Non vivens nisi per unum diem. A Winged Aquatic Animal on Its Way from Aristotle to Thomas of Cantimpré

Apart from more or less well-known names of animals which are attested already in the Classical Latin and whose origins and meanings have been studied and traced by modern scholars, it is possible to find in medieval encyclopaedias other expressions that still lack a proper explanation of their etymology and meaning. Many unusual terms can be found in the encyclopaedia Liber de natura rerum written by Thomas of Cantimpré (13th century). Although modern researchers have gradually discovered that the curious animals were originally the species described by ancient natural scientists, medieval encyclopaedists could not decipher the unfamiliar names. One of these new terms is the name dies which denotes an unknown winged fish in medieval Latin encyclopaedias and glossaries. Thomas of Cantimpré invoked Aristotle to validate the information about the creature and modern researches have assumed that Thomas’ source was a passage concerning mayfly in the fifth book of Aristotle’s Historia animalium and that the word dies is a direct equivalent of the Greek ἐφήμερον, «mayfly » . In fact, Thomas found this term and the description of the animal in the Book I of Latin version of Aristotle’s Historia animalium, translated by Michael Scotus around 1220 from Arabic. Aristotle’s description of a bloodless animal endowed with four legs and four wings, which only lives one day after it reaches maturity, kept its original sense in the Arabic version of his treatise, in which the Greek adjective ἐφήμερον, «one-day » , was replaced with the Arabic equivalent yaumī of the same meaning. Michael Scotus also translated the name, replacing the adjective with the noun dies, «day » . Thomas of Cantimpré, consequently, accepted Michael’s description, but asserted that dies is a bloodless marine fish which only lives one day and has two wings and two legs. His description of a «new » creature fascinated both the authors of encyclopaedic works (Albert the Great, Vincent of Beauvais, Jacob van Maerlant) and the medieval illustrators who depicted the dies as a hybrid with a fish head, tail and scales, with strong legs resembling lion’s paws, and with two massive feathered wings which allow it to fly over expanses of water.