His lecturing career started in 1883 at the Faculty of Philosophy of the University of Zagreb, where he taught paleontology of vertebrates.

Gorjanović-Kramberger discovered, described, classified, systemized, aged, and determined environments for numerous new species of fossilized fishes.

As a young scientist at the end of the 19th century, he had already published more than fifty works in prestigious European scientific journals.

Gorjanović continued extensive scientific research of osteological human material, fauna, ecological conditions, and the life and culture of people once living in Croatia.

His analysis and interpretation of fossil remains proved the existence of early humans which he called Homo primigenius,[citation needed] an ancestor of modern man.

He started the study of skeletons relating to modern humans and developed a technique that analyzes the fluorine in bones to calculate their age.