Shelton P. Applegate

EARLY CRETACEOUS ARTHROPODS FROM THE TLAYUA FORMATION AT TEPEXI DE RODRIGUEZ, PUEBLA, MEXICO

The arthropod macrofauna from the Middle Member of the lithographic limestones of the Tlayda Formation, in quarries at Tepexi, Mexico, is comprised of marine and nonmarine components. Marine taxa include a new species of flabelliferid isopod, a new genus and species of an anomuran, and a new genus and species of a brachyuran crab. Remains of an arachnid and an odonate nymph represent nonmarine constituents. Previous paleoenvironmental interpretations of a restricted lagoon, with periodic episodes of marine and freshwater influences are consistent with the nature of the arthropod fauna. Isopod remains, represented only by corpses, that resemble moder ectoparasites of fishes suggest that they are directly associated with the abundant fish remains found in the quarries, either as ectoparasites that released their hosts before they died or possibly as scavengers that fed on fish remains. The next most abundant arthropods are the crabs, most of which are corpses, suggesting that this group lived in or very near to the depositional site of the Tlayia Formation. Based upon the new fossil material, the stratigraphic range for the Aeglidae has been extended to span Albian to Holocene time. Extant representatives of this family inhabit fresh water environments of South America.

Revision of Recent Investigations in the Tlayúa Quarry

The Tlayua Quarry in Tepexi de Rodriguez, Puebla, Mexico, is one of the most important localities in the New World because of its uniquely rich biota. For the last twenty years, its exceptionally well-preserved fossil content and its taphonomical and paleoecological implications have caught the attention of many geologists and paleontologists since this Lagerstatte represents an important new asset in Mexican Paleontology. In this paper, we review all the recent investigations related to a development of the paleoecological models to explain the extraordinary conservation of the rich and diverse fossil assemblage of Tlayua.

A NEW WORLD MACROSEMIID (PISCES: NEOPTERYGII-HALECOSTOMI) FROM THE ALBIAN OF MÉXICO

Abstract A new genus and species belonging to the Macrosemiidae is described. This is the first record of a macrosemiid in the New World. The material was collected from the Early Cretaceous (Albian) Tlayúa Quarries, in Tepexi de Rodríguez, central México. The new taxon is a small, elongated fish that bears a combination of apomorphic and plesiomorphic characters including a divided dorsal fin with an area devoid of scales on either side, prearticular and coronoid bones with small pointed teeth, and strongly ornamented body scales. Phylogenetic analysis using PAUP revealed a close relationship of this new genus to Macrosemius and Legnonotus. The occurrence of macrosemiids in the Tlayúa beds indicates a wider distribution of the group within the Tethys Ocean, and represents the westernmost record of this group of neopterygians.

Onshore marine Cenozoic along southwest Pacific coast of Mexico

Reconnaissance exploration along the Pacific coast of Mexico from the Isthmus of Tehuantepec to Puerto Vallarta in the northwest, beginning in 1977, has shown the presence of at least seven previously unreported areas with late Cenozoic sedimentary deposits. In addition marine Pleistocene deposits on the coast of Oaxaca were previously reported. In four of the newly discovered areas marine sediments occur. All of these occurrences, excepting the two southeastern ones, were encountered along the Federal coastal highway, route F 200. Beginning in the northwest these areas are: along the Rio Ameca, 10 km north of Puerto Vallarta; 10 km south of Puerto Vallarta; Tomatlan Basin (named herein), 79 km south of Puerto Vallarta, with fossil vertebrates; Campo Acosta Basin (named herein) beginning 115 km south of Puerto Vallarta, sediments at least partly marine; La Mira Basin (named herein), straddling the mouth of the Rio Balsas, with at least two marine incursions; San Nicolas Basin (named herein) about 200 km southeast of Acapulco, marine sediments encountered in water well; Colotepec Formation, marine, along the coast of Oaxaca between Puerto Angel and Puerto Escondido; marine deposits near Santa Cruz, Oaxaca, about 100 km southwest of Salina Cruz, Oaxaca. Of the seven new areas, only the La Mira Basin has been examined in more than a most cursory manner. In the La Mira Basin four formations are recognized: Ferrotepec Formation (named herein), marine, late early to middle Miocene in age; Barranca del Perro Muerto Formation (named herein), nonmarine; El Bordonal Conglomerate (named herein), nonmarine; Abanico Brisa Mar Formation (named herein), at least partly marine, of undifferentiated Plio-Pleistocene age. If the attitudes observed in the Ferrotepec Formation continue seaward, the total thickness of the sediments in the basin might attain 1,500 m. The fossils from the Ferrotepec Formation mostly belong to the “Tertiary Caribbean Province” of Woodring, but a few show affinities to north Pacific coast Miocene faunas. The La Mira Basin sediments indicate that the Rio Balsas has existed since early Miocene time. The few fossils from the San Nicolas Basin suggest a late Miocene to Pliocene age. The few fossils from the beds near Santa Cruz are suggestive of a Plio-Pleistocene age. Insofar, as is known, the sediments in the areas northwest of the La Mira Basin only attain a few meters in thickness. Offshore from the San Nicolas Basin, at Deep Sea Drilling Project (DSDP) Site 493, about 670 m of early Miocene to Pleistocene sediments are reported. The Santa Cruz beds appear to be about 50 m thick, and Palmer reports a 15 m thickness for the Colotepec Formation.

PRESENCE OF HELICOPRION (CHONDRICHTHYES, ELASMOBRANCHII) IN THE PERMIAN PATLANOAYA FORMATION, PUEBLA, MEXICO

A newly discovered Helicoprion specimen from the Patlanoaya Formation, State of Puebla, represents the southernmost finding of this genus of edestoid-shark in the Western Hemisphere. It was found in sediments assigned to the upper part of the Early Permian, based on its association with Perrinites hilli, an index ammonoid for the Leonardian age. Since the first description of this enigmatic Permian shark by Karpinsky in 1899, the genus Helicoprion has been reported from Leonardian sediments, with one exception in Texas, where the age of the fossils corresponds to the Wolfcampian. The regions in which Helicoprion has been found include Eurasia, Australia, and North America. In Eurasia, this taxon has been collected in Spitsbergen (Nassichuk, 1971), on the western flank of the Ural Mountains (Karpinsky in Wheeler, 1939), Pakistan (Koken in Chorn, 1978), Indochina (Hoffet, 1933), Japan (Yabe in Teichert, 1940), and possibly Iran (Obruchev in Chorn, 1978). As for the Southern Hemisphere, Helicoprion has not been found in South America nor in Africa, although it is known to occur in several outcrops in western Australia (Teichert, 1940). In the North American region it has been reported from the Canadian Arctic and Alberta (Wheeler, 1939; Logan and McGugan, 1968; Nassichuk, 1971), British Columbia (Henderson and McGugan, 1987), Idaho (Williams and Dunkle, 1948; Bendix-Almgreen, 1966; Foss, 1980), California and Nevada (Wheeler, 1939), and Texas (Kelly and Zangerl, 1976; Chorn, 1978). This last report from Texas has been referred to the Wolfcampian (Kelly and Zangerl, 1976), making it the oldest record of this taxon worldwide. In Mexico the presence of Helicoprion has been reported in the northern states of Coahuila (Mullerried, 1945) and Chihuahua (Bridges and DeFord, …