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Tytuł:
A probable oligochaete from an Early Triassic Lagerstatte of the southern Cis-Urals and its evolutionary implications
Autorzy:
Shcherbakov, D.E.
Timm, T.
Tzetlin, A.B.
Vinn, O.
Zhuravlev, A.Y.
Powiązania:
https://bibliotekanauki.pl/articles/2082181.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Annelida
Clitellata
Oligochaeta
Mesozoic
Lagerstätte
Russia
Opis:
Oligochaetes, despite their important role in terrestrial ecosystems and a tremendous biomass, are extremely rare fossils. The palaeontological record of these worms is restricted to some cocoons, presumable trace fossils and a few body fossils the most convincing of which are discovered in Mesozoic and Cenozoic strata. The Olenekian (Lower Triassic) siliciclastic lacustrine Petropavlovka Lagerstätte of the southern Cis-Urals yields a number of extraordinary freshwater fossils including an annelid. The segmented body with a secondary annulation of this fossil, a subtriangular prostomium, a relatively thick layered body wall and, possibly, the presence of a genital region point to its oligochaete affinities. Other fossil worms which have been ascribed to clitellates are reviewed and, with a tentative exception of two Pennsylvanian finds, affinities of any pre-Mesozoic forms to clitellate annelids are rejected. The new fossil worm allows tracing of a persuasive oligochaete record to the lowermost Mesozoic and confirms a plausibility of the origin of this annelid group in freshwater conditions.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 2; 219-233
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A new genus of lance lacewings from the Middle Jurassic of Inner Mongolia, China
Autorzy:
Ma, Y.
Shih, C.
Ren, D.
Wang, Y.
Powiązania:
https://bibliotekanauki.pl/articles/2082186.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Insecta
Neuroptera
Osmylidae
Osmylinae
Mesozoic
Asia
China
Opis:
Fossils of Osmylinae are rare, currently only one fossil genus of this subfamily is known, Lithosmylus which is recorded from the late Eocene Florissant Formation of USA. Herein, we report a new Osmylinae genus with two new species, Vetosmylus tentus gen. et sp. nov. and Vetosmylus maculosus gen. et sp. nov. from the Middle Jurassic Jiulongshan Formation of Daohugou Village, Inner Mongolia, China, The new genus shares many apomorphic characters with extant osmyline relatives, e.g., forked subcostal veinlets in forewing; dense cross-veins present in radial sector, usually forming one complete outer gradate series in forewing; the region between MA and MP significantly broadened in hind wing, but with only one row of cells, implying a likely morphological stasis during the evolution of Osmylinae. The new genus Vetosmylus, the first and earliest record hitherto of Osmylinae from the Mesozoic, enhances our understanding of the early stages of their evolution.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 2; 363-369
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
New diplodocoid sauropod dinosaur material from the Middle Jurassic of European Russia
Autorzy:
Averianov, A.O.
Zverkov, N.G.
Powiązania:
https://bibliotekanauki.pl/articles/2082206.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Dinosauria
Sauropoda
Diplodocoidea
Mesozoic
Russia
Fennoscandian landmass
Opis:
Two anterior caudal vertebrae from apparently a single individual from the Callovian (Middle Jurassic) marine deposits of the Podosinki Formation at Peski Quarry near Moscow, Russia, are attributed by the phylogenetic analyses of two independent datasets to the sauropod clade Diplodocoidea. Morphologically, these vertebrae differ from the anterior caudals of Diplodocidae and Rebbachisauridae, but are similar to those of Dicraeosauridae. This finding is in line with a recent discovery of the dicraeosaurid sauropod Lingwulong from the late Early–early Middle Jurassic of China, and suggests earlier diversification of the main neosauropod lineages and Asiatic origin for Dicraeosauridae. The Peski sauropod is the first Jurassic terrestrial vertebrate from the Fennoscandian landmass. Diplodocoid sauropods likely dispersed to this land massive before the Bathonian, when it was still connected with Asia.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 3; 499-509
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Re-evaluation of pachycormid fishes from the Late Jurassic of Southwestern Germany
Autorzy:
Maxwell, E.E.
Lambers, P.H.
Lopez-Arabello, A.
Schweigert, G.
Powiązania:
https://bibliotekanauki.pl/articles/2082225.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Actinopterygii
Pachycormidae
Lagerstätte
Mesozoic
Kimmeridgian
Bavaria
Nusplingen
Opis:
Pachycormidae is an extinct group of Mesozoic fishes that exhibits extensive body size and shape disparity. The Late Jurassic record of the group is dominated by fossils from the lithographic limestone of Bavaria, Germany that, although complete and articulated, are not well characterized anatomically. In addition, stratigraphic and geographical provenance are often only approximately known, making these taxa difficult to place in a global biogeographical context. In contrast, the late Kimmeridgian Nusplingen Plattenkalk of Baden-Württemberg is a well-constrained locality yielding hundreds of exceptionally preserved and prepared vertebrate fossils. Pachycormid fishes are rare, but these finds have the potential to broaden our understanding of anatomical variation within this group, as well as provide new information regarding the trophic complexity of the Nusplingen lagoonal ecosystem. Here, we review the fossil record of Pachycormidae from Nusplingen, including one fragmentary and two relatively complete skulls, a largely complete fish, and a fragment of a caudal fin. These finds can be referred to three taxa: Orthocormus sp., Hypsocormus posterodorsalis sp. nov., and Simocormus macrolepidotus gen. et sp. nov. The latter taxon was erected to replace “Hypsocormus” macrodon, here considered to be a nomen dubium. Hypsocormus posterodorsalis is known only from Nusplingen, and is characterized by teeth lacking apicobasal ridging at the bases, a dorsal fin positioned opposite the anterior edge of the anal fin, and a hypural plate consisting of a fused parhypural and hypurals. The holotype specimen contributes additional palaeobiological information, with small teleosteans preserved as gastric contents and ribs showing signs of callus formation. These new findings extend our knowledge of the anatomy and diversity of Pachycormidae, and represent an important first step in understanding factors controlling their distribution and morphological variation in the Late Jurassic of Europe.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 3; 429-453
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Comparative bone microstructure of three archosauromorphs from the Carnian, Late Triassic Chanares Formation of Argentina
Autorzy:
Marsa, J.A.G.
Agnolin, F.L.
Novas, F.E.
Powiązania:
https://bibliotekanauki.pl/articles/2082158.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Archosauromorpha
Lagerpeton
Tropidosuchus
paleobiology
paleohistology
Mesozoic
South America
Opis:
The Chañares Formation exhibits one of the most important archosauriform records of early Carnian ecosystems. Here we present new data on the palaeohistology of Chañares archosauriforms and provide new insights into their paleobiology, as well as possible phylogenetically informative traits. Bone microstructure of Lagerpeton chanarensis and Tropidosuchus romeri is dominated by fibro-lamellar tissue and dense vascularization. On the other hand, Chanaresuchus bonapartei is more densely vascularized, but with cyclical growth characterized by alternate fibro-lamellar, parallel-fibered and lamellar-zonal tissues. Dense vascularization and fibro-lamellar tissue imply fast growth and high metabolic rates for all these taxa. These histological traits may be tentatively interpreted as a possible adaptative advantage in front of Chañares Formation environmental conditions.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 2; 387-398
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Evolution and identity of synapsid carpal bones
Autorzy:
Kummel, S.
Abdala, F.
Sassoon, J.
Abdala, V.
Powiązania:
https://bibliotekanauki.pl/articles/2082235.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Synapsida
carpus
intermedium
lunate
manus
homology
Permian
Mesozoic
Opis:
To date there is little information on carpal bone homology in late Palaeozoic and Mesozoic Synapsida. Crucial to the understanding of homology in synapsid carpal elements is the fact that different nomenclatures are used for the carpals of non-mammaliamorph Synapsida (Gegenbauer’s canonical nomenclature) and Mammaliaformes (mammalian nomenclature). The homologies of the carpals of non-mammaliamorph synapsids and mammals were established early last century and have not been reviewed since then. Here we provide a detailed study of the carpal bones of synapsids ranging in age from the early Permian to Late Cretaceous. The mammaliamorph lunate, previously considered the homologue of the intermedium of non-mammaliamorph synapsids, is interpreted here as homologous to their lateral centrale. We interpret the single mammaliamorph centrale as a homologue of the medial centrale of non-mammaliamorph synapsids. In some synapsid specimens, we found that one or two centralia are fused to the radiale (e.g., the gorgonopsian Arctognathus and tritylodontid Bienotheroides), supporting a digging habit. A third centrale is present in the therocephalian Theriognathus, very likely an abnormal duplication. An additional medial bone in a biarmosuchian was interpreted as a prepollex/ sesamoid. A cartilaginous prepollex/sesamoid may also have been present in several non-mammaliamorph synapsids, which have an open space proximal to distal carpal I. Distal carpal V is completely lost in dicynodonts and it is mainly fused to distal carpal IV in the adult stage of most other therapsid groups, but showed a delayed development in most non-mammaliamorph cynodonts. In mammaliamorphs, distal carpal V is not present. Our observations provide an updated revision of synapsid carpal homologies, mainly on the basis of position and anatomical contacts and also taking into account the results of embryological studies.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 4; 649-678
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
New findings reveal that the Middle Triassic ichthyosaur Mixosaurus cornalianus is the oldest amniote with a dorsal fin
Autorzy:
Renesto, S.
Dal Sasso, C.
Fogliazza, F.
Ragni, C.
Powiązania:
https://bibliotekanauki.pl/articles/2082209.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Ichthyosauria
Mixosauridae
soft tissue preservation
functional morphology
Mesozoic
Italy
Opis:
Two excellently preserved specimens of Mixosaurus cornalianus from the Anisian layers of the Middle Triassic Formazione di Besano, with soft parts associated with well-articulated skeletal elements, revealed the presence in this species of a dorsal fin and of a well-developed, triangular dorsal lobe of the caudal fin, both stiffened by an array of fibre bundles, as in Jurassic fast-swimming ichthyosaurs. This finding testifies that efficient swimming exaptations were already present in some Middle Triassic ichthyosaurs. Mixosaurus is then the oldest amniote so far known that developed a dorsal fin. The preservation of the fin shapes, scaleless skin, and three-dimensional dermal fibres is remarkable, allowing observation of their microstructure, and ruling out any artefactual interpretation. Stomach contents indicate that both specimens preyed upon cephalopods and small fishes. An internal organ, possibly a tract of the intestine, is also preserved in one specimen, which represents the first documented case in the ichthyosaurs of the Besano Formation, and a rarity in the fossil record of the clade.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 3; 511-522
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
New protoceratopsid specimens improve the age correlation of the Upper Cretaceous Gobi Desert strata
Autorzy:
Czepiński, L.
Powiązania:
https://bibliotekanauki.pl/articles/2082224.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Dinosauria
Ceratopsia
Protoceratopsidae
biostratigraphy
gradual evolution
anagenesis
Mesozoic
Mongolia
Opis:
New protoceratopsid (Dinosauria: Ceratopsia) specimens from two Late Cretaceous Mongolian localities with problematic stratigraphy are described. A specimen of Protoceratops andrewsi from the Zamyn Khond locality enables its correlation with other sites of the Djadokhta Formation. P. andrewsi is also abundant in the Üüden Sair locality, variously assigned to the Djadokhta or Baruungoyot formations. However, one new specimen from that site exhibits a fused nasal horn and a sharp buccal crest of the dentary. With these apomorphic features, it resembles Bagaceratops rozhdestvenskyi, known from the Baruungoyot and Bayan Mandahu formations. It may be an evidence for: sympatric evolution of B. roz hdestvenskyi and P. andrewsi; a dispersal of Bagaceratops to Üüden Sair; hybridization between the two parapatric taxa; or the anagenetic evolutionary transition from P. andrewsi to Bagaceratops. The anagenetic explanation appears to be most strongly supported by given data. This new record advocates for the age of the sediments from the Üüden Sair locality being intermediate between the Djadokhta and Baruungoyot formations. The observed changes in the frequency of the apomorphic features within protoceratopsid samples from various Late Cretaceous sites of the Gobi Desert potentially enable their correlations and chronological ordering.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 3; 481-497
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Docodonts from the British Mesozoic
Autorzy:
Sigogneau-Russell, D
Powiązania:
https://bibliotekanauki.pl/articles/22512.pdf
Data publikacji:
2003
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Mesozoic
Great Britain
docodont
Docodonta
Mammalia
Berriasian
Bathonian
paleontology
Opis:
This paper deals with new docodont teeth from the upper Bathonian of Forest Marble, collected by Prof. K.A. Kermack and his team, and from the basal Cretaceous of the Purbeck Limestone Group, collected by P. Ensom. Study of this materialled to the recognition of three new taxa: Borealestes mussettisp. nov. and Krusatodon kirtlingtonensis gen. et sp. nov. from Forest Marble, Peraiocynodon majorsp. nov. from Purbeck; this makes the Bathonian locality the richest (four species) docodont locality so far known. The possible synonymy of Cyrtlatherium–Simpsonodon (Forest Marble) and of Peraiocynodon–Docodon (Purbeck−Morrison) suggested by several authors is discussed. In conclusion, phyletic relationships between the known docodont genera are proposed, based on lower molars.
Źródło:
Acta Palaeontologica Polonica; 2003, 48, 3
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Xenoxylon synecology and palaeoclimatic implications for the Mesozoic of Eurasia
Autorzy:
Oh, C.
Philippe, M.
Kim, K.
Powiązania:
https://bibliotekanauki.pl/articles/945484.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
paleontology
fossil wood
Xenoxylon
phytocoenosis
paleoecology
paleoclimate
Mesozoic
Eurasia
Opis:
The distribution of fossil wood genera has been demonstrated to be an effective proxy for Mesozoic terrestrial climates. In this study, we investigated the phytocoenoses, which were associated with Xenoxylon confirmed to be a marker for a cool and/or wet climate in a boreal hemisphere (i.e., Xenoxylon-phytocoenoses) during the Mesozoic, using specimens of fossil wood. It was confirmed that Xenoxylon co-occurs more often with some wood genera than with others. For example, Protocedroxylon, a wood that is most likely related to the Pinaceae, is the genus most often associated with Xenoxylon-phytocoenoses. Although Taxodioxylon is also found in Xenoxylon-phytocoenoses, it is not found, however, as consistently as Protocedroxylon. The distribution and diversity of Xenoxylon-phytocoenoses changed throughout the Mesozoic. During the Late Triassic and Late Cretaceous, Xenoxylon-phytocoenoses had low diversity and were restricted to higher palaeolatitudes during the Late Cretaceous. However, during the Early to Middle Jurassic, Xenoxylon-phytocoenoses were distributed much farther south, while their diversity concomitantly increased sharply. From the Late Jurassic to the Early Cretaceous, the distribution of Xenoxylon phytocoenoses moved northward in Europe and even more so in East Asia. The changes in the distribution of Xenoxylon-phytocoenoses are in agreement with changes in both global and regional climates. Our results also demonstrated that, within the Xenoxylon distribution range, the corresponding phytocoenoses were differentiated along a latitudinal gradient and according to the global climate change patterns during the Mesozoic.
Źródło:
Acta Palaeontologica Polonica; 2015, 60, 1; 245-256
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A new Early Cretaceous flea from China
Autorzy:
Zhang, Y.
Shih, C.
Rasnitsyn, A.P.
Ren, D.
Gao, T.
Powiązania:
https://bibliotekanauki.pl/articles/2082117.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Insecta
Siphonaptera
Saurophthiridae
Saurophthirus
ectoparasitic insects
compression fossils
Mesozoic
Asia
Opis:
Fleas are highly specialized holometabolic insects. So far, only 16 species of fossil fleas in five families have been reported due to the rare fossil records. At present, the earliest flea fossils are reported from the Middle Jurassic Jiulongshan Formation of Northeastern China. The descriptions of these earliest species pushed back the origin of Siphonaptera by at least 40 million years. It is generally accepted that saurophthirids are the “transitional” taxa from stem Jurassic fleas to living crown groups. Herein, we described a new “transitional” flea species, Saurophthirus laevigatus Zhang, Shih, Rasnitsyn, and Gao sp. nov., from the Lower Cretaceous Yixian Formation of Northeastern China, assigned to Saurophthiridae. The new species provides new evidence to support saurophthirids as a “transitional” group. Sexual dimorphism suggests significant differences in biology of opposite sexes in Saurophthirus. Analysis of described Mesozoic species demonstrates the body size reduction from the Middle Jurassic to the Early Cretaceous. Smaller body size was likely advantageous in reducing the probability of being detected and removed by the host and in minimizing flea’s demand for blood intake and energy input, indicating the adaptation of the ectoparasitic lifestyle of fleas in their early stage of evolution.
Źródło:
Acta Palaeontologica Polonica; 2020, 65, 1; 99-107
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The extent of the pterosaur flight membrane
Autorzy:
Elgin, R.
Hone, D.
Frey, E.
Powiązania:
https://bibliotekanauki.pl/articles/23515.pdf
Data publikacji:
2011
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
paleontology
Reptilia
Pterosauria
flight
wing
Mesozoic
pterosaur
wing membrane
fossil
Opis:
The shape and extent of the membranous brachioptagium in pterosaurs remains a controversial topic for those attempting to determine the aerodynamic performance of the first vertebrate fliers. Various arguments in favour of the trailing edge terminating against either the torso or hip, the femur, the ankle, or different locations for various taxa, has resulted in several published reconstructions. Uncertainty over the correct model is detrimental to both aerodynamic and palaeoecological studies that are forced to simultaneously consider multiple and highly variable configurations for individual taxa. A review of relevant pterosaur specimens with preserved soft tissues or impressions of the wing membrane, however, strongly suggests that the trailing edge of the wing extended down to the lower leg or ankle in all specimens where the brachiopatagium is completely preserved. This configuration is seen across a phylogenetically broad range of pterosaurs and is thus likely to have been universally present throughout the Pterosauria. Support for opposing hypotheses where the trailing edge terminates against the body, hip, or knee are based on several specimens where the wing membrane is either incomplete or has undergone post−mortem contraction. An ankle attachment does not rule out a high aspect ratio wing as the curvature of the trailing edge and the ratio of the fore to hind limbs also play a major role in determining the final shape of the membrane.
Źródło:
Acta Palaeontologica Polonica; 2011, 56, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Macroevolutionary and morphofunctional patterns in theropod skulls: A morphometric approach
Autorzy:
Foth, C.
Rauhut, O.W.M.
Powiązania:
https://bibliotekanauki.pl/articles/21033.pdf
Data publikacji:
2013
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
macroevolution
theropod dinosaur
skull
Theropoda
feeding ecology
biomechanics
evolution
Mesozoic
paleontology
Opis:
Theropod dinosaurs are one of the most remarkable lineages of terrestrial vertebrates in the Mesozoic, showing high taxo− nomic and ecological diversity. We investigate the cranial diversity of non−avian theropods and some basal birds, using geometric morphometrics to obtain insights into the evolutionary modifications of the skull. Theropod skulls mostly vary in the shape of the snout and length of the postorbital region (principal component [PC] 1), with further variation in orbit shape, depth of the postorbital region, and position of the jaw joint (PC 2 and PC 3). These results indicate that the cranial shape of theropods is closely correlated with phylogeny and dietary preference. Skull shapes of non−carnivorous taxa dif− fer significantly from carnivorous taxa, suggesting that dietary preference affects skull shape. Furthermore, we found a significant correlation between the first three PC axes and functional proxies (average maximum stress and an indicator of skull strength). Interestingly, basal birds occupy a large area within the morphospace, indicating a high cranial, and thus also ecological, diversity. However, we could include only a small number of basal avialan species, because their skulls are fragile and there are few good skull reconstructions. Taking the known diversity of basal birds from the Jehol biota into account, the present result might even underestimate the morphological diversity of basal avialans.
Źródło:
Acta Palaeontologica Polonica; 2013, 58, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The dorsal shell wall structure of Mesozoic ammonoids
Autorzy:
RADTKE, GREGOR
KEUPP, HELMUT
Powiązania:
https://bibliotekanauki.pl/articles/945306.pdf
Data publikacji:
2017
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
ammonoidea
internal structure
dorsal shell wall
wrinkle layer
spiral ornament
ritzstreifen
mesozoic
Opis:
The study of pristine preserved shells of Mesozoic Ammonoidea shows different types of construction and formation of the dorsal shell wall. We observe three major types: (i) The vast majority of Ammonoidea, usually planispirally coiled, has a prismatic reduced dorsal shell wall which consists of an outer organic component (e.g., wrinkle layer), which is the first layer to be formed, and the subsequently formed dorsal inner prismatic layer. The dorsal mantle tissue suppresses the formation of the outer prismatic layer and nacreous layer. With the exception of the outer organic component, secretion of a shell wall is omitted at the aperture. A prismatic reduced dorsal shell wall is always secreted immediately after the hatching during early teleoconch formation. Due to its broad distribution in (planispiral) Ammonoidea, the prismatic reduced dorsal shell wall is probably the general state. (ii) Some planispirally coiled Ammonoidea have a nacreous reduced dorsal shell wall which consists of three mineralized layers: two prismatic layers (primary and secondary dorsal inner prismatic layer) and an enclosed nacreous layer (secondary dorsal nacreous layer). The dorsal shell wall is omitted at the aperture and was secreted in the rear living chamber. Its layers are a continuation of an umbilical shell doubling (reinforcement by additional shell layers) that extends towards the ventral crest of the preceding whorl. The nacreous reduced dorsal shell wall is formed in the process of ontogeny following a prismatic reduced dorsal shell wall. (iii) Heteromorph and some planispirally coiled taxa secrete a complete dorsal shell wall which forms a continuation of the ventral and lateral shell layers. It is formed during ontogeny following a prismatic reduced dorsal shell wall or a priori. The construction is identical with the ventral and lateral shell wall, including a dorsal nacreous layer. The wide distribution of the ability to form dorsal nacre indicates that it is a plesiomorphic trait which either was passed on from gyrocone ammonoid ancestors or (re-)developed in post-Triassic ammonoids.
Źródło:
Acta Palaeontologica Polonica; 2017, 62, 1; 59-96
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
First post-Mesozoic record of Crocodyliformes from Chile
Autorzy:
Walsh, S A
Suarez, M.
Powiązania:
https://bibliotekanauki.pl/articles/21357.pdf
Data publikacji:
2005
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Mesozoic
Neogene
Crocodyliformes
extinction
Bahia Inglesa Formation
crocodile
Chile
paleontology
climate change
Opis:
Fossil crocodilians are well known from vertebrate bearing localities in South America, but the last record of the group in Chile is from the Cretaceous. No living crocodilians occur in Chile today, and the timing of their disappearance from the country is unknown. We provide the first post−Mesozoic report of crocodilian remains from late Miocene marine deposits of the Bahía Inglesa Formation, northern Chile. The fragmentary material provides proof that Crocodiliformes were present in Chile until at least seven million years ago. We suggest that late Neogene climatic cooling and changes in South American palaeophysiography caused the extinction of the group in Chile.
Źródło:
Acta Palaeontologica Polonica; 2005, 50, 3
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł

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