The Mishna in Kelaim 8:5 talks about the אדני השדה . I know of a few perushim who say that this is a type of monkey (Tiferes Yisroel syas that it's an orangutang). If you look in the Yerushalmi on this mishna it says that this animal is attached to the ground by a tube from it's belly button. Does anyone know of a perush that incorporate this Yerushalmi into their explanation? Thanks.
The first actual description of it is given by the Ohr Zarua (Kilayim 1:288): A sort of animal (named yedua, used to do yidoni) attached to the ground, that can destroy anything that approaches it; but if someone somehow manages to disconnect it from the ground, it dies immediately.
In the introduction to Tanchuma, it relates a story that someone invited a guest to his house and told him that they would eat "their man." The guest got afraid, thinking they were cannibals. The guest later found out that he was referring to one of these adnei hasadeh.
Claude Duret says that he thought he remembered reading this Yerushalmi and seeing it said that there were lambs attached to the ground instead of people. The Maaseh Tuvia and Rabbi Pinchas Eliyahu Hurwitz also have this text in the Yerushalmi. Apparently, vegetable lambs were very popular in those days. Others say that they were really only cotton plants that looked like wool.
Rabbi Shimon Schwab says that the description of adnei hasadeh is really a metaphor, referring to someone so physical that he is as if attached to the ground.
Rabbi Dr. Daniel Sperber of Bar-Ilan University says that it is possible that the Yerushalmi never really said it was connected with its navel; it really said טור (mountain) which was accidentally changed to טוור (meaningless, as far as I know) which was accidentally changed to טבור (navel). If so, the Yerushalmi may easily have been referring to an orangutan.