admin.py

from django.contrib import admin
from foobar import models

class CommonSearchCriteria(admin.ModelAdmin):
    search_fields = ('title',)

class AdvancedOptions(admin.ModelAdmin):
    fieldsets = ( 
        ('Advanced options', {
            'classes': ('collapse',),
            'fields': ('area',),
        }), 
    )   
    
class EllipseAdmin(CommonSearchCriteria, AdvancedOptions):
    pass

admin.site.register(models.Ellipse, EllipsisAdmin)
admin.site.register(models.Rectangle)

"""
from django.db.models import base
m = models.__dict__
for k in m.iterkeys():
    klass = m[k]
    if type(klass) == type(base.Model):
        admin.site.register(klass)
"""

models.py

from django.db import models

class Shape(models.Model):
    area = models.PositiveIntegerField(default=0)

class Ellipse(Shape):
    radius = models.PositiveIntegerField(default=0)

class Rectangle(Shape):
    width = models.PositiveIntegerField(default=0)
    height = models.PositiveIntegerField(default=0)