Question

The distribution of trilobite fossils from various periods in the fossil record are shown in the map here. Fossil species on both side of the red line differ for the Cambrian and Ordovician periods. Which statements are supported by the evidence shown in the map? Select ALL that apply.
Responses
A Trilobites from different periods fossilized, but ocean currents moved them to new locations.Trilobites from different periods fossilized, but ocean currents moved them to new locations.
B Trilobites from different periods fossilized, and plate tectonic movement relocated those fossils.Trilobites from different periods fossilized, and plate tectonic movement relocated those fossils.
C Trilobites from different periods fossilized at different times but were once separated by an ocean.Trilobites from different periods fossilized at different times but were once separated by an ocean.
D Trilobites from different periods fossilized on land which was later flooded during the Ordovician period.Trilobites from different periods fossilized on land which was later flooded during the Ordovician period.
E Pangea formed more recently than the trilobite fossil formation, bringing the fossils together from different regions of the world.Pangea formed more recently than the trilobite fossil formation, bringing the fossils together from different regions of the world.

Answer 1

Choose B, C, and E.

Why:
- C is supported: different fossil species on the two sides for Cambrian and Ordovician implies the regions were biologically separated (most likely by an ocean) when those sediments formed.
- E is supported: Cambrian and Ordovician rocks are ~541–444 Ma, while Pangea assembled much later (late Paleozoic, ~335–175 Ma), so the later assembly could bring distant fossil-bearing regions together.
- B is supported: plate tectonic movement (continental drift/Pangea assembly) is the mechanism that can relocate fossil-bearing crust from different ancient locations into their present proximity.

Why A and D are not supported:
- A: ocean currents do not transport buried fossils across continents; the patterns reflect where organisms lived and were buried, not drift of already-buried fossils by currents.
- D: trilobites were marine animals and fossilized in sea sediments, not on land that was later flooded; the map pattern instead indicates marine basins and plate positions.