Fossil X can be considered to have evolved earlier than fossil Y is :

Options

A. Y has vestigial structures that are homologous to functions structures in fossil X
B. Y is structurally more complex than fossil X
C. Y is in better state of preservation than X
D. X is found in lower stratum of undisturbed sedimentary rock than Y

Answer

To determine why fossil X can be considered to have evolved earlier than fossil Y, we can follow these steps:

### Step 1: Understand Vestigial Structures
Vestigial structures are remnants of organs or structures that had a function in an early ancestor but are no longer useful in the same way in the current organism.

### Step 2: Analyze Fossil Y
Fossil Y has vestigial structures that are homologous to functional structures found in fossil X. This indicates that these structures were once useful in the ancestor of both fossils.

### Step 3: Complexity Comparison
Fossil Y is structurally more complex than fossil X. This complexity suggests that Y has evolved more recently, as evolution often leads to increased complexity over time.

### Step 4: Preservation State
Fossil Y is in a better state of preservation than fossil X. While preservation state can provide information about the fossil's age, it does not necessarily indicate which evolved first.

### Step 5: Stratigraphy
Fossil X is found in a lower stratum of undisturbed sedimentary rock compared to fossil Y. In geology, lower strata are typically older than those above them.

### Conclusion
Considering all the evidence, fossil X can be considered to have evolved earlier than fossil Y because Y has vestigial structures that are homologous to functional structures in fossil X, indicating a lineage where X is an ancestor to Y.

### Final Answer
Fossil X can be considered to have evolved earlier than fossil Y because Y has vestigial structures that are homologous to functional structures in fossil X.

---