Discussion
The first appearance datum (FAD) of which fossil species demarcate the Cambrian-Ordovician boundary ?
Answer: C
The boundary is defined by the FAD of Iapetognathus fluctivagus, printed here as Lapetognathus.
The Global Boundary Stratotype Section and Point for the base of the Ordovician, at Green Point in Newfoundland, is placed at the first appearance of this conodont species.
The other species mark other boundaries. The trace fossil Trichophycus pedum marks the base of the Cambrian. The trilobite Oryctocephalus indicus marks the base of the Wuliuan stage in the middle Cambrian. The graptolite Tetragraptus approximatus marks the base of the Floian, the second stage of the Ordovician.
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