This Seminal 16th Century Animal Encyclopedia Includes Mermaids and Unicorns

The Swiss naturalist Conrad Gessner, born 500 years ago today, was reppin' a Big Data mindset centuries before it was cool. A compulsive collector of information, Gessner accumulated an enormous haul of natural specimens and library resources before he succumbed to bubonic plague at the age of 49.

His meticulous approach to cataloging his finds provided the bedrock for numerous scientific and archival fields, and yielded two major masterpieces: Bibliotheca universalis ("The Universal Library"), an expansive attempt to collate all the books in the known world, and Historiae animalium ("History of the Animals"), a 4,500-page-long illustrated encyclopedia of the animal kingdom that is now considered to be the foundational text of modern zoology.

Fortunately, Gessner's efforts to preserve as many snapshots of 16th century wildlife as humanly possible were not in vain. Historiae animalium became the most popular natural history of the Renaissance, and dramatically advanced conversations over the origins and ecological dynamics of animal and plant species.

Several editions of the megatome have survived in museum collections, and some excerpts are even for sale to the public, provided you have around $30,000 lying around. A full digital copy of the book has also been released online by the Biodiversity Heritage Library.

So, in celebration of the 500th birthday of this influential luminary—this "one-man search engine, a sixteenth-century Google," as author Anna Pavord described Gessner—here are some of the most captivating pages from his zoological magnum opus. Half a millennium is a long time, but Gessner's clear passion and sense of wonder at the natural world live on vividly through his work.

This illustration demonstrates that there was already a diversity of dog breeds in the 16th century. Bonus points for the grumpy-looking pooch in the foreground.

This depiction of a rhinoceros is a great example of the amount of guesswork involved in zoological research during the Renaissance. Gessner's illustration above is based on iconic woodcut of the species made by Albrecht Durer in 1515. But neither Durer or Gessner had ever observed the animal in person, and so both artists interpreted descriptions of its "armor" quite literally.

Yes, that is a unicorn, and yes, it is glorious. As evidenced by the rhino entry, Gessner caught wind of all kinds of exotic animals that he never saw in person, so he included many cryptozoological animals in Historiae animalium. After all, if there was an armored, horned beast roaming the African wilderness, it wasn't a huge jump to imagine that rumors of a maned, horned horse also had some basis. Gessner was skeptical of these mythical animals, but he included them in the history just in case.

This trippy riff on mermaids also made the cut for Gessner's voluminous natural history. Imagine encountering that thing on your next beach day.

This page is particularly insane. On it, Gessner outlines his conception of a fictional human-fish hybrids that took the shape of leading religious figures, which were popularly believed to be signs from God during this period of strife between Catholics and Protestants.

In the top figure, Gessner depicts a "monk fish," while the bottom is a "bishop fish." Images like this speak volumes about the porous interchange between scientific and religious ideas during the Renaissance. Even a textbook empiricist like Gessner could not overlook the possibility that these spectacular creatures might exist, and so could not omit them from his compendium.

Among his many other achievements, Gessner was the first person to publish visual representations of fossils, such as this illustration of an ammonite shell from his treatise On Fossil Objects. Being the zoological genius that he was, Gessner explicitly recognized the similarities between extinct creatures and their living relatives—a revelation that paved the way for the fields of paleontology and evolutionary biology.

This image seems to suggest that Renaissance beavers were a lot more intense and scary than the modern versions, what with the bared teeth and demon eyes. But maybe Gessner just had droferanophobia, or a fear of beavers, and used his encyclopedia as an outlet. Whatever the case, that is one seriously gnarly-looking rodent.

This portrait of whales attacking whalers—and vice versa—open a fascinating window into the development of industrial hunting of these animals. Note how sketchy Gessner is about the details of these beasts, depicting them with massive fangs and facial decorative displays.

While many of Gessner's renderings of sea animals are spectacularly fanciful due to a lack of verifiable observations, he really nailed the morphology of the octopus. That's some premium cephalopod veracity right there.

Let's cap off with this perplexing portrait of two pigs either making out or facing off. But we recommend taking a scroll through more of the pictures in the many online galleries that display Gessner's colossal creative output. From images of cat-headed hydras to adorable bunnies, there is a lot to ogle over 500 years on.