To determine which of the statements is true, let’s analyze each one based on geological time periods and the position of the listed fossils in the geological time scale:
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Cactocrinus multibrachiatus and Prolecanites gurleyi are from different geological periods.
- Cactocrinus multibrachiatus is from the Mississippian period, while Prolecanites gurleyi is from the Permian period. Therefore, this statement is true.
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The index fossils of the Jurassic Period are Perisphinctes tiziani and Monotis subcircularis.
- This statement needs to be verified. If both fossils are listed under the Jurassic period in the chart, then this statement would be true. However, I can't visually confirm this without the chart.
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The oldest index fossils within the chart are from the Cenozoic Era (i.e., Pecten gibbus and Neptunea tabulate).
- This statement is false because the oldest index fossils are generally from earlier geological eras (such as Paleozoic and Mesozoic), not the Cenozoic.
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The index fossil Leptodus americanus is “younger” than Lophophyllidium proliferum.
- This statement needs to be checked against the chart to confirm which of these fossils belongs to an earlier or later period.
Based on the first statement alone, it is definitely true. The second statement requires verification against the chart for accuracy. The third statement is false, and the fourth one cannot be confirmed without further information from the chart.
Thus, without further context, the first statement about Cactocrinus multibrachiatus and Prolecanites gurleyi being from different geological periods stands as true.