એરિસ્ટોટલ is the earliest natural historian whose work has survived in some detail. એરિસ્ટોટલ certainly did research on the natural ઇતીહાસ of Lesbos, and the surrounding seas and neighbouring areas. The works that reflect this research, such as "History of Animals", "Generation of Animals", and "Parts of Animals", contain some observations and interpretations, along with sundry myths and mistakes. The most striking passages are about the sea-life visible from observation on Lesbos and available from the catches of fishermen. His observations on catfish, electric fish (Torpedo) and angler-fish are detailed, as is his writing on cephalopods, namely, "Octopus", "Sepia" (cuttlefish) and the paper nautilus ("Argonauta argo"). His description of the hectocotyl arm was about two thousand years ahead of its time, and widely disbelieved until its rediscovery in the ઓગણીસમી સદી. He separated the aquatic mammals from fish, and knew that sharks and rays were part of the group he called Selachē (selachians).

Another good example of his methods comes from the "Generation of Animals" in which એરિસ્ટોટલ describes breaking open fertilized chicken eggs at intervals to observe when visible organs were generated.

He gave accurate descriptions of ruminants' four-chambered fore-stomachs, and of the ovoviviparous embryological development of the hound shark "Mustelus mustelus".

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