26. One reason Tetragraptus is considered a good index fossil is that:

A) It existed during a large part of the Paleozoic Era

B) It has no living relatives found on Earth today

C) It existed over a wide geographic area

D) It has been found in New York State

Correct Answer: Option C - It existed over a wide geographic area

Tetragraptus is a genus of extinct graptolites (colonial animals related to the chordates) that occur as fossils in marine rocks of the Early Ordovician Epoch (505 to 478 million years ago). The genus is a useful guide, or index, fossil for the Early Ordovician; long-distance correlations between rock units are possible employing the many known Tetragraptus species. As its name implies, Tetragraptus is distinguished by its four branches, which are suspended from a thin filamentous support.

Hence, options A, B and D are incorrect.