77,002 research outputs found
The postcranial skeleton of monolophosaurus jiangi (dinosauria: Theropoda) from the Middle Jurassic of Xinjiang, China, and a review of Middle Jurassic Chinese theropods
The Middle Jurassic was a critical time in the evolution of theropod dinosaurs, highlighted by the origination and radiation of the large-bodied and morphologically diverse Tetanurae. Middle Jurassic tetanurans are rare but have been described from Europe, South America and China. In
particular, China has yielded a number of potential basal tetanurans, but these have received little detailed treatment in the literature. Here we redescribe the postcranial skeleton of one of the most complete Chinese Middle Jurassic theropods, Monolophosaurus. Several features confirmthe tetanuran affinities of Monolophosaurus, but the possession of âprimitiveâ traits such as a double-faceted pubic peduncle of the ilium and a hood-like supracetabular crest suggest a basal position within Tetanurae. This conflicts with most published cladistic analyses that place Monolophosaurus in a more derived position within Allosauroidea.We review the Middle Jurassic record of Chinese theropods and compare Monolophosaurus to other Middle Jurassic theropods globally. These comparisons suggest that Monolophosaurus and Chuandongocoelurus formed an endemic theropod clade limited to the Middle Jurassic of Asia. Other Middle Jurassic Chinese theropods deserve further study
The discovery of <i>Isocrinus</i> cf. <i>robustus</i> from the Lias Group (Lower Jurassic) near Dunrobin Castle, Sutherland, Scotland
A single stem section (pluricolumnal) belonging to a post-Palaeozoic crinoid (sea lily) is reported from a small outcrop of Lower Jurassic Lias Group strata exposed in low cliff near Dunrobin Castle. This is the first Jurassic crinoid recorded from Eastern Scotland and the small fragment has enough diagnostic characters to be assigned to the species Isocrinus cf. robustus; a crinoid found commonly in the Lower Jurassic of England. The Scottish form collected has unusual morphology that is atypical of the genus
Geology and Jurassic paleogeography of the Mt. Primo-Mt. Castel Santa Maria ridge and neighbouring areas (Northern Apennines, Italy)
This paper presents the results of a geological mapping project across the Mt. Primo ridge and neighbouring areas (Umbria-Marche Domain â Northern Apennines), where a thick Meso-Cenozoic carbonate succession is exposed. A geological map on the 1:15,000 scale, illustrates the main stratigraphic, paleogeographic and structural features of the area. The geometries of Jurassic stratigraphic units, were mainly controlled by the complex submarine topography resulting from an Early Jurassic extensional phase. The three-dimensional distribution of Jurassic rocks in turn conditioned the structural evolution of this part of the Apennines during the chain building phase
A problematic zygopleuroid gastropod Acanthostrophia revisited
SEM examination of the type series of Acathostrophia acanthica CONTI & FISCHER, 1984 from Middle Jurassic of Italy has shown that this gastropod most likely belongs to the family Protorculidae as previously suggested by NĂTZEL (1998). It is also similar to some Jurassic species of Polygyrinidae, which might also be related to Protorculidae. The supposition of KAIM et al. (2008) that Acanthostrophia is an early member of Abyssochrysidae could not be confirmed
Macroevolutionary Patterns In The Evolutionary Radiation Of Archosaurs (Tetrapoda: Diapsida)
The rise of archosaurs during the Triassic and Early Jurassic has been treated as a classic example of an evolutionary radiation in the fossil record. This paper reviews published studies and provides new data on archosaur lineage origination, diversity and lineage evolution, morphological disparity, rates of morphological character change, and faunal abundance during the TriassicâEarly Jurassic. The fundamental archosaur lineages originated early in the Triassic, in concert with the highest rates of character change. Disparity and diversity peaked later, during the Norian, but the most significant increase in disparity occurred before maximum diversity. Archosaurs were rare components of EarlyâMiddle Triassic faunas, but were more abundant in the Late Triassic and pre-eminent globally by the Early Jurassic. The archosaur radiation was a drawn-out event and major components such as diversity and abundance were discordant from each other. Crurotarsans (crocodile-line archosaurs) were more disparate, diverse, and abundant than avemetatarsalians (bird-line archosaurs, including dinosaurs) during the Late Triassic, but these roles were reversed in the Early Jurassic. There is no strong evidence that dinosaurs outcompeted or gradually eclipsed crurotarsans during the Late Triassic. Instead, crurotarsan diversity decreased precipitously by the end-Triassic extinction, which helped usher in the age of dinosaurian dominance
Dinosaurs in Scotland
Dinosaurs in Scotland are not something that is generally known. Yet, there are at least three different families represented from bones and a number of different footprint types from the Middle Jurassic. Of the bones, there is a sauropod, a thyreophoran, a coelophysid and another theropod. The footprints include large carnosaur-like footprints, smaller theropod footprints, and ornithopod footprints of different types. All this put together sounds like a decent representative dinosaur fauna from a poorly represented part of the Jurassic worldwide. Sadly, most of these dinosaurs are represented by only one or two identifiable bones. Having said that, the fossil remains that we do have in Scotland, contribute significantly to our knowledge of Middle Jurassic dinosaurs. The footprints are more common but are no less important, helping us to understand little known aspects of dinosaur movement and interactions
Environmental and climatic proxies for the Cañadón Asfalto and Neuquén basins (Patagonia, Argentina): review of middle to upper jurassic continental and near coastal sequences
In this review, we include several proxies (sedimentology, palynology, invertebrates) from the CañadĂłn Asfalto and NeuquĂ©n basins, to infer the environments and regional climatic context during the Middle to Late Jurassic of Patagonia. In central Patagonia, early in the Middle Jurassic, and associated with a magmatic arc, began the sedimentary fi lling of Jurassic continental sub-basins in the CañadĂłn Asfalto Basin. Lacustrine and fl uvio-deltaic sediments, bearing a continental Middle Jurassic palynobiota, correspond to the Las Chacritas Member, while the sediments and palynobiota from the Late Jurassic Puesto Almada Member (both in the CañadĂłn Asfalto Formation) indicate a palustrine wetland subenvironment immersed within an arid macroenvironment. Paleoinvertebrates (conchostracans and sponges) of this formation suggest wet-dry cycles in the water bodies they inhabited. The sedimentological information together with the continental and coastal palynomorph assemblages of the back arc NeuquĂ©n Basin, allowed distinguishing a complete regressive-transgressive sequence for the Middle Jurassic Lajas Formation. For the Upper Jurassic in this basin, the thick gypsum and anhydrite deposits of the evaporitic coastal Auquilco Formation correlate with extended deposits of eolian sandstones corresponding to the BotucatĂș paleodesert, and a saltmarsh environment is inferred from the palynofl ora. The palynologic associations from both basins indicate a regional warm climate with seasonal aridity. Climatic conditions would have been drier in the continental interior (CañadĂłn Asfalto Basin), with strongly seasonally distributed temperatures, and moister in the western coast of the continent (NeuquĂ©n Basin), during the marine transgressions.Na presente revisĂŁo foram incluĂdos vĂĄrios proxies (sedimentologia, palinologia, invertebrados), das bacias de CañadĂłn Asfalto e NeuquĂ©n, para inferir o contexto climĂĄtico regional e ambiental durante o JurĂĄssico MĂ©dio e Superior da PatagĂŽnia. Na regiĂŁo central da PatagĂŽnia, no inĂcio do JurĂĄssico MĂ©dio, e associado a um arco magmĂĄtico, começou o preenchimento sedimentar de sub-bacias continentais jurĂĄssicas na bacia CañadĂłn Asfalto. Os sedimentos flĂșvio-deitaico e lacustres, tendo uma palinobiota continental do JurĂĄssico MĂ©dio correspondente ao Membro Las Chacritas, enquanto os sedimentos e a palinobiota do JurĂĄssico Superior do Membro Puesto Almada (ambos na Formação CañadĂłn Asfalto) indicam um subambiente palustre Ășmido imerso em um macroambiente ĂĄrido. Os paleoinvertebrados (conchostrĂĄceos e esponjas) desta formação sugerem ciclos Ășmidos-secos nos corpos de ĂĄgua por eles habitados. A informação sedimentolĂłgica juntamente com as assembleias de palinomorfos continentais e costeiros do âback arcâ da bacia NeuquĂ©n permitiu distinguir uma sequĂȘncia completa regressiva-transgressiva para o JurĂĄssico MĂ©dio da Formação Lajas. Para o JurĂĄssico Superior, os depĂłsitos de anidrita e gesso espessos da Formação Auquilco costeira evaporĂtica correlacionam-se com depĂłsitos extensos de arenitos eĂłlicos correspondentes ao paleodeserto Botucatu. Um ambiente âsaltmarshâ Ă© inferido a partir da palinoflora. As associaçÔes palinolĂłgicas de ambas as bacias indicam um clima regional quente com aridez sazonal. As condiçÔes climĂĄticas teriam sido mais secas no interior continental (bacia CañadĂłn Asfalto), com temperaturas fortemente distribuĂdas de forma sazonal, e Ășmidas na costa ocidental do continente (bacia de NeuquĂ©n), durante as transgressĂ”es marinhas.Fil: Volkheimer, Wolfang. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mendoza. Instituto Argentino de NivologĂa, GlaciologĂa y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de NivologĂa, GlaciologĂa y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de NivologĂa, GlaciologĂa y Ciencias Ambientales; ArgentinaFil: Quattrocchio, Mirta Elena. Universidad Nacional del Sur. Departamento de GeologĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Cabaleri, Nora Graciela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de GeocronologĂa y GeologĂa Isotopica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de GeocronologĂa y GeologĂa IsotĂłpica; ArgentinaFil: Narvaez, Paula Liliana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mendoza. Instituto Argentino de NivologĂa, GlaciologĂa y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de NivologĂa, GlaciologĂa y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de NivologĂa, GlaciologĂa y Ciencias Ambientales; ArgentinaFil: Rosenfeld, U.. WestfĂ€lische Wilhelms-universitĂ€t MĂŒnster; AlemaniaFil: Scafati, Laura Haydee. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; ArgentinaFil: Melendi, Daniel Luis. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentin
Provenance history of a Late Triassic-Jurassic Gondwana margin forearc basin, Murihiku Terrane, North Island, New Zealand: petrographic and geochemical constraints
The Murihiku Terrane in the North Island was a forearc basin adjacent to a volcanic arc along the eastern margin of Gondwana during the Mesozoic. The rocks that infill the basin are mainly volcaniclastic sandstones and mudstones, often turbiditic, with sparse shellbeds, rhyolitic tuffs, carbonaceous sandstones, plant beds, concretionary horizons, and rare thick granitoid-rich conglomerates. Petrographic studies of the rock fragments in the sandstones show that andesites are the dominant lithic type, but there is a wide range of other lithologies, including dacites, rhyolites, ignimbrites, granitoids, quartzofeldspathic mica schists, rare amphibolites, and reworked mudstones and sandstones. The sandstones are texturally and mineralogically immature and suggest deposition relatively close to a source of high relief, undergoing physical rather than chemical weathering in cool- to cold-temperate conditions. Geochemical analyses of 67 whole-rock volcaniclastic sandstones and siltstones indicate that they were derived from an active and dissected volcanic arc in a convergent margin setting built upon relatively thin continental crust. Modal petrographic data and whole-rock geochemistry both confirm that there were systematic variations with time in the composition of clastic material being supplied to the basin. From the Late Triassic to Middle Jurassic, there was a decrease in silicic volcanic material, plutonics, and metamorphics, and an increase in the supply of andesitic detritus. This was followed in the Late Jurassic by a broader range of volcanic detritus, varying from basaltic andesite to rhyolite, which may have been caused by progressive extension of the volcanic arc and thinning of the crust, a precursor to the breakup of Gondwana in the Early-Middle Cretaceous. Comparison with the Southland segment of the Murihiku Terrane in the South Island suggests that there were significant along-arc source variations, with relatively less silicic but greater andesitic and continental crust contributions in the North Island than in Southland. This may be analogous to the modern Taupo-Kermadec arc where there is a south-north along-arc transition from a continental to an oceanic arc
New Bathonian (Middle Jurassic) sauropod remains from the Valtos Formation, Isle of Skye, Scotland
The discovery of a sauropod tooth and a single sauropod footprint from the Valtos Formation supplements our knowledge of these dinosaurs from the Middle Jurassic of the Isle of Skye. Although the family cannot be determined from this single tooth, it is thought that it represents a primitive eusauropod and may belong to a similar sauropod to that previously described from limited isolated osteological evidence (caudal vertebra, damaged humerus and a rib). The characteristics that suggest this affinity include evidence of denticles on one edge of the tooth, wrinkling and granulation of the enamel, wear suggesting crown-to-crown occlusion, and the spatulate tooth shape. The single sauropod footprint is the oldest record of a sauropod footprint from the Middle Jurassic of Skye
The effects of the spreading of the Central Atlantic during the Middle Jurassic on dinosaur faunas
The spreading of the Central Atlantic is a complex series of
events that include a ridge jump to the east and a ridge jump to the west at c. 170Ma and c. 162Ma respectively. These jumps were influenced by plate interactions as Laurasia separated from Gondwana, although the second jump may have been influenced by spreading in the Gulf of Mexico, which occurred at about the same time. Dinosaur evolution and diversity were influenced by the spreading of the Central Atlantic that split Laurasia from Gondwana. The presence of dinosaurs, from the same taxonomic groups existed in the two regions from the Triassic until the Early
Cretaceous, suggests that there continued to be at least some mixing between Laurasian and Gondwanan faunas. This may
have been due to the proximity of the continents during the early stages of opening of the Atlantic, island hopping, or other means, enabling limited contact between Laurasia and Gondwana throughout the Mesozoic. Dinosaur faunas did, however, become more isolated and diverse later, in the Cretaceous, due to higher sea levels and seafloor spreading, but some elements of the faunas were still common to both continents. Similarities in faunas between North America and Asia, suggest that there were still links between these regions until the Maastrichtian at the end of the Late Cretaceous. In Laurasia some apparently endemic dinosaur groups (ceratopsians, pachycephalosaurs, therizinosaurs
and others) developed as a result of the break up of the continents and do not seem to have had any contact with Gondwana.
The diversity of dinosaurs has some differences between
Laurasia and Gondwana from the Late Jurassic onwards. During
the Cretaceous, Laurasian hadrosaurs and ceratopsians dominated the herbivores. Both these groups of ornithischian
dinosaurs were able to chew their food, which aided their ability to digest tough vegetation making it possible for them to evolve to be much smaller in size than their Gondwanan counterparts, the titanosaurid sauropods â a surviving group of the giant saurischian hebivores characterised by their inability to chew and by their enormous size.
There is also always the possibility that the apparent differences between the faunas are due to collecting bias and to differences in outcrop exposure in the present-day remnants of these once vast continents. There are certainly a lot fewer localities in the land masses that made up Gondwana as compared to Laurasia
- âŠ