinal ribs, crossed by five spiral lines.
Material examined. One specimen, CPC-2160, height = 23.2 mm, width = 8.4 mm, whorls = 5.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. This species was reported from the Maastrichtian Coffee Sand of Mississippi (Sohl, 1964).
Superfamily LittorinoideaChildren, 1834
Family LittorinidaeChildren, 1834
Genus indeterminate
Description. Small trochiform shell, protoconch not preserved, spire with three whorls; narrow umbilicus; aperture wide, subovate.
Material examined. One specimen, CPC-2161, height = 15.1 mm, width = 18.6 mm, whorls = 3.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. The single specimen is poorly preserved and a more detailed identification is not possible.
Superfamily RissooideaGray, 1847
Family HydrobiidaeStimpson, 1865
GenusBirgellaBaker, 1926
Birgella burchiNaranjo-García and Aguillón, new
Species
Diagnosis. Shell small, globose; growth lines marked; small umbilicus with lip of columella bent over; aperture roundly-lunate.
Description. Shell globose, small, round whorls, slightly indented suture. Growth lines marked, more so, near to suture. Apex unknown, lip of columella bent over the small umbilicus.Aperture roundly lunate. Height of aperture about two- thirds the height of shell.
Material examined. Two specimens, holotype CPC-1032, height = 8.5 mm, width = 8.5 mm, whorls = 6; paratype CPC-1033, height = 7.4 mm, width = 7.4 mm whorls = 5.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. Birgella burchi n. sp. is closer toB. subglobosa(Say, 1825), a Recent species from the Great Lakes, United States. The species differ in the size, withB. burchin. sp. being taller. InB. subglobosa theaperture is round and less than two-thirds the height of shell. It possesses fewer whorls (4), the suture is more deeply marked and the whorl of the spire has a shoulder.B. subglobosahas also an umbilicus with a straight lip of the columella. InB. burchin. sp., the spire is shorter and the aperture taller. The width and height of the shell are equal, whileB. subglobosais taller than wide. The Family Hydrobiidae is widely distributed and common around the world in temperate, subtropical, and tropical regions. The vast majority of species inhabitfreshwater bodies, although few inhabit brackish water (Burch, 1989). Recent molecular-based studies (Wilke et al., 2013) strongly support the monophyly of the family Hydrobiidae, which is part of the big and taxonomically problematic superfamily Rissooidea. For the moment, Wilke et al. (2013) remarked that more in-depth studies are needed to identify its sister group relationships. The Hydrobiidae is distributed in western Palearctic, eastern Nearctic, northern Neotropic and in South Africa (Wilke et al., 2013).
Etymology. The species is named after Dr. John B. Burch, who had greatly contributed to the knowledge of freshwater mollusks of North America.
Order CephalaspideaFischer, 1883
Superfamily Cylichnoidea Adams and Adams, 1854
Family CylichnidaeAdams and Adams, 1854
GenusCylichnaLovén, 1847
Cylichnasp.
Description. Shell small, slender, rounded at inferior extremity, subtruncated above. Shell smooth. Aperture long. Columella twisted and bears weak fold.
Material examined. Two specimens, CPC- 2162, height = 6.5 mm, width = 2.9 mm; hypotype CPC-2163, height = 7.2 mm, width = 2.9 mm.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion.Perrilliat et al. (2000) reportedCylichna secalinaShumard, 1861 from the late Maastrichtian Mexcala Formation of Guerrero, Southern Mexico. The species was originally reported from the Upper Cretaceous Nacatoch Sand of Texas and the Ripley Formation of Mississippi. The poor preservation of the specimens here reported prevents a specific determination.
Order BasommatophoraSchmidt, 1855
Superfamily PlanorboideaRafinesque, 1815
Family PhysidaeFitzinger, 1833
Description. Shell small, elongate; protoconch unknown; teleoconch of five whorls, flat; suture chanelled; surface smooth; aperture not preserved. Material examined. Two specimens, CPC-2164, height = 8.1 mm, width = 2.6 mm, whorls = 4; CPC-2165, height = 10.1 mm, width = 5.4 mm, whorls = 4.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. The specimens resembleBulinussp. 4, reported byPerrilliat et al. (2008), p. 264, fig. 5.16, 5.17) from the upper Campanian Cerro del Pueblo Formation at General Cepeda,Coahuila.
GenusPhysaDraparnaud, 1801
Physasp.
Figure 5.18
Description. Shell sinistral, oval, of medium size, with marked growth lines over the body whorl (just in one specimen), whorls slightly swollen, suture slightly indented, shiny shell surface, apex and aperture of shell not present.
Material examined. Ten specimens, see Table 3.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. Physa sp. resembles some forms ofP. acutaDraparnaud, 1805, in particular that from Connecticut, Litchfield County, Salisbury, north shore of Lake Wononscopomuc (Taylor, 2003). However, our specimens ofPhysasp. reach higher sizes andP. acutafrom Lake Wononscopomuc is 13.5 to 12.2 mm in height. InPhysasp. the aperture of the shell inserts in the body whorl at about half the height of the shell, while inP. acutafrom Lake Wononscopomuc the aperture inserts in the first third of the body whorl.
GenusMesolanistesYen, 1945
Mesolanistessp.
Table 3 Measurements of Physa sp., from the upper Campanian Cerro del Pueblo Formation, Parras Basin.
| Catalogue number | Type | Height mm | Width mm | Whorls number |
|---|---|---|---|---|
| CPC-1,059 | Hypotype | 19.2 | 10.5 compressed specimen | 5 |
| CPC-1,060 | Hypotype | 15.8 | 7.5 compressed specimen and cast | 3 1/2 |
| CPC-1,061 | Hypotype | 15.5 | 8.0 cast | 4 1/2 |
| CPC-1,062 | Hypotype | 15 | 9.1 cast | 3 ½ |
| CPC-1,063 | Hypotype | 14.9 | 8.5 | 5 1/2 |
| CPC-1,064 | Hypotype | 14.7 | 8.7 cast | 2 1/2 |
| CPC-1,065 | Hypotype | 13.5 | 6.1 compressed specimen | 5 1/2 |
| CPC-1,066 | Hypotype | 10.1 | 4.9 compressed specimen and collapsed over itself | 5 |
| CPC-1,067 | Hypotype | 9 | 4.9 collapsed over itself | 5 |
| CPC-1,068 | Hypotype | 8.9 | 4.8 | 4 |
Figure 6 1, 2,Haitia tayloriNaranjo-García and Aguillón, n. sp.; 1, pa.1070, ad.; 2a, ho. 1069, ad.; 2b, ap. 3 - 5,Mesolanistessp.; 3, 2166, ad.; 4a, 2167, ad.; 4b, ap.; 5a, 2168, ad.; 5b, ap. 6 - 9,Holospira thompsoniNaranjo-García and Aguillón, n. sp.; 6a, ho. 1,071, ad.; 6b, ap.; 8a, pa.1,072, ad.; 8b, ap.; 9a, pa. 1,073, ad.; 9b, ap. 10, 11,Holospirasp.; 10a,1,074, ad.; 10b, ap.; 11a, 1,075, ad.; 11b, ap. 12, 13, Helicidae; 12, 2169, an.; 13a, 2170, an.; 13b, po. 14, 15, Zonitidae; 14a, 2171, an.; 14b, po.; 15a, 2172, an.; 15b, po. 16, 17, Physidae; 16a, 2164, ad.; 16b, ap.; 17a,2165, ad.; 17b, ap. Coahuila, Cerro del Pueblo Formation, Campanian. Ad= adapertural, an = anterior, ap = apertural, ho = holotype, pa = paratype, po = posterior.
Description. Shell small to medium-sized, ovate; commonly with moderately elevated spire of three whorls but depressed in some specimens; suture incised; last whorl enlarging rapidly; aperture ovate; sculpture of fine axial ribs.
Material examined. Three specimens, CPC- 2166, height = 28.1 mm, width = 26.6 mm, whorls = 3; CPC-2167, height = 30.2 mm, width = 25.6 mm, whorls = 3; CPC-2168, height = 42.5 mm, width = 33.6 mm, whorls = 3.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion.Perrilliat et al. (2008)described two species ofMesolanistesfrom the upper Campanian Cerro del Pueblo Formation, in outcrops found near Rincón Colorado, Coahuila. The specimens here reported cannot be assigned to any of those species, due to the poor preservation of the hematized remains.
GenusHaitiaClench and Aguayo, 1932
Haitia tayloriNaranjo-García and Aguillón, new
Species
Diagnosis. Shell broadly conic, small, sinistral; growth lines marked; height of aperture half the height of shell.
Description. Small, sinistral shell; broadly conic; whorls somewhat round ; suture slightly indented, growth lines marked. Apex not preserved. Height of aperture about half the height of shell, aperture not preserved.
Material examined. Two specimens, holotype CPC-1069, height = 7.62 mm, width = 4.15 mm, whorls = 6 ½; paratype CPC-1070, height = 6.96 mm, width = 3.55 mm, whorls = 6.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. Haitia taylori n. sp. resemblesH. pomilia(Conrad, 1834) of Alabama, Randons Creek, near Clairborne, Monroe County of the Recent (Taylor, 2003). These species are alike in the general shape of the shell. The height of the aperture reaches over half the lenght of the shell but both species differ in size;H. pomiliais over two times the size ofH. taylori, which is less globose thanH. pomilia. The Physidae are found from the northern temperate to the Arctic, as well as throughout the Americas. These freshwater mollusks live in small tolarge water bodies (ditches, ponds, lakes, brooks and rivers). The genusPhysais distributed from Eurasia, in the temperate and Arctic zone, and in North America (Taylor, 2003). Todaysome species ofPhysabecame invasive in places where they have been introduced, for examplePhysa acutaDraparnaud, 1805is found in Europe, Africa, some places in Asia, Australia, and South Africa (Pointier and Marquet, 1990; Appleton, 2003; Guo et al., 2009;Zukowski and Walker 2009;Van Leeuwen et al., 2013). In addition, the genusHaitiais part of the fauna of the temperate and tropical areas of North America, the Antilles, Colombia, and the western side of South America, from Peru to middle Chile (Taylor, 2003). Physids can be found in alltypes of freshwater habitats (Burch, 1989).
Etymology. Named after the late Dr. Dwight W. Taylor, who dedicated much of his life to the study of the family Physidae.
Order Stylommatophora Schmidt, 1855
Superfamily UrocoptoideaUit de Weerd, 2008
Family HolospiridaePilsbry, 1946
Holospiravon Martens in Albers, 1860
Holospira thompsoniNaranjo-García and Aguillón,
new species
Diagnosis. Shell subcylindrical, small, 7 to 8 whorls; suture nearly linear, surface smooth.
Description. Shell small, subcylindrical, obtuse apex, 7 to 8 whorls, compactly coiled firsts three whorls, the other four or five more loosely coiled; suture nearly linear. Surface smooth. Aperture unknown.
Material examined. Three specimens, holotype CPC-1071, height = 12.3 mm, width = 6.4 mm, whorls = 7; (two compressed specimens) paratype CPC-1072, height = 14.4 mm, whorls = 8 remaining; paratype CPC-1073, height = 13.1 mm, whorls = 7.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. Holospira thompsoni n. sp. differs fromHolospira sp. from Temalac, Guerrero, Lower Maastrichian, Mexcala Formation (Perrilliat et al., 2000) in the general shape of the shell which inHolospirasp. is subcylindrical with the obtuse apex, and has compactly coiled whorls, while inH. thompsonin. sp. whorls grow slower and are ample. They also differ in size, being 9.5 to 12.1 mm inHolospirasp. while inH. thompsoniits height is 12.3 to 14.4 mm. Holospiridae are terrestrial pulmonate gastropods that inhabit submesic and xeric environments, from southern United States (south Texas, New Mexico and Arizona) to the north of Oaxaca (mid Mexico). They require limestone or dolomite terrains and their distribution is in narrow areas (Thompson and Mihalcik, 2005).
Etymology. Holospira thompsoni n. sp. is named after the late Fred G. Thompson of the University of Florida, because of his enormous contributions to the knowledge of the Central American non-marine mollusks of the area.
Holospirasp.
Description. Shell of medium size, ovate-conic, apex absent, 5 whorls remaining, it has very narrow whorls near the apex, increasing relatively faster in width toward the aperture. Whorls flattened, suture slightly indented. Surface smooth, aperture not preserved.
Material examined. Two specimens, CPC- 1074, height = 8.1 mm, width = 6.7 mm, whorls = 5; CPC-1075, height = 8.5 mm, width = 6.1 mm, whorls = 5.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. Holospira sp. differs from other Recent species in the shape of the first whorls, including H. mesolia from Sanderson, Terrell County, Texas, United States (Pilsbry, 1946) and H. pasonisDall, 1895 of Mule canyon, El Paso County, Texas, United States (Pilsbry, 1946). However, it is not possible to assign thisHolospirato any other known species or subgenera of thegenusHolospira, which differ in the inside of the columella and in the presence or absence of lamellae (Thompson, 2011). Additionally, specimens are incomplete or they could be of juvenileage, and measure 8.1 and 8.5 mm and have 5 whorls.H. mesoliahas a height that goes from 20 to 23.5 mm and has 12– to 14 whorls,H. pasonishas a height of 22.3 to 24.7 mm and has 11 to 11 ½ whorls.
For Recent specimens of the genusHolospirathe geographical distribution ranges from Texas, Arizona, New Mexico (Pilsbry, 1946) to most of Mexico (except The Peninsula of Baja California, Chiapas, Tabasco, Campeche and Yucatán) The genusHolospiragets to Oaxaca at about 29 degrees of latitude (Bequaert and Miller, 1973). Fossil specimens of the family Holospiridae date back to the New Mexico Paleocene (Cockerell, 1914), Lower Maastrichtian (Mexcala Formation), Temalac, Guerrero, Mexico (Perrilliat et al., 2000), and the Tertiarydeposits of Wyoming (Henderson, 1935). In the Recent the Family Holospiridae is distributed from the states of Arizona, New Mexico, and Texas to central Mexico, these terrestrial snails today live and are abundant in dry climates where there are limestone and dolomite beds (Thompson and Mihalcik, 2005). The genusHolospirais known to inhabit the Recent from western Arizona, New Mexico and Texas in the United States to northern Oaxaca, Mexico (Thompson, 2011).Holospiraspp. are usually found in limestone outcrops, where colonies have several individuals (Bequaert and Miller, 1973).
Superfamily HelicoideaRafinesque, 1815
Family HelicidaeRafinesque 1815
Description. Small, discoidal and compressed shell; umbilicus narrow; aperture not preserved.
Material examined. Two specimens, CPC- 2169, height = 4.8 mm, width = 16.2 mm, whorls = 5; CPC-2170, height = 4.5 mm, width = 14.4 mm, whorls = 5.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. The hematized specimens represent the first record of helicid snails for the upper Campanian Cerro del Pueblo Formation.
Superfamily ZonitoideaMørch, 1864
Family ZonitidaeMørch, 1864
Figures 6.14, 6.15
Description. Shell small, smooth, trochoid; umbilicus narrow.
Material examined. Two specimens, CPC- 2171, height = 4.1 mm, width = 5.4 mm, whorls = 5; CPC-2172, height = 3.9 mm, width = 5.1 mm, whorls = 5.
Occurrence. Las Águilas/Porvenir de Jalpa, General Cepeda, Coahuila, Cerro del Pueblo Formation, upper Campanian.
Discussion. The specimens are very small and their preservation prevents offering a more precise identification.
4. Conclusions
The great diversity and abundance of continental mollusks found in the upper Campanian Cerro del Pueblo Formation is related to the paralic environments whose outcrops are found in a broad area. Their distribution includes several localities found west of Saltillo to north of the Parras Basin, near the border with the La Popa Basin. The lithology of these areas wascontrolled by mainly salt tectonics that formed small sub-basins, where brackish and freshwater environments prevailed during Paleocene times. Although the preservation of the shell of many species of continental gastropods from the Difunta Group can be acceptable, the main problem relies on that modern systematics of continental gastropods is based mainly on soft body morphology and more recently, molecular biology. This report is presented in the hope that it can be useful as foundation for future work on paleoecology and evolution of the continental mollusk communities during the Late Cretaceous and Paleogene.
