Sara A. Quiroz-Barroso

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.

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, …

PSEUDOMULCEODENS: A MISSISSIPPIAN ROSTROCONCH FROM MEXICO

This finding of Pseudomulceodens in Mississippian-age rocks of the Santiago Formation provides the first evidence of the molluscan class Rostroconchia in Mexico. Elsewhere in North American Mississippian rocks the class occurs in Arkansas (Hoare et al., 1982, 1988); Illinois (Weller, 1916); Indiana (Beede, 1906); Iowa (White and Whitfield, 1862); Michigan (Winchell, 1870); Montana and Nevada (Pojeta and Runnegar, 1976); Ohio (Hyde, 1953; Hoare, 1990); and Oklahoma (Branson, 1958). Pseudomulceodens cancellatus (Hyde, 1953) confirms the Osagean age (Early Mississippian) of the Santiago Formation, and reinforces the conclusion that there is paleobiogeographic similarity between faunas of the Nochixtlan region of Oaxaca, Mexico and the midcontinent of the USA during Early Carboniferous time. It seems likely that there was a close connection between southwestern Mexico and the Mid-Continent Paleoprovince, located in the east and central regions of the United States. Prior to this study the rostroconch genera Aphelakardia and Pseudomulceodens were placed in the family Hippocardiidae; they are here transferred to the family Conocardiidae. The rostroconchs figured here were collected 18 m above the base of the Santiago Formation, in the stream bed of Arroyo Las Pulgas. This locality is 600 m north of Santiago Ixtaltepec town, 17°29′–17°34′N, 97°05′–97°08′W, in the Nochixtlan Region, State of Oaxaca, Mexico. The Santiago Formation was first described by Pantoja-Alor (1970); we use the term Santiago Formation as redefined by Sour-Tovar et al. (1997), who considered only the first 67 m of the …

Fossil record of Upper Paleozoic Marine Invertebrates from Mexico

Upper Paleozoic fossil invertebrates of Mexico represent communities of marine environments associated with continental margins. A high percentage of very diverse brachiopods and mollusks, accompanied by other lesser diverse groups such as echinoderms, arthropods, bryozoans and corals occur throughout the Upper Paleozoic sequence of Mexico. Outcrops of Carboniferous and Permian rocks are especially abundant and Mexican fossil faunas from those systems exhibit an affinity to similar age fossil faunas from the rest of North America; this is especially true in the youngest faunas. This similarity may be explained by the configuration and geographic position of the Late Paleozoic crustal portions that form modern day Mexico. During the Late Paleozoic Pangea was forming and the ocean that existed between Gondwana and the northern continents was narrowing: during the entire Carboniferous and Early-Middle Permian, that ocean covered large regions of North America and extended over the majority of what constitutes present-day Mexico.