Nowa wersja platformy, zawierająca wyłącznie zasoby pełnotekstowe, jest już dostępna.
Przejdź na
Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 33

Liczba wyników na stronie
first rewind previous Strona / 2 next fast forward last
Wyniki wyszukiwania
help Sortuj według:

help Ogranicz wyniki do:
first rewind previous Strona / 2 next fast forward last
Content available Upper Cretaceous amniotic eggs from Gobi Desert
There are described several types of Upper Cretaceous fossil amniote eggs, clutches and eggshells, collected during the Polish-Mongolian Paleontological Expeditions (1963—1971) in several localities of the Gobi Desert. Isotopic ratios of C and О are reported and discussed. The eggs may be attributed to saurischian and ornithischian dinosaurs, and palaeognathous birds. Four types of problematica are also described. Taphonomy and restoration of eggshells’ diffusive properties as compared with modern hard-shelled eggs suggest paleoecological interpretation of the nesting conditions as rather dry for smooth-shelled eggs, humid for ornamented eggs, and very humid for the thickest-shelled eggs. Different nest types are postulated for ornamented and smooth eggs, based on taphonomy and shell parameters.
Praca zawiera opis kolekcji późnokredowych jaj ptaków, dinozaurów gadzio- i ptasiomiedniczych, oraz prawdopodobnych skamieniałości miękkoskorupowych jaj innych gadów, odkrytych w latach 1963—71 przez Polsko-Mongolskie Wyprawy Paleontologiczne na pustyni Gobi (fig. 1). Kolekcja ta, gromadząca bogaty materiał kopalny, obejmujący kilkanaście typów jaj późnokredowych, należy do najbogatszych w świecie. Poza przeglądem mikrostruktury skorup (fig. 3, 4, 8) i kształtów jaj (fig. 2, 6; pl. 11—20), przedstawiono szacunkowe wyliczenia objętości, powierzchni, wydłużenia jaj, porowatości skorupy i jej przepuszczalności dla gazów oddechowych, porównując je z równaniami allometrycznymi dla współczesnych jaj ptasich (fig. 7, 9, tab. 1). Zaproponowano funkcjonalne wyjaśnienie roli ornamentacji, kształtu jaj i różnic tafonomicznych między gniazdami jaj ornamentowanych i gładkich (fig. 5) oraz oszacowano warunki i długość trwania inkubacji różnych typów jaj. Wyniki badań składu izotopowego węgla i tlenu w próbkach skorup (fig. 10) wskazują na przewagę lokalnych czynników diagenetycznych w kształtowaniu proporcji trwałych izotopów, nie pozwalając na wiarygodne wnioskowanie o klimacie lub diecie dinozaurów i ptaków kopalnych. Pracę wykonano w Instytucie Paleobiologii PAN w ramach problemu CPBP 04.03.
The skull of a newly prepared Tarbosaurus bataar is described bone by bone and compared with a disarticulated skull of Tyrannosaurus rex. Both Tarbosaurus bataar and Tyrannosaurus rex skulls are deep in lateral view. In dorsal view, the skull of T. rex is extremely broad posteriorly but narrows towards the snout; in Ta. bataarthe skull is narrower (especially in its ventral part: the premaxilla, maxilla, jugal, and the quadrate complex), and the expansion of the posterior half of the skull is less abrupt. The slender snout of Ta. bataaris reminiscent of more primitive North American tyrannosaurids. The most obvious difference between T. rex and Ta. bataar is the doming of the nasal in Ta. bataar which is high between the lacrimals and is less attached to the other bones of the skull, than in most tyrannosaurids. This is because of a shift in the handling of the crushing bite in Ta. bataar. We propose a paleogeographically based division of the Tyrannosaurinae into the Asiatic forms (Tarbosaurus and possibly Alioramus) and North American forms (Daspletosaurus and Tyrannosaurus). The division is supported by differences in anatomy of the two groups: in Asiatic forms the nasal is excluded from the major series of bones participating in deflecting the impact in the upper jaw and the dentary−angular interlocking makes a more rigid lower jaw.
Elusive tracks of stegosaurs have been long searched for by ichnologists, and various purported stegosaur imprints have recently been reported. A fragmentary trackway of a large, quadrupedal ornithischian dinosaur was found on an isolated slab of Oxfordian dolomite, on the northeastern slope of Holy Cross Mountains, Poland. The track is similar to large, blunt−toed Late Jurassic ichnites from North America. The footprints show a distinctive morphology, which fits the stegosaurian foot. The newly described ichnites from the Upper Jurassic of Poland provide the second ichnological evidence of the Late Jurassic dinosaurs in this country; numerous rich dinosaur footprint assemblages were previously known only from the Lower Jurassic outcrops.
Fossils plants (less than 0.5 m high) preserved in upright position were found in Śmiłów Quarry (E of Szydłowiec) at the northern slope of the Holy Cross Mountains. The plants were preserved as impressions of ascending narrow-leafed stems in fine-grained sandstone of the Drzewica Formation (upper Pliensbachian). The leaves are 5-25 cm long and about 2-5 mm wide; the angle between them and the short main axis ranges within 20-30o. Morphology of the plant resembles schizeacean ferns, but also that of Aethophyllum stipulare Brongniart 1828 from Anisian of France, recognized by Grauvogel-Stamm (1978) as an herbaceous gymnosperm. Grauvogel-Stamm (1978) supposed that the leaves Podozamites and cone scales Swedenborgia, common in Jurassic strata of higher palaeolatitudes, are derived from descendants of Aethophyllum. Podozamites leaves often occur in many dinosaur track-bearing horizons in the Polish Jurassic. Thus, herbaceous conifers might have played an important and often underestimated role in the Mesozoic ecosystems (possibly as a substantial part of dinosaur diet). The possiblity of coniferous equivalents of Cenophytic herbaceous angiosperms, as well as a possibility of their coevolution with Mesozoic low browsing and grazing herbivore megafauna is worth further palaeobotanical and palaeoecological studies.
Tyrannosauridae can be subdivided into two distinct subfamilies—the Albertosaurinae and the Tyrannosaurinae. Previously recognized subdivisions Aublysodontinae and Shanshanosaurinae are rejected because they are based on insufficient material and juvenile specimens. Our results are based upon a phylogenetic analysis using PAUP program (Swofford 1999) of 77 skull characters and seven genera (Albertosaurus, Alioramus, Daspletosaurus, Gorgosaurus, Nanotyrannus, Tarbosaurus, and Tyrannosaurus); with Allosaurus as outgroup. Of the 77 characters used, more than half were parsimony informative. Asingle most parsimonious tree was obtained with the Tree Length being 88. The analysis of cranial characters and comparison of postcranial features reveal that Tarbosaurus bataar is not the sister taxon of Tyrannosaurus rex (contra Holtz 2001). Their similarities are partially due to the fact that both are extremely large animals. Thus, Tarbosaurus should be considered a genus distinct from Tyrannosaurus.
first rewind previous Strona / 2 next fast forward last
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.