Who had the first animal contract?

[Yusuke Urameshi]

What do you guys think? Who was the first and what do you think it was?

Edit: Animal contract or Summoning Contract or whatever.. Muh bad.

 

[Twin Steps]

SO6P was first in it most likely.

 

[Joten Uchiha]

Fluck knows.

 

[Joon]

I assume the Sage or Uzumaki's.

 

[Yusuke Urameshi]

SO6P was first in it most likely.

Well then what do you think it was?

 

[zinescience]

what animal did hashirama summon?