The mid-Cretaceous Burmese amber (~99 Ma, Myanmar), widely known for exquisite preservation of theropods, also yields microfossils, which can provide important contextual information on ...paleoenvironment and amber formation. We report the first Cretaceous ostracod in amber-the gigantic (12.9 mm) right valve of an exclusively marine group (Myodocopa: Myodocopida) preserved in Burmese amber. Ostracods are usually small (0.5-2 mm), with well-calcified carapaces that provide an excellent fossil record extending to at least the Ordovician (~485 million years ago), but they are rarely encountered in amber. The new specimen effectively doubles the age of the ostracod amber record, offering the first representative of the Myodocopa, a weakly calcified group with a poor fossil record. Its carapace morphology is atypical and likely plesiomorphic. The preserved valve appears to be either a moulted exuvium or a dead and disarticulated specimen, and subsequent resin flows contain forest floor inclusions with terrestrial arthropods, i.e., fragmentary remains of spiders, and insect frass. These features resolve an enigmatic taphonomic pathway, and support a marginal marine setting for resin production.
Burmese Cretaceous amber (~99 Ma, Myanmar) is famous for the preservation of a wide range of fauna and flora, including representatives of marine, freshwater and terrestrial groups. Here, we report ...on three ostracod specimens, that came visible as syninclusions to an aquatic isopod. The three specimens represent three different taxa, that were found preserved in a single piece of amber. One of the described specimens was studied using microCT scanning data. On the basis of general carapace morphology we assign all three to the group Podocopida, and (tentatively) its ingroup Cypridocopina. A lack of visibility of more particular diagnostic features such as adductor muscle scars and details of the marginal zone precludes a further identification, but we discuss possible affinities with either the marine-brackish group Pontocypridoidea or the non-marine group Cypridoidea. The taphonomy indicates that the studied ostracods had been subject to limited (if any) post-mortem transport, which could be consistent with marginal marine environments.
Earth＇s climate has oscillated between greenhouse （warm） and icehouse （cold） modes throughout Earth history. At present, Earth is in the midst of an icehouse climate interval, despite the ...anthropogenic contribution to global warming and sea-level rise due to industrialization during the past two centuries. This led to a dramatic increase in atmospheric CO2, mainly caused by the extensive burning of fossils fuels. The Cretaceous （145 to 66 million years ago） is the youngest prolonged greenhouse climate interval in the Phanerozoic, marked by very high global mean temperatures with some extreme warming peaks （＇hothouse＇ or ＇supergreenhouse＇）, largely absence of permanent continental ice sheets, a mean global sea-level having been some 250 m higher than that of today, and levels of carbon dioxide 4 to 10 times higher than those of the pre-industrial era. If temperature will continue to rise as quickly as in the last three decades, we are close to being at the cusp to a new greenhouse climate interval facing quickly rising global sea-level and reaching atmospheric CO2 levels of the ＇Cretaceous supergreenhouse＇ in about the years 2190-2260 （Hay, 2011）. Evidence from Earth＇s history indicates that glacial-interglacial climate mode changes as well as past sea-level changes such as in the Cretaceous greenhouse occurred at rates orders of magnitude slower than observed at present. The recent rise in global sea-level in response to rising levels of atmospheric greenhouse gases, the associated global warm- ing, and the waning of continental ice shields is a primary concern for human society. To predict future sea-levels we need a better understanding of the record of past sea-level changes, especially in the greenhouse palaeoclimate modes. Therefore, understanding the Cretaceous palaeoclimate is essential for a more accurate prediction of future global climate, sea-level rise and environmental changes in a prospective ＇Cretaceous-like＇ greenhouse Earth.
Marginal-marine to non-marine ostracod assemblages from the Bajocian (Mid-Jurassic) of southern Tunisia, precisely from the Krachoua Formation at the Kef El Anneba section near the Beni Kheddache ...area, are here described and tested for their utility to improve the stratigraphic accuracy and palaeoenvironmental reconstructions. This particular microfauna consists of 11 species belonging to 6 genera and represents 2 distinct types of species-rich assemblages from this time interval, allowing the interpretation of the depositional setting of the fossiliferous horizon from which the samples derive. The first ostracod assemblage is mainly composed of the brackish to shallow marine species Fastigatocythere sp. Mette, 1995; Vernoniella aff. V. bajociana Bate, 1965b; Paracypris sp. A, Paracypris sp. B, Fabanella sarda Malz et al., 1985; Marslatourella aff. M. bathonica Andreu, 1999; and Fabanella aff. F. bathonica Oertli, 1957. This ostracod biofacies reflects marginal marine (shallow platform, restricted lagoon) conditions in the studied area. In contrast, the second ostracod assemblage is exclusively dominated by the non-marine limnic species Alicenula sp., Theriosynoecum pusilla Rohr, 1976; Theriosynoecum aff. T. aveyronensis Rohr, 1976; and Theriosynoecum sp. Such ostracod biofacies reflects the establishment of (a) permanent freshwater lake(s) in the studied area, triggered by the total emersion of the Bajocian Krachoua platform, presumably as response to the short-term sea-level fall event JBj3 of Haq (2017). The recognized ostracod species from the upper part of the Krachoua Formation at Kef El Anneba section (Medenine area) are particularly similar to those already described from the neighbouring sections of Kezzani (Dhaher area) and Krachoua (Tataouine area), facilitating a stratigraphic calibration of the Krachoua Formation, as well as regional correlations of the respective Bajocian continental event within the southern Tunisian palaeogeographic domain. Moreover, the biogeography of the studied ostracod microfauna from the Mid-Jurassic of southern Tunisia provides further arguments to support the hypothesis of significant biological exchanges between Laurasian and Gondwanan islands, as recently demonstrated by means of a charophyte microflora, indicating that Peri-Tethyan biogeography remained relatively uniform during that time interval and challenging the previous assumption of their endemism.
Cypridea Bosquet 1852 (Cypridoidea, Cyprideidae) is a Kimmeridgian to Lower Eocene nonmarine ostracod genus, the representatives of which are very common and stratigraphically useful in Late ...Tithonian to earliest Barremian "Purbeck/Wealden-like" nonmarine deposits of the world. The revision of particularly North American representatives led to progress in its taxonomy, and a breakthrough in its biostratigraphic supraregional biostratigraphic application. Key to their successful application is an upgraded taxonomic concept including new insights into the coherences of specific reproductive mechanisms (asexual and mixed reproduction) in the context with diversity and dispersal modes, combined with the understanding and evidence that these ostracods are not as endemic as erstwhile believed. This taxonomic concept resolves crucial problems resulting from an overestimation of the taxonomic significance of several carapace characters (particularly ornamentation elements and the outline), and facilitates improved stratigraphic and paleoecologic applications as well as providing the basis for further research. The revision includes an extensive historic overview of most relevant publications. Representatives of Cypridea have great utility in improving the biostratigraphic age determination for and correlation of Early Cretaceous formations of the Western Interior foreland basin. With respect to suprageneric taxonomy, the family Cyprideidae Martin 1940 is partially revised as well. Longispinella Sohn 1979 is now considered a subgenus of Cypridea while Cypridea (Guangdongia) Guan 1978 is allocated to Bisulcocypridea Sohn 1969, and the genus Praecypridea Sames, Whatley and Schudack 2010(b) is included. The genus Cypridea is emended anew. As for the subgeneric taxonomy, the North American species Cypridea (Pseudocypridina) inornata (Peck 1951) is now considered a junior synonym of Cypridea (P.) setina (Anderson 1939), Cypridea (P.) laeli Sohn 1979 considered an ecophenotype of Cypridea (P.) piedmonti (Roth 1933), and Cypridea (Longispinella) asymmetrica Sohn 1979 designated synonymous (sexual dimorph) to C. (L.) longispina Peck 1941. Sexual dimorphism is presumed in several species of Cypridea and mixed reproduction corroborated as being the most likely reproductive mechanism among taxa of this genus. Cypridea? minuta (Peck 1951) most probably represents an early representative of the sulcate Bisulcocypridea Sohn. Ostracod correlations mainly based on representatives of Cypridea strongly suggest a much higher maximum age for some Lower Cretaceous formations (Lakota Formation, South Dakota and Wyoming, and Cedar Mountain Formation, Utah) of the Western Interior foreland basin, i.e., Berriasian to Early Valanginian instead of Barremian or Aptian.
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Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The revision of Theriosynoecum Branson 1936, a common ostracod genus of Middle Jurassic to Early Cretaceous nonmarine deposits worldwide, demonstrates that its representatives—particularly the Early ...Cretaceous North American ones—are not as endemic as hitherto assumed. The taxonomic concept applied herein resolves many problems resulting from an overestimation of the taxonomic (in-)significance of some ornamentation elements in the genus as well as the too regional view of the faunas during the second half of the 20th century. This is the first step to a supraregional biostratigraphic and improved paleoecologic application of representatives of the extinct genus Theriosynoecum (Cytheroidea, Limnocytheridae, Timiriaseviinae). Theriosynoecum fittoni (Mantell 1844) and Theriosynoecum alleni (Pinto and Sanguinetti 1962) are proposed for being synonymous because of their many striking similarities. The species Theriosynoecum forbesii (Jones 1885) and T. verrucosa (Jones 1885) are considered separate and not subspecies of T. forbesii. Theriosynoecum verrucosa occurs in the uppermost Morrison Formation of the Black Hills area, South Dakota, U. S. A., Theriosynoecum fittoni in the Lakota Formation of the same area. Theriosynoecum pahasapensis (Roth 1933) is, thus far, endemic to North America. A key to the described species is presented. Early Cretaceous species of Theriosynoecum are not yet as applicable biostratigraphically in North America as in Europe (e. g. the English Purbeck/Wealden), but this is due to the lack of data from the former area and considered to be promising once more data are available. Nevertheless, the "classic" taxonomic approach provides a considerable step towards better application of these taxa as well as future analysis and robust discussion regarding the phylogeny, evolution and distribution of the limnocytherid subfamily Timiriaseviinae. The genus Metacypris is now restricted to an Aptian to recent lineage of small, weakly monosulcate Timiriaseviinae. Middle Jurassic to Early Cretaceous bisulcate and large taxa formerly designated as Metacypris are now assigned to Theriosynoecum.
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Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Orbital cyclicity is a fundamental pacemaker of Earth's climate system. The Newark–Hartford Basin (NHB) lake sediment record of eastern North America contains compelling geologic expressions of this ...cyclicity, reflecting variations of climatic conditions in tropical Pangea during the Late Triassic and earliest Jurassic (~233 to 199 Ma). Climate modeling enables a deeper mechanistic understanding of Earth system modulation during this unique greenhouse and supercontinent period. We link major features of the NHB record to the combined climatic effects of orbital forcing, paleogeographic changes, and atmospheric pCO2 variations. An ensemble of transient, orbitally driven climate simulations is assessed for nine time slices, three atmospheric pCO2 values, and two paleogeographic reconstructions. Climatic transitions from tropical humid to more seasonal and ultimately semiarid are associated with tectonic drift of the NHB from ~5 ∘N to 20 ∘N. The modeled orbital modulation of the precipitation–evaporation balance is most pronounced during the 220 to 200 Ma interval, whereas it is limited by weak seasonality and increasing aridity before and after this interval. Lower pCO2 at around 205 Ma contributes to drier climates and could have led to the observed damping of sediment cyclicity. Eccentricity-modulated precession dominates the orbitally driven climate response in the NHB region. High obliquity further amplifies summer precipitation through the seasonal shifts in the tropical rainfall belt. Regions with other proxy records are also assessed, providing guidance toward an integrated picture of global astronomical climate forcing in the Late Triassic and ultimately of other periods in Earth history.
Orbital cyclicity is a fundamental pacemaker of Earth’s climate system. The Newark–Hartford Basin (NHB) lake sediment record of eastern North America contains compelling geologic expressions of this ...cyclicity, reflecting variations of climatic conditions in tropical Pangea during the Late Triassic and earliest Jurassic (~233 to 199 Ma). Climate modeling enables a deeper mechanistic understanding of Earth system modulation during this unique greenhouse and supercontinent period. We link major features of the NHB record to the combined climatic effects of orbital forcing, paleogeographic changes, and atmospheric
p
CO
2
variations. An ensemble of transient, orbitally driven climate simulations is assessed for nine time slices, three atmospheric
p
CO
2
values, and two paleogeographic reconstructions. Climatic transitions from tropical humid to more seasonal and ultimately semiarid are associated with tectonic drift of the NHB from
~
5
°
N
to
20
°
N
. The modeled orbital modulation of the precipitation–evaporation balance is most pronounced during the 220 to 200 Ma interval, whereas it is limited by weak seasonality and increasing aridity before and after this interval. Lower
p
CO
2
at around 205 Ma contributes to drier climates and could have led to the observed damping of sediment cyclicity. Eccentricity-modulated precession dominates the orbitally driven climate response in the NHB region. High obliquity further amplifies summer precipitation through the seasonal shifts in the tropical rainfall belt. Regions with other proxy records are also assessed, providing guidance toward an integrated picture of global astronomical climate forcing in the Late Triassic and ultimately of other periods in Earth history.
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