Question

9/10
which index fossil is from the cretaceous period?
pectin
ammonoid
crynoid
trilobite

Explanation:

Index fossils are used to date rock layers. Ammonoids existed through the Cretaceous period and went extinct at the end of it. Pectins (bivalves) have a broader range, crinoids are not Cretaceous-specific, and trilobites went extinct before the Cretaceous.

Answer:

Ammonoid