Other weaker storm currents, in deeper areas slightly below the reach of waves, merely toppled crinoids and other organisms more or less in their life positions. Such preservation is typical of the cystoid bed where whole Caryocrinites were more gently uprooted and knocked over without being torn apart.
The normally low current and wave energy settings of deeper Rochester environments may have limited certain organisms that required water movement to provide feeding currents, such as most echinoderms. It may also have promoted a multi-tiered community in which different groups of organisms fed at different levels above the seafloor (see Ausich and Bottjer, 1982). Brachiopods and bryozoans, which could produce their own filter feeding currents (active filter feeders) may have benefitted from living close to the seafloor where suspended food was concentrated by gravity settling, whereas crinoids that relied strictly on external currents (passive suspension feeders) survived by elevating their crowns up away from the stagnant boundary zone near the sediment surface and into levels of at least some current energy.
Modes of Life of Silurian Organisms and Community Paleoecology
Marine ecologists classify organisms into guilds or generalized modes of life based upon their: a) position with respect to their life in the water column, planktonic (floating) and nektonic (swimming) or on seafloor, benthic as well as b) their feeding or trophic types. Benthic organisms are further identified as infaunal (living within the sediment) or epifaunal (living on the sediment surface). Many, such as brachiopods and crinoids, are sessile or sedentary, while others like gastropods, are vagrant, crawling on the seafloor.
All ecosystems have complex interactive webs or trophic pyramids that require an external energy source, generally sunlight, primary production by autotrophic organisms, mainly photosynthetic green plants and algae, consumers (heterotrophs) animals that feed on plants, or other animals, and decomposers, primarily bacteria, that degrade organic matter and recycle its contained nutrients. Such relationships based upon modes of feeding are called trophic systems. In the case of marine systems, common trophic modes include removal of suspended planktonic algae and zooplankton or particulate organic detritus from seawater. Such suspension feeding may include passive suspension feeding, as in crinoids, which rely upon external currents in seawater to bring food particles to sticky feeding surfaces, and active filter feeding in which organisms create their own feeding currents using movements of flagella (as in sponges), cilia (e.g., in brachiopods and bryozoans) and/or whole limbs as in certain arthropods. Infaunal organisms, termed deposit feeders, live in the substrate and actively ingest sediment and extract food from it. In addition, other organisms are scavengers or grazers, rasping or scraping up dead or living organic matter typically plants. Still others are predators, mainly active or vagrant swimming or crawling forms that kill and consume other animals for food.
Attached epifauna may show tiering, feeding at different levels above the sediment surface. Low-level organisms occupy a zone of abundant suspended food particles just 1 or 2 centimeters above the seafloor. Intermediate level suspension feeders such as many bryozoans, and some crinoids are elevated about 5-10 cm above the bottom, while some long stemmed crinoids may feed at levels exceeding a meter above the seabed.
Exquisite preservation of Rochester Shale fossils from the Caleb Quarry and elsewhere provides rare glimpses of ancient organisms preserved very nearly in life position permitting virtual snapshots of a Silurian seafloor. Interpretation of the modes of life and ecology of ancient ecosystems involves a combination of functional morphology that uses the form of skeletons to infer their function, in conjunction with direct evidence from fossils and surrounding sediments and information on the biology of mostly closely related living organisms.
The normally low current and wave energy settings of deeper Rochester environments may have limited certain organisms that required water movement to provide feeding currents, such as most echinoderms. It may also have promoted a multi-tiered community in which different groups of organisms fed at different levels above the seafloor (see Ausich and Bottjer, 1982). Brachiopods and bryozoans, which could produce their own filter feeding currents (active filter feeders) may have benefitted from living close to the seafloor where suspended food was concentrated by gravity settling, whereas crinoids that relied strictly on external currents (passive suspension feeders) survived by elevating their crowns up away from the stagnant boundary zone near the sediment surface and into levels of at least some current energy.
Modes of Life of Silurian Organisms and Community Paleoecology
Marine ecologists classify organisms into guilds or generalized modes of life based upon their: a) position with respect to their life in the water column, planktonic (floating) and nektonic (swimming) or on seafloor, benthic as well as b) their feeding or trophic types. Benthic organisms are further identified as infaunal (living within the sediment) or epifaunal (living on the sediment surface). Many, such as brachiopods and crinoids, are sessile or sedentary, while others like gastropods, are vagrant, crawling on the seafloor.
All ecosystems have complex interactive webs or trophic pyramids that require an external energy source, generally sunlight, primary production by autotrophic organisms, mainly photosynthetic green plants and algae, consumers (heterotrophs) animals that feed on plants, or other animals, and decomposers, primarily bacteria, that degrade organic matter and recycle its contained nutrients. Such relationships based upon modes of feeding are called trophic systems. In the case of marine systems, common trophic modes include removal of suspended planktonic algae and zooplankton or particulate organic detritus from seawater. Such suspension feeding may include passive suspension feeding, as in crinoids, which rely upon external currents in seawater to bring food particles to sticky feeding surfaces, and active filter feeding in which organisms create their own feeding currents using movements of flagella (as in sponges), cilia (e.g., in brachiopods and bryozoans) and/or whole limbs as in certain arthropods. Infaunal organisms, termed deposit feeders, live in the substrate and actively ingest sediment and extract food from it. In addition, other organisms are scavengers or grazers, rasping or scraping up dead or living organic matter typically plants. Still others are predators, mainly active or vagrant swimming or crawling forms that kill and consume other animals for food.
Attached epifauna may show tiering, feeding at different levels above the sediment surface. Low-level organisms occupy a zone of abundant suspended food particles just 1 or 2 centimeters above the seafloor. Intermediate level suspension feeders such as many bryozoans, and some crinoids are elevated about 5-10 cm above the bottom, while some long stemmed crinoids may feed at levels exceeding a meter above the seabed.
Exquisite preservation of Rochester Shale fossils from the Caleb Quarry and elsewhere provides rare glimpses of ancient organisms preserved very nearly in life position permitting virtual snapshots of a Silurian seafloor. Interpretation of the modes of life and ecology of ancient ecosystems involves a combination of functional morphology that uses the form of skeletons to infer their function, in conjunction with direct evidence from fossils and surrounding sediments and information on the biology of mostly closely related living organisms.
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