So, as many of you are probably aware, there are several living groups of fish which are able to use electroreception to some degree to either passively sense the world around them or, in some cases, actually stun or kill other animals. In particular, I'm thinking of members of the Gymnotiformes (including the electric eel), the electric catfish (Malapteruridae), the torpedo rays (Torpediniformes) and several families of the Osteoglossiformes (Mormyridae and Gymnarchidae).
I was wondering if anyone knew of any evidence that a now totally-extinct group of fish may have possessed similar electroreceptive/generative abilities (that is to actually generate electric fields, rather than sense them as in sharks or paddlefish). I know that in South American knifefish (Gymnotiformes), the development of an electricity-generating system has strongly constrained the development of their locomotion, which makes me wonder whether a similar morphology among extinct fish (say, xenacanth sharks) might be indicative of such behavior.
I believe that's not something easy to assess. Mormyridae have a very big cerebellum which is thought to be related with that perception of the environment based on electric fields. If fish with abnormally big cerebella endocasts are found, then one of the hypothesis is that they had the features you're looking for. I suggest "The Comparative Anatomy and Histology of the Cerebellum" by Larsell (1967). Read it and learn a bit more about brains. Hope this helps.
I vaguely remember that I heard some theories about Galeaspida or Osteostraci possibly having an electrogenetic sense.
But the only "reference" I can give you at the moment is just the page about Osteostraci on the tree of life project page:
http://tolweb.org/Osteostraci
I (or you) will have to dive more deeply into the literature aboput them to get some usefull, quoteable references.
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