Natural history encyclopedias existed in Europe from at least the first century BCE, though Pliny the Elder’s Natural Histories, published c. 77-79 AD is the oldest surviving work we have. Volumes such as these were immensely popular as botanical, zoological, medical and historical repositories through the medieval and Renaissance periods, but even as late as the 17th century their content unreservedly mixed what we would today term scientific knowledge with fanciful invention and hearsay.
Ulisse Aldrovandi’s stunningly illustrated Monstrorum historia is in many ways groundbreaking in its documentation of diseases and congenital afflictions: it is the first known work to document neurofibromatosis, for instance. However, Aldrovandi discusses merfolk, giants and centaurs with the same seriousness. Konrad Gesner, another encyclopedist of Aldrovandi’s era, is recorded as explaining that the goal of such texts was simply to acquaint readers with the unusual.
This was no less true closer to Dante’s time. Works such as the Ortus sanitatis, which discusses the medicinal uses of herbs and plants, also includes a bestiary of birds, fish, and mammals along with dragons, harpies and hydra. Medieval bestiaries and early Roman natural histories were likely sources for some of Dante’s creations, and his audiences would have been familiar with either the texts or the traditions that inspired them.