Neogene

Mollusca Bivalvia

During the Miocene and most of the Pliocene, the shores of the North Sea Basin lay to the east of Britain, and marine deposition took place in northern Germany and Denmark. The shoreline advanced westwards again in the late Pliocene and early Pleistocene. From the Miocene onwards, marine faunas consist increasingly of extant species, including, in the north-west European deposits, species found today in the west Atlantic and the Mediterranean. The present day latitudinal sequence of faunas, or...

Upper Jurassic

Photos Jurassic Bivalves

The late Middle Jurassic witnessed a phase of deepening seas accompanied by marine invasion of the earlier Middle Jurassic lagoons and deltas. The resulting environmental changes led to the deposition of more uniform marine sediments over much of northwestern Europe and provided sharp environmental contrasts with those that had preceded them. Although major marine invasion began in the late Middle Jurassic, as defined by ammonite zones, for convenience we have included these latest Middle...

Silurian

The marine faunas in the Silurian were dominated by benthic brachiopods and pelagic graptolites. Although trilobites occur in many environments, they were far less important than in the Or-dovician. Molluscs, bryozoans, ostracodes and crinoids are also present, but only common in some habitats. Towards the end of the Silurian, the land was just beginning to be colonized by plants, but animals with hard parts were absent from the land, although some arthropods and worms may have become...

Lower Cretaceous

Lower Cretaceous Bivalves

91 Lower Cretaceous Terrestrial Communities In parts of northern Europe the end of the Jurassic witnessed a phase of marked earth movements which caused some of the old subsiding marine basins to become swamps and marshlands. These early Cretaceous flood-plain regions were periodically inundated by seasonal rivers. In shallow pools along the watercourses and in the waterlogged parts of the flood plains horsetails (Equisetales) grew. One genus of this group of pteridophytes (Equisetum) still...

Reef Communities

The following account of Reef Communities Nos. 44 48 ofmid-Vis'ean Asbian age has been contributed by Mr. D. Mundy. Mid-Visean reef limestones are generally associated with a marginal situation between a stable shallow water 'shelf environment and a deeper subsiding'basin' environment, and are usually characterized by a marked contemporary topographic relief. This can take the form of discrete 'knolls' as in the 'Craven reef belt' or a continuous 'apron' as in north Derbyshire . In both cases...

Permian

Dibujo Del Mundo

During the Permian and especially the early part of the period the seas withdrew from the continental masses, to a greater or less extent, in many parts of the world Fig. j . But some areas, including parts of Australia and the United States, contain marine sequences in which, in broad terms and with different taxa, many of the types of community seen in the Carboniferous persist. Permian marine onshore faunas, like those of the Carboniferous, are dominated by the brachiopods, which occupy...

Freshwater Communities

Organisms Freshwater System Habitats

Freshwater Middle Jurassic assemblages occur within the deltaic and lagoonal sequences as transported accumulates in marine and brackish water sediments. Characteristic Middle Jurassic freshwater mollusca included the turreted gastropod Bathonella Viviparus , the planospiral gastropod Valvata, and the bivalve Unio their descendants live in the same habitats today. The freshwater sediments are silty clays and sands which probably accumulated in rivers and low-lying lakes The sediments never...

Tentaculites Silur

Maclurite Cambrian

E Lingulella Brachiopoda Inarticulata f Callograptus Hemichordata Dendroidea g Conotreta Brachiopoda Inarticulata e Lingulella Brachiopoda Inarticulata f Callograptus Hemichordata Dendroidea g Conotreta Brachiopoda Inarticulata Homalopteon, a nileid, is smooth and has much larger eyes than Asaphus or Ogygiocaris the smooth outline to the carapace may have been an adaptation for easier movement through the mud on the sea floor. The trinucleids have long genal spines extending back from the sides...

Cardiaster Fossarius

Mollusca Bivalves

Neohibolites minimus Mollusca Cephalopoda Coleoidea belemnite bivalves by boring small circular holes in the valves with its specialized radula. Byssally attached inoceramids are common in clusters, as in the Lower Gault, but the ribbed Inoceramus concen-tricus is replaced by Actinoceramus sulcatus, a descendant with coarse radial ribs. Coelenterates are represented by the tiny, solitary, ahermatypic cup coral Trochocyathus. Deposit feeders dominate the infauna, and the sediment is bioturbated,...

Present day

Lithotrya Structure

Six present communities are illustrated here four of these from around Britain and two from the tropical Indo-Pacific Province. The tropical communities are more diverse than comparable communities in higher latitudes Thorson, 1957 . The sands, sandy muds and muds in the shelf seas around the British Isles support a diversity of benthic communities, most of which became established after the beginning of the last major glacial advance about 15,000 years ago. The community illustrated is based...

Lingkungan Hidup Brachiopoda

Cricoconarida

Table III The Silurian ecogroups and chief animal communities and their evolution with time Table III The Silurian ecogroups and chief animal communities and their evolution with time low. A few species change from one habitat to another with time, but the great majority of Silurian brachiopod lineages remain in the same habitat throughout the period. The succession of communities in one habitat with component genera changing through time must be distinguished from a single community where the...

Upper Cretaceous Faunas

Bathrotomaria Ecology

While the British Lower Cretaceous is characterized by diverse and variable facies, the Upper Cretaceous is characterized by the a Siphonia tulipa Porifera Demospongea b Hallirhoa costata Porifera Demospongea c Doryderma bennetiae Porifera Demospongea d Doryderma dichotomum Porifera Demospongea e Chlamys aspera Mollusca Bivalvia Pterioida pectinid f Exogyra obliquata Mollusca Bivalvia Pterioida oyster g Neithea gibbosa Mollusca Bivalvia Pterioida pectinid presence of fine grained pelagic...

Low Diversity Temporarily Stable Calcarenite Community

Rhynchonella

This sediment consisted of finely broken shell debris which was the result of a combination of predation and mechanical erosion. It is likely that originally the sediment surface was rippled and provided a fairly mobile substrate. Thus, the fauna which inhabited it consisted of fairly specialized animals all adapted to withstand the somewhat rigorous environmental stresses. Many of the colonizing animals took refuge within the sediment and, consequently, many of the original sedimentary...

Lower Jurassic

In the Lower Jurassic, the marine benthos consisted mostly of invertebrates bivalves, gastropods and crustaceans are the commonest groups. These three groups all show major evolutionary advances when compared with their ancestors of the Palaeozoic. More bivalve taxa had developed siphons which enabled them Fig. n. Geography of the North Atlantic region during the Middle Jurassic Fig. n. Geography of the North Atlantic region during the Middle Jurassic to burrow more efficiently this was either...