María del Carmen Perrilliat

EARLY MAASTRICHTIAN MOLLUSCA FROM THE MEXCALA FORMATION OF THE STATE OF GUERRERO, SOUTHERN MEXICO

Abstract Forty species of gastropods (six of them new: Calliomphalus (Planolateralus) mexcalensis, Nododelphinula diminuta, Potamides temalacensis, Ptychopotamides ancestralus, Amaurellina guerrera, and Drilluta gloriae), and 13 species of bivalves are described from the lower Maastrichtian marls of the basal Mexcala Formation from Guerrero State, southern Mexico. Age interpretation was based on planktic foraminiferans. Associated fauna includes planktic and benthic foraminiferans, ostracods, solitary corals, crustaceans, echinoids, and vertebrates. The distribution of bivalve and gastropod species suggests that this area has affinities with the Gulf Coast Plain Province of the United States, although some species also are reported from the Middle East, Europe, and South America.

Pennsylvanian bivalves from the Ixtaltepec Formation, Mexico

Twenty species of bivalves are described from the Ixtaltepec Formation, in Nochixtlan, Mexico. Representatives of the genera Parallelodon, Myalinella, ptimyalina, Leptodesma, Pterinopectinella, Aviculopecten, Limipecten, Streblopteria, Euchondria, Schizodus, Permophorus, Astartella, Edmondia, and Ectogrammysia are present. These species, and those of nuculoid bivalves previously described from the same formation, include infaunal and epifaunal forms that lived in shallow marine environments from Morrowan to Desmoinesian ages. Pennsylvanian bivalves from Nochixtlan are related to the Midcontinent and Appalachian faunas, which indicate that there was an oceanic connection between these areas in a latitudinal belt near the equator that partially covered southeastern Mexico.

Late Cretaceous and Paleogene Freshwater Gastropods from Northeastern Mexico

Abstract Twenty-three species of Campanian, Maastrichtian, Paleocene, and Eocene freshwater gastropods from northeastern Mexico are described, including eight new species: Viviparus mcbridei, Pachychilus (Pachychiloides) lawtoni, Melanoides (Melanoides) yolandae, Melanoides (Melanoides) wollebeni, Physa cepedaensis, Mesolanistes magnus, Mesolanistes murrayi, and Gyraulus zoltani. Specimens were collected from fine-grained, green sandstone and mudstone, red mudstone, and as hematized remains in fine light-brown sandstones belonging to the following stratigraphic units of northeastern Mexico: Cerro del Pueblo (Campanian, Parras Basin), Olmos (Maastrichtian, Sabinas Basin), Las Encinas (Paleocene, Parras Basin), and Carroza (Eocene, La Popa Basin) Formations. All except two of the genera (?Pyrgulifera and Mesolanistes) have recent representatives. Review of habitats of living species of the six extant genera and interpretations of sample lithologies support the inference of dominantly freshwater paleoenvironments. Only one Maastrichtian locality is interpreted confidently to have had a brackish water influence.

On some Paleocene invertebrates from the Portrerillos Formation (Difunta Group), northeastern Mexico

Three species of mollusks and one annelid are described from the Paleocene upper mudstone member of the Potrerillos Formation (La Popa Basin), and from the upper part of the Rancho Nuevo Formation (Parras Basin). The species described include a gastropod, a bivalve, a nautiloid and a serpulid worm, which are formally reported for first time as Paleocene fauna of the Difunta Group in northeastern Mexico. The nautiloid species provides the basis for correlation between the two sedimentary basins of the Difunta Group, as it is reported for Paleocene layers of the two formations studied. Shoreface and tidal-flat depositional environments are inferred for the Paleocene rocks of the Difunta Group.

Freshwater gastropods from Early Eocene Difunta Group, northeastern Mexico

Three new species of freshwater gastropods are described from the lower Eocene Adjuntas Formation. Five more species are reported from the same fauna. This is the first report of Tertiary freshwater Mollusca of the Campanian–lower Eocene Difunta Group. The three new species ( Hemisinus ( Longiverena ) reticulosus, Hemisinus ( Longiverena ) adjuntaensis , and Melanatria ypresiana ) belong to the family Thiaridae, which today is a worldwide distributed group of freshwater gastropods of medical importance. Paleoenvironmental interpretation for red, green, and yellow beds of Adjuntas Formation suggests delta-plain deposits. Gastropods here described lived in swamps and marshes of this portion of the ancestral Gulf of Mexico.

Mesozoic and Tertiary Decapod Crustacea from Mexico

In recent years, the number of described species of fossil crustaceans from Mexico has increased noticeably. Numerous new occurrences and new taxa were described from lithostratigraphic units that range in age from Early Cretaceous to Miocene. These reports included not only the systematic description of the specimens, but also information on paleoenvironment, paleoecology and evolution. The present work is a review of the fossil record of fossil crustaceans from Mexico, including comments on new localities and fauna that are under study. Based on the ongoing research in this field, it is possible that the number of fossil species of brachyurans will reach twice as much as the ones reported nowadays in a few years.

Pennsylvanian nuculoids (Bivalvia) from the Ixtaltepec Formation, Oaxaca, Mexico

Five species of nuculoid bivalves are described from Pennsylvanian outcrops of the Ixtaltepec Formation, Oaxaca, Mexico: Nuculopsis sp., Palaeoneilo sinuosus new species, Paleyoldia sp., Phestia bellistriata, and Phestia sp. have been collected in clastic rocks and in association with other marine invertebrate groups, which represent a peri-reefal environment.

MEXFUSUS ROTUNDICOSTATUS, A NEW GENUS AND SPECIES OF NEOGASTROPOD FROM THE LATE CRETACEOUS OF SOUTHERN MEXICO

Abstract Mexfusus rotundicostatus new genus and species is a neogastropod of uncertain affinities from the Late Cretaceous (Early Maastrichtian) Mexcala Formation of southern Mexico. It is characterized by strong, rounded, axial ribs, fine spinelets at the intersection of axial ribs and sharp spiral cords, subsutural cord, strong simple spiral cords, and an apparently smooth, glazed columellar lip. A possible second species is Peristernia conica Riedel, 1932 from the Coniacian of Cameroon.