Getting a BaseAnimation animLayer node.

 def getBaseAnimationLayerNode():

    ret= [];

    import maya.cmds as mc;

    animLayerNodes= mc.ls(type="animLayer");

    for ALN in animLayerNodes:

        attr= ALN+".parentLayer";

        if mc.objExists(attr) and not mc.listConnections(attr):

            ret.append(ALN);

    return( ret );