Ograniczanie wyników

Czasopisma help
Autorzy help
Lata help
Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 36

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych:  amphibian
help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
A new albanerpetontid, Wesserpeton evansae gen. et sp. nov., from the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern England, is described. Wesserpeton is established on the basis of a unique combination of primitive and derived characters relating to the frontals and jaws which render it distinct from currently recognized albanerpetontid genera: Albanerpeton (Late Cretaceous to Pliocene of Europe, Early Cretaceous to Paleocene of North America and Late Cretaceous of Asia); Celtedens (Late Jurassic to Early Cretaceous of Europe); and Anoualerpeton (Middle Jurassic of Europe and Early Cretaceous of North Africa). Although Wesserpeton exhibits considerable intraspecific variation in characters pertaining to the jaws and, to a lesser extent, frontals, the new taxon differs from Celtedens in the shape of the internasal process and gross morphology of the frontals in dorsal or ventral view. It differs from Anoualerpeton in the lack of pronounced heterodonty of dentary and maxillary teeth; and in the more medial loca− tion and direction of opening of the suprapalatal pit. The new taxon cannot be referred to Albanerpeton on the basis of the morphology of the frontals. Wesserpeton currently represents the youngest record of Albanerpetontidae in Britain.
The albanerpetontid fossil record in Asia was limited to five dentaries of unidentified genus from the Upper Cretaceous Khodzhakul (lower Cenomanian) and Bissekty (Turonian) formations, Kyzylkum Desert, Uzbekistan. Here I describe two fragmentary frontals from the Khodzhakul local fauna as the first unequivocal record of the genusAlbanerpeton in Asia.
Cytochrome b is the central catalytic subunit of the quinol : cytochrome c oxidoreductase of complex III of the mitochondrial oxidative phosphorylation system and is essential to the viability of most eukaryotic cells. Partial cytochrome b gene sequences of 14 species representing mammals, birds, reptiles and amphibians are presented here including some species typical for Poland. For the analysed species a comparative analysis of the natural variation in the gene was performed. This infor­mation has been used to discuss some aspects of gene sequence — protein function relationships. Review of relevant literature indicates that similar comparisons have been made only for basic mammalian species. Moreover, there is little information about the Polish-specific species. We observed that there is a strong non-random dis­tribution of nucleotides in the cytochrome b sequence in all tested species with the highest differences at the third codon position. This is also the codon position of the strongest compositional bias. Some tested species, representing distant systematic groups, showed unique base composition differing from the others. The quail, frog, python and elk prefer C over A in the light DNA strand. Species belonging to the ar- tiodactyls stand out from the remaining ones and contain fewer pyrimidines. The ob­served overall rate of amino acid identity is about 61%. The region covering Qo cen­ter as well as histidines 82 and 96 (heme ligands) are totally conserved in all tested species. Additionally, the applied method and the sequences can also be used for di­agnostic species identification by veterinary and conservation agencies.
The Late Carboniferous amphibian genus Limnerpeton Fritsch, 1881 is revised on the basis of the type specimens of the eight original species described by Fritsch using material from Nýřany, Třemošná and Kounov, now in the Czech Republic. The type species Limnerpeton modestum is a nomen dubium restricted to a mandible that almost certainly belongs to an amphibamid temnospondyl but is not critically diagnostic. “Limnerpeton” laticeps and “Limnerpeton” macrolepis lectotypes are both small individuals of the same taxon as the later described Mordex calliprepes Steen, 1938 and thus form part of the hypodigm of Mordex laticeps comb. nov. “Limnerpeton” elegans is now Limnogyrinus elegans and is a member of the temnospondyl family Micromelerpetontidae. “Limnerpeton” obtusatum is a specimen of the microsaur Microbrachis pelikani. “Limnerpeton” dubium is an indeterminate tetrapod, probably either a temnospondyl or a pelycosaur. “Limnerpeton” difficile is a nomen dubium but the type is probably a small specimen of the tuditanomorph microsaur Crinodon limnophyes. “Limnerpeton” caducum is almost certainly a specimen of the ophiderpetontid aïstopod Oestocephalus granulosus. Several other described small temnospondyls from Nýřany are discussed and shown to be specimens of either Limnogyrinus elegans, Mordex laticeps or Amphibamidae incertae sedis. The tetrapod fauna at Nýřany includes four dissorophoid temnospondyls as proposed by Milner (1986) but with two changes in nomenclature. They comprise the branchiosaurid Branchiosaurus salamandroides, the micromelerpetontid Limnogyrinus elegans, the amphibamid Platyrhinops cf. lyelli and the primitive trematopid Mordex laticeps. These represent four of the five major dissorophoid families and demonstrate that the group had already diversified by the late Westphalian.
Re−investigation of the skull roof in Metoposaurus diagnosticus from the German Middle Keuper revealed that in contrast to previous opinions, the lacrimal bone in this species enters the orbital margin.The same pattern is demonstrated by the skulls of a newly discovered metoposaur from the Keuper of Krasiejów in Poland.The difference in the shape of the parietal between the population from Krasiejów and the type population of Metoposaurus diagnosticus enables the discrimination of two separate subspecies within Metoposaurus diagnosticus.For the specimens from the Late Carnian of Drawno Beds at Krasiejów, Poland and its lateral equivalents Lehrberg Beds at Stuttgart−Sonnenberg and Kieselsandstein at Fichtenberg, Germany, a new chronosubspecies Metoposaurus diagnosticus krasiejowensis is erected.The new subspecies differs from the older nominal subspecies M. diagnosticus diagnosticus in having a shorter and wider prepineal part of the parietal.If one accepts that the nominal subspecies is the ancestor of M. krasiejowensisthe change in the shape of the parietal would be a reversal of the trend towards elongating postorbital part of the skull observed in ancestors of the metoposaurids.It seems that the skull development in ontogeny changed after the anterior shift of the orbits occurred in the phylogenetic history of the metoposaurids.The difference in ornamentation of the interclavicle between European Metoposaurus and North American genera is corroborated by Polish material.
To evaluate stratigraphic evidence for the time of origin of the clade of extant amphibians (Lissamphibia), we attempt to establish a confidence interval on the lower bound of the stratigraphic range of this clade. This is based on the stratigraphic distribution of 1207 fossiliferous localities that have yielded lissamphibians, the relative area of sedimentary rocks from various periods (upper Paleozoic to present) exposed on the continents, and ten exponential−growth models of lissamphibian diversity that differ by the assumed effects of three major biological crises and the assumed starting times of lissamphibian diversification. The results suggest a more recent origin of Lissamphibia than advocated in most recent molecular studies. They are also more compatible with monophyly than with polyphyly of the extant amphibians, but heavily depend on poorly constrained assumptions about lissamphibian extinction rates during biological crises. Counts of lissamphibian diversity through time that consider ghost lineages and stage durations show moderate declines across the Cretaceous–Paleogene and Oligocene–Miocene boundaries.
Studies on amphibians of permanent water bodies and marshes in the Wawer district of Warsaw were carried out in the spring of 2007. This terrain is situated on the right bank of the Vistula River, and is one of the least urbanized areas of the city. In this study, species composition, frequency of occurrence and number of individuals on breeding sites were determined. Surprisingly, only six amphibian species were found, which was two times lower than found during previous research in the left bank area of Warsaw. The most common species occurring in Wawer were: moor frog (Rana arvalis) and common toad (Bufo bufo). Only 69.2 % of permanent water bodies were inhabited by any amphibian species. To enable future comparative studies to be made on the impact of urban development and increased human activity on local amphibian populations, the precise locality of breeding sites were provided.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.