The teeth in cartilaginous fishes are formed due to modification of which type of scales?

Answer

To answer the question about the type of scales from which teeth in cartilaginous fishes are formed, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Group of Fishes**: Recognize that the question pertains to cartilaginous fishes, which belong to the class Chondrichthyes. This class includes sharks, rays, and skates.

2. **Understand the Structure of Cartilaginous Fishes**: Know that the endoskeleton of cartilaginous fishes is made of cartilage rather than bone. This is a key characteristic of Chondrichthyes.

3. **Examine the Skin Structure**: Learn that the skin of cartilaginous fishes is covered with special types of scales known as placoid scales. These scales are small, tooth-like structures that provide a tough texture to the skin.

4. **Relate Scales to Teeth Formation**: Understand that the teeth of cartilaginous fishes are actually modified placoid scales. This means that the same material and structure that make up the placoid scales are adapted to form the teeth.

5. **Conclude the Answer**: Based on the above understanding, conclude that the teeth in cartilaginous fishes are formed due to the modification of placoid scales.

### Final Answer:
The teeth in cartilaginous fishes are formed due to the modification of placoid scales.