Low Taxonomic Diversity Research Articles

Decoupling of taxonomic diversity and morphological disparity during decline of the Cambrian trilobite family Pterocephaliidae

Although discordance between taxonomic diversity and morphological disparity is common, little is known about the underlying dynamics that drive this decoupling. Early in the history of the Cambrian trilobite family Pterocephaliidae, there was an increase in taxonomic diversity and morphological diversity. As taxonomic diversity declined in the later history of the clade, range of variation stayed high and disparity continued to increase. However, per-branch rates of morphological evolution estimated from a recent phylogeny decreased with time. Neither within-trait nor within-species variation increased or decreased, suggesting that the declining rates of morphological evolution were more likely related to ecological opportunity or niche partitioning, rather than increasing intrinsic constraints. This is further supported by evidence for increased biofacies associations throughout the time period. Thus, the high disparity seen at low taxonomic diversity late in the history of this clade was due to extinction - either random or targeting mean forms - rather than increased rates of morphological evolution. This pattern also provides a scenario that could account for instances of low taxonomic diversity but high morphological disparity in modern groups.

Subgingival microbiome in smokers and non‐smokers in periodontitis: an exploratory study using traditional targeted techniques and a next‐generation sequencing

To compare the results of two targeted techniques to an open-ended technique in periodontitis patients, differentiated on the basis of smoking habit. Thirty periodontitis patients (15 smokers and 15 non-smokers) provided subgingival plaque samples for 16S rRNA gene amplicon sequencing, culturing and quantitative polymerase chain reaction (qPCR). No differences were found in the composition of the subgingival microbiome between smokers and non-smokers with culture and qPCR. With pyrosequencing, operational taxonomic units (OTUs) classified to genera Fusobacterium, Prevotella and Selenomonas were more abundant in smokers, while OTUs belonging to the genera Peptococcus and Capnocytophaga were more abundant in non-smokers. Principal coordinate analysis identified two clusters; one was composed mainly of smokers (80%) and revealed significantly lower taxonomic diversity, higher attachment loss and higher proportion of the genera Fusobacterium, Paludibacter and Desulfobubus. In periodontitis, there is a difference in the composition of the subgingival microbiome between smokers and non-smokers, as revealed by pyrosequencing. This difference was not identified by the targeted techniques. Low taxonomic diversity was associated with higher disease severity, especially in smokers. This supports the hypothesis of the ecological microbial-host interaction in the severity of periodontal disease.

Multiple routes to mass accumulations of clypeasteroid echinoids: A comparative analysis of Miocene echinoid beds of Sardinia

Although clypeasteroid echinoids are very common in the shallow water sediments of the Miocene of Sardinia, they have received little attention as far as their origin is concerned. In this paper, three sand dollar dominated mass accumulations from the Lower Miocene of Sardinia are studied and compared in order to understand their genesis and palaeoecology. Two clypeasteroid assemblages were found in the Sarcidano region (Central Sardinia) within the Nurallao Formation (Late Oligocene–Burdigalian). The third sand dollar mass occurrence crops out in the Logudoro region (northern Sardinia) within the Calcari di Mores Formation (Late Burdigalian). These fossil echinoid deposits show a low taxonomic diversity; two assemblages are dominated by the genus Amphiope while the other is dominated by Parascutella with subordinate Clypeaster. An integrated stratigraphic, taphonomic and sedimentological approach allows different genetic mechanisms for these shallow water, sandy, shoreface deposits to be inferred. The origin of these deposits is related to ecological, morphological and sedimentological factors. The sand dollars of Cuccuru Tuvullao (Nuragus) show high degrees of abrasion and fragmentation and represent a multiple in situ reworked accumulation while the assemblage of Duidduru (Genoni), with low abrasion and variously oriented complete and fragmented specimens constitutes an example of a proximal storm deposits. The sand dollar bed of Monte Sa Loca (Chiaramonti) consists of a dense accumulation of well-preserved, mainly concordant-oriented, juvenile and adult specimens and is considered to represent an autochthonous assemblage. This paper explores the role of detailed sedimentological and taphonomic analysis in the palaeoecological and genetic interpretations of the sand dollar beds and points out the widespread distribution and diversification of these echinoids in the Miocene deposits of the Mediterranean area.

The urban ecology of Iron Age Tel Megiddo: using microvertebrate remains as ancient bio-indicators

The potential of microvertebrate remains for reconstructing the paleoecology of urban sites remains largely untapped except for extensive research carried out at Roman and medieval sites in Britain. We apply taphonomic and ecological approaches to analyzing an assemblage of microvertebrate remains from the Iron Age IIA of Tel Megiddo, Israel. Sampling in a dense residential area including house floors and various fills produced 1080 identifiable specimens including fish, mammal, reptile and bird remains. The mammalian remains show a number of distinct patterns pointing to accumulation from the community of small animals which lived and died on-site. These patterns include evidence for fragmentation due to trampling and presence of burned specimens. The mammalian remains also differed in their taphonomy from an assemblage from Early Bronze Age II Megiddo which originated from predator accumulation during a period of abandonment. These analyses point to an especially low taxonomic diversity in the Iron Age residential assemblage suggesting that the urban environment of Megiddo supported a unique community of small mammalian animals. This differs markedly from ecological conditions in modern day cities which in some cases show greater than background levels of diversity and suggests a dense, homogenous urban environment. We suggest that reconstructing the evolution of urban fauna in greater detail will provide a sensitive tool for tracing historical processes of growth, decline and increasing complexity of urban sites in the Near East as well as other regions of the world.

Composition and Seasonal Variation of Rhipicephalus turanicus and Rhipicephalus sanguineus Bacterial Communities

A 16S rRNA gene approach, including 454 pyrosequencing and quantitative PCR (qPCR), was used to describe the bacterial community in Rhipicephalus turanicus and to evaluate the dynamics of key bacterial tenants of adult ticks during the active questing season. The bacterial community structure of Rh. turanicus was characterized by high dominance of Coxiella and Rickettsia and extremely low taxonomic diversity. Parallel diagnostic PCR further revealed a novel Coxiella species which was present and numerically dominant in all individual ticks tested (n = 187). Coxiella sp. densities were significantly higher in female versus male ticks and were overall stable throughout the questing season. In addition, we revealed the presence of the novel Coxiella sp. in Rh. sanguineus adult ticks, eggs, and hatched larvae, indicating its vertical transmission. The presence of both spotted fever group Rickettsia spp. (SFGR) and non-SFGR was verified in the various individual ticks. The prevalence and density of Rickettsia spp. were very low compared to those of Coxiella sp. Furthermore, Rickettsia sp. densities were similar in males and females and significantly declined toward the end of the questing season. No correlation was found between Coxiella sp. and Rickettsia sp. densities. These results suggest different control mechanisms in the tick over its different bacterial populations and point to an obligatory and facultative association between the two tick species and Coxiella sp. and Rickettsia spp., respectively.

海草场生态系统及其修复研究进展

海草场生态系统及其修复研究进展

Differential Extinction and the Contrasting Structure of Polar Marine Faunas

BackgroundThe low taxonomic diversity of polar marine faunas today reflects both the failure of clades to colonize or diversify in high latitudes and regional extinctions of once-present clades. However, simple models of polar evolution are made difficult by the strikingly different faunal compositions and community structures of the two poles.Methodology/Principal FindingsA comparison of early Cenozoic Arctic and Antarctic bivalve faunas with modern ones, within the framework of a molecular phylogeny, shows that while Arctic losses were randomly distributed across the tree, Antarctic losses were significantly concentrated in more derived families, resulting in communities dominated by basal lineages. Potential mechanisms for the phylogenetic structure to Antarctic extinctions include continental isolation, changes in primary productivity leading to turnover of both predators and prey, and the effect of glaciation on shelf habitats.Conclusions/SignificanceThese results show that phylogenetic consequences of past extinctions can vary substantially among regions and thus shape regional faunal structures, even when due to similar drivers, here global cooling, and provide the first phylogenetic support for the “retrograde” hypothesis of Antarctic faunal evolution.

Response of biota to land use changes and water quality degradation in two medium-sized river basins in southwestern Greece

Abstract To assess biotic responses to anthropogenic pressures, a seasonal monitoring of benthic macroinvertebrates, physicochemical and hydromorphological parameters has been applied in 11 sites along two highly impacted river basins in southwestern Greece, mainly during the year 2006. In the first river basin, the upper reaches were covered by thick riparian forest, replaced by intensive agriculture and livestock in the mid-reaches, while the lower parts were characterized mainly by agroindustrial activities. The second river basin was impacted by the discharge of raw cheese whey effluents in the mid-reaches, while the lower parts were protected by thick riparian vegetation. The mid- and lower parts of the first river basin (Peiros–Parapeiros rivers) were impaired by dam constructions, agricultural intensity and urbanization. In the second river basin (Vouraikos river), the 3/5 of the river length, located in the mid-reaches, was degraded due to the discharge of untreated cheese whey effluents. Water quality of the lower reaches was highly recovered due to the presence of thick riparian vegetation. Macroinvertebrate diversity was strongly correlated to pollution, as sites with major physicochemical and hydromorphological degradation presented low taxonomic richness and diversity values, while non-impacted sites were characterized by a considerable presence of E.P.T. taxa and higher diversity. The current study indicates the significant impact of land use changes to the water quality, which consequently influence the distribution of biota, pointing out the critical role of the riparian vegetation to the detoxification of surface waters.

Non-native Ecosystem Engineer Alters Estuarine Communities

Many ecosystems are created by the presence of ecosystem engineers that play an important role in determining species' abundance and species composition. Additionally, a mosaic environment of engineered and non-engineered habitats has been shown to increase biodiversity. Non-native ecosystem engineers can be introduced into environments that do not contain or have lost species that form biogenic habitat, resulting in dramatic impacts upon native communities. Yet, little is known about how non-native ecosystem engineers interact with natives and other non-natives already present in the environment, specifically whether non-native ecosystem engineers facilitate other non-natives, and whether they increase habitat heterogeneity and alter the diversity, abundance, and distribution of benthic species. Through sampling and experimental removal of reefs, we examine the effects of a non-native reef-building tubeworm, Ficopomatus enigmaticus, on community composition in the central Californian estuary, Elkhorn Slough. Tubeworm reefs host significantly greater abundances of many non-native polychaetes and amphipods, particularly the amphipods Monocorophium insidiosum and Melita nitida, compared to nearby mudflats. Infaunal assemblages under F. enigmaticus reefs and around reef's edges show very low abundance and taxonomic diversity. Once reefs are removed, the newly exposed mudflat is colonized by opportunistic non-native species, such as M. insidiosum and the polychaete Streblospio benedicti, making removal of reefs a questionable strategy for control. These results show that provision of habitat by a non-native ecosystem engineer may be a mechanism for invasional meltdown in Elkhorn Slough, and that reefs increase spatial heterogeneity in the abundance and composition of benthic communities.

Ectomycorrhizal fungal community of naturally regenerated Pinus thunbergii seedlings in a coastal pine forest

To add to knowledge of ectomycorrhizal (ECM) community structure on the roots of Pinus thunbergii seedlings in a Japanese coastal forest, we sampled naturally regenerated current-year and 1- to 5-year-old seedlings. We classified the 667 root tips on current-year seedlings and the 1,927 root tips on older seedlings into 13 phylotypes based on morphological and genetic analyses. Cenococcum geophilum, members of the families Clavulinaceae, Russulaceae, or Thelephoraceae or the genus Trichophaea, were indicated to be fungi forming P. thunbergii ectomycorrhizas. Among them, C. geophilum and Clavulinaceae sp. 1 were the most or second most dominant species. A species accumulation curve based on the number of samples nearly reached a plateau, with observed species richness equal to 11 species and the Jackknife2 and Chao2 richness estimators indicating 14 and 12 species, respectively. In addition, Simpson's 1/D was 3.89 and Shannon–Wiener's H′ was 1.71, indicating a relatively low taxonomic diversity. There was no significant difference in the ectomycorrhizal formation rate, or the occurrence frequency and the number of ECM phylotypes between current-year and older seedlings. These results indicated that less diverse fungi were involved in ectomycorrhizal formation on coastal pine seedlings compared with those in comparable inland forests in the study area.

Silicified Anisian (Middle Triassic) Spiriferinid Brachiopods from Guizhou, South China

A newly discovered silicified brachiopod interval from the Upper Member of the Guanling Formation (Late Anisian, Middle Triassic) in Guizhou Province (South China) is described for the first time. The most remarkable feature of this brachiopod assemblage, besides the very good preservation, is the very low taxonomic evenness and diversity. This impoverished, low diversity/high density assemblage is represented by more than 700 recovered specimens belonging to three species within two spiriferinid genera (Pseudospiriferina multicostata, P. pinguis, and Punctospirella fragilis). It is characterized by the overwhelming abundance of an endemic spiriferinid species, P. multicostata, which contributes to more than 90% of the community. Silicified valves of P. multicostata and Punctospirella fragilis allow detailed descriptions of the internal morphology based on direct observation. Brachiopod paleoecology, assessed by considering host-rock lithology, shell disarticulation, and shell size suggests that this ende...

Why is there discordant diversity in sengi (Mammalia: Afrotheria: Macroscelidea) taxonomy and ecology?

AbstractThe seventeen species of sengis or elephant‐shrews form a well‐defined clade of mammals endemic to Africa that occupy the extremes of terrestrial habitats, from coastal deserts to montane forests. Because of their isolation on Africa soon after the break‐up of Gondwanaland, theoretically sengis initially evolved with little competition from other placental radiations. Their life history features include myrmecophagy, saltatorial gaits, no or limited use of nests, social monogamy, small litters of precocial young and absentee maternal care of neonates. These traits together are unique to the Macroscelidea and represent a wedding of features usually associated with either small antelopes or anteaters. Combined, these features define an adaptive syndrome that presumably has been relatively immune to competition from contemporary mammals, partially due to phylogenetic inertia. Yet paradoxically, the syndrome is well suited to a wide range of terrestrial habitats, resulting in low taxonomic diversity. Because of their unusual phylogeny and low species diversity, conservation interest is high for those sengis with relatively low densities in fragmented forests.

Late Neogene paleoclimate and paleoenvironment reconstructions from the Pipe Creek Sinkhole, Indiana, USA

The Late Neogene represents warm Earth conditions immediately prior to the development of extensive northern hemisphere glaciation, and this period in Earth history may therefore provide the best available analog for the projected outcome of continued global warming. There are few interior continental sites of Late Neogene age from the eastern half of North America and subsequently very little is known about the conditions characterizing climate. The Early Pliocene (~ 5 Ma) Pipe Creek Sinkhole (PCS) includes the sediment fill of a complex karst environment that developed in north-central Indiana, USA (Lat. 40° 27′ 25.4″, Long. 85° 47′ 37.2″). The site includes more than 3 m of high-chroma, red-colored silty-clay sediment interpreted to be terra rossa. The terra rossa δ 13C values average − 20 ± 0.7‰ PDB and are interpreted to represent sediment deposited in a closed cave system under high summer temperatures and with well-drained soils. An in-situ paleosol at the top of the terra rossa represents a transition from a closed cave to an open environment that eventually flooded, thereby becoming a small pond. δ 13C values from lacustrine sediments with organic matter derived dominantly from algae average − 20.6‰ and suggest the pond was stagnant and enriched with bicarbonate from the underlying limestones or via aquifers. Pond sediments include abundant vertebrate fossils, which are broadly consistent with those inhabiting an open ecosystem such as a savannah or parkland. However, the PCS pollen includes low taxonomic diversity that is dominated by pine with some hickory and flowering plants, but no grass pollen. We propose two hypotheses to explain the PCS stratigraphic record: (1) The pollen assemblage may represent a local pine dominated ecosystem associated with the pond paleoenvironment, such as a riparian community, and that the greater landscape was drier and open; (2) Alternatively, the climate may have became wetter raising the elevation of the groundwater table and initiating the formation of the pond. Then in response to the wetter conditions an early succession forest ecosystem developed.

The palynology of the Hannibal Shale (Mississippian) of Northeastern Missouri, U.S.A. and correlation with Western Europe

Mississippian palynomorphs have been recovered from two successions of the Hannibal Shale in Missouri, U.S.A., which is the lowermost Carboniferous unit in the Mississippi Valley. The assemblages are dominated by acanthomorph acritarchs, with Micrhystridium stellatum being the principal species. The miospore assemblages are well‐preserved and of low taxonomic diversity. They are dominated by long‐ranging taxa that survived the latest Devonian mass extinction event. This assemblage closely resembles assemblages assigned to the Vallatisporites verrucosus‐Retusotriletes incohatus (VI) Biozone of Western Europe. However the assemblage from the Mississippi Valley is relatively impoverished in comparison with European assemblages, and many key European zonal taxa are absent. Independent biostratigraphic correlation suggests that the Hannibal Shale is equivalent to the VIBiozone, the Cristatisporites hibernicus‐ Umbonatisporites distinctus (HD) Biozone, and possibly the lowermost part of the Spelaeotriletes balteatus‐Rugospora polyptycha (BP) Biozone in Europe. This indicates the relatively condensed nature of the succession. Palynofacies analysis suggests a shelf to basin depositional environment for the Hannibal Shale; this is consistent with the paleogeographic location of this area during the Early Carboniferous.

Early Anisian (Triassic) foraminifers from the Hiraki Formation of the Maizuru Terrane in the Tatsuno-Aioi area, Hyogo Prefecture, Japan

The Maizuru Terrane in the Tatsuno-Aioi area, Hyogo Prefecture is composed of the Upper Permian Tatsuno Formation and the Middle Triassic Hiraki Formation, besides the Yakuno Complex. Both formations are redefined based on fossil evidence from the limestone. They are correlatable to the Middle and Upper formations of the Maizuru Group and the Waruishi Formation of the Yakuno Group in the type area, respectively. The Hiraki Formation consists mostly of mudstone and sandstone and contains limestone blocks less than 20 m in longer diameter in three horizons. Limestones consist of bioclastic oolid grainstone/packstone with many detrital quartz grains, and arrange irregularly regardless the general stratification of the formation. Mode of occurrence and lithologic characters of limestone blocks of the Hiraki Formation are closely similar to those of the Kaizawa Formation and Tanoura Formation. Eight species of foraminifers including Meandrospira dinarica and M. pusilla are identified from limestone blocks of the Hiraki Formation. Taxonomic diversity of the Hiraki foraminiferal fauna is exceedingly low in comparison with the Kaizawa and the Tanoura faunas. Along with low taxonomic diversity, absence of Pilammina densa and involutinid foraminifers, which are characteristic in Kaizawa, Tanura and other late Anisian (Pelsonian and Illyrian) faunas, suggests early Anisian age (Aegean) of the Hiraki fauna.

THE PALYNOLOGY OF THE HANNIBAL SHALE (MISSISSIPPIAN) OF NORTHEASTERN MISSOURI, U.S.A. AND CORRELATION WITH WESTERN EUROPE

Abstract Mississippian palynomorphs have been recovered from two successions of the Hannibal Shale in Missouri, U.S.A., which is the lowermost Carboniferous unit in the Mississippi Valley. The assemblages are dominated by acanthomorph acritarchs, with Micrhystridium stellatum being the principal species. The miospore assemblages are well-preserved and of low taxonomic diversity. They are dominated by long-ranging taxa that survived the latest Devonian mass extinction event. This assemblage closely resembles assemblages assigned to the Vallatisporites verrucosus-Retusotriletes incohatus (VI) Biozone of Western Europe. However the assemblage from the Mississippi Valley is relatively impoverished in comparison with European assemblages, and many key European zonal taxa are absent. Independent biostratigraphic correlation suggests that the Hannibal Shale is equivalent to the VI Biozone, the Cristatisporites hibernicus-Umbonatisporites distinctus (HD) Biozone, and possibly the lowermost part of the Spelaeotril...

How and why did the Lingulidae (Brachiopoda) not only survive the end-Permian mass extinction but also thrive in its aftermath?

The end-Permian mass extinction devastated most of the organisms in the sea and on land. However, a few Late Permian taxa survived the mass extinction and also the subsequent Early Triassic post-extinction catastrophic environments. Among them, the Lingulidae brachiopods were perhaps one of the most noted conquerors. Not only had they survived the mass extinction, but also they thrived in the Early Triassic marine realm, forming a nearly globally distributed Lingulidae fauna characterized by low taxonomic diversity but high abundance of individuals. The reasons that this group of brachiopods was able to achieve this remain unclear, and could possibly include a number of interacting factors. Among them are their wide ecological adaptations and their shell composition and appearance. The long-term evolutionary trends in the shell microstructure and exterior of the Lingulidae since the Late Devonian are thought to have advanced considerably by the end-Permian to the extent that the shells of the brachiopods were able to sustain stressful (e.g. anoxic) environments. In addition, a variety of short-term adaptive changes in the shell size (reducing shell size), shape (shells became more pointed and flatter anteriorly), and thickness (reducing shell thickness) are believed to have also aided the survival of the brachiopods through the highly toxic marine environments from the latest Permian to the Early Triassic. The long-term unchanged organophosphatic shell composition of Lingulidae brachiopods is considered to be another key feature that must have aided the survival of this group in the end-Permian to the Early Triassic Period, for organophosphatic shell composition would have prevented the brachiopods from dissolution in the highly acidic marine environment prevailing globally during the Permian–Triassic transition. The ability that the lingulids had to live in a wide range of environmental conditions, from high-latitude to low-latitude and from the shoreface to the relatively deep sea environments, is also considered vital for the group to have managed to survive the catastrophic event in the latest Permian and then thrive in the vacated ecological space in the ensuing Early Triassic disaster period.

Taphonomic analysis of skeletal remains from chimpanzee hunts at Ngogo, Kibale National Park, Uganda

This study provides a taphonomic analysis of the largest known sample of bone fragments collected from chimpanzee hunts. The entire sample consists of 455 bone fragments from 57 chimpanzee hunting episodes of 65 prey individuals at Ngogo, Kibale National Park, Uganda. It has low taxonomic diversity, consisting overwhelmingly of primates, especially red colobus monkeys. The age distribution of the prey remains is skewed towards pre-adults. Cranial bones are the dominant element, followed by long bones. Axial postcranial elements have low survivorship, with a complete absence of pre-caudal vertebrae. Bone is damaged in distinct ways, such as: destruction of long bone ends, typically with intact but chewed shafts; fragmentation and compression cracking of crania; and preservation of only the iliac blades of the innominates. Tooth marks are present but uncommon (4.4% of total NISP). These analyses enable us to: 1) describe and characterize consistent patterns of bone damage inflicted by chimpanzees across a much larger prey sample than has been previously studied; 2) make a preliminary comparison of the generalized chimpanzee taphonomic signature to that of leopard and eagle consumption of primates, as well as modern human consumption of small mammals; and 3) assess the utility of such samples for recognition of early hominin small mammal carnivory. We present a model that may be useful for detecting a pre-technological hominin carnivory and suggest some fossil locales at which close inspection of cercopithecoid remains for the above patterns might reveal traces of hominin hunting, though we caution that a pre-technological hominin hunted “assemblage” is not likely to be archaeologically visible.

Fossilized embryos are widespread but the record is temporally and taxonomically biased

We report new discoveries of embryos and egg capsules from the Lower Cambrian of Siberia, Middle Cambrian of Australia and Lower Ordovician of North America. Together with existing records, embryos have now been recorded from four of the seven continents. However, the new discoveries highlight secular and systematic biases in the fossil record of embryonic stages. The temporal window within which the embryos and egg capsules are found is of relatively short duration; it ends in the Early Ordovician and is roughly coincident with that of typical "Orsten"-type faunas. The reduced occurrence of such fossils has been attributed to reducing levels of phosphate in marine waters during the early Paleozoic, but may also be owing to the increasing depth of sediment mixing by infaunal metazoans. Furthermore, most records younger than the earliest Cambrian are of a single kind-large eggs and embryos of the priapulid-like scalidophoran Markuelia. We explore alternative explanations for the low taxonomic diversity of embryos recovered thus far, including sampling, size, anatomy, ecology, and environment, concluding that the preponderance of Markuelia embryos is due to its precocious development of cuticle at an embryonic stage, predisposing it to preservation through action as a substrate on which microbially mediated precipitation of authigenic calcium phosphate may occur. The fossil record of embryos may be limited to a late Neoproterozoic to early Ordovician snapshot that is subject to dramatic systematic bias. Together, these biases must be considered seriously in attempts to use the fossil record to arbitrate between hypotheses of developmental and life history evolution implicated in the origin of metazoan clades.

DICKINSARTELLA FAUNA FROM THE SAIWAN FORMATION (OMAN): A BIVALVE FAUNA TESTIFYING TO THE LATE SAKMARIAN (EARLY PERMIAN) CLIMATIC AMELIORATION ALONG THE NORTH-EASTERN GONDWANAN FRINGE.

The transitional faunas of the Permian Huqf succession of Oman make it one of the key-sections for the intercalibration of Early to Middle Permian biostratigraphical scales. The abundance of fossils improved the knowledge of some marine faunas which populated the North-Eastern Gondwanan fringe during times of climatic changes in the Permian. A Sterlitamakian (upper Sakmarian, Lower Permian) bivalve from the Saiwan Formation in the Huqf area, informally named Dickinsartella Fauna, is described in the present paper. The specimens examined were collected from the Pachycyrtella (Auctorum), the basal of the Formation in its type locality. The Dickinsartella Fauna can be identified for the presence of the new genus Dickinsartella , which dominates the bivalve thanatocoenosis with D. pistacina sp. n. (type species). The bivalve from the Pachycyrtella Bed includes the new species Stutchburia sangallii and Promytilus mazzolenii, and also Astartella obliqua Dickins, 1963, Nuculopsis cf. bangarraensis Dickins, 1963, ? Oriocrassatella sp., and indeterminable aviculopectinids. This shows a low taxonomic diversity. Nevertheless, some species are represented by a high number of generally well-preserved specimens, i.e. some specimens of S. sangallii sp. n. and A. obliqua show part of the ligament. The good preservation of the shells permitted the microstructural analysis of D. pistacina sp. n. and S. sangallii sp. n. The microstructure of S. sangallii sp. n. supports the close phylogenetical link between modiomorphids and crassatelloids recognized by some previous authors. The new genus Dickinsartella includes the more recent species belonging to the important Paleozoic Order Cyrtodontida Scarlato & Starobogatov, 1971. The discovery of Dickinsartella gen. n. and other taxa of the Pachycyrtella Bed, present also in the Sakmarian levels of the Carnarvon and Perth Basins in Western Australia, indicates a wider distribution of the Dickinsartella Fauna and confirms the correlation between Arabian and Australian series already remarked by previous authors. The Dickinsartella fauna is the first bivalve testifying to the climatic amelioration gradually affecting the North-Eastern Gondwanan fringe at the end of the Early Permian glacial events. This pioneer spread out, probably in a cool-temperate climate, on the substrate provided by the mid-Sakmarian (basal Sterlitamakian) transgression, connected with the final stages of the Gondwanan deglaciation and/or with initial sea-floor spreading in the Neotethys. In the present paper some remarks on the autecology of the new species from the Pachycyrtella bed are also discussed.