[Campbell Biology P.774] Based on the provided text, which of the following sequences accura... | Practice Question
Based on the provided text, which of the following sequences accurately describes the evolutionary steps in the development of the vertebrate internal skeleton?
A: Vertebrate skeleton initially unmineralized cartilage → Appearance of mineralized bone on outer surface of skull (470 mya) → Internal skeleton begins to mineralize as calcified cartilage → Thin layer of bone lining internal cartilage (430 mya).
B: Mineralized bone on outer surface of skull → Unmineralized cartilage skeleton → Internal skeleton mineralizes as calcified cartilage → Thin layer of bone lining internal cartilage.
C: Internal skeleton mineralizes as calcified cartilage → Thin layer of bone lining internal cartilage → Mineralized bone on outer surface of skull → Unmineralized cartilage skeleton.
D: Unmineralized cartilage skeleton → Thin layer of bone lining internal cartilage → Internal skeleton mineralizes as calcified cartilage → Mineralized bone on outer surface of skull.
Explanation
The text explicitly states: 'the vertebrate skeleton evolved initially as a structure made of unmineralized cartilage.' Then, 'Steps toward a bony skeleton began 470 million years ago, with the appearance of mineralized bone on the outer surface of the skull in some jawless vertebrates.' 'Shortly after that time, the internal skeleton began to mineralize, first as calcified cartilage.' Finally, 'By 430 million years ago, some vertebrates had a thin layer of bone lining the cartilage of their internal skeleton.' This confirms option A as the correct chronological order.