Science historians separated the scientific origins of ichnology and body fossil paleontology; the birth of body fossil paleontology is attributed to the Renaissance, whereas the beginnings of ichnology are placed in the 19th century. The present study shifts the boundaries of the history of paleontology and provides new information on an obscure chapter of scientific thought: the ichnological studies of Leonardo da Vinci. This report examines the ichnological observations of Leonardo da Vinci by (1) interpreting the Codex Leicester and the ichnosites described therein, and (2) studying the ichnological drawing included in the Codex I. This paper demonstrates the modernity and correctness of the observations and interpretations made by da Vinci, who used trace fossils to complement his hypothesis concerning the relationship of body fossils to the host sediment. The result from new information presented here is the establishment of a line of continuity between the two main branches of paleontology—trace fossils and body fossils—that emerge united by the genius of Leonardo da Vinci, the founding father of ichnology.