Life at the start of the Ordovician remained confined to the seas with new animals evolving in place of those that didn't survive the Cambrian. Chief among them were the squidlike nautiloids, a type of tentacled mollusk. The nautiloids lifted off from life on the seabed as gas-filled chambers in their conical shells made them buoyant. They were accomplished swimmers, propelling themselves by jetting water through their body cavity. Equipped with grasping tentacles, the nautiloids were effective predators.
Another group of marine hunters were the mysterious conodonts, known mainly from the tiny fossil teeth they left behind. The few complete fossils that have been found suggest they were finned, eel-like creatures with large eyes for locating prey. The conodonts are now thought to have been true vertebrates; however, this line of backboned animals later went extinct.
Fish started becoming more widespread in the fossil record. They were small and had downward-pointing, jawless mouths, indicating they lived by sucking and filtering food from the seabed. Bony shields covered the front of their bodies—the beginnings of a fashion for armor plating among fish. Lampreys and hagfish are these fishes' living descendants.
The archaic sponge reef-dwellers of the Cambrian gave way to bryozoans—tiny, group-living animals that built coral-like structures. Ordovician reefs were also home to large sea lilies, relatives of sea stars. Anchored to the bottom inside calcareous tubes, they collected food particles with feathery arms that waved in the ocean currents.
Another group of marine hunters were the mysterious conodonts, known mainly from the tiny fossil teeth they left behind. The few complete fossils that have been found suggest they were finned, eel-like creatures with large eyes for locating prey. The conodonts are now thought to have been true vertebrates; however, this line of backboned animals later went extinct.
Fish started becoming more widespread in the fossil record. They were small and had downward-pointing, jawless mouths, indicating they lived by sucking and filtering food from the seabed. Bony shields covered the front of their bodies—the beginnings of a fashion for armor plating among fish. Lampreys and hagfish are these fishes' living descendants.
The archaic sponge reef-dwellers of the Cambrian gave way to bryozoans—tiny, group-living animals that built coral-like structures. Ordovician reefs were also home to large sea lilies, relatives of sea stars. Anchored to the bottom inside calcareous tubes, they collected food particles with feathery arms that waved in the ocean currents.
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