Barry S. Kues

MIDDLE PENNSYLVANIAN GASTROPODS FROM THE FLECHADO FORMATION, NORTH-CENTRAL NEW MEXICO

Abstract The lower Desmoinesian part of the Flechado Formation near Taos, New Mexico, contains a diverse marine fauna within predominantly dark gray shale and siltstone facies representing deposition in shallow marine environments adjacent to prograding lobes of a fan delta system. Gastropods are particularly abundant and diverse in a 60-m-thick section south of the town of Talpa; 157 species are described in this paper, including 19 new species and two new genera. New species are Euphemites hermosus, Luciellina ocultabanda, Spiroscala georgiannae, Glabrocingulum (Glabrocingulum) globosum, G. (Ananias) talpaensis, Worthenia legrandi, Cyclites diminutus, Platyzona hespera, Anomphalus? blancus, Stegocoelia (Donaldospira) taosensis, S. (Hypergonia) hoffmani, S. (H.) agraciada, Bicuerda procolumnare, new genus and species; Hermosanema varium, new genus and species, Pseudozygopleura (Stephanozyga) granda, P. (S.) lisaspira, Hemizyga (Hemizyga) larga, Strobeus immanis, and Meekospira delgada. Species of Pleurotomarioidea, Neritoidea, Trochoidea, and Murchisonioidea comprise 64 percent of the total gastropod specimens, with most specimens of each of the last three groups being contributed by large numbers of one or two very abundant species. The 20 most abundant species are represented by about 65 percent of all specimens, whereas 62 species (39 percent of total species richness, but only 1.1 percent of all specimens) are represented by six or fewer specimens, illustrating the significant contribution of rare species to total species richness. The Flechado gastropod fauna contains many species known from Desmoinesian strata in the Midcontinent and Appalachian Basin regions of the U.S.; many elements of Desmoinesian gastropod assemblages were distributed widely in shallow marine environments across North America. Potential paleogeographic barriers in the Colorado–New Mexico region, however, may have facilitated evolution of some endemic species in this area.

Decapod crustaceans from the Semilla Sandstone Member, Mancos Shale (Upper Cretaceous), north-central New Mexico

The decapods Linuparus grimmeri Stenzel, Protocallianassa mortoni (Pilsbry) and Necrocarcinus (Cenomanocarcinus) vanstraeleni (Stenzel)? are described from the middle Turonian Semilla Sandstone Member, Mancos Shale, of north-central New Mexico. The main specimen ofP. mortoni is unusually complete, consisting of a complete left first cheliped, parts of other pereiopods, and most of the abdomen. Both L. grimmeri and P. mortoni are reported for the first time from the southern Western Interior. The stratigraphic range of L. grimmeri is extended upward from the upper Cenomanian, and the range of P. mortoni downward from the Campanian.

HOMEOMORPHY IN THE ASTEROIDEA (ECHINODERMATA); A NEW LATE CRETACEOUS GENUS AND SPECIES FROM COLORADO

Abstract Codellaster keepersae new genus and species, from the Upper Cretaceous Codell Sandstone Member of the Carlile Shale of Colorado (U.S.A.), is assigned to the asteroid (Echinodermata) family Goniasteridae. Although clearly a goniasterid, the flattened body form and details of morphology of C. keepersae are remarkably similar to corresponding features of the modern astropectinid Astropecten regalis and also of the luidiid Luidia (Platasterias) latiradiata. The discovery facies of C. keepersae includes low-angle crossbeds and asymmetrical ripple marks that are suggestive of a very shallow marine environment. Both the modern species occur in shallow, turbulent settings, and homeomorphy beween ancient and modern asteroids suggests similar selective pressures and evolutionary responses. Limited evidence suggests goniasterids might have been more common in shallower waters during the Cretaceous than they are today, and absence of modern Codellaster-like goniasterids indicates that the family abandoned these habitats, although the fundamental morphological response to such settings remained viable for asteroid organization.

TAXONOMY AND VARIABILITY OF THREE TEXIGRYPHAEA (BIVALVIA) SPECIES FROM THEIR LOWER CRETACEOUS (ALBIAN) TYPE LOCALITIES IN NEW MEXICO AND OKLAHOMA

The benthic, free-living oyster Texigryphaea was the dominant constituent of many late Albian marine communities in the Texas and southern Western Interior regions. Large topotypic assemblages of three common lower-middle Washita Group species (T. navia and T. pitcheri in Oklahoma and T. tucumcarii in New Mexico) each display considerable morphological variation in valve shape and the proportions and expression of various features. Variation within an assemblage is partly due to ontogenetic changes but is mainly ecophenotypic, with local variation in nature of substrate, water turbulence, length of attachment time, and other factors influencing the final morphology of the mature shell. The T. navia assemblage is distinct in several important mor- phological characters from the other species, and the differences become more pronounced with growth. Texigryphaea navia appears to have been adapted to relatively firm substrates in moderately agitated conditions, in contrast to the other species, which occupied softer substrates in quieter environments. The essentially contemporaneous T. pitcheri and T. tucumcarii assemblages display much overlap in all measured dimensions of the left valve and in the range of intergrading morphs that compose each assemblage. Accordingly, T. tucumcarii is considered a synonym of T. pitcheri, representing populations of that species that lived in the West Texas-New Mexico area and developed only minor differences from the eastern populations. Within the T. navia topotypic assemblage are specimens intermediate between T. navia and T. pitcheri, and the eastern and western T. pitcheri assemblages contain forms apparently transitional to two other species, T. washitaensis and T. belviderensis. Ecophenotypic variation in the T. pitcheri assem- blages appears to be greater than that in European Jurassic Gryphaea species and mirrors to some extent phyletic variation in European Jurassic Gryphaea lineages.

NEW GENERA AND SPECIES OF MIDDLE PENNSYLVANIAN GASTROPODS FROM WEST TEXAS

Abstract Desmoinesian strata of the lower Bishop Cap Formation in Vinton Canyon, northern Franklin Mountains, west Texas, contain a rich gastropod fauna, in general resembling that of the upper Flechado Formation in north-central New Mexico. Distinctive elements of the Bishop Cap fauna include two new genera and five new species. Each species is represented by 30 or more specimens, sufficient to document ontogenetic change and intraspecific variability. The new taxa described here include the murchisonioid Altadema convexa new genus and species; the pseudozygopleurids Microptychis insolita new species, Trepsipleura chordanodosa new genus and species, and T. nodosa new species; and the orthonemid Hermosanema carinatum new species.

Provenance evidence for major post–early Pennsylvanian dextral slip on the Picuris-Pecos fault, northern New Mexico

The Picuris-Pecos fault is a major strike-slip fault in northern New Mexico (USA) that exhibits ∼37 km of dextral separation of Proterozoic lithotypes and structures. The timing of dextral slip has been controversial due largely to a lack of definitive piercing points of Phanerozoic age. The Picuris-Pecos fault formed the western boundary of the late Paleozoic Taos trough. A distinctive metasedimentary terrane that shed detritus into the western Taos trough was exposed on the Uncompahgre uplift west of the fault during the early to middle Pennsylvanian. We use the distribution of metasedimentary clasts and the age of monazite grains within clasts from conglomeratic strata of the western Taos trough to determine the paleolocation of the southern boundary of this metasedimentary terrane during the middle Pennsylvanian (Desmoinesian), and thereby quantify the subsequent separation on the fault. The rematching of detrital petrofacies with source terranes in the adjacent uplift requires ∼40–50 km of dextral separation on the Picuris-Pecos fault since the early Desmoinesian. This exceeds the present ∼37 km dextral separation of Proterozoic features by the fault, and thus implies that an ∼3–13 km sinistral separation existed on the fault in the early Desmoinesian. The ∼40–50 km of post–early Desmoinesian dextral separation on the Picuris-Pecos fault is the result of slip that accumulated late in the Ancestral Rocky Mountain deformation and/or during the Laramide orogeny.

PHARKIDONOTUS MEGALIUS, A LARGE NEW GASTROPOD SPECIES FROM THE MIDDLE PENNSYLVANIAN OF SOUTH-CENTRAL NEW MEXICO

Pharkidonotus megalius n. sp. is described from the Desmoinesian of the Mud Springs Mountains, New Mexico. This unusually large bellerophontid reaches a length of at least 90 mm and is also characterized by a prominent high median ridge bearing a narrow selenizone and subdued collabral ornamentation on the whorl surface at all stages of growth. Its size and subdued ornamentation are quite different from that of the two previously known North American Penn- sylvanian species of Pharkidonotus. Although steinkerns of comparable size have been reported from several localities in North America, the specimens discussed here are the first relatively well preserved shells of very large Pennsylvanian bellerophontids to be described.

A LATE PERMIAN CHINESE GASTROPOD SPECIES, POSSIBLY LARVAL, IN THE MIDDLE PENNSYLVANIAN OF NEW MEXICO

Kues and Batten (2001, p. 30, fig. 6.17–6.20) described several distinctive, minute, low-spired gastropod specimens from the Desmoinesian (Middle Pennsylvanian) Flechado Formation of northcentral New Mexico, assigning them questionably to Lunulazona Sadlick and Nielsen, 1963 because of the strongly developed collabral elements similar to those of that genus. These shells, consisting of three or four inflated whorls, are at most 1 mm in height and the later whorls bear conspicuous, sharp, widely spaced collabral ribs that bend strongly across a wide, slightly flattened band interpreted as a peripheral selenizone. While recognizing these specimens as a distinct, unnamed taxon, Kues and Batten (2001) believed that they likely represent juveniles of an as yet unrecognized larger species of gastropod with a different mature morphology. Recently, Pan and Erwin (2002) described diverse gastropod assemblages from southern China, most of them from Late Permian (Changhsingian) strata. Most of these taxa are very small, possibly reflecting differential silicification rather than adverse or unusual ecological conditions. Among the specimens is a single, beautifully preserved shell, described as Naticasinus sinus new genus and species (p. 6, fig. 4.14–4.16), from the upper member of the Heshan Formation, of very late Permian age. This specimen is similar in size, whorl proportions, and number of whorls to the New Mexico Middle Pennsylvanian specimens, and furthermore possesses nearly identical ornamentation. Pan and Erwin interpreted a sinus and lunulae just below midheight, but lacking the parallel sides that would indicate the presence of a slit. The shell characters of the New Mexico Middle Pennsylvanian specimens are so closely similar to those of the Chinese species that, on purely morphological grounds, they would appear to represent an early occurrence of Naticasinus sinus n. gen. and sp. The similarity between Lunulazona ? sp. and Naticasinus sinus n. gen. and sp. was noted by Bandel …

New Bivalve Taxa from the Tucumcari Formation (Cretaceous, Albian), New Mexico, and the Biostratigraphic Significance of the Basal Tucumcari Fauna

Basal strata of the Tucumcari Formation south of San Jon, New Mexico, contain a bivalve assemblage different from that of the remainder of the formation. Ceratostreon texanum and two new species herein described ( Gyrostrea hinchada, Plicatula quayensis ) are the dominant faunal elements of these basal strata. A fourth bivalve, long known as Lopha quadriplicata, ranges downward approximately to the upper limit of C. texanum. However, reevaluation of the taxonomy of this and related species indicates that 1) they have little in common with typical representatives of Lopha and are grouped in a new genus, Peilinia, and 2) specimens from the Tucumcari and related formations formerly assigned to L. quadriplicata are a separate new species, P. levicostata, which appeared in the southern Western Interior before P. quadriplicata appeared in eastern Texas and Oklahoma. The biostratigraphic ranges of several widely distributed bivalves are utilized with ammonite range zones to refine the correlation of several southern Western Interior sequences with the classic lower Washita sequence of Texas and Oklahoma. Because ammonites are rare in the western area, bivalves are locally more important in establishing the age of some exposures. For example, the boundary between or slight overlap of the successive zones of C. texanum and P. levicostata in eastern New Mexico and west-central Texas marks the position of the Craginites serratescens ammonite zone to the east. Strata previously called Kiamichi and Duck Creek in west-central Texas are best considered part of the Tucumcari Formation, representing deposition that occurred mainly earlier than the main Tucumcari sequence in New Mexico.