When early systematists distinguished chondrichthyes (cartilaginous fish) from osteichthyes (bony fish), it was not clear exactly when bony skeletons first appeared in the vertebrates. which of these suggests that a reduction of bone in chondrichthyes is a derived condition that emerged after the origin of bony skeletons? a) all fish except agnatha have jaws.
b) chondrichthyes and osteichthyes have paired fins and lateral lines. c) traces of bone tissue are found in living and fossil chondrichthyes. d) the cartilage skeleton of chondrichthyes is impregnated with calcium.

The correct answer is option C.

Explanation:

The Chondrichthyes is a class that comprises the cartilaginous fishes such as batoids, ratfish, sharks and others, The Chondrichthyes and the Osteichthyes also known as bony fish were distinguished in early classification but it was not clear at that time when bony skeletons appeared in the vertebrates.

Traces of bone tissues that are found in fossil and living Chondrichthyes are suggested that these cartilaginous fishes derived after the origin of the bony skeleton in vertebrates.

Thus, the correct answer is option C.

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