Permian Bivalves Research Articles

The role of taphonomy in cladistic analysis: A case study in Permian bivalves.

The Megadesmidae (Bivalvia, Anomalodesmata) fossil record was examined in order to assess the role of taphonomy in cladistic analysis. Megadesmids are thick-shelled, infaunal, suspension-feeding bivalves. Our data indicate that their fossil record seems biased in favor of thick-shelled, shallow-burrowing genera and/or deep­burrowing forms. Consequently, there is a relation between the mode of life (shallow versus deep) and the resolution and quality of the fossil record. Deep-burrowers (Vacunella) are often preserved in life position offering a more accurate (temporal and spatial) fossil record, adequate for paleoecological inferences, while shallow-burrower shells (Plesiocyprinella), that are more prone to post-mortem transport and temporal mixing, offer a record with poor spatial and temporal resolution. The identification of homoplasy among infauna! bivalves constitutes a major challenge for their cladistic analysis. Within Megadesmidae intrinsic (bauplan limitations) and extrinsic (better preservational potential) factors favor the occurrence and preservation of homoplasy among the deep-burrowers. The implications are: a) clustering of deep-burrowing bivalves (Vacunella, Roxoa) due to parallel homoplasies, forming "adaptive", not necessarily "evolutive" taxa, and b) lower consistency indices in their cladistic analysis.

Permian Bivalves of the Pronchishchev Ridge (North Siberia): New Data on Taxonomic Composition, Biostratigraphy, and Biogeographic Relationships

Permian Bivalves of the Pronchishchev Ridge (North Siberia): New Data on Taxonomic Composition, Biostratigraphy, and Biogeographic Relationships

New Data on Permian Bivalves and the Age of the Volcanogenic Beds of the Arman-Viliga Folded Zone, Northeastern Asia

Taxonomic data on Permian bivalve mollusks and the structure of the middle part of essentially volcanogenic section on the Nyavlenga River in the northeastern Okhotsk Region, Armano-Viliga Folded Zone are reported for the first time. Fossil fauna is composed exclusively of Inoceramus-like bivalves of the genera Kolymia, Cigarella, Okhotodesma, and Maitaia, which frequently form shell rocks and date the Bocharian Horizon (upper part of the Wordian Stage) as the Middle Permian. Lithologic and paleontological characteristics of the beds are considered; it is shown that volcanites are widespread; turbidites and diamictites similar to those previously investigated in the Okhotsk and Ayan-Yuryakh basins are recorded. Permian kolymiids are figured.

Paleoecology and paleoenvironments of Permian bivalves of the Serra Alta Formation, Brazil: Ordinary suspension feeders or Late Paleozoic Gondwana seep organisms?

This is the first record of a Permian seep deposit and an associated, morphologically bizarre, bivalve-dominated fauna from the Passa Dois Group, Paraná Basin, Brazil. Shales of the outer-shelf facies of the Serra Alta Formation preserve a low-diversity but high-abundant, large-sized bivalve fauna with unusual morphologies inside discoidal carbonate concretions. The bivalves are about ten times larger than tiny bivalves found scattered in laterally equivalent mudstones of the same unit. Intercalated between two concretion-bearing horizons, a cm-thick, sheet-like, disrupted, “brecciated”, partially silicified carbonate layer with microbially-induced lamination is recorded. In some areas, the carbonate layer shows vertical structures formed by injections of mud mixed with white limestone clasts and microbial linings. Immediately above this, silicified mudstones preserve small domal structures (= mounds) with a slightly depressed center. Monospecific concentrations of closed articulated shells of Tambaquyra camargoi occur at the base of these domes. Carbon-isotope (δ13C) values from the shells, “brecciated” carbonates, and fossil-rich concretions are all depleted (negative values ∼ −6.1 to −7.6‰). Combined taphonomic, sedimentological, petrographic, geochemical and paleontological data suggest that the disrupted, “brecciated” carbonate and associated fauna and domes may have formed by an exudation system. Indeed, this interval of the Serra Alta Formation is ∼8.7 m above the contact with the underlying, oil-rich Irati Formation. This unit has very high total organic carbon (up to 23%) values and high sulphur contents, supporting the interpretation of the lithological and paleontological features as result of seepage of organic compounds at the seafloor. Where the gases and hydrocarbons escaped, the seabed was colonized by, at least facultatively, chemosymbiotic bivalves. The species above belong to a highly endemic group of pachydomids that were shallow infaunal bivalves (SIB). Hence, they are not related to “classical” bivalves with extant representatives, which are chemosymbionts. This may reflect an extreme adaptive radiation and repopulation of anoxic-dysoxic bottoms of the Paraná Basin by SIB species.

The Permian Tiaraju bivalve assemblage, Passa Dois Group, southern Brazil: biostratigraphic and paleobiogeographic significance

ABSTRACT: Permian bivalves of the Paraná Basin evolved in a large inland sea, under conditions of extreme isolation and environmental stress. Although known since 1918, its evolutionary history is still obscure due to the incomplete and biased information on faunal composition and stratigraphic distribution of various assemblages. Hence, the description of the Tiaraju assemblage, the only known bivalve occurrence in the Passa Dois Group from the southernmost Brazil, adds new key information on the composition, biocorrelation and age of this unique molluscan fauna. Terraia falconeri, Cowperesia emerita, Holdhausiella elongata, and Terraia altissima were recorded and described. T. falconeri is the commonest species, followed by C. emerita, H. elongata and T. altissima. The faunule is mainly composed by Terrainae, lacking Pinzonellinae. Assemblage is, thus, poorly diversified, both regarding the faunal composition and guild structure (only infaunal, facultatively motile, unattached, suspension feeders present). Cowperesia emerita and T. altissima strongly indicate biocorrelation with assemblages of the Rio do Rasto and Gai-As formations, Brazil and Namibia, providing an age no younger than the mid-Permian (Wordian-Captianian). On the light of this information, the current geological map of the Tiaraju region, São Gabriel, and the local boundary between the Teresina and Rio do Rasto formations requires reevaluation.

Permian bivalves of the Taciba Formation, Itararé Group, Paraná Basin, and their biostratigraphic significance

A small and poorly diversified bivalve fauna from Taciba Formation, Itarare Group, Parana Basin (State of Santa Catarina, Mafra Municipality), is described in this paper for the first time, based on new findings. The fauna is recorded in a 30 cm thick interval of fine sandstone locally at the top of Taciba Formation, in the Butia quarry. The studied fossil-bearing sandstone bed is a marine intercalation recording a brief eustatic rise in sea-level, probably following glacier retreat and climate amelioration at the end of a broad glacial scenario. The fauna is mainly dominated by productid brachiopods, which are not described here, and rare mollusk shells (bivalves and gastropods). Two bivalve species were identified: Myonia argentinensis (Harrington, 1955), and Aviculopecten multiscalptus (Thomas, 1928). The presence of Myonia argentinensis is noteworthy since this species is also present in the Baitaca assemblage found in marine siltstones (Baitaca assemblage) of the Rio do Sul Formation, cropping out at the Teixeira Soares region, Parana State. This species is also recorded in the bivalve fauna from the Bonete Formation, Pillahinco Group, Sauce Grande Basin, Buenos Aires Province, in Argentina. Hence, the marine bivalves of the Taciba Formation are associated with the transgressive event that characterizes the Eurydesma fauna, indicating a Late Asselian-Sakmarian age for the bivalve fauna. Presence of the Myonia argentinensis megadesmid species reinforces the Gondwanic nature of the studied fauna.

Developmental stages of Permian bivalves of northeast Asia

In the development of Permian bivalves of northeastern Asia, the following five large stages have been recognized: Asselian-Middle Artinskian, Late Artinskian-Kungurian, Roadian-Wordian, Capitanian-Early Wuchiapingian, and Late Wuchiapingian-Changhsingian. The boundaries between stages correspond to great biotic events and frequently display a sharp change in species diversity of bivalves. During the Permian, brachiopods were gradually replaced by bivalves; this was promoted by repeated sharp changes in the environment.

A new permian bivalve (megadesmidae, plesiocyprinellinae) from the serrinha member, Rio do Rasto Formation, Paraná Basin, Brazil

During a recent inspection in the Paleontological Collection of the Institute of Geosciences, University of Sao Paulo, we have identified some specimens of undescribed mollusk bivalves. These called our attention for the following reasons: a) all specimens are internal molds of conjugated and closed articulated valves, some of them presenting fragments of silicified shells; b) all internal molds have similar general shape and internal characters, representing specimens of the same taxon; c) the internal molds and silicified valves are well preserved, including fragile structures, which are hardly preserved, such as the internal mold of the external ligament and muscle scars; d) and equally important, according to the labels of all specimens, they were collected from rocks of the Passa Dois Group (Permian), Serrinha Member of the Rio do Rasto Formation. Although who collected the shells and the precise geographic location of the specimens are still unknown, the detailed study of these fossils brings us to the conclusion that they are morphologically distinct from any heretofore published genus of the endemic fauna of bivalves from Passa Dois Group. Based in its general shape, hinge structure and muscles scars, the new form can be classified under the Family Megadesmidae Vokes, 1967, the most diverse group of Permian bivalves of the Parana Basin. The specimens are referred as Beurlenella elongatella new gen. and sp. The shell shape and taphonomy indicate that this bivalve was a shallow, rapid, active burrower, suspension feeder, probably preserved in situ, in event deposits.

Permian bivalves from West Spitsbergen, Svalbard Islands, Norway.

Permian bivalves from West Spitsbergen, Svalbard Islands, Norway.

Lower Permian bivalves from central Patagonia, Argentina

The earliest Permian faunal successions of central Patagonia show compositional changes that probably reflected the environmental warming at the end of the Gondwana glaciations. Bivalves of Asselian to probably Early Tastubian age are described. A new genus,Sueroa, is proposed to reunite a previously known species and a new species,Sueroa andreisi n. sp. Another five new species:Parallelodon? quichaurensis n. sp.,Heteropecten cortignasi n. sp.,Etheripecten saraviae n. sp.,Streblopteria montgomeryi n. sp. andPraeundulomya moreli n. sp. are described. Two previously known species:Malimania patagoniensis (Gonzalez) andEuchondria sabattiniae Gonzalez are revised and new occurrences are reported. A further eleven species are described, but they are left in open nomenclature being because they are insufficiently known; these are:Phestia? n. sp.,Modiolus sp.,Palaeoneilo sp.,Stutchburia sp.,Schizodus sp.,Vacunella? sp.,Edmondia sp.,Myonia? n. sp.,Myonia? sp. andPachymyonia? n. sp.

Permian bivalves from the H. S. Lee Formation, Malaysia

Permian bivalves from the H. S. Lee Formation, Malaysia

Permian bivalves from New Zealand

Abstract Some twenty bivalve species are described from the Productus Creek Group, western Southland, and from the Arthurton Group, South Otago. Thirteen species are described for the first time and two new species are proposed, Palaeosolen permiana n.sp. from New Zealand and Parallelodon dickinsi n.sp. from Western Australia. Most of the species are shared with eastern Australia, and a few are also found in Western Australia. Replacement of the shell by chlorite in a number of species suggests that many of the shells were originally composed of a high proportion of aragonite.

Postmortem History of a Permian Pelecypod Assemblage from Wyoming: ABSTRACT

The full understanding of fossils must include consideration of their burial (taphonomy) and subsequent alteration (diagenesis). Analysis of time and mode of burial enhances interpretation of depositional environments. Furthermore, insight into diagenetic changes in fossiliferous rocks may be acquired from studies of physical changes in fossils. Yet these important aspects of the history of fossils commonly are neglected in both paleontologic and petrologic studies. Field and laboratory studies of silicified Permian bivalves in Wyoming have provided a complex case history of one fossil assemblage. These surficial and shallow-burrowing pelecypods commonly are broken and randomly scattered through about 6 in. of calcarenite. Circumstantial evidence suggests that the bottom disturbance was caused by rooting predatory fish. Subsequently, valves were dissolved selectively from hardening sediment not far below the sea bottom. Induration of sediment and removal of buried shells apparently took place during an interruption in sedimentation. At that time burrowers penetrated the bottom and introduced younger quartz sand and fine shell debris into the substrate and into some of the shallowest molds of valves. The infilling produced detrital casts. Unfilled molds then were lined with precipitated fine-grained quartz, chalcedonic laminae, and euhedral quartz crystals, as in geodes. Such silicified fossils are essentially silica casts rather than the result of replacement in the usual sense. Finally, the fossiliferous stratum was buried under a new increment of pebbly, calcareous quartz sand similar to that of the detrital casts below the now-obscure stratigraphic discontinuity. End_of_Article - Last_Page 708------------

Systematics and biology of some desmodont bivalves from the Australian Permian

The Australian Permian bivalves Megadesmus, Astartila, Pyramtis, and Myonia have previously been grouped in either the Family Pachydomidae (Fischer, 1887) or the Family Edmondiidae (King, 1850). Because of similarities in their musculature (in addition to those in dentition, micro‐ornament, and to some extent, shape) they can now be included in the same family as the deep‐burrowing bivalve Vacunella (previously Chaenomya). Vacunella is closely related to the living genus Pholadomya which has existed at least since the Mesozoic, and the two can be placed in the same family — Pholadomyidae (Fleming, 1828). Because of these similarities between Pholadomya, Vacunella, and the “Pachydomidae” it seems likely that the middle and upper Palaeozoic edmondioid bivalves gave rise to the Mesozoic and Cainozoic pholadomyoids, and that these two groups together constitute a major division of the Class Bivalvia — a division that may have been relatively distinct since Ordovician time.