Answer:
Cambrian 
Step-by-step explanation:
The fossil from the Cambrian is older than the one from the Triassic. This is because in the geologic time scale, the Cambrian is older than the Triassic. 
- Absolute age of the Cambrian is between 541 - 484mya
- It is the first geological period in the Paleozoic era. 
- The Triassic is the earliest period of the Mesozoic era
- It occurred about 237mya ago. 
- Therefore, the fossils which corresponds to the Cambrian is the oldest.