The Jurassic rocks of Gebel Maghara, northern Sinai, Egypt, contain a well-preserved and highly diverse macrobenthic fauna, dominated by bivalves. This fauna, particularly bivalves and gastropods, have received little attention in the... more
The Jurassic rocks of Gebel Maghara, northern Sinai, Egypt, contain a well-preserved and highly diverse macrobenthic fauna, dominated by bivalves. This fauna, particularly bivalves and gastropods, have received little attention in the last 100 years. In an attempt to provide a sound database on the marine bivalve diversity of Egypt during the Jurassic period, a first faunal group, the protobranch bivalves, is reviewed in detail. Sixteen taxa (three of them new), belonging to two orders, five families, and nine genera are systematically described and compared to closely related Jurassic taxa from various locations, particularly in Europe and India. New species are Nuculoma douvillei n. sp., N. sinaiensis n. sp., and Palaeoneilo aegyptiaca n. sp. In addition, Palaeonucula cuneiformis (J. de C. Sowerby), P. muensteri (Goldfuss), Dacryomya diana (d'Orbigny), D. lacryma (J. de. C. Sowerby), and Praesaccella juriana Cox are identified from Jurassic strata of Egypt for the first time. ...
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A diverse molluscan assemblage dominated by turritellid gastropods found in Kachchh, western India, has been interpreted in the past as Late Jurassic (Oxfordian) in age, based on associated undoubtedly Oxfordian ammonites. Recently,... more
A diverse molluscan assemblage dominated by turritellid gastropods found in Kachchh, western India, has been interpreted in the past as Late Jurassic (Oxfordian) in age, based on associated undoubtedly Oxfordian ammonites. Recently, several investigations focused on the assemblage dealing with taxonomic, paleoecological, and evolutionary aspects. An analysis of the associated bivalve fauna, foraminiferal assemblage, and the geological context strongly suggests a Miocene rather than a Jurassic age and invalidates several conclusions drawn from the alleged Jurassic age of the fossils.
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The present study describes and illustrates six bivalve taxa from the Early Bathonian to Early Callovian Ferruginous Oolite Formation and 24 taxa from the Callovian to basal-most Cretaceous Spiti Shale Formation of the Spiti and Zanskar... more
The present study describes and illustrates six bivalve taxa from the Early Bathonian to Early Callovian Ferruginous Oolite Formation and 24 taxa from the Callovian to basal-most Cretaceous Spiti Shale Formation of the Spiti and Zanskar areas in the Indian Himalayas. The Spiti Shale Formation contains a low-diversity bivalve fauna that is concentrated in few horizons, particularly in the lower member of the formation. With few exceptions, the bivalves are poorly preserved. Bivalve taxa recorded by earlier studies are revised wherever possible. Several of the taxa, most of which are from mid- to outer shelf environments, are characteristic of the south-eastern margin of the Neotethys, but some are also closely related to forms occurring in Kachchh, a rift basin situated at the western margin of the Indian Craton.
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Abstract Brachyurans played important ecological and evolutionary roles in the marine benthic communities of the past and were the components of the Mesozoic Decapod Revolution. Therefore, the search for their fossil remains is... more
Abstract Brachyurans played important ecological and evolutionary roles in the marine benthic communities of the past and were the components of the Mesozoic Decapod Revolution. Therefore, the search for their fossil remains is fundamental to understanding the composition, diversity, and ecological structure of Mesozoic marine benthic communities. Brachyuran remains are uncommon in the decapod record of the Aptian Romualdo Formation in the Araripe Basin. In this context, we recorded and described new occurrences of Exucarcinus gonzagai, preserved in shales from the middle portion of the Romualdo Formation, near the city of Jardim in the State of Ceara. Comparisons between these new specimens and former specimens from the Exu locality, State of Pernambuco, including the type material, allowed us to recognize, for the first time, three distinct ontogenetic stages (i.e., informally referred as I, II, and III). Throughout ontogenetic development, the carapace becomes wider and spinier. Stage III carapaces exhibit a large number of grooves, although the grooves are poorly impressed, and some are pitted. Growth also resulted in better-developed orbital lobes and fissures. In addition, the preservation of some anatomical structures is highly influenced by the carapace fossilization process (i.e., molds or cuticles), including the tubercles, grooves, and spines. Unfortunately, those characters that can vary according to ontogenetic development or fossilization are commonly used in the systematic and phylogenetic decisions of the group. Hence, it is advisable to consider these changes whenever possible to avoid the erection of taphotaxons and mistaken phylogenetic decisions.
Research Interests: Geology, Geophysics, Paleontology, Biology, Taphonomy, and 7 morePergamon, Ontogeny, Cretaceous, Aptian, Yixian Formation, Fossilization, and Carapace
The Garedu Red Bed Formation (GRBF) of the northern Tabas Block (Central-East Iranian Microcontinent, CEIM) is a lithologically variable, up to 500-m-thick, predominantly continental unit. It rests gradually or unconformably on marine... more
The Garedu Red Bed Formation (GRBF) of the northern Tabas Block (Central-East Iranian Microcontinent, CEIM) is a lithologically variable, up to 500-m-thick, predominantly continental unit. It rests gradually or unconformably on marine limestones of the Esfandiar Subgroup (Callovian–Oxfordian) and is assigned to the Kimmeridgian–Tithonian. In the lower part, it consists of pebble- to boulder-sized conglomerates/breccias composed of limestone clasts intercalated with calcareous sandstones, litho-/bioclastic rudstones and lacustrine carbonates. Up-section, sharp-based pebbly sandstones and red silt-/fine-grained sandstones of braided river origin predominate. Palaeocurrent data suggest a principal sediment transport from west to east and a lateral interfingering of the GRBF with marine greenish marls of the Korond Formation at the eastern margin of the Tabas Block. Westwards, the GRBF grades into the playa deposits of the Magu Gypsum Formation. Red colours and common calcretes suggest ...
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A Hildoglochiceras-rich horizon is reported from a thin carbonate intercalation within the siliciclastic Upper Jurassic Jhuran Formation of the Jara Dome, western Kachchh Mainland. The Hildoglochiceras specimens have been used for the... more
A Hildoglochiceras-rich horizon is reported from a thin carbonate intercalation within the siliciclastic Upper Jurassic Jhuran Formation of the Jara Dome, western Kachchh Mainland. The Hildoglochiceras specimens have been used for the first population-level study of the genus based on a multivariate analysis. High phenotype instability in the large sample confirms the occurrence of transient forms between morphospecies. Key morphological traits for interpreting Hildoglochiceras are stated, and the morphospecies Hildoglochiceras kobelli (Oppel) and H. kobelliforme (Bonarelli) are interpreted as a dimorphic pair. The ammonite-rich level is interpreted as a Hildoglochiceras Horizon, which is related to a transgressive pulse and maximum flooding zone interrupting largely restrictive conditions for ammonites. The endemic character of Hildoglochiceras is confirmed and related to its environmental restriction to shelf areas on the palaeomargins of the Trans-Erythraean Trough. A comprehensi...
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Middle to Upper Jurassic platform and slope deposits, called Esfandiar Limestone Formation and Qale Dokhtar Formation, respectively are widespread in the Shotori Mountains, east-central Iran and contain minor reef and reefal limestones.... more
Middle to Upper Jurassic platform and slope deposits, called Esfandiar Limestone Formation and Qale Dokhtar Formation, respectively are widespread in the Shotori Mountains, east-central Iran and contain minor reef and reefal limestones. Together with the silty Middle-Upper Jurassic Baghamshah Formation they contain abundant sponges, including hexactinellids, lithistids, demospongids (mainly chaetetids) and calcispongids ("pharetronids"). The following sponge taxa are described in this paper: Endostoma intermedia (Münster), E. perplexa (Quenstedt), E. stellata n. sp., Eudea perforata (Quenstedt), E. maxima n. sp., Pareudea bronni (Münster), P. gemella (Quenstedt), Preperonidella tabasensis n. sp., P. cf. tabasensis, P. sp.1, P. sp. 2, P. sp. 3, Polyendostoma? regularis n. sp., P.? irregularis n. sp., Seriespongia iranica n. gen., n. sp., and Iniquispongia iranica n. gen., n. sp. The most abundant taxon in the collection is Preperonidella represented by several species.
Fifty heterodont bivalve species, belonging to 35 genera, 15 families and six orders, from the Cenomanian–Coniacian Cotinguiba Formation of the Sergipe Basin, north-eastern Brazil, are systematically described and figured. Thirty-three... more
Fifty heterodont bivalve species, belonging to 35 genera, 15 families and six orders, from the Cenomanian–Coniacian Cotinguiba Formation of the Sergipe Basin, north-eastern Brazil, are systematically described and figured. Thirty-three species are recorded from the basin for the first time. The new species Callucina (C.) itaporangensis sp. nov. from the lower Cenomanian is characterised by its heart-shaped to sublanceolate and slightly asymmetric lunule, narrow, shallow and elongated escutcheon, widely spaced commarginal ribs crossed by faint radial striations, rod-like anterior adductor muscle scar (separated ventrally from the pallial line) and straight postero-dorsal and posterior margins with an angular junction. The fauna shows little endemism, which indicates that the larvae were long-lived and possessed a high dispersal potential. The fauna occurred across a wide geographic area, from the Middle East, northern Africa and southern Europe to western Africa and the Pacific rim o...
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A late early Maastrichtian dinosaur trampling site is reported from the Farrokhi Formation of the Khur area, Central Iran. The largely indeterminate footprints, some of which may represent undertracks, can be classified as natural moulds... more
A late early Maastrichtian dinosaur trampling site is reported from the Farrokhi Formation of the Khur area, Central Iran. The largely indeterminate footprints, some of which may represent undertracks, can be classified as natural moulds (i.e. concave epireliefs) bordered by a raised rim of displaced sediment. They reach diameters of up to 0.5 m and were impressed under very shallow to subaerial conditions in an inter- to supratidal environment. Two generations of traces have been imprinted, initially into a soft, fine-grained carbonate sand and afterwards into a superficially hardened substrate that was still plastic underneath; the change in substrate consistency is supported by a conspicuous cracking pattern around the footprints. As a result, hardly any details of the foot morphology of the trackmakers are recorded. Nevertheless, the occurrence improves our knowledge about dinoturbation and its preservation in different kinds of substrates. Furthermore, it is the youngest record...
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The Aldinger Elv Member (Upper Oxfordian) of Milne Land, East Greenland, is a wedge-shaped sand body up to 90 m thick, intercalated between silty shales. The combination of sedimentological, biostratinomic and palaeoecological data... more
The Aldinger Elv Member (Upper Oxfordian) of Milne Land, East Greenland, is a wedge-shaped sand body up to 90 m thick, intercalated between silty shales. The combination of sedimentological, biostratinomic and palaeoecological data allows a detailed reconstruction of the morphology, genesis, and palaeogeography of the bar complex. Sedimentary structures, macrobenthos and trace fossils exhibit a zonation across the sand body. The well-sorted fine-grained sands exhibit sedimentary structures, bioturbation and numerous shell beds. Three macrobenthic associations and four ichnocoenoses are distinguished. The former occur in situ as well as in various stages of reworking. Convex-upward shell pavements were formed by currents, while unsorted shell beds were generated by storms. The sand wedge is interpreted as a shallow offshore sand complex separated from the shore by a broad swale and supplied with sediment from the north along a shoal which extended southwards, while the coastline ...
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The hexactinellid sponge genera Casearia Quenstedt, Caseispongia Quenstedt, and Cypellia Pomel are all morphologically similar and externally annulated. Caseispongia is internally a chambered sponge, like the hypercalcified genus ... more
The hexactinellid sponge genera Casearia Quenstedt, Caseispongia Quenstedt, and Cypellia Pomel are all morphologically similar and externally annulated. Caseispongia is internally a chambered sponge, like the hypercalcified genus Amblysiphonella . The internal construction of almost all externally annulated specimens illustrated as Casearia by Quenstedt and some other authors is not known enough. Despite of this lack of knowledge the genus name Caseispongia is synonymized with Casearia based on observations of Muller and the description of Schmidel. Both genera were described originally from the Upper Jurassic of southern Germany. Hexactinellid sponges, described in this paper, are reported for the first time from the Jurassic of the Shotori Mountains in east-central Iran. The following species are new to science: Casearia tabasensis , Cypellia irregularis , C. cylindrica , and C. tabulata .
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Twenty taxa of ammonites, represented by 53 specimens, are described from three sections of the highly ferruginous Umia Ammonite Beds of western Kachchh, Gujarat. The ammonites are representatives of the families Phylloceratidae,... more
Twenty taxa of ammonites, represented by 53 specimens, are described from three sections of the highly ferruginous Umia Ammonite Beds of western Kachchh, Gujarat. The ammonites are representatives of the families Phylloceratidae, Haploceratidae, Perisphinctidae, Ataxioceratidae, and Berriasellidae and belong to the genera Ptychophylloceras, Holcophylloceras, Hildoglochiceras, Virgatosphinctes, Parapallasiceras, Paraulacosphinctes, Micracanthoceras, and Himalayites. Four ammonite levels can be distinguished. They are, in stratigraphic order, the Hildoglochiceras Horizon, and the Denseplicatus, Microcanthum, and Frequens ammonite zones, and stratigraphically represent the middle Lower to lower Upper Tithonian. The Umia Ammonite Beds are a condensed unit representing the maximum flooding zone of a transgressive-regressive cycle. The degree of condensation varies between the sections: While the four ammonite levels can be differentiated in the Katesar section, they are less clearly deve...
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A palynological study of the Nayband Formation (central eastern Iran) has been carried out in order to review and update its stratigraphic framework. In its type locality the formation crops out on the southern flank of Nayband Mountain,... more
A palynological study of the Nayband Formation (central eastern Iran) has been carried out in order to review and update its stratigraphic framework. In its type locality the formation crops out on the southern flank of Nayband Mountain, about 200 km south of Tabas. It consists of a thick, mixed siliciclastic-carbonate sequence subdivided into four members; in ascending order: the Gelkan Member (mainly shales and silstones), the Bidestan Member (marls, siltstones with minor sandstones and fossiliferous limestones), the Howz-e-Sheikh Member (sandstones and siltstones), and the Howz-e-Khan Member (sponge and coral dominated reefs alternating with marls and sandstones). Three palynological assemblages have been recognised; in ascending order: a) an assemblage characterised by the presence of Annulispora folliculosa and A. microannulata which allows the Gelkan Member and most of the Bidestan Member to be assigned an early Norian age; (b) an assemblage marked by the first occurrence of P...
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A high resolution study of sediments, microfaunas (ostracods and foraminifers), and stable isotopes of ostracod shells from core PRD05, sampled from the Da'ao plain of the Pearl River Delta, provides new data about palaeoenvironmental... more
A high resolution study of sediments, microfaunas (ostracods and foraminifers), and stable isotopes of ostracod shells from core PRD05, sampled from the Da'ao plain of the Pearl River Delta, provides new data about palaeoenvironmental changes during the Late Quaternary. The basal fluvial gravelly sediments of the core, representing the lowest deposits of the Quaternary at the core site, were possibly formed prior to the transgression associated with the last interglacial stage. This fluvial setting changed into a marginal marine setting during the last interglacial stage, any record of calcareous fossils were destroyed by subsequent dissolution during the last glacial phase, when the upper part of the deltaic sediments experienced subaerial oxidation, indicated by a mottled clay layer in the core. The postglacial sea-level rise in the South China Sea began at ~16,700 cal yr B. P. During the first phase of sea-level rise (from ~16,700 to 10,100 cal yr B. P.), a swamp environment ...
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Apart from global sea-level fluctuations, the sedimentary pattern of the northern Tabas Block during the Middle and Late Jurassic was mainly governed by tectonic events of varying intensity and areal extent. These events took place during... more
Apart from global sea-level fluctuations, the sedimentary pattern of the northern Tabas Block during the Middle and Late Jurassic was mainly governed by tectonic events of varying intensity and areal extent. These events took place during the Middle Bajocian (mid-Cimmerian tectonic phase), Early Bathonian, Late Bathonian, Early Callovian, Late Oxfordian, and Late Kimmeridgian. The importance and extent of each event and its influence on the facies pattern of the northern Tabas Block is briefly discussed and demostrated by some examples.
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The following ammonoid and nautiloid taxa are described for the first time from the Upper Triassic succession (Ekrasar Formation, Shemshak Group) of northern Alborz, Iran: Arcestes sp., Arcestes ( Pararcestes ?) sp., Thisbites cf.... more
The following ammonoid and nautiloid taxa are described for the first time from the Upper Triassic succession (Ekrasar Formation, Shemshak Group) of northern Alborz, Iran: Arcestes sp., Arcestes ( Pararcestes ?) sp., Thisbites cf. agricolae Mojsisovics, Stikinoceras cf. kerri Mc Learn, Giesbachites sp., Griesbachites cf. pseudomedleyanus Diener, Griesbachites cf. himalayanus Wang & He, and Proclydonautilus ? sp. Palaeobiogeographically, the studied ammonoids are Tethyan in character, and stratigraphically attributed to the lower Lower Norian ( Guembelites jandianus Zone, possibly also Malayites paulckei Zone). The biostratigraphic data of this study demonstrate the diachronous base of the Shemshak Group: it is older in the northern Alborz (lower Lower Norian), but younger in Central Iran and probably also in the southern Alborz (Middle Norian).
Research Interests: Geology, Paleontology, Biostratigraphy, Iran, Alborz, and 4 moreUpper Triassic, Ammonoids, Norian, and Taxon
The rocks of the Jurassic System in North and Central Iran are represented by very thick sedimentary successions reflecting the deposition during two tectono-stratigraphic megacycles, bounded by three important unconformities. The older... more
The rocks of the Jurassic System in North and Central Iran are represented by very thick sedimentary successions reflecting the deposition during two tectono-stratigraphic megacycles, bounded by three important unconformities. The older (Early to early Middle Jurassic) cycle starts, after the Late Triassic closure of the Palaeotethys and the collision of the Iran Plate with the southern margin of Eurasia (Turan Plate), with an abrupt uplift of the Cimmerian Mountains around the Triassic–Jurassic boundary (Main-Cimmerian Event) and is terminated by the Mid-Cimmerian Tectonic Event in the mid-Bajocian. The predominantly siliciclastic sediments of this tectono-stratigraphic cycle are accommodated in the Ab-e-Haji Subgroup of the (upper) Shemshak Group. The Ab-e-Haji Subgroup consists of thick and widespread, partly coal-bearing siliciclastic strata and also records some important marine ingressions, especially in the Toarcian and Aalenian. The younger tectono-stratigraphic cycle starts...
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Porosphaera , an abundant small spherical calcisponge, well known from Cretaceous strata of Europe, was found in Middle and Upper Jurassic deposits of east-central Iran. This is the first record of Porosphaera from the Jurassic, except... more
Porosphaera , an abundant small spherical calcisponge, well known from Cretaceous strata of Europe, was found in Middle and Upper Jurassic deposits of east-central Iran. This is the first record of Porosphaera from the Jurassic, except for a questionable occurrence of the genus from the Upper Jurassic of Canada, described by Jansa et al. (1982). The following species are new: P. regularis n. sp., P. biporata n. sp., P.? labyrinthica n. sp., and P.? asymmetrica n. sp.
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Twenty gastropod taxa, belonging to thirteen genera and twelve families, are systematically described from the Cenomanian-Turonian rocks of eastern Sinai. Most of the gastropods are internal moulds, some of which are, in addition,... more
Twenty gastropod taxa, belonging to thirteen genera and twelve families, are systematically described from the Cenomanian-Turonian rocks of eastern Sinai. Most of the gastropods are internal moulds, some of which are, in addition, incomplete (e.g., nerineids). Consequently, many species identified in the past had to be revised because they are junior synonyms or do not justify identification at the species level. Due to the lack of some important characters such ornamentation, protoconch, outer lip, and aperture the generic position of some gastropods cannot be identified with certainty. The genus Sogdianella Djalilov, 1972 of the family Acteonellidae Gill, 1871, hitherto known only from central Europe, the Middle East, and Transcaucasia, is recorded from the Lower Turonian of Egypt and North Africa for the first time. Similarly, Ampullina dupinii (Deshayes in Leymerie, 1842), Sogdianella? laevis laevis (J. de C. Sowerby, 1835), and Diozoptyxis? blancheti (Pictet & Campiche, 1864) a...
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The Mesozoic Malagasy Seaway was a southward-directed extension of the Neotethys between India, Madagascar and eastern Africa. Originating as a series of late Palaeozoic and Triassic pull-apart basins in context with the break-up of... more
The Mesozoic Malagasy Seaway was a southward-directed extension of the Neotethys between India, Madagascar and eastern Africa. Originating as a series of late Palaeozoic and Triassic pull-apart basins in context with the break-up of Gondwana (e.g., Montenat et al. 1996; Geiger et al. 2004; Schandelmeier et al. 2004), its Jurassic record consists of non-marine to shallow marine sediments and faunas that are locally preserved in rift basins at both margins of the seaway. Probably from the Callovian onwards, sea-floor spreading transformed the rift basin into the incipient Indian Ocean (Coffin & Rabinowitz 1992; Montenat et al. 1996). Jurassic bivalves colonizing the margins of the seaway have received comparably little attention in the last decades, except for those from the Kachchh rift basin of western India (Jaitly et al. 1995; Pandey et al. 1996; Fürsich & Heinze 1998; Fürsich et al. 2000) and a brief record of Upper Jurassic bivalves from Ethiopia (Kiessling et al. 2011). Older l...
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Marine Jurassic sediments (Bajocian-Tithonian) of the Kachchh Basin were deposited in a ramp setting. Except during the Middle and Late Bathonian, when a carbonate regime became established, the fill of the basin consists predominantly of... more
Marine Jurassic sediments (Bajocian-Tithonian) of the Kachchh Basin were deposited in a ramp setting. Except during the Middle and Late Bathonian, when a carbonate regime became established, the fill of the basin consists predominantly of siliciclastics. The sediments represent environments that range from coastal plains (rivers and associated flood plains with caliche nodules), deltas, brackish water lagoons, nearshore sand and iron-oolite bars of the inner ramp, generally situated above fair-weather wave-base, to the middle ramp influenced by storm-waves and by storm-generated currents, and finally to the outer ramp which is characterised by low energy, fine-grained sediments. Changes in relative sea level produced a cyclic sedimentation pattern. The rich benthic fauna of macroinvertebrates is dominated by bivalves, followed by brachiopods, gastropods, corals, serpulids, and sponges. The analysis of 370 statistical samples and more than 27, 000 specimens produced more than 40 bent...
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In the Upper Triassic Nayband Formation of east-central Iran, bivalves repeatedly form small patch reefs on a mid to outer mixed carbonate-siliciclastic ramp in close stratigraphic neighbourhood to coral and coralsponge reefs. In contrast... more
In the Upper Triassic Nayband Formation of east-central Iran, bivalves repeatedly form small patch reefs on a mid to outer mixed carbonate-siliciclastic ramp in close stratigraphic neighbourhood to coral and coralsponge reefs. In contrast to other Triassic-Jurassic bivalve-dominated patch reefs, the bivalve reefs of the Nayband Formation are characterized by a comparatively high diversity of framebuilding taxa. These include taxa from three different families, i.e., the ostreids Umbostrea emamii, U. iranica and U.? aff. parasiticum, the prospondylids Newaagia stocklini and Persia monstrosa, and the plicatulids Eoplicatula parvadehensis and Pseudoplacunopsis asymmetrica. The bivalve reef constructors may have had a competitive advantage over coral and calcareous sponges in environments characterized by a higher degree of turbidity and/or higher nutrient contents.
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Research Interests: Evolutionary Biology, Geology, Biology, Ecology, Cretaceous, and 3 moreBivalvia, Mollusca, and Affinities
Abstract New Aptian (Lower Cretaceous) bakevelliid bivalves are described for the Romualdo Formation, Santana Group, Araripe Basin, northeastern Brazil. Together with the other known member of the family Bakevelliidae, already recorded... more
Abstract New Aptian (Lower Cretaceous) bakevelliid bivalves are described for the Romualdo Formation, Santana Group, Araripe Basin, northeastern Brazil. Together with the other known member of the family Bakevelliidae, already recorded from the unit (i.e., Aguileria dissita), the new bivalves (Araripevellia musculosa gen. et sp. nov., Aguileria romualdoensis sp. nov., and Gen. et sp. indet.) indicate that the Romualdo bakevelliid fauna was more diverse than previously realized. Bakevelliid-rich carbonates, some with specimens preserved in situ, are restricted to the upper third of this unit, a stratigraphic interval yielding also echinoderm-, gastropod- and stromatolite-bearing limestones. These pteriomorphian bivalves were widely distributed in the Romualdo Formation and are a testimony of the short-lived Bakevelliid-Sea that flooded the whole Araripe Basin during the Aptian. Notably, Aguileria romualdoensis sp. nov. closely resembles Aguileria renauxiana from the Cenomanian Woodbine Formation, Texas, US. In addition, Aguileria dissita is also recorded in the upper Aptian–Albian Riachuelo Formation of the Sergipe-Alagoas Basin. Together with other macroinvertebrates (i.e., gastropods, echinoderms, bivalves) the bakevelliid fauna of the Romualdo Formation can be tightly correlated with that of the Riachuelo Formation, supporting a paleogeographic scenario with a marine ingression flooding the Araripe Basin from the southeast, probably via the seaway developed in the Reconcavo-Tucano basin area. Finally, sedimentologic, stratigraphic and paleontological data indicates that the fate of the bakevelliids in the Romualdo Formation was linked to the onset of continentalization of the Araripe Basin.
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Protandrous sex change (sex change from male to female) is one of the diverse sexual expressions exhibited by bivalves, but its expression in the shell is quite rare. Previous studies on living and fossil astartids suggest a relationship... more
Protandrous sex change (sex change from male to female) is one of the diverse sexual expressions exhibited by bivalves, but its expression in the shell is quite rare. Previous studies on living and fossil astartids suggest a relationship between protandrous sex change and the formation of crenulations on the ventral shell margin at later ontogenetic stages. Here we report the formation of such crenulations in the Early Jurassic astartid Nicaniella rakoveci (Kuhn, 1935) from the Amaltheenton Formation at Buttenheim, Franconia. This is the earliest known record of protandrous hermaphroditism in fossil bivalves, predating previous reports by at least 13 Myr. A principal component analysis of linear size measurements and Fourier shape analysis of the shell outlines revealed that the outline of Nicaniella rakoveci specimens varies from subquadrate to subcircular, but this variation is independent of the presence or absence of crenulations and therefore not associated with sex. Crenulated...
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Lithological and especially palacontological data allow reconstruction of the palaeogeographic history of Hohxil, the source area of the Yangtze River in the northern Tibet Plateau, since the Late Palaeozoic. Early Carboniferous - Early... more
Lithological and especially palacontological data allow reconstruction of the palaeogeographic history of Hohxil, the source area of the Yangtze River in the northern Tibet Plateau, since the Late Palaeozoic. Early Carboniferous - Early Permian deep water environments, part of the Palaeotethys, were replaced by a Late Permian shelf sea following convergence of the Qiangtang and Kunlun blocks. During the Triassic, a varied facies pattern existed with open shelf to deep sea sediments in the north and non-marine to marginally marine environments in the south. Renewed compression between the Qiangtang and Kunlun blocks at the end of the Triassic led to formation of a mountain range. Subsequently, it was only during the Middle Jurassic that, due to renewed transgression, a shallow shelf sea extended into the southern parts of Hohxil. Collision of the Lhasa block with the Qiangtang block at the end of the Jurassic caused the final retreat of the sea from the area. From the Cretaceous throughout most of the Tertiary, lacustrine and fluvial sedimentation prevailed, with a distinct sedimentary gap during the Paleocene and Eocene due to collision of the Indian and Eurasian plates. Pliocene events include volcanic eruptions and strong uplift, the latter continuing to the present day, resulting in an average altitude of the area of more than 5,000 in; this extremely elevated region became the source of the Yangtze River.