The physical and chemical processes involved in the fossilization of sharks' teeth are as common as those involved in the fossilization of shark skeletons. Unlike the bony skeletons of other vertebrates, shark skeletons are composed of cartilage, and teeth and bone are much more likely to fossilize than cartilage is. The rare fossilized skeletons of sharks that are found are often found in areas other than those in which fossils of shark teeth are plentiful. Fossils of sharks' teeth are quite difficult to distinguish from fossils of other kinds of teeth.
Shark teeth are among the most common vertebrate fossils; yet fossilized shark skeletons are much less common -- indeed, comparatively rare among fossilized vertebrate skeletons.
Which one of the following, if true, most helps to resolve the apparent paradox described above?