Getting the oid of an anyelement

If I've got a function (sql or plpgsql) that takes anyelement as a
param, how do I determine the type name or oid that was actually passed
in? I figure there is probably a function for this but darn if I can
find it.

Specifically, I'm trying to make a function like Oracle's dump that will
take anything as input and return the internal representation of it. So
I want to determine what type was passed in and call the appropriate
send function.

  SELECT dump(current_date);

  dump
  ------------------------------------------
  Type=date OID=1082 Len=4 Data=(0,0,13,212)