Search USGS⌕ Search

Geology topics

J. Pojeta

Publications and source records attributed to J. Pojeta.

17 recordsLinked to original sources
USGS2017

Ascaulocardium armatum (Morton 1833), new genus (Late Cretaceous): the ultimate variation on the bivalve paradigm

Cretaceous clavagellid pelecypods are a poorly known group, and have previously received little study. Ascaulocardium armatum is conchologically the most complex burrowing pelecypod known. From the study of living clavagellids, it is possible to interpret the various tubes extending outward from the adventitious crypt of A. armatum as devices for hydraulic burrowing and deposit feeding. The conchologically complex A. armatum occurs near the beginning of the history of the Clavagellidae, and does not seem to have given rise to any younger species. Ascaulocardium armatum is known only from the Upper Cretaceous rocks (Santonian–Maastrichtian) of the east Gulf and Atlantic Coastal Plains of the United States of America, as is probably the genus Ascaulocardium . All known Cretaceous clavagellids are burrowing species having a free right valve, and this is the ancestral mode of life of the Clavagellidae. Clavagellids that have a boring habit are a more recent evolutionary development, as are burrowing species having both juvenile valves cemented to the crypt. Clavagellids probably evolved from Jurassic–Early Cretaceous pholadomyids. Almost all Cretaceous clavagellids occur outside the Tethyan Zoogeographic Realm; this distribution is in marked contrast to the modern distribution of the family. Living species mostly inhabit clear, shallow seas in subtropical to tropical shelf areas.

Journal of Paleontology↗
USGS2016

Early and middle(?) Cambrian metazoan and protistan fossils from West Africa

Supposed Upper Proterozoic strata in the southwest Taoudeni Basin, Guinea and Senegal, and from the Mauritanide fold belt, Mauritania, have yielded mostly poorly preserved small skeletal fossils of metazoan and protistan origin. Problematic, but possible echinoderm material and spicules of the heteractinid sponge Eiffelia dominate the Taoudeni Basin assemblage. The age of the material is not certain but the paleontologic data suggest an Early Cambrian age for the stratigraphically lowest faunas, and a Middle Cambrian age is possible for the stratigraphically highest collections.

Journal of Paleontology↗
USGS2010

Upper Cambrian chitons (Mollusca, polyplacophora) from Missouri, USA

Numerous new specimens reveal a greater presence of chitons in Upper Cambrian rocks than previously suspected. Evidence is presented showing that the chiton esthete sensory system is present in all chiton species in this study at the very beginning of the known polyplacophoran fossil record. The stratigraphic occurrences and paleobiogeography of Late Cambrian chitons are documented. The 14 previously-named families of Cambrian and Ordovician chitons are reviewed and analyzed. Aulochitonidae n. fam. is defined, based on Aulochiton n. gen.; A. sannerae n. sp. is also defined. The long misunderstood family Preacanthochitonidae and its type genus Preacanthochiton Bergenhayn, 1960, are placed in synonymy with Mattheviidae and Chelodes Davidson & King, 1874, respectively; Eochelodes Marek, 1962, also is placed in synonymy with Chelodes, and Elongata Stinchcomb & Darrough, 1995, is placed in synonymy with Hemithecella Ulrich & Bridge, 1941. At the species level, H. elongata Stinchcomb & Darrough, 1995, and Elongata perplexa Stinchcomb & Darrough, 1995, are placed in synonymy with H. eminensis Stinchcomb & Darrough, 1995. The Ordovician species H. abrupta Stinchcomb & Darrough, 1995, is transferred to the genus Chelodes as C. abrupta (Stinchcomb & Darrough, 1995). The Ordovician species Preacanthochiton baueri Hoare & Pojeta, 2006, is transferred to the genus Helminthochiton as H. ? baueri (Hoare & Pojeta, 2006). The Ordovician species H. marginatus Hoare & Pojeta, 2006, is transferred to the genus Litochiton as L. marginatus (Hoare & Pojeta, 2006). Matthevia walcotti Runnegar, Pojeta, Taylor, & Collins, 1979, is treated as a synonym of Hemithecella expansa Ulrich & Bridge, 1941. In addition, other multivalved Cambrian mollusks are discussed; within this group, Dycheiidae n. fam. is defined, as well as Paradycheia dorisae n. gen. and n. sp. Cladistic analysis indicates a close relationship among the genera here assigned to the Mattheviidae, and between Echinochiton Pojeta, Eernisse, Hoare, & Henderson, 2003, and mattheviids. The results suggest treating these taxa as stem-lineage chitons, and do not support the hypothesis that they are aplacophorans.

Bulletins of American Paleontology↗
USGS2008

New information about Echinochiton dufoei, the Ordovician spiny chiton

Echinochiton dufoei Pojeta et al ., 2003 is now known from seven specimens. The new material shows the anterior end and allows for a full reconstruction of the animal. The hollow spines are circumsomal; they were flexible and perhaps moveable in rotary anterior-posterior directions. Possible functions for the hollow spines are discussed. The relationships of E. dufoei to other chitons and to other molluscs and mollusc-like organisms are presented.

American Malacological Bulletin↗
USGS2007

Nucularcidae: A new family of palaeotaxodont Ordovician pelecypods (Mollusca) from North America and Australia

The new Ordovician palaeotaxodont family Nucularcidae and the new genus Nucularca are described. Included in Nucularca are four previously described species that have taxodont dentition: N. cingulata (Ulrich) (the type species), N. pectunculoides (Hall), N. lorrainensis (Foerste), and N. gorensis (Foerste). All four species are of Late Ordovician (Cincinnatian; Katian) age and occur in eastern Canada and the northeastern USA. Ctenodonta borealis Foerste is regarded as a subjective synonym of Nucularca lorrainensis. No new species names are proposed. The Nucularcidae includes the genera Nucularca and Sthenodonta Pojeta and Gilbert-Tomlinson (1977). Sthenodonta occurs in central Australia in rocks of Middle Ordovician (Darriwilian) age. The 12 family group names previously proposed for Ordovician palaeotaxodonts having taxodont dentition are reviewed and evaluated in the Appendix. ?? 2007 NRC Canada.

Canadian Journal of Earth Sciences↗
USGS2007

Dycheia shergoldi, a new genus and species of Late Cambrian Multivalved Mollusc from Oklahoma, USA

A new mollusc from the Upper Cambrian Fort Sill Limestone of Oklahoma, U.S.A. is described. Dycheia shergoldi has at least two types of valves, but the total number of valves is unknown, because the species is known only from disarticulated specimens. The valves show various morphological similarities to Cambrian and Ordovician paleoloricate chelodid chitons, but differ in their lack of apical areas. D. shergoldi is assigned with question to the Polyplacophora.

Oklahoma↗
USGS2003

Echinochiton dufoei, a new spiny Ordovician chiton

Echinochiton dufoei new genus and species is described from the Ordovician age Forreston Member, Grand Detour Formation (Blackriveran) near Beloit, Wisconsin. For a variety of reasons, we regard E. dufoei as a chiton; the species is known from four articulated or partially articulated specimens, one of which has eight plates and two of which have a mucro on the tail plate. Echinochiton dufoei differs from other chitons in having large hollow spines that project from each of the known plates. In plate shape and position, E. dufoei is much like the Upper Cambrian species Matthevia variabilis Walcott, 1885, and the Lower Ordovician species Chelodes whitehousei Runnegar, Pojeta, Taylor, and Collins (1979).

Wisconsin↗
USGS2003

Shell microstructure of the late Carboniferous rostroconch mollusc Apotocardium lanterna (Branson, 1965)

The Late Carboniferous bransoniid conocardioidean Apotocardium lanterna ( Branson, 1965 ) had an entirely aragonitic shell with a finely prismatic outer shell layer, a predominantly crossed lamellar to complex crossed lamellar middle shell layer, and an “inner” shell layer of finely textured porcelaneous and/or matted structure. This “inner” layer is probably homologous with the inner part of the middle shell layer and the inner layer sensu stricto of bivalved molluscs. Shell morphological and microstructural convergences between conocardioids and living heart cockles suggest that at least some conocardioids may have farmed algal endosymbionts in their posterior mantle margins. This symbiosis may have helped conocardioids compete with the biomechanically more efficient bivalves during the latter part of the Paleozoic.

Journal of Paleontology↗
USGS2000

Cambrian Pelecypoda (Mollusca)

The record of Cambrian bivalved organisms that have been placed in the Mollusca includes undoubted pelecypods and other bivalved shells. This record is reviewed herein. Additional topotype material of Delgado's (1904, Communicacoes da Commissao do Servico Geologico de Portugal 5:307-374) Lower Cambrian specimens from Portugal shows that they are distorted brachiopods. Restudy of Zhang's (1980a, Bulletin Chinese Academy of Geological Sciences, Series 8, 1:1-19; 1980b, 26th International Geological Congress 4:121-129) type specimens from the Lower Cambrian of China shows that most of them are also brachiopods. New specimens of Tuarangia MacKinnon indicate that this genus is a Middle-Upper Cambrian pelecypod.

American Malacological Bulletin↗
USGS1980

New evidence for the age of the Quantico Formation of Virginia

A new fossil locality within the Quantico Formation of the Virginia Piedmont in Dale City, Virginia, about 40 km south of Washington, D.C., has yielded crinoids and a cephalopod that re-establishes an age younger than Cambrian for this formation. On the basis of regional considerations and the work of investigators in the early 1900s, an Ordovician age for the Quantico seems likely. Also, the Dale City pluton is not intrusive into the Quantico but is unconformable beneath it. Hence, the 560-m.y. zircon age for the Dale City pluton is no longer inconsistent with the temporal and stratigraphic relationships established for the stratigraphic units in the area. © 1980 Geological Society of America.

Virginia↗
USGS1974

Molluscan phylogeny: The paleontological viewpoint

Stasek theorized that the extant mollusks are the progeny of three separate lineages that separated before the phylum was well established. He wrote that no known intermediate forms, fossil or living, bridge the "enormous gaps between any two of the three lineages," and therefore treated each as a separate subphylum. These subphyla are (i) the subphylum Aculifera Hatscheck 1891, containing only the class Aplacophora, derived from the most primitive ancestors of the Mollusca; (ii) the subphylum Placophora von Jhering 1876, containing only the class Polyplacophora, and emphasizing the pseudometamerism of its more advanced premollusk ancestor; and (iii) the subphylum Conchifera Gegenbaur 1878, containing the Monoplacophora and the other classes derived from it. We point out that the Polyplacophora may be derived from the Monoplacophora instead of a more primitive ancestral stock. We also suggest that the Conchifera can be separated into two major lineages, each worthy of the rank of subphylum. The fossil record indicates that the Monoplacophora gave rise to the Gastropoda, Cephalopoda, Rostroconchia, and possibly Polyplacophora, and that the Pelecypoda and Scaphopoda are derived from the Rostroconchia. These last three classes thus form a lineage that diverged from the Monoplacophora in the Early Cambrian. They emphasized a shell form that in all groups is primitively open at both ends, allowing the gut to remain relatively straight, with an anterior mouth and posterior anus. They became burrowing (infaunal) deposit or filter feeders. We coin the term Diasoma (through-body) for the subphylum containing these three classes (Rostroconchia, Pelecypoda, and Scaphopoda). The remaining three classes (Monoplacophora, Gastropoda, and Cephalopoda) emphasize a conical univalved shell, usually twisted into a spiral. The relatively small single aperture forces the anus to lie close to the mouth, and the gut is bent into a "U." Most are surface-dwelling (epifaunal) grazers or carnivores. We coin the name Cyrtosoma (hunchback-body) for the subphylum containing these three classes. Strictly speaking, the cyrtosomes are the ancestors of the diasomes but, in fact, both subphyla appeared and began to diversify within a few million years in the Early Cambrian.

Science↗
USGS1973

Fordilla troyensis Barrande: The oldest known pelecypod

Specimens of the small bivalved animal Fordilla troyensis Barrande from New York State show that this fossil is the oldest known pelecypod mollusk and not a conchostracan arthropod. This finding extends the range of the class Pelecypoda backward in time from the Early Ordovician (about 495 million years ago) to the Early Cambrian (about 540 to 570 million years ago). The morphology of Fordilla troyensis suggests that it lived infaunally and that it was ancestral to the pelecypod subclasses Heteroconchia and Isofilibranchia.

New York↗
USGS1972

Rostroconchia: A new class of bivalved mollusks

Four Paleozoic bivalved genera are assigned to the new molluscan class Rostroconchia: Eopteria, Euchasma, Conocardium , and Pseudoconocardium . These mollusks have an uncoiled univalved larval shell; an untorted bivalved adult shell; no hinge teeth, ligament, or adductor muscles; and a fused, almost inflexible. hinge. Rostroconchians developed separately from the pelecypods through the ribeirioids, but are regarded as more closely related to the Pelecypoda and Scaphopoda than to other known classes of mollusks.

Science↗