ACT (Enhanced)ScienceHard
A paleontologist discovers a fossilized footprint trail in a sedimentary rock layer. The trail shows a distinct pattern of bipedal locomotion. In a stratigraphically older (deeper) layer, they find only fossilized remains of four-legged (quadrupedal) creatures. In an even older (deeper) layer, they find no evidence of large vertebrate life. This observation supports the idea that bipedalism evolved after quadrupedalism, and large vertebrate life appeared more recently than simpler life forms. This interpretation is an example of applying which geological principle?
- APrinciple of Original Horizontality
- BPrinciple of Faunal Succession
- CPrinciple of Cross-Cutting Relationships
- DPrinciple of Superposition
Show answer & explanationAnswer & explanation
Correct answer: B. Principle of Faunal Succession
The Principle of Faunal Succession states that fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content. The observation of different types of organisms (bipedal, quadrupedal, no large vertebrates) in different, ordered layers directly supports this principle, indicating evolutionary change over geological time.
Why the other options are wrong
- A. Original Horizontality states that sediments are deposited in horizontal layers, not about fossil content.
- C. Cross-Cutting Relationships states that a geological feature that cuts across another is younger than the feature it cuts, not about the order of fossils.
- D. Superposition states that in undisturbed rock layers, the oldest layers are at the bottom and the youngest are at the top, which is the basis for understanding the order, but Faunal Succession specifically addresses the *change in fossil types* over that order.
Principle of Faunal Succession
States that fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content. This principle is fundamental to biostratigraphy and the relative dating of rock layers.
- Fossils appear and disappear in a predictable sequence.
- Allows for relative dating of rock strata across different locations.
- Supports the concept of evolution and the progression of life forms over geological time.
Memory trick: Super Cross-Cut Original Fauna