The medieval bestiary ultimately derives from the Greek-language Physiologus, a text whose precise date and place of origin is disputed, but which was most likely written in North Africa sometime in the second or third century.
[4] The most important of the Latin Physiologus translations — the one now known by scholars as the "B Version" — was expanded even further in the twelfth century (most likely in the 1160s or 1170s), with more additions from Isidore, to become the so-called "Second Family" standard form of what now may be properly termed as the bestiary.
[5][6] This text was much longer than the original Physiologus and included in its typical format over 100 sections, distributed among nine major divisions of varying size.
[9] Its principle contents are a bestiary, but it also contains a short lapidary (a treatise on stones) in French prose and, as the flyleaves, two leaves of a 14th-century service book.
[6][10] A complete copy of the Pantheologus, now extant as British Library, Royal MS. 7 E.viii, was located in Rochester in the early 13th century, and may have been the direct source for the bestiary additions.