Why were the fossil fishes of Glarus and Monte Bolca important to Louis Agassiz?

The fossil fishes of Glarus and Monte Bolca were central to Louis Agassiz’s research because they provided the foundational material for his epoch-making work, Recherches sur les poissons fossiles (1833–1843).1

At the time Agassiz began his studies, only a few of these specimens had been critically examined. By gathering and analyzing these extensive collections, Agassiz was able to identify and name more than 1,700 species of fossil fishes. This research was significant because it gave a major impetus to the study of extinct life, effectively allowing scientists to reconstruct the inhabitants of ancient seas. His systematic classification of these fossils established his reputation as a leading ichthyologist and provided a comprehensive framework for understanding the history of fish forms.1