摘要:

The Wessex Formation on the Isle of Wight yields an Early Cretaceous dinosaur fauna. Sedimentological evidence shows that this represents a mosaic of fluvial, floodplain and lacustrine environments within a relatively narrow east‐west oriented valley. The vegetational cover on the alluvial plain had a savannah‐or chaparral‐like aspect, probably of low productivity. The relative scarcity of small aquatic vertebrates, absence of coals, abundance of oxidixed sediments and the presence of immature calcretes indicate seasonal water supply. The dinosaur taxa compising the Wessex Formation faunal assemblage represent a single palaeocommunity which inhabited the local alluvial plain, although some species may have been transient. The fauna had a relatively low diversity and this is attributed to the low productivity of the local vegetation. Iguanodontids andHypsilophodonwere the dominant elements in the fauna. In contrast to Late Jurassic dinosaur faunas, sauropods are less abundant in the Wessex Formation, although they remain taxonomically diverse. It is concluded that climatic changes which took place in the Late Jurassic or Early Cretaceous resulted in the appearance of low productivity vegetation and that this was incapable of supporting large sauropod popula

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1994.tb00318.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Rhaetian fossil vertebrate faunas of Britain represent rich but biased samples of taxonomic diversity during uppermost Triassic time. Review of the Westbury Formation, Penarth Group, in particular, reveals a combination of marine, littoral, and terrestrial elements. Minimally, six species of shark are preserved along with a myriacanthid holocephalan, at least four actinopterygian taxa, a characteristic lungfish, ichthyosaurs, plesiosaurs, dinosaurs, and potentially the earliest representative of the Choristodera. Rare mammalian occurrences in the Westbury beds are also possible.Severnichthys gen. nov.is a large osteichthyan, probably a palaeonisciform chondrostean, which historically has been mistaken for a labyrinthodont amphibian. At least two additional actinopterygian species and a holocephalan are known from die Lilstock Formation, and a mammal or mammallike reptile is recorded from the uppermost Blue Anchor Formation. Analysis of element abundance in the disarticulated Westbury Formation assemblage indicates that many parts of some taxa are never preserved while other elements of the same form are common. Such preservational bias suggests that many species may be missing entirely from this long‐studied but poorly understood taphocoenosis. Possibly contemporaneous cave faunas from nearby upland areas give a similarly biased picture of the terrestrial fauna during this time of widespread marine transgressio

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1994.tb00319.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The sediments rilling underground cavities and open fissures represent a major source of fossil vertebrate remains. The significance of such sites is disproportionate to the relatively small volume of sediment which they contain, and arises from the enhanced preservation, compared with surface sites, of both bones and sediments and the operation of one or more concentrative processes. Isolation of vertebrate material from temperature and humidity changes, scavenging and soil organisms greatly increases their preservation potential. Three main types of concentrative mechanism can be recognized: where the animals lived and died in that environment (biotic autochthonous); where the animal remains were transported into that environment by some biotic agency, such as a predator (biotic allochthonous); and where the animal remains were introduced into that environment as a result of some abiotic process, such as flooding (abiotic allochthonous). The precise mechanism operating in a particular case may be deduced from a consideration of faunal composition, taphonomic criteria and geomorphological and sedimentological contexts, with each concentrative process being characterized by a distinctive combination of these.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1994.tb00320.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

A combined field‐based/petrographic study to investigate the formation of Rhaetian ‘bone‐beds’ from the Westbury Formation, Upper Triassic of south‐west Britain, has been undertaken. ‘Bone‐beds’ in the Westbury Formation have been found at the top of coarsening upward successions, on flooding surfaces which underlie organic‐rich mudstones. These ‘bone‐beds’ are frequently found either overlying or amalgamated with ‘shell‐beds’, and often contain large (up to cobble‐sized) intraclasts. This work indicates that they formed during a period of relative sea‐level rise, when the sediment was being reworked (forming a transgressive lag) and a condensed section had developed. Phosphate authigenesis is thought to have occurred at the oxic/Fe‐reduction interface, where the pore waters were dysoxic, enriched with dissolved phosphate and relatively acidic. ‘Bone‐bed’ formation was terminated when siliciclastic mud prograded over the condensed section and ‘normal’ anoxic/sulfidic pore wate

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1994.tb00321.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1994.tb00308a.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY