Strict Single Table Inheritence?s

Is there a way to set the base class to abstract? or otherwise enforce
that no one can create a "Pet"?

Pet < ActiveRecord
Dog < Pet
Pig < Pet

I've tried:

class Pet < ActiveRecord::Base
validates_presence_of :type
end

but I get an error about
../vendor/rails/activerecord/lib/active_record/validations.rb:74:
warning: Object#type is deprecated; use Object#class