Deleting duplicate rows using ctid ?

I have a table with 4 columns, none of them unique. I want to delete all
but one of the duplicate records. I think there's a way to do this with
ctid. Examples that pop up in google searches always rely on something
like a unique (id) field, like a primary key, (no good in my case)

create table dog (variety varchar, name varchar, color varchar, age int);
insert into dogs
('lab','moby','white',12),
('lab','moby','white',12),
('spaniel','max','black',13),
('spaniel','max','black'),13,
('lab','moby','white',12);

I want the result to be just 2 recs, one for each dog.