The Carboniferous was a time of diverse marine invertebrates. The Late Devonian Period experienced major extinctions within some marine invertebrate groups, and Carboniferous faunas reflect a different composition from what had prevailed earlier in the Paleozoic Era.
Most notably, reef-forming organisms, such as tabulate corals and stromatoporoids (large colonial marine organisms similar to hydrozoans), were limited. Consequently, Carboniferous reefs were poorly developed because of this lack of framework builders. Benthic, or sea-bottom, marine communities were dominated by the crinoids, a group of stalked echinoderms (invertebrates characterized by a hard, spiny covering or skin) that still lives today. These animals were solitary suspension feeders that grew in such great profusion that they affected bottom currents and water circulation. The calcareous (containing calcium carbonate) remains of these organisms are significant rock-forming materials.
A related, but extinct, group of stalked echinoderms, the blastoids, also characterize Carboniferous deposits. Areas favorable for crinoids and blastoids were occupied by other filter-feeding organisms. Colonies of stenolaemate bryozoans (moss animals) and articulate brachiopods (lamp shells) are common associates of the crinoids. The bryozoans attached their undersurfaces to the seafloor and formed either fanlike, twiglike, or small knobby colonies of calcium carbonate in areas characterized by low rates of sedimentation. Articulate brachiopods formed a bivalved shell of calcium carbonate that either rested free on the seafloor or was attached by a fleshy stalk. The brachiopods and bryozoans both pumped the water column and removed food and oxygen by a tentacular lophophore (a horseshoe-shaped feeding organ). Brachiopods are particularly common, and all orders except the Pentamerida are found in Carboniferous rocks. Both calcareous and agglutinate foraminifers (pseudopod-using unicellular organisms protected by a test or shell) are represented in Carboniferous deposits, particularly limestones.
In the Pennsylvanian, an unusual group of these protozoans (single-celled eukaryotic organisms), the fusulinids (single-celled amoeba-like organisms with complex shells), appeared and dominated assemblages through the Permian Period, when they became extinct. The fusulinids secreted a tightly coiled calcareous test that was chambered, but they lived free on the seafloor.
Some benthic organisms that were common to early and middle Paleozoic times began to decline during the Carboniferous. These included the trilobites (which became extinct at the end of the Permian), rugose corals, and sponges. The pelagic, or water column, environment was inhabited by a profusion of cephalopods. These included both straight and coiled nautiloids (early relatives of the chambered Nautilus), the ammonoids (extinct members of the same class), and the first squids. Carboniferous cephalopods were either predators or scavengers, and they swam by jet propulsion. Some of the straight nautiloids grew exceedingly large (greater than 3 metres [10 feet]). The ammonoids exhibit rapid evolutionary development through the Carboniferous and, along with the calcareous foraminifers, provide the biostratigraphic data for age dating and correlating the boundaries and various subdivisions of the period. Graptolites (small colonial planktonic animals) extend into the Carboniferous, but they became extinct during the Mississippian.
Insects had occupied terrestrial environments since the Devonian, but they diversified during the Carboniferous Period. No winged insects are known from Devonian or Mississippian times, but wings probably evolved during the Mississippian. By the Pennsylvanian subperiod, dragonflies and mayflies were abundant and had reached large sizes, with some of the earliest ancestors of modern dragonflies (Protodonata) possessing wingspans of approximately 70 cm (28 inches). Some scientists maintain that higher oxygen concentrations present in the atmosphere during the Carboniferous Period (some 30 percent compared with just 21 percent during the early 21st century) may have played a role in enabling these insects to grow so large. In addition, fossils of more advanced insects capable of folding their wings, particularly cockroaches, are well represented in rocks of the Pennsylvanian subperiod. Other Pennsylvanian insects include the ancestral forms of grasshoppers and crickets and the first terrestrial scorpions.
Most notably, reef-forming organisms, such as tabulate corals and stromatoporoids (large colonial marine organisms similar to hydrozoans), were limited. Consequently, Carboniferous reefs were poorly developed because of this lack of framework builders. Benthic, or sea-bottom, marine communities were dominated by the crinoids, a group of stalked echinoderms (invertebrates characterized by a hard, spiny covering or skin) that still lives today. These animals were solitary suspension feeders that grew in such great profusion that they affected bottom currents and water circulation. The calcareous (containing calcium carbonate) remains of these organisms are significant rock-forming materials.
A related, but extinct, group of stalked echinoderms, the blastoids, also characterize Carboniferous deposits. Areas favorable for crinoids and blastoids were occupied by other filter-feeding organisms. Colonies of stenolaemate bryozoans (moss animals) and articulate brachiopods (lamp shells) are common associates of the crinoids. The bryozoans attached their undersurfaces to the seafloor and formed either fanlike, twiglike, or small knobby colonies of calcium carbonate in areas characterized by low rates of sedimentation. Articulate brachiopods formed a bivalved shell of calcium carbonate that either rested free on the seafloor or was attached by a fleshy stalk. The brachiopods and bryozoans both pumped the water column and removed food and oxygen by a tentacular lophophore (a horseshoe-shaped feeding organ). Brachiopods are particularly common, and all orders except the Pentamerida are found in Carboniferous rocks. Both calcareous and agglutinate foraminifers (pseudopod-using unicellular organisms protected by a test or shell) are represented in Carboniferous deposits, particularly limestones.
In the Pennsylvanian, an unusual group of these protozoans (single-celled eukaryotic organisms), the fusulinids (single-celled amoeba-like organisms with complex shells), appeared and dominated assemblages through the Permian Period, when they became extinct. The fusulinids secreted a tightly coiled calcareous test that was chambered, but they lived free on the seafloor.
Some benthic organisms that were common to early and middle Paleozoic times began to decline during the Carboniferous. These included the trilobites (which became extinct at the end of the Permian), rugose corals, and sponges. The pelagic, or water column, environment was inhabited by a profusion of cephalopods. These included both straight and coiled nautiloids (early relatives of the chambered Nautilus), the ammonoids (extinct members of the same class), and the first squids. Carboniferous cephalopods were either predators or scavengers, and they swam by jet propulsion. Some of the straight nautiloids grew exceedingly large (greater than 3 metres [10 feet]). The ammonoids exhibit rapid evolutionary development through the Carboniferous and, along with the calcareous foraminifers, provide the biostratigraphic data for age dating and correlating the boundaries and various subdivisions of the period. Graptolites (small colonial planktonic animals) extend into the Carboniferous, but they became extinct during the Mississippian.
Insects had occupied terrestrial environments since the Devonian, but they diversified during the Carboniferous Period. No winged insects are known from Devonian or Mississippian times, but wings probably evolved during the Mississippian. By the Pennsylvanian subperiod, dragonflies and mayflies were abundant and had reached large sizes, with some of the earliest ancestors of modern dragonflies (Protodonata) possessing wingspans of approximately 70 cm (28 inches). Some scientists maintain that higher oxygen concentrations present in the atmosphere during the Carboniferous Period (some 30 percent compared with just 21 percent during the early 21st century) may have played a role in enabling these insects to grow so large. In addition, fossils of more advanced insects capable of folding their wings, particularly cockroaches, are well represented in rocks of the Pennsylvanian subperiod. Other Pennsylvanian insects include the ancestral forms of grasshoppers and crickets and the first terrestrial scorpions.
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