The oldest surviving copy of Pedanius Dioscorides's treatise on medical botany and pharmacology, De materia medica, is an illuminated Byzantine manuscript produced about 512 CE. Dioscorides, a Greek physician, who may have served in the Roman army, wrote De materia medica in the first century CE.
"Presented in appreciation for her patronage in the construction of a district church in Constantinople, the parchment codex comprises 491 folios (or almost a thousand pages) and almost four hundred color illustrations, each occupying a full page facing a description of the plant's pharmacological properties. . . .
"In the Anicia codex, the chapter entries of De Materia Medica have been rearranged, the plants alphabetized and their descriptions augmented with observations from Galen and Crateuas (Krateuas), whose own herbal probably had been illustrated. Five supplemental texts also were appended, including paraphrases of the Theriaca and Alexipharmaca of Nicander and the Ornithiaca of Dionysius of Philadelphia (first century AD), which describes more than forty Mediterranean birds, including one sea bird shown with its wings both folded and open" (http://penelope.uchicago.edu/~grout/encyclopaedia_romana/aconite/materiamedica.html, accessed 11-22-2008)
The Anicia Juliana codex also contains the earliest illustrated treatise on ornithology. It is one of the earliest surviving relatively complete codices of a scientific or medical text, one of the earliest relatively complete illustrated codices on any medical or scientific subject, and arguably the most beautiful of the earliest surviving scientific codices. It also contains what are probably the earliest surviving portraits of scientists or physicians in a manuscript. See Singer, Charles. "The herbal in antiquity and its transmission to later ages, " J. Hellen. Stud. 47 (1927) 1-52. For further details about this manuscript see the entry at HistoryofInformation.com at this link.