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Why are shark teeth considered modified scales?

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southern stingray (Dasyatis americana or Hypanus americanus) — chondrichthyan Southern stingrays (*Dasyatis americana* or *Hypanus americanus*) are found in the western Atlantic Ocean.

Shark teeth are considered modified scales because they share the same structural origin and composition as the placoid scales—also known as dermal denticles—that cover the skin of cartilaginous fishes (chondrichthyans).123

Both shark teeth and these scales consist of a hollow cone of dentine surrounding a pulp cavity, capped by a hard, enamel-like substance. In sharks, these denticles are essentially minute teeth embedded in the skin. Because of this shared developmental biology, scientists consider teeth to be structurally modified scales.231

Unlike the scales of bony fishes, which grow throughout the animal's life, shark denticles have a limited size and are replaced as the body grows. Similarly, the teeth in a shark's mouth are not firmly attached to the jaw but are embedded in a fibrous membrane; when they are lost or worn down, they are replaced by new teeth moving forward from rows located behind them.2