The primary producers in Rochester Shale ecosystems are poorly represented in the fossil record but given the abundance and diversity of suspension feeding organisms we must presume that a large base of green phytopanktonic algae provided the basis for the food web. In fact, fossil acritritarchs, organic-walled microfossils of probable planktonic algae are abundant in the Rochester Shale (Thusu, 1972). Possible green benthic algae may be represented by Acanthograptus and Inocaulis (Figures 118 - 122; LoDuca and Brett, 1997, S.T. LoDuca, personal communication 2014).
Infaunal deposit feeders within the Rochester seafloor are represented primarily by trace fossils, particularly the feeding burrows Planolites and Chondrites that are abundant and/or well preserved in silty beds. These are traces of sediment mining worms. The rare machaeridian Lepidocoleus (Figures 198 - 203) may have been an armor plated deposit-feeding worm. Certain trilobites may also have been deposit feeders. Illaenids like Bumastus (Figures 369 - 375) are common dwellers on Silurian reefs and bioherms and seem to have occupied pockets in these structures feeding from the sediment (Sarle, 1907).
The most abundantly represented trophic groups are suspension feeders. This category takes in a wide array of filter feeders, including the varied brachiopods and bryozoans and probably also the dendroid graptolites. Most of these are low tier sedentary organisms.
Brachiopods and bryozoans generate feeding currents using ciliated tentacles on their looped or coiled lophophores that produce rhythmic beats that propel water and suspended particles. Many of these organisms have morphological strategies that may have aided in water flow. For example, the groove at the center of the valves (fold and sulcus) in Striispirifer, Howellella, and other spiriferids, as well as rhynchonellids such as Ancillotoechia, Rhynchotreta, and Stegerhynchus (Figures 104, 106 and 78), served to funnel the wastewater away from the lateral incurrent streams and may have had some Venturi effect that helped to promote water flow. Likewise the bumps or monticules on the surfaces many of the bryozoans (e.g., Trematopora tuberculata, Figures 35 and 36) may have promoted water flow off the surface of larger colonies to prevent stagnation of filtered water. Many brachiopods may have initially settled on small hard substrate objects; however, as adults, these organisms often were free-resting on the seafloor. The large, broad surface area of shells in forms like Coolinia and Amphistrophia helped to spread out the weight of the free-resting brachiopods like a snowshoe to prevent them sinking into soft muds. The concentric growth rings or rugae of Leptaena (Figures 74 and 75) not only provided increased frictional contact with the substrate but may have strengthened the shell against physical damage or predation. Striispirifer appears to have been an opportunistic form that thrived in somewhat stressed low energy settings. It may have possessed a functional pedicle stalk at least initially, but its broad interarea also provided a base to help stabilize the shell. The rhynchonellids (e.g. Stegerhynchus) were attached by pedicle stalks and may have initially settled on shell fragments and other skeletal materials. They were evidently even capable of attaching to living substrates, as they have been found in life position on the exoskeletons of Arctinurus trilobites (Taylor and Brett, 1996 and Tetreault 1990, 1992).
Certain bryozoans, such as Chilotrypa (Figures 7 - 9), were capable of surviving in relatively muddy seafloor environments not only because of active filter pumping but also elevation of growing portions of their colonies into areas above the low energy seafloor. Their slender branching shapes, adaptive for low energy environments may also have helped in shedding sediment from the surfaces of colonies. However, most bryozoans are sensitive to high turbidity, probably because suspended silt may clog their delicate filtration meshes. In slightly more energetic settings represented by the Lewiston E bryozoa bed limestones, other growth strategies aided in feeding. For example, the mesh-like networks and fan or funnel shapes of fenestrate bryozoan colonies (Figures 15,16 and 23 - 26) promoted water flow through the colonies.
As noted, echinoderms do not generate their own feeding currents; therefore, many, such as edrioasteroids (Figures 237 - 243a) and stalked crinoids and cystoids were passive suspension feeders dependent upon external currents to bring suspended food particles into the vicinity of their food grooves, which were covered with tube feet and mucous to trap these particles.
Infaunal deposit feeders within the Rochester seafloor are represented primarily by trace fossils, particularly the feeding burrows Planolites and Chondrites that are abundant and/or well preserved in silty beds. These are traces of sediment mining worms. The rare machaeridian Lepidocoleus (Figures 198 - 203) may have been an armor plated deposit-feeding worm. Certain trilobites may also have been deposit feeders. Illaenids like Bumastus (Figures 369 - 375) are common dwellers on Silurian reefs and bioherms and seem to have occupied pockets in these structures feeding from the sediment (Sarle, 1907).
The most abundantly represented trophic groups are suspension feeders. This category takes in a wide array of filter feeders, including the varied brachiopods and bryozoans and probably also the dendroid graptolites. Most of these are low tier sedentary organisms.
Brachiopods and bryozoans generate feeding currents using ciliated tentacles on their looped or coiled lophophores that produce rhythmic beats that propel water and suspended particles. Many of these organisms have morphological strategies that may have aided in water flow. For example, the groove at the center of the valves (fold and sulcus) in Striispirifer, Howellella, and other spiriferids, as well as rhynchonellids such as Ancillotoechia, Rhynchotreta, and Stegerhynchus (Figures 104, 106 and 78), served to funnel the wastewater away from the lateral incurrent streams and may have had some Venturi effect that helped to promote water flow. Likewise the bumps or monticules on the surfaces many of the bryozoans (e.g., Trematopora tuberculata, Figures 35 and 36) may have promoted water flow off the surface of larger colonies to prevent stagnation of filtered water. Many brachiopods may have initially settled on small hard substrate objects; however, as adults, these organisms often were free-resting on the seafloor. The large, broad surface area of shells in forms like Coolinia and Amphistrophia helped to spread out the weight of the free-resting brachiopods like a snowshoe to prevent them sinking into soft muds. The concentric growth rings or rugae of Leptaena (Figures 74 and 75) not only provided increased frictional contact with the substrate but may have strengthened the shell against physical damage or predation. Striispirifer appears to have been an opportunistic form that thrived in somewhat stressed low energy settings. It may have possessed a functional pedicle stalk at least initially, but its broad interarea also provided a base to help stabilize the shell. The rhynchonellids (e.g. Stegerhynchus) were attached by pedicle stalks and may have initially settled on shell fragments and other skeletal materials. They were evidently even capable of attaching to living substrates, as they have been found in life position on the exoskeletons of Arctinurus trilobites (Taylor and Brett, 1996 and Tetreault 1990, 1992).
Certain bryozoans, such as Chilotrypa (Figures 7 - 9), were capable of surviving in relatively muddy seafloor environments not only because of active filter pumping but also elevation of growing portions of their colonies into areas above the low energy seafloor. Their slender branching shapes, adaptive for low energy environments may also have helped in shedding sediment from the surfaces of colonies. However, most bryozoans are sensitive to high turbidity, probably because suspended silt may clog their delicate filtration meshes. In slightly more energetic settings represented by the Lewiston E bryozoa bed limestones, other growth strategies aided in feeding. For example, the mesh-like networks and fan or funnel shapes of fenestrate bryozoan colonies (Figures 15,16 and 23 - 26) promoted water flow through the colonies.
As noted, echinoderms do not generate their own feeding currents; therefore, many, such as edrioasteroids (Figures 237 - 243a) and stalked crinoids and cystoids were passive suspension feeders dependent upon external currents to bring suspended food particles into the vicinity of their food grooves, which were covered with tube feet and mucous to trap these particles.
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