J. Paleont., 81(3), 2007, pp. 483–489 Copyright ᭧ 2007, The Paleontological Society 0022-3360/07/0081-483$03.00
NEW PALEOCENE RHYNCHONELLIDE BRACHIOPODS FROM THE POTRERILLOS FORMATION, NORTHEAST MEXICO
SUSAN L. KLOSTERMAN,1 MICHAEL R. SANDY,1 FRANCISCO J. VEGA,2 KATHERINE A. GILES,3 KYLE GRAF,3 DAVID SHELLEY,3 AND JESU´ S SOLE´ 2 1Department of Geology, University of Dayton, Dayton, Ohio 45469-2364, Ͻ[email protected]Ͼ, Ͻ[email protected]Ͼ, 2Instituto de Geologı´a, UNAM, Ciudad Universitaria, Me´xico, D. F. 04510, Ͻ[email protected]Ͼ, Ͻ[email protected]Ͼ, and 3Institute of Tectonic Studies, New Mexico State University, Las Cruces 88003, Ͻ[email protected]Ͼ
ABSTRACT—Two new species of the rhynchonellid brachiopod Probolarina are described, Probolarina neoleonensis new species and Probolarina papalotensis new species. They were collected from a Paleocene limestone lens associated with a diapir in the La Popa basin, northeastern Mexico. Thousands of these brachiopods occur in this lens and constitute the first report of brachiopods for the Difunta Group, from which a diverse paleobiota has been previously reported. This occurrence represents the oldest record for the genus in the Western Hemisphere, as the only other Paleocene occurence of this genus was reported from New Zealand. Recent studies suggest that the carbonate lentil from which the brachiopods were collected were deposited in the shadow-effect area adjacent to the diapir, which affected the sediment influx into the basin.
INTRODUCTION (Fig. 3). The locality has been registered in the Museo de Pa- ALEONTOLOGIC STUDIES from the Difunta Group in northeast- leontologı´a, Instituto de Geologı´a, National Autonomous Univer- P ern Mexico have yielded an important number of contribu- sity of Mexico (UNAM), as locality IGM 3303. Lens number 1 tions on some of the groups that lived in shallow marine and is included in the Lower Mudstone Member. It includes red algae paralic environments during Campanian through Eocene times. and Maastrichtian foraminifera (Hunnicutt, 1998). An unconfor- Several papers have been published on Campanian and Maastrich- mity between the Cretaceous and Tertiary has been documented tian invertebrates, vertebrates, coprolites and plants (Bo¨se, 1913; (Vega et al., 1989; Giles et al., 1999; Lawton et al., 2002). A Imlay, 1937; Murray and Wolleben, 1960; Wolleben, 1977; Vega conglomerate discordantly overlies the uppermost Maastrichtian and Perrilliat, 1989a, 1990; Vega and Feldmann, 1991; Herna´n- Delgado Sandstone Member, on top of the Middle Siltstone Mem- dez, 1992; Herna´ndez and Kirkland, 1993; Rodrı´guez de la Rosa ber. This conglomerate includes reworked ammonoids and Paleo- and Cevallos-Ferriz, 1994, 1995; 1998; Vega et al., 1994; Kirk- cene nautiloids (Lawton et al., 2002). land and Aguillo´n-Martı´nez, 1995; Vega et al., 1995; Rodrı´guez Previous paleontological reports from black shales of the Upper de la Rosa, 1996; Rodrı´guez de la Rosa et al., 1998). Lower Mudstone Member of the Potrerillos Formation include the nau- Tertiary beds of the Difunta Group are also fossiliferous (Murray tiloid Cimomia haltomi (Aldrich, 1931), an index fossil for the and Wolleben, 1959; Echanove, 1967; Vega and Perrilliat, 1989b, Paleocene in the Parras and La Popa basins. In both basins, this 1989c, 1992, 1995; Perrilliat and Vega, 1993; Vega et al., 1999). nautiloid and other invertebrates are found in concretions. The Despite this abundance and diversity of fossil groups, no bra- gastropod Elimia cf. E. trigemmata (Conrad, 1860) and the bi- chiopods have previously been reported from the Difunta Group. valve Venericardia (Baluchicardia) francescae (Gardner and This paper documents two new species of brachiopods and the Bowles, 1939) were also found in this same member (Vega and very peculiar paleoenvironmental setting in which they lived by Perrilliat, 1995). the hundreds of thousands. Lenses 2–6 are included in the Upper Mudstone Member (Fig. 2). They include abundant mollusk and echinoid fragments, and represent shallow-marine, subtidal environments adjacent to the STRATIGRAPHY AND PALEOENVIRONMENT diapir (Lawton et al., 2002). The brachiopods are found in lens The Difunta Group occurs in northeast Mexico (Fig. 1) and 6, included in the Upper Mudstone Member. The lens lies in direct was subdivided between two sedimentary basins, known as Parras contact with the gypsum diapir at its base, with a mean thickness and La Popa (McBride et al., 1974). Most of the paleoenviron- of approximately 10 m. Echanove (1967) reported on benthic fo- ments for the eight Maastrichtian Formations of the Parras basin raminifera, suggesting an Eocene age for this lens. Brachiopods were interpreted as nearshore, deltaic plain, and fluviatile (Mc- are distributed uniformly along the lens. In thin section, benthic Bride et al., 1975). The depositional history in the La Popa basin foraminifera, corals, small gastropods, and bryozoans were also was different. Here, Maastrichtian and Paleocene units are pre- observed. The limestone is very pure, and may represent calcium dominantly marine, whereas Eocene Formations are mostly inter- carbonate precipitation in a shadow effect area of the diapir. tidal and fluviatile. Basin topography and deposition were influ- The precise stratigraphic age for lens 6 is still unknown. We enced by local salt tectonics. Three diapirs and one weld have made 87Sr/86Sr measurements of the well preserved calcitic shells been recognized, with limestone lenses associated with the evo- of several specimens of the more abundant P. neoleonensis n. sp., lution of these structures (McBride et al., 1974; Laudon, 1984; as there is no discrete distribution of both species throughout the 1996; Giles and Lawton, 1999; Lawton et al., 2002). The diapirs lens. The measurement of this ratio can be compared directly to were active during the Late Cretaceous and Early Tertiary. Car- the seawater 87Sr/86Sr curve for an age derivation. The table of bonate lenses formed on top of the topographic rise of the diapirs Howarth and McArthur (1997) was used. The sample was ex- during episodes of low sediment input to the basin and are in- tracted from the brachiopods by handpicking it with a pin. It was cluded in the Maastrichtian Lower Mudstone Member and the then pulverized with an agate mortar, acid-digested, catonic resin Paleocene Upper Mudstone Member, both from the Potrerillos separated, and measured for Sr isotopic composition at the Iso- Formation (Fig. 2). topic Geochemestry Laboratory (LUGIS) of the National Auton- The specimens reported here were collected from lens number omous University of Mexico. The 87Sr/86Sr measurement was 6 of the El Papalote Diapir, located in the Can˜on de Potrerillos done with a Finnigan 252 in static mode, giving a value of 483 484 JOURNAL OF PALEONTOLOGY, V. 81, NO. 3, 2007
FIGURE 1—Location map of the La Popa basin in northeastern Mexico.
0.707776 ϩ/Ϫ 0.000038. Using the above cited table, this value can correspond either to the Late Cretaceous, late Paleocene, or Middle Eocene. However, the first and last ages are not consistent with local stratigraphy, and therefore, the late Paleocene age (57.4 FIGURE 2—Composite stratigraphic section from La Popa basin, includ- Ma) coincides well with the suggested age derived from previous ing position of carbonate lentils adjacent to El Papalote and Gordo biostratigraphic studies (Vega et al., 1989; Vega and Perrilliat, diapirs. No vertical scale. 1995). TECHNIQUES Discussion.⎯Tertiary rhynchonellid brachiopods are rarely Transverse serial sections have been taken to investigate the found in North America and the genus Probolarina is represented internal structures of Probolarina neoleonensis new species and by a small number of specimens. The genus was first described P. papalotensis new species. A full description of the technique by Cooper in 1959, with the redescription of species P. salpinx and equipment used in the preparation of serial sections was given and P. holmesii. Three additional species, P. brevirostris, P. hol- by Sandy (1989), where additional references can be found. Serial mesii santeenis, and P. transversa were described by Cooper in sections are drawn with the dorsal valve oriented uppermost. 1988. All of these species date from the Eocene and were located in the Castle Hayne and Santee Formations of North and South SYSTEMATIC PALEONTOLOGY Carolina (Cooper, 1959, 1988). Harper (1993) described a single, Phylum BRACHIOPODA Dume´ril, 1806 poorly preserved individual from the Eocene in the Swanswick Subphylum RHYNCHONELLIFORMEA Williams, Carlson, Brunton, Formation of Jamaica and tentatively assigned it to the genus Holmer, and Popov, 1996 Probolarina. Wiedman et. al. (1988) collected a specimen from Class RHYNCHONELLATA Williams, Carlson, Brunton, Holmer the Eocene in the La Mesta Formation from Seymour Island, Ant- and Popov, 1996 arctica which bore resemblance to Probolarina but could not ver- Order RHYNCHONELLIDA Kuhn, 1949 ify this assignment due to the the poor preservation of the spec- Superfamily PUGNACOIDEA Rzhonsnitskaia, 1956 imens. The only other possible Paleocene occurrence of Family BASILIOLIDAE Cooper, 1959 Probolarina which has been described is P. chathamensis (Lee, Subfamily BASILIOLINAE Cooper, 1959 1980) from the Chatham Islands (Late Paleocene to Early Eocene) Genus PROBOLARINA Cooper, 1959 near New Zealand. In contrast to the sparse number of specimens Type species.⎯Rhynchonella holmesii Dall, 1903, p. 1536, pl. of Probolarina located in the eastern coast of the Carolinas, P. 58, figs. 10, 12. chathamensis was found in much greater abundance. KLOSTERMAN ET AL.—NEW PALEOCENE BRACHIOPODS FROM MEXICO 485
FIGURE 3—Location map of fossil locality at lens 6, northeast of El Papalote diapir.
PROBOLARINA NEOLEONENSIS new species Figures 4–6 Diagnosis.⎯Roundly triangular with narrow costae beginning near umbo; dorsal valve interior with narrow sockets and nearly erect socket ridges; ventral valve interior with strong, vertical den- tal plates; subfalciform crura. Description.⎯Medium size, subpentagonal to triangular out- line, length slightly greater than width, both greater than thick- ness, maximum width at midvalve to two-thirds from posterior; dorsibiconvex profile; beak moderately long, nearly straight to slightly incurved; small, oval foramen, submesothyrid, auriculate margins, visible conjunct deltidial plates; apical angle varies from acute to obtuse; lateral commissure straight, anterior commissure uniplicate; 8–12 narrow costae beginning near umbo; dorsal valve strongly convex, low fold extending to anterior from midlength and merging into the lateral slopes without disrupting outline in frontal view; ventral valve in lateral profile evenly and slightly convex, shallow sulcus in anterior portion of valve. Dorsal valve interior with narrow sockets and nearly erect sock- et ridges, no median septum, crural bases attached to socket ridges by flat outer hinge plates, subfalciform crura long, crescentic, con- cave outward, reaching to one-quarter of length of valve; ventral valve interior with strong, subparallel, vertical dental plates sep- arated from side wall by narrow umbonal chambers, small teeth. Etymology.⎯Nuevo Leo´n, Mexico, where this fossil was col- lected. Types.⎯Holotype IGM 7979; paratypes IGM 7980 to IGM 7986, deposited in the Museo de Paleontologı´a, Instituto de Geo- logı´a, UNAM. Occurrence.⎯Locality IGM 3303. Limestone lens 6, Upper Mudstone Member, Potrerillos Formation, Paleocene, northeast edge of El Papalote Diapir, Nuevo Leo´n, Me´xico. Discussion.⎯Probolarina neoleonensis differs from other de- scribed species of Probolarina due to the more prominent, narrow
→
FIGURE 4—Plots of length versus thickness (1), length versus width (2), and width versus thickness (3) for specimens of Probolarina neoleo- nensis n. sp. (triangles) and Probolarina papalotensis n. sp. (circles). Trendline calculated using the ‘‘least squares’’ method. Dimensions in mm. 486 JOURNAL OF PALEONTOLOGY, V. 81, NO. 3, 2007
FIGURE 5—Probolarina neoleonensis n. sp. Collected in lens 6, Paleocene El Papalote diapir, La Popa basin, Mexico. 1–4, Holotype IGM 7979, dorsal,ventral, lateral, and anterior views; 5–8, paratype IGM 7981, dorsal, ventral, lateral, and anterior views; 9–12, paratype IGM 7982, dorsal, ventral, lateral, and anterior views; 13–16, paratype IGM 7983, dorsal, ventral, lateral, and anterior views. 17–20, paratype IGM 7984, dorsal, ventral, lateral, and anterior views; 21–24, paratype IGM 7985, dorsal, ventral, lateral, and anterior views; 25–28, paratype IGM 7986, dorsal, ventral, lateral, and anterior views. All ϫ2. KLOSTERMAN ET AL.—NEW PALEOCENE BRACHIOPODS FROM MEXICO 487
←
FIGURE 6—Transverse serial sections through a specimen of Probolarina neoleonensis n. sp. Features observed include: development of dental plates (0.4 mm); beginning of socket ridge (1.0 mm); teeth and sockets begin to form (1.3 mm); teeth and sockets fully visible, hinge plates are nearly flat and horizontal, dental plates are short in proportion to height of pedicle valve, socket ridges are narrow, teeth are correspond- ingly small (1.4 mm); teeth and dental plates are diminishing, crural bases are attached to socket ridges by flat outer hinge plate (2.0 mm); crura are free and form a concave outline facing the dorsal valve (2.1 mm); crura traced to 3.6 mm. Initial section at 0.0 mm is at tip of ventral valve umbo. Cumulative distance from initial section given in mm. Paratype IGM 7980. Collected in lentil 6, Paleocene El Papalote diapir, La Popa basin, Mexico. Dimensions of specimen: length 14.4 mm; width 15.7 mm; thickness 10.2 mm.
FIGURE 7—Probolarina papalotensis n. sp. Collected in lens 6, Paleocene El Papalote diapir, La Popa basin, Mexico. 1–4, Holotype IGM 7987, dorsal, ventral, lateral, and anterior views; 5–8, paratype IGM 7988, dorsal, ventral, lateral, and anterior views; 9–12, paratype IGM 7990, dorsal, ventral, lateral, and anterior views; 13–16, paratype IGM 7991, dorsal, ventral, lateral, and anterior views; 17–20, paratype IGM 7992, dorsal, ventral, lateral, and anterior views. All ϫ2. 488 JOURNAL OF PALEONTOLOGY, V. 81, NO. 3, 2007
Etymology.⎯El Papalote Diapir, locality where this fossil was collected. Types.⎯Holotype IGM 7987; Paratypes IGM 7988 to IGM 7992, deposited in the Museo de Paleontologı´a, Instituto de Geo- logı´a, UNAM. Occurrence.⎯Locality IGM 3303. Limestone lens 6, Upper Mudstone Member, Potrerillos Formation, Paleocene, northeast edge of El Papalote Diapir, Nuevo Leo´n, Me´xico. Discussion.⎯Probolarina papalotensis has the broad, low cos- tae which appear to be more similar to other described species of Probolarina. The overall size of P. papalotensis is larger than the FIGURE 8—Transverse serial sections through a specimen of Probolarina papalotensis n. sp. Features observed include: pedicle collar (0.4 mm); species identified by Cooper but appears within the size range of development of dental plates (1.0 mm); beginning of socket ridge, nar- P. chathamensis. However, P. papalotensis has more costae and row umbonal chambers are present (1.8 mm); teeth and sockets are P. chathamensis has receding rather than vertical dental plates fully visible, hinge plates are flat, nearly horizontal, dental plates are (Lee, 1980). short in comparison to height of pedicle valve, narrow socket ridges, small teeth (2.3 mm); teeth and sockets are diminishing (3.0 mm); crura ACKNOWLEDGMENTS are free and form a concave outline facing the dorsal valve (3.6 mm); We are grateful to Drs. E. F. Owen and M. Mancen˜ido for crura traced to 3.9 mm. Initial section at 0.0 mm is at tip of ventral 87 86 valve umbo. Cumulative distance from initialsection given in mm. reviews that improved the paper. Sr/ Sr isotopic determinations Paratype IGM 7989. Collected in lens 6, Paleocene El Papalote diapir, were made at the Laboratorio Universitario de Geoquimica Iso- La Popa basin, Me´xico. Dimensions of specimen: length 12.0 mm; topica (LUGIS) of UNAM. Special thanks to G. Solis and J. J. width 11.0 mm; thickness 8.3 mm. Morales, whose help was valuable during the laboratory process. A. Altamira, Instituto de Geologia, UNAM, helped with the im- ages. MRS acknowledges the donors of The American Chemical costae which begin at the umbo. It is also thicker than other spe- Society Petroleum Research Fund for support. cies, with a thickness to length ratio of 0.72. In contrast, P. pa- palotensis has a thickness to length ratio of 0.61, and P. chathe- REFERENCES mensis has a ratio of approximately 0.66 (Lee, 1980). The internal ALDRICH, T. H. 1931. Description of a few Alabama Eocene species and features appear to be very similar to other described species of remarks on varieties. Alabama Geological Survey, Museum Paper, 12: Probolarina. No pedicle collar was observed but the beak of the 1–21. sectioned specimen (Fig. 6) appears to have been damaged. BO¨ SE, E. 1913. Algunas faunas del Creta´cico Superior de Coahuila y Several members of the subfamily Pamirorhynchiinae, includ- regiones limı´trofes. Boletı´n del Instituto de Geologı´a, Me´xico, 30, 56 ing Orbirhynchia, Parthirhynchia, and Riorhynchia, are similar p. to P. papalotensis in terms of their more fully costate shells. Yet, CONRAD, T. A. 1860. Descriptions of new species of Cretaceous and Eocene fossils of Mississippi and Alabama. Journal of the Academy the genera in this subfamily do not have the prominent, elongated of Natural Sciences of Philadelphia, Second Series 4:275–297. beak associated with Probolarina. Parthirhynchia has an elon- COOPER, G. A. 1959. Genera of Tertiary and Recent Rhynchonelloid bra- gated-oval shape, atypical to the subfamily Pamirorhynchiinae chiopods. Smithsonian Miscellaneous Collections, 139, no. 5, 90 p. (and Probolarina). Its subfamily assignment is due to its similar- COOPER, G. A. 1988. Some Tertiary brachiopods of the East Coast of the ity to Orbirhynchia, but with a longer smooth stage. Orbirhynchia United States. Smithsonian Contributions to Paleobiology, 64, 45 p. generally has an orbicular shell shape and falciform crura. In ad- DALL, W. H. 1903. Contributions to the Tertiary fauna of Florida. Trans- dition, the elements of cardinalia in Riorhynchia are all massive actions of the Wagner Free Institute of Science. 3(6):1535–1540, pl. and thickened and the crura are hamiform. 58. DUME´ RIL, A. M. C. 1806. Zoologie analytique ou methode naturelle de PROBOLARINA PAPALOTENSIS new species classifications des animaux. Allais, Paris, 344 p. Figures 4, 7, 8 ECHANOVE, O. 1967. Informe fotogeolo´gico del a´rea de Paredo´n, Coa- huila. Superintendencia General de Exploracio´n, Petro´leos Mexicanos, Diagnosis.⎯Triangular with low, broad costae beginning mid- Archivo Te`cnico NEM- 1005, 127 p. valve; dorsal valve interior with narrow sockets and nearly erect GARDNER, J. A., AND E. BOWLES. 1939. The Venericardia planicosta socket ridges; ventral valve interior with strong, vertical dental group in the Gulf Province. U. S. Geological Survey Professional Pa- plates; subfalciform crura. per, 189-F:143–215. Description.⎯Medium size, subpentagonal to triangular out- GILES, K. A., AND T. F. L AWTON. 1999. Attributes and evolution of an line, length slightly greater than width, both greater than thick- exhumed salt weld, La Popa basin, northeastern Mexico. Geology, 27: ness, maximum width at midvalve or two-thirds from posterior; 323–326. GILES, K. A., T. F. LAWTON, AND F. J. VEGA. 1999. Salt tectonics of dorsibiconvex profile; beak long, nearly straight to slightly in- Cretaceous-Paleogene La Popa Basin, Nuevo Leo´n, Me´xico. Third curved; small, oval foramen, submesothyrid, auriculate margins, Joint AMPG/AAPG International Conference Guidebook. Las Cruces, visible conjunct deltidial plates; apical angle acute; lateral com- New Mexico, 109 p. missure straight, anterior commissure uniplicate; broad, low cos- HARPER, D. A. 1993. Cretaceous and Cenozoic Brachiopoda of Jamaica, tae beginning at midlength; dorsal valve strongly convex, fold p. 105–114. In R. M. Robinson (ed.), Biostratigraphy of Jamaica. Geo- extending to anterior from midlength; ventral valve in lateral pro- logical Society of America Memoir, 182. file evenly and slightly convex, sulcus in anterior portion of valve. HERNA´ NDEZ, R. 1992. New dinosaur finds in the Cerro del Pueblo For- Dorsal valve interior with narrow sockets and nearly erect sock- mation (Upper Cretaceous, Campanian) from Coahuila State, Me´xico. et ridges, no median septum, crural bases attached to socket ridges Journal of Vertebrate Paleontology 13(Supplement to No. 3):32A. HERNA´ NDEZ, R., AND J. I. KIRKLAND. 1993. The rediscovery of a rich by flat outer hinge plates, subfalciform crura long, crescentic, con- Uppermost Campanian dinosaur locality in the Cerro del Pueblo For- cave outward, reaching to one-third of length of valve; ventral mation, Coahuila, Me´xico. Journal of Vertebrate Paleontology, 13(Sup- valve interior with pedicle collar, strong, vertical dental plates plement to No. 3):41A. separated from side wall by narrow umbonal chambers, small HOWARTH, R. J., AND J. M. MCARTHUR. 1997. Statistics for strontium teeth. isotope stratigraphy: A robust LOWESS fit to the Marine Sr-Isotope KLOSTERMAN ET AL.—NEW PALEOCENE BRACHIOPODS FROM MEXICO 489
Curve for 0 to 206 Ma, with look-up table for derivation of numeric Formation), southeastern Coahuila, Mexico. Journal of Vertebrate Pa- age. Journal of Geology, 105:441–456. leontology, 18:751–764. HUNNICUTT, L. A. 1998. Tectonostratigraphic interpretation of Upper RODRIGUEZ DE LA ROSA, R., S. R. S. CEVALLOS-FERRIZ, AND A. SILVA- Cretaceous to lower Tertiary limestone lentils within the Potrerillos PINEDA. 1998. Paleobiological implications of Campanian coprolites. Formation surrounding El Papalote diapir, La Popa basin, Nuevo Leon. Palaeogeography, Palaeoclimatology, Palaeoecology, 142:231–254. Unpublished M.S. thesis, New Mexico State University, Las Cruces, RZHONSNITSKAIA, M. A. 1956. Systematization of Rhynchonellida. In E. 181 p. Guzma´n and others (eds.), Resumenes de Los Trabajos Presentados. IMLAY, R. W. 1937. Stratigraphy and paleontology of the Upper Creta- International Geological Congress, Mexico, Report 20:125–126. ceous beds along the eastern side of Laguna de Mayra´n, Coahuila, SANDY, M. R. 1989. Preparation of serial sections, p. 146–156. In R. M. Me`xico. Geological Society of America Bulletin, 48:1785–1872. Feldmann, R. E. Chapman, and J. T. Hannibal (eds.), Paleotechniques. KIRKLAND, J. I., AND M. C. AGUILLON-MARTINEZ. 1995. Schizorhiza Paleontological Society Special Publication, Number 4. from the Late Cretaceous of northern Mexico: The ultimate sawfish. VEGA,F.J.,AND R. M. FELDMANN. 1991. Fossil crabs (Crustacea: De- Journal of Vertebrate Paleontology, 15(Supplement to No. 3):39A. capoda) from the Maastrichtian Difunta Group, northeastern Mexico. KUHN, O. 1949. Lehrbuch der Palaeozoologie. E. Schweizerhart, Stutt- Annals of Carnegie Museum, 60:163–177. gart, 326 p. VEGA,F.J.,AND M. C. PERRILLIAT. 1989a. Una especie nueva del ge´nero LAUDON, R. C. 1984. Evaporite diapirs in the La Popa basin, Nuevo Costacopluma (Arthtropoda: Decapoda) del Maastrichtiano de Nuevo Leon, Mexico. Geological Society of America Bulletin, 95:1219–1225. Leo´n. Me´xico, Universidad Nacional Auto´noma, Instituto de Geologı´a, LAUDON, R. C. 1996. Salt dome growth, thrust fault growth, and syn- Revista, 8:84–87. deformational stratigraphy, La Popa basin, northern Mexico. Transac- VEGA,F.J.,AND M. C. PERRILLIAT. 1989b. La presencia del Eoceno tions of the Gulf Coast Association of Geological Societies, 46:219– marino en la cuenca de La Popa (Grupo Difunta), Nuevo Leo´n; oro- 228. genia postypresiana. Me´xico, Universidad Nacional Auto´noma, Insti- LAWTON, T. F., F. J. VEGA,K.A.GILES, AND M. C. ROSALES. 2002. tuto de Geologı´a, Revista, 8:67–70. Stratigraphy and evolution of the La Popa basin, Nuevo Leon and VEGA,F.J.,AND M. C. PERRILLIAT. 1989c. On a new species of Vener- Coahuila, Mexico. In C. Bartolini, R. T. Buffler, and A. Cantu-Chapa icardia from the Lower Eocene in northeastern Mexico (Difunta (eds.), The Western Gulf of Mexico Basin: Tectonics, Sedimentary Ba- Group). Tulane Studies in Geology and Paleontology, 22:101–106. sins, and Petroleum Systems. American Association of Petroleum Ge- VEGA,F.J.,AND M. C. PERRILLIAT. 1990. Moluscos del Maastrichtiano ologists Memoir, 75. de la Sierra El Antrisco, Nuevo Leo´n. Me´xico, Universidad Nacional LEE, D. E. 1980. Probolarina and Streptaria, two Cenozoic Rhyncho- Auto´noma, Instituto de Geologı´a, Paleontologı´a Mexicana, 55, 63 p. nellide brachiopods new to New Zealand. Journal of the Royal Society VEGA,F.J.,AND M. C. PERRILLIAT. 1992. Freshwater gastropods from of New Zealand, 10:137–144. lower Eocene Difunta Group, northeastern Mexico. Journal of Pale- MCBRIDE, E. F., A. E. WEIDIE, AND J. A. WOLLEBEN. 1975. Deltaic and ontology, 66:603–609. associated deposits of the Difunta Group (Late Cretaceous to Paleo- VEGA,F.J.,AND M. C. PERRILLIAT. 1995. On some Paleocene inverte- cene), Parras and La Popa basins, northeastern Mexico, p. 485–522. In brates from the Potrerillos Formation (Difunta Group), northeastern M. L. Broussard (ed.), Deltas; Models for Explorations. Houston Geo- Mexico. Journal of Paleontology, 69:862–869. logical Society. VEGA, F. J., R. M. FELDMANN, AND V. D AVILA-ALCOCER. 1994. Cuticular MCBRIDE, E. F., A. E. WEIDIE,J.A.WOLLEBEN, AND R. LAUDON. 1974. structure in Costacopluma mexicana Vega and Perrilliat, from the Di- Stratigraphy and structure of the Parras and La Popa basins, north- funta Group (Maastrichtian) of northeastern Mexico, and its paleoen- eastern Mexico. Geological Society of America Bulletin, 84:1603– vironmental implications. Journal of Paleontology, 68:1074–1081. 1622. VEGA, F. J., R. M. FELDMANN, AND J. L. VILLALOBOS-HIRIART. 1995. MURRAY,G.E.,AND J. A. WOLLEBEN. 1959. Difunta strata of Tertiary Additions to the crustacean (Decapoda) fauna from the Potrerillos For- age, Coahuila, Mexico. American Association of Petroleum Geologists mation (Late Cretaceous) in northeastern Mexico. Annals of Carnegie Bulletin, 43:2492–2495. Museum, 64:39–49. MURRAY,G.E.,AND J. A. WOLLEBEN. 1960. Late Cretaceous fossil VEGA, F. J., L. M. MITRE-SALAZAR, AND E. MARTINEZ-HERNANDEZ. locality, eastern Parras Basin, Coahuila, Mexico. Journal of Paleontol- 1989. Contribucio´n al conocimiento de la estratigrafı´a del Grupo Di- ogy, 34:368–370. funta (Creta´cico Superior-Terciario) en el noreste de Me´xico. Univer- PERRILLIAT, M. C., AND F. J. VEGA. 1993. Early Eocene ostreids from sidad Nacional Auto´noma, Instituto de Geologı´a, Revista 8:179–187. the Adjuntas Formation (Difunta Group), northeastern Mexico. Tulane VEGA, F. J., M. C. PERRILLIAT, AND L. M. MITRE-SALAZAR. 1999. Pa- Studies in Geology and Paleontology, 26:15–25. leocene ostreids from the Las Encinas Formation (Parras basin: Difunta RODRIGUEZDELAROSA, R. 1996. Vertebrate remains from a Late Cre- Group), northeastern Mexico; stratigraphic implications. Geological taceous locality (Campanian, Cerro del Pueblo Formation), Coahuila, Society of America Special Paper, 340:105–110. Mexico. Journal of Vertebrate Paleontology, 16(Supplement to No. 3): WIEDMAN, L. A., R. M. FELDMANN,D.E.LEE AND W. J. ZINSMEISTER. 60A. 1988. Brachiopoda from the La Meseta Formation (Eocene), Seymour RODRIGUEZDELAROSA, R., AND S. R. S. CEVALLOS-FERRIZ. 1994. Island, Antartica. Geological Society of America Memoir, 169:449– Upper Cretaceous zingiberlean fruits with in situ seeds from south- 457. eastern Coahuila, Mexico. International Journal of Plant Sciences, 155: WILLIAMS, A., S. J. CARLSON,C.H.C.BRUNTON,L.E.HOLMER, AND 786–805. L. POPOV. 1996. A supra-ordinal classification of the Brachiopoda. RODRIGUEZDELAROSA, R., AND S. R. S. CEVALLOS-FERRIZ. 1995. Philosophical Transactions of the Royal Society, London, B, 351:1171– Plant-bearing coprolites from the El Cerro del Pueblo Formation, 1193. southeastern Coahuila. American Journal of Botany (Supplement), 82: WOLLEBEN, J. A. 1977. Paleontology of the Difunta Group (Upper Cre- 260. taceous-Tertiary) in northern Mexico. Journal of Paleontology, 51:373– RODRIGUEZDELAROSA, R., AND S. R. S. CEVALLOS-FERRIZ. 1998. 398. Vertebrates of the El Pelillal locality (Campanian, Cerro del Pueblo ACCEPTED 25 JANUARY 2006