Jurassic Research Articles

The Guarani Aquifer System – from regional reserves to local use

The Guarani Aquifer System is a massive groundwater body underlying large areas of Brazil, Paraguay, Uruguay and Argentina, with a thickness of 50–600 m (averaging about 250 m). It is one of the world's largest sandstone aquifers. The mainly weakly-cemented sandstones were formed by aeolian, fluvial and lacustrine continental deposition during the Triassic–Jurassic period and are overlain by extensive Cretaceous basalt lava-flows. The system is totally storage-dominated, with recharge amounting to only about 0.2% of the estimated 30 000 km 3 of water stored. Using 14 C and 81 Kr techniques, it was possible to confirm extremely slow flow rates, with groundwater older than 730 000 years BP in some parts of São Paulo State, Brazil. The vast regional freshwater storage contrasts sharply with localized active flow systems of recharge areas, which are strongly impacted by land-use change. The aquifer is the best known and most exploited in São Paulo State (80% of total extraction) and the experience of groundwater use for the supply of Ribeirão Preto and São José do Rio Preto (both with populations of over 0.5 million), together with one transboundary urban area, will be summarized. Thematic collection: This article is part of the Hydrogeology of Sandstone collection available at: https://www.lyellcollection.org/cc/hydrogeology-of-sandstone

Ostracods of the Toarcian (Jurassic) of Peniche, Portugal: taxonomy and evolution across and beyond the GSSP interval

Ostracods of the Toarcian (Jurassic) of Peniche, Portugal: taxonomy and evolution across and beyond the GSSP interval

Testing pterosaur ingroup relationships through broader sampling of avemetatarsalian taxa and characters and a range of phylogenetic analysis techniques.

The pterosaurs first appear in the fossil record in the middle of the Late Triassic. Their earliest representatives are known from Northern Hemisphere localities but, by the end of the Jurassic Period, this clade of flying reptiles achieved a global distribution, as well as high levels of diversity and disparity. Our understanding of early pterosaur evolution and the fundamental interrelationships within Pterosauria has improved dramatically in recent decades. However, there is still debate about how the various pterosaur subgroups relate to one another and about which taxa comprise these. Many recent phylogenetic analyses, while sampling well from among the known Triassic and Early Jurassic pterosaurs, have not included many non-pterosaurian ornithodirans or other avemetatarsalians. Given the close relationship between these groups of archosaurs, the omission of other ornithodirans and avemetatarsalians has the potential to adversely affect the results of phylogenetic analyses, in terms of character optimisation and ingroup relationships recovered. This study has addressed this issue and tests the relationships between the early diverging pterosaur taxa following the addition of avemetatarsalian taxa and anatomical characters to an existing early pterosaur dataset. This study has, for the first time, included taxa that represent the aphanosaurs, lagerpetids, silesaurids and dinosaurs, in addition to early pterosaurs. Anatomical characters used in other recent studies of archosaurs and early dinosaurs have also been incorporated. By expanding the outgroup taxa and anatomical character coverage in this pterosaur dataset, better resolution between the taxa within certain early pterosaur subclades has been achieved and stronger support for some existing clades has been found; other purported clades of early pterosaurs have not been found in this analysis—for example there is no support for a monophyletic Eopterosauria or Eudimorphodontidae. Further support has been found for a sister-taxon relationship between Peteinosaurus zambelli and Macronychoptera, a clade here named Zambellisauria (clade nov.), as well as for a monophyletic and early diverging Preondactylia. Some analyses also support the existence of a clade that falls as sister-taxon to the zambellisaurs, here named Caviramidae (clade nov.). Furthermore, some support has been found for a monophyletic Austriadraconidae at the base of Pterosauria. Somewhat surprisingly, Lagerpetidae is recovered outside of Ornithodira sensu stricto, meaning that, based upon current definitions at least, pterosaurs fall within Dinosauromorpha in this analysis. However, fundamental ornithodiran interrelationships were not the focus of this study and this particular result should be treated with caution for now. However, these results do further highlight the need for broader taxon and character sampling in phylogenetic analyses, and the effects of outgroup choice on determining ingroup relationships.

Petrogenesis and Tectonic Setting of the Highly Fractionated Junye Granitic Intrusion in the Yiliu Tungsten Polymetallic Deposit, Guangdong Province, South China: Constraints from Geochemistry and Sr-Nd-Pb-Hf Isotopes

The Yiliu tungsten polymetallic deposit, located in the south central portion of the Nanling nonferrous metal metallogenic province in South China, is an area with common Yanshanian tectonothermal events. Early Yanshanian magmatism leads to the emplacement of voluminous tungsten-bearing granite intrusions, such as the Baoshan, Benggangling and Junye plutons, which are considered temporally and spatially associated with W-polymetallic mineralization in the Yiliu region. Here, we investigate the basic geological and petrological characteristics of the Junye granites, and present major and trace element geochemical data and bulk-rock Sr-Nd-Pb-Hf isotopic data to gain insight into the petrogenesis and tectonic setting of granitic intrusions in the region. The Junye granites are high-K calc-alkaline and metaluminous to weakly peraluminous [A/CNK = molar ratios of Al2O3/(CaO + Na2O + K2O) = 0.97–1.02] with enrichment in SiO2 (75.68–76.44 wt.%), relatively high total alkalis (K2O + Na2O = 8.06–8.45 wt.%) with K2O/Na2O ratios ranging from 1.12 to 1.42, and moderate Al2O3 (12.62–13.00 wt.%), but low in P2O5 (<0.01 wt.%), MgO (0.02–0.04 wt.%), CaO (0.78–0.95 wt.%) and Fe2O3T (0.93–1.07 wt.%). They show spectacular tetrad effect REE (rare earth element) patterns with low ΣREE content (53.2–145.3 ppm), negative Eu anomalies (δEu = 0.09–0.17) and slight enrichment of LREEs (light rare earth elements) relative to HREEs (heavy rare earth elements). The granites are enriched in Rb (481–860 ppm), Th (16.2–46.1 ppm) and U (25.4–40.8 ppm) but depleted in Ba (1.0–5.8 ppm), Sr (11.1–23.4 ppm), P (9.5–26.7 ppm) and Ti (241–393 ppm). All geochemical features lead us to interpret the Junye granites as highly fractionated I-type granites. These granites underwent intense interaction between highly evolved magma and volatile-rich hydrothermal fluids during the late stage of formation, and accompanied fractional crystallization of biotite, plagioclase and accessory minerals, such as apatite, monazite and allanite. Additionally, the granites show uniform Nd isotopic ratios with calculated εNd (152 Ma) values of −8.28 to −8.91 and Nd model age (TDM2) of 1645 to 1698 Ma, stable age-corrected initial Pb isotopic compositions with (206Pb/204Pb)i of 18.646–19.010, (207Pb/204Pb)i of 15.767–15.786 and (208Pb/204Pb)i of 39.113–39.159, respectively, and homogeneous Hf isotopic values yielding εHf (152 Ma) values from −6.9 to −9.5 with TDM2 ages of 1680 to 2214 Ma, collectively suggesting that the granitic magma was probably derived from the remelting of ancient infracrustal materials in the basement of the Nanling region. Consequently, we consider that the Junye granites are the products of partial melting of Paleoproterozoic infracrustal medium- to high-K metamorphic basaltic rocks in the Cathaysia Block, which was caused by the underplating of coeval mantle basaltic magmas that provided abundant heat energy for melting in a tectonic setting, with lithospheric extension and thinning during the late Jurassic period.

Decomposition of dinosaurian remains inferred by invertebrate traces on vertebrate bone reveal new insights into Late Jurassic ecology, decay, and climate in western Colorado.

A survey of 2,368 vertebrate fossils from the Upper Jurassic Mygatt-Moore Quarry (MMQ) (Morrison Formation, Brushy Basin Member) in western Colorado revealed 2,161 bone surface modifications on 884 specimens. This is the largest, site-wide bone surface modification survey of any Jurassic locality. Traces made by invertebrate actors were common in the assemblage, second in observed frequency after vertebrate bite marks. Invertebrate traces are found on 16.174% of the total surveyed material and comprise 20.148% of all identified traces. Six distinct invertebrate trace types were identified, including pits and furrows, rosettes, two types of bioglyph scrapes, bore holes and chambers. A minimum of four trace makers are indicated by the types, sizes and morphologies of the traces. Potential trace makers are inferred to be dermestid or clerid beetles, gastropods, an unknown necrophagous insect, and an unknown osteophagus insect. Of these, only gastropods are preserved at the site as body fossils. The remaining potential trace makers are part of the hidden paleodiversity from the North American Late Jurassic Period, revealed only through this ichnologic and taphonomic analysis. Site taphonomy suggests variable, but generally slow burial rates that range from months up to 6 years, while invertebrate traces on exposed elements indicate a minimum residence time of five months for carcasses with even few preserved invertebrate traces. These traces provide insight into the paleoecology, paleoclimate, and site formation of the MMQ, especially with regards to residence times of the skeletal remains on the paleolandscape. Comprehensive taphonomic studies, like this survey, are useful in exploring patterns of paleoecology and site formation, but they are also rare in Mesozoic assemblages. Additional work is required to determine if 16.174% is typical of bulk-collected fossils from Jurassic ecosystems in North America, or if the MMQ represents an unusual locality.

Geological characteristics and distribution law of sub-salt Jurassic large and medium gas fields in the right bank of the Amu Darya River

Geological characteristics and distribution law of sub-salt Jurassic large and medium gas fields in the right bank of the Amu Darya River

Sm-Nd geochronology and petrologic investigation of sub-ophiolite metamorphic sole from the Dinarides (Krivaja-Konjuh, Ophiolite Complex, Bosnia and Herzegovina)

The Dinaridic segment of Neotethys was affected by a widespread shortening and related subduction-accretion-obduction processes that commenced in the middle Jurassic. In the Dinarides, the Krivaja-Konjuh Ophiolite Complex (KKOC) stands as the largest ophiolite complex with a well-exposed metamorphic sole which is the key to understanding the dynamics of intraoceanic subduction initiation in this part of Neotethys. In this contribution we present Sm-Nd geochronology on a granulite facies amphibolite from the KKOC, as well as a detailed petrological description. A five-point isochrone age calculated from clinopyroxene, plagioclase, garnet, amphibole and whole rock is 162 ± 14 Ma (MSWD = 6.2), whereas garnet and whole rock yield 160 ± 7 Ma. Ages calculated from all data points except clinopyroxene are 162 ± 5 Ma (MSWD = 1.09). Petrographic investigations suggest that these ages date granulite facies metamorphic conditions (i.e. peak metamorphism of Grt-Cpx amphibolite) rather than post-peak exhumation or obduction processes. Phase textural relationships are in line with previous research, which indicated a peak metamorphism equilibration pressure and temperature of ~1 GPa and ~800 °C, respectively. Granulite facies conditions are elucidated for an igneous precursor, which underwent a multi-stage metamorphism that gave rise to recrystallization of igneous clinopyroxene and plagioclase, epitaxial growth of amphibole, and garnet blastosis. Taking into account the age of gabbronorite from the youngest segment of the KKOC oceanic crust (Taorcian to Bathonian) and ages of radiolarian assemblages from the KKOC melange (Bajocian to Bathonian), it may be inferred that within ~25 Ma the Dinaridic segment of Neotethys evolved rapidly from active ridge spreading through a stage of intraoceanic subduction and arc magmatism toward sub-ophioliteexhumation and further obduction along the Adria passive margin at the end of the Jurassic era.

Division of Methane Weathering Zones in the Middle and Lower Jurassic Coal Seams of Santanghu Basin

Division of Methane Weathering Zones in the Middle and Lower Jurassic Coal Seams of Santanghu Basin

Geochronology and geochemistry of late Jurassic–Early Cretaceous volcanic rocks in the southern Great Xing’an range, NE China: constraints for late Mesozoic tectono-magmatic evolution

ABSTRACT Late Mesozoic volcanic rocks are widespread in the Great Xing’an Range (GXR), Northeast (NE) China. However, details of the tectono-magmatic evolution during the Late Mesozoic are poorly understood. In this paper, new zircon U–Pb, Lu–Hf, and whole-rock geochemical data from Late Mesozoic volcanics in the southern GXR, are used to further constrain the tectono-magmatic evolution of the region. Late Mesozoic magmatism in the GXR, eastern Mongolia and southern Transbaikalia occurred during the Early Cretaceous (120–140 Ma) and Late Jurassic (150–163 Ma) periods. Late Jurassic trachyandesites-trachytes show a low rare earth element and moderate light rare earth element (LREE) enrichment with no Eu anomalies. Early Cretaceous trachytes are characterized by an LREE enrichment and negative Eu anomalies. Contemporaneous rhyolites exhibit a significant LREE enrichment, A–type granitoid affinity, and pronounced negative Eu anomalies. Different negative Nb, Ta, and Ti anomalies, and positive zircon εHf(t) values, indicate that the ~160 Ma trachyandesites-trachytes are derived from partial melting of the lithospheric mantle that was metasomatized by subduction-related fluids. The ~125 Ma trachytes and rhyolites were possibly generated by partial melting of the accreted Meso-Neoproterozoic lower crust. New and previously published geochemical, isotopic and geochronological data from the southern GXR, eastern Mongolia and East-Transbaikalia, suggest that Late Jurassic–Early Cretaceous volcanism in the southern GXR occurred during the post-collisional extension after the closure of the Mongol–Okhotsk Ocean.

Lower Cretaceous inversion of the European Variscan basement: record from the Vendée and Limousin (France)

The post-orogenic evolution of the European Variscan basement remains difficult to constrain due to the absence of post-orogenic sedimentary records. One of the current ways to access this history is to constrain the thermal evolution of these basement areas through indirect methods such as low-temperature thermochronology (LTT) thermal modelling. In this study, apatite fission-track (AFT) data have been acquired for the north-eastern part (Vendee and Limousin) of the French Massif Central Variscan basement. Similar thermal inversion procedure has been done, assuming that some samples were close to the surface during Triassic times. The results show a complex post-Variscan evolution of the western part of the Massif Central. Inversion of the AFT data indicates a high-temperature event during the Jurassic period. This thermal event can be interpreted as the deposition of a significant sedimentary cover which has been later eroded during the Late Jurassic and/or Early Cretaceous. Interpretation of the thermal models implies the presence of the sampled rocks close to the surface during Cretaceous and Eocene times. The estimated volume of this eroded sedimentary cover suggests a probable larger extension of the surrounding sedimentary basins (Paris Basin and Aquitaine Basin) across the Variscan basement area.

Early–Middle Jurassic paleogeography reconstruction in the Western Qaidam Basin: Insights from sedimentology and detrital zircon geochronology

The Western Qaidam Basin (WQB) is situated at the northeastern margin of the Tibetan Plateau. It is adjacent to the Altyn Tagh Range to the west and is bordered at the south and north by the Eastern Kunlun Range and Southern Qilian Range, respectively. Sporadic Jurassic outcrops are exposed along the Altyn Tagh Range. Although subsurface data have revealed that the Jurassic rocks also developed in the basin interior, little is known about their distribution and depositional characteristics. Hydrocarbon exploration has revealed that the Lower–Middle Jurassic strata are important source rocks and reservoirs in the WQB. However, due to post-depositional uplifting, exhumation or deep burial, the sediments provenance, paleogeography and the basin properties during the Early–Middle Jurassic in the whole WQB remain less understood. In this study, we examine the sedimentary records combined with detrital zircon U–Pb geochronology based on an analysis of post-depositional modification, to reveal the source-to-sink relationship between the WQB and surrounding potential source areas, and to further reconstruct the Early–Middle Jurassic paleogeography of the WQB. During the Early Jurassic, there were a series of small-scale, separated rift basins which were characterized by proximal sedimentation and rapid facies shift in the WQB. Specifically, the Lower Jurassic sediments in the southern WQB mainly originated from the Eastern Kunlun Range with minor supply from the Paleozoic intrusions that might have been exposed in the hinterland of the Qaidam Block; the provenance in the northern WQB was dominated by the uplift area to the west. There was a broader depression basin in the southern WQB. The Eastern Kunlun Range and the ancestral Altyn Mountains, served as the two dominant source areas for the clastic material of the southern WQB during the Middle Jurassic. Integrated analysis on sedimentology and provenance reveals that the southeastern Tarim Basin and the WQB were likely to have been interconnected or adjacent during Middle Jurassic period. We thus infer that no large-scale strike-slip displacement along the Altyn Tagh Fault occurred during that period. Combining regional tectonic settings, we tentatively suggest that the extensional setting following the orogenic movement in the eastern part of the Paleo–Tethys Ocean could have been responsible for the formation of the Early Jurassic rift basins. By the early Middle Jurassic, the Bangonghu–Nujiang Tethys Ocean and the Mongol–Okhotsk Ocean were subducted northward beneath the Qiangtang terrane and Siberian continent, respectively. These led to the presence of an extensional stress field and the formation of a broader depression basin in the southern WQB during the Middle Jurassic. Paleogeography reconstruction results indicate that the northern WQB should have much potential for hydrocarbon exploration.

Sedimentary-diagenetic ore formation in the Jurassic system terrigenous deposits of the Tatarstan Republic

Authigenic ore mineralization of the Jurassic terrigenous complexes rocks, widespread in the Tatarstan, is considered. It has been established that the ore minerals associations’ composition is determined by geochemical conditions of mineral formation environment. In rocks of oxide geochemical facies (sandstones, siltstones), iron, manganese and titanium oxides predominate. Pyrite framboids and copper-nickel intermetallide compounds predominate in rocks of neutral geochemical facies (green clays). The rocks of anoxic geochemical facies (black clay, oil shale) contain only pyrite framboids. The main factor determining the authigenic ore minerals associations composition is redox potential of environment.

Triassic magmatism in the European Southern Alps as an early phase of Pangea break-up

AbstractMagmatic rocks from the Dolomites, Carnic and Julian Alps, Italy, have been sampled to investigate the origin and geodynamic setting of Triassic magmatism in the Southern Alps. Basaltic, gabbroic and lamprophyric samples have been characterized for their petrography, mineral chemistry, whole-rock major and trace elements, and Sr, Nd and Pb isotopic compositions. Geothermobarometric estimates suggest that the basaltic magmas crystallized mostly at depths of 14–20 km. Isotopic data show variable degrees of crustal contamination decreasing westwards, probably reflecting a progressively more restitic nature of the crust, which has been variably affected by melting during the Permian period. Geochemical and isotopic data suggest that the mantle source was metasomatized by slab-derived fluids. In agreement with previous studies and based on geological evidence, we argue that this metasomatism was not contemporaneous with the Ladinian–Carnian magmatism but was related to previous subduction episodes. The lamprophyres, which likely originated some 20 Ma later by lower degrees of melting and at higher pressures with respect to the basaltic suite, suggest that the mantle source regions of Triassic magmatism in the Dolomites was both laterally and vertically heterogeneous. We conclude that the orogenic signatures of the magmas do not imply any coeval subduction in the surrounding of Adria. We rather suggest that this magmatism is related to the Triassic rifting episodes that affected the western Mediterranean region and that were ultimately connected to the rifting events that caused the break-up of Pangea during the Late Triassic – Early Jurassic period.

Excavating Jurassic Giants

Excavating Jurassic Giants

A Building Material from the Upper Jurassic Period into the Canarian Architectural Heritage: The Durability of the Heartwood of Pinus Canariensis

ABSTRACT The durability of building materials is a fundamental issue addressed by many researchers who seek to improve working life by obtaining durable and more sustainable materials. In the Canary Islands, there are traditional buildings with carpentry elements that remain unchanged, without any apparent degradation. Specifically, the wood used in Canarian heritage comes from the resinous heartwood of Pinus canariensis. Most of these buildings were built between the sixteenth and nineteenth centuries, and their architectural relevance has been decisive in declaring the city of La Laguna a World Heritage Site by UNESCO. The objective of this research is to identify the carpentry elements made with the heartwood of Pinus canariensis within the Canarian architectural heritage and to evaluate its durability. The results show that the loss of mass for the heartwood of Pinus canariensis after the incubation of the fungus was less than 1% in all cases. However, other conifers show a considerable loss of mass, between 25% and 38%.

Role of inherited structure on granite emplacement: An example from the Late Jurassic Shibei pluton in the Wuyishan area (South China) and its tectonic implications

The Shibei pluton is a Late Jurassic granitic body in the South China Block (Fujian province), featured by macroscopically isotropic granite and undeformed margins, which are also characteristics for most of the Late Jurassic plutons in southeastern China. Our field observations, fabric investigations and gravity modelling allow us to decipher the internal structure, overall geometry, magma accumulation and emplacement processes of the Shibei pluton. Magnetic fabrics of the Shibei pluton can be divided into two distinct groups. The first one, observed in the southern-central part of the pluton, is characterized by high-angle to sub-vertical (54°-90°) NE-SW-striking magnetic foliations and variably plunging magnetic lineation. The second group, recognized in the northern part of the pluton, shows variably dipping (22°-88°) magnetic foliation, which generally strikes subparallel to pluton-country rock contacts, and irregularly oriented magnetic lineation. The Bouguer gravity modelling demonstrates that the pluton has a tabular geometry with a N-S-striking long axis, and a length-width-thickness ratio of ~32:8:1. The intrusion thickness gradually decreases from the southwest margin (ca. 2.5 km) to the northeast margin (ca. 0.5 km). Moreover, an undulating bottom with one or more convex intruding roots can be observed. Integrating published geochronological and regional tectonic data, we propose that the Shibei pluton was constructed by successive NE-SW-striking magma injections. Emplacement of early magma batches started in the SW part of the pluton by magma injection, which was guided by inherited structures produced by pre-emplacement tectonic events. Continuous magma injections were laterally accreted to earlier emplaced magma intrusions, and/or injected along lithological and/or structural discontinuities within the country rocks at upper crustal level without producing ductile deformation in the pluton-country rock contact zone. Our structural and fabric investigations indicate that the SE South China Block was not subjected to a major tectonic deformation during the Late Jurassic period.

The earliest Jurassic A-type rhyolites and high-Mg andesites–dacites in southern Jiangxi Province, southeast China: Evidence for delamination of a flat-slab?

Early Jurassic igneous rocks are abundant in the Nanling Range, southeastern China. They are closely related with economically significant deposits, but the tectonic-magmatic controls on their formation are still controversial. This paper reports zircon U–Pb–Hf–O isotopes for the rhyolites, and whole-rock major–trace element and SrNd isotope compositions for the rhyolites and andesites/dacites in the Changpu and Dongkeng basins located in the southern part of Jiangxi Province. The Changpu and Dongkeng rhyolites have high K2O contents (4.1–7.6 wt%) and K2O/Na2O ratios (> 1). Both groups are enriched in HFSE, LREE and show pronounced Nb–Ta–Eu–Sr–P–Ti negative anomalies. Geochemically, they can be classified as A-type and are similar to A2-type granitoids globally. Their highly evolved whole-rock SrNd isotopes and elevated zircon δ18O (Changpu rhyolites: (87Sr/86Sr)i = 0.7140 to 0.7156, εNd(t) = −7.2 to −8.7, δ18O = 8.76 to 9.93‰; Dongkeng rhyolites: (87Sr/86Sr)i = 0.7149 to 0.7162, εNd(t) = −6.4 to −7.9, δ18O = 7.04 to 9.78‰) are consistent with their generation dominated by remelting of exisiting crustal materials in an extensional environment. The slightly more radiogenic zircon Hf isotopes of the Dongkeng rhyolites, εHf(t) = −2.1 to −7.1 as compared with −6.1 to −8.3 of Changpu rhyolites, likely signify some mantle contribution. The Changpu high-Mg andesites–dacites are geochemically similar to high-Mg andesites (HMAs) of the Setouchi arc volcanic belt in Japan and the Piip Volcanos in the western Aleutian Arc. They have very low εNd(t) from −7.8 to −11.3 and highly radiogenic (87Sr/86Sr)i values from 0.7143 to 0.7154. Similar to HMAs in Setouchi, we suggest that they may be derived from melting of subducted sediments and followed by melt-mantle interaction.SIMS zircon UPb dating yielded extrusive ages of ~190 Ma for both Changpu and Dongkeng rhyolites. The new dating results constrain the minimum age of extrusion of rhyolites and andesites-dacites from the same volcanic sequence to be the earliest Jurassic period. Igneous rocks of this age have very limited distribution in south China. While those found in the coastal regions show features similar to arc rocks, these in the hinterland are rift related. We propose that formation of the Early Jurassic A-type rhyolites and high-Mg andesites–dacites may provide evidence for foundering/delamination of a previously subducted oceanic plateau beneath southeastern China.

Литолого-петрофизическая характеристика продуктивных интервалов позднеюрско-раннемеловых отложений Средне-Назымского месторождения

Литолого-петрофизическая характеристика продуктивных интервалов позднеюрско-раннемеловых отложений Средне-Назымского месторождения

The Ander's organ: a mechanism for anti-predator ultrasound in a relict orthopteran.

ABSTRACTThe use of acoustics in predator evasion is a widely reported phenomenon amongst invertebrate taxa, but the study of ultrasonic anti-predator acoustics is often limited to the prey of bats. Here, we describe the acoustic function and morphology of a unique stridulatory structure – the Ander's organ – in the relict orthopteran Cyphoderris monstrosa (Ensifera, Hagloidea). This species is one of just eight remaining members of the family Prophalangopsidae, a group with a fossil record of over 90 extinct species widespread during the Jurassic period. We reveal that the sound produced by this organ has the characteristics of a broadband ultrasonic anti-predator defence, with a peak frequency of 58±15.5 kHz and a bandwidth of 50 kHz (at 10 dB below peak). Evidence from sexual dimorphism, knowledge on hearing capabilities and assessment of local predators, suggests that the signal likely targets ground-dwelling predators. Additionally, we reveal a previously undescribed series of cavities underneath the organ that probably function as a mechanism for ultrasound amplification. Morphological structures homologous in both appearance and anatomical location to the Ander's organ are observed to varying degrees in 4 of the 7 other extant members of this family, with the remaining 3 yet to be assessed. Therefore, we suggest that such structures may either be more widely present in this ancient family than previously assumed, or have evolved to serve a key function in the long-term survival of these few species, allowing them to outlive their extinct counterparts.

The Metamorphosis of Stephen Da(e)dalus: The Plesiosaurus and the Slimy Sea

In Joyce’s scholarship, very little critical attention has been paid to the monstrous creature depicted in Stephen Hero, the plesiosaurus, a large marine reptile of the Lower Jurassic Period. It appears when the protagonist envisions the birth of prehistoric art: “He doubled backwards into the past of humanity and caught glimpses of emergent art as one might have a vision of the pleisiosauros [sic] emerging from his ocean of slime” (SH 33). The prime concern of this essay is to inquire into why Joyce conjures up such paleo-imagery as that of the plesiosaurus, rather than other extinct creatures, and how he represents the “ocean of slime” as the nonhuman geological actor in his own background. I first highlight the actual plesiosaurus fossil discovered in 1848 and brought into Dublin in 1853. The fact that it had been moved to the Natural History Museum, Dublin, in 1890 will suggest the possibility that the direct inspiration for Joyce’s description was the Plesiosaurus cramptoni (now known as Rhomaleosaurus cramptoni) fossil. I then examine the traditional imagery of the slime-clad plesiosaurus in paleo-geological writings to elucidate how he employs conventional verbal representation, despite Stephen’s search for primordial art. Finally, I will analyze the hidden nexus between the plesiosaurus and Stephen’s monstrous egotism, or “self-centred” spirit as opposed to “self-submersive reptiles,” shedding new light on the “ocean of slime” as an image symbolic of the geological soil of Dublin out of which the fledging artist attempts to rise. The argument regarding two nonhuman actors will illuminate a different form of “the square ditch” into which young Stephen (in A Portrait of the Artist as a Young Man) is pushed and reveal his monstrous animality as a plesiosaurus before becoming a bird.