Choose the precise single-word term for the description below.

A specialist who investigates ancient organisms by examining fossil evidence.

The correct option is Palaeontologist.

Step-by-Step Explanation:
To identify the correct single-word term, let us break down the given description and evaluate each option.

1. Understanding the Given Description:
The question asks for the term that describes a specialist who investigates ancient organisms by examining fossil evidence (such as preserved bones, footprints, or plant imprints).

2. Evaluating the Options:
• Botanist: A scientist who specializes in the study of plant life.
• Ethnologist: A social scientist who analyzes and compares human cultures, origins, and characteristics.
• Palaeontologist: A scientist who studies the history of life on Earth by analyzing fossils of ancient plants, animals, and microorganisms. This directly corresponds to the description.
• Seismologist: A geologist who studies earthquakes and the movement of seismic waves through the Earth.

Conclusion:
Therefore, the precise single-word term for a specialist who examines fossil evidence to investigate ancient organisms is a Palaeontologist.